Ageing reduces sympatho‐suppressive response to head‐out water immersion in humans

Abstract

Muscle sympathetic nerve activity (MSNA) is suppressed during thermoneutral head-out water immersion (HOI) in humans. In this study, the effects of ageing on the suppressive response of MSNA to HOI were determined. MSNA was recorded microneurographically from the tibial nerve in 16 healthy men, 10 of whom were aged 19-30 years (young group) and six aged 45-67 years (older group). MSNA was suppressed in all the subjects during HOI. The suppressive response was significantly less prominent in the older group than in the young group. A significant negative correlation between age and the suppressive response of MSNA induced by HOI (r = -0.53, P < 0.05) was found. We conclude that suppressive response of sympathetic nerve activity to HOI is reduced with age.

Effects of Aging on Cardiovascular Responses to Gravity-Related Fluid Shift in Humans

“…† p Ͻ .05 vs supine, # p Ͻ .05 vs young subjects. was suppressed by head-out water immersion in the young subjects and that the suppression of muscle sympathetic nerve activity by immersion is reduced with advancing age (3). In the present study, blood pressure was significantly elevated in the elderly subjects with a lack of buffering autonomic responses, in spite of less fluid shift.…”

“…Head-out water immersion induces a cephalad fluid shift (13-15) that loads baroreceptors, eliciting activation of cardiac vagal activity and relative suppression of cardiac and vasomotor sympathetic nerve activities to compensate an increased cardiac filling (3,16). There is little in the literature that discusses the neural control of systemic circulation during head-out water immersion, especially in elderly people.…”

“…In contrast, head-out water immersion induces cephalad fluid shift, resulting in an increase in cardiac filling and loading mainly of the cardiopulmonary baroreceptor. Slowing the heart rate and reducing vascular resistance buffer the hypertensive effects of the increased stroke volume by enhancing cardiac vagal activity and suppressing sympathetic nerve activity (3). These buffering effects of autonomic nerve activity contribute to maintaining stable blood pressure.…”

Environmental noise alters gastric myoelectrical activity: Effect of age

“…This may, in part, explain why GMA of older individuals is diminished during exposure to stimuli such as meal [27] , or head out of water immersion [28] . Finally, in an animal study by Pharm and Willott [29] , it was determined that the "threshold" auditory stimulus required to initiate an acoustic startle response grew with age.…”

Osteoporosis in Spaceflight

“…MSNA was found to be suppressed during an exposure to short-term microgravity induced by parabolic flight [Iwase et al, 1999], to mild lower body positive pressure (10-20 mmHg LBPP) [Fu et al, 1998], and to thermoneutral head-out water immersion [Miwa et al, 1996] responding to the loading or unloading of cardiopulmonary receptor stimulated by cephalad fluid shift. Contrarily, MSNA was enhanced after an exposure to long-term microgravity in spaceflight and its simulation induced by dry immersion , and 6°head-down bed rest , caused by various mechanisms including plasma volume loss, changes in baroreflex, and vascular compliance after the human body has acclimated to microgravity situation..…”