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1 !] mJ REFERENCE

A 11 10b MM1M7S PUBLICATIONS

NBSIR 77-1310

Microcalorimetric Study of

Cardiac Pacemakers and

Batteries

Edward J. Prosen and Jennifer C. Colbert

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

September 1977

Final

5** V/ \

I.S. DEPARTMENT OF COMMERCE

ytQ Ij-jj/Q IATIONAL BUREAU OF STANDARDS

/f77

NBSIR 77-1310

MICROCALORIMETRIC STUDY OF

CARDIAC PACEMAKERS AND

BATTERIES

Edward J. Prosen and Jennifer C. Colbert

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

September 1977

Final

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Microcalorimetric Study of Cardiac

Pacemakers and Batteries*

by

Edward J. Pro sen and Jennifer C. Colbert

National Bureau of Standards, Institute for Materials Research

Washington, DC 20234

Abstract

A feasibility study was carried out to determine if microcalorimetry

could be used to measure the energy loss or self-discharge of cardiac

pacemakers and power cells. Alkaline and mercury batteries, camera and

watch type, were measured both under external load and open-circuit

conditions. The results indicate that microcalorimetry can be both a

sensitive and useful tool for measuring the self-discharge of cardiac

pacemakers and power cells. Microcalorimetry can also be used to measure

nondestructively , the power output from the completed (sealed) pacemaker itself.

Keywords: Battery; microcalorimetry; pacemaker; power cell;

self-discharge

This work is supported by the Non-Destructive Evaluation Program,

Institute for Materials Research, National Bureau of Standards.

1
INTRODUCTION

The present work was undertaken to test the feasibility of using a

microcaloriraeter for the study of batteries or power cells for cardiac

pacemakers and also for developing a possible non-destructive test for

the complete pacemaker.

One characteristic of power cells is that of self-discharge or

gradual loss of deliverable energy after the cell is stored opencircuited for long periods of time. This is called shelf-life. The

self-discharge characteristic is not completely understood and the amount

varies for different types of power cells and for different manufacturing methods and sometimes occurs in differing degrees under the "same"

manufacturing conditions. Thus it is important to be able to measure

this characteristic to gain a more thorough understanding of its causes

and hence possible prevention.

It is also not clear at present whether this self-discharge is

present when the power cell is under load as in a pacemaker circuit. That

is, during use, is energy being drawn from the power cell both by the

external circuit and by the self-discharge mechanism or is the selfdischarge mechanism absent or perhaps increased during actual usage?

Microcalorimetry is a possible tool for the study of these questions.

The useful lifetime of a power cell for implantable cardiac pacemaker use is of prime importance. Present pacemakers using chemical

power cells may last four years or more before requiring power cell

replacement. It is desirable that the useful lifetime of the power cell

be as predictable as possible especially since it is very difficult or

impossible in many cases to detect when the power cell is close to

failure or complete discharge.
A pertinent question with respect to self-discharge is the following:

Is the self-discharge power an appreciable proportion of the power

delivered to the working circuit and hence does it have an appreciable

effect on the life of the power cell under use? As will be shown, the

self-discharge power of some small power cells for camera use may typically

be as much as 5 microwatts and it may be larger for the larger pacemaker power cells. Typical pacemakers may draw as little as 25 microwatts of power. Thus the self-discharge may account for 20 percent of

the active material depletion of the cell. This, of course, assumes that

the self-discharge mechanism is operating at its open-circuit rate during

use and is not enhanced or absent. We are thus talking about a possible

1 year loss of life for a 5 year power cell.

