Simultaneous derivation of clothing-specific heat exchange coefficients.

Clothing adds resistance to heat exchange between the wearer and the environment. If clothing-specific heat exchange coefficients are known, a combined rational/empirical approach can be used to describe thermal exchange between clothed humans and the environment. However, during exercise these coefficients--typically calculated using thermal manikins--change, primarily due to wetting of the fabric during intense sweating and body movement. A procedure is described that allows for the simultaneous determination of both total insulation (IT) and resistance to water vapor permeation (Re) on exercising clothed subjects without the need to directly measure skin water vapor pressure or continuously weigh the subjects. Two tests are performed by each subject in each clothing ensemble. In one test, ambient water vapor pressure (Pa) is systematically increased in stepwise fashion while dry-bulb temperature (Tdb) is held constant; in the second test protocol Pa is held constant while Tdb is increased. Heat exchange data are collected at the time at which core temperature is forced out of equilibrium by the environment (according to the assumption that heat production is balanced by heat loss immediately prior to this critical environmental limit). Previous studies using similar approaches have typically estimated IT a priori and used this value in the subsequent derivation of Re for each clothing ensemble or condition tested. In the proposed method, IT and Re are derived from the solution of two simultaneous equations based on heat balance data from both tests. This paper describes and critiques this methodology via an error analysis, and compares the coefficients obtained with those from similar trials using other physiological and nonphysiological approaches.

Estrogen replacement in middle-aged women: thermoregulatory responses to exercise in the heat.

Thermoregulatory, cardiovascular, and body fluid responses during exercise in the heat were tested in five middle-aged (48 +/- 2 yr) women before and after 14-23 days of estrogen replacement therapy (ERT). The heat and exercise challenge consisted of a 40-min rest period followed by semirecumbent cycle exercise (approximately 40% maximal O2 uptake) for 60 min. At rest, the ambient temperature was elevated from a thermoneutral (dry bulb temperature 25 degrees C; wet bulb temperature 17.5 degrees C) to a warm humid (dry bulb temperature 36 degrees C; wet bulb temperature 27.5 degrees C) environment. Esophageal (Tes) and rectal (Tre) temperatures were measured to estimate body core temperature while arm blood flow and sweating rate were measured to assess the heat loss response. Mean arterial pressure and heart rate were measured to evaluate the cardiovascular response. Blood samples were analyzed for hematocrit (Hct), hemoglobin ([Hb]), plasma 17 beta-estradiol (E2), progesterone (P4), protein, and electrolyte concentrations. Plasma [E2] was significantly (P < 0.05) elevated by ERT without affecting the plasma [P4] levels. After ERT, Tes and Tre were significantly (P < 0.05) depressed by approximately 0.5 degrees C, and the Tes threshold for the onset of arm blood flow and sweating rate was significantly (P < 0.05) lower during exercise. After ERT, heart rate during exercise was significantly lower (P < 0.05) without notable variation in mean arterial pressure. Isotonic hemodilution occurred with ERT evident by significant (P < 0.05) reductions in Hct and [Hb], whereas plasma tonicity remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of captopril and enalapril on the progression of chronic renal disease in partially nephrectomized rats.

Comparative effects of the angiotensin converting enzyme inhibitors captopril and enalapril on progression of chronic renal disease was studied in 3/4 nephrectomized rats. Rats were divided into sham and nephrectomized groups, and treated with plain water or water containing captopril (150 mg/liter) or enalapril (50 mg/liter). Evaluations were made 4 weeks before and 0, 4, 8, and 10 weeks after nephrectomy. Endogenous creatinine clearance decreased in drug-treated, nephrectomized rats to values less than sham controls, but remained greater than water-treated rats. Significant (P less than 0.05) proteinuria developed 4 weeks post-nephrectomy in water-treated rats, 8 weeks post-nephrectomy in captopril-treated rats, but did not develop in enalapril treated rats. Regression analysis of carbamylated plasma protein values vs plasma creatinine revealed significant (P less than 0.05) relationships only in the water-treated, nephrectomized rats from weeks 0 through 8, but were otherwise unaffected by treatment. Both drugs resulted in significantly (P less than 0.05) improved scores for renal histologic lesions as compared to water treatment. Modifications of proteinuria in captopril and enalapril-treated rats occurred prior to onset of changes in systolic blood pressure, which was significantly elevated only in water-treated, nephrectomized rats at weeks 8 and 10. We conclude that angiotensin converting enzyme inhibitors may ameliorate progression of experimental renal disease through intrarenal effects, independent of modulation of systemic blood pressure, and that enalapril may be superior to captopril in some regards.