Effect of posture on body temperature of young men in cold air

We studied eight young adult men to see whether a supine posture caused a fall in body core temperature in the cold, as it does in thermoneutral conditions. In air at 31°C (thermoneutral), a supine posture for 3 h reduced mean aural, gastric, oesophageal and rectal temperatures by 0.2–0.4°C, compared to upright and increased femoral artery blood flow from 278 (SEM 42) ml · min⁻¹ whilst upright to 437 (SEM 42) ml·min⁻¹ whilst supine. In cold air (8°C) the supine posture failed to reduce these temperature differences significantly, or to increase femoral blood flow; it reduced heart rate, and increased arterial systolic and pulse pressures adjusted to carotid sinus level, less than in thermoneutral conditions. However, the behaviour of core temperature at the four sites was significantly nonuniform between the two postures in the cold, mainly because the supine posture tended to reduce rectal temperature. It may have done so by reducing heat production in the muscles of the pelvis, since it reduced overall metabolic rate from 105 (SEM 8) to 87 (SEM 4) W · m⁻² in the cold. In other respects the results indicated that posture ceased to have an important effect on body core temperatures during cold stress.