CA1260612A - Outpatient monitoring systems - Google Patents

Abstract

TITLE

OUTPATIENT MONITORING SYSTEMS
AND METHODS

ABSTRACT OF THE DISCLOSURE

The invention provides a system and a method for obtaining from the patient's body information pertaining to the blood pressure and heart rate of a patient for the purpose of enabling a physician to monitor and prescribe treatment intended to maintain a patient's blood pressure within a predetermined range, for encouraging the patient to follow the treatment and for collecting information relating to the patient's blood pressure and heart rate. Signals are generated that represent the level of blood pressure and pulse rate of a patient in a form suitable for telephonic communication. The signals are transmitted to a remote central digital processor for storage and analysis. Data resulting from the analysis is submitted to the patient or physician. An off hook and ring detect circuit is provided preventing actuation of the system when telephonic access is unavailable.

Description

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:, . . . --l~l S P E C I F I C A T I O N
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Be it known that we, JACQUES J. OHAYON and GLEN P.
WILLIAMS, citizens of the United States residing at Pittsburgh, County of Allegheny, Commonwealth of Pennsylvania, have invented certain new and useful improvements in OUTPATIENT MONITORING
5 ~' SYSTEMS AND METHODS of which the following is a specificationO

FIELD OF THE INVENTION
i The invention relates to the continuous treatment and diagnosis of blood pressure disorders as well as the monitoring of a prescribed treatment of medication for a patient on an l ongoing basis.
, i DESCRIPTION OF THE PRIOR ART

It has been a long standing goal in the heath care Il community to integrate advanced communications systems with ¦l information processing systems to provide superior medical I services. By way of ex~mple, United States patent No. 4,004,577 ~, discloses a method for treating coronary prone patients when heaxt attack symptoms occur before qualified direct contact 1, personal care can be administered to the patient. A device provides auditory signals indicative of the existing heart beat condition and telephone communication is established between , !
; the patient and a source capable of making a qualified response based on the auditory signals.
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There has been a continuing need for improved monitoring techniques for patients suffering from blood pressure disorders, such as hypertension or hypotension. Hypertension, in particular, Il ls a pxevalent health problem in the United States and is the f major cause of early death and serious disability in an estimated 25 million persons annually. One of the most menacing aspects of hypertension is the fact that it remains undetected and untreated in many persons and, therefore, causes permanent ~ damage before it can be discovered. Since blood pressure ~ normally varies in healthy persons, the state of hypertension is somewhat relative in nature. Because of the many factors which influence blood pressure, the measurement of a single elevated blood pressure is not necessarily significant. However, every person with a blood pressure reading above normal should be ll reexamined several tumes to determine if the measurement persists.
The treatment of a blood pressure disorder is subject to the same difficulty as the initial detection or~ that disorder, that is, the many factors which influence blood pressure.
j Therefore, there is a need for a method for obtaining I
I information pertaining to the blood pressure and heart rate of ¦, a patient in an outpatient environment and for providing an !
analysis of that information~ Further, there is a need for a I method for enabling a physician to prescribe treatment intended j to maintain a patient's blood pressure within a predetermined ,~ range and for collecting information relating to the patient's Il .

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blood pressure. There also e~ists a need for a method for enabling a physician to prescribe treatment intended to main-tain a patient's blood pressure within a predetermined range for encouraging the patient to follow the treatment and for , collecting information relating to the patient's blood pressure by periodicall~ generating and storing such information for selective later analysis.
SUMMARY OF THE INVEMTION
The invention is a system and method, each of which provides information pertaining to the blood pressure and heart rate of an outpatient. The information enables a physician to monitor and prescribe treatment and can be utilized to encour-age the patient to follow a prescribed course of treatment by the scheduled monitoring of his o~n condition. The invention includes a method and system for generating a first signal representative of the patient's vital signs and a second signal identifying the individual patient from one or more other patients monitored using the present method. The signals are in a form suitable for telephone communication with a central digital processor which analyzes and stores -the information.
The information is then submitted to the patient or the patient's physician. The physician can use the information, at least in part, in reaching a prescribed course of treatment for his patient.

