Initial experience with a new plethysmograph for zero-G use

A system for venous occlusion plethysmography (SVOP) suited for use in Spacelab was developed and tested. This unit measures changes in limb circumference by using an optical shaft encoder connected to a band encircling the limb. Circumference changes are converted to digital pulses and displayed. Flow is then calculated in ml/min/100 ml. This instrument was compared to mercury-in-silastic (Whitney) gauges at rest and with hyperemia after 3 min of arterial occlusion. Overall the correlation coefficient was 0.95, SVOP = 0.90 x Whitney + 0.44; at rest alone the correlation coefficient was 0.89, SVOP = 0.62 x Whitney + 0.75. It is concluded that the SVOP produces good flow data, needs no calibration, and contains no toxic materials making it suitable for zero-G use.