CA2619986A1 - Implant transmitter - Google Patents

Abstract

A monitoring system is provided that enables the monitoring of a heart in a living organism by continuously measuring both pressure and volume in a chamber of the heart, preferably the left ventricle (LV). The pressure and volume measurements are acquired using a single sensing tip and are communicated to a transmitting device to be wirelessly transmitted to a receiving device, wherein they are used to monitor the heart. The system may also incorporate a temperature measurement that can be transmitted with the volume and pressure measurement to provide further data for monitoring. The system may also extract an electrocardiogram (ECG) signal from the volume measurement. This allows the monitoring of up to four signals that can be used to determine the beat by beat state of cardiac output and any changes caused by disease or therapy. In addition to a compact design, the system may also incorporate an energy saving timing scheme that reduces the power required per acquisition cycle and thus increases the operational lifetime of the transmitting device.

Description

WO 2007/022620 PCTICA2006/0013~8 IMPLANT TRANSMITTER

4 FIELD OF THE INVENTION:
6 [0001] The present invention relates generally to data acquisition systems and particularly 7 to acquiring data from a heart in a living organism.

100021 In the field of cardiac research the standard test for measuring cardiac efficiency is 11 the pressure volume graph. This test correlates Left Ventricle (LV) chamber pressure and 12 volume: as the heart contracts and expands. Pressure and volume values are important for 13 quantifying efficiency in any pump system, and can be used to calculate volumetric 14 efficiericy of such systems. Cardiac efficiency is a useful measurement for studying heart disease, by quantifying the progress of the disease and measuring the effectiveness of the 16 treatment.

17 100031 Recently, gene altered mice have increased in popularity as a means for studying 18 heart diisease, and for modelling human heart disease. Typically, LV data is measured using a 19 catheter that is inserted into the LV. The catheter typically has separate instrumentation for ?0 measuring blood pressure and blood volume. There are several drawbacks to using data 21 taken fi-om anaesthetized mice, most significantly the fact that it has been found that Z2 cardiovascular data taken from an anaesthetized specimen differs significantly from free-23 roaming specimens.

?4 [0004] In order to measure cardiovascular data from a free-roaming specimen, an ?5 implanted device is required that can operate while the specimen is active, and transmit data ?6 to the exterior of the specimen for processing. This need presents several design problems, ?7 notably size and battery life. Particularly, a reduced size provides a less invasive device, and ?8 a longer battery life decreases the number of surgical operations required to change or ?9 recharge a device. The need to reduce repeated trauma due to surgery and the cost of the ,0 surgery are driving reasons for the need to extend battery life in biological implants. These concerns are heightened when extending the application to human specimens.

21552232.1 WO 2007/022620 PCT/CA2006/0013~8 1 [0005] There are numerous devices that have been developed for measuring physiological 2 pressure in living specimens, e.g., those shown in US Patent Nos. 4,796,641;
4,846,191; and 3 6,033,366. These devices include a catheter having a pressure sensor that is inserted into an 4 area in the specimen having a physiological pressure, such as an artery. The sensors include a pressure transmitting catheter filled with a pressure transmitting fluid. A
pressure 6 transducer communicates with the fluid to provide an electric pressure signal representing 7 variations in physiological pressure that can be transmitted to the exterior of the specimen.
8 These clevices are only concerned with measuring pressure, and the use of a fluid filled 9 catheter can lead to undesirable frequency response characteristics and may exhibit head pressure artefacts.

11 100061 Other devices, e.g., that shown in US Patent No. 6,409,674 provide an implantable 12 sensor being anchored to the interior wall of the LV in a living specimen.
The sensor 13 acquires and transmits data from within the heart to an external data receiver. This device is 14 concerned with only measuring a single parameter, and specifically illustrates measuring pressure.

16 100071 There exists a need for an implantable data acquisition device to acquire more 17 comprehensive cardiovascular data, which presents minimal invasiveness and has a I S prolonged battery life.

19 [00081 It is therefore an object of the present invention to obviate or mitigate at least one ?0 of the above-mentioned disadvantages.

?1 ?2 SUMMARY OF THE INVENTION

?3 [0009] In one aspect, the present invention provides a method of monitoring a heart of a ?4 living organism comprising the steps of situating a sensing tip within a chamber of the heart, ?5 the sensing tip extending through the chamber and comprising a pressure sensing device and ?6 a volume sensing device; obtaining a pressure measurement and a volume measurement in '.7 the chamber using the pressure sensing device and the volume sensing device respectively;
'.8 communicating the measurements to a transmitting device; and wirelessly transmitting 21552232.1 1 electrical representations of the measurements to a receiving device, the electrical 2 representations being used to monitor the heart.