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~~ -3a- 71548-27 In accordance with the present invention, there is provided a system for providing information pertaining to the blood pressure of a patient utili~ing telephone lines, including a ring line and a tip line, said system comprising:
means for generating signals representing the level of blood pressure of a patient and signals representing the identity of to which patient, of at least two patients, the blood pressure signals pertain, said signals being suitable for transmission over said telephone lines; a remote central diyital processor;
and means for transmitting said blood pressure signals and said patient identifying signals over said telephone lines to said remote central digital processor, and including an off hook detecting circuit having voltage r.1easuring means for measuring voltage across said ring and tip lines, and switching means responsive to the measured voltage and operative to connect .
said transmitting means to the telephone lines only when said voltage is above a predetermined voltage indicating that the telephone lines are not in use; said central processor including store means which stores said blood pressure signals in a form suitable for later access, and analyzing means which analyzes said blood pressure signals according to predetermined criteria.
BRIEF DESCRIPTION OF TE-IE DRAWINGS

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The above as well as other features and advantages of the present invention will be more clearly appreciated through a consideration of the detailed description of the invention in , conjunction with the drawings in which Figure 1 is a block diagr~mmatic representation of the , method of the invention;
'~ Figure 2 is a block diagrammatic representation of an I alternative embodiment of the method of the invention;
ll Figure 3 is a telemanometer block diagram for a preferred embodiment;
~, Figure 4 is a schematic diagram of a preferred ¦ microprocessor, réset and time base system used in the tele-: ~ manometer of Figure 3;
I Figure 5 is a schematic diagram of a preferred memory chip and address decode system used in th~ telemanometer of Figure 3;
Figure 6 is a schematic diagram of modem and SPHYG
¦l interface system used in the telemanometer of Figure 3;
Figure 7 is a schematic diagram of lights and switches ¦~ in the preferred system of Figure 3, and Figure 8 ~s a schematic diagram of the off-hook and ring detect circuit of this invention.

DETAILED DESCRIPTION OF THE P~ r~R~rD E~ODI~E~
1, The present invention provides a method and system 25. 1 through which several objectives can be accomplished. Patient 1 1 ' ' I ~I
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1, 1 ., , ~2~ 2 compliance with a prescribed course of medical treatment as well as the effectiveness of the treatment can be monitored, recorded and analyzed. The patient's medical condition can ` be periodically monitored over an extended period of time on an ., outpatient basis in order to provide the treating physician with an additional diagnostic tool. The patient can also be provided with a treatment feedback system which enables the 1 patient to recognize his compli~nce with, or his failure to '~ adhere to, a particular course of medical treatment. Such a feedback system also facilitates an analysis of the patient's developing medical history and a comparison of the patient's condition with the original prognosis coupled to a predetermined course of treatment.
It is to he appreciated that a variety of individual 1I pieces of equipment can be integrated into the system of the ¦ present invention which carries out the method of this ¦~1 invention. The equipment itself is available and upon a full appreciation of the invention, those skilled in the art will recognize that subs~itutions to the equipment so utilized can ~ be made and that such substitutions are well within the scope of the invention as defined by the several claims appended i here~oO
Accordingly f the following description of equipment } employed by the system is provided only as an examplel The I present trend in the production of instrumentation for llse in 1, 'I

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.~6~ 6~2 71548-27 blood pressure and heart rate measurement is toward the manufacture of automatic or semi-automatic devices. The pre-sent invention contemplates the use of an electronic sphygmano-meter in which a microphone or transducer is provided for the detection of korotkoff sounds. A microprocessor can be included to control inflation and deflation rates of the cuff on the patient's arm. The information obtained from the trans-ducer is converted into a siynal suitable for telephone trans-mission by means of a system as typified in United States patent No. 4,068,096. Another example of a suitable communica-tion system for use with existing telephone equipment is commercially available and consists of a pair of send/receive acoustic coupling systems or modems. It is anticipated that the several individual components described above could be incorporated into a single integrated apparatus comprising an electronic sphygmanometer with automatic tele-phone dialing and modem capabilities which permits a very large number of individual patients to transmit vital blood pressure ; and heart beat functions to a central computer facility. The central facility would include equipment for establishing two way communication with a patient to provide both instantaneous feedback as well as later hard copy information, such as a print out of the patient's medical status and a record of the blood pressure and heart beat informa-tion submitted to the central facility.

