Arterial elasticity and physical working capacity in young men

We have tested the hypothesis that there is a positive relation between arterial elasticity and physical working capacity (PWC) at a given age. The subjects were 28 young men, 16-18 yr old. Arterial elasticity was evaluated by measuring the carotid to femoral pulse-wave velocity (c) at rest. The slope, S(c) of the relation between c and the diastolic blood pressure was studied during a cold pressor test to test vascular reactivity. The relationship between heart rate (HR) and work load was determined using a cycle ergometer; the variables measured were the slope of this relation S(PWC) and the power output at a HR of 170 min-1 (PWC170). The PWC170 ranged from 1.8 to 4.6 W/kg, and values of c ranged from 3.9 to 6.8 m/s. A strong inverse linear relation was found between c and PWC170 (r = -0.76), whereas the HR at rest was positively related to both c (r = 0.68) and PWC170 (r = 0.74). There was no relationship between HR at rest and the slopes S(c) and S(PWC); the latter two variables depend mainly on the sympathetic response. These results show the importance of the intrinsic mechanical properties of the cardiovascular system, particularly arterial elasticity, in human adaptations to muscular exercise.     

Thermoregulation in the cold after physical training at different ambient air temperatures

Since human thermoregulation at rest is altered by cold exposure, it was hypothesized that physical training under cold conditions would alter thermoregulation. Three groups (n = 8) of male subjects (mean age 24.3 +/- 0.9 years) were evaluated: group T (interval training at 21 degrees C), group CT (interval training at 1 degrees C), and group C (no training, equivalent exposure to 1 degrees C). Each group was submitted, before and after 4 weeks of interval training (5 d/week), to a cold air test at rest (SCAT) (dry bulb temperature (Tdb) = 1 degrees C) for a 2-h period for evaluation of the thermoregulatory responses. During SCAT, after the training/acclimation period, group T exhibited a higher rectal temperature (Tre) (P < 0.05) without significant change in mean skin temperature (Tsk) whereas metabolic heat production (M) was higher at the beginning of the SCAT (P < 0.05). For group CT, no thermoregulatory change was observed. Group C showed a lower Tre (P < 0.05) without significant change in either Tsk or in M, suggesting the development of a hypothermic general cold adaptation. This study showed, first, that the cold thermoregulatory responses induced by an interval training differed following the climatic conditions of the training and, second, that this training performed in the cold prevented the development of a general cold adaptation.     

Comparability of tympanic and oral mercury thermometers at high ambient temperatures

ABSTRACT: BACKGROUND: Body temperature can be measured in seconds with tympanic thermometers as opposed to minutes with mercury ones. The aim of this study was to compare tympanic and oral mercury thermometer measurements under high ambient field temperatures. RESULTS: Tympanic temperature (measured thrice by 3 operators) was compared to oral temperature measured once with a mercury-in-glass thermometer in 201 patients (aged [greater than or equal to]5 years), on the Thai-Myanmar border. Ambient temperature was measured with an electronic thermo-hygrometer. Participants had a mean [min-max] age of 27 [5-60] years and 42% (84) were febrile by oral thermometer. The mean difference in the mercury and tympanic temperature measurement for all observers/devices was 0.09 (95%CI 0.07-0.12)degreesC and intra-class correlation for repeat tympanic measurements was high ([greater than or equal to]0.97) for each observer. Deviations in tympanic temperatures were not related to ambient temperature. CONCLUSION: Clinically significant differences were not observed between oral and tympanic temperature measurements at high ambient temperatures in a rural tropical setting.     

