EPH KONIGSBERG 
1149 
Ames, and some have been used with Sigmatron 
or Biosentry. They change, and there may be 
some home-grown ones. Those are the only telem- 
etry systems I have any knowledge of and 
have received no comparative data at all. In- 
deed, the only long-term comparative data on 
drift that I've ever seen have been at Dean 
Franklin's lab. It costs a lot of money to reduce 
these data, and that's probably why most peo- 
ple either think it's great or not so great and 
don't put numbers down. So, until very recently, 
we haven't good numbers. We think it's 100 
per cent a month or 50 per cent a month, but 
we haven't had numbers until very, very re- 
cently. 
Dr. Somani : May I ask a technical question ? 
What happens when these transducers begin to 
improve with the chronic use, you know, how do 
they improve? 
Dr. Konigsberg : They improve because their 
linearity and hysteresis is invariably better. If 
you want to know specifically why they improve, 
the answer is that we noticed that we always 
require less balancing of the bridge. What hap- 
pens is we take four string gauges that all 
match. They're all 500 ohms. After they are 
epoxied in place and closed up, we will find that 
they are 460, 480, and 470 ohms, for example. 
And because of this imbalance, we'll put in 
about 100 ohm or 120 ohm resistor to bring the 
bridge into balance. Invariably, well not invar- 
iably, but let's say 80 per cent of the time when 
we get a transducer back, we rebalance the 
bridge, because let's say a wire's been cut or 
something like that, we use a smaller value of 
resistance to balance the bridge. What is hap- 
pening is that as a result of this exercising, 
the locked-in stresses from any epoxy that is 
cured tend to diminish with time. I might add 
that these locked-in stresses are not the cause of 
instability as we know it. We thought they were, 
but they are not. Surprisingly enough, it's other 
instabilities. But anyway, that's the reason. We 
always use less balancing and that's why we be- 
lieve they're better. They're closer to their orig- 
inal state in the free condition. 
K. Sagawa, Johns Hopkins Medical School : I 
would like to ask about this chronic in vivo de- 
calibration of zero point. How do people get the 
same reproducible zero reference point to check 
this in vivo transducer? 
Dr. Konigsberg: I cannot answer that ques- 
tion. You'll have to ask somebody who actually 
works with animals and he happens to be right 
here. 
Chairman: Is Steve Vatner here? Would 
you care to answer that, Steve ? 
S. F. Vatner, University of California, San 
Diego : He'll have to repeat the question. 
Dr. Sagawa: My question is how can you 
really test the zero point in a reproducible man- 
ner when you are concerned with 0.1 mm of 
mercury in vivol I mean, using an extracorpo- 
real string gauge. 
Dr. Vatner : Well, I think if you're concerned 
with .1 mm of mercury, that's out of the ball 
park that we're generally used to working in. 
If we can get within 4 or 5 mm of mercury, 
I think, that's as good as we can do with just 
a regular catheter implant and Stathum trans- 
ducer measurement of pressure. So, maybe, 
we're interested in whether the mean pressure 
is 96 and if it's 98, it doesn't really matter. 
But if it is 96.5, you know, and we measure it 
96, I don't think we're that accurate in any of 
our measurements. 
Dr. Sagawa : The reason I raised this is again 
relates to Dr. Topham's thesis that venous pres- 
sure and interventricular pressure must be 
measured very accurately and that is really seri- 
ous problem I think. To understand saturation, 
you just can't ignore venous pressure and end- 
diastolic pressure volume relationship. 
Chairman : You can't ignore that it's an ex- 
tremely important problem, but I also think 
that it's almost impossible to measure and 
that's why the earlier paper was, I thought, so 
very interesting. I think end-diastolic pressures 
and inferior venous pressures, in general, are 
an area probably of ignorance due to our in- 
ability to measure them. I think the point is 
very well taken. The instrumentation we have 
today, probably, is incapable of it, or turning 
it the other way around : an individual, who is 
drawing conclusions about the physiological 
status of end-diastolic pressure and its impli- 
cations, better be very cautious in the interpre- 
tation of the output of his pressure gauge. 
Would you care to comment? 
