FR2491324A1 - PNEUMATIC TOURNIQUET - Google Patents

Abstract

PNEUMATIC TURNSTILE WITH TURNING PRESSURE REGULATION. IT INCLUDES AN INFLATABLE GARROT 10, GARROT PRESSURIZER 14 AND DECOMPRESSOR 16 MEANS, A GARROT INFLATION PRESSURE SENSOR 18 AND A PRESSURE REGULATOR ACTING SELECTIVELY ON MEANS 14 AND 16 TO MAINTAIN THE NEIGHBORHOOD PRESSURE CHOSEN VALUE. OPTICAL AND AUDIBLE ALARM SIGNALS WILL BE ISSUED IF THE GARROT PRESSURE EXCEEDS AN UPPER LIMIT OR FALLS BELOW A LOWER LIMIT, OR IF THE GARROT INFLATION TIME REACHES OR EXCEEDS A SELECTED VALUE. WATER PRESSURE REGULATION MAY BE PROVIDED BY A MICROPROCESSOR 22. APPLICATION TO THE LIMITATION OF DISORDERS AND INJURIES RESULTING FROM THE LAYING OF A GARROT.

Description

t491324

  The present invention relates to pneumatic tourniquets

  to prevent blood flow from serving a limb during a surgical procedure performed on the limb. In particular, the invention relates to pneumatic tourniquets comprising means for detecting and automatically adjusting the pressure in a tourniquet.

inflatable that encircles the member.

  A conventional pneumatic tourniquet typically comprises

  an inflatable tourniquet whose limb can be circled

  of a patient, a source of compressed gas for inflation of the

  rot, a pressure gauge of the tourniquet pressure, and a pressure regulating mechanism. Typically, the tourniquet is placed around the patient's limb and inflated with

  compressed gas at a pressure of up to 87 kPa for the purpose of

  break the flow of blood to the limb. The surgeon

  thus has an "empty icon" to carry out an inter-

  on the member. The pressure gauge provides the operator with an indication of tourniquet pressure. The pressure regulating mechanism is intended to maintain the tourniquet pressure

substantially constant.

  It has been estimated that approximately 10,000 pneumatic tourniquets

  Classics are used in North America to operate around

  one million surgeries a year. Unfortunately

  Since the widespread use of tourniquet

  pneumatic (and non-pneumatic)

  limb paralysis, nerve damage and other

  the damage, it is believed, to be attributed to

  Quets. A study of all the published texts indicates that these complications can result from four factors: 1. excessive tourniquet pressure (which can lead to

  compression of nerves and other damage to the tourniquet).

  2. Inadequate tourniquet pressure (may result in passive congestion or haemorrhagic infiltration of

nervous tissue).

  3. Excessive time maintaining an inflated tourniquet

on a member.

  4. Installing the tourniquet operated without taking into account

the local anatomy of the limb.

  Many reported cases of damage are thought to be

  avoidable: nerve damage, limb paralysis and

  are due to the factors listed above, the most common of which

  rant seems to be excessive tourniquet pressure [see:

  D. K. Wheeler and P. R. Lipscomb, A Safety Device for Pneumatics

  Tourniquet, J. Bone Joint Surg., 45A: 870, 1964; W. K.

  Hamilton and M.D. Sokoll, Tourniquet Paralysis, Journal of

  the American Medical Association, 199: 37, 1967; S. H.

  Prevoznik, Injury from Use of Pneumatic Tourniquets, Anesthesiology, 32: 177, 1970; J.M. Bruner, Time, Pressure and Temperature Factors in the Safe Use of the Tourniquet, Hand, 2: 39-42, 1970; D. Fry, Inaccurate Tourniquet Gauges, Br Med. J., 1: 511, 1972; A.K.E. Flatt, Tourniquet Time in Hand Surgery, Arch. Surg., 104: 190-192, 1972; G. Burchell and G. Stack, Exsanguination of the Arm and Hand, Hand, 5: 124:

  126, 1973]. Unfortunately, the current frequency of

  surgical complications of tourniquet

  can not be reliably estimated because the "syndrome"

  "Paralysis paralysis" (expression borrowed from J. Moldaver, Tourniquet Paralysis Syndrome, Arch Surg., 68: 136-144, 1954) may be difficult to detect or masked by the effects of the intervention, because the damage is usually transient and reversible to a large extent

  and because such incidents may not be regular

  reported because of the liability risk that may be incurred. (A hospital was recently declared responsible for nerve damage that resulted for a patient from excessive pressure applied to the arm by a patient.

  Tourniquet ["Hospital Liable to Patient for Tourniquet Para

  lysis ", Citation, 38: 5, 15 October 1978]).

  Classic turnstiles, examined by the inventor,

  which may have resulted in nerve or

  lysies resulting from excessive tourniquet pressure have been shown to have defective or hysteretic pressure-regulating mechanisms that allow for tourniquet pressure

  to exceed the desired value by about 10 to 54 kPa (typical

  between 27 and 87 kPa). Other turnstiles are shown to contain aneroid gauges displaying the

  pressure with a margin of inaccuracy of about 27 kPa.

  Attempts have been made to limit injuries due to

  tourniquet pressures by incorporating safety devices into the pneumatic tourniquets. For example, pressure relief valves of the type provided in pressure cookers have been used as pressure relief valves [see: Wheeler

  and Lipscomb (op. cit.) and Hamilton and Sokoll (op. cit.).

  Nevertheless, some limitations inherent in conventional turnstile technology seem to have precluded the practical development of real security measures. At best, rigorous use, inspection, and maintenance protocols could be established to try to ensure that conventional turnstiles are used in a way that would minimize the differences in or out of pressure.

  of tourniquet and would make it possible to detect malfunctions of

  equipment. However, compliance with such protocols could result in a lot of work and

  much of the time available to a nurse or technical

nician of the operating room.

  The object of the present invention is to propose a

  pneumatic turnstile capable of detecting and automatically adjusting

  the tourniquet pressure to keep it close to a chosen value (for example between 27 and 54 kPa

to + 0.8 kPa>.

  A related goal is to provide a tire turnstile

  tick with automatic means to detect a

  tourniquet overpressure and trigger an appropriate alarm.

  (For example, the tourniquet pressure warning device may sound if the actual pressure of the tourniquet exceeds the chosen value by more than approximately 1 kPa). A purpose closely related to the previous one is the automatic triggering of a second alarm to signal an insufficient tourniquet pressure (for example falling to a value of more than 1 kPa).

about to the chosen value).

