The effect of postural changes on body temperatures and heat balance

Early studies have demonstrated that rectal temperature (T _re) decreases and mean skin temperature (T _sk) increases in subjects changing their posture from standing to supine, and vice versa. Such changes have important implications insofar as thermal stress experiments are conducted and interpreted. However, the extent of these changes between steady-state conditions is not known. In addition, it is not known whether thermal balance is also affected by postural changes. To examine these questions, 11 healthy males were exposed to a thermoneutral air environment (28.2–28.5°C and 40% relative humidity) in various postures at rest. Body temperatures, heat losses, and metabolic rate were measured. Subjects wore shorts only and began in an upright posture (standing or sitting at an inclination of 7.5°) on a customized tilt-table. They were tilted twice, once into a supine position and then back to the original upright position. Each tilt occurred after steady state was satisfied based on the subject's circadian variation of T _re determined previously in a 4.25 h control supine trial. Times to supine steady state following the first tilt were [mean (SE)] 92.6 (6.4) and 116.6 (5.1) min for the standing and sitting trials, respectively. Times to upright steady state following the second tilt were 107.9 (11.4) and 124.1 (9.0) min. Mean steady-state T _re and T _sk were 36.87 (0.07) and 34.04 (0.14), 37.47 (0.09) and 33.48 (0.14), and 37.26 (0.05) and 33.49 (0.10) °C for supine, standing, and sitting, respectively. Thermal balance was attained in all steady-state conditions, and allowing for a decrease in the weighting factor of T _re for mean body temperature in the upright postures, it also appears that thermal balance was preserved between changes in posture. These results are consistent with no perceived changes by the subjects in their thermal comfort and skin wetness.     

Maximal REM sleep time defines a narrower thermoneutral zone than does minimal metabolic rate

Sleep states and oxygen consumption were simultaneously measured in rats at environmental temperatures of 23, 25, 27, 29, 31, and 33°C. Rapid eye movement (REM) sleep was more sensitive to environmental temperature than was metabolic rate. Oxygen consumption was minimal and constant between 25 and 31°C, whereas REM sleep time varied significantly over this range, with a peak at 29°C. Thus, maximal REM sleep time defines a more precise thermoneutral zone than does minimal metabolic rate. Furthermore, REM sleep time at 29°C was more than double the amount seen at 23°C, which is a standard laboratory temperature. Thus, varying the thermal environment is a simple noninvasive way to manipulate REM sleep time, and could be used to assess the effects of differing amounts of REM sleep on waking behaviors.     

Bradycardia and desaturation during skin-to-skin care: no relationship to hyperthermia

OBJECTIVE: We recently found increased temperature and increased bradycardia and desaturation during skin-to-skin care (SSC). We wanted to determine if these effects were related. STUDY DESIGN: Twenty-two infants (median gestational age at birth 28.5 weeks [range 24-31], median age at study 25.5 days [range 10-60 days], median birth weight 1025 g [range 550-1525 g], median weight at study 1320 g [range 900-2460 g]) underwent three 2-hour recordings of breathing movements, nasal airflow, heart rate, and pulse oximeter saturation (SpO 2 ): at thermoneutrality (TN) during incubator care, at TN during SSC, and at elevated temperature (ET) during incubator care. Core temperature was measured via a rectal probe. Recordings were analyzed for the summed rate of bradycardia and desaturation (heart rate <2/3 of baseline; SpO 2 相似文献   

Effect of clothing on the temperature distribution of human thermal system.

A mathematical model is developed for the calculation of detailed steady-state temperature distribution throughout the clothed human body. The analytical expressions obtained depend on the local metabolic rate, local blood flow rate, heat loss of conduction, convection and evaporation, geometry of the body, and the physical properties of the clothes. The analysis has shown that the thermal resistance across the clothing layer and the still air layer is the controlling factor on the warmth of the human body. The total metabolic heat generation which operates to maintain thermal equilibrium can also be calculated from the model by an iterative method.     

Consequences of a small decrease of air temperature from thermal equilibrium on thermoregulation in sleeping neonates

A new heating unit (servocontrolled skin temperature derivative system) has been designed to control the thermal environment in closed incubators. This type of control acts to attain and closely maintain a thermal equilibrium between a neonate's skin temperature and the environment. The present study aims to discover if thermal equilibrium is located within a thermoneutral range defined from oxygen consumption ( ) and body temperature, and whether it is more appropriate to define an optimal thermal environment. As regards and body temperature, results show that the air temperature reached at thermal equilibrium fulfils the definition of thermoneutrality. According to these criteria, a small decrease (1.5°C) from thermal equilibrium also provides a near thermoneutral environment to the neonate but induces sleep disturbances and an increase in body movements. These two additional parameters delineate a narrower thermoneutral zone than does minimal metabolic rate because can stay constant even when air and body temperatures decrease. The results suggest that thermal equilibrium might be assimilated with a thermal comfort zone.     

Is the mattress important in helping babies keep warm?—Paradoxical effects of a sleeping surface with negligible thermal resistance

BACKGROUND: Heavy wrapping and head covering are risk factors for Sudden Infant Death Syndrome. A new mattress construction, PurFlo, has extremely low thermal resistance, and when used with an infant sleeping bag minimizes the risk of head covering. AIM: To investigate the thermal balance and metabolic rate of infants sleeping on a conventional mattress or a Purflo mattress in infant sleeping bags. METHODS: A longitudinal study of thermal balance of infants during day-time sleep on both mattress types in thermoneutral and cool conditions at ages 3 weeks (n = 24), 3 months (n = 22) and 5 months (n = 18). RESULTS: In thermoneutral conditions axillary temperatures in quiet sleep were lower on the conventional mattress than on the PurFlo mattress (p < 0.05, Wilcoxon test). On lowering room temperature to 15-16 degrees C axillary temperatures fell, particularly in the older babies, and at each age were lower on the conventional mattress than the Purflo (differences 0.14-0.72 degrees C, p < 0.05, Wilcoxon test). CONCLUSION: In both thermoneutral and cool conditions, infant temperatures were higher on the PurFlo than the conventional mattress. The more deformable surface of the PurFlo mattress may lead to more effective insulation by the sleeping bag despite a lack of mattress insulation.