Evaporative heat loss from group-housed growing pigs at high ambient temperatures

The effects of relative humidity and ambient temperature on evaporative heat loss were studied in 12 trials each with a group of 10 gilts with an initial BW of 61.7 kg (58.0–65.5 kg). The ambient temperature inside a respiration chamber was increased by 2 °C d⁻¹ starting at 16 °C and ending at 32 °C. Relative humidity was set at 50%, 65% or 80% and remained constant within each trial. The animals had free access to feed and water. Skin temperature (SkinT), total heat production (HP), evaporative heat loss (EvapH), respiration rate (RR), and wallowing of the animals were recorded. SkinT was lowest at 80% relative humidity (P<0.05). For each degree Celsius rise in SkinT, wallowing increased by 0.19% (P<0.05). For each degree Celsius rise in ambient temperature, total HP decreased by 115 kJ pig⁻¹ d⁻¹ and EvapH increased by 290 kJ pig⁻¹ d⁻¹ (P<0.05). It was concluded that under constant high ambient temperature and relative humidity, the pigs clearly employ respiratory evaporation to lose heat. Wallowing showed the importance of skin EvapH with higher temperatures, especially at high relative humidity. This study shows the importance of evaporative cooling from the skin. The implication is that pigs at high ambient temperatures, especially in combination with a high relative humidity, should be able to wet themselves. For animal welfare and environmental reasons, it is important that they are able to wet their skin.     

Behavioural responses of young cape gannets Sula capensis to high ambient temperatures

A young Cape Gannet Sula capensis responded to high ambient temperatures in the laboratory by standing, gular fluttering with raised head and open bill, wing drooping, defaecating at a fast rate close to or onto the feet, “paddling”; in the excreta, and increased breathing rate. Standing initially caused a decline in foot temperature which rose with rising ambient temperature. Gular flutter and wing drooping assisted the bird in tolerating heat stress. Reduction in heat‐load occurred when standing on a wet surface, presumably due to evaporative heat loss (of excreta on the feet = urohidrosis) and an enhanced conduction of heat to substrate. Field observations confirmed that young Cape Gannets defaecate onto their feet at high ambient temperatures. This species appears preadapted for this behaviour since it builds a solely guano nest, defaecating onto the rim which is compacted by “paddling”;.     

The development of rating of perceived exertion-based tests of physical working capacity

The purpose of the present study was to use ratings of perceived exertion (RPE) from the Borg (6-20) and OMNI-Leg (0-10) scales to determine the Physical Working Capacity at the Borg and OMNI thresholds (PWC(BORG) and PWC(OMNI)). PWC(BORG) and PWC(OMNI) were compared with other fatigue thresholds determined from the measurement of heart rate (the Physical Working Capacity at the Heart Rate Threshold: PWC(HRT)), and oxygen consumption (the Physical Working Capacity at the Oxygen Consumption Threshold, PWC(VO2)), as well as the ventilatory threshold (VT). Fifteen men and women volunteers (mean age +/- SD = 22 +/- 1 years) performed an incremental test to exhaustion on an electronically braked ergometer for the determination of VO2 peak and VT. The subjects also performed 4 randomly ordered workbouts to exhaustion at different power outputs (ranging from 60 to 206W) for the determination of PWC(BORG), PWC(OMNI), PWC(HRT), and PWC(VO2). The results indicated that there were no significant mean differences among the fatigue thresholds: PWC(BORG) (mean +/- SD = 133 +/- 37W; 67 +/- 8% of VO2 peak), PWC(OMNI) (137 +/- 44W; 68 +/- 9% of VO2 peak), PWC(HRT) (135 +/- 36W; 68 +/- 8% of VO2 peak), PWC(VO2) (145 +/- 41W; 72 +/- 7% of VO2 peak) and VT (131 +/- 45W; 66 +/- 8% of VO2 peak). The results of this study indicated that the mathematical model used to estimate PWC(HRT) and PWC(VO2) can be applied to ratings of perceived exertion to determine PWC(BORG) and PWC(OMNI) during cycle ergometry. Salient features of the PWC(BORG) and PWC(OMNI) tests are that they are simple to administer and require the use of only an RPE scale, a stopwatch, and a cycle ergometer. Furthermore, the power outputs at the PWC(BORG) and PWC(OMNI) may be useful to estimate the VT noninvasively and without the need for expired gas analysis.