Low doses of melatonin and diurnal effects on thermoregulation and tolerance to uncompensable heat stress

1999 ◽  
Vol 87 (1) ◽  
pp. 308-316 ◽  
Author(s):  
Tom M. McLellan ◽  
Greg A. Gannon ◽  
Jiri Zamecnik ◽  
Valerie Gil ◽  
Greg M. Brown
Keyword(s):  
Heat Stress ◽  
Protective Clothing ◽  
Low Dose ◽  
Heart Rate Response ◽  
Heat Storage ◽  
Stress Exposure ◽  
Double Blind ◽  
Early Afternoon ◽  
Hypothermic Effect ◽  
Uncompensable Heat Stress

This study examined whether the reported hypothermic effect of melatonin ingestion increased tolerance to exercise at 40°C, for trials conducted either in the morning or afternoon, while subjects were wearing protective clothing. Nine men performed four randomly ordered trials; two each in the morning (0930) and afternoon (1330) after the double-blind ingestion of either two placebo capsules or two 1-mg capsules of melatonin. Despite significant elevations in plasma melatonin to over 1,000 ng/ml 1 h after the ingestion of the first 1-mg dose, rectal temperature (Tre) was unchanged before or during the heat-stress exposure. Also, all other indexes of temperature regulation and the heart rate response during the uncompensable heat stress were unaffected by the ingestion of melatonin. Initial Tre was increased during the afternoon (37.1 ± 0.2°C), compared with the morning (36.8 ± 0.2°C) exposures, and these differences remained throughout the uncompensable heat stress, such that final Tre was also increased for the afternoon (39.2 ± 0.2°C) vs. the morning (39.0 ± 0.3°C) trials. Tolerance times and heat storage were not different among the exposures at ∼110 min and 16 kJ/kg, respectively. It was concluded that this low dose of melatonin had no impact on tolerance to uncompensable heat stress and that trials conducted in the early afternoon were associated with an increased Tre tolerated at exhaustion that offset the circadian influence on resting Tre and thus maintained tolerance times similar to those of trials conducted in the morning.

Heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress

1998 ◽  
Vol 84 (5) ◽  
pp. 1731-1739 ◽  
Author(s):  
Stephen S. Cheung ◽  
Tom M. McLellan
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Aerobic Fitness ◽  
Protective Clothing ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Short Term ◽  
Chemical Protective Clothing ◽  
Uncompensable Heat Stress ◽  
C 30

—The purpose of the present study was to determine the separate and combined effects of aerobic fitness, short-term heat acclimation, and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40°C, 30% relative humidity). Men who were moderately fit [(MF); <50 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 7] and highly fit [(HF); >55 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 8] were tested while they were euhydrated or hypohydrated by ∼2.5% of body mass through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after 2 wk of daily heat acclimation (1-h treadmill exercise at 40°C, 30% relative humidity, while wearing the nuclear, biological, and chemical protective clothing). Heat acclimation increased sweat rate and decreased skin temperature and rectal temperature (Tre) in HF subjects but had no effect on tolerance time (TT). MF subjects increased sweat rate but did not alter heart rate, Tre, or TT. In both MF and HF groups, hypohydration significantly increased Tre and heart rate and decreased the respiratory exchange ratio and the TT regardless of acclimation state. Overall, the rate of rise of skin temperature was less, while ΔTre, the rate of rise of Tre, and the TT were greater in HF than in MF subjects. It was concluded that exercise-heat tolerance in this uncompensable heat-stress environment is not influenced by short-term heat acclimation but is significantly improved by long-term aerobic fitness.

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

2000 ◽  
Vol 89 (6) ◽  
pp. 2283-2293 ◽  
Author(s):  
Raymond J. Geor ◽  
Laura Jill McCutcheon ◽  
Gayle L. Ecker ◽  
Michael I. Lindinger
Keyword(s):  
Heat Stress ◽  
Heat Storage ◽  
Heat Acclimation ◽  
Exercise Duration ◽  
Moderate Intensity ◽  
Moderate Intensity Exercise ◽  
Exercise Tests ◽  
Before And After ◽  
Uncompensable Heat Stress ◽  
Globe Temperature

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°C; 84–86% relative humidity (RH); wet bulb globe temperature (WBGT) index ∼32°C]. Horses completed exercise tests at 50% of peak O2 uptake until a pulmonary arterial temperature (Tpa) of 41.5°C was attained in cool dry (CD) (20–21.5°C; 45–50% RH; WBGT ∼16°C), hot dry (HD 0) [32–34°C room temperature (RT); 45–55% RH; WBGT ∼25°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 (Ereq/Emax) for CD, HD, and HH were ∼1.2, 1.6, and 2.5, respectively. Preexercise Tpa and rectal temperature were ∼0.5°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 Tpa (and therefore exercise duration) nor the rate of heat storage. In contrast, exercise duration was longer, rate of rise in Tpa 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 Ereq/Emax was ∼1.6, but at higher Ereq/Emax no advantages were observed.