  A typical current turnstile does not typically include

  no way to measure the exposure time of the tourniquet.

  on the limb of a patient. A classically inflated tourniquet

  therefore, the risk of remaining on the limb for a dangerously long time simply because the operating room personnel may have other concerns and lose sight of the time that has elapsed. Consequently, another related object is to propose a pneumatic tourniquet capable of emitting an alarm signal if the tourniquet remains inflated for a time reaching or exceeding a chosen value.

  which typically varies between 0 and about 180 minutes.

  The subject of the invention is a pneumatic tourniquet

  comprising an inflatable tourniquet, an inflation pressurizing means

  flage of the tourniquet, a decompressor means of deflating the tourniquet, a pressure detector means capable of generating a

  first output signal representative of the inflation pressure

  flaring of the tourniquet, and a pressure regulating means which, in response to the first output signal, selectively activates the pressurizing means and the decompressor means for maintaining the inflation pressure of the tourniquet in the vicinity of a value

chosen.

  The pressure regulating means may be constituted by an electronic detection and control apparatus adapted to compare the first output signal with a signal representative of the selected pressure, to generate a second output signal to act on the decompressor means and to deflate the tourniquet if tourniquet inflation pressure

  exceeds a first limit pressure and to emit a third

  me output signal to act on the medium pressurizer and inflate the tourniquet if the tourniquet inflation pressure falls

  below a second limit pressure. The means decompress-

  may be a standard electronic decompression valve

  closed. The pressurizing means can be a pump

  electric air. Preferably, the pump is capable of

  the tourniquet at a pressure not exceeding 67 kPa

  ron. The detector means may be a transducer

electronic transmitter.

  Advantageously, the tourniquet has a first air intake port and a second evacuation port

  air. The pressurizing means and the decompressing means can

  connected to the first port and the detector means of

  pressure, be connected to the second port.

  Preferably, the pneumatic tourniquet further comprises a first warning means intended to generate a first alarm signal when the tourniquet is inflated to a

  pressure exceeding a third limit pressure. The third

  my pressure-limit can be about 1 kPa higher than the

  chosen pressure. A second warning means is preferably

  expected to generate a second alarm signal when

  the tourniquet pressure falls below a fourth pressure-

  limit. The fourth limit pressure may be less than about 1 kPa at the selected pressure. A third way

  may also be provided to generate a third

  alarm signal when the tourniquet has remained inflated for a period of time reaching or exceeding a chosen value. A fourth warning means can be provided for

  generate a fourth alarm signal during an interrup-

  the external power supply of the press medium

  riser, the decompressor means, the pressure detecting means

  pressure regulating means. Advantageously, a storage battery is provided for supplying energy to at least the pressure sensor means during an interruption of the external power supply. A fifth

  warning means may be provided to generate a fifth

  me alarm signal when the output voltage of the battery

  falls below a prefixed threshold.

  We will now describe the preferred mode of realization

  invention with reference to the accompanying drawings, in which:

  Figure 1 is a block diagram of the realization of

  preferred; Fig. 2 is a concrete representation of a control / display panel for the preferred embodiment; Figure 3 is a block diagram of a unit

249 1324

  for the preferred embodiment FIG. 4 is an electronic circuit diagram

  auxiliary battery power supply and battery

  battery age for the preferred embodiment; Figs. 5A-5D including electronic circuit diagrams of the microprocessor and associated control circuit sections according to the preferred embodiment; FIG. 5e illustrates the connection mode between the circuit sections shown separately in the figures.

5A to 5D;

  Figs. 6A and 6B are electronic circuit diagrams of the control / display circuit sections of the preferred embodiment; Fig. 6C illustrates the mode of connection between the circuit sections shown separately in Figs. 6A and 6B; FIGS. 7A to 7G are flowcharts showing the operating sequence of the automatic detection and control components included in the preferred embodiment

of the invention.

  I - Introduction Figure 1 is a block diagram of a pneumatic turnstile according to the invention illustrating the operation of the preferred embodiment. An inflatable tourniquet tourniquet 10 for surrounding the patient's limb is coupled by a hose 12 to a pressurizer means 14 such as an electric air pump. The hose 12 is also coupled to a decompression means 16 such as a normally closed valve which can be opened by electronic control to deflate the tourniquet 10. A pressure sensing means 18, such as an electronic pressure transducer, is coupled by a

  flexible hose 20 to a second orifice of the tourniquet 10.

  The pressurizing means 14, decompressor 16 and detecting

  pressure transmitter 18 are in electronic coupling with a

  microprocessor 22 with which a memory 24 is associated.

  A user control panel 26 is provided to allow the user to select various operating parameters. For example, the user can, using the control panel 26, set the chosen pressure

  inflating the tourniquet 10 and the period of time during the

  the tourniquet 10 must remain under pressure reaching or approaching the chosen value. The pressure detector means 18 provides a first output signal, representative of the pressure in the tourniquet 10. The microprocessor 22 is pre-programmed (in a manner to be discussed) to compare the first output signal with a signal representative of the tourniquet pressure chosen and to act selectively on the means

  decompressor 16 (if the tourniquet pressure exceeds a

  first "pressure-limit), or on the medium pressurizer 14

  (if the door pressure falls below a "second"

  limit-sion) to maintain the pressure of the tourniquet 10 close to the chosen value. In the preferred embodiment, the first pressure-limit is greater than about 0.8 kPa at the selected pressure and the second pressure-limit is

  less than about 0.8 kPa at the selected pressure. The mic-

  processor 22 is also pre-programmed to monitor the

  period of inflation time of the tourniquet.

  A number of status / alarm indicators 28

  provide the operator with information on the state of

  the pneumatic tourniquet and warning

  optical and audible warnings of dangerous conditions such as putting the tourniquet under excessive or insufficient pressure. Optical and audible warnings are also issued if the tourniquation time of the tourniquet is reached.

  or exceeds the chosen value. The operator has indications

  digital procedures on instant tourniquet pressure,

  on a pressure display device

  rot 38, and the time elapsed since inflation of the tourniquet, displayed on an elapsed time display device 40. We will now describe the preferred embodiment of a pneumatic tourniquet according to the invention from the point of view of the typical user , for example the nurse or

  operating room technician. Then we will give

  Technical description of the structure and operation according to the preferred embodiment, then an explanation of the programming software mode of the microprocessor used in the preferred embodiment. II - Order by nurse or technician

  Figure 2 shows a control / display panel

  chage assigned to the pneumatic tourniquet. The socket (not shown) of the AC power supply of the device is connected to an AC power socket and

  closes the on / off switch 34 to turn the

  quet tire under tension. Closing the switch

  34 automatically turns the pneumatic turnstile

  "self-test" test, which is indicated by the illumination of a

  36. This self-test procedure allows the operator to

  to check the correct operation of the device.

