The Impact of Elevated Body Core Temperature on Critical Power as Determined by a 3-min All-Out Test

Critical power (CP) delineates the heavy and severe exercise intensity domains, and sustained work rates above CP result in an inexorable progression of oxygen uptake to a maximal value and, subsequently, the limit of exercise tolerance. The finite work capacity above CP, W′, is defined by the curvature constant of the power-duration relationship. Heavy or severe exercise in a hot environment generates additional challenges related to the rise in body core temperature (Tc) that may impact CP and W′. The purpose of this study was to determine the effect of elevated Tc on CP and W′. CP and W′ were estimated by end-test power (EP; mean of final 30s) and work above end-test power (WEP), respectively, from 3-min "all-out" tests performed on a cycle ergometer. Volunteers (n = 8, 4 female) performed the 3-min tests during a familiarization visit and two experimental visits (Thermoneutral vs Hot, randomized crossover design). Before experimental 3-min tests, subjects were immersed in water (Thermoneutral: 36°C for 30 min; Hot: 40.5°C until Tc was ≥ 38.5°C). Mean Tc was significantly greater in Hot compared to Thermoneutral (38.5±0.0°C vs. 37.4±0.2°C; mean±SD, P<0.01). All 3-min tests were performed in an environmental chamber (Thermoneutral: 18°C, 45% RH; Hot: 38°C, 40% RH). EP was similar between Thermoneutral (239 ± 57W) and Hot (234 ± 66W; P = 0.55). WEP was similar between Thermoneutral (10.9 ± 3.0 kJ) and Hot (9.3 ± 3.6; P = 0.19). These results suggest that elevated Tc has no significant impact on EP or WEP.

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Control of breathing during prolonged exercise

Journal of Applied Physiology ◽

10.1152/jappl.1981.50.1.27 ◽

1981 ◽

Vol 50 (1) ◽

pp. 27-31 ◽

Cited By ~ 14

Author(s):

B. J. Martin ◽

E. J. Morgan ◽

C. W. Zwillich ◽

J. V. Weil

Keyword(s):

Core Temperature ◽

Cycle Ergometer ◽

Body Core Temperature ◽

Heavy Exercise ◽

Arterial Lactate ◽

Arterial Ph ◽

Ergometer Exercise ◽

Constant Work Rate ◽

Body Core

Ventilation (VE) climbs steadily throughout prolonged heavy exercise. While this VE "drift" has implications for the adequacy of gas exchange in long-term exercise, its mechanism remains unknown. We examined the behavior of previously proposed mediators of VE drift during one hour of cycle ergometer exercise at constant work rate requiring 2/3 VO2 max in 10 subjects. VE increased 13% from 12 to 61 min of exercise (P less than 0.05). Although body core temperature rose as VE rose, equal elevation of core temperature by passive means failed to increase exercise VE. Rising VE during the hour of exercise occurred despite unchanged arterial pH, PCO2, and lactate and despite unchanged VCO2. Thus, all of the VE increase was calculated to be due to increased dead space ventilation (VD). Tidal volume (VT) was unchanged, while VD/VT rose from 0.16 to 0.24 from 12 to 61 min of work (P less than 0.05). These results show that increased body core temperature does not mediate VE drift, and that changes in previously proposed mediators (arterial pH, arterial lactate, and VCO2) are not necessary for a slow VE rise to occur in prolonged heavy exercise.

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Influence of insufflated carbon dioxide on abdominal temperature compared to oesophageal temperature during laparoscopic surgery

Surgical Endoscopy ◽

10.1007/s00464-020-08196-x ◽

2020 ◽

Author(s):

Philipp Groene ◽

Ufuk Gündogar ◽

Klaus Hofmann-Kiefer ◽

Roland Ladurner

Keyword(s):

Carbon Dioxide ◽

Laparoscopic Surgery ◽

Core Temperature ◽

Room Temperature ◽

Skin Incision ◽

Body Core Temperature ◽

Oesophageal Temperature ◽

Observational Trial ◽

Body Core ◽

The Impact

Abstract Background Body core temperature is an important vital parameter during surgery and anaesthesia. It is influenced by several patient-related and surgery-related factors. Laparoscopy is considered beneficial in terms of a variety of parameters, for example, postoperative pain and length of hospital stay. Non-humidified, non-warmed insufflated CO2 applied during laparoscopy is standard of care. This prospective observational trial therefore evaluates the impact of non-humidified CO2 at room temperature on abdominal temperature and its correlation to body core temperature. Methods Seventy patients undergoing laparoscopic surgery were included in this prospective observational study. Temperature was measured oesophageal and abdominal before induction of anaesthesia (T1), right before skin incision (T2), 15 min, 30 min and 60 min after skin incision. All patients were treated according to actual guidelines for perioperative temperature measurement. Results Body core temperature and abdominal temperature correlated moderately (r = 0.6123; p < 0.0001). Bland–Altman plot for comparison of methods showed an average difference of 0.4 °C (bias − 0.3955; 95% agreement of bias from − 2.365 to 1.574). Abdominal temperature further decreased after establishing pneumoperitoneum (T2: 36.2 °C (35.9/36.4) to T5: 36.1 °C (35.6/36.4); p < 0.0001), whereas oesophageal temperature increased (T2: 36.2 °C (35.9/36.4) to 36.4 °C (36.0/36.7); p = 0.0296). Values of oesophageal and abdominal measurement points differed at T4 (36.3 °C (36.0/36.6) vs. 36.1 °C (35.4/36.6); p < 0.0001) and T5 (36.4 °C (36.0/36.7) vs. 36.1 °C (35.6/36.4) p = 0.0003). Conclusion This prospective observational trial shows the influence of insufflated, non-humidified carbon dioxide at room temperature on abdominal temperature during laparoscopic surgery. We show that carbon dioxide applied at these conditions decreases abdominal temperature and therefore might be a risk factor for perioperative hypothermia.

