CA2264015A1 - Measurement of fluid pressure such as blood pressure - Google Patents

Abstract

Circuitry and a sensor (2050) suitable for measuring blood pressure are described. The sensor (2050) of the present invention has a flexible piezoelectic material (1011, 1013, 1015) covering the opening of a chamber (1019). The chamber (1019) contains an electrically nonconductive, elastomeric material (1017), and needs no pump to pressurize the chamber (1019). An array of sensors and circuitry for measurement of fluid pressure fluctuation in a flexible environment is given.

Description

?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 13551MEASUREMENT OF FLUID PRESSURE SUCH AS BLOOD PRESSUREFIELD OF THE INVENTIONThis invention relates to the measurement ofpressure of a fluid pumped through a flexible tubecontained in a flexible environment such as bloodpressure.BACKGROUND OF THE INVENTIONBlood circulates from the heart through arteries,capillaries and veins and back to the heart to berecirculated. when leaving the heart it measures as ahigher (systolic) pressure when the heart contracts, forexample in a normal range of about 120 mm Hg, and a lower(diastolic) of about for example in a normal range of 80mm Hg as the heart relaxes. Measurement of pressure isimportant as high blood pressure can indicate suchproblems as kidney disease or toxemia and low bloodpressure can indicate shock.Measurement is usually made with a sphygmomanometer,a device having an inflatable cuff connected to ameasuring device, often a clear tube containing mercury.The cuff is placed around a limb and inflated until itcompresses an artery until blood flow stops. Thistemporarily shuts off the blood flow of the artery, andmercury rises in the tube. As the cuff is slowlydeflated, mercury drops in the tube. With a stethoscope,the operator listens for the flow of blood to begin,?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/US96/ 13551indicating pressure in the cuff is just below thepressure in the artery. At this point, a note of mercuryheight is made. The cuff is further slowly deflated untilthe beating sound disappears and blood flows moresteadily. This gives a systolic reading. Such a device isuncomfortable and limits readings to highest and lowest,rather than continuous pressures, and is time consuming.Further, locations at where a cuff device can be used arelimited to areas which the cuff can be wrapped around alimb. Further the cuff is sensitive to physiology of thesubject, requiring different sizes for average, small andlarge limbs and varies with position of the limb relativeto the subject's body.The diastolic and systolic blood pressures representapproximate points of a continually varying pressurecurve.The two methods of obtaining accurate continuoustotal blood pressure are surgical insertion of a sensorinto the artery or’ employment of doppler (sound) tomeasure a series of echoes as blood passes a particularpoint.Surgical process is invasive and carries with it allof surgery's undesirable risks including anaesthesia andinfection. Doppler devices are considered to be of equalaccuracy to pressure sensors inserted surgically, but arelimited in requiring large support equipment to receive,?10ll121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18 _PCT/U S96/ 13551analyze, record and report the data obtained. Surgicallyinserted sensors also have a she1f—life of only a fewmonths and are intended to be non-reusable. Dopplerdevices require application of conductive ointments toachieve maximum function.In heart tissue, electrical charges are continuallygenerated within specific clusters of cells, accumulatingan electrical potential in each cluster similar toelectrical build—up in a Van de Graaf generator. When thestored electrical charge exceeds the storage capacity ofeach cluster, the clusters (ideally) dischargesimultaneously, causing the heart muscle to contract. Asthe heart contracts, accumulated fluid (i.e. blood in theheart chamber) is forced through a flexible tube (i.e.artery) and through the pipeline of arteries andcapillaries and eventually returns to the chamber throughthe venous system.This is mechanically analogous to a ‘piston typepumping system which circulates water ix: a municipalwater supply, as distinguished from a rotatingcirculating pump.An electrocardiograph measures the buildup anddischarge of electrical charges in the heart, but doesnot measure the blood pressure.With each contraction, the heart muscle generatespressure on the blood which is forced into the closed?10ll1213141516171819202122232425WO 98/07365CA 02264015 1999-02-18PCT/US96/13551environment of the arterial system which is contained inother tissue resulting in pressure of fluid against thewalls of the arterial tubes, creating a contained forceat each