The thermoregulatory responses to severe exercise of 1-h duration have been studied in 11 healthy subjects, and the effects of skin wetting have been examined in 6 of them. Measurements in the laboratory included metabolic (M) and total (H) heat production, rectal (Tre) and mean skin (Tsk) temperatures, evaporative sweat loss (E), and peripheral tissue conductance (K). In addition Tre and changes in body weight were measured in 18 conpetitors following a 20-km road race run at approximately 90% of their maximal oxygen intake (Vo2 max). The results showed that Tre was curvilinearly related to %Vo2 max. In contrast Tsk was independent of M, H, E, and %Vo2 max, and reached similar and constant values at the end of exercise in all subjects. E was appropriate for a given H, but K was lower in the sedentary subjects than in the athletes. Skin wetting had no effect on Tre but reduced E by 10%. It is suggested that the pattern of Tre rise in excercise reflected the nature of the controlling system and was not due to a failure of the heat-dissipating mechanisms.

A study of exercise performance was carried out in 17 obese girls and young adults. During submaximal steady-state bicycle exercise oxygen intake (Vo2) for a given work output (W) was raised in obese subjects but minute ventilation at a fixed carbon dioxide output, gas exchange, blood gases, and cardiac output at a given VO2 were similar to the values previously found for normals. In obese subjects high levels of VO2 for fixed W were also obtained on the treadmill but when these were standardized for body weight (unlike the bicycle test) it was shown that the obese girls and women exercised within the normal (expected) range of aerobic energy expenditure. During maximal performance the absolute VO2 max was the same in obese and nonobese subjects but for a given body weight, lean body mass, and leg muscle (plus) bone volume, VO2max was reduced by 23.8, 16.3, and 24.5% respectively, in the former group. It was concluded that obesity though having minimal affect on responses to submaximal exercise is nevertheless associated with a marked reduction in physiological performance at or near maximal effort.

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S U M M A R YI. The protective effect of different particle sizes of sodium cromoglycate (SCG) was assessed by exercise challenge in nine asthmatic patients.2. SCG particles of 11.7 pm or 2 0 pm mass median diameter were generated by a spinning disc and compared with lactose placebo particles. The drugs were given 10 min before a 6 min run on a treadmill.3. The post-exercise bronchoconstriction caused a 48% fall in peak flow rate in the placebo test, a 41% fall after the large SCG particles and a 20% fall after the small particles.4. It is concluded that the site of action of SCG is probably in the smallest airways.

A nitrous oxide rebreathing method was used to measure recirculation time and cardiac output (as pulmonary blood flow) in adults and children during exercise. The method was compared with the indirect (CO2) Fick rebreathing method in almost simultaneous measurements of cardiac output. Recirculation time varied from about 15 s at rest to 8.5 s at high levels of exercise, and was slightly longer in children than adults. Cardiac output estimated by both methods was within the normal range for children and adults, being lower for a given oxygen consumption in children. For the adults the mean intrasubject variability of the N2O rebreathing method, measured as the coefficient of variation of cardiac output, was in the range of 6-8% at all levels of work. This was lower than reported for other N2O rebreathing methods, and similar to values based on the indirect (CO2) Fick, direct (O2) Fick, and dye-dilution methods of estimating cardiac output. The method is therefore proposed as a noninvasive technique suitable for rapid, accurate, and reproducible measurements of cardiac output.