Abstract
To examine the possible age-related blood pressure (BP) deregulation in response to central hypervolemia, we measured spontaneous baroreflex sensitivity (SBRS), carotid arterial compliance (CC), and R-R interval coefficient of variation (RRICV) during basal and thermoneutral resting head-out-of-water immersion (HOWI) in 7 young (YG = 24.0 +/- 0.8 years) and 6 middle-aged/older (OL = 59.3 +/- 1.3 years) healthy men. Compared with basal conditions (YG = 19.6 +/- 4.0 vs OL = 6.1 +/- 1.5 ms/mmHg, P < 0.05), SBRS remained higher in YG than OL during rest HOWI (YG = 23.6 +/- 6.6 vs OL = 9.3 +/- 2.1 ms/mmHg, P < 0.05). The RRICV was significantly different between groups (YG = 6.5 +/- 1.4 vs OL = 2.8 +/- 0.4%, P < 0.05) under HOWI. The OL group had no increase in CC, but a significant increase in systolic BP (basal = 115.3 +/- 4.4 vs water = 129.3 +/- 5.3 mmHg, P < 0.05) under HOWI. In contrast, the YG group had a significant increase in CC (basal = 0.16 +/- 0.01 vs water = 0.17 +/- 0.02 mm(2)/mmHg, P < 0.05) with no changes in systolic BP. SBRS was positively related to CC (r = 0.58, P < 0.05 for basal vs r = 0.62, P < 0.05 for water). Our data suggest that age-related vagal dysfunction and reduced CC may be associated with SBRS differences between YG and OL groups, and with BP elevation during HOWI in healthy older men.
Highlights
Orthostatic hypotension is prevalent with aging [1] and a proposed underlying mechanism is associated with impaired arterial baroreflex sensitivity (BRS; 2,3)
The Stroke volume (SV) and Cardiac output (CO) were significantly increased while total peripheral resistance was slightly decreased in both groups during rest head-out-of-water immersion (HOWI) compared with basal conditions, with no significant differences between groups
The YG group showed no increase in resting SBP or pulse pressure (PP) while the OL group showed a significant increase in SBP and PP during rest HOWI
Summary
Orthostatic hypotension is prevalent with aging [1] and a proposed underlying mechanism is associated with impaired arterial baroreflex sensitivity (BRS; 2,3). Arterial baroreceptors are sensory nerve endings that innervate large arteries (carotid sinuses and aortic arch) and appear to contribute importantly to the regulation of blood pressure (BP) by the withdrawal of cardiac vagal tone (the immediate increase in heart rate (HR) determined by the acceleration of the electrocardiographic (ECG) R-R interval) during orthostatic challenge [5]. Age-related changes seem to provoke autonomic changes with impairment of vagal baroreflex and increases of baseline muscle sympathetic nerve activity [2]. Shi et al [6] demonstrated that age-related cardiac vagal dysfunction is associated with an attenuated response of BP regulation during hypovolemic stress. Their study showed that the elderly experienced orthostatic hypotension at the onset of orthostatic challenge because of a diminished HR response, but the increased vasoconstriction helped maintain their BP during a hypovolemic stress
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