position along the arterial tubes.Piezoelectricity is a reversible relationshipbetween mechanical and electrostatic stress exhibited bycertain crystals which lack a center of symmetry. Forexample, when pressure is applied 1x) a piezoelectriccrystal such as quartz, positive and negative electriccharges appear on opposite crystal faces. Replacingpressure with tension reverses the sign of the electricalcharges. Piezoelectric systems are used as sensorsbecause they are sensitive to slight changes in pressureand have an electrical output which is easily amplifiedfor display.Blood pressure is essentially a varying pressure ina flexible tube encased in a flexible environment wherea fluid is moved by varying pressures through the tube.Since piezoelectric crystals respond to mechanicalstress, it has been attempted to measure blood pressurenoninvasively with piezoelectric crystals. US Patent No4,269,193 discloses such a device. However, gas or air isused to press on the artery, and the transducer must becapable of sensing force applied to the artery. The arrayuses individual silicon rectangular chips which are?10ll121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 13551relatively difficult and expensive to make and use.Further, the device has proved less than satisfactory.US Patent No 5,033,471 discloses a means formeasuring blood pressure, without use of a separate cuff,and suggests possible use of a piezoelectric sensor fordetectimg a pulse wave. However, a pump for applyingpressure is still required.other materials than crystals are known whichdemonstrate piezoelectric properties, or can bemanipulated to demonstrate such properties. Suchmaterials are used in sonic sensors. US Patent 4,578,613discloses an electroacoustic device with two sheets offoil stretched about a curve in perpendicular directions.The foil has been permanently altered to provide direc-tional piezoelectric action (nu a curved. surface. Thesecond foil measures perpendicular strain. A suggesteduse is amplification of acoustic signals. The jpiezo-electric material is overstretched precharged polymericfilm.US Patent No 4,737,676 discloses a piezoelectrictransducer for measuring mechanical quantities in hollowbodies which can be used at temperatures exceeding 80degrees C. This is given as a temperature which limitspiezo-effects in many piezo-polymer materials. Materialsupporting the metallic portion of the film is flexibleand forms a transducer.?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 13551US Patent No 4,833,659, incorporated herein byreference, shows a sonar system with solid materialbetween piezoelectric films, for damping the signal.US Patents Nos 4,782,469 and 5,159,228 disclosepiezoelectric sensors for use in ultrasonic detectiondesigned to withstand shock waves.There is a need for a suitable piezoelectric sensorand apparatus which is compact, reusable, can externallymeasure dynamic pressure in a flexible conduit in aflexible environment such as an artery, is usable in avariety of sites, and in human and veterinary practicewill directly and continuously monitor arterial pressureand is economical to manufacture.There also exists a need for a compact apparatushaving at least the same measurement capabilities as theinserted sensor and the doppler devices, which willmeasure pressure force at each point along an arterialtube system and process the measurements intoquantifiable data.The state of the art establishing the need for andlack of blood. pressure ‘measurement devices with suchcapabilities is demonstrated in "DEFENSE TECHNOLOGYCONVERSION, REINVESTMENT, AND TRANSITION ASSISTANCE",Small business innovation Research (SBIR) Programsolicitation dated May 1993, at page 19 from the AdvancedResearch Projects Agency (ARPA) of the Department of?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96! 13551Defense and other agencies:"Objective: Advance sensortechnology and information technology to speed care totrauma cases. Special emphasis on (1) non-invasivesensing, (2) portable laboratory testing, and (3) medicalimaging devices.Description: There is a need for timely medicalinformation to support decisions at the injuryscene/battlefield to plan and manage overall responses.Survival rates decrease dramatically if treatment isdelayed for more than one hour... There is a need fornon—invasive sensing of vital signs and body chemistrywhich can acquire information continuously, even prior toinjury or illness, and transmit this information...; andadvanced, mobile, low powered medical imaging devicesthat provide for field/remote use."SUMMARY OF THE INVENTIONThe sensor of the present invention has a flexibleelectrically nonconductive film sandwiched between twoflexible metallic layers (one for the positive side andone for the negative side). One metallic layer isconnected to a positive and the other metallic layer toa negative electrical output. Neutral electricallynonconductive housing surrounds the perimeter of thesandwich and forms a closed chamber above the film. Thechamber contains an electrically nonconductive,?