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PubMed1986

Effect of mesomorphy on hyperthermia during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 27 men who exhibited a wide range of body physique in terms of the mesomorphy component of somatotype. Increase in tympanic temperature (Yty) was significantly dependent on mesomorphy rating (X) according to the regression equation Yty = -0.390 + 0.088X. Increase in rectal temperature (Yre) was also significantly dependent on mesomorphy rating according to the equation Yre = -0.100 + 0.066X. The hyperthermic response was significantly correlated with other measures of physique, including ectomorphy, surface area/weight ratio, and body weight, but was not correlated with fatness or fitness. The results support the generalization that during exercise in a warm, humid environment individual differences in heat strain can be highly dependent on physique, especially if fitness and fatness are similar. In this context, mesomorphy appears to provide the optimum description of physique variation. Individuals with a mesomorphy rating greater than 7 warrant designation as being at high risk for heat intolerance during exercise in environments that significantly impair the rate of body heat loss.

Adolescent↗
PubMed1986

Physique and thermoregulation in prepubertal males during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 23 prepubertal males. After the initial increase of core temperatures (tympanic and rectal) to elevated set points, further hyperthermia was minimal and was unrelated to any physique variable except for the case of endomorphy, which was weakly correlated with hyperthermia at the rectal site. This result for boys is attributed to the combination of small body size (relative to adults) and absence of pronounced, age-dependent muscular development as evidenced by low rating and small variation of the mesomorphy component of somatotype. Both of these factors were associated with a high surface area to weight ratio compared to adults, which facilitated heat loss. It is concluded that prepubertal males thermoregulate efficiently during moderate exercise in a warm, humid environment. Other than cases of obesity, variation in physique is not an important consideration for assessing the risk of heat strain.

Adolescent↗
PubMed1994

Fractal-like patterns in DNA films, B form at 0% relative humidity, and antiheteronomous DNA: an IR study.

This report details the observation of (a) the intact double helix of DNA at 0% relative humidity in poly(dA).poly(dT) and poly(dA-dT).poly(dA-dT) films, (b) the fractal-like growth of DNA crystals in films of poly(dA).poly(dT), and (c) poly(dA).poly(dT) with adenines in the B form and thymines in the A form. Observation (a) is based on the behavior of the middle ir signature of double-helical base stacking, the 1714 cm-1 peak, at low water activity. This observation is modeled as a trapping of water in the polycrystalline part of these films. We interpret the glycosidic region of the middle ir spectra of the polycrystalline films of poly(dA).poly(dT) at 0% relative humidity to indicate that at least part of the adenine strand in is the B conformation and the thymine strand is in the A form, whereas previous assignments of poly(dA).poly(dT) films at 75% relative humidity indicated the opposite strand conformation assignment [E. Taillandier et al. (1987) Biochemistry, Vol. 26 p. 3361].

Chemical Phenomena↗
PubMed1994

Effect of type of container, storage temperature and humidity on the biological activity of freeze-dried alkaline phosphatase.

The suitability of butyl rubber-stoppered vials was compared with that of ampoules for the storage of freeze-dried biological materials under a variety of temperature and humidity conditions using alkaline phosphatase as a model. Immediately after freeze-drying, alkaline phosphatase activity in vials and ampoules was similar but decreased at temperatures of 37 degrees C, 45 degrees C and at cycling temperatures with high relative humidities over the 12-month test period, with the least activity in vials with untreated stoppers. By the end of the study at 12 months post-preparation, moisture levels were lowest (0.4%) in the vials where stoppers had been treated with industrial methylated spirit and air-dried, intermediate (1.0%) in DIN ampoules and highest and most variable (1-4%) in vials with untreated stoppers. There was no apparent exchange between the external atmosphere and that within the vials via the stoppers and the moisture in the vials with untreated stoppers appeared to have originated from the stoppers themselves. It was concluded that the use of vials with treated stoppers was almost as effective as the use of DIN ampoules for the freeze-drying and storage of alkaline phosphatase activity under a range of temperatures and humidities. Fluctuating temperatures were more detrimental to alkaline phosphatase activity than continuous storage at a single high temperature.

Alkaline Phosphatase↗
PubMed1990

Responses of young and older men during prolonged exercise in dry and humid heat.

Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (Td) 21 degrees C, relative humidity (r.h.) 43%)], a warm humid (Tdb 30 degrees C, r.h. 80%) and a hot dry (Tdb 40 degrees C, r.h. 20%) environment while wearing ordinary working clothes (0.7 clo). Their oxygen consumption, heart rate (fc), rectal (Tre) and mean skin temperature (Tsk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of Tre, Tsk, fc, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the Tre and RPE of the older subjects increased continuously (P less than 0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in Tre, RPE, and ER, the older subjects did not exhibit higher fc during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

The relative influence of body characteristics on humid heat stress response.

The present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake (VO2max), adiposity, DuBois body surface area (AD), surface to mass ratio (AD: mass) and body mass, for the individual's reaction to humid heat stress. For this purpose 27 subjects (19 men, 8 women), with heterogeneous characteristics (VO2max 1.86-5.28 1.min-1; fat% 8.0%-31.9%; mass 49.8-102.1 kg; AD 1.52-2.33 m2) first rested (30 min) and then exercised (60 W for 1 h) on a cycle ergometer in a warm humid climate (35 degrees C, 80% relative humidity). Their physiological responses at the end of exercise were analysed to assess their relationship with individual characteristics using a stepwise multiple regression technique. Dependent variables (with ranges) included final values of rectal temperature (Tre 37.5-39.0 degrees C), mean skin temperature (Tsk 35.7-37.5 degrees C), body heat storage (S 3.2-8.1 J.g-1), heart rate (HR 100-172 beat.min-1), sweat loss (397-1403 g), mean arterial blood pressure (BPa, 68-96 mmHg), forearm blood flow (FBF, 10.1-33.9 ml.100ml-1.min-1) and forearm vascular conductance (FVC = FBF/BPa, 0.11-0.49 ml.100ml-1.min-1.mmHg-1). The Tre, Tsk and S were (34%-65%) determined in the main by VO2max or by exercise intensity expressed as a percentage of VO2max (% VO2max). For Tre, AD: mass ratio also contributed to the variance explained, with about half the effect of VO2max. For Tsk, fat% contributed to the variance explained with about two-third the effect of VO2max. Total body sweat loss was highly dependent (50%) on body size (AD or mass) with regular activity level having a quarter of the effect of body size on sweat loss. The HR, similar to Tre, was determined by VO2max (48%-51%), with less than half the effect of AD or AD:mass (20%). Other circulatory parameters (FBF, BPa, FVC) showed little relationship with individual characteristics (< 36% of variance explained). In general, the higher the VO2max and/or the bigger the subject, the lower the heat strain observed. The widely accepted concept, that body core temperature is determined by exercise intensity expressed as % VO2max and sweat loss by absolute heat load, was only partially supported by the results. For both variables, other individual characteristics were also shown to contribute.

Blood Flow Velocity↗
PubMed1980

Breathing dry or humid air and exercise-induced asthma during swimming.

Recent studies have shown the relevance of air humidity to the provocation of bronchoconstriction by running. The present study was undertaken to ascertain whether the humid air breathed during swimming could explain the protective effect of swimming on the asthmatic. Nine asthmatic children 9--15 years old swam while inspiring dry (15--35% R.H.) or humid (80--90% R.H.) air administered in a random order, a week separating the two sessions. The exercise challenge was an 8-min tethered swim at a metabolic rate (VO2) of 29 ml.kg-1.min-1, minute ventilation (VE) of 34 L.min-1, and a heart rate (HR) of 161 beats.min-1. Ambient air and water temperature were 28 +/- 2 degrees C and 27 +/- 2 degrees C, respectively. Pulmonary functions were tested pre and post swimming. Exercise VE, VO2 and HR were similar under the two conditions. No reduction in any of the pulmonary functions (FVC,FEV1.0,MMEFR,MBC) was found after 5 and 10 minutes following the swimming exercise in either of the conditions. In contrast, a treadmill run of similar metabolic and ventilatory intensity induced bronchoconstriction when room air was dried to 25--30% R.H. It is suggested that, unlike running, swimming is of low asthmogenicity even when inspired air is dried to 25--30% at neutral temperatures.

Adolescent↗
PubMed1990

The effects of elevated temperature and humidity on rectal temperature and respiration rate in the New Zealand white rabbit.