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-Figure 1 describes the several steps of the present invention followed by the system of the present invention.
The method provides information pertaining to the blood pressure and heart rate of an identifiable patient and is presented in Figure 1 in block d~agrammatic form. The method permits the monitoring of the blood pressure and heart rate of at least one patient in a group of patients, the number of which is limited only by the capability of a remote central data collecting and processing system. Each patient is provided with a device which the patient can employ to take his own heart rate and blood pressure. The device includes apparatus which generates a signal representing the blood pressure, that is a systolic value and a di~stolic value, and heart rate of the patient.
' The device also includes apparatus which generates a second : 15 ll signal which represents the identity of the patient. Such a signal could provide, for exa~ple, the patient's name, social security number or some such similar coded indicia which particularly identifies a specific patient within the monitoring network. The patient identification signal is preferably provided through the programming of an Plectrically 1 alterable memory device. Thus, a particular device is adaptable~
to the indicia requirements of the health care system which is utilizing the method of this invention. ~oth signals representing the patient's monitored vital signs and the patient's identity are generated in a format which is suitable ~ for telephonic transmission.

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The patient's blood pressure, heart rate and identity signals are then transmitted, over telephone lines, to a remote central data collecting and processing system which stores the monitored vital sign signals in a patient file in a form suitable for later access. The signals are analyzed by the processing system and compared to a set of predetermined criteria established by the patient~'s treating physician.
The results of the analysis are then submitted to the patient.
As a result, the patient gains the advantage of regular ~ feedback concerning his blood pressure.
The results of the blood pressure data analysis can be supplied to the patient's physician~ Based at least in part on the analysis results, there can also be submitted to the patient information specified by his physician pertaining to If his measured and analyzed blood pressure and heart rate.
I While the collection analysis and feedback of medical ¦l information has been described in conjunction with a single I
¦I patient and that patient's physician, it is to be understood Il that, by employing the aforedescribed indicia system, more than -jl one physici~n can be provided with information pertaining to ¦l a single patient and that more ~han one physician can be in ¦I communication through this method with the data reflecting the l immediate condition of the physician's respective patients.
The method also includes steps by which immediate feedback to the patient can be effected. Upon receipt of the , I .

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signals representing the patient's blood pressure, the central data collecting and processing system can make an immediate determination as to whether or not the incoming data is I sufficient for analysis, and activate an indicia means, such as , a warning light, at the patient's location advising the patient that an additional blood pressure reading is required for analysis. Also, if the reading is abnormal for a particular patient, the central data collecting and processing system can I be programmed to request that the patient take one or more additional readings, or signal the patient or the patient's il physician that immediate medical attention is advisable.
Under what could be described as a typical patient monitoring and information feedback program, the patient's ~ blood pressure information and analysis would be generated in ¦ a hard copy format for distribution to the patient and his I physi~ian. Additionally, notices could be periodically generated, if necessary, to remind the patient of the required schedule for vital signs readings.
While specific medications are readily available for the treatment of blood pressure related disorders, the particular dosage which is suitable to the unique condition of a particular patient must be carefully monitored and controlled. According ¦¦ to the techniques of this invention, the presumptive aspect of dosage determination can be substantially eliminated through f the continuous monitoring and analysis of the patient's condition.

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The method represented by the block diagram enables a physician to prescribe treatment intended to maintain a patient's blood pressure within a predetermined range to both encourage the ~ patient to follow the treatment through continuous monitoring and the behavioral reinforcement of frequent feedback, and to collect information relating to the patient's blood pressure to establish a complete history of the treatment process.
A modification of the method of the present invention Il is also illlustrated in the block diagram of Figure 2. The ~ patient is provided with a device with which the patient is trained to take blood pressure. The device includes apparatus which generates a signal representing the patient's blood i¦ pressure and heart rate readings. The device also includes an ¦l electronic data storage medium for storing the generated ~I signals in a form suitable for transmission by means of i existing telephonic communcation systems~ A remote central digital processor includes apparatus for addressing the ~i patient's electronic data storage medium according to a ; ~ predetermined schedule to access the stored signals representing the patient's blood pressure and heart rate readings.