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96! 13551compressible, elastomeric material such as air. Aprotective neutral layer on the sensor rests directly onthe surface of the flexible environment. There is no needfor a pump to pressurize the chamber.Circuitry, suitable for miniaturization, formeasurement of continuous pressure and pressurefluctuation in a flexible environment is given.BRIEF DESCRIPTION OF THE DRAWINGSFigure 1 is a cross sectional view of one embodimentof a sensor according to the present invention.Figure 2 is an overhead view of a sensor array foruse in measuring blood pressure.Figure 3 is a block diagram of circuitry for usewith the sensor array shown in Figure 2.Figures 4A - 4H detail the circuit of Figure 3.Figures 5A and 5B are outputs from a carotid artery.Figures 6A and 6B are outputs from temporalarteries.Figure 7 shows a device measuring right and lefttemporal blood pressures.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSThe sensor (2050) of Fig 1 has a flexibleelectrically nonconductive film (1013), or other flexibleelectrically nonconductive material such as KYNAR PIEZO?10ll121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 13551FILM available from AMP, Inc. which has piezoelectricproperties (i.e. separates charges to each of twosurfaces when mechanically stressed.) It is sandwichedbetween upper and lower flexible, electricallyconductive metallic layers (1011, 1015) which collect andtransmit the separated charges to positive and negativeoutputs (1021, 1022). Metallic layers (1011, 1015) may beformed by sputtering, for example with a Nicu amalgam orby silkscreening with a metal such as silver. For largescale production any known method of lightly coating anonconductive material can be used, several of which areused in production of integrated circuits and metallizedfilms such as MYLAR. An electrically nonconductivematerial (1017) is used to house the film (1013),metallic layers (1011, 1015), and outputs (1021, 1022).Additionally the housing has a central chamber (1019)which is filled with air, gas or other elastomericcomponent which is electrically nonconductive. Sincepressure in the chamber (1019) is relatively constant, nopump is required. The lower metallic layer is protectedby a neutral layer (1009), preferably of a material whichcan be disinfected, ie. by swabbing with alcohol. onesuch material is chromium (electrical resistivity = 12.9microhm-cm.).The sensor rests on the surface (1007) of a flexibleenvironment (1001) such as skin. Located in the environ-?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 1355110ment (1001) is a tube (1003) such as an artery, which hasflowing through it a fluid (gas or liquid) (1005) such asblood. As fluid (1005) pulses in the ‘tube (1003) itexerts varying pressure on the film (1013) causingmeasurable differences in electrical potential (voltage)between the positive and negative outputs (1021, 1022).For measuring blood pressure, an array of sensors(seven in the example shown) is located in anelectrically nonconductive casing (2002) as shown in Fig2. The casing is made of a supportive material whichisolates reception of each sensor from other sensors.Outputs of the sensors are connected to inputs s1, s2,s3, s4, s5, s6 and s7 of the circuit as shown in Figs 3and 4.Each casing can be held in a selected location onthe subject by a variety of means, including taping, hookand loop closing wrap (using VELCRO brand fasteners),installation on an elastic or U—shaped band (2052), orhand held, for example without distorting the artery. Fig7 shows an arrangement. which can Ibe used easily formeasuring left and right carotid or temporal bloodpressure. Since both sides can be measured simul-taneously, unbalance is readily detected.The circuit of Fig 3 is suitable for use with a dualarray such as pictured in Fig 7. A master timing circuit(3000) has an output which is split into signals?10111213141516171819202122232425WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 1355111traveling to right and left logic gates (4100, 4200).Output from right and left sensor arrays (2100, 2200) andfrom logic gates (4100, 4200) is processed into asequential output by right and left sequencers (5100,5200). The sequential output passes through right andleft filters (6100, 6200); amplifier—drivers (7100,7200); and then to a display (8000).The master timing circuit is controlled by a 555timer (3002) grounded at pin 1, connected to a voltagesource at pin 8, a master reset at pin 4, and hasdischarge, threshold, and