3 100101 In another aspect, the present invention provides a system for monitoring a heart 4 of a living organism comprising a sensing tip situated within a chamber of the heart and extending therethrough, the sensing tip comprising a pressure sensing device and a volume 6 sensing device, the pressure sensing device adapted to obtain a pressure measurement in the 7 chamber, the volume sensing device adapted to obtain a volume measurement in the 8 chamber, and the sensing tip adapted for communicating the measurements; a transmitting 9 device for receiving the measurements from the sensing tip, the transmitting device being adapted to wirelessly transmit electrical representations of the measurements;
and a receiving 11 station for receiving the electrical representations, the electrical representations being used to 12 monitor the heart.

13 [0011] In yet another aspect, the present invention provides a method for obtaining an 14 intracardiac electrocardiogram signal comprising the steps of measuring a conductance signal from a heart chamber in a living organism, the conductance signal indicative of the volume of 16 the chamber; conditioning the conductance signal to separate a noise portion of the 17 conductance signal comprising the electrocardiogram signal from a conductance portion of 18 the coriductance signal; and extracting the electrocardiogram signal from the noise portion.

?0 BRIEF DESCRIPTION OF THE DRAWINGS

? 1 [0012] An embodiment of the invention will now be described by way of example only ?2 with reference to the appended drawings wherein:

?3 100131 Figure 1 pictorially shows a wireless cardiovascular data acquisition system.
?4 100141 Figure 2 is a schematic representation of the system of Figure 1.

',5 100151 Figure 3 is a magnified view of a portion the heart shown in Figure 1.

'.6 100161 Figure 4a is a partial plan view of the pressure sensing device of Figure 2.
21552232.1 - ~ -1 100171 Figure 4b is a sectional view of the sensing device shown in Figure 4a along the 2 line B-B.

3 100181 Figure 5 is an electric schematic of the pressure sensing device.

4 [0019] Figure 6 is a schematic diagram of the transmitter processing module of Figure 2.
[0020] Figure 7 is a schematic diagram of the receiver processing module of Figure 2.

6 [0021] Figure 8 is a timing diagram for the timing controller of Figure 6.

7 [0022] Figure 9 is a flow chart showing an acquisition and transmission cycle.
8 [0023] Figure 10 shows another embodiment of the sensing tip of Figure 3.

DETAII.ED DESCRIPTION OF THE INVENTION

11 [0024] Referring therefore to Figure 1, one embodiment of a wireless cardiovascular data 12 acquisition system is generally denoted by numeral 10. The system 10 operates to measure 13 physical parameters of a heart 12 located within a body 14. The heart 12 and body 14 form 14 part of a living organism, such as a gene altered mouse or a human. The heart 12 includes a heart chamber, in this example a Left Ventricle (LV) 16 that in part communicates with the 16 body 14 via a heart valve 18. A sensing tip 22 is situated in the LV 16 by insertion thereof 17 through the valve 18, and has a communication path 24 leading to a transmitting device 20 18 implanted in a portion 15 of the body 14, which in this example is external to the heart 12. In 19 the example shown in Figure 1, the portion 15 is in proximity of the body's clavicle. It will >_0 be appreciated that the transmitting device 20 may be situated anywhere as desired, e.g.
?1 within the heart 12 or heart chamber (i.e. LV 16).

?2 [0025] The transmitting device 20 wirelessly transmits data to a receiving device 26 that ?3 in this example is attached to a belt 27 external to the body 14. The receiving device 26 may ?4 display data on a screen 28 as shown in Figure 1, and may comprise a keypad 30 for scrolling '.5 between different views. A schematic of the system 10 is shown in Figure 2.

21552232.1 WO 2007/022620 PCT/CA2006l001358 1 [0026] Referring now to Figure 2, the path 24 communicates data acquired by the sensing 2 tip 22 to a transmitter processing module 32 in the transmitting device 20.
The transmitting 3 device 20 is powered by obtaining energy from a battery 34, and has a transmitter 36. It will 4 be appreciated that the use of a battery 34 is for illustrative purposes only and that any suitable means for powering the transmitting device 20 may be used such as power 6 scavenging (converting environmental energy into electricity) or RF power transmission 7 (energy transmitted to the device 20 from an external source through a radio frequency 8 signal).

