H. SANDLER, T. B, FRYER AND H. L. STONE 
1205 
These periods have allowed for zero determina- 
tion to as accurate a degree as occluders. Often 
in the resting dog long periods of diastolic filling 
occur due to normal sinus arrythmia and pro- 
vides a good check as to whether or not you're 
approaching a good zero. The basic system has 
very good zeros with the square waves in single 
channel checks at the bench and when we've 
done acute experiments. But like any system, 
it's not perfect, and it's never as good as you 
want it. 
C. Grant, Veterans Hospital, Albany: I'd 
like to ask about the state of development of 
this from the point of view of consumers. Are 
there suppliers to whom somebody without spe- 
cial high quality electronic facilities can go and 
buy a telemetry device for electrocardiogram 
and pressure recording? 
Dr. Fryer : We have contracted with a num- 
ber of people at various times who have been in- 
terested in the commercial market. Currently, 
we have been getting some work done by Kon- 
igsburg Instrument Company which makes the 
pressure cells. Possibly if you contact them, 
they might be in a position to supply the types 
of systems you're talking about. 
D. PURDY, ARCO Nuclear Co., Pittsburgh: 
You mentioned that one of your limitations 
may be power. As you know, the radiosotope 
power cardiac pacemaker program has de- 
veloped a nuclear battery for pacemaking, and 
I wonder if you had considered that type of 
power for some of your applications? 
Dr. Fryer: Yes we had. In fact, just two 
weeks ago, we got in two nuclear batteries that 
we've just attached to two transmitters. I might 
mention that they cost $3000 per battery, so 
I don't think they're very practical at this 
time. We are testing the system with the hope 
that they'll be available at a much more modest 
cost in the future. 
I should mention now that you've brought 
up the question of power supplies for the 
electromagnetic flowmeter, is considerably 
greater than for the other systems. I didn't 
really have time to go into it during the presen- 
tation. However, we are using rechargeable 
batteries, and we're using the type of system 
that they have also used in the artificial heart 
program, which allows for recharging the bat- 
teries. Our power requirements however, are 
so much lower than those for a heart so that 
we can get four to five hours from two 
pen-light size cells. With periodic recharging 
this system can be used over and over again. 
I also should mention that we're currently in 
the process of assembling a totally implanted 
flowmeter with pressure and EKG measure- 
ments in a multiple channel system. 
A. SCRIABINE, Merck Institute, West Point, 
Penna. : For how long were you able to keep 
your systems functioning inside of the animals ? 
This is the first question. The second question is 
about calibration and sensitivity. How did you 
correct for zero in your pressure cells? 
Dr. Fryer: Well, let me answer the second 
question. As far as the calibration of the pres- 
sure cells, for zero, we do this as have others by 
insertion of a catheter. Calibration as far as 
sensitivity, which normally doesn't change so 
much, can be done with a chamber that will 
allow you to change the atmospheric pressure 
since these are sealed cells. You can get a dy- 
namic calibration that way and we have done 
that. The only way I know of obtaining zero 
calibrations for long periods would be from a 
chronically implanted catheter. We have found 
very little drift over weeks and months. They 
stabilize, but you would want to periodically 
check them at least to verify zero. The other 
question ? 
Dr. Scriabine: How long were you able to 
keep them functioning? 
Dr. Fryer : This has been a fairly long-term 
program in that we've made a lot of measure- 
ments with pressure but without the flow. 
Initial units were manufactured by hand, more 
recent units are utilizing integrated circuit 
techniques. We have had systems that are non- 
functioning after a couple of months or so, 
others have functioned in excess of one year. 
We have three dogs that have lived in excess of 
four years with the hardware in them. These 
animals have the hardware implanted in the 
chest cavity. They have pressure cells in the 
right and left ventricles and the aorta, and 
these dogs are perfectly normal and healthy. 
I haven't mentioned the fact that these units 
have their greatest application with those ani- 
mals that are not very cooperative. We do work 