trigger lines connected at pins7, 6, and 2 respectively. The master reset has a systemsupply ‘voltage (3004) which feeds three lines (3006,3008, 3010) The central line (3008) has a resistor(3012), grounded capacitor (3014) and switch (3016).Closing the switch (3016) activates the system. A 1.3 MEGresistor (3018) is located on a line (3006) connectingthe system supply current (3004) and discharge pin 7, anda 72K resistor (3020) is located in a line (3022)connecting discharge pin 7 with triggering pin 2. Betweenthe resistor (3020) and triggering pin 2 is a lineconnecting that line (3022) with threshold pin 6. Thatline (3022) is grounded through a 10 MF (3024) capacitorand branches to the anode of a 324 amplifier (3026). Aresistor (3028) is located between a supply voltage and?10ll121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT /US96/1355112the cathode of the amplifier (3026) and ‘the line isgrounded through another resistor (3030).The output of the master timing control leaves the555 timer at pin 3 through a line (3032) which branchesto the right and left logic gates (4100, 4200). Theoutput of the amplifier (3026) flows to the logic gates(4100, 4200) and sequencing systems (5100, 5200) over abranched line (3034). This configuration allows themaster timer (3000) to set the system to a predeterminedstarting value each time the system is turned on or incase of power interruption, and start an automatic sensorselection process.Right and left circuits after the master timingsystem (3000) are essentially identical, and the systemcan easily be adapted to one or several sensor arrays.The right logic gate (4100) has a manual switch (4102)connected to the supply voltage through a 100K resistor(4104) for overriding the master system. Output from thismanual switch (4102) and from the amplifier (3026) areinputs to a 4044 MOS SR (set-reset) flip flop (4106).Output from the 555 timer (3002) and from a lineconnecting the left flip flop (4206) are fed to a first4011 NAND gate (4108) to choose either manual orautomatic mode. Output from the first NAND gate (4108)and from the SR flip flop (4106) become inputs to asecond 4011 NAND gate (4110). The logic gate (4100) also?10ll121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 1355113has a manual clock with a manual switch (4112) connectedto the supply voltage through a 100K resistor (4111). Anormally open master switch (4002) grounds input voltagewhich has passed through a 100K resistor (4004) whenclosed. This input enters a main 4044 SR flip flop (4006)along with input from branched line (3034). Output fromthe main flip flop (4006) feeds into the multiplexer-counter system (5100, 5200). when the right switch (4112)is closed, current flows to ground and the input into afirst 4011 NAND (4114) gate of a modified flip flop dropsto low; if it is open, the input is high. A 4023 3 inputNAND gate (4116) has input from the amplifier (3026)which is alternating between high and low; input from thefirst NAND gate (4114) and input which is lower thandirect output from the NAND gate (4114) under automaticclock conditions since it travels through a :resistor(4118) and into a second 4011 NAND gate (4120) via abranched input. Since both inputs would then be low,output of the NAND gate (4120) is high. However, closingthe manual clock switch 4112 causes a change in strengthsince a capacitor (4122) is already in'a discharged stateand is charged through a resistor (4118) causing an inputon the 4023 gate (4116) to change to low. A diode (4124)in located in parallel with the resistor (4118) with theanode toward the capacitor (4122). By choosing amomentary switch for the manual switch (4112), a one shot?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/US96/ 1355114effect is achieved, that is, each closure of the switch(4112) puts out only one pulse, enabling selection ofsensors from an array to be done manually. Output fromthe 4023 NAND gate (4116) and second SR NAND gate (4110)become input for a final 4011 NAND gate (4126) output ofwhich is either an alternating automatic signal or analternating signal which is manually controlled. Thisoutput is fed into a 4516 BCD (binary coded decimal)counter (5102) in the sequencer (5000). Output from themaster timer (3000) is fed into one port of a NAND gate(5104), output of which is connected to the reset pin ofthe counter (5102). The D output pin is connected by abranched connector to another NAND gate (5105), output ofwhich is connected to the other port of the NAND gate(5104). The counter is set to count to 7 (sampling eachsensor in the array) and start over. Output from thecounter is fed to a MC14097 Multiplexer (5106) and 4511BCD to a 7 segment decoder driver (5108), operating a 7segment number display (5109), thus indicating the sensorbeing sampled at a given point. The multiplexer (5106)takes output from the counter (5102), samples output fromcorresponding sensors (s1, s2, s3, s4, s5, s6, or s7),and input from the left SR flip flop (4206) controlled bythe left manual override (4202). Output from themultiplexer (5106) is fed into the system wave filter(6100). The first component of the filter is an OP—15?