Date of Award
Spring 1992
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Fitts, Robert
Second Advisor
Eddinger, Thomas
Third Advisor
Foster, Carl
Abstract
Humans exposed to long term spaceflight experience cardiovascular deconditioning and progressive weakness, fatigue, and diminished coordination of skeletal muscles. Elucidating the physiological basis by which zero gravity alters cardiovascular and muscle function is of particular importance for the development of preventative measures and the successful exploration of space. An approach for the study of the hemodynamic and muscle changes caused by zero gravity is the hindlimb suspension (HS) model. This model simulates weightlessness by allowing unloaded contractions without restricting the range of motion of the non-weight bearing limbs. HS has been found to elicit detrimental changes in the cardiovascular system resulting in the reduction of total blood volume and maximal oxygen uptake. HS also produced significant reductions in the size and tension-generating capacity of anti-gravity postural muscles such as the soleus. The following studies were undertaken to I.) characterize the effects of 15 d HS on the distribution of blood flow in the rat; 2.) examine whether 15 d HS alters the blood flow and fatigability of the soleus muscle during high intensity contractile activity; and 3.) investigate the time course of, and cellular mechanisms underlying, the HS induced changes in the morphological and physiological properties of soleus muscle fibers.