AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 1 86-R92, Copyright © 1997 by American Physiological Society
Effects of an eight-day space flight on microvibration and physiological tremor
E. Gallasch, M. Moser, I. B. Kozlovskaya, T. Kenner and A. Noordergraaf
Physiologisches Institut, Universitat Graz, Austria.
Microgravity was used to study accelerometrically recorded microvibration
(MV) and postural tremor (PT) at reduced muscle tone on one cosmonaut
before, during, and after an 8-day space flight on the Russian Mir station.
MV of the relaxed forearm in the 1 g environment showed the typical 7- to
13-Hz resonance oscillations triggered by the heart beat. In 0 g, these
pulsations shifted to below 5 Hz and the waveform became similar to an
ultralow frequency acceleration ballistocardiogram. PT of the arm stretched
forward showed an irregular waveform in 1 g. In 0 g, the higher-frequency
components were reduced and again an ultralow frequency ballistocardiogram
emerged. As a control, hand force tremor was recorded as well; it was not
affected by the gravity condition. A second-order analog with muscle
stiffness (C) as parameter was used to evaluate the measurements. For MV it
could be shown that cardiac impacts produce damped resonance oscillations
when C is high enough (1 g). At low C (0 g), this resonance phenomenon is
essentially filtered out. For PT both neuromuscular and cardiovascular
forces produce an irregular output; when C is lowered (0 g) the
higher-frequency content is strongly reduced. It is concluded that both MV
and PT waveforms are sensitive to musculoskeletal stiffness, such that at
the lowest stiffness achieved the cardiac impact dominates. In 1 g, the
cosmonaut's data were not significantly different from the results in a
control group (n = 6).
