EP0060876A1 - Absolute pressure, pulse rate and temperature meter - Google Patents

Abstract

Device making it possible to measure, in a direct way, the parameters relating to the pressure (in particular the values of the systolic and diastolic pressures), the frequency of the pulse and the temperature. Direct measurements of pressure and pulse rate are made by transmitting pressure pulses from a sleeve (pressure chamber) (12) to a mechanical-electronic transducer (1), and temperature measurement can be performed in any part of the body under examination by means of a temperature transducer (7). The system may include electronic memories. The measurement results are more precise and are obtained more quickly than with traditional systems and are displayed in digital or graphic form. Such a display (4) also contains light and / or sound signals, used to indicate the existence of pulse signals, or as alarm signals relating to selected critical values of the measured parameters. The device is compact, practical in use and the measurements can be carried out simultaneously.

Description

Descriptive Report of the Invention of an ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER.

The present invention refers to a device which is able to con tinuosly measure absolute pressure, pulse rate and tempera ture. The device basically consists of a mechanical system coupled to transducers which in turn are coupled to an electronic system which is able to convert the results of measurements to digits and/or ghaphics and which can also contain audio or light signals. The meter is mainly intended to meas ure phisiological parameters.

The measurements of blood pressure are usually taken with the use of a cuff (pressure chamber) fitted to the person's body. Increasing the pressure in the cuff, through the use of a pump, there is a value of pressure above which the flux of arterial blood is interrupted in that part of the body.As a gradual reduction of pressure is made through the valve in the pump, a value of pressure is reached in which the blood starts to flow again in the artery, in a pulsed way. This pressure value corresponds to the so-called maximum pressure or systolic pressure. When the pressure in the chamber (cuff) is further reduced, there is a value of the pressure for which the pulses, which are the heart pulses, are not felt any more in the cuff. This value corresponds to the so-called minimum pressure or diastolic pressure. It is noted here that all the pressure pulses, which correspond to the heart pulses, are naturally transmitted by the body to the cuff under the form of small pressure variations. In order to take the measurements of the systolic (Pmax) and diastolic (Pmin) pressures, one usually uses mechanical manometers (aneroid) which are calibrated, for example, in units of mm Hg. The determination of Pmax and Pmin could ideally be made directly through the respective determination of the appearance and disappearance of the pressure pulses of the air in the cuff. However due to the inertia and intrinsic mechanical inaccuracies of the manometers these determinations have not yet been made possible with enough precision.

