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Age, splanchnic vasoconstriction, and heat stress during tiltingDuring upright tilting, blood is translocated to the dependent veins of the legs and compensatory circulatory adjustments are necessary to maintain arterial pressure. For examination of the effect of age on these responses, seven young (23 +/- 1 yr) and seven older (70 +/- 3 yr) men were head-up tilted to 60 degrees in a thermoneutral condition and during passive heating with water-perfused suits. Measurements included heart rate (HR), cardiac output (Qc; acetylene rebreathing technique), central venous pressure (CVP), blood pressures, forearm blood flow (venous occlusion plethysmography), splanchnic and renal blood flows (indocyanine green and p-aminohippurate clearance), and esophageal and mean skin temperatures. In response to tilting in the thermoneutral condition, CVP and stroke volume decreased to a greater extent in the young men, but HR increased more, such that the fall in Qc was similar between the two groups in the upright posture. The rise in splanchnic vascular resistance (SVR) was greater in the older men, but the young men increased forearm vascular resistance (FVR) to a greater extent than the older men. The fall in Qc during combined heat stress and tilting was greater in the young compared with older men. Only four of the young men versus six of the older men were able to finish the second tilt without becoming presyncopal. In summary, the older men relied on a greater increase in SVR to compensate for a reduced ability to constrict the skin and muscle circulations (as determined by changes in FVR) during head-up tilting.
Document ID
Document Type
Reprint (Version printed in journal)
Minson, C. T. (University Park Pennsylvania 16802-6900, United States)
Wladkowski, S. L.
Pawelczyk, J. A.
Kenney, W. L.
Date Acquired
August 22, 2013
Publication Date
January 1, 1999
Publication Information
Publication: The American journal of physiology
Volume: 276
Issue: 1 Pt 2
ISSN: 0002-9513
Subject Category
Life Sciences (General)
Funding Number(s)
Distribution Limits
NASA Discipline Cardiopulmonary
Non-NASA Center