Key Points
- To determine whether alterations in central blood volume elicit reflex regulatory effects on sympathetic sudomotor nerve traffic and sweating in heated humans.
- Assessed 11 healthy volunteers undergoing whole-body heating to stimulate sudomotor nerve traffic and sweating.
- Recorded multi-unit skin sympathetic nerve activity (SSA), skin electrical resistance, and skin blood flow from forearm cutaneous or radial nerve branches.
- Displaced central blood volume to the lower body using lower body negative pressure (LBNP; 5 and 10 mmHg) and 30-degree head-up tilt maneuvers.
- Low levels of LBNP (5 and 10 mmHg) promptly inhibited SSA and reduced transient skin resistance changes (n = 9) without altering blood pressure, heart rate, or skin blood flow, rapidly returning to baseline upon cessation.
- Head-up tilting similarly diminished SSA across 19 tilt maneuvers (n = 3), whereas the capacity for mental stress-induced SSA elevation remained intact during LBNP.
- Spontaneous blood pressure fluctuations did not alter SSA, demonstrating that unloading of cardiopulmonary low-pressure receptors, rather than arterial high-pressure baroreceptors, suppresses sudomotor outflow.
Structured PICO
Does central blood volume displacement via LBNP or tilting reduce sympathetic sudomotor nerve traffic and sweating in warm healthy humans?
PPopulation11 healthy volunteers
IInterventionLower body negative pressure (LBNP) at 5 and 10 mmHg and 30-degree head-up tilting
CComparatorBaseline/control levels before and after intervention
OOutcomeSkin sympathetic nerve activity (SSA) and skin electrical resistance (sweating)surrogate
Unloading of cardiopulmonary volume receptors reduces sympathetic sudomotor nerve traffic and sweating, suggesting a reflex mechanism to counteract hypovolemia.