Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “humidity response”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1989

Temperature and humidity modify airway response to inhaled histamine in normal subjects.

The airway response to inhaled histamine is known to be influenced by various stimuli (e.g., infection, ozone). Temperature (T) has been shown to affect it in vitro. We studied whether T and humidity (H) modify airway response to inhaled histamine in normal subjects. Twelve normal subjects 21 to 46 yr of age (mean age, 29 yr) performed two similar histamine inhalation tests, the only difference being the conditions of the inspired air. One test was done while breathing cold dry air (mean T +/- SEM, -17.3 +/- 1.8 degrees C; relative H, 0%), and the other while breathing warm humid air (mean T +/- SEM, 33.9 +/- 0.5 degrees C; relative H, 100%). Whereas the geometric mean histamine concentration required to produce a 15% fall in FEV1 in the warm humid tests was 22.7 mg/ml, it was 11.9 mg/ml in the cold dry test (p less than 0.01). It is concluded that the T and H of inspired air modify the airway response to inhaled histamine in normal subjects.

Administration, Inhalation↗
PubMed1996

Lack of effect of hot, humid air on response to nasal challenge with histamine.

We have previously shown that whole body exposure of human subjects to environmental conditions of 37 degrees C and 90% relative humidity (RH) prior to and during nasal challenge with antigen decreases the early response. In this study, we evaluated 1) whether the decreased responses observed resulted from decreased end organ sensitivity to histamine and 2) whether the effect of hot, humid air persisted after the subject exited the hot, humid environment. Ten asymptomatic seasonal allergic subjects and 11 nonallergic subjects were randomized to environmental chamber conditions of either 20 degrees C, 30% RH or 37 degrees C, 90% RH for 1 hour prior to and during performance of a nasal challenge with histamine. Twenty-two hours after exiting the environmental chamber, the allergic subjects were challenged with antigen. During both chamber conditions, histamine challenge was associated with a significant increase in all measured parameters compared to sham challenge, except for the sensations of pruritus and congestion. The response to histamine challenge was not different under the two experimental conditions or between allergic and nonallergic subjects. Following both exposure conditions, allergen challenge was associated with an increase in all measured parameters compared to sham challenge, with no significant difference between the two conditions. Exposure to 37 degrees C, 90% RH minimally affects the response to nasal challenge with histamine, and thus, the previously reported decreases in the early nasal response to antigen may primarily result from reduction in mast cell activation. The effect on antigen does not persist 22 hours after exposure.

Adult↗
PubMed1981

Influence of environmental temperature and humidity on bronchial responses during assessment of selectivity of beta-adrenoceptor antagonists in man.

1 The effects of beta-adrenoceptor antagonists given intravenously in single doses were examined in a double-blind, placebo controlled study performed in six healthy volunteers. Heart rate and peak expiratory flow rate (PEFR) were measured at rest and during standardised exercise. 2 Atenolol 0.2 mg/kg, betaxolol 0.15 mg/kg, practolol 1 mg/kg and propranolol 0.2 mg/kg all reduced heart rate to a similar extent during exercise at 2 and 4 h after administration; betaxolol 0.6 mg/kg had a significantly greater effect than the other treatments at all times. Only betaxolol 0.15 and 0.6 mg/kg significantly inhibited exercise tachycardia at 24 h. 3 None of the treatments studied had any effect on PEFR at rest or during exercise. 4 A second study was performed to determine whether this lack of effect of propranolol on exercise PEFR could have been due to the warm and humid conditions prevailing during the experiment. Eight healthy men underwent a standardised exercise test under alternately 'warm and humid' and 'cool and dry' conditions before and after propranolol 0.2 mg/kg or saline placebo intravenously. 5 Propranolol treatment did not influence resting or exercise PEFR in either environment, but did reduce FEV1 immediately after exercise under the cool and dry conditions but not under the warm and humid conditions. 6 Comparison of the effects of beta-adrenoceptor antagonists on exercise heart rate and PEFR is not a reliable or sensitive method of measuring the cardioselectivity of these drugs. 7 Environmental temperature and humidity should ideally be controlled when the action of any drug on airflow resistance is being studied.

Adrenergic beta-Antagonists↗
PubMed1972

Phycomyces: growth responses of the sporangium.

During the development of the sporangiophore of the fungus Phycomyces blakesleeanus there occurs a period of several hours when the sporangiophore does not elongate; instead, its "growth" is diverted into the formation of a sporangium at its top. This period of head formation is called stage II. Clearly, growth has not ceased but rather the geometry of the growing area has changed from that of a cylinder to a sphere. The growing sphere is found to have properties similar to the stage IV growing zone in that it functions as a sensory receptor and effector. The growing sporangium responds to both light (light head response) and humidity (wet head response). A model is presented giving a possible mechanism by which the ultimate size of the sporangium is regulated.

Journal Article↗
PubMed1989

Potato growth in response to relative humidity.