I Utilizing such a system, a series of vital signs readings I
could be taken over a predetermined period of time and stored in the data storage medium located, for example, in the patient's home. The remote central digital processor which I can be located, for example, in a physician's office or other 1 10.
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health care institution, would access and interrogate the home storage medium according to an established routine which would include repeated attempts to contact or reinterrogate the home storage medium if the phone line were to be in use during a ~ previously attempted interrogation. Such attempts to reinterrogate the home storage medium would be expected after the expiration of a time period of a predetermined duration~
I As previously described, the remote central digital 1 processor is programmed to include a predetermined set of ~ criteria for each patient's blood pressure data. The results of the analysis of the blood pressure reading can alternately be submitted to the patientls physician or the patient himself.
In the case of submission to the physician, the physician would be in a position to develop a course of treatment based at least 1 in part on the results of the data analysis. The physician ¦~ could then specify the particular information to be submitted ll to the patient.
; 1l In addition to the periodic interrogation of the patientls ¦I home data storage medium by the central digital processor as ~i described above, the present method can incorporate an additional ¦ step. The central digital processor can include, in combination with the home apparatus, apparatus for notifying the patient that a scheduled blood pressure reading should be made~ or that i one or mQre scheduled readings has ~een missed.
~~ In Figures 3 through 6 there is illustrated in schematic , ' ', Il 11. ' ~2~

form a preferred embodiment of telemanometer for use in this ll invention. In these figures ~here is illustrated a general purpose 8 bit microcomputer 10 which performs all of the arithmetic and logic operations necessary to control a remote sphygmanometer. Decoder 11 decodes address bits AB12, AB13 and AB14 of microcomputer 10 to provide unique select lines for all the RAM, ROM and 1/0 devices on the printed circuit board~
¦~ Reset circuitry 12 provides an automatic "power onl' I reset function for the processor 10 and 1/0 devices. The RES
]0 l, line is held low for a fixed time period immediately following ., application of power to the printed circuit board~
An Ultra Violet "Erasable/Programmable Read Only Memory" (EPROM) 13 provides 4,096 x 8 bits o~ read only memory i~ which contains all the program instructions required by the 15 ~ m~croprocessor 10. The EPROM 13 is factory progra~med and cannot i be field altered. The memory of the EPROM 13 is "non-volatile"
¦! and will not be erased when power is removed from the printed I
circuit board.

¦ A random access memory (RAM) 14 having 2,048-x 8 bits ¦ of memory is connected to a data bus lS and an address bus 16 along with EPRAM 13, This R~M provides temporary storage for ¦~ variables and data needed by the microprocessor 10. The contents of this memory will be lost if power is removed from the printed circuit board.
!l 1 EEPROM 17 is connected to data bus lS and address 12.
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bus 16 and provides 128 x 8 bits of non-volatile random access memory. Data written into EEPROM 17 will survive even if power is removed from the microprocessor circuit board. The EEPROM 17 is used to store "user specific" data that cannot be lost if power is removed from the board.
Time base circuitry (Fi~ure 4~ is provided which generates several highly accurate clock frequencies using a 4O032 MH2 crystal as a time base. A 1/0 clock in the microcomputer ~ 10, an XTALl clock in an Asynchronou~ Communications Interface Adapter (ACIA) 18, and a program clock in the EEPROM 17 are all derived by dividing the 4.032 MH~ clock rate by fixed constants.
The ~synchronous Communications Interface Adapter 18 provides standard ASC II Serial to Parallel and Parallel to , Serial Conversion for the microcomputer 10. All functions of the ¦l ACIA 18 are fully controlled by microcomputer 10.
~ ', A complete Bell 201 modern interface l9 allows ; 1 standard ASC II transmission over ordinary customer telephone t ~1 lines~ Fully bidirectional (Full Duplex) communication is !I provided using two frequencies for transmission and two for ¦l~reception.
¦l A programmable dialer interface 20 provides both pulse ., ~1 and touch tone (DTMF) dialing capabilities as a companion to the ¦ modem 19 and shares related circuitry with the modem.
¦ ,~ A duplexer circuit 21 provides transmit gain control, telephone line impedance matching and transmit signal nulling functions.