Microcalorimetry , as will be shown, can measure open-circuit selfdischarge and therefore can non-destructively discover cells which have

inordinately large self-discharge rates. Secondly, it can set limits on

how long the power cells can be stored before use. Also, with further

measurements, it can determine optimum conditions for storage (e.g.

temperature)

Measurements on the total pacemaker will constitute a non-destructive

test which can help detect any pacemaker which is drawing too much

power. This will add a useful test to those already being performed on

completed pacemaker circuits and is a test which is performed after the

hermetic sealing of the unit. *

A microcalorimeter capable of measuring the larger power cells for

cardiac pacemakers and for measuring the pacemakers themselves is being

assembled

3
EXPERIMENTAL

An NBS microcalorimeter (1) was used for these measurements. The

detector in the calorimeter is a solid-state thermopile (Metal Specialities Company) which has an output of 1 microvolt per 4.90 microwatts of

power generated within the sample box of the calorimeter. The output is

amplified by a factor of 1000 by an operational amplifier (Analog

Devices 261 K) kept at constant temperature (+0.001 °C) within the

calorimeter jacket. This output voltage can then be recorded by a

millivolt potentiometric recorder or read by a digital voltmeter and

recorded on magnetic tape cassettes and digitally plotted. The latter

procedure was used for the plots shown below.

The noise level and stability was such that a few tenths of a

microwatt of power could be detected. The calibration factor of 4.90

microwatts /microvolt (at the pile) was determined by use of a four- lead

electrical heater in the sample box.

The silver sample box space of the present calorimeter was 3.8 cm x

2.5 cm x 0.8 cm and therefore could accomodate small disc type camera

and watch power cells but could not accomodate the larger pacemaker power

cells. The camera and watch power cells were therefore used to test the

feasibility of the microcalorimeter method for this work. The type, usage,

and size of the power cells used in this study are given in Table 1.

4
Table 1

BATTERY DESCRIPTION

Size, cm Cell No. Type Use Diameter x Thickness

X-2 alkaline camera 2.3 x 0.6

X-3 mercury camera 1.55 x 0.6

X-4 alkaline camera 2.3 x 0.6

X-5 mercury watch 1.15 x 0.35

X-6 mercury camera 1.55 x 0.6

To improve thermal contact of the power cell with the sample box, a

nonconducting hydrocarbon oil (Cenco Hyvac Oil) was placed in the

sample box so as to almost cover the power cell. Transparent adhesive

tape was placed over one terminal of the cell to prevent shorting to

the box.

Figure 1 shows a test record of self-discharge of power cell X-5

(a mercury watch battery) . The initial portion of the curve is the baseline of the calorimeter without any power cell in the sample box. The

cell is then inserted and the output is now lower, which is in the

exothermic direction. Due to the fact that the power cell is not

initially very close in temperature to .the calorimeter block, a large

) offset is first observed and the block temperature is disturbed slightly.

Therefore a more reliable effect is observed upon removal of the power

cell. Thus a signal of 0.4 uV (the vertical height shown in Figure 1) at

the pile is recorded, which corresponds to 2.0 uW, and is the selfdischarge rate of the power cell.

5
RESULTS

Results on four power cells are given in Table 2. It is seen that

the alkaline power cells give approximately 4 to 5 microwatts of selfdischarge and the mercury power cells give 1.5 to 2 microwatts.

Table 2

MICROCALORIMETRIC DETERMINATION OF

SELF-DISCHARGE

Cell uW

X-4 ALK( CAMERA) 3.9

X-2 ALK( CAMERA) 4.9

X-6 Hg( CAMERA) 1.5

X-5 Hg (WATCH) 2.0

UNDER LOAD IN CALORIMETER

yW

X-3 Hg( CAMERA) with 110 kfi load in calorimeter 17.6

Power due to 110 kfi load 15.4

Difference 2.2

Since only a few measurements were made these results are preliminary

and are perhaps uncertain by + 1 or 2 microwatts. No attempt was made

to obtain typical or representative samples and therefore more

exhaustive calibrations should b£ made.

6
One additional test which was made is shown in Figure 2 and tabulated

in the lower part of Table 2. In this test a small 110 kfi resistor was

soldered to a mercury power cell and the whole unit placed in the sample

box of the calorimeter. Figure 2 shows two insertions and removals of

the unit from the calorimeter; the second removal being performed after

the unit had been in the calorimeter for several hours and the result

(17.6 uW) tabulated in Table 2. The power dissipated in the 110 kft load

is calculated to be 15.4 yW, leaving 2.2 yW unaccounted for. This may

have been leakage or self-discharge. However, no great significance can

be attached to this difference since only one experiment of this type

was performed and only rough measurements of the power cell voltage

before and after the run were made. This value of 15.4 yW is the AH

of the cell reaction, where both the battery and resistor are in the

calorimeter. It does illustrate that power can be measured under load

as with a complete pacemaker in the calorimeter and that the result is

close to what one would calculate from the load plus leakage or selfdischarge .

