Frequency spectra and cosinor for evaluating circadian rhythms in rodent data and in man during Gemini and Vostok flights.

With the advent of a capability for extraterrestrial existence of lifeforms, chronobiology--the study of biological rhythms--has reached a position analogous to that of classical endocrinology. Just as an endocrine gland can be removed from an experimental animal, the effects of removal examined and the gland (or an extract) then replaced to determine whether the removal effects are reversible, lifeforms should be rigorously evaluated by rhythmometry before and during their (attempted) removal from Earth effects, as well as following their return to Earth. Methods lending themselves to such studies before, during and after travel in extraterrestrial space are illustrated herein, and their applications may be of value to preventive medicine as well as to basic science. Analyses of terrestrial control data and of restricted time series from extraterrestrial missions indicate that substantial scientific returns on Earth can be anticipated if in the routine of all mammalian space travelers provisions are made for: (1) monitoring body core temperature so as to evaluate its stable circadian rhythm--a phenomenon of interest in itself and also a reference rhythm for other variables; (2) saving aliquots from all urine samples, whereby a spectrum of diverse rhythms can be examined; (3) repeating simple performance tests, e.g., of grip strength or eye-hand coordination. Plans also should be implemented in unmanned space vehicles for explicit chronobiologic studies so designed that daily cosinor analysis can determine, e.g., whether circadian phase control or the desynchronized period length be altered as we move away from the Earth. Thus, some of the mechanisms underlying rhythms are now amenable to study on experimental mammals in unmanned space vehicles. In view of the high degree of generality of mammalian rhythms--many related to human well-being and optimal performance--and of dramatic consequences from some rhythmic variations in man, such studies deserve time and attention equal to that expended on weather and communication satellites.