Cardiac function during heat stress: impact of short-term passive heat acclimation

2020 ◽  
Vol 319 (4) ◽  
pp. H753-H764
Author(s):  
Lukas D. Trachsel ◽  
Hadiatou Barry ◽  
Hugo Gravel ◽  
Parya Behzadi ◽  
Christine Henri ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Cardiac Function ◽  
Systolic Function ◽  
Heat Exposure ◽  
Heat Acclimation ◽  
Passive Heating ◽  
Lower Heart Rate ◽  
Short Term ◽  
Cardiac Systolic Function

A lower heart rate during heat exposure is a classic marker of heat acclimation (HA). It remains unknown if improved cardiac function contributes to this response. A 7-day passive HA protocol did not alter cardiac systolic function during passive heating, whereas it improved some indexes of diastolic function in young adults. Nonetheless, heart rate during heating was unaffected by HA. These results suggest that passive HA induces limited adaptations in cardiac function during passive heating.

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.

A Field Evaluation of Construction Workers’ Activity, Hydration Status, and Heat Strain in the Extreme Summer Heat of Saudi Arabia

2020 ◽  
Vol 64 (5) ◽  
pp. 522-535 ◽  
Author(s):  
Mohammed Al-Bouwarthan ◽  
Margaret M Quinn ◽  
David Kriebel ◽  
David H Wegman
Keyword(s):  
Heart Rate ◽  
Saudi Arabia ◽  
Heat Stress ◽  
Heat Exposure ◽  
Heat Strain ◽  
Construction Workers ◽  
Hydration Status ◽  
Summer Heat ◽  
Cardiovascular Strain ◽  
Indoor And Outdoor

Abstract Objectives Assess the impact of summer heat exposure (June–September) on residential construction workers in Al-Ahsa, Saudi Arabia by evaluating (i) heart rate (HR) responses, hydration status, and physical workload among workers in indoor and outdoor construction settings, (ii) factors related to physiological responses to work in hot conditions, and (iii) how well wet-bulb globe temperature-based occupational exposure limits (WBGTOELs) predict measures of heat strain. Methods Twenty-three construction workers (plasterers, tilers, and laborers) contributed 260 person-days of monitoring. Workload energy expenditure, HR, fluid intake, and pre- and postshift urine specific gravity (USG) were measured. Indoor and outdoor heat exposures (WBGT) were measured continuously and a WBGTOEL was calculated. The effects of heat exposure and workload on heart rate reserve (HRR), a measure of cardiovascular strain, were examined with linear mixed models. A metric called ‘heat stress exceedance’ (HSE) was constructed to summarize whether the environmental heat exposure (WBGT) exceeded the heat stress exposure limit (WBGTOEL). The sensitivity and specificity of the HSE as a predictor of cardiovascular strain (HRR ≥30%) were determined. Results The WBGTOEL was exceeded frequently, on 63 person-days indoors (44%) and 91(78%) outdoors. High-risk HRR occurred on 26 and 36 person-days indoors and outdoors, respectively. The HSE metric showed higher sensitivity for HRR ≥30% outdoors (89%) than indoors (58%) and greater specificity indoors (59%) than outdoors (27%). Workload intensity was generally moderate, with light intensity work more common outdoors. The ability to self-pace work was associated with a lower frequency of HRR ≥30%. USG concentrations indicated that workers began and ended their shifts dehydrated (USG ≥1.020). Conclusions Construction work where WBGTOEL is commonly exceeded poses health risks. The ability of workers to self-pace may help reduce risks.

Seven days of hot water heat acclimation does not modulate the change in heart rate variability during passive heat exposure

2020 ◽  
Author(s):  
Philippe Gendron ◽  
Hugo Gravel ◽  
Hadiatou Barry ◽  
Daniel Gagnon
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
High Frequency ◽  
Water Immersion ◽  
Heat Exposure ◽  
Thermal Strain ◽  
Heat Acclimation ◽  
Hot Water ◽  
Frequency Range ◽  
The Mean

We examined if the change in heart rate variability (HRV) during passive heat exposure is modified by hot water heat acclimation (HA). Sixteen healthy adults (28 ± 5 years, 5 females/11 males) underwent heat exposure in a water-perfused suit, pre and post 7 days of HA (60 minutes at rectal temperature ≥38.6°C). During passive heat exposure, heart rate (HR), the standard deviation of NN intervals (SDNN), the square root of the mean squared differences of successive NN intervals (RMSSD) and the power in the high frequency range (HF) were measured. No difference in HR (P=0.22), SDNN (P=0.87), RMSSD (P=0.79) and HF (P=0.23) was observed at baseline. The increase in HR (pre-HA: 43 ± 10, post-HA: 42 ± 9 bpm, P=0.57) and the decrease of SDNN (pre-HA: -54.1 ± 41.0, post-HA: -52.2 ± 36.8 ms, P=0.85), RMSSD (pre-HA: -70.8 ± 49.5, post-HA: -72.7 ± 50.4 ms, P=0.91) and HF (pre-HA: -28.0 ± 14.5, post-HA: -23.2 ± 17.1%, P=0.27) were not different between experimental visits at fixed increases in esophageal temperature. These results suggest that 7 consecutive days of hot water HA does not modify the change in HRV indices during passive heat exposure. Novelty bullets: - It remains unclear if heat acclimation alters the change in heart rate variability that occurs during passive heat exposure. - At matched levels of thermal strain, 7 consecutive days of hot water immersion did not modulate the change in indices of heart rate variability during passive heat exposure.

