To study the reliability of formulas for calculating mean skin temperature (Tsk), values were computed by 18 different techniques and were compared with the mean of 10,841 skin temperatures measured by infrared thermography. One hundred whole-body infrared thermograms were scanned in ten resting males while changing the air temperature from 40 degrees C to 4 degrees C. Local, regional average and mean skin temperatures were obtained using an image processing system. The agreement frequency, defined as the percentage of the calculated Tsk values which agreed with the corresponding infrared thermographic Tsk within +/- 0.2 degree C, ranged for with the various formulas from 7% to 80%. In many sites, the local skin temperature did not coincide with the regional average skin temperature. When the local skin temperatures which showed the highest percentage similarity to the regional average skin temperature within +/- 0.4 degree C were applied to the formula, the agreement frequency was markedly improved for all formulas. However, the agreement frequency was not affected by changing the weighting factors from specific constants to individually measured values of regional surface area. By applying the physiologically reliable accuracy range of +/- 0.2 degree C in the moderate and +/- 0.4 degree C in the cool condition, agreement frequencies of at least 95% were observed in formulas involving seven or more skin temperature measurement sites, including the hand and foot. We conclude that calculation of a reliable mean skin temperature must involve more than seven skin temperature measurement sites regardless of ambient temperature. Optimal sites for skin temperature measurement are proposed for various formulas.

The role of renal sympathetic nerve activity (RSNA) in the natriuresis and diuresis induced by head-out water immersion (WI) was studied in eight conscious female dogs. The dog was instrumented chronically with a stainless steel electrode for the measurement of RSNA and two catheters for the measurements of systemic arterial (Pa) and central venous (Pv) pressures. The WI caused an immediate reduction of RSNA by 43 +/- 7% (P less than 0.05), and this low level was sustained throughout a 120-min WI under thermoneutral conditions (37 degrees C). Urine flow and sodium excretion increased by 211 +/- 54 (P less than 0.05) and 240 +/- 122% (P less than 0.05), respectively, but creatinine clearance did not change significantly during WI. A step increase in Pa (by 10 +/- 4 mmHg, P less than 0.05) and Pv (by 10.0 +/- 0.8 mmHg, P less than 0.05) was observed also during WI. In another series of studies, renal denervations were performed 2-4 wk before the experiment in six of the same dogs. Dogs with renal denervation showed no significant changes in urine flow and sodium excretion in response to WI, whereas Pa and Pv increased by 10 +/- 7 and 10.0 +/- 2.0 mmHg relative to the control level, respectively. It is concluded that the reduction of RSNA observed during WI plays a major role in the natriuresis in the dog.

To examine the baroreflex response in humans during acute high-altitude exposure, the carotid baroreflex cardiac responsiveness was studied using a neck chamber in seven unacclimatized male subjects. Measurements were made in a high-altitude chamber on separate days at sea level and during 1-h exposure at two different altitudes of 3,800 m [partial pressure of oxygen in inspired air (Pi O2 ) = 90 mmHg] and 4,300 m (Pi O2  = 82 mmHg). R-R intervals were plotted against neck chamber pressures, and the baroreceptor response was analyzed by applying a four-parameter sigmoidal logistic function. The baroreceptor response curve shifted downward in either altitude, reflecting a tachycardic response at high altitude, and the magnitude of the shift was greater at 4,300 m than at 3,800 m. There was no change in the sigmoidal parameters at 3,800 m compared with sea level except for a reduction ( P < 0.05) of the minimum R-R interval. At 4,300 m the maximal R-R range, slope coefficient, minimum R-R interval, and maximal gain of the curve decreased significantly ( P < 0.05) compared with sea level values, whereas the centering point of the curve remained unchanged. These results suggest that hypoxia (Pi O2  = 82 mmHg) reduces the sensitivity of carotid baroreflex cardiac response.

Esophageal, rectal, tympanic, and central blood temperature, i.e., pulmonary artery and aortic arch, were recorded in three patients during iatrogenic whole-body hyperthermia for the treatment of advanced malignant metastatic cancer. Aortic temperature closely followed changes in pulmonary arterial temperature, with an average delay time of 27 s. Esophageal temperature reflected quantitatively and more quickly (avg lag time, 80 s) the temperature changes in the pulmonary artery than tympanic membrane temperature. Tympanic temperature was consistently lower than the blood temperature of the heart during steady state. Therefore it is suggested that esophageal temperature is a preferable index of central blood temperature. Additionally, measurement of esophageal temperature can be made more easily and safely than tympanic membrane temperature.

Temperature within the brain and the esophagus and at the tympanum were obtained in a 12-yr-old male in a series of experiments that began 8 days after surgery for implantation of a drainage catheter. Fanning the face did reduce tympanic temperature but not temperature in the brain; brain temperatures followed esophageal temperatures. In long-term monitoring, temperature in the lateral ventricle was 0.5 degree C above esophageal temperature and 0.2 degree C below that in white matter 1 cm above, with the offsets fixed throughout the overnight cycle. All temperatures went through similar excursions when the face was excluded from fanning applied to the body. These observations highlight the fact that in humans the defense against hyperthermia takes advantage of cooling distributed over the entire skin surface.