  (a) Self-test procedure In the self-test mode, it is arranged that the pressure display 38 and time display devices 40 (both of the three-digit light-emitting diode type and 7 segments) both display the number "888" to allow the operator to verify the operation of all display segments. A buzzer (no

  shown in FIG. 2) also resonates so that the operation

  rator can check that it is working properly.

  The operator must then disconnect the power supply

  alternatively, ensure that the power failure indicator 58 then illuminates. He then reconnects

  taken, which must cause the indicator 58 to go out.

  After verifying the proper functioning of the

  visualization systems 38 and 40, the power failure indicator

  58 and the buzzer, the operator may momentarily set the switch 42 to the "reset" position to terminate the self-test sequence and establish

  the "normal" operating mode (the switch 42 remains normal

  in the high position marked "on" in Figure 2). Once the normal operating mode has been established, the light 36

turns off and a light 44 turns on.

  (b) Normal procedure The operator first chooses the pressure and period

  desired time for inflating tourniquet 10.

  To select the tourniquet pressure, it puts a switch 46 in the "down" position shown in Fig. 2. The display 38 displays a preselected nominal pressure of 27 kPa. By maintaining

  switch 46 in the down position, the operator can either be

  to reduce the selected tourniquet pressure from the nominal value of 27 kPa by putting a switch 48 in the "increase" position (if the desired chosen pressure is greater than 27 kPa) or in the "decrease" position (if the pressure desired choice is less than 27 kPa). When the switch 48 is in the "increase" position, the pressure

  displayed on the display device 38 increases

  up to a maximum of 54 kPa. When the switch 48 is in the "decrease" position, the pressure displayed on the display 38 decreases gradually to a minimum of 0 kPa. When the selected tourniquet pressure appears on the visualization device 38, we release

  switch 46. It should be noted that two

  to choose the tourniquet pressure. This is a safety measure to avoid inadvertently changing the tourniquet pressure. When released, the

  switch 46 returns to the "detected" position, and the

  display 38 continuously displays for the opera-

  the inflation pressure of the withers 10 (which initially

is zero).

  The tourniquet inflation time period is chosen

  in a similar way. A switch 50 is placed in the position

  Low "established" signal shown in Figure 2 and the display device 40 then displays a nominal time prefixed 60 minutes. Holding switch 50 in position

  low, the operator can either increase or reduce the

  the period of inflating the tourniquet relative to the nominal period of 60 minutes by placing a switch 52 in the "increase" position (if the desired period of time for inflating the tourniquet exceeds 60 minutes) or in the "decrease" position (if the desired period of inflation time

  tourniquet is less than 60 minutes). Depending on the case,

  time period displayed in minutes on the device

  visualization 40 gradually undergoes an increase

  up to a maximum of 180 minutes) or a reduction (up to a minimum of 0 minutes). When the chosen time interval appears on the display device 40, the operator releases the switches 50 and 52. Again, as a

  security measure, two separate switches are required.

  to set the inflation time period of the tourniquet,

  so that this period of time is not changed by

  keep. When released, the switch 50 resumes its

  position "elapsed" and the display device 40 furnaces

  continually provide the operator with a digital display of

  the period of time during which the withers 10 is

  re inflated to a pressure that reaches, or substantially, the pressure selected (initially, the displayed period of time

is "0").

  Patient member is prepared and equipped with

  tourniquet 10 according to established medical protocols.

  The hose 12 couples an intake port

  of the air of the tourniquet 10 by means of pressurizer 14 and by means of

  compressor 16, through an orifice 54 shown in Figure 2. The hose 20 couples an outlet port

  of the air of the tourniquet 10 by means of a pressure detector 18,

  to an orifice 56 shown in Figure 2. [Preferably,

  flexible intake and return hoses of

  compressed air wind, on arrival and return, tourniquet 10.

  Such a split can facilitate the detection of "kinks"

  or occlusions of flexible hoses. If, however, we must use

  To fit a conventional single-port tourniquet, it is necessary to provide a suitable three-prong connection to connect to the orifices 51 and 56 a single flexible hose starting from the withers]. Once selected the tourniquet pressure and period

24913 24

  At the moment of inflation, a switch 60 is momentarily put in the "start" position to actuate the pressurizing means 14 and inflate the tourniquet 10. The instantaneous values of the tourniquet pressure in kPa appear on the display device 38. inflation of the tourniquet reached, at + 0.8 kPa, the chosen value, a clock of

  elapsed time starts automatically to "count" the period

  of tourniquet inflation time, and the instantaneous values

  the time elapsed (in minutes) appear on the

  40. The device automatically adjusts the tourniquet pressure (as will be discussed below).

  to keep it, + 0.8 kPa close, the chosen value.

  To deflate the tourniquet 10 at the end of

  tion, the switches 46 and 48 are operated in order to establish at a zero value the selected tourniquet pressure. The tourniquet then deflates to zero pressure as soon as the switch 46 is released. Once the tourniquet 10 deflated, it

  switch 34 to the "off" position and

shake the patient with the tourniquet.

(c) Horns

  There are five separate alarms, each of which

  one can be triggered when the device is in

  normalization to report potentially dangerous conditions. A first horn is triggered if the tourniquet pressure exceeds a "third" limit pressure which, in

  the preferred embodiment exceeds by 1 kPa the pressure chosen

  sie. A second horn is triggered if the tourniquet pressure falls below a "fourth" limit pressure which, in the preferred embodiment, is 1 kPa lower than the selected pressure. In either case, an audible alarm is triggered and the display device 38 will flash to draw the operator's attention to the pressure value, excessive or insufficient, that it displays. The audible pressure alarm can be temporarily interrupted by setting the switch 42 to the "reset" position. This action interrupts the audible alarm for 30 seconds, but the display device 38

keep flashing.

  In the event of the first or second alarm being triggered, the operator must check whether the flexible hoses 12 and 20 are not bent or plugged, which may impede

  the flow of compressed air reaching and leaving the withers.