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Transformer 22 provides the necessary isolation between the printed circuit board electronics and the user's telephone line.
~ An Aromat DS2-M-DC5~ relay 23 provides an electronically isolated means of connecting and disconnecting the modem and dialing electronics from the user telephone line. If pulse dialing is selected, this relay is opened and closed under the control o~ dialer 20 to dial a telephone numberO
~l A general purpose input/output port 24 is used to buffer output and input signals needed by the microcomputer 10.
il In addition, two internal programmable timers are used as an ¦ accurate time base for software controlled timing functions.
An on chip shift register is also used in this post to receive serial data from the sphygmanometer microcomputer 10.
¦ A second general purpose input/output port 25 is used to buffer user selected switch inputs.
A buffer LED driver chip 26 allows the microcomputer 10 to turn on and off the indicator lamps (LED) (Figure 7) I I used to show the system status.
¦ An off hook and ring detect circuit 27 generates ¦an "off hook" condition to obtain a dial tone from a local ,phone office. Dialing can thereafter be carried out. This ~circuitry also checks to see if the phone line is already in ' use before attempting to dial out. This circuit is particularly set out in Figure 8 and forms an important part of the invention.

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The purpose of the off hook and ring detect circuit ¦ 27 is to determine whether any other telephone device connected to this trunk line is currently off hookO If another device on '~ the line is already "off hook", then the telemanometer will not attempt to go off hook. This prevents the telemanometer from interfering with an ongoing telephone conversation or other use of the phone line.
Il The off--hook detect circuit is directly connected to ¦1 the incoming trunk line's "ring" and "tip1' circuits. For 11 safety reasons, and to comply with FCC Regulations, the "ring"
¦, and "tip" lines must be electrically isolated from the low voltage circuitry associated with the microprocessor. The ¦1 required 1500 VOLT isolation is provided by the optocoupler 28 11 and the optically coupled triac 29. These optically coupled lS ~ devices provide sufficient isolation to prevent lightening-strikes or accidental shorting of the phone lines and power lines from creating a danger to anyone using the telemanometer.
"Off-Hook" detection is accomplished by measuring the absolute voltage present across the incoming "ring" and "tip"
1 linesO If no other de~ice is currently "off-hook" on this circuit, then the central office battery voltage will appear ¦1 across the "ring" and "tip" lines. The central office battery ~ voltage is nominally 48 Vol~s DC. The polarity of this voltage 1 1l is supposed to be guaranteed. However, faulty interior telephone wiring wi11 often cause the "ring" and "tip" lines to be reversed.

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Therefore, this circuitry was designed to operate with any battery polarity. Detection of the central office battery voltage indicatec that the phone line is not currently occupied.
If another telephone device is currently "off-hook" on the same trunk line then the voltage across the "ring" and "tip" will drop to below 10 Volts DC. Detection of this lower voltage indicates that the phone line is currently occupied. The circuit which detects this voltage difference is decribed below.
1 For the first case, assume that no devices, including , the telemanometer, are "off-hook". Thus a DC Voltage of approximately 48 Volts and unknown polarity exists across the ¦l "ring" 30 and "tip" 31 lines.
¦I Before activation, our circuitry presents a very high impedance to the phone lines. This high impedance is insured ¦¦ by the de-energized triac output of the optically isolated triac 29 labeled "O.C.T~l". 'rhus, until aYtivation, our detection ¦¦ circuitry will in no way interfere with the normal operation of 1 1l the phone lines.
; ~I To activate the "off-hook" detect circuit, pin 2 of I triac 29 ~O.C.T.l) is driven to near ground potential by an external circuit i.e~ drive 26 (NE590) controlled by the microprocessor chip 10. This allows sufficient current, determined by resistance 32, also labeled "R5", to flow 1i through the Light Emitting Diode to activate the triac output 1l of O.C.T.l~ The "tip" line will therefore be electrically 1, ' . .