9 [0027] Since the processing module 32 is preferably implanted in the body 14, the signal sent via the tra.nsmitter 36 should pass through body tissue before reaching the air. The 11 attenuation of an RF signal by different body materials is typically highly frequency 12 dependent. Therefore, the transmitter 36 should be selected so as to minimize the attenuation 13 of the signal it transmits. Typically, a lower frequency is preferred to transmit the signals 14 since the lower the frequency, the greater the depth of penetration.
However, the lower the frequency, the higher the wavelength and thus the longer the antenna required at the receiving 16 end. Therefore, the transmitter 36 should be chosen to balance these requirements depending 17 on the particular application. A suitable frequency to achieve such a balance is 40MHz. The 18 power consumed by the transmitter 36 should also be considered so that it can be faithfully 19 detected at its receiving end whilst conserving energy.

[0028] The transmitting device 20 communicates wirelessly with the receiving device 26 21 through a receiver 40. The device 26 has a receiver processing module 38 that is adapted for 22 processing data received from the device 20. The device 26 is powered by a battery 42 or Z3 suitable AC or DC power source (not shown). The device 26 has a series of signals (44-50) ?4 for providing electrical representations of measurements acquired using the sensing tip 22, ?5 including a pressure signal 44, a volume signal 46, a temperature signal 48, and an ?6 electrocardiogram (ECG) signal 50.

>.7 [0029] In Figure 2 these signals are shown as being external to the processing module 38 ?8 and communicably connected to an external computing device 52 having an analog-to-digital >.9 (A!D) converter 54 connected thereto. However, it will be appreciated that the A/D converter 10 54 may be included in either the processing module 38 or processing module 32, and I computing device 52 may be replaced by any suitable alternative such as processing 21552232.1 1 capabilities provided by the processing module 38. The communicable link between the 2 receiving device 26 and the computing device 52 and/or AfD converter 54 may be any 3 hardwired or wireless communication channel, e.g., using Bluetooth technology.

4 100301 The computing device 52, external or internal to the receiving device 26, may be any device that is capable of acquiring data and communicating with the processing module 6 38. In the example shown in Figure 2, the device 52 is a standard personal computer (PC) 7 having a monitor, central processing unit (CPU), keyboard, and mouse.

8 [0031] The sensing tip 22 is shown in greater detail in Figure 3. The sensing tip 22 has a 9 rounded end 70 to facilitate the deployment thereof through the valve 18. In this example, a proximal electrode 62 and a distal electrode 60 each following the circumference of the 11 sensing tip 22 flank a pair of inner electrodes 64, 66, a pressure sensing device 68, and a 12 temperature sensing device 69. The electrodes 60, 62, 64 and 66 are used to measure the 13 volume of blood in the LV 16 and are herein collectively referred to as the volume sensing 14 device denoted by numeral 67. The proximal electrode 62 transmits a signal, and the distal electrode receives same to create an electric field in the LV 16. The inner electrodes 64, 66 16 sense this electric field to perform a conductance measurement indicative of the volume in 17 the LV 16. The inner electrodes 64, 66 can be modeled conceptually as measurement probes 18 on either side of a "resistor", wherein the "resistor" represents the resistivity of the blood in 19 the LV 16, the inner electrodes 64, 66 are arranged to measure the potential across the "resistor". The volume measurement and/or volume signal may also be referred to as a 21 conductance measurement and/or conductance signal respectively, and it will be appreciated 22 that this terminology may herein be considered interchangeable.

23 100321 The pressure sensing device 68 is used to sense the pressure of the blood in the 24 LV 16. The temperature sensing device 69 is used to sense the temperature of the body 14, ?5 since it is substantially uniform throughout. The temperature sensing device 69 is preferably ?6 comprised of a thermistor or equivalent component. The volume sensing device 67, ?7 pressure sensing device 68, and temperature sensing device 69 communicate data to the ?8 transmitting device 20 through the path 24, thus the path 24 typically carries a number of ?9 wires, enabling data to be transmitted from the sensing tip 22 to the device 20. The length of ;0 the path 24 is dependent upon the location of the device 20 relative to the heart 12.

21552232.1 1 100331 Although the temperature sensing device 69 is shown in Figure 3 as part of the 2 sensing tip 22, it will be appreciated that the device 69 may be situated anywhere in the body 3 14 enabling the internal temperature of the body 14 to be measured, and this may be inside or 4 outside of the heart 12.

