Influence of temperature on the distribution of blood in humans as assessed by electrical impedance

This study investigated whether ambient temperature influences the distribu tion of blood as indicated by electrical impedance. In ten supine humans, t he room temperature was raised from 14 to 35 degrees C. Skin temperature an d blood flow on the thorax increased by 3.6 (SD 0.3)degrees C and 84 (SD 40 )%, respectively, and by 9.8 (SD 1)degrees C and 115 (SD 45)%, respectively , on the extremities (P < 0.05). Cardiac output remained unchanged, ear tem perature and heart rate became elevated, and the oesophageal temperature an d mean arterial pressure decreased (P < 0.05). At five discrete frequencies (1.5, 5, 50, 100, 200 kHz) thoracic impedance was increased by 1.2 (SD 1) to 1.5 (SD1) Ohm (P < 0.05). In contrast, total body impedance was reduced by 16.4 (SD 5) Ohm and leg impedance was reduced by 4.0 (SD 2) Ohm, while a n index of intracellular water within the thorax (the difference between th e admittances at 100 kHz and 1.5 kHz) was decreased by 10 (SD 1) . 10(-4) S (P < 0.05). The results would suggest that total body impedance is dominat ed by the impedance of the extremities. The increase in thoracic impedance and a decrease in leg impedance las in total body impedance) could be expla ined by a redistribution of blood from the thorax to the extremities during heating. Such a translocation of blood was confirmed by a reduced impedanc e based index of intracellular water within the thorax.