Barnett, R.D., Schade, C.M., Gowen, R.J., “Processing of the Leg Volume Data Obtained on the MO92 Skylab Missions,” Instrumentation Laboratory Report, Department of Electrical Engineering, United States Air Force Academy, Colorado, 1974.

The design of the leg volume measuring system employed for the Skylab mission involved the development of a capacitive measurement system to detect small changes in leg volume. These changes in volume of the calf were produced in response to the stress of a Lower Body Negative Pressure Device (LBNPD) or by venous occlusion.

The prototype capacitance plethysmograph was designed at the Air Force Academy and space qualified by the Martin-Marietta Corporation, Denver, Colorado for use on the Skylab Missions.

A capacitive plethysmograph must be calibrated once to establish the correlation between change in capacitance and change in volume of the limb segment being monitored. Each leg band contained its own internal reference as shown in Figure 1 which was used to establish the final calibration number for each individual leg band. The devices and techniques used to obtain the calibration numbers and the associated calibration curves for the seventy-six Skylab leg bands have been described in a previous technical report dated April, 1974. All calibration testing was performed by the instrumentation Laboratory.

This report describes the system, techniques and algorithms used to process the Skylab Mission data and deals specifically with the signal processing performed at the Instrumentation Laboratory.