In 2 replicated factorial experiments, 7-h climate chamber exposures were used to study the responses of adult NZW rabbits to a range of elevated temperatures and humidities. At 18 mm Hg water vapour pressure, 23.8 degrees C was well tolerated, rectal temperature (RT) and respiration rate (RR) averaging 38.6 +/- 0.3 degrees C and 82.9 +/- 15.5 breaths/min, respectively. Both parameters were elevated (P less than 0.001) at 32.2 degrees, 37.8 degrees and 43.3 degrees C. RT and RR reached plateau levels of 39.5-40.1 degrees C and 410-460/min at 32.2 degrees C, which was tolerated for the full 7-h test period. Test temperatures of 37.8 degrees and 43.3 degrees C, on the other hand, could be tolerated for only 80 and 40 min respectively, before RT reached the safe upper limit of 41.7 degrees C. Final RR values at 37.8 degrees and 43.3 degrees C were 701.6 +/- 42.7 and 812 +/- 55.1/min, respectively. In a 34.5 degrees C atmosphere a humidity of 21 mm Hg water vapour pressure was classified as "dry", and was tolerated for 323 +/- 123 min. RT and RR increased by 0.6 degrees C and 316/min during the first 20 min of exposure (P less than 0.05). Thereafter both parameters increased progressively, but with no significant differences between successive recording periods, until RR reached 550.3 +/- 88.8/min at 41.7 degrees C RT. Humidities of 25, 29 and 33 mm Hg water vapour pressure were, on the other hand, classified as "wet" and were tolerated for only 92 +/- 22, 81 +/- 16 and 119 +/- 50 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Population increase and damage by three species of mites on wheat at 20 degrees C and two humidities.

Twenty bisected grains of wheat infested with five pairs of the three commonest British grain-storage mites, Acarus siro L., Glycyphagus destructor (Shrank) and Tyrophagus longior (Gervais), were examined every week for 20 weeks. Mite populations, the resulting damage to germ and endosperm, and visible fungal growth were observed at 20 degrees C and relative humidities (r.h.) of 90% and 75%. At 90% r.h., A. siro populations reached nearly 14,000 per test-tube before slowly dropping to 5000. The mites ate the germ before the endosperm, leaving an impenetrable layer of crushed endosperm cells between these regions. The G. destructor population reached only 800 before declining to 300; these mites ate over 75% of the germ and small amounts of endosperm. Tyrophagus longior populations rose to 2200 mites before crashing at week 12 to the initial population level; these mites ate over 75% of the germ and small amounts of endosperm. At 75% r.h., both A. siro and T. longior populations were lower than at the higher r.h., peaking at 3000 and 1000 respectively and decreasing to 500 and 600 mites respectively. Glycyphagus destructor did markedly better than at 90% r.h., reaching 1500 before falling to 400. The damage at this humidity was slower to occur but was similar to that at 90% r.h. at the end of 20 weeks. At both humidities visible fungus was always less abundant on infested grain that uninfested grain.

Animals↗
PubMed1983

Differential effects of hot-humid and hot-dry environments on mental functions.

Twenty five subjects acclimatised to heat artificially were exposed to "basic effective temperatures" (BET) of 25.0 degrees, 29.6 degrees, 32.2 degrees, 33.3 degrees and 35.0 degrees C BET under conditions of both humid and dry heat. The object of the investigation was to ascertain the nature of effects of varying degrees of heat stress on mental alertness, associative learning, reasoning ability and dual-performance efficiency. A further aim was to determine the temperature levels at which impairment of psychological functions was severe enough to be of practical concern. The duration of each exposure was four hours, during which subjects performed physical exercise followed by rest every 30 min. It was found that all the psychological functions tested were adversely affected under extreme heat, and that a significant drop in various psychological functions was seen at effective temperatures of 32.2 degrees C and 33.3 degrees C in hot-humid and hot-dry conditions respectively. It is concluded that at the same effective temperatures the magnitude of the overall effect on psychological functions under humid conditions is relatively greater than that under dry conditions.

Adult↗
PubMed1996

[Is reduction of intraoperative heat loss and management of hypothermic patients with anesthetic gas climate control advisable? Heat and humidity exchangers vs. active humidifiers ina functional lung model].