  The tourniquet 10, the hoses 12 and 20 and the various fittings should also be checked to see if they are damaged, leaking or clogged. Each of the two alarms is automatically put out of action when it is remedied

the fault that triggered it.

  A third horn is triggered if the withers

  remains inflated for a period of time equal to or greater than

  than the period of inflation time chosen.If the third

  alarm is triggered, the audible alarm sounds.

  and the display device 40 flashes to

  the attention of the operator to the exceeding of the

  period of inflation time. There is no deflation of the gar-

  rot. To put the time alarm out of action for the completion of an operation, the operator can change the tourniquet inflation time period to a new value of up to 180 minutes from the beginning of the procedure. "counting". The time alarm can be temporarily disabled by setting the switch 42 to the "reset" position. This action interrupts the operation of the audible alarm for 30 seconds,

  but the display device 40 continues to flash.

  A fourth alarm, of "power failure", is triggered when the external alternative source stops feeding the device. If the AC power is interrupted, the audible alarm is triggered and the LED 58 comes on. In case of failure of the AC power supply, an internal storage battery is automatically

  in order to supply at least the detector detector means

  18 and the electronic circuits so that the operator can continue to monitor the tourniquet pressure and elapsed time. The "power failure" alarm is automatically disabled when the AC power of the unit is restored. Operation

  the audible alarm signaling an alternating power supply failure

  native can also be temporarily interrupted for 30 seconds by setting the switch 42 to the low position of

"reset".

  A fifth horn, "low battery"

* is triggered, triggering the audible alarm and provoking

  the illumination of the indicator 62, if the voltage of a bat-

  The internal auxiliary voltage drops below a predetermined threshold (which is, in the preferred embodiment, 10.2 volts), indicating that the battery is only able to power the apparatus for a short period of time. If the alarm

  low battery is tripped, you have to connect immediately

  the device to an AC power source for re-

  charge the battery. The discharge horn is automatically

  switched off once the battery is charged.

  III - Structure and technical operation (a) Power unit and auxiliary battery

  FIG. 3 represents in the form of a functional diagram

  the power supply unit, the auxiliary battery and the battery charger. The power supply unit converts a 110 volt AC current, from outside, continuous

  in output currents of +13.8 volts (or +12 volts without

  if the auxiliary battery is in use), + 5V, + 15V

and -15V. The accumulator battery 74 is a battery of 12 volts, 5 Ah, of the type

lead. Charging circuit 76

  is intended to maintain the voltage across the bat-

  74 at approximately +13.8 volts when the device is connected to

  an external AC source of 110 volts.

  FIG. 4 is a diagram of the electronic circuits of the supply circuit, the auxiliary battery and the

battery charging circuit.

  A transformer Tl reduces the voltage to 16 volts

  AC power, which is then rectified.

  by a diode bridge rectifier Dl. A voltage regulator U1 and a transistor Qi set the voltage at 13.8 volts to apply across the battery 74. A transistor Q2 limits the current applied to the battery 74 to 3 A approximately to avoid overcharging the battery. drums. A diode D2 prevents the battery current from being

  flow to the voltage regulator Ul.

  Rl sett to adjust the voltage at the battery terminals 74

  at 13.8 volts when a current supply signal

  A battery charging voltage of +13.8 volts is applied to the input terminals of the transformer Tl. A battery charging voltage of +13.8 volts ensures the charging of each element of the battery 74 at a constant voltage of 2.3 volts. A regulated voltage of

  +13.8 volts is thus available on pin 1 of a connector

  P2 if an AC input signal of 110

  volts is applied to the input terminals of the transformer T1.

  In the absence of an AC input signal, a voltage of +12 volts of unregulated power (from battery 74) is applied to pin 1 of connector P2. Pin 1 of connector P2 is coupled to pin 4 of connector P2 to power other parts

of the supply circuit 64.

  A U2 switch regulator provides a high efficiency control that lowers +5 volts supply voltage by +13.8 (or +12) volts. The signal of +5 volts

  used to power the microprocessor 66 and the associated memories.

  as well as an analogue / digital converter, a

  timer, control circuits of the visual display devices

  semiconductor relays, LEDs and a

  horn, which will be described below.

  An oscillator U3 and transistors Q4, Q5 and Q6 excite a step-up transformer T2 at 20 kHz. The

  transformer secondary output signal T2 is

  erected and regulated at +15 volts and -15 volts by voltage regulators U4 and U5 respectively. Voltages of +15 volts and -15 volts supply the detector means of

  18 and associated processing circuits (which are

will cry further).

  A quad-operational amplifier U6 serves in a voltage comparator mode to provide "low battery", "power failure" and "low power" signals.

  at the battery stop. "A reference diode of high pre-

  D3, with temperature compensation, provides the

  voltage testers a reference voltage.

  A variable resistor R2 is set to cut the excitation signal presented by the voltage comparator U6A to the Darlington switching transistor Q3 if the voltage at the output terminals of the battery falls below the 10.2 volt threshold. The transistor Q3 thus disconnects the battery 74 to prevent its complete discharge. A resistance

  R4 introduces a slight hysteresis to prevent the

  sistor Q3 does not work in its linear region.

  A variable resistor R3 is set so that the voltage comparator U6B emits a "low battery" signal.

  charged "if the voltage at the terminals of battery 74 falls

  below a threshold of 11.4 volts. This signal is used to excite

  light 62 shown in Figure 2.

  U6C and U6D voltage comparators are used to de-

  the absence of the AC power signal

  110-volt pulse from outside to energize the "power failure" LED 58 shown in FIG. 2 and provide a TTL (transistor-transistor) in-logic signal suitable for application to the microprocessor input

as we will expose it.

  The parts list below details the

  components used to make the power supply unit

  Figure 4. The set of resistances and conden-

  not included in this list are standard components

  dards whose values are indicated on the circuit diagram. Item Nature Quantity Circuit Breaker D1 Battery D2 Qi, Q2 Q3

Q41 Q5 'Q6

  Q7 T1 T2 U1 U2 U3 U4 U5 U6 Potter & Brumfield 37-401-101 Motorola MDA-97021 Gates 2V, 5A-h, 0800-0004 Motorola 1N5402 Motorola MJE2955 Motorola T1P 126 Motorola 2N3904 Motorola 2N4123 Hammond 166M16 Toroid, 7/8 " OD, No. 26 AWG Fairchild uA78G

T / 260T,

  Fairchild SH1605 Motorola MC1455 Motorola 78L15 Motorola 79L15 National LM324 National LM113H (b) Medium pressurizer In the preferred embodiment, the medium pressurizer

  14 is a WISA model 300 air pump. This is a gen-

  Solenoid / diaphragm pressure switch with 110 volt, 60 Hz AC power and power consumption of approximately 5 watts. This pump is capable of generating a maximum tourniquet pressure of about 67 kPa. This is a safety measure because it is estimated that tourniquet pressures not exceeding approximately 54 kPa should be sufficient to maintain

  a bloodless surgical field [see: L. Klenerman and G.H.