[0034] An embodiment of the sensing tip 22 is shown in Figures 4a and 4b. It will be 6 appreciated that the relative dimensions of the sensing tip 22 have been exaggerated for 7 illustrative purposes only. The pressure sensing device 68 may be any device capable of 8 sensing; a pressure. In this example, the pressure sensing device comprises a piezoresistive 9 deflection sensor, specifically a cantilevered sensor beam 80 having a base portion 82 that is attached to the housing of the sensing tip 22. A base window 85 in the sensing tip 22 enables 11 the base of the beam 80 to experience external pressure, and a tip window 86 enables the tip 12 of the beam 80 to experience external pressure. A layer of sealant 88 inhibits the beam 80 13 from direct contact with its surrounding environment. However, the layer 88 permits external 14 pressure to effect flexure of the beam 80 due to variations in the pressure of the surrounding blood. It can be seen in Figure 4b that electrical wires run from the sensing devices 67, 68 16 and 69 to the path 24.

17 [00351 An implementation of the beam 80 is shown schematically in Figure 5, being a I 8 strain gauge sensor, on which two resistors Rxl and R 2 are mounted. When the beam bends 19 as a result of a pressure experienced thereby, the resistances of these resistors change in ?0 opposite directions. That is, the resistance of one of the resistors increases while that of the ? 1 other one decreases. As a result, the accompanying electronic circuits may be designed in a ?2 fully differential architecture which provides a higher signal to noise ratio (SNR) compared ?3 to a single ended architecture.

?4 [0036] The following lists suitable specifications for the pressure sensing device 68, but ?5 shall in no way be considered limited thereto: nominal resistance of each resistor R;j, R,,2 ?6 being 10,000 Ohms; gauge factor of 70-80; total resistor manufacturing tolerance of +/- 10-?7 15%; maximum resistance value mismatch between the resistors of 2.4%;
temperature '.8 coefficient of resistance of +5% / 100 F; and a breakdown voltage of 20V.

:9 [0037] These exemplary specifications illustrate that typically there may be non-idealities ;0 for the sensing device 68 that would preferably be addressed when designing the circuitry 21552232.1 I therefor. For instance, due to process variations, the resistances of R,1 and Ri2 are in all 2 likelihood not going to be equal. This may generate some offset at the output. Moreover, 3 since the resistance of the resistors R,1 and R,2 is a temperature dependent parameter, the 4 temperature coefficient of resistance (TCR) may cause an offset due to mismatch. Hence, even if the offset is cancelled at one temperature it may not be zero at another temperature.
6 Finally, the temperature coefficient of the gauge factor (TCGF) makes the gain of the sensing 7 device 68, temperature dependent.

8 [0038] The above parameters are typically sources for measurement inaccuracies. As a 9 result, the output of the sensing device 68 may have some offset error and be dependent on temperature. In order to compensate for the above parameters, typically a signal conditioning 11 scheme is utilized. In the example shown in Figure 5, a Wheatstone bridge configuration is 12 used to measure the resistance variations with two current sources I1 and 12.

13 100391 As indicated above, R] and Rx2 change in opposite direction as a function of 14 strain or equivalently blood pressure in the heart as: Rxl = R~>1(1 + GF.x) and Rx2 = Ra2(1 +
GF.x) where Ro] and R02 are the sensor resistances at zero strain, GF is the gauge factor of the 16 sensing device 68, and x is the strain. The two current sources I1 and 12 complete the bridge, 17 and are: preferably integrated into the processing module 32 as shown in Figure 5. In order to 18 cancel out the resistor mismatch, TCR, and TCGF, the following equations should be valid:
19 Ri,1I02 -- Ro]Io] = 0; and TCI = - (TCR + TCGF); where TCI represents the temperature coefficient of the current sources, Ral and R02 represent the resistor values at the reference 21 temperature, and lo] and 102 represent the current of the two current sources at the reference 22 temperature. The technology used to implement the processing module 32 should be capable 23 of implementing a current source with any specific temperature coefficient, and the current ?4 sources should preferably be designed to have the lowest possible supply voltage sensitivity.
?5 100401 A block diagram of the transmitter processing module 32 is shown in Figure 6.
26 The module 32 comprises a sensing block 90 and a transmitting block 92 controlled by a ?7 timing controller 94. The battery 34 which is connected to the module 32 may be controlled 18 by a switch 96. The battery 34 is preferably a miniature battery of a suitable size and having >_9 a battery life that is as long as possible. A suitable battery has a life of 180mAh, weight of ;0 2.3g, 1.5Vdc, and a volume of 0.57cc. The switch 96 may be, e_g., magnetic or radio 1 controlled, i.e. any suitable device capable of controlling the main power to the module 32 21552232.1 I from the battery 34. Between the timing controller 94 and the switch 96 is a voltage regulator 2 that provides a regulated voltage to the timing controller 94 for controlling the blocks 90 and 3 92. With the above battery specifications, a suitable regulated voltage is a IV output.

