H. L. STONE AND H. SANDLER 
595 
cage contained the actuating switch for the im- 
planted units enclosed in a plastic protected 
shield; actuation was accomplished by manual 
or remote means. The implanted unit is 
powered by two pacemaker cells providing 1000 
milliampere hours of power which allows for 
500 hours of continuous operation of the unit. 
With intermittent sampling it is anticipated 
that 1-2 years of data can be obtained from ap- 
propriately instrumented animals. One such im- 
planted unit has now operated with intermit- 
tent samplings for 11 months and continues to 
operate at the time of this writing. All data was 
recorded on an Ampex FR 1300 tape recorder 
for subsequent analysis or display. 
The manner of calibration of the implanted 
units has been previously described.^^ Units 
were carefully bench calibrated prior to implan- 
tation and by direct and indirect means while 
within the chest cavity of each respective ani- 
mal. EGG was measured in all animals. Three 
pressures were recorded in two animals, six 
pressures were recorded in one animal, four 
pressures and two single axis accelerometers in 
two animals and three pressures and one three 
axis accelerometer in the last two animals. Ac- 
celerometers were used as dimensional gages 
and to study the vibrational characteristics of 
the left ventricular walU^-^'' Pressure cells 
were implanted in the right and left ventricles 
and left atrium in all animals. Figure 2 shows a 
lateral chest x-ray in one animal illustrating the 
placement of the transmitter and various trans- 
ducers. Additional cells were left in the apical 
TRANSMITTER 
AND BATTERY 
PACK 
PRESSURE CELL 
LEFT VENTRICLE 
PRESSURE CELL 
LEFT ATRIUM 
PRESSURE CELL 
PULMONARY 
ARTERY 
DOPPLER 
FLOW 
METER 
Figure 2. — Lateral chest radiograph in a chimpanzee. 
