H. L. STONE AND H. SANDLER 
605 
that this unit has not hurt this animal. We've 
done periodic blood studies in terms of white 
counts, hemoglobin and the surviving animals 
have thrived. There has been no evidence of any 
ill effect from the implantation. 
G. F. Gestring, Newark Beth Israel Medical 
Center, Newark, New Jersey: What do you 
mean by zero estimation in a clinical fashion? 
And what about the ST changes ? 
Dr. Sandler : In terms of zero, we have used 
the reference point that is classically used 
which means the level of right atrial distance in 
the chest. We estimate where the level of the 
mid right atrium is and zero our pressure 
gauges when we use the standard clinical car- 
diac catherization technique. We have not made 
a study of ST changes. We find, however, after 
surgery, that there are significant ST changes, 
but you know we have incised both the right 
and the left ventricles in order to insert the 
pressure gauges through the wall of the left 
ventricle. However, the animal recovers back to 
a nomal position. We have not used any stand- 
ard placing of EKG leads from the animals. At 
times we've experimented with this but we can- 
not make any real comments about where and 
what the significance of the EKG changes are at 
this time. 
Chairman : I might say that almost every- 
body that uses this method of measuring pres- 
sure calibrates it from a comparative pressure, 
from say a Stathum transducer and a tube in 
the ventricle or chamber. 