The pulses, felt between Pmax and Pmin, which correspond to the heart pulse rate can, sometimes, be sensed as small oscil lations, of aproximately 2 mm Hg of the manometer pointer. However there is not great precision in the heart beat counting through these oscillations due to the cited imprecisions and inertia of the mechanical system and also due to the need of simultaneously using a timer, which implies the observation of two separate meters at the same time. The respective values of Pmax and Pmin are then, usually, determined by observation of the pressure values indicated in the manometer when, with the aid of an stethoscope, one feels the begining and the end of the flow of blood in the artery under the cuff's pressure. The counting of the heart beat (pressure pulse rate) is also usually taken by the auscultation of the pulses in an artery with an stethoscope and with the use of a timer. In the literature one finds descriptions of proposed devices to measure blood pressure where microphones are placed in the cuff and over the artery under pressure. Such systems are said to detect the appearing and desappearing of sound signals (korotkov sounds) and so determine, indirectly, Pmax and Pmin. Those systems, however, also have serious difficulties, ranging from the need to filter and choose which sounds are the correct ones to the taken into account, because other sounds can interfer, till individual problems whereby there exists, for some pacients, an absence of such sounds in a certain pressure interval. Somewhat complicated schemes and algorithms are then devised to select one or more sounds as the true korotkov sounds between Pmax and Pmin and to synchronize them with the heart pulses. Other disadvantages of those proposed systems are that the microphone in the cuff must be placed correctly over the artery, and the fact that the microphone is in the cuff, which is an interface that must be handled constantly, thereby causing possible damage to the delicate microphone. There are proposed systems where the heart beat count is taken through the electrical activity of the heart, sensed, for instance, by electrodes placed in the pacient's mouth with the disadvantage of using material that must be discarded. Besides, such systems are not fit to take the measurements of absolute pressure including Pmax (systolic) and Pmin (diastolic). It is then clear that the purely conventional mechanical systems described in the beginning suffer from intrinsic inaccuracies which are enhanced by the need to use several differ ent meters for taking measurements of pressure and pulses which are usually taken at the same time. In such systems one uses a manometer in the cuff and an stethoscope to measure pressure and a timer and stethoscope to measure heart beat. The measurement of another important phisiological parameter as the temperature requires another device, usually an Hg thermometer. Such diversity of devices together with their intrinsic inertias and inaccuracies cause thereby more time and error in the results of the measurements. The proposed electromechanical devices, besides difficulties such as those decribed above, generally sacrifice time or accuracy and in general are not proposed to execute simultaneously the diverse measurements of the phisiological parameters necessary in the usual clinical examinations, such as pressure, pulse rate and temperature. It is an objective of the present invention to make possible the simultaneous measurement of pressure, pulse rate and tem perature . It is also the objective of the present invention to make possible the construction of a compact mechanical- electronic device, optionally portable, which allows the measurements of pressure, pulse rate and temperature, with greater accuracy and speed than the conventional systems.The accuracy and speed in the measurements is the result not only of the electronic circuit used but also as a result of simplicity of the interface pacient/meter and of the working principle of the instrument. The pacient/instrument interface, to measure pressure (including systolic and diastolic) and also to count pulse rate, consists in the conventional cuff ( pressure chamber) with a pressure pump and air scape valve, which is connected to the box of the meter only through a flexible tube. Such an interface is practical and traditional, facilitating the operations of measurements of pressure and pulse rate with the proposed meter. The operator can even take this interface (cuff and pump) from his conventional mechanical manometer, and couϋle it directly to the meter box, proposed here, and also vice-versa - this represents versatility and economy. The fragile part of the device,such as transducers and electronic part is contained within the rigid meter box and not in the interface, and this represents less risk of damages during usage. Such interface also allows measurements of pressure variations directly in the pressure/ pulse transducer (or transducers), which is located in the rigid body of the instrument and which is connected to the cuff only through the flexible tube. In this way, one avoids the need to find the appropriate location of a microphone over the artery, as needed in systems which intend to sense pulse through the presence or absence of sound signals, and one also avoids possible damage to transducers due to the handling of the cuff. The present system allows for minimum variations of pressure communicated to the inflated cuff, to be directly transmitted to the pressure/pulse transducer, which will be described later on.

It is an objective of this invention to describe a pressure/ pulse transducer which is versatile and capable-of sensing very small pressure variations (on the order of 0.1 mm Hg). The measurements of pressure are taken in a direct way,contrary to what occurs with systems which propose such measurements through the indirect detection of pulses using,for instance, sound signals. The pulse rate measurements are also taken directly in the transducer.

The measurements of temperature are rapidly taken, in any part of the body, as the temperature transducer, of low heat capacity and of small dimensions is placed in a small housing of high thermal conductivity and is connected to the meter box through a flexible cable.

Another objective of the present invention is to take a set of measurements of the parameters of interest (pressure, pulse rate and temperature), to be stored in electronic memories for later usage, such as in statistical averages and in the observation of the evolution of a pacient or other system under observation.

A further objective of the present invention is to present the results of measurements of the diverse parameters in a way that allows a better visualization than the conventional sys terns. Thus, the results can be displayed in the form of numer ical digits, and/or in an analogical form through graphics in paper or TV tube (cathode ray), and the display can also include light and audio signals to indicate preselected levels reached by pressure/temperature or to indicate the existence of pulse signals or still as alarm signals.

Besides the advantages already decribed, it is noted that the present system is compact and eliminates the need of the diverse meters tradiσionally used to measure pressure, pulse rate and temperature, which are: manometer, stethoscope,timer and the Hg thermometer.

It is then more practical, faster in response, and more precise than the conventional systems besides presenting the results in a display with better visualization. Othe objec tives and advantages of the present invention will become evident through the description of the basic or preferred embodiment of the device, which is described in the following typical setup.