Potato plants (Solanum tuberosum L. cvs. Russet Burbank, Norland, and Denali) were grown for 56 days in controlled-environment rooms under continuous light at 20C and 50% or 85% RH. No significant differences in total plant dry weight were measured between the humidity treatments, but plants grown under 85% RH produced higher tuber yields. Leaf areas were greater under 50% RH and leaves tended to be larger and darker green than at 85% RH.

Biomass↗
PubMed2006

Physiological and subjective responses to low relative humidity in young and elderly men.

In order to compare the physiological and the subjective responses to low relative humidity of elderly and young men, we measured saccharin clearance time (SCT), frequency of blinking, hydration state of the skin, transepidermal water loss (TEWL), sebum level recovery and skin temperatures as physiological responses. We asked subjects to evaluate thermal, dryness and comfort sensations as subjective responses using a rating scale. Eight non-smoking healthy male students (21.7+/-0.8 yr) and eight non-smoking healthy elderly men (71.1+/-4.1 yr) were selected. The pre-room conditions were maintained at an air temperature (Ta) of 25 degrees C and a relative humidity (RH) of 50%. The test-room conditions were adjusted to provide 25 degrees C Ta and RH levels of 10%, 30% and 50%. RH had no effect on the activity of the sebaceous gland or change of mean skin temperature. SCT of the elderly group under 10% RH was significantly longer than that of the young group. In particular, considering the SCT change, the nasal mucous membrane seems to be affected more in the elderly than in the young in low RH. Under 30% RH, the eyes and skin become dry, and under 10% RH the nasal mucous membrane becomes dry as well as the eyes and skin. These findings suggested that to avoid dryness of the eyes and skin, it is necessary to maintain greater than 30% RH, and to avoid dryness of the nasal mucous membrane, it is necessary to maintain greater than 10% RH. On the thermal sensation of the legs, at the lower humidity level, the elderly group felt cooler than the young group. On the dry sensation of the eyes and throat, the young group felt drier than the elderly group at the lower humidity levels. From the above results, the elderly group had difficulty in feeling dryness in the nasal mucous membrane despite being easily affected by low humidity. On the other hand, the young group felt the change of humidity sensitively despite not being severely affected by low humidity. Ocular mucosa and physiology of skin by dryness showed no difference by age. In the effect of longer exposure (180 min.) to low RH, only TEWL showed a slight decrease after 120 minutes in 30% RH, and all the measured results showed no noticeable differences compared with the result at 120 minutes.

Acclimatization↗
PubMed1984

Comparative effects of sulfur dioxide exposures at 5 degrees C and 22 degrees C in exercising asthmatics.

Either airway cooling or sulfur dioxide (SO2) can induce bronchoconstriction in many asthmatics. Whether these two stresses act synergistically is a question with important public health implications. Eight young adult asthmatic volunteers were exposed to SO2 at 0.0, 0.2, 0.4, and 0.6 ppm, during 5 min heavy exercise at 5 degrees C, both with high (approximately 85%) and with low (approximately 50%) relative humidity. Physiologic response increased with increasing SO2 concentration but did not vary significantly with humidity. Symptom response was marginally greater at low than at high humidity. Twenty-four asthmatics were exposed similarly to clean air and to 0.6 ppm SO2, at 5 degrees C and also at 22 degrees C, always at high relative humidity. For this group, physiologic and clinical responses to SO2 (in excess of responses to clean air) were highly significant, regardless of temperature. The mean excess responses at 5 degrees compared with those at 22 degrees C were not statistically significant in clean air or SO2. Thus, moderate cold stress exacerbated the untoward response to SO2 only slightly and inconsistently in these asthmatic subjects.

Adolescent↗
PubMed1976

Stomatal response of engelmann spruce to humidity, light, and water stress.

Stomatal response of Engelmann spruce (Picea engelmannii Engelm.) to environmental conditions was studied in the natural subalpine environment and under controlled laboratory conditions. Stomata of naturally occurring trees responded to the difference in absolute humidity from leaf to air. When foliage was exposed to full sunlight, stomatal conductance decreased as the absolute humidity difference increased. In the shade, where photosynthetically active radiation was 10% of that in full sunlight, stomatal closure at large absolute humidity differences was much more complete. No effect of soil or air temperatures on stomatal aperture was observed in the field, nor were differences among three contrasting sites detected. Under growth chamber conditions, stomata responded to photosynthetically active radiation, but conductances were influenced by leaf-to-air differences in absolute humidity. Leaf water potentials below - 15 bars resulted in lower conductances over a range of humidity and light conditions. Because net photosynthesis under shaded conditions in the natural environment must be very low, stomatal closure could result in considerable savings in water while having a minimum effect on net photosynthesis.

Journal Article↗
PubMed2006

The identification of genes involved in the stomatal response to reduced atmospheric relative humidity.