Physiological tolerance to uncompensable heat stress: effects of exercise intensity, protective clothing, and climate

1994 ◽  
Vol 77 (1) ◽  
pp. 216-222 ◽  
Author(s):  
S. J. Montain ◽  
M. N. Sawka ◽  
B. S. Cadarette ◽  
M. D. Quigley ◽  
J. M. McKay
Keyword(s):  
Heat Stress ◽  
Relative Humidity ◽  
Core Temperature ◽  
Exercise Intensity ◽  
Protective Clothing ◽  
Heat Exposure ◽  
Heat Strain ◽  
Published Data ◽  
Physiological Tolerance ◽  
Uncompensable Heat Stress

This study determined the influence of exercise intensity, protective clothing level, and climate on physiological tolerance to uncompensable heat stress. It also compared the relationship between core temperature and the incidence of exhaustion from heat strain for persons wearing protective clothing to previously published data of unclothed persons during uncompensable heat stress. Seven heat-acclimated men attempted 180-min treadmill walks at metabolic rates of approximately 425 and 600 W while wearing full (clo = 1.5) or partial (clo = 1.3) protective clothing in both a desert (43 degrees C dry bulb, 20% relative humidity, wind 2.2 m/s) and tropical (35 degrees C dry bulb, 50% relative humidity, wind 2.2 m/s) climate. During these trials, the evaporative cooling required to maintain thermal balance exceeded the maximal evaporative capacity of the environment and core temperature continued to rise until exhaustion from heat strain occurred. Our findings concerning exhaustion from heat strain are 1) full encapsulation in protective clothing reduces physiological tolerance as core temperature at exhaustion was lower (P < 0.05) in fully than in partially clothed persons, 2) partial encapsulation results in physiological tolerance similar to that reported for unclothed persons, 3) raising metabolic rate from 400 to 600 W does not alter physiological tolerance when subjects are fully clothed, and 4) physiological tolerance is similar when subjects are wearing protective clothing in desert and tropical climates having the same wet bulb globe thermometer. These findings can improve occupational safety guidelines for human heat exposure, as they provide further evidence that the incidence of exhaustion from heat strain can be predicted from core temperature.

Effects of Dehydration, Hypohydration, and Hyperhydration on Tolerance During Uncompensable Heat Stress

1999 ◽  
Vol 24 (4) ◽  
pp. 349-361 ◽  
Author(s):  
Tom M. Mclellan ◽  
Stephen S. Cheung ◽  
William A. Latzka ◽  
Mike N. Sawka ◽  
Kent B. Pandolf ◽  
...  
Keyword(s):  
Body Weight ◽  
Heat Stress ◽  
Rectal Temperature ◽  
Protective Clothing ◽  
Cardiovascular Responses ◽  
Hydration Status ◽  
Fluid Restriction ◽  
Prior Exercise ◽  
Key Words Thermoregulation ◽  
Uncompensable Heat Stress

The present study examined the effects of dehydration from prior exercise on subsequent exercise tolerance time (TT) that involved wearing nuclear, biological, and chemical (NBC) protective clothing. It was hypothesised that TT would be reduced in the dehydrated state. Ten men undertook continuous treadmill walking at 4.8 km • h−1 at 35 °C and 50% relative humidity, wearing NBC clothing while euhydrated (EU) or dehydrated (D) by 2.3% of body weight. Hydration status had no impact on thermoregulatory or cardiovascular responses during exercise. Also rectal temperature at exhaustion did not differ between EU (38.52 ± 0.39 °C) and D (38.43 ± 0.45 °C). Exercise TT during this uncompensable heat stress was reduced significantly for D (47.7 ± 15.3 min) compared with EU (59.0 ± 13.6 min). It was concluded that prior exercise leading to levels of dehydration to 2.3% of body weight, together with subsequent fluid restriction during exposure to uncompensable heat stress, impaired TT while wearing the NBC protective clothing. The integration of these findings together with other comparable studies that have examined the influence of hypo- and hyperhydration on TT while wearing NBC protective clothing revealed that hydration status has less effect on TT as the severity of uncompensable heat stress increases. Key words: thermoregulation, protective clothing, heat tolerance, rectal temperature

scholarly journals Therapeutic potential of targeting Tfr/Tfh cell balance by low-dose-IL-2 in active SLE: a post hoc analysis from a double-blind RCT study