4 100411 The sensing block 90 includes a current source block 100 for the pressure sensing device 68 (described above with current sources I1 and 12) to compensate for sensor non-6 idealities, and are the basis of temperature compensation for the pressure sensing device 68.
7 The block 90 also includes a conductance current source 102 for generating the electric field 8 using the electrodes 60 and 62; and a thermistor current supply 104 for the temperature 9 sensing device 69, that preferably comprises a high resistance thermistor for minimal current drain. The outputs from these current sources (100-104) are sent to the sensing tip 22 over 11 the path 24.

12 [0042] The measurements acquired by the sensing devices 67, 68 and 69 are sent back to 13 the sensing block 90 over the path 24. The temperature signal is fed through an amplifier 106 14 and sainpled and held for transmission by a sample and hold component 112.
Similarly, the pressure signal is fed to an amplifier I 10 and sample and hold component 116;
and the 16 volume signal is fed to an amplifier 108 and sample and hold component 114.
The amplifiers 17 106, 108 and 110 are preferably used to encourage the fidelity of the signals. The sample and 18 hold components 112, 114 and 116 hold the signal samples while the timing controller 94 19 switches power from the sensing block 90 to the transmission block 92.

[0043] The transmission block 92 has a multiplexer 118 and a voltage controlled 21 oscillator (VCO) 120. The multiplexer 118 will read the samples from the blocks 112-116 22 and arrange the signals for transmission by the VCO 120. For example, the multiplexer 118 23 may arrange the signals in sequential order for transmission. The VCO 120 is connected to 24 an antenna 121 and together make up the transmitter 36 shown in Figure 2. A
suitable VCO
120 is a Colpitts type that consumes an average current of 32 A. The antenna 121 is 26 preferably connected in parallel with the frequency determining inductor of the VCO 120, 27 and preferably serves as an FM transmitter with a 42MHz transmission frequency.

28 [0044] A block diagram of the receiver processing module 38 is shown in Figure 7. The ?9 module 38 comprises a demultiplexer 122 connected to the receiver 40 of the receiving device 26. The demultiplexer 122 separates the signals that have been transmitted by the 2]552232.]

I transmitter 36 and received by the receiver 40. If the signals are transmitted as analog 2 signals, the demultiplexer 122 separates the received signal into individual analog signals, 3 and in this example would provide three individual signals, a temperature signal 124, a 4 pressure signal 126, and a volume signal 128. The temperature signal 124 may be immediately available as output 48, and the pressure signal 126 may be immediately 6 available as output 44 for further processing and/or transmission to the computing device 52.
7 It will be appreciated that the module 38 may also comprise a further internal component for 8 processing and analysing the signals 124, 126 and 128, e.g., for display purposes. Moreover, 9 the module 38 may comprise an alarm or other device to notify a wearer of the receiving device 26 of abnormal heart conditions. The display 28 may also be used with such 11 additional processing to output heart parameters or a computed index that represents heart 12 health.

13 [0045] The volume signal 128 may be sent through a buffer 129 and be available as 14 output 46. The volume signal 128 may also be captured at block 130 for further processing to extract the ECG signal. This preliminary signal 130 is preferably converted using an analog-16 to-digital converter (A/D) 132, which enables signal manipulation while preserving the 17 integrity of the original signal. It will be appreciated that the A/D 132 would not be needed if 18 the signals received have already been converted to digital signals. The A/D 132 has two 19 identical outputs, one of which is input to a digital signal processor (DSP) 134. The DSP 134 is used to clean the ECG signal from the volume signal, and allows for complex signal 21 processing. The extraction of the ECG signal is described in greater detail later.

Z2 [0046] The signal emerging from the DSP 134 is inverted by an inverter 136.
The ?3 inverter 136 may also be part of the DSP 134. The other output from the A/D
132 is buffered 24 by the buffer 138 and the inverted signal and the buffered signal are summed at 140 to ?5 produce the ECG signal 142 that may also be available as output 45. The buffer 138 is used ?6 to mairitain the synchronicity of the raw volume signal and the digitally manipulated version 27 (i.e. by the DSP 134). The delay imposed by the DSP 134 would otherwise affect the results ?8 of the sum 140. The summer 140 adds the two volume signals, and since one has been ?9 inverted, the conductance part of the volume signal will be eliminated and the remaining signal will represent the ECG signal 142.