UNLABELLED: Heated humidifiers (HH) as well as heat and moisture exchangers (HME) are commonly used in intubated patients as air-conditioning devices to raise the moisture content of the air, thus preventing mucosal damage and heat loss resulting from ventilation with dry inspired gases. In contrary to HME, HH are able to add heat and moisture to the inspired air in surplus, which is often stressed as an advantage in warming hypothermic patients or reducing major heat losses, e.g., during long operations. The impact of air conditioning on the energy balance of man was calculated comparing HME and HH. METHODS: The efficiency of a HME (Medisize Hygrovent) and a HH (Fisher & Paykel MR 730) was evaluated in a mechanically ventilated lung model simulating the physiological heat and humidity conditions of the upper airways. The gas flow from the central supply was dry; the model temperature varied between 32 and 40 degrees C. By using a HH in the inspiratory limb, a circle system was simulated with water-saturated inspired air at room temperature. The water content of the ventilated air was determined at the tracheal tube connection using a fast, high-resolution humidity meter and was compared with the moisture return of the HME. The energy balance was calculated according to thermodynamic laws. RESULTS: Both HME and HH were able to create physiological heat and humidity conditions in the airways. With the normothermic patient model, the moisture return of the HME was equal to that of the HH set at 34 degrees C. Increasing the heating temperature resulted only in reduced water loss from the lung; heat and water input in the normothermic model was not possible. This was only effective with almost negligible amounts under hypothermic patient model conditions. DISCUSSION: The water content in the inspired and expired air is the most important parameter for estimating pulmonary heat loss in mechanically ventilated patients. In adults (minute volume approximately 71/min) the main fraction of pulmonary heat loss results from water evaporation from the airways (approximately 6 kcal/h), whereas the heat loss due to convection is negligible (approximately 1.2 kcal/h). In intubated patients ventilated with dry air, the heat loss increases to approximately 8 kcal/h due to greater water evaporation from the airways. Both HME and HH are able to reduce the pulmonary heat loss to 1-2 kcal/h. In normothermic as well as hypothermic patients, HH do not offer significant advantages in heat balance compared to effective HME. In conclusion, air conditioning in intubated patients is neither a powerful too for maintaining body temperature during long-lasting anaesthesia nor a sufficient method of warming hypothermic patients in intensive care units.

Air Conditioning↗
PubMed1998

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise.

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (VO2max). Tests were undertaken in either a thermoneutral (22-23 degrees C; 56-62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25-35 degrees C; 66-77% RH). The subjects were 15 young adult male Singaporeans [VO2max=55.5 (4.4 SD) ml kg(-1) min(-1)]. The RE was measured at 3 m s(-1) [65 (6)% VO2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean=17.4 ml min(-1)). The VO2 during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in VO2 from RE1 to RE2 ranged from 3.4 to 4.7 ml kg(-1) min(-1) across treatments. In conclusion, the deterioration in RE at 3 m s(-1) (65% VO2max) after 60 min of running at 80% VO2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment.

Adult↗
PubMed1988

Effects of environmental temperature, relative humidity and vaccination on Pasteurella haemolytica in lungs of mice.

Groups of mice were kept in four combinations of environmental temperature (8 and 20 degrees C) and humidity [50 per cent and 90 per cent relative humidity (RH)]. The mice were anaesthetized and inoculated intranasally with Pasteurella haemolytica growing logarithmically. Groups of 11 mice were killed at 0.5 h intervals for 6 h after inoculation and the number of colony-forming-units (CFU) of Pasteurella haemolytica in the lungs was determined. The CFU in the lungs of mice were affected by a significant interaction of temperature, relative humidity and time after inoculation (P less than 0.01). From 0.05 to 5.0 h after inoculation, fewer CFU were found in the lungs of mice kept in 8 degrees C 50 per cent RH than in mice kept in 8 degrees C 90 per cent RH, 20 degrees C 50 per cent RH and 20 degrees C 90 per cent RH. In each environment, CFU in the lungs of mice increased from inoculation to approximately 3.5 h after inoculation and then decreased (P less than 0.01). In a similar experiment in an environment of approximately 20 degrees C and 50 per cent RH, there were significantly fewer CFU in the lungs of mice vaccinated intranasally 21 days earlier with live P. haemolytica than in the lungs of mice either vaccinated intranasally with formalized P. haemolytica or not vaccinated with P. haemolytica (P less than 0.01).

Animals↗
PubMed1980

The influences of temperature and humidity upon the isolated surfactant film of the dog.

