W. S. TOPHAM 
1241 
fort in making very precise venous pressure 
measurement, and I think the same thing ap- 
plies to ventricular pressure measurement dur- 
ing diastole. I think Konigsberg will bring up 
later what we and many others find : that inter- 
ventricular pressure during artery diastole is 
quite often negative, even if the chest is open. I 
have seen several records, even during this 
meeting, showing this negative pressure. It may 
be a physiological problem, but to really discuss 
this kind of dynamics, you have to have very 
precise measurements. Just a comment on your 
effort. Thank you. 
N. P. Ching, St. Vincent's Hospital, New 
York City, N.Y. : Two questions. One, you 
didn't identify the product, by manufacturer. Is 
there a reason ? And secondly, have you had any 
experience with the new intervascular flowme- 
ter that they've put on the catheter? 
Dr. Topham : I have had no experience with 
the catheter tip flowmeters. There are several 
kinds available. Some use hot wire anemome- 
try; others use the electromagnetic flow princi- 
ple. Biotronics has made one of the latter, which 
was reported in the Journal of Applied Physiol- 
ogy. The only knowledge I have of those is from 
reading the literature. 
I can give you the names of the commercial 
flowmeter manufacturers that we evaluated. 
They may want to talk to me after I get 
through, but the first one that I showed was 
Biotronics, the second one was Carolina Medical 
Instruments, and the third one was Statham. 
P. SOMANI, Abbot Laboratories, North Chi- 
cago: We have had some experience with this 
new type of flow probe, and we have been very 
successful in recording the flow. We have used 
the Carolina system, too, and compared the in- 
tervascular flow measurement from extra-cor- 
poreal flow measurements and they match very 
well. I'd like to note that we have been using 
Carolina flowmeters, and we have not seen the 
drift that you have. We find it very stable in our 
hands, at least. 
Dr. Topham : I appreciate that comment. I 
was very surprised myself as we evaluated 
these flowmeters to see that type of response. 
We talked with the Carolina people and asked 
them why it might be. In fact, I sent a copy of 
our records to them and asked them to give me 
some suggestions. Nothing seemed to come 
back, and I was unable to correct the problem in 
my own laboratory. So I could do nothing ex- 
cept report what I found. 
E. Konigsberg, Konigsberg Instruments, 
California: I think your reduction of 25 times 
the power on the catheter tip flowmeter is sig- 
nificant in another area, namely on the sample 
and hold circuit, and that is with telemetry sys- 
tems which are completely sealed. This can 
mean an appreciable reduction in power. Right 
now pressure transducers burn a lot of power 
as compared with the more passive types of in- 
struments. So I think there would be a signifi- 
cance there, too. 
Dr. Topham : Thank you. I felt that perhaps 
this might be a good way to excite those trans- 
ducers and maybe give us a better zero as well 
as reducing the power into the transducer. 
Mr. Clark, "Medical Electronics News," 
Philadelphia, Pa. : Who makes the fiber optic 
oximeter ? 
Dr. Topham : It is commercially available. It 
was developed by Dr. Curtis Johnson at the 
University of Washington and there are two 
firms which are making it, but I can't give you 
their names, I'm sorry. 
Dr. Konigsberg: Physiocontrols ? 
Dr. Topham : Physiocontrols is one, Dr. Kon- 
igsberg says, and I'm not sure of the other one. 
I know that there is some effort to sell that 
particular fiber optics catheter and I'm sure 
that we'll hear more about it, but my com- 
munication is directly with Dr. Johnson. Thank 
you. 