Short term heat acclimation reduces heat stress, but is not augmented by dehydration

2018 ◽  
Vol 78 ◽  
pp. 227-234 ◽  
Author(s):  
Michael W. Schleh ◽  
Brent C. Ruby ◽  
Charles L. Dumke
Keyword(s):  
Heat Stress ◽  
Heat Acclimation ◽  
Short Term

scholarly journals The role of cardiac sympathetic innervation and skin thermoreceptors on cardiac responses during heat stress

2015 ◽  
Vol 308 (11) ◽  
pp. H1336-H1342 ◽  
Author(s):  
Manabu Shibasaki ◽  
Yasunori Umemoto ◽  
Tokio Kinoshita ◽  
Ken Kouda ◽  
Tomoyuki Ito ◽  
...  
Keyword(s):  
Heat Stress ◽  
Diastolic Function ◽  
Systolic Function ◽  
Sympathetic Innervation ◽  
Ventricular Systolic Function ◽  
Cardiac Sympathetic Innervation ◽  
Cardiac Responses ◽  
Cardiac Systolic Function ◽  
Stimulation Of

The mechanism(s) for the changes in cardiac function during heat stress remain unknown. This study tested two unique hypotheses. First, sympathetic innervation to the heart is required for increases in cardiac systolic function during heat stress. This was accomplished by comparing responses during heat stress between paraplegics versus tetraplegics, with tetraplegics having reduced/absent cardiac sympathetic innervation. Second, stimulation of skin thermoreceptors contributes to cardiovascular adjustments that occur during heat stress in humans. This was accomplished by comparing responses during leg only heating between paraplegic versus able-bodied individuals. Nine healthy able-bodied, nine paraplegics, and eight tetraplegics participated in this study. Lower body (i.e., nonsensed area for para/tetraplegics) was heated until esophageal temperature had increased by ∼1.0°C. Echocardiographic indexes of diastolic and systolic function were performed before and at the end of heat stress. The heat stress increased cardiac output in all groups, but the magnitude of this increase was attenuated in the tetraplegics relative to the able-bodied (1.3 ± 0.4 vs. 2.3 ± 1.0 l/min; P < 0.05). Diastolic function was maintained in all groups. Indexes of left atrial and ventricular systolic function were enhanced in the able-bodied, but did not change in tetraplegics, while these changes in paraplegics were attenuated relative to the able-bodied. These data suggest that the cardiac sympathetic innervation is required to achieve normal increases in cardiac systolic function during heat stress but not required to maintain diastolic function during this exposure. Second, elevated systolic function during heat stress primarily occurs as a result of increases in internal temperature, although stimulation of skin thermoreceptors may contribute.

scholarly journals Exercise intolerance in volume overload heart failure is associated with low carotid body mediated chemoreflex drive

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
David C. Andrade ◽  
Esteban Díaz-Jara ◽  
Camilo Toledo ◽  
Karla G. Schwarz ◽  
Katherin V. Pereyra ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cardiac Function ◽  
Training Program ◽  
Carotid Body ◽  
Exercise Tolerance ◽  
Systolic Function ◽  
Volume Overload ◽  
Exercise Intolerance ◽  
Ventilatory Responses ◽  
Cardiac Systolic Function

AbstractMounting an appropriate ventilatory response to exercise is crucial to meeting metabolic demands, and abnormal ventilatory responses may contribute to exercise-intolerance (EX-inT) in heart failure (HF) patients. We sought to determine if abnormal ventilatory chemoreflex control contributes to EX-inT in volume-overload HF rats. Cardiac function, hypercapnic (HCVR) and hypoxic (HVR) ventilatory responses, and exercise tolerance were assessed at the end of a 6 week exercise training program. At the conclusion of the training program, exercise tolerant HF rats (HF + EX-T) exhibited improvements in cardiac systolic function and reductions in HCVR, sympathetic tone, and arrhythmias. In contrast, HF rats that were exercise intolerant (HF + EX-inT) exhibited worse diastolic dysfunction, and showed no improvements in cardiac systolic function, HCVR, sympathetic tone, or arrhythmias at the conclusion of the training program. In addition, HF + EX-inT rats had impaired HVR which was associated with increased arrhythmia susceptibility and mortality during hypoxic challenges (~ 60% survival). Finally, we observed that exercise tolerance in HF rats was related to carotid body (CB) function as CB ablation resulted in impaired exercise capacity in HF + EX-T rats. Our results indicate that: (i) exercise may have detrimental effects on cardiac function in HF-EX-inT, and (ii) loss of CB chemoreflex sensitivity contributes to EX-inT in HF.

