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Interactions between surface cooling and LBNP-induced central hypovolemia
Aviation, Space, and Environmental Medicine
|May 1, 1980
Summary
Whole body surface cooling (WBSC) significantly reduced leg volume and heart rate while increasing stroke volume and blood pressure. These hemodynamic effects persisted during lower body negative pressure (LBNP) application.
Area of Science:
- Physiology
- Cardiovascular Research
- Thermoregulation
Background:
- Understanding the physiological responses to thermal stress and altered hydrostatic pressure is crucial for human physiology research.
- Investigating the combined effects of whole body surface cooling (WBSC) and lower body negative pressure (LBNP) can reveal synergistic or antagonistic cardiovascular adaptations.
- Previous studies have explored WBSC and LBNP independently, but their interaction requires further elucidation.
Purpose of the Study:
- To investigate the interaction between whole body surface cooling (WBSC) and progressive lower body negative pressure (LBNP) on cardiovascular hemodynamics.
- To determine if WBSC-induced hemodynamic changes are maintained under LBNP stress.
- To assess the impact of WBSC on central blood volume displacement and its effect on stroke volume.
Main Methods:
- Nine healthy male volunteers were subjected to WBSC using a cooling garment with 16°C water circulation.
- Lower body negative pressure was applied progressively up to -50 torr.
- Hemodynamic parameters including cardiac output (Q), heart rate, stroke volume, arterial blood pressure, and leg volume (LgV) were measured.
Main Results:
- WBSC significantly decreased mean skin temperature, leg volume, and heart rate, while increasing systolic blood pressure.
- The observed hemodynamic effects of WBSC, including reduced leg volume and heart rate, were sustained throughout the LBNP protocol.
- Stroke volume and systolic pressure increased significantly (p < 0.01) during WBSC and LBNP, indicating maintained or enhanced cardiovascular function.
Conclusions:
- Whole body surface cooling induces a central displacement of cutaneous venous blood volume.
- This central blood volume shift results in an increase in stroke volume, an effect that is maintained under the stress of lower body negative pressure.
- The findings suggest that WBSC can modulate cardiovascular responses beneficially, potentially impacting tolerance to orthostatic stress.