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connected to the lower AC input connection of the diode bridge 33 labeled "DBl". The "ring" line is connected to the top AC input of DBl by resistance 34 (Rl) and condenser 35 (Cl). Resistance 34 IR1) serves to limit the current taken from the phone lines to approximately 2 mA. This small current will not significantly affect the voltage across the "ring" and "tip" lines. Diode bridge 33 (DBl) insures that the current flow through the rest of the detection circuitry is of known polarity regardless of the , polarity of the incoming voltageO The current flowing from the , ~ (positive) terminal of DBl is split between the Zener Diode ¦l 36 ~Z2) and ~he resistor 37 (R2) . The current through R2 is limited to approximately 1.8 mA by the voltage clamping action of Zener Diode 36. Thus, approximately 0. 2 mA of the available ~¦ 2 . O mA of current flows through Z2 . The 1.8 mA flowing through l R2 also flows through the Light emitting input diode of the optical coupler labeled "O.C.lU. This current and the remaining current from Z2 flow back through Zener Diode 38 (Zl), through the - (negative) input of DBl, and subsequently back into the I¦ telephone lines. The approximately 35 Volt drop across Zener ¦¦ Diodes Zl and Z2 insure that this c~rcuit will not conduct I current unless at least 35 Volts appears across the "ring" and tip~ lines. In this case, sufficient current will be provided by the 48 Volt central office battery to activate the Light ¦, Emitting Diode in O.C.l~ me resulting photons will excite Lbe output transistor of O.C.l. Current will thus flow from the Il 17.

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, +5 Volt power supply through resistor 39 (R3), through the output transistor of O.C.l, and into resistor 40 (R4) and the ~ase of transistor 41 (Ql). This current is sufficient to saturate transistor Ql and to drive it's collector to near ground potentialO The saturation of Ql is used to indicate that the full 48 Volt battery voltage is present across the "ring"
and "tip" lines.
In the second case, some other device is "off-hook"
' and the voltage across "ring" and "tip" is less than 10 voltsO
Here, the activation of O.C.T.l brings only 10 Volts across the ; AC inputs of DBl. The resulting output voltage across the I + and - pins of DBl is insufficient to activate Zener Diode ¦I Zl. Thus, no current may flow through Zener Diode Z2 or the Light Emitting Diode input of OoC~l~ With no current input to OoC~l ll ~here will be no current flow through the output transistor of Il OoC~l~ The emitter-base voltage of Ql will fall to 0 (zero) ¦¦ Volts and Ql will turn off. When transistor Ql is off, it ¦¦ indicates (through a line to VIA2) that some other device is "off-hook" on this circuit.
I What has been describ~d above is a method for the continuous treatment and diagnosis of cardiovascular disorders as Il ~ell as a method for the monitoring of a prescribed treatment of ¦1l medication for a patient with immediate feedback provided with Il analysis to the patient and his physician.
The foregoing specification sets out cer~ain preferred I I .

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,: -practices and embodiments of this invention, however it will beunderstood that this invention may be otherwise embodied within the scope of the following claims.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A system for providing information pertaining to the blood pressure of a patient utilizing telephone lines, including a ring line and a tip line, said system comprising:
means for generating signals representing the level of blood pressure of a patient and signals representing the identity of to which patient, of at least two patients, the blood pressure signals pertain, said signals being suitable for transmission over said telephone lines;
a remote central digital processor; and means for transmitting said blood pressure signals and said patient identifying signals over said telephone lines to said remote central digital processor, and including an off hook detecting circuit having voltage measuring means for measuring voltage across said ring and tip lines, and switching means responsive to the measured voltage and operative to connect said transmitting means to the telephone lines only when said voltage is above a predetermined voltage indicating that the telephone lines are not in use;
said central processor including store means which stores said blood pressure signals in a form suitable for later access, and analyzing means which analyzes said blood pressure signals according to predetermined criteria.

2. The system of Claim 1 wherein said voltage measuring means includes a diode bridge circuit, connecting means for selectively connecting the ac inputs of the diode bridge across the ring and tip lines, and a voltage divider connected across the output terminals of said diode bridge and comprising a zener diode in series with a resistor, and wherein said switch-ing means includes a light emitting diode in series with said resistor and zener diode, said light emitting diode being turned on only when the voltage across said ring and tip line is above said predetermined voltage, a photo transistor which is turned on by photons emitted by said light emitting diode when the light emitting diode is turned on, and a saturable transistor which is driven into saturation when said photo transistor is turned on, saturation of said saturable transis-tor providing the indication that the telephone lines are not in use.

3. The system of claim 1 wherein said analyzing means includes means for determining the sufficiency of said signals representing the level of blood pressure of the patient, and means for sending over the telephone lines back to said means for generating said blood pressure signals, a feedback signal calling for an additional blood pressure reading when said signals representing the level of blood pressure are insuffi-cient, and wherein said means for generating said blood pres-sure signals includes means responsive to the feedback signal for generating an indication of a need for an additional blood pressure reading.