RESUMEN
The zone of thermal comfort was determined during normoxia and hypoxia in 15 healthy normothermic young subjects. Subjects dressed only in shorts/shorts and bikini top donned a water-perfused suit and assumed a supine position on a bench. The ambient temperature was maintained at a mean (SD) of 25.7 (0.3) degrees C. The thermal comfort zone was determined by increasing the temperature of the water perfusing the suit from cool to warm. During the heating process, subjects were instructed to report when their perception of the thermal stimulus provided by the suit changed from unpleasant to pleasant, and again from pleasant to unpleasant. The boundaries of the thermal comfort zone were assumed to be the temperatures of the water perfusing the suit at the time the subjects reported a change in the affective component of their thermal perception. In normoxia, subjects inspired room air and in hypoxia a gas mixture containing 10% O(2) in N(2). Tympanic temperature was similar in the normoxia and hypoxia conditions (P>0.05). The average (SD) lower and upper limits of the thermal comfort zone were 30.5 (1.5) and 34.7 (3.3) degrees C, respectively, during normoxia, and 30.5 (1.7) and 35.1 (3.4) degrees C, respectively, during hypoxia. No significant differences were observed between the normoxia and hypoxia conditions (P>0.05). Also, no gender-related differences were observed in the characteristics of the thermal comfort zone. The results of the present study indicate that acute hypoxic exposure simulated in the present study does not affect the zone of thermal comfort in humans.
Asunto(s)
Hipoxia , Percepción , Temperatura , Adulto , Temperatura Corporal , Ambiente , Femenino , Humanos , Masculino , Oxígeno , AguaRESUMEN
Cutaneous temperature sensitivity was tested in 13 male subjects prior to, during and after they breathed either a hypocapnic hypoxic (HH), or a normocapnic hypoxic (NH) breathing mixture containing 10% oxygen in nitrogen. Normocapnia was maintained by adding carbon dioxide to the inspired gas mixture. Cutaneous thresholds for thermal sensation were determined by a thermosensitivity testing device positioned on the plantar side of the first two toes on one leg. Heart rate, haemoglobin saturation, skin temperature at four sites (arm, chest, thigh, calf) and adapting temperature of the skin (T(ad); degrees centigrade), i.e. the temperature of the toe skin preceding a thermosensitivity test, were measured at minute intervals. Tympanic temperature (T(ty); degrees centigrade) was measured prior to the initial normoxic thermosensitivity test, during the hypoxic exposure and after the completion of the final normoxic thermosensitivity test. End-tidal carbon dioxide fraction and minute inspiratory volume were measured continuously during the hypoxic exposure. Ambient temperature, T(ty), T(ad) and mean skin temperature remained similar in both experimental conditions. Cutaneous sensitivity to cold decreased during both HH (P<0.001) and NH conditions (P<0.001) as compared with the tests undertaken pre- and post-hypoxia. No similar effect was observed for cutaneous sensitivity to warmth. The results of the present study suggest that sensitivity to cold decreases during the hypoxic exposure due to the effects associated with hypoxia rather than hypocapnia. Such alteration in thermal perception may affect the individual's perception of thermal comfort and consequently attenuate thermoregulatory behaviour during cold exposure at altitude.
Asunto(s)
Regulación de la Temperatura Corporal/fisiología , Hipoxia de la Célula/fisiología , Umbral Diferencial/fisiología , Oxígeno/metabolismo , Temperatura Cutánea/fisiología , Sensación Térmica/fisiología , Adulto , Humanos , MasculinoRESUMEN
The thermal behaviour and melting characteristics of diclofenac sodium were investigated using various instrumental techniques--differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) spectroscopy and thin layer chromatography (TLC). DSC analysis of diclofenac sodium performed under dynamic flow of either synthetic air or helium or nitrogen did not produce any sharp endothermic peak characteristic of melting peak of a pure substance. Both the rate of scanning of the sample and the environmental atmospheric condition significantly affected the thermographic profile of diclofenac sodium. An exothermic peak prior to an endothermic peak corresponding to melting of the substance appeared when heated under dynamic flow of synthetic air suggesting oxidation (decomposition) of diclofenac sodium before reaching its melting point. In fact, at a scanning rate of 1 degree C/min only the exothermic peak appeared in the thermogram, suggesting complete decomposition prior to melting under the dynamic flow of synthetic air. DSC, FT-IR and TLC data obtained from samples heated under the dynamic flow of either helium or nitrogen revealed formation of a related compound, 1-(2,6-dichlorophenyl)-indolin-2-one, an indol-cyclic amide, as a result of an intramolecular cyclization reaction during the heating process. TGA data demonstrated a loss of 11.4-20.2% of the mass of diclofenac sodium when heated under various environmental conditions, and also supported the oxidative nature of degraded product(s) when the thermal process occurred slowly under a dynamic flow of synthetic air.