Effect of alteration of pheripheral blood flow on the central circulation in man during supine cycling in different ambient temperatures

Energetic responses of head-out water immersion at different temperatures during post-exercise recovery and its consequence on anaerobic mechanical power

PURPOSE

While exercise recovery may be beneficial from a physiological point of view, it may be detrimental to subsequent anaerobic performance. To investigate the energetic responses of water immersion at different temperatures during post-exercise recovery and its consequences on subsequent anaerobic performance, a randomized and controlled crossover experimental design was performed with 21 trained cyclists.

METHOD

Participants were assigned to receive three passive recovery strategies during 10 min after a Wingate Anaerobic Test (WAnT): control (CON: non-immersed condition), cold water immersion (CWI: 20 ℃), and hot water immersion (HWI: 40 ℃). Blood lactate, cardiorespiratory, and mechanical outcomes were measured during the WAnT and its recovery. Time constant (τ), asymptotic value, and area under the curve (AUC) were quantified for each physiologic parameter during recovery. After that, a second WAnT test and 10-min recovery were realized in the same session.

RESULTS

Regardless the water immersion temperature, water immersion increased [Formula: see text] (+ 18%), asymptote ([Formula: see text]+ 16%, [Formula: see text] + 13%, [Formula: see text] + 17%, HR + 16%) and AUC ([Formula: see text]+ 27%, [Formula: see text] + 18%, [Formula: see text] + 20%, HR + 25%), while decreased [Formula: see text] (- 33%). There was no influence of water immersion on blood lactate parameters. HWI improved the mean power output during the second WAnT (2.2%), while the CWI decreased 2.4% (P < 0.01).

CONCLUSION

Independent of temperature, water immersion enhanced aerobic energy recovery without modifying blood lactate recovery. However, subsequent anaerobic performance was increased only during HWI and decreased during CWI. Despite higher than in other studies, 20 °C effectively triggered physiological and performance responses. Water immersion-induced physiological changes did not predict subsequent anaerobic performance.

The Cardiovascular Reserve Index-A Noninvasive Clinical Insight Into Heat Intolerance

OBJECTIVE

To noninvasively explore the heat intolerance condition during exercise-heat stress by assessing cardiovascular (CV) performance.

DESIGN

Prospective study of participants undergoing a standard heat-tolerance test (HTT).

SETTING

Institutional study.

PARTICIPANTS

Ninety-five young males: 16 heat-intolerant (HI) and 79 heat-tolerant (HT).

INTERVENTIONS

Cardiovascular performance during an HTT was estimated by heart rate (HR) and blood pressure measurements.

MAIN OUTCOME MEASURES

The sensitivity of the cardiovascular reserve index (CVRI) and the dynamic heart rate reserve (dHRR) index to predict heat intolerance was compared.

RESULTS

A significant difference in the CV reserve during exercise-heat stress was exhibited between the HI and the HT groups. Starting at a similar level, the reduction in the CV reserve at HTT endpoint was much greater in the HI than the HT individuals (P < 0.0001), as depicted by both the CVRI and the dHRR. This result indicates a greater utilization of the CV reserve by HI individuals. The CVRI is likely to be better predictor of heat intolerance than the dHRR because the partial area under the curve in the high sensitivity (>90%) region of its receiver operating characteristic curve is higher (93.2 vs 76.8).

CONCLUSIONS

More than being a predictor, the CVRI may provide a new clinical insight into