The drafts included in this report, illustrate the intended innovations. Figure 1 is a schematic representation, for medical use, of the proposed device, in a block diagram form, and where the mechanical-electronic sensor-transducer proposed for pressure/pulse measurements is indicated by numbers (1) and (10). The figure 2 represents in. a more detailed schematic diagram the amplifier circuir shown as block (2) in figure 1. Figure 3 is. a schematic diagram of the analog-digital converter shown as block (3) in figure 1. Figure 4 is a more detailed diagram of the filter circuit, shown in figure 1 as block (5), and its connection to the counter circuit. Figure 5 shows a diagram of the counter circuit shown as block (6) in figure 1. Figure 6 is a schematic representation of one of the basic arrangements proposed for measuring temperature. Figure 7 is a schematic representation of an alternative proposed arrangement for measuring temperature, where the transducer is a diode.

Figure 1 illustrates, schematically and for medical use, the proposed device in a block diagram form. The measurements of pressure and pulse rate are taken as follows: the pump (14), manually driven, fills up the pressure chamber (cuff) (12) which is in contact with the person's body under examination, and deforms the diaphragm (10). Above a certain value of pressure in the cuff the flux of arterial blood is interrupted and the pulses due to the heart beat disappear in that part of the body. As a gradual reduction of pressure in the cuff is made, through the valve in the pump, a value of pressure is reached in which the blood starts to flow again in the artery in a pulsed way. These pressure pulses are transmitted, through the cuff (12) and the flexible connector tube (11), to the diaphragm (10) which is located in the rigid box of the meter. The detector-transducer system (10 and 1 - Fig. 1), referred to here, is located inside the rigid box of the device and consists of a transducer (1) and a diaphragm (10) which is airtight when externally connected to the the cuff through the flexible connector tube. The diaphragm may have several configurations with the basic requirement that it be elastic and easily deformable and that this deformation be comunnicated to the deformation transducer which will generate the electrical signals which will then be amplified and appropriately processed in the electronic circuit. Experiments and tests made with cylindrical or circular metallic diaphragms, have shown a much better linearity as compared with the tradicional clinical manometers. The deformation transducer (1) can be connected diretly to the diaphragm, as for example, a strain-gauge glued to the elastic circular and smooth plate of the diaphragm. Another example of a configuration that gives good results is obtained- by connecting the deformation transducer to a flexible rectangular metallic plate, anchored to the structure of the meter by one or by both ends, and such that the diaphragm can through direct contact, communicate the pulses of the cuff to the flexible plate. Due to the design and geometry of this sensor-transducer, the mechanical effect of the pulses in the cuff is amplified and directly applied to the deformation transducer (1) itself, in the case of measurements of pressure/ pulse rate. Optionally one can use one transducer for pressure and another for pulse rate.

With the basic arrangements described above and using, for example, strain-gauges in the sensor-transducer setup, where the deformations of the cuff are directly transmitted to the transducer, one gets better linearity and a much greater accuracy than with conventional systems, as will be described. The arrangements of the sensor-transducer setup can have configurations dif ferent from the basic one described above and other deformation transducers, besides the strain-gauges, cited above, can be used, as for example, piezoelectric crystals or differential transformers (LVDT). The results are similar and this does not affect the scope of the invention. The results of pressure meas urements at each instant are amplified by the amplifier (2) and converted to digits by the converter (3) and are continuously displayed in the display (4). The amplifier, block (2) of fig.1, shown in greater detail in Fig. 2, consists in an operational amplifier of very high gain and high sensibility, which is able to amplify signals corresponding to pressure variations with val ues below 0.1 mmHg when coupled to the sensor-transducer (10,1) described above. Such a pressure value is on the order of 20 times more accurate than the clinical (aneroid) pressure gauges. This result allows determinations of systolic and diastolic pressures with much greater accuracy than with conventional meters and enlarges the difference between those two values ofpressure. The converter, block (3) of Fig. 1, shown in Fig.3, transforms the analog signals, coming from, the amplifier (2),on the order of mV, to digital signals of three digits, expressed in pressure units (mm Hg, for example), to be displayed in the display (4). The pulses may be observed through light and/or audio signals and also observed in the display (4) as will be described later on. The systolic pressure (Pmax) corresponds to the pressure value displayed in the display (4) when the pulse signals start after decreasing the pressure in the cuff (12) from the value where there is oclusion of the flux of arterial blood. This starting of the pulses is indicated by light and/or audio signals, as said before. With a further deacreasing of pressure in the cuff (and consequently in the diaphragm) a value of pressure is reached when the pulses are not sensed anymore by the cuff and, consequently not sensed by the transducer, as described above. The diastolic pressure (Pmin) corresponds to the pressure value registered in the display (4) when these pulses disappear which is accompanied by the disappearance of the light and/or audio signals which indicate these pressure pulses.