  Hulans, Tourniquet Pressures for Lower Limb, J. Bone Joint Surg., 61B: 124, 1979; and R. Sanders, The Tourniquet Instrument or Weapon? Hand, 5: 119-123, 1973]. The mode of control of the pressurizer means 14 by the microprocessor is set forth below under the heading "microprocessor and cir-

digital cooked ".

  A normally closed, three-way, Clippard EV-3 style lift valve (not shown) is placed in the hose 12 between the pump and the tourniquet 10 to save the pump diaphragm the damage that could be caused by the pressure of the pump. air in the pipe.

  action of the pump, the valve is operated electronically

  in order to couple the pump to the withers 10 so that

  compressed air -can enter the latter. When the pom-

  For example, the valve is actuated so as to seal the pipe 12 (thus preventing the air from escaping from the withers) and to put the outlet port of the pump in the atmosphere ( which dissipates any back pressure

applied to the pump diaphragm).

  (c) Medium decompressor In the preferred embodiment, the decompressor means

  16 is a Clippard EV0-3-12 electronic valve.

  This is a three-way lift valve, normally

  open, with a lifting stroke of 0.254 mm, at a pressure

  from 0 to 724 kPa, with an air flow rate of 0.014 m 3 / min at 689 kPa and a response time of ms at 689 kPa. A signal

  +12 volts direct current feeds the valve which

  about 0.65 watts below its rated pressure. The mode of control of the decompressor means by the microprocessor will be

  discussed below under "microprocessor and cir-

digital cooked ".

  (d) Pressure sensor means In the preferred embodiment, the pressure sensor means 18 is an electronic pressure transducer

  National Semiconductor LX1702GN shown at 88 in FIG.

  6. The tourniquet 10 is coupled by the hose 20 and

  orifice 56 (FIG. 2) at the inlet of the transducer

  The pressure transducer 88 provides an output voltage in the range of 2.5 to 12.5 volts corresponding to the pressure range of 0 to 101 kPa. Operational amplifiers 90, 92 and 94, National Semiconductor Model LM324A, bring, in a proportion ratio

  tionality, the output voltage of the transducer in the in-

  from 0 to 5 volts for application to a

  analog / digital converter 84, visible in FIG.

  To make the representation clearer, the micro-

  processor and the associated digital circuits have been

  separately in FIGS. 5A to 5D. Figure 5D shows

  that how the circuit segments according to Figs. 5A to D are arranged to be suitably coupled to each other. Hereinafter, we will call "figure 5" all the

Figures 5A to 5D.

  The control / display circuits are shown in two separate figures 6A and 6B. Fig. 6C shows how the circuit sections according to Figs. 6A and 6B are arranged to be suitably coupled to each other. Hereinafter, we will call "figure 6" all the

Figures 6A and 6B.

  The output voltage of the pressure transducer

  must be calibrated when the device has remained

  in the "normal" operating mode for about 5 minutes.

  With a tourniquet pressure of 0 kPa (obtained by disengaging

  plant flexible hoses 12 and 20 of the withers 10), the variable resistor R5 is set so that the output voltage of the operational amplifier 92 is equal to 0.000 volts, +0.010 volts. It is then necessary to bring the tourniquet pressure

  at 40 kPa (by connecting the transducers with

  pressure sensor 88 to an external pressure source and

  to an error gauge less than 1%) and to adjust the resistance

  variable R6 so that the output signal of the amplifier

  operational fold 92 is 1,850 volts, at +0,010

near volt.

  (e) Microprocessor and digital circuits The microprocessor which regulates the tourniquet pressure,

Z491324

  controls the display devices, etc., is a half

  Intel 8085A croprocessor, shown at 78 in FIG.

  Two integrated circuits of programmable read only memory

  Typically, 2K x 8-bit TMS 2516 ("EPROM"), represented at 82A and 82B in FIG. 5, store the logic programs defining the sequence of operations by which the microprocessor 78 controls the pneumatic turnstile. Two Intel 8155 random access memory ("RAM") chips represented at 80A and 80B in FIG. 5 each constitute a 256 byte 256-byte work memory in which non-permanent data is stored. The EPROM memories 82A and 82B are designed to have memory addresses 0000 to 07FF (hexadecimal system) and 0800 to OFFF respectively. RAMs 80A and 80B are designed to have memory addresses 2700 through 27FF

and 2800 to 28FF respectively.

  ADO to AD7 lines provide 8-bit data transmission between the microprocessor 78, the RAMs 80A and 80B, the EPROMs 82A and 82B, a display device interface 96 (which controls, as

  it will be exposed, the formatting of the information of pres-

  and time displayed on visualization devices.

  38 and 40), and a timer 86 (which keeps track of

time elapsed).

  To simplify the transmission of received data

  and issued by the microprocessor 78, the interface of the device

  The display 96 and the timer 86 are arbitrarily defined as having memory locations 3000

  at 37FF and 3800 at 3FFF respectively, although they do not

  do not set up "memories" in the classical sense.

  The addressing information presented by the micro-

  processor 78 on lines A1 to A15 are sufficient to identify an address among the set of addresses represented by one of the EPROM memories 82A or 82B, one of the RAM memories 80A or

  80B and the display device interface 96 or the minute

  86. A "chip selection" integrated circuit is connected to the address lines A1 to A15. By decoding the information present on these lines, the chip selector 100 is able to identify the unit: memory

  RAM 80A or 80B, EPROM memory 82A or 82B and interface of the dis-

  positive display 96 or timer 86 to which must address the microprocessor 78. The output lines CSO, CS1, CS4, CS5, CS6 and CS7 of the chip selector 100 are used to "validate" respectively one of the memories EPROM 82A and 82B, RAMs 80A and 80B, and the interface

  of the display device 96 or the timer 86.