2021 ◽  
Vol 23 (1) ◽  
Author(s):  
Miao Miao ◽  
Xian Xiao ◽  
Jiayi Tian ◽  
Yunzhi Zhufeng ◽  
Ruiling Feng ◽  
...  
Keyword(s):  
Low Dose ◽  
Activity Index ◽  
Cell Subset ◽  
Immunoglobulin M ◽  
Controlled Clinical Trial ◽  
Double Blind ◽  
Post Hoc Analysis ◽  
Immune Balance ◽  
Cell Balance ◽  
Post Hoc

Abstract Objective To investigate the regulation of T follicular regulatory (Tfr) and T follicular (Tfh) cell subtypes by low-dose IL-2 in systemic lupus erythematosus (SLE) in a randomized, double-blind, placebo-controlled clinical trial. Methods A post hoc analysis was performed in a randomized cohort of SLE patients (n=60) receiving low-dose IL-2 therapy (n=30) or placebo (n=30), along with the standard of care treatment. The primary endpoint was the attainment of SLE responder index-4 (SRI-4) at week 12 in the trial. Twenty-three healthy controls were enrolled for T cell subset detection at the same time as the trial. The t-stochastic neighbor embedding (tSNE) analysis of CD4 T subsets based on immune cells flow cytometry markers was performed to distinguish Tfh, Tfh1, Tfh2, Tfh17, and Tfr cell subsets. Results Compared with HC, the frequency of Tfr (CXCR5+PD-1low Treg and CXCR5+PD-1high Treg) cells was significantly reduced, while the pro-inflammatory Tfh cells were increased in patients with SLE. The imbalanced Tfh cell was associated with several pathogenic factors (anti-dsDNA antibodies (r=0.309, P=0.027) and serum IL-17 (r=0.328, P=0.021)) and SLE Disease Activity Index (SLEDAI) score (r=0.273, P=0.052). Decreased CXCR5+PD-1low Treg/Tfh and CXCR5+PD-1low Treg/Tfh17 were both associated with increased immunoglobulin M (IgM) (r=−0.448, P=0.002 and r=−0.336, P=0.024, respectively). Efficacy of low-dose IL-2 therapy was associated with a restored Tfr/Tfh cell balance. Conclusion These data support the hypothesis that promotion of Tfr is associated with decreased disease activities and that low-dose IL-2 therapy can recover Tfr/Tfh immune balance. Trial registration number ClinicalTrials.gov Registries (NCT02465580).

PREVENTING VENOUS THROMBOSIS (VT) WITH HEPARIN ALONE OR WITH HEPARIN/DIHYDROERGOTAMINE AFTER ELECTIVE HIP REPLACEMENT, A DOUBLE-BLIND, RANDOMISED, VENOGRAM END-POINT COMPARISON

1987 ◽  
Author(s):  
J F Cade ◽  
K W Mills ◽  
A S Gallus ◽  
W Murphy
Keyword(s):  
Venous Thrombosis ◽  
General Surgery ◽  
Hip Replacement ◽  
Low Dose ◽  
Double Blind ◽  
Randomised Study ◽  
Sodium Heparin ◽  
End Point ◽  
Small Doses

Dihydro-ergotaraine (DHE) appears to be synergistic with small doses of hepari when used to prevent VT after general surgery. However, doubt remains whether DHEhas this effect in patients with elective hip replacement (THR). We have therefore compared the results of VT prophylaxis using sub-cutaneous (sc) low-dose heparinalone or sc heparin plus sc DHE in a double-blind, randomised, study of 126 patientshaving elective THR, 98 at centre (1)and 28 at centre (2).All received 5000 iu sodium heparin, hourly for 7 days, starting 2 hours before surgery at centre (1), or immediately after surgery at centre (2). Patients alsoreceived a separate 0.5 ml (0.5 mg) DHEorplacebo injection each time they receivedheparin. Patients had bilateral ascendingvenography on the 7th postoperativeday, and venograms were read before the treatment code was broken.These results do not support the presence of synergism between heparin and DHE in this situation.

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