The pulse rate counting is made as follows. The pressure variations in the cuff, which appear as mechanical oscillations in the diaphragm (10) and transducer (1) coupled to it, are continuously monitored by the circuits of: filter (A), shaper (B) and counter (C), as is shown in fig. 4 which shows block (5) of Fig. 1 in detail. The filter circuit separates the pulse signals from noise to avoid false values of oscillations to be registered. This circuit consists of a filter (A) tuned at low frequencies on the order of 1 Hz. The shaper circuit (B) permits only signals in form of digital pulses to be sent to the counter (C). These pulses are also sent to a light bulb or light emitting diode (LED) in the display (4), which generates the light signals indicative of the existence of pulses. An audio signal can also be simultaneously generated with the same objective. Counter (6) (fig.1), represented by (C) in Fig. 4, is shown in detail in Fig. 5, and consists of 3 decades (BCD) and its corresponding BCD/7 segment converters, which send to the display (4), (LED or LCD, for example), the values stored in the counter, in a preselected time interval, which is given by the timing and control circuit (Fig. 5). The timing and control circuit (Fig. 5) is responsible for the generation of the pulses which control the interval of time for the counting/sampling of the pulse rate (heart beat). The time intervals can be chosen according to the required accuracy, for example 15,30 or 60 seconds. In the case of 15 or 30 s, a multiplier circuit (D) Fig. 4, of respectively, 4 or 2 times, connects the shaper (B) to the counter (C), as in Fig. 4. The measurements of temperatures are taken with the temperature transducer (7), which can be placed in contact with the body under examination through a flexible cable which allows temperatures of any part of the body to be taken easily. In the basic configuration shown in Fig. 1, the sensor-transducer (7) acts as an active element in an digital oscillator (8), shown in Fig. 6. Small variations in the temperature under observation cause variations in the RLC parameters of the transducer, causing thereby variations in the oscillator frequency. The oscillator (8) in tuned so as to make possible measurements of temperature in the 15 to 50 C range, with an accuracy of 0.1°C. The frequency divider (9) matchs the oscil lator frequency to the requirements of counter (6) so as to show the correct values of temperature in the display (4). In another similar configuration shown in Fig. 7, the temperature transducer (7) of Fig. 1, for example a diode of low heat capacity, sends voltage signals through a flexible cable, as described above, to an analog comparator which subtracts these signals from a reference value for scale adjustment. The output of the comparator is connected to an amplifier capable of transmitting to the analog-digital converter (3) the signal at an adequate level. As previously described the converter sends the results of the measurements to the display (4). With this configuration it is possible to easily measure temperatures in the 0°C to 70°C range with accuracy of at least 0.1°C, with a stabilization time lower than 30 s, i.e., at least 4 times as faster as a clinical Hg thermometer. The basic configurations to measure temperature which were described above, should not be considered as the only ones, because other types of transducers, such as a thermistor, can be used without changing the scope of the invention. As the display (4) is common to all measurement modes one or more displays can be used for the three types of measurements referred to here. Analog displays for graphic output can also be used.