In Figure 3 is shown the result of measurements made with the

external load outside of the calorimeter while the power cell is inside

the calorimeter. In this way various resistors could be connected and

disconnected to give the power dissipated in the power cell in the

calorimeter and, by measurement of current and voltage, the power W

dissipated in the resistor outside the calorimeter. These measurements

were made by attaching small copper leads (No. 32 AWG) to the power cell

and running these leads out of the calorimeter to an external resistor.

7
In Figure 3 a 5 kft, 10 kft, and 3 kfi resistor were connected and disconnected as shown. Similar experiments were performed on two other

power cells and the results for two alkaline power cells are tabulated

Table 3

ALKALINE BATTERIES WITH EXTERNAL LOAD

52

X-2 ALK( CAMERA)

I W

x pA yW

W

i

uW

VW

x

10010

4996

3005

146

292

484

213

426

703

8.3

17.2

29.4

.0390

.0404

.0418

9999

5003

3005

2004

1001

X-4 ALK( CAMERA)

144 207 8.8

285 405 18.1

476 681 29.9

711 1012 47.7

1412 1996 101.9

.0425

.0447

.0439

.0471

.0511

in Table 3 and for a mercury power cell in Table 4. Listed are the

values of the external resistor R

x

(fi) , the current through the external

resistor I(yA), the external power delivered W

x

(uW), the power

dissipated internally in the power cell W^yW), and the ratio of the

internal power to the external power W /W . In Figure 4 the internal

power is plotted against the external power for the three power cells

tested. It will be noted that W. is a linear function of W and that i x
Table 4

MERCURY BATTERIES WITH EXTERNAL LOAD

X-3 Hg( CAMERA)

R I W W. W./W

x x 1 IX

fl yA yW yW

4996 269 361 2.1 .0058

3005 445 596 6.6 .0111

2005 666 889 10.8 .0121

1001 1329 1767 27.0 .0153

the sloper or ratio W. /W is about 4 percent (W. is 4% of W ) for the

i x

r i x

alkaline cells and about 1 percent for the mercury cell . It will also

be noted that the lines in Figure 4 extrapolate to near zero for zero

W

x

(or open-circuit). Some curvature can be noted. This is due to the

finite internal resistance of the power cell. However, extrapolation

to zero W. is inevitable here since the method used for measuring W.

i l

excluded any open-circuit power. That is, was obtained in these

external load experiments from the vertical height (for example, A in

Figure 3) of the shift of output upon connecting and disconnecting the

external load.

It should also be stated that the ratio of W. /W does not give a IX

measure of lost power over what could be obtained if the cell reaction

taking place were ideal. Each type of cell reaction has a characteristic

which must be dissipated internally. This can be calculated from the

thermodynamics of the cell reaction if all the thermodynamic quantities

are known. Alternatively, such measurements could aid in obtaining these

9
thermodynamic properties . Theoretically should be a linear function

of since both of them are proportional to the amount or number of moles

of cell reaction taking place. Variation from strict linearity may be

due to the effect of self-discharge or leakage or high internal resistance

of the power cell or other non-ideal effects. Such non-ideal or selfdischarge effects are not truly significant in Figure 4 and Tables 3

and 4 and the difference in the two alkaline power cells, X-2 and X-4,

is also not significant.

10
SUMMARY

The feasibility of using a heat conduction type of microcalorimeter

for measuring self-discharge of pacemaker power cells and for measuring

internal power dissipation under external load was tested by means of an

NBS microcalorimeter on small camera and watch power cells. Preliminary

results on small alkaline type power cells for camera use indicated 4 to

5 microwatts of self-discharge and small mercury type power cells for

camera or watch use showed 1.5 to 2 microwatts of self-discharge. A test

of a power cell with a resistor across it in the calorimeter yielded a

power value in fair agreement with that calculated as dissipated across

the resistance load plus the self-discharge.

