Upright posture reduces thermogenesis and augments core hypothermia

Area of Science:

• Physiology
• Thermoregulation
• Human Physiology

Background:

• Baroreceptor-mediated reflexes are known to modulate thermoregulatory vasoconstriction.
• Postural changes can alter baroreceptor loading, potentially influencing thermoregulatory responses.

Purpose of the Study:

• To investigate if postural differences and associated baroreceptor loading alterations modulate the human thermogenic (shivering) response to hypothermia.
• To examine the impact of upright versus supine posture on core temperature decrease, thermogenic threshold, and peripheral vasoconstriction during induced hypothermia.

Main Methods:

• Healthy participants (n=7) underwent intravenous cold saline infusion to induce hypothermia.
• Core temperature and oxygen consumption were monitored in both supine and upright positions.
• Plasma norepinephrine concentrations were measured to assess sympathetic nervous system activity.

Main Results:

• Upright posture resulted in a greater core temperature decrease compared to the supine position.
• The threshold temperature for thermogenesis (shivering) was significantly lower in the upright posture.
• Peripheral vasoconstriction and plasma norepinephrine levels were augmented in the upright posture, indicating increased sympathetic response.

Conclusions:

• Upright posture attenuates the thermogenic response to hypothermia while augmenting peripheral vasoconstriction.
• Baroreceptor input appears to modify individual thermoregulatory pathways at a site distal to the central thermoregulatory center.