21552232.1 1 100471 The sensing block 90 and the transmitting block 92 are selectively powered using 2 the timing controller 94 in order to conserve power. A timing diagram is shown in Figure 8 3 illustrating the operation of the timing controller 94. The period T
represents an entire 4 monitoring cycle for the system 10 including measurement and transmission.
Specifically, T, represents the period in which the sensing block 90 is powered in order to obtain the 6 necessary measurements and sample and hold the signals; and T2 represents the period in 7 which the transmitting block 92 is powered in order to execute transmission of data from the 8 transmitting device 20 to the receiving device 26.

9 [0048] For example, a 2kHz sampling rate provides a period T of 500p.s to sample and transmit data. If the acquisition period T2 is 20 s, and transmission period T3 is 50 s, there I 1 exists 430 s during each cycle, in which either the block 90 or the block 92 is waiting. The 12 timing controller 94 uses this timing scheme to selectively turn off either the block 90 or 13 block 92 that is not being used to conserver power, which provides an increase in battery life.
14 [0049] Another benefit arises from using such an energy saving timing scheme, namely the reduction of noise. Specifically, since the block 90 is powered whilst the block 92 is not, 16 the transmitter 36 will not be affected by the noise generated by the signal conditioning, and, 17 conversely, the sensing circuitry (block 90) will not be subject to noise from the transmitter 18 36. A 10N.s period, represented by T3, is left between the end of one period and the beginning 19 of the next, which enables any circuitry that needs stabilizing to do so.

[0050] Therefore, since the transmitting block 92 typically cannot transmit data that has 21 not yet been collected, it would be wasting power while the sensing block 90 is performs its 22 function. If the transmitting block 92 is turned off when it is not needed, power is not 23 consumed, and thus conserved. Similarly, the sensing block 90 typically is not adding any 24 data while the transmitter 36 is sending the previous sample, and thus does not need to consume power during that time.

26 100511 Figure 9 shows a flow chart illustrating an example of the steps taken by the 27 system 10 during one complete cycle T, and the subsequent processing by the receiving 28 device 26. The sensing block 90 is powered which enables the current sources to power the 29 measurement devices 67, 68 and 69 and obtain the measurements. These measurements are then arnplified and undergo a sample and hold. The sensing block 90 is then powered "off' 21552232.1 1 and the transmitting block 92 is powered "on", wherein the time lag between theses steps is 2 represented by T3 as explained above. Once the block 92 has power, the multiplexer 118 is 3 then able to obtain the signals stored in the sample and hold components 112-116, and 4 combirne these signals for transmission. In this example the multiplexer 118 preferably operates by arranging the signals in a particular sequential order that would be known to the 6 demultiplexer 122 in order to enable the demultiplexer 122 to separate the signals at the 7 receivimg end.

8 100521 The multiplexer 118 passes this "combined" signal to the VCO 120 that uses the 9 antenna 121 to transmit the "combined" signal to receiving device 26. At this point, a complete measurement cycle has been executed, and the signal that has been transmitted 11 continues to the receiving device 26 for further processing and/or output.
The transmitting 12 device 20 may then repeat this cycle as required or desired.

13 100531 The receiving device 26 receives the "combined" signal from the receiver 40. The 14 signal is passed to the demultiplexer 122 where it is separated into its components. The temperature and pressure signals 124 and 126 respectively, may be available as outputs or for 16 further processing by the module 38. The volume signal 128 may be buffered and output at 17 46, and. may also be obtained for extracting the ECG signal 142 and providing output 45.
18 The extraction of the ECG signal 142 from the raw volume signal 128 is described in greater 19 detail below, while referring to the functional blocks shown in Figure 7 that relate thereto.

ZO [0054J As indicated above, the conductance or volume signal 128 acquired using the 21 volume sensing device 67 is used to extract the ECG signal 142.

22 [0055J The conductance signal acquired using the volume electrodes 67 consists of the ?3 conductance value of the blood in the LV 16, any noise generated by the system or in the ?4 environment, and the ECG signal 142 that is picked up as a component of environmental ?5 noise. As described above, in this example, the raw signals are collected and transmitted, ?6 e.g., as a combined analog waveform, without performing any signal conditioning, to the ?7 receiving device 26. When the combined signal is received by the receiving device 26, the ?8 individual pressure, volume and temperature signals (124, 126 and 128) are separated, and a 19 process begins to separate the various components of the volume signal 128 (i.e. at 130).
21552232.11 WO 2007/022620 PCT/CA2006/0013--)8 1 100561 The conductance signal 128 is the result of an electrical field generated, by means 2 of the electrodes 60, 62, from the apex of the heart to the carotid artery.
Due to myocardial 3 contact of the conductance rings, the resulting conductance signal will also carry the ECG
4 signal. It is generally common practice to use signal conditioning and filtering to eliminate the environmental and ECG noise components to extract the conductance signal 128. In this 6 embodiment, signal conditioning is used to not only remove the ECG component of noise to 7 extract the conductance signal, but also to separately condition the ECG
signal 142 to remove 8 the conductance portion of the signal. The result is that an ECG signal 142 can be collected 9 without introducing any additional instrumentation into the LV 16.
Therefore, the sensing tip 22 can be used to provide a more thorough cardiac assessment, using a single device.