  A double decoder "one out of four" 102, of National Semiconductor model 74LS139, generates commands of

  additional synchronization to address one of the memo-

  EPROM 82A or 82B. A demultiplexer 98 (8-bit Intel 8212 latch IC) demultiplexes the data on the ADO to AD7 lines to send to one

EPROM memories 82A and 82B.

  The proportionate output signal, from 0 to 5 volts, of the pressure transducer 88 is sent to the input terminal

  "INO" of the analogue / digital converter 84. The micropro-

  78 is programmed as will be explained to send

  appropriate signals at the "SlTART" and "ALE" terminals of the conver-

  analog / digital weaver 84 to provoke the conversion

  output of the pressure transducer from the analog state to the digital state. The 8-bit digital result is transmitted from the analog / digital converter 84 to the input port "A" of the RAM 80A to be

written in this one.

  The signals generated by the switches 46, 48,

  , 52 and 60 of the front panel are transmitted through

  connector J5 / J6 (FIGS. 6 and 7) to the input port "B" of the RAM 80A to be written therein. Gate "B" of RAM 80A is configured to admit these signals as follows:

  Gate "C" of the RAM 80A includes a single

  the PCO line which transmits to the microprocessor 78 the logic signal TTL "power failure" generated in the power unit.

  RAM 80B contains the information of de-

  tripping the various alarms and activating the pressurizer means 14 and decompressor 16. The "A" gate of the RAM 80B is configured to transmit the following signals: Output line RAM signal 80B PAO Triggering the alarm sound PAl Triggering the PA2 time alarm Triggering the pressure alarm (excessive or insufficient pressure) PA3 Not used Input line RAM signal BOA Sga PBO Switch 50 Time "elapsed" or "set-up" PB1 Switch 52 PB2 "Decrease" or "increase" in time (2 bits) PB3 Switch 46 "Detected" or "Established" pressure PB4 Switch 48 PB5 "Increase" or "Decrease" in pressure (2 bits) PB6 Not used PB7 Switch 60 "Priming of inflation" RAM 80B output line Signal (continued) PA4 Activation signal of the pressurizer medium 14 PA5 Activation signal of the decompressor means 16 PA6 Validation of the PA7 timer Not used The "B" gate of the memory RAM 80B is configured to transmit the following signals: Output Line RAM 80B Signal PBBO Normal Mode Status Signal PBB1 PBB2-PBB7 Self-Test Mode Status Signal Not Used

  The display device interface 96 is a circuit

  Built-in Intel 8279 Display / Keyboard Device Interface Controller that Operates the Information Format Format

  appearing on the display devices 30 and 40.

  The microprocessor 78 sets the "pressure" or "time" information to be displayed in a BCD (binary coded decimal) format which is transmitted to the display device interface 96 when the address presented to the microprocessor lines All and A15 causes "validation" of the display device interface 96 by the chip selector 100. The BCD digits representing the "pressure" are transmitted on lines OAO to OA3, from the display device interface. 96, via a J5 / J6 connector, to a decoder / control circuit 104 BCD with 7 segments of

  National Semiconductor Model DS858 (Figure 6), which trans-

  sets the decoded information in 7 segments to the display device 38. The BCD digits representing the "time" are similarly transmitted, by lines OBO to OB3, from the interface 96 to the display device 40 through a second decoder. control circuit 105. The display device interface 96 also generates a signal of 3

  appropriate bits on the lines SO to S2 to determine the

  which of the six individual display digits of the

  Visualization 38 and 40 are to be activated. The signals SO to S2 pass through a hexadecimal inverter buffer 106 of the National Semiconductor DS8863 model (FIG. 6) which absorbs

  the collector current from the visualization devices

lisation.

  As noted above, visualization devices

  "time" and "pressure" will flash when an alarm related to the pressure or

  time. As shown in Figure 6, one half of a quarter

  National Semiconductor 74LS32 gate or gate 108 provides the transfer of the time and pressure alarm signals which appear on the lines PAI and PA2 respectively of the RAM 80B with a clock signal of 3 Hz to send them to the transmitter. erase input decoders / circuits

  104 and 105 so that they flash or

  the display when the alarm was triggered, the con-

  identifying. The "normal" or "self-test" status signals appearing on the PBBO and PBB1 lines respectively of the RAM 80B are sent through connectors

  J5 / J6 to LEDs 44 and 36 respectively through the medium of

  res of a National Semiconductor 75451 Device Interface Control Circuit 110, as shown in FIG.

Figure 6.

  The audible alarm trigger signal that appears

  on the PAO line of the RAM 80B is sent, via connectors J5 / J6, to the buzzer

  70 through a peripheral interface control circuit

  112, as shown in FIG. 6. The buzzer 70 is a "SONALERT" buzzer with a single tone. The switch 42 is directly coupled to one of the "interrupt" lines of the microprocessor 78.

  the depression of the switch 42, there occurs a break

  under the effect of which the microprocessor 78 transmits the command (in a manner that will be exposed) to a program

  temporarily disabling the horn 70.

  The activation signals of the pressurizing means 14 and the decompressor means 16 which appear on the lines PA4 and PA5 respectively of the RAM 80B are sent,

  through connectors J5 / J6, through a third

  3rd device interface control circuit 114 such

  shown in FIG. 6. The activation signal

  the line PA4 is used to validate the semiconductor relay.

  115 which, in turn, sends a control signal in

  alternating current of 110 volts by means of pressurizer 14.

  A crystal oscillator of 6.144 MHz, 116,

  (Figure 5) is the master clock or timer of the micropro-

  78. The microprocessor 78 divides the frequency by

  this clock to provide a signal at 3.072 MHz at the output

  "CLK" clock of the microprocessor 78, which signal is then

  sent you to RAM 80B. An internal timer provided on the RAM 80B divides by five the frequency of the clock signal "CLK" to provide a 614.4 kHz signal which is sent to the analog / digital converter84 and the timer 86. (The signal frequency CLK clock is divided because the integrated circuit timer used in the preferred embodiment is suitable only for processing signal frequencies below 2 MHz). The timer 86 provides a 600 Hz output signal that is sent to the RAM 80A. An internal timer provided on RAM 80A divides the signal frequency to 600 Hz to provide a 3 Hz signal which is used as described above to flash display devices 38 or 40 if

  a time or pressure alarm is triggered.