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18 ‘PCTIUS96/1355115buffer amplifier (6102). The signal then passes througha bandpass filter which selects low frequencies (i.e.1-100 cps). The filter has a 1K resistor (6104), a 100Kresistor (6106), and a 1 MF (6108) capacitor arranged inparallel as shown in Fig 4. Located between the resistors(6104, 6106) is a 10 MF capacitor (6110) and between thesecond resistor (6106) and the 1 MF (6108) capacitor isa 10K resistor (6112). The sensor system (2100) —consisting of sensors (2150) and a voltage reference(2102) — supplies the input to sensor (2050) and allowsdetection of system voltage fluctuations. The voltagereference (2102) is also connected to analog amplifiers(7100, 7200) after passing through two 1. K resistors(7102, 7104). Output from the first resistor (7102) isfed through a branched line to the cathode of an LM324operational amplifier (7106) and a circuit connected tothe output of the amplifier (7106) by a 1 I< resistor(7110) and a 1 MF capacitor (7114) in parallel. Outputfrom the upper line of the bandpass filter is input forthe amplifier (7106) anode. Output from the secondresistor (7104) is fed through a branched line to thecathode of an LM324 operational amplifier (7108) and acircuit connected to the output of the amplifier (7108)by a 20 K resistor (7112) and a 1 MP capacitor (7116) inparallel. Output from the first amplifier (7106) is inputfor the anode of the second amplifier (7108). Output from?10ll121314151617181920212223242526W0 98l0736SCA 02264015 1999-02-18PCT/U S96/ 1355116the second amplifier (7108) is fed to a computer (8002)for analysis by software and display and/or printing ofa hard copy. The computer (8002) shows output of eachsensor as it is automatically sampled. Using the manualclock switch (4112) allows the operator to focus on asingle sensor or control the rate of selection. The leftlogic gate (4200) has a manual switch (4202) connected tothe system voltage through a 100K resistor (4050). Outputfrom this manual switch (4202) and from the amplifier(3026) are inputs to a 4044 MOS SR (set-reset) flip flop(4206). Output from the 555 timer (3002) and from a lineconnecting the right flip flop (4206) are fed to a 4011NAND gate (4208). Output from the NAND gate (4208) andfrom the SR flip flop (4206) become inputs to a 4011 NANDgate (4210). The logic gate (4200) also has a manualclock with a manual switch (4212) connected to the supplyvoltage through a 100K resistor (4211). A 4023 3 inputNAND gate (4216) has input from the amplifier (3026);input from the NAND gate (4214) and input which is lowerthan direct output from the NAND gate (4214) underautomatic clock conditions since it travels through aresistor (4228) and into a second 4011 NAND gate (4220)via a branched input. A diode (4224) in parallel with theresistor (4228) with the anode toward a capacitor (4222),which when charged through a resistor (4228) causes aninput on the 4023 gate (4216) to change to low. Output?1011121314151617181920212223242526WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 1355117from the 4023 NAND gate (4216) and second SR NAND gate(4210) become input for a final 4011 NAND gate (4226).This output is fed into a 4516 BCD (binary coded decimal)counter (5202) in the sequencer (5000). Output from themaster timer (3000) is fed into one port of a NAND gate(5204) output of which is connected to the reset pin ofthe counter (5202). The D output pin is connected by abranched connector to another NAND gate (5205), output ofwhich is connected to the other port of the NAND gate(5204). Output from the counter is fed to a MC14097Multiplexer (5206) and 4511 BCD to a 7 segment decoderdriver (5208), operating a 7 segment number display(5209), thus indicating the sensor being sampled at agiven point. The multiplexer (5206) takes output from thecounter (5102); samples output from corresponding sensors(s1, s2, s3, s4, s5, s6, or s7), and input from the rightSR flip flop (4106) controlled by the left manualoverride (4102). Output from the multiplexer (5206) isfed into the system wave filter (6200). The firstcomponent of the filter is an OP—15 buffer amplifier(6202). The signal then passes through a bandpass filterwhich selects low frequencies (i.e. 1-100 cps). Thefilter has a 1K resistor (6204), a 100K resistor (6206),and a 1 MP (6208) capacitor arranged in parallel as shownin Fig 4. Located between the resistors (6204, 