After several days in microgravity, return to earth is attended by alterations in cardiovascular function. The mechanisms underlying these effects are inadequately understood. Three clinical disorders of autonomic function represent possible models of this abnormal cardiovascular function after spaceflight. They are pure autonomic failure, baroreflex failure, and orthostatic intolerance. In pure autonomic failure, virtually complete loss of sympathetic and parasympathetic function occurs along with profound and immediate orthostatic hypotension. In baroreflex failure, various degrees of debuffering of blood pressure occur. In acute and complete baroreflex failure, there is usually severe hypertension and tachycardia, while with less complete and more chronic baroreflex impairment, orthostatic abnormalities may be more apparent. In orthostatic intolerance, blood pressure fall is minor, but orthostatic symptoms are prominent and tachycardia frequently occurs. Only careful autonomic studies of human subjects in the microgravity environment will permit us to determine which of these models most closely reflects the pathophysiology brought on by a period of time in the microgravity environment.
Center for Space Physiology and Medicine, Departments of Medicine, Pharmacology and Neurology, Vanderbilt University, Nashville, TN 37232-2195
Submitted for publication December 1995.
Accepted for publication May 1996.
This work was supported in part by National Institutes of Health grants RR00095, NS33460, and HL46680 and National Space and Aeronautics Administration grants NCC 2-696, NAG 9-563, and NAGW 3873, Andrew Ertl is a NASA Research Scholar, and Giris Jacobs is a Merck International Fellow at Vanderbilt University.
Address for correspondence: David Robertson, Clinical Research Center, AA3228 MCN, Vanderbilt University, Nashville, TN 37232-2195. E-mail:firstname.lastname@example.org.