11 [0057] Once the signal is obtained at 130, an A/D converter 132 in the processing module 12 38 converts the raw signal to a digital signal and passes the signal to each of an ECG digital 13 signal processor (DSP) and a buffer 138. Once the respective signals are processed, they are 14 summed and a final ECG signal 142 is produced.

100581 In another embodiment, the volume sensing device 67 comprises a plurality of 16 inner electrode rings, for example four as shown in Figure 10. Since the optimal conductance 17 measurement is performed by transmitting along the entire length of the LV
16, and different 18 organisms have different sized hearts 12, it may be desirable to incorporate multiple sets of 19 inner electrode ring pairs. In Figure 10, the LV 16 shown in Figure 3 is provided, as well as ?0 an LV 1016 from a smaller organism shown in dashed lines. The pair 164, 166 is similar to ? 1 the pair 64, 66 described above, however, the sensing tip 22 now includes the pairs 168, 170;
?2 172, 174; and 176, 178 arranged progressively closer together and situated between the outer ?3 electrode pair 60, 62.

?4 100591 In such an embodiment, it may be possible to selectively operate any of the ?5 electrode rings as a transmitting ring, but typically the electrode 60 would remain as the '.6 receiving electrode. In the example shown in Figure 10, the electrode 170 would be selected '.7 as the optimal transmitting electrode for the LV 1016 and then the inner sensing electrode !8 pair would comprise the electrodes 164 and 174. Therefore, numerous configurations of !9 receivirig, and sensing electrodes can be selectively chosen in order to obtain an optimal ;0 conductance signal, depending on the size of the LV (e.g. 16 or 1016).

21552232.1 WO 2007/022620 CA o2619986 2oo8-o2-21 PCT/CA2006/001358 1 100601 Therefore, the system 10 enables the monitoring of a heart in a living organism by 2 measuring both pressure and volume in a chamber of the heart, preferably the LV 16. The 3 pressure and volume measurements are acquired using a single sensing tip 22 and are 4 communicated to a transmitting device 20 to be wirelessly transmitted to a receiving device 26, wherein they are used to monitor the heart. The system 10 may also incorporate a 6 temperature measurement that can be transmitted with the volume and pressure measurement 7 to proviide further data for monitoring. The system 10 may also extract an ECG signal from 8 the volume measurement. This allows the monitoring of up to four signals that can be used to 9 determine the health of a heart.

l0 100611 In addition to a compact design, the system 10 may also incorporate an energy 11 saving timing scheme that reduces the power required per acquisition cycle and thus 12 increases the operational lifetime of the transmitting device 20.

13 100621 Although the invention has been described with reference to certain specific 14 embodiments, various modifications thereof will be apparent to those skilled in the art withoui: departing from the spirit and scope of the invention as outlined in the claims 16 appended hereto.

21552232.1

Claims (29)

1. A method of monitoring a heart of a living organism comprising the steps of:
situating a sensing tip within a chamber of said heart, said sensing tip comprising a pressure sensing device and a volume sensing device;

obtaining a pressure measurement and a volume measurement in said chamber using said pressure sensing device and said volume sensing device respectively;
communicating said measurements to a transmitting device; and wirelessly transmitting electrical representations of said measurements to a receiving device, said electrical representations being used to monitor said heart.

2. The method of claim 1 wherein said transmitting device is located external to said heart.

3. The method of claim 1 further comprising the step of analysing said electrical representations to generate data indicative of the health of said heart.

4. The method of claim 3 wherein said data is a computed index based on said electrical representations.

5. The method of claim 3 wherein said data is displayed by said receiving device.

6. The method of claim 1 wherein said sensing tip extends along substantially the entirety of the longitudinal axis of said chamber.

7. The method of claim 1 wherein said pressure sensing device comprises a piezoresistive deflection sensor arranged on said sensing tip, said pressure measurement being sensed through flexure of said sensor.