scholarly journals Moderate Exercise Based on Artificial Gravity Preserves Orthostatic Tolerance and Exercise Capacity During Short-Term Head-Down Bed Rest

2017 ◽  
pp. 567-580 ◽  
Author(s):  
X.-T. LI ◽  
C.-B. YANG ◽  
Y.-S. ZHU ◽  
J. SUN ◽  
F. SHI ◽  
...  
Keyword(s):  
Aerobic Exercise ◽  
Plasma Volume ◽  
Systolic Function ◽  
Bed Rest ◽  
Control Group ◽  
Orthostatic Tolerance ◽  
Short Term ◽  
Exercise Endurance ◽  
Physical Deconditioning ◽  
Cardiac Systolic Function

Numerous countermeasures have been proposed to minimize microgravity-induced physical deconditioning, but their benefits are limited. The present study aimed to investigate whether personalized aerobic exercise based on artificial gravity (AG) mitigates multisystem physical deconditioning. Fourteen men were assigned to the control group (n=6) and the countermeasure group (CM, n=8). Subjects in the CM group were exposed to AG (2 Gz at foot level) for 30 min twice daily, during which time cycling exercise of 80-95 % anaerobic threshold (AT) intensity was undertaken. Orthostatic tolerance (OT), exercise tests, and blood assays were determined before and after 4 days head-down bed rest (HDBR). Cardiac systolic function was measured every day. After HDBR, OT decreased to 50.9 % and 77.5 % of pre-HDBR values in control and CM groups, respectively. Exercise endurance, maximal oxygen consumption, and AT decreased to 96.5 %, 91.5 % and 91.8 % of pre-HDBR values, respectively, in the control group. Nevertheless, there were slight changes in the CM group. HDBR increased heart rate, sympathetic activity, and the pre-ejection period, but decreased plasma volume, parasympathetic activity and left-ventricular ejection time in the control group, whereas these effects were eliminated in the CM group. Aldosterone had no change in the control group but increased significantly in the CM group. Our study shows that 80-95 % AT aerobic exercise based on 2 Gz of AG preserves OT and exercise endurance, and affects body fluid regulation during short-term HDBR. The underlying mechanisms might involve maintained cardiac systolic function, preserved plasma volume, and improved sympathetic responses to orthostatic stress.

scholarly journals Additive effects of heating and exercise on baroreflex control of heart rate in healthy males

2017 ◽  
Vol 123 (6) ◽  
pp. 1555-1562 ◽  
Author(s):  
Tiago Peçanha ◽  
Cláudia L. M. Forjaz ◽  
David. A. Low
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Baroreflex Sensitivity ◽  
Whole Body ◽  
Additive Effects ◽  
Passive Heating ◽  
Baroreflex Control ◽  
Rr Intervals ◽  
Body Heat

This study assessed the additive effects of passive heating and exercise on cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV). Twelve healthy young men (25 ± 1 yr, 23.8 ± 0.5 kg/m2) randomly underwent two experimental sessions: heat stress (HS; whole body heat stress using a tube-lined suit to increase core temperature by ~1°C) and normothermia (NT). Each session was composed of a preintervention rest (REST1); HS or NT interventions; postintervention rest (REST2); and 14 min of cycling exercise [7 min at 40%HRreserve (EX1) and 7 min at 60%HRreserve (EX2)]. Heart rate and finger blood pressure were continuously recorded. cBRS was assessed using the sequence (cBRSSEQ) and transfer function (cBRSTF) methods. HRV was assessed using the indexes standard deviation of RR intervals (SDNN) and root mean square of successive RR intervals (RMSSD). cBRS and HRV were not different between sessions during EX1 and EX2 (i.e., matched heart rate conditions: EX1 = 116 ± 3 vs. 114 ± 3 and EX2 = 143 ± 4 vs. 142 ± 3 beats/min but different workloads: EX1 = 50 ± 9 vs. 114 ± 8 and EX2 = 106 ± 10 vs. 165 ± 8 W; for HS and NT, respectively; P < 0.01). However, when comparing EX1 of NT with EX2 of HS (i.e., matched workload conditions but with different heart rates), cBRS and HRV were significantly reduced in HS (cBRSSEQ = 1.6 ± 0.3 vs. 0.6 ± 0.1 ms/mmHg, P < 0.01; SDNN = 2.3 ± 0.1 vs. 1.3 ± 0.2 ms, P < 0.01). In conclusion, in conditions matched by HR, the addition of heat stress to exercise does not affect cBRS and HRV. Alternatively, in workload-matched conditions, the addition of heat to exercise results in reduced cBRS and HRV compared with exercise in normothermia. NEW & NOTEWORTHY The present study assessed cardiac baroreflex sensitivity during the combination of heat and exercise stresses. This is the first study to show that prior whole body passive heating reduces cardiac baroreflex sensitivity and autonomic modulation of heart rate during exercise. These findings contribute to the better understanding of the role of thermoregulation on cardiovascular regulation during exercise.

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