  IV - Software Aspect FIGS. 7A to 7G are flow diagrams indicating the sequence of operations that the microprocessor 78

  performs according to its program. To simplify the

  Given the software aspect, we will refrain from describing in detail the control signals produced by the software to act on the components described above. Nevertheless, the technician conceives that in order, for example, to turn on the self-test light 36 ", the microprocessor 78 must generate appropriate commands to make a signal appear on the line PBB1 of the RAM memory 80B which can be coupled with

  LED 36 via the interface 110.

  The main control program is shown in Figure 7A. After initialization of the RAMs 80A and 80B, the interface of the display device 96 and the timer 86 for data transfer, the control

  passes to the "AUTO-TEST" subprogram shown in the

re 7B.

  AUTO-TEST subroutine generates commands

  suitable for turning on the self-test light 36, making the

  display the visualization devices 38 and 40 and trigger

  the horn 70 until the

  mutator 42 to terminate the self-test sequence; at this moment, the horn 70 is de-energized, each of the

  display devices 38 and 40 is set to display status.

  "000" and the command returns to the main program.

  The main program then transfers the command to the NORMAL routine shown in Fig. 7B, which itself repeatedly requests the subprograms.

  PRESSURE ESTABLISHMENT and ESTABLISHMENT OF TIME

  respectively shown in Figures 7C and 7D until the switch 60 is lowered to inflate the tourniquet 10;

  at this point, the command returns to the main program.

  The PRESSURE SETUP routine simply returns to routine NORMAL unless the detected / established pressure switch 46 is depressed to the "set" position.

  lowered, the pressure of the withers 10 is displayed on the device.

  visualization device 38. The alarm trigger signal

  pressure "ALP" is disabled to avoid triggering

  an insufficient or excessive pressurization alarm

  during the choice of tourniquet pressure. There is then

  state of the switch increase / decrease of pres-

  48. If this switch is in the neutral position, the

  back to the beginning of the PRESSURE SETTING routine. Otherwise, the stored value of the selected pressure is increased or decreased in increments

  in the range of 0 to 54 kPa depending on the position of the switching

  48. If a pressure exceeding 54 kPa is selected, buzzer 70 is triggered and there is

  flashing on the display device 38 of the va-

  their maximum pressure that can be chosen, 54 kPa.

  Scheduled time controllers are used to delay

  from 0.5 seconds the return of the order to the beginning of the sub-

  PRESSURE PLANNING program during the 2.5 sec-

  initials for lowering the switches 46 and 48.

  If you do, the command returns every 30 milliseconds at the beginning of the PRESS SETUP subprogram. In other words, the value of the chosen pressure changes slowly

  relative (at 0.5-second intervals) during the 2.5

  initial counts, but then with relative speed, which establishes a "slow" or "fast" mode of increase or

  reducing the chosen pressure.

  The TIME SETTING sub-program is

  the same as that of PRESSURE SETTING, except that it is the states of the switches 50 and 52 that are examined and the selected time is displayed on the display device 40. It is possible to choose the inflation time of

  tourniquet in an interval ranging from 0 to 180 minutes.

  When releasing one or the other of the switches

  46 and 50, the command returns from the sub-program of ETABLISSE-

  PRESSURE or TIME ESTABLISHMENT to the sub-program

  NORMAL which, as noted above, continues to require the

  subprograms of PRESSURE AND ESTABLISHMENT-

  MENT OF TIME until the switch is lowered 60

  to inflate the tourniquet 10. During this lowering, the

* Reversal NORMAL subroutine to the main program.

  The main program then initializes certain variables

  and reset an internal elapsed time counter.

  The main program then establishes the sub-pro-

  PRESSURE UPGRADE (Figure 7E) that samples

  sends the pressure output signal from the transducer 88 and then returns the command to the main program unless

  the elapsed time counter does not contain an even number.

  With this measurement, the pressure displayed on the display device 38 changes at intervals not greater than

  two seconds, which gives the operator a

  latively "stable". However, the pressure detected by the transducer 88 continues to be sampled at each

  transition to the PRESS UPDATE subroutine. The

  their which is displayed on the display device 38 is the average of two numbers taken from the transducer

  88 during the minimum interval of change of

  chage, two seconds. After viewing a new

  detected pressure value, the control returns to the program

me main.

  The main program then causes a comparison

  sound of the actual tourniquet pressure established by the sub-

  PRESSURE UPDATE program from the transduc-

  56 with the selected tourniquet pressure. If the pressure

  actual tourniquet is less than the pressure of

  If the command goes to INFLATION subroutine

  GARROT (FIG. 7F) which activates the medium pressurizer 14 during

  about 2 seconds. (The pressurizer means used in the preferred embodiment increases the tourniquet pressure by about 1.2 kPa in 2 seconds). The command then returns to the main program, then to the UPDATE DETEMP routine (FIG. 7E) which simply reads the elapsed time in the timer 96 and its display on the display device 40. The MISE routine A DAY OF TIME then returns the order to the main program.

  pal, which continues the cyclic action until inflation of

tourniquet 10 at the chosen pressure.

  If the actual tourniquet pressure is greater than the

  With the selected tourniquet pressure, the control moves to the sub-pro-

  ALTERNATIVE POWER control (FIG. 7F) which triggers horn 70 if the signal "malfunction"

  "feed" was generated by the feed unit.

  (If the switch 42 is depressed, an interruption by the hardware is generated, which causes the microprocessor to transfer the command to the ALARM / RESET A subroutine.

  ZERO (FIG. 7E) according to which the current time is recorded

  in a variable called "ADA". Before the horn 70 is triggered by the ALTERNATIVE POWER control routine, the current time is compared with the value present in the ADA variable. Yes

  the difference exceeds 30 seconds, the audible alarm is de-

  clenchée; otherwise, the "AUD" signal for validation of the warning

  sound is invalidated. Thus, the switch 42 invalid

  the buzzer for a maximum of 30 seconds).

  The main program then calls the sub-pro-

  grams of ESTABLISHMENT OF TIME and ESTABLISHMENT OF

  SION to allow the operator to choose new values of inflation time and inflation pressure, at

  where it is desirable to modify these values to

  see an intervention. The TIME UPDATE program then ensures l. has updated the elapsed time displayed on the

  visualization device 40. The VERIFICATION sub-program

  TIME CATION (Figure 7F) is then established to determine

  if the tourniquet inflation time has reached or exceeded the selected tourniquet inflation time and, if so, triggers horn 70 and activates time alarm signal "ALT" to flash the alarm. time display on the display device 40. Again, the variable ADA is compared with the current time to determine

  if buzzer 70 has been temporarily disabled.