A model of the gas-liquid barrier (surfactant film) of the lung was used to investigate the influence of temperature and of humidification of the gas upon the behaviour of films during rhythmic compression and expansion of their surface. Film behaviour was studied at room temperature or 37 degrees C, and at ambient humidity or high relative humidity. Changes of minimal surface tension (gamma min) and maximal surface tension (gamma max) were followed up to 1000 cycles. At 37 degrees C we measured higher values for gamma min and lower values for gamma max. At room temperature complete humidification does not influence surface tension, but at 37 degrees C gamma min increases. Thus both high temperature and high relative humidity result in sharp rise of gamma min, whereas high temperature alone is responsible for the temporary drop of gamma max. Considering these effects, investigations to study influences of foreign gases and of air pollution upon the surfactant film should be performed under conditions which approach those of the lung as close as possible. The possible influence of CO2 is discussed.

Animals↗
PubMed1996

Airway blood flow responses to temperature and humidity of inhaled air.

We determined the effect of breathing cold dry air (-39 degrees C, 0.1% relative humidity, RH) and warm humid air (43 degrees C, 100% RH) on airway mucosal blood flow (Qaw) in normal human subjects (n = 8, age 25-53 years) at rest. Qaw was measured with a dimethylether uptake technique which reflects blood flow in the mucosa of large airways corresponding to a 50 ml anatomical dead-space segment extending distally from the trachea. Mean Qaw was 10.1 +/- 1.9 ml min-1 (mean +/- S.D.) during room air breathing (25 degrees C, 70% RH) and decreased to 4.7 +/- 2.1 ml min-1 during cold dry air breathing (p < 0.05). Within 20 min of resuming room air breathing, mean Qaw had returned to baseline. Breathing warm humid air had no significant effect on mean Qaw (8.2 +/- 1.4 ml min-1). These results indicate that quiet breathing of frigid air causes vasoconstriction in central airways.

Adult↗
PubMed1984

The effect of humidity on the transmission of Brugia pahangi infective larvae to mammalian hosts by Aedes aegypti.

The transmission of Brugia pahangi by Aedes aegypti to the mammalian host was compared at low and high humidity. There was no statistical difference between the number of infected mosquitoes feeding or the egress of infective larvae from these mosquitoes at high or low humidity. The penetration of the host by the infective larvae was however significantly greater (p less than 0.05) at high than at a low humidity.

Aedes↗
PubMed1994

Relationship of air temperature, relative humidity, precipitation, photoperiod, wind speed and solar radiation with serum insulin-like growth factor I (IGF-I) concentration in Angus beef cattle.

Eight paternal half-sib Angus calves born in late April and early May, 1988 were used to investigate the potential relationship of serum IGF-I concentration with photoperiod and various weather variables including minimum, maximum and average air temperatures, relative humidity, precipitation, wind speed and solar radiation. To determine IGF-I concentration, blood samples were obtained at birth and then weekly until the calves reached 1 mo of age and bi-weekly thereafter. Blood sampling continued until the calves reached puberty as determined by progesterone and testosterone assays. Photoperiod and each weather variable were averaged over the 3 d prior to and including the day of blood sampling (4-d average). Data were divided into two periods: (1) birth through the end of the postweaning period and (2) postweaning period only. Serum IGF-I concentrations were analyzed using a model which included the fixed effects of sex and sample number, the random effect of calf nested within sex and the fixed interaction of sex x sample number, in addition to covariates for weight, photoperiod and weather variables. From birth through the end of the postweaning test, none of the weather variables or photoperiod had significant effects on serum IGF-I concentrations when each was fitted separately. For the postweaning period only, cubic regression coefficients for minimum and average temperatures were .0962 +/- .0325 ng/ml/degrees C3 and .0976 +/- .0272 ng/ml/degrees C3, respectively (P < .01). The quadratic regression coefficient for relative humidity during the postweaning period was -.2991 +/- .1142 ng/ml/%2 (P < .05). The quartic regression coefficient for wind speed during the postweaning period was -36.435 +/- 13.00 ng/ml/(km/hr)4 (P < .01). Maximum temperature, precipitation, solar radiation and photoperiod did not have significant effects on postweaning serum IGF-I concentrations. Based on these data, we conclude that temperature, humidity and wind speed were contributing factors to variation in serum IGF-I concentrations in postweaned beef calves.

Aging↗