6 Stationary Controls (12 Frogs); 12 Centrifuge Controls (24 Frogs)

Frog Otolith Experiment Package (FOEP); FOEP Life Support System (LSS)

The inflight results of the OFO-A experiment put forward several questions and problems, some of which could be answered by means of additional ground control studies. For example, a leakage of the O2 supply had significantly increased the pressure inside the canister. Also there was a remote possibility that vibrations produced inflight by the water pump may have affected vestibular activity. The objective of this study was to essentially eliminate as many as possible variables other than weightlessness to explain the changes observed in orbit. Additional control experiments were performed on the ground with a much closer sampling time than used in the original flight controls.

A variety of environmental variables were investigated using the FOEP module: temperature increase; hyperoxia/hypoxia; K+, Na+ and Ca++ variations in canister water; and natural decay (prolonged exposure), to assure that the responses observ- ed were due to the microgravity component of space flight. The water circulation pump was suspended separately from the FOEP, connected by long polyethylene tubing, and package was mounted on a special anti-vibratory base. Vibrations were measured by a three-way accelerometer. In experiments at rest, samplings were recorded fifteen minutes every hour, and EKGs were recorded simultaneously, each time carefully maintaining the correct environmental variables (water temperature, water pressure, PO2, etc.). In additional experiments, responses to centrifuge spin cycles were recorded for each hour for several days through computer operated automatic control.

Vibrations were maintained below 10-3 in all directions. At rest the closer sampl- ing confirmed the basic characteristic at rest with a range between one and four seconds, and 100% standard deviation with a coefficient of variation = 1 was confirmed. It was observed that occasionally the frequency of the discharge became heart rate dependent, although no explanation for this phenomenon could be found. It was thought that further experimentation with continuous recording for 48-72 hours was needed to understand vestibular activity at rest. The most intriguing effect of weightlessness was the changing of the vestibular statorecep- tors mode from tonic to phasic and phasic to tonic; in all responses recorded from centrifuge spin cycles no change of mode was detected. Such control studies revealed that on the ground the response does not change in mode but in gain, as the decaying process continues. It was concluded that the periodical change of mode is a typical effect of weightlessness.

Title of Study: Orbiting Frog Otolith Experiment: Comparison to Control Studies

OFO-A Control Experiments. OFO-A Conclusive Report, Contract NAS 2-7699, 1977, NASA personnel only, NASA CR-153102.

¥ = publication of related ground-based study