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Faculty Opinions recommendation of Circadian disruption of body core temperature and rest-activity rhythms after general (propofol) anesthesia in rats.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1162503.624034 ◽

2009 ◽

Author(s):

Misha Perouansky

Keyword(s):

Core Temperature ◽

Circadian Disruption ◽

Body Core Temperature ◽

Activity Rhythms ◽

Body Core ◽

Rest Activity

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The recommended Threshold Limit Values for heat exposure fail to maintain body core temperature within safe limits in older working adults

Journal of Occupational and Environmental Hygiene ◽

10.1080/15459624.2017.1321844 ◽

2017 ◽

Vol 14 (9) ◽

pp. 703-711 ◽

Cited By ~ 13

Author(s):

Dallon T. Lamarche ◽

Robert D. Meade ◽

Andrew W. D'Souza ◽

Andreas D. Flouris ◽

Stephen G. Hardcastle ◽

...

Keyword(s):

Core Temperature ◽

Heat Exposure ◽

Body Core Temperature ◽

Limit Values ◽

Threshold Limit Values ◽

Working Adults ◽

Threshold Limit ◽

Body Core ◽

Safe Limits

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Hypothalamic paraventricular nucleus is critical for renal vasoconstriction elicited by elevations in body temperature

AJP Renal Physiology ◽

10.1152/ajprenal.00488.2007 ◽

2008 ◽

Vol 294 (2) ◽

pp. F309-F315 ◽

Cited By ~ 12

Author(s):

Joo Lee Cham ◽

Emilio Badoer

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Blood Flow ◽

Renal Blood Flow ◽

Core Temperature ◽

Paraventricular Nucleus ◽

Hypothalamic Paraventricular Nucleus ◽

Body Core Temperature ◽

Control Group ◽

Body Core

Redistribution of blood from the viscera to the peripheral vasculature is the major cardiovascular response designed to restore thermoregulatory homeostasis after an elevation in body core temperature. In this study, we investigated the role of the hypothalamic paraventricular nucleus (PVN) in the reflex decrease in renal blood flow that is induced by hyperthermia, as this brain region is known to play a key role in renal function and may contribute to the central pathways underlying thermoregulatory responses. In anesthetized rats, blood pressure, heart rate, renal blood flow, and tail skin temperature were recorded in response to elevating body core temperature. In the control group, saline was microinjected bilaterally into the PVN; in the second group, muscimol (1 nmol in 100 nl per side) was microinjected to inhibit neuronal activity in the PVN; and in a third group, muscimol was microinjected outside the PVN. Compared with control, microinjection of muscimol into the PVN did not significantly affect the blood pressure or heart rate responses. However, the normal reflex reduction in renal blood flow observed in response to hyperthermia in the control group (∼70% from a resting level of 11.5 ml/min) was abolished by the microinjection of muscimol into the PVN (maximum reduction of 8% from a resting of 9.1 ml/min). This effect was specific to the PVN since microinjection of muscimol outside the PVN did not prevent the normal renal blood flow response. The data suggest that the PVN plays an essential role in the reflex decrease in renal blood flow elicited by hyperthermia.

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MK801 impairs thermoregulation in the heat

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y02-055 ◽

2002 ◽

Vol 80 (3) ◽

pp. 226-232 ◽

Cited By ~ 5

Author(s):

Frédéric Canini ◽

Nadine Simler ◽

Lionel Bourdon

Keyword(s):

Locomotor Activity ◽

Nmda Receptor ◽

Receptor Antagonist ◽

Core Temperature ◽

Exposure Duration ◽

Heat Exposure ◽

Nmda Receptor Antagonist ◽

Dopamine Metabolism ◽

Body Core Temperature ◽

Body Core

The effects of MK801 (dizocilpine), a glutamate NMDA receptor antagonist, on thermoregulation in the heat were studied in awake rats exposed to 40°C ambient temperature until their body core temperature reached 43°C. Under these conditions, MK801-treated rats exhibited enhanced locomotor activity and a steady rise in body core temperature, which reduced the heat exposure duration required to reach 43°C. Since MK801-treated rats also showed increased striatal dopaminergic metabolism at thermoneutrality, the role of dopamine in the MK801-induced impairment of thermoregulation in the heat was determined using co-treatment with SCH23390, a dopamine D1 receptor antagonist. SCH23390 normalized the locomotor activity in the heat without any effect on the heat exposure duration. These results suggest that the MK801-induced impairment of thermoregulation in the heat is related to neither a dopamine metabolism alteration nor a locomotor activity enhancement.Key words: heatstroke, NMDA receptor, thermoregulation, dopamine, locomotion.

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