8. The method of claim 1 wherein said volume sensing device comprises a first set of electrodes for transmitting and receiving an electrical signal through said chamber, said first set of electrodes being arranged at opposite ends of said sensing tip and flanking said pressure sensing device; and at least one set of inner electrodes for sensing said electrical signal transmitted and received by said first set of electrodes to obtain said volume measurement, said at least one set of inner electrodes flanking said pressure sensing device and being arranged between respective ones of said first set of electrodes and said pressure sensing device.

9. The method of claim 1 wherein said transmitting device is implanted into a portion of said living organism.

10. The method of claim 1 further comprising the step of transmitting said electrical representations to a computing device.

11. The method of claim 1 wherein said transmitting device operates by obtaining a supply of energy to enable continuous monitoring.

12. The method of claim 1 further comprising the steps of obtaining an internal temperature measurement using a temperature sensing device, communicating said temperature measurement to said transmitting device, and transmitting an electrical representation of said temperature measurement to said receiving device.

13. The method of claim 1 further comprising the step of obtaining an electrocardiogram measurement from said volume measurement by conditioning said volume measurement to separate a noise portion of said volume measurement comprising said electrocardiogram measurement from a conductance portion of said volume measurement, and extracting said electrocardiogram measurement from said noise portion.

14. A system for monitoring a heart of a living organism comprising:

a sensing tip situated within a chamber of said heart and extending therethrough, said sensing tip comprising a pressure sensing device and a volume sensing device, said pressure sensing device adapted to obtain a pressure measurement in said chamber, said volume sensing device adapted to obtain a volume measurement in said chamber, and said sensing tip adapted for communicating said measurements;

a transmitting device for receiving said measurements from said sensing tip, said transmitting device being adapted to wirelessly transmit electrical representations of said measurements; and a receiving station for receiving said electrical representations, said electrical representations being used to monitor said heart.

15. The system of claim 14 wherein said transmitting device is external to said heart.

16. The system of claim 14 further comprising a processor in communication with said receiving station for analysing said electrical representations to generate data indicative of the health of said heart.

17. The system of claim 16 wherein said data is an index computed by said processor based on said electrical representations.

18. The system of claim 16 wherein said receiving station comprises a display for displaying said data.

19. The system of claim 14 wherein said sensing tip extends along substantially the entirety of the longitudinal axis of said chamber.

20. The system of claim 14 wherein said pressure sensing device comprises a piezoresistive deflection sensor arranged on said sensing tip, said pressure measurement being sensed through flexure of said sensor.

21. The system of claim 14 wherein said volume sensing device comprises a first set of electrodes for transmitting and receiving an electrical signal through said chamber, said first set of electrodes being arranged at opposite ends of said sensing tip and flanking said pressure sensing device; and at least one set of inner electrodes for sensing said electrical signal transmitted and received by said first set of electrodes to obtain said volume measurement, said at least one set of inner electrodes flanking said pressure sensing device and being arranged between respective ones of said first set of electrodes and said pressure sensing device.

22. The system of claim 14 wherein said transmitting device is implanted into a portion of said living organism.

23. The system of claim 22 wherein said living organism is a human and said transmitting device is implanted in proximity of the clavicle.

24. The system of claim 14 wherein said system comprises an analog to digital converter, said electrical representations are analog, and said system is adapted to convert said electrical representations from analog to digital using said analog to digital converter.

25. The system of claim 14 further comprising a computing device for receiving said electrical representations from said receiving device.

26. The system of claim 14 wherein said transmitting device obtains a supply of energy to enable continuous monitoring.

27. The system of claim 14 further comprising a temperature sensing device for obtaining an internal temperature measurement, said system being adapted for communicating said temperature measurement to said transmitting device, and said transmitting device being adapted for transmitting an electrical representation of said temperature measurement to said receiving device.

28. The system of claim of claim 15 wherein said processor is adapted to obtain an electrocardiogram measurement from said volume measurement by conditioning said volume measurement to separate a noise portion of said conductance signal comprising said electrocardiogram measurement from a conductance portion of said conductance signal, and extracting said electrocardiogram measurement from said noise portion.

29. A method for obtaining an intracardiac electrocardiogram signal comprising the steps of:

measuring a conductance signal from a heart chamber in a living organism, said conductance signal indicative of the volume of said chamber;

conditioning said conductance signal to separate a noise portion of said conductance signal comprising said electrocardiogram signal from a conductance portion of said conductance signal; and extracting said electrocardiogram signal from said noise portion.