6206) isa 10 MF capacitor (6210) and between the second resistor?10ll1213141516171819202122232425WO 98107365CA 02264015 1999-02-18PCT/U S96/ 135511 8(6206) and the 1 MF (6208) capacitor is a 10K resistor(6212). The sensor system (2200) — consisting of sensors(2250) and a voltage reference (2202) — supplies theinput to sensor (2050) and allows detection of systemvoltage fluctuations. The voltage reference (2202) isalso connected to analog amplifiers (7100, 7200) afterpassing through two 1 K resistors (7202, 7204). Outputfrom the first resistor (7202) is fed through a branchedline to the cathode of an lM324 operational amplifier(7206) and a circuit connected to the output of theamplifier (7206) by a 1 K resistor (7210) and a 1 MFcapacitor (7214) in parallel. Output from the upper lineof the bandpass filter is input for the amplifier (7206)anode. Output from the second resistor (7204) is fedthrough a branched line to the cathode of an LM324operational amplifier (7208) and a circuit connected tothe output of the amplifier (7208) by a 20 K resistor(7212) and a 1 MF capacitor (7216) in parallel. outputfrom the first amplifier (7206) is input for the anode ofthe second amplifier (7208). Output from the secondamplifier (7208) is fed to a computer (8002) for analysisby software and display and/or printing of a hard copy.The continuous output of data allows comparison ofdata produced simultaneously by multiple sensor arraysplaced at selected locations on the subject.?10ll1213141516171819202122232425WO 98/07365CA 02264015 1999-02-18PCT/US96/ 1355119Since comparison of curves is presently availablethrough software, it is foreseen that an exemplar curve(or curves) could be stored and accessed, and the sensorwithin each array having the most desired similarity beselected automatically for display, enabling the operatorto select sensors which are best positioned to achievethe operator's goals. Algorithms for curve fitting can befound in many books. Programs which are presentlyavailable which could be adapted for the curve comparisonare sold under the names MATHCAD and TABLECURVE.TABLECURVE curve fitting software is a product of JandelScientific. To adapt the TABLECURVE software, a "normal"curve could be analyzed and placed into the selection ofx,y curves, and then all new curves analyzed from thissynthesized x,y curve.Time intervals between repeated events, such asfirst pressure upon contraction of the heart muscle ineach successive sequence can be measured to obtain apulse rate, and also to demonstrate the pulse frequencybetween contractions and variations in the timing andintensity of each pulsation.The device can be combined with other sensors, suchas thermistors, to measure additional variables such asskin temperature at various locations and coretemperatures both by correlation of skin—to-core?10111213141516171819202122232425WO 98/07365CA 02264015 1999-02-18PCT/US96/1355120temperatures and direct measurement of core temperatureson accessible target organs.Figs 5A and 5B each displays actual output from aworking prototype of the invention generated by placingthe sensor element over a carotid artery in a humansubject at different occasions.Figs 6A and 6B respectively display actual outputsfrom working prototypes of the invention generated byplacing the sensor element over a left temporal and also,over a right temporal artery in a human subject atdifferent occasions.This invention provides a flexible system which canbe used for a wide variety of applications and requiresminimal skill to obtain a continuous measurement of bloodpressure. The sensor is useful for a variety ofapplications involving differential pressure, includingindustrial flow through tubes to sense blockage, e.g. inNuclear Energy facilities.Another medical application is location of lumpssuch as tumors. For example, in manual breastexamination, pressure is applied and resistance to thepressure is felt for" variations. With ‘this inventionsensors could be arranged in a cup, pressure applied tofill the cup and. make contact. with the sensors, andvariations in resistance mapped for analysis. other?10ll1213WO 98/07365CA 02264015 1999-02-18PCT/U S96/ 1355121arrays could be used for detection of such problems aspotential and developing hernias and aneurysms.other arrays can be used to detect potential andexisting ruptures in hoses.This invention can measure pressure aspects ofliquids and gases pumped from one source to another, asin transport of liquids and gases through pipelines,including the small conduit pipes bringing fuel oil fromtank to precombustion chambers in diesel engines.This invention permits the creation of selectivedata reporting and display such as diastolic, systolic,and mean blood pressure; and specific Korotkoff positionssuch as Korotkoff V for neonates.