Electronic memories (RAM, ϋVPROM, EEPROM) can be included in the system for storing data for later use by an "inteligent system", such as a microprocessor or host computer, through operation of direct access to the memory (ADM) . This enables the system to perform programmed tasks as for example, automatic registration of systolic and diastolic pressures through a system fed in closed loop. Critical values of pressure, pulse and temperature can also be indicated by sound and/or light alarm signals, which is very useful in surgical monitoring. This also makes possible the interpolation and extrapolation of values of pressure, pulse rate and temperature to follow the clinical evolution of pacients. Together or separately, the pressure and temperature meters can be used in industry and scientific instrumentation, where accurate and fast measurements of these parameters are needed. For non medical use it suffices to modify the already described interface between the device with the object of the measurement.

Claims

CLAIMS 1. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, which consists of a mechanical-electronic device capable of continu ously measuring the parameters of pressure (including systolic and diastolic pressures), pulse rate (heart beat count) and temperature, built in compact form, optionally portable,easy to use with handling similar to the traditional medical devices for measuring pressure, characterized by having a pump with air escape valve connected, through a flexible airtight tube, to a cuff (or pressure chamber), so that when the pressure is increased or decreased in said cuff, which is adapted to a convenient part of the body under examination, the arteri al pulses are continuously transmitted, through a flexible tube, to an airtight diaphragm, elastic and easily deformable under the action of pressure variations in said cuff or pressure chamber and so that said diaphragm amplifies the mechanical effect of said pressure variations in a way that even very small pressure variations or pulses can be detected as deformationswhich are communicated to one, or more, electronic deformation transducer which transforms said deformations in electric signals that will be amplified by the amplifier (2) and sent to the electronic circuit for processing the pressure/pulse rate measurements; and for measuring temperature through a temperature transducer (7) connected to the end of a flexible cable so that said transducer sends, through the cable, electric signals to be processed by the temperature electronic circuit in the meter and to be displayed.

2. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claim one wherein said deformation transducer is rigidly coupled to said diaphragm, or is in contact with a flexible plate, which is anchored to the structure of the meter, so that such plate bends under the action of the diaphragm deformations, which are in any case transmitted to said pressure/pulse sensor-transducer, which transforms such deformations into electric signals which are, in turn, amplified.

3. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claims one or two, wherein the processing of the pressure signals is accomplished through the conversion of said electric signals to digits and/or graphics that are registered in a display ( 4 ) .

4. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claims one or two wherein the pulse signals are monitored by circuits of filter (A), shaper (B) and counter (C) and sent to the display (4).

5. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claim one wherein the processing of the temperature signals is to be accomplished by a piezoelectric crystal associated to a digital oscillator (8), a frequency divider (9), a counter (6), and the result is sent to the display (4), or to be accαiplished by a diode where the temperature to be measured is compared with a reference value, amplified and converted by an analog digital converter (3) and the result is sent to the display (4), or to be accomplished by a thermistor connected to a volt age controlled oscillator or yet by a thermocouple, and where in any case the temperature values are shown in the display (4) in the form of digits or graphs.

6. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claims one, two or four, wherein the pulse rate counting is taken in convenient intervals of time and wherein the result of such counting is automatically indicated by numerical digits in the display (4) and such that said pulse signals are indicated by light signals and/or audio signals and/or graphs.

7. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claims one,three or six wherein the results of pressure measurements are continuously indicated in the display (4) and where the value of Pmax (systolic pressure) is the pressure value indicated in the display at the time of the starting of the pulse signals which are indicated by light and/or sound signals,and where the value of Pmin (diastolic pressure) corresponds to the pressure value indicated in the display at the time of the end of the pulse signals, which corresponds to the end of the light and/or sound signals.

8. ABSOLUTE PRESSURE, PULSE RATE AND TEMPERATURE METER, as in claim one, wherein the data resulting from measurements can be stored in electronic memories (RAM, UVPROM, EEPROM) which can be included in the apparatus and which can be coupled to a microprocessor or host computer or other "intelligent system" which enables the system to indicate through light and/or sound alarm signals preselected critical levels of pressure, pulse rate and temperature,enabling also the automatic indication of the values of systolic and diastolic pressures in the display and also allowing for the interpolation or extrapolation of values of pressure, pulse rate and temperature.