Tests of internal power dissipated in the power cell in the calor

imeter as a function of external power W dissipated in a resistor outsid

the calorimeter yielded results which are characteristic of the ideal

cell reaction; that is, W. is a linear function of W (within the

i x precision of the measurements) . This was true for both the alkaline and

the mercury power cells tested within the precision of the present tests.

Valuable thermodynamic information can be obtained from the ratio

W^/W

x

» For example, is mainly the -TAS term of the cell reaction and

2

W is the useful work or -AG. There is also an I R„ term in W. , where x 0 i

Rq is the internal resistance of the power cell. There are also small

junction potential terms. If both the power cell and the external resistance are in the calorimeter (as in Figure 2) then -AH of the cell

reaction is measured. Therefore the self-discharge is also -AH and it

should be corrected by +TAS to get -AG which is the true self-discharge

loss. It should also be noted that "self-discharge" may also be caused

11
by side reactions, such as corrosion reactions in the power cell. A

search for thermodynamic data on the cell reactions involved has not as

yet been made for comparison with these experimental results. More

thorough and accurate measurements of versus W"x will need to be made

in order to be able to state whether self-discharge or leakage is

increased or absent when the power cell is in use (under load)

Thus it has been shown that valuable measurements of self-discharge

of small power cells can be made with an NBS microcalorimeter or other

microcalorimeter of comparable sensitivity. This will be useful for

eliminating cells with higher than normal self-discharge rates and for

determining the shelf life of the power cells. Measurements under load

may be useful in determining whether leakage or self-discharge is operating when the power cell is under load. Valuable thermodynamic data for

the cell reaction may be obtained by these microcalorimetric methods.

A new conduction calorimeter similar to the NBS microcalorimeter is

being assembled. Some improvements are planned with the capability for

handling the larger pacemaker type power cells or the complete pacemaker.

This will allow us to develop a non-destructive test method for pacemaker

power cells and for the complete pacemaker.

12
REFERENCES

1. Prosen, E. J., "Design and Construction of the NBS Clinical

Microcalorimeter," NBS Report 73-179 (April 1973).

Prosen, E. J., and Goldberg, R. N., "Testing of the NBS Clinical

Microcalorimeter," NBS Report 73-180 (April 1973).

Prosen, E. J., Goldberg, R. N., Staples, B. R. , Boyd, R. N., and

Armstrong, G. T e , "Microcalorimetry Applied to Biochemical Processes,

p. 253-289 of "Thermal Analysis: Comparative Studies on Materials,"

H. Kambe and P. D. Garn, editors, John Wiley and Sons (1974)

New York.

13
LEGEND FOR FIGURES

Figure 1. Battery X-5 Self-Discharge

Figure 2. Battery X-3 with 110 kfi Load in Calorimeter

Figure 3. Battery X-2 with 5 kfi, 10 kfi and 3 kfi External Load

Figure 4. Plot of (energy discharged in the calorimeter or power cell)

Versus W (useful energy discharged into the external load)

X




NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 77-13102. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Microcalorimetric Study of Cardiac Pacemakers and

Batteries

5. Publication Date September 1977

6. Performing Organization Code

7. AUTHOR(S)

Edward J. Prosen and Jennifer C. Colbert

ort No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as above

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) A feasibility study was carried out to determine if microcalorimetry could be

used to measure the energy loss or self-discharge of cardiac pacemakers and power cells.

Alkaline and mercury batteries, camera and watch type, were measured both under external

load and open-circuit conditions. The results indicate that microcalorimetry can be

both a sensitive and useful tool for measuring the self-discharge of cardiac pacemakers

and power cells. Microcalorimetry can also be used to measure nondestructively , the

power output from the completed (sealed) pacemaker itself.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Battery; microcalorimetry; pacemaker; power cell; self-discharge

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