Claims (21)

What is claimed is:

1. A piezoelectric sensor comprising:
a housing having a chamber, said chamber having only one opening;
a flexible piezoelectric material having first and second sides covering said opening:
a compressible fluid within said chamber; and means for measuring electrical charges on said first side.

2. The sensor of Claim 1 further comprising:
means for measuring electrical charges on said second side.

3. The sensor of Claim 2 further comprising:
an electrically neutral, flexible protective covering located over said flexible piezoelectric material.

4. The sensor of Claim 2 wherein said material further comprises:
a flexible nonconductive film having a conductive layer.

5. The sensor of Claim 4 wherein said conductive layer is metallic.

6. The sensor of Claim 4 wherein said material further comprises:
a second conductive layer.

7. An apparatus for surface measurement of pressure change within a flexible environment comprising:
at least one piezoelectric sensor comprising:
a chamber having a single opening located in a housing; and a flexible piezoelectric material having a first side and a second side covering said opening:
compressible fluid within said chamber;
means for measuring electrical charge on said first and second sides; and means for reporting output from said first and second measuring means.

8. The apparatus of Claim 7 further comprising:
a first array of piezoelelectric sensors.

9. The apparatus of Claim 8 wherein said reporting means further comprises:
display means chosen from the group consisting of video screens and printers.

10. The apparatus of Claim 9 further comprising:
means for reporting said output as a function of time.

11. An apparatus for surface measurement of pressure change within a flexible environment comprising:
a first array of piezoelectric sensors, said sensors comprising:
a chamber having a single opening located in a housing; and a flexible piezoelectric material having a first side and a second side covering said opening;
compressible fluid within said chamber; and means for measuring electrical charge on said first and second sides;
means for reporting output from said means for measuring, said means for reporting output further comprising:
a display means chosen from the group consisting of video screens and printers;
means for reporting said output as a function of time; and means for measuring and reporting surface temperature of said environment.

12. The apparatus of Claim 9 wherein said reporting means further comprises:
a signal processor.

13. The apparatus of Claim 12 wherein said signal processor further comprises:
signal identification means;
signal amplification means; and signal selection means.

14. The apparatus of Claim g wherein said signal processor further comprises:
means for determining and reporting time intervals between repeated events.

15. The apparatus of Claim 8 further comprising a second array of sensors.

16. The apparatus of Claim 15 wherein said first and second array of sensors are located at the terminals of a U shaped band.

17. A method for surface measurement of pressure change within a flexible environment comprising:
placing a sensor having flexible piezoelectric material over a sole opening of a chamber containing a compressible fluid onto the surface of said flexible environment;
measuring electrical charge on said material;
and reporting output of said electrical change.

18. The method of Claim 17 further comprising the step of:
measuring time and said reporting step further comprises reporting said charge change as a function of time.

19. A method for surface measurement of pressure change within a flexible environment comprising:
placing a sensor having flexible piezoelectric material over a sole opening of a chamber containing a compressible fluid onto the surface of said flexible environment;
measuring electrical charge on said material;
reporting output of said electrical change;
measuring the temperature of said surface; and reporting said temperature measurement.

20. The method of Claim 18 wherein said reporting step further comprises:
identifying electrical signals;
amplifying said signals; and selecting signals for reporting.

21. The method of Claim 20 further comprising:
comparison of said selected signals to an exemplar signal.