Stomatal pores of higher plants close in response to decreases in atmospheric relative humidity (RH). This is believed to be a mechanism that prevents the plant from losing excess water when exposed to a dry atmosphere and as such is likely to have been of evolutionary significance during the colonization of terrestrial environments by the embryophytes. We have conducted a genetic screen, based on infrared thermal imaging, to identify Arabidopsis genes involved in the stomatal response to reduced RH. Here we report the characterization of two genes, identified during this screen, which are involved in the guard cell reduced RH signaling pathway. Both genes encode proteins known to be involved in guard cell ABA signaling. OST1 encodes a protein kinase involved in ABA-mediated stomatal closure while ABA2 encodes an enzyme involved in ABA biosynthesis. These results suggest, in contrast to previously published work, that ABA plays a role in the signal transduction pathway connecting decreases in RH to reductions in stomatal aperture. The identification of OST1 as a component required in stomatal RH and ABA signal transduction supports the proposition that guard cell signaling is organized as a network in which some intracellular signaling proteins are shared among different stimuli.

Abscisic Acid↗
PubMed2003

Low rates of change enhance effect of humidity on the activity of insect hygroreceptors.

The inability to measure humidity during stimulation has so far prevented us from understanding the contribution of moist cells and dry cells to orientation in a gradient of humidity. The problem was solved in the present study by means of a UV-absorption hygrometer that made it possible to monitor humidity at a rate of 100 Hz. The antennal moist and dry cells of the cockroach were exposed to humidities alternatively falling or rising at low rates between -1% RH s(-1) and +1% RH s(-1) (relative humidity). Impulse frequency of both types of cells depended simultaneously on instantaneous humidity and its rate of change. High frequencies of the moist cells signal high humidity. But at a given humidity, the response frequency is higher still when humidity is also rising. Conversely, high frequencies of the dry cell signal low humidity, and frequency is higher still at a given humidity when humidity is also falling. These responses ensure that the cockroach spent a minimum time in environments where desiccation or hydration occur and may thus protect the animal from emerging accidentally from under cover into moving air. In the constant-humidity retreat of the cockroach, fluctuating or even drifting discharge frequencies could serve as an early warning: return!

Animals↗
PubMed2002

Effects of ventilation, humidity and temperature on airway responsiveness to methacholine in rats.

Exercise-induced bronchoconstriction is associated with heat and water loss from the airways. It is not known whether these conditions can influence the response to bronchoactive agonists. The effects of different degrees of alveolar ventilation on the pulmonary response to methacholine and the role of humidity and temperature in this response were evaluated. Wistar rats were anaesthetized, tracheostomized and mechanically ventilated. Increasing doses of methacholine were infused intravenously and respiratory system resistance (Rrs) and elastance (Ers) were measured. The rats were ventilated with dry air at 13 degrees C, dry air at 37 degrees C, humid air at 13 degrees C and humid air at 37 degrees C. These four groups were further divided into three subgroups with a respiratory frequency adjusted to reach a carbon dioxide tension in arterial blood of 30, 40 and 50 mmHg. Temperature, humidity and level of alveolar ventilation did not influence the position of the dose/response curve to methacholine. However, the maximal changes in Ers were significantly lower in the rats ventilated with humid air. In addition, maximal changes in Ers were significantly higher in the rats with lower alveolar ventilation. These differences were not observed for maximal values of Rrs. The pulmonary response to methacholine in normal rats is significantly affected by the humidity of inspired air and the level of alveolar ventilation. This influence is more intense in the small airways and/or distal airspaces. This suggests that exercise or hyperventilation can change the behaviour of airway smooth muscle.

Airway Resistance↗
PubMed2000

Heat storage in horses during submaximal exercise before and after humid heat acclimation.

The effect of humid heat acclimation on thermoregulatory responses to humid and dry exercise-heat stress was studied in six exercise-trained Thoroughbred horses. Horses were heat acclimated by performing moderate-intensity exercise for 21 days in heat and humidity (HH) [34.2-35.7 degrees C; 84-86% relative humidity (RH); wet bulb globe temperature (WBGT) index approximately 32 degrees C]. Horses completed exercise tests at 50% of peak O(2) uptake until a pulmonary arterial temperature (T(pa)) of 41.5 degrees C was attained in cool dry (CD) (20-21.5 degrees C; 45-50% RH; WBGT approximately 16 degrees C), hot dry (HD 0) [32-34 degrees C room temperature (RT); 45-55% RH; WBGT approximately 25 degrees C], and HH conditions (HH 0), and during the second hour of HH on days 3, 7, 14, and 21, and in HD on the 18th day (HD 18) of heat acclimation. The ratios of required evaporative capacity to maximal evaporative capacity of the environment (E(req)/E(max)) for CD, HD, and HH were approximately 1.2, 1.6, and 2.5, respectively. Preexercise T(pa) and rectal temperature were approximately 0.5 degrees C lower (P < 0. 05) on days 7, 14, and 21 compared with day 0. With exercise in HH, there was no effect of heat acclimation on the rate of rise in T(pa) (and therefore exercise duration) nor the rate of heat storage. In contrast, exercise duration was longer, rate of rise in T(pa) was significantly slower, and rate of heat storage was decreased on HD 18 compared with HD 0. It was concluded that, during uncompensable heat stress in horses, heat acclimation provided modest heat strain advantages when E(req)/E(max) was approximately 1.6, but at higher E(req)/E(max) no advantages were observed.

Acclimatization↗