  Next, the PRESS UP UP routine is set up to update the display of the actual pressure existing in the tourniquet 10 for the PRESSURE CONTROL routine to proceed (Fig. 7G). If the actual tourniquet pressure exceeds the selected tourniquet pressure by more than 0.8 kPa, the PRESSURE CONTROL subroutine establishes the EXCESSIVE PRESSURE subprogram (Figure 7G) that triggers horn 70 (unless

  this has been temporarily invalidated by means of

  42) and blinks the pressure display on the display device 38 if the tourniquet pressure

  actual pressure exceeds by more than 1 kPa the pressure of tourniquet

  sie. The EXCESSIVE PRESSURE subprogram also establishes the GARROT DEFLATION sub-program (FIG. 7G) which activates the decompressor means 16 to lower about

0.4 kPa tourniquet pressure.

  If the actual tourniquet pressure is lower than

  more than 0.8 kPa at the selected tourniquet pressure, the

  PRESSURE CONTROL program establishes the subroutine

  INSUFFICIENT PRESSURE (Figure 7G) to determine if the difference

  The difference is greater than 1 kPa, in which case the horn 70 is triggered (unless it has been temporarily disabled by the switch 42) and the pressure display flashes on the display 38. The LOW PRESSURE subprogram also establishes the subprogram of

  INFLATION OF GARROT to activate the medium pressurizer 14 pen-

  2 seconds and slightly raise the tourniquet pressure.

  The main program continues the cyclic action by comparing the actual and selected tourniquet pressures and

  acting accordingly as stated above.

Claims (25)

  1. Pneumatic turnstile, characterized in that   comprises: (a) an inflatable tourniquet (10); (b) a means of   suriseur (14) for inflating said tourniquet; (c) decompressor means (16) for deflating said tourniquet; (d) pressure sensing means (18) for generating a first output signal representative of the pressure at which said tourniquet is inflated; and (e) pressure regulating means (22) responsive to said first output signal for selectively energizing said pressurizer and decompressor means to maintain the pressure at which said tourniquet is inflated; in the vicinity of a chosen value.   Pneumatic turnstile according to claim 1, characterized in that said pressure regulating means   (22) is constituted by a device for detecting and com-   electronic control: (a) to compare the first   output signal with a signal representative of said pres-   chosen decision; (b) generating a second output signal   to actuate said decompressor means (16) to deflate   fling the tourniquet if the pressure at which is inflated   tourniquet exceeds a first limit pressure; and (c) to   deriving a third output signal to actuate said pressurizer means (14) to inflate the tourniquet if the pressure at which the tourniquet is inflated is less than a second limit pressure. pneumatic 3. Tourniquet / according to claim 2, characterized in that said decompressor means (16) is a valve of   electronic decompression normally closed.   pneumatic 4. Tourniquet / tire according to claim 3, characterized in that said pressurizing means (14) is a electric air pump.   5. 8Esea Tournet oThe claim 4, characterized in that said pressure sensor means (18) is a   electronic pressure transducer (88).   6. pneumatic turnstile according to claim 2, characterized in that said first pressure-limit is greater than about 0.8 kPa at said selected pressure and   that said second pressure-limit is less than   0.8 kPa at said selected pressure.   Pneumatic tourniquet according to claim 2, characterized in that said pump is capable of inflating said tourniquet at a pressure not exceeding about 67 kPa. 8. pneumatic tourniquet according to claim 1 or 2, characterized in that said tourniquet has a first   air inlet in the withers, and a second   this evacuation of air from the withers.   9. pneumatic turnstile according to claim 8, characterized in that said pressurizer means (14) and decompressor (16) are coupled to said second first orifice. Pneumatic turnstile according to claim 8   or 9, characterized in that said detector means for pres-   sion (18) is coupled to said second port.   Pneumatic turnstile according to claim 2, characterized in that said electronic detection and control device (22) comprises means (38, 46, 48).   for selectively modifying said selected pressure.   Pneumatic turnstile according to claim 11, characterized in that said selected pressure is comprised   between limits of approximately 0 to 54 kPa.   Pneumatic tourniquet according to claim 2 or 11, characterized in that said electronic detection and control device comprises means (50, 52) for selecting the period of time during which the tourniquet must stay inflated.   Pneumatic turnstile according to claim 13, characterized in that said selected time is limited to one maximum of about 180 minutes.   Pneumatic turnstile according to claim 1   or 2, characterized in that it comprises a first warning   to emit a first warning signal when the withers   is inflated to a pressure exceeding a third pressure-   limit. Pneumatic turnstile according to claim 15,   characterized in that the third pressure limit is greater than   about 1 kPa at said selected pressure.   Pneumatic tourniquet according to claim 15, characterized in that it comprises a second horn for emitting a second alarm signal when the tourniquet is deflated.   to a pressure lower than a fourth pressure-   limit. Pneumatic turnstile according to claim 17, characterized in that said fourth pressure-limit is   less than about 1 kPa at said selected pressure.   Pneumatic turnstile according to claim 13, characterized in that it comprises a third alarm to emit a third alarm signal when the withers has remained inflated for a time equal to or greater than said chosen time.   Pneumatic turnstile according to claim 1   or 2, characterized in that it comprises a fourth warning   to emit a fourth alarm signal during a   cutting off the external supply of said pressurizing means   said decompressor means (16), said pressure sensor means (18) or said regulator means pressure (22).   Pneumatic turnstile according to the claim   characterized in that it comprises an accumulator battery   latters (74) for supplying said at least said means for   pressure sensor during a break in said external power supply. 22. pneumatic turnstile according to claim 21, characterized in that it comprises a fifth horn to emit a fifth alarm signal when the voltage   the output of said battery falls below a pre-determined threshold   fixed. Pneumatic turnstile according to claim 13, characterized in that it comprises a timer (86) for   measure said chosen period of time.   Pneumatic turnstile according to claim 23, characterized in that it comprises means for initiating the   measure of the said period of time chosen by the said minute   when the inflation pressure of the tourniquet approaches the chosen pressure.   Pneumatic turnstile according to claim 24, characterized in that it comprises a third horn   to emit a third alarm signal when said half   Nuterie measured a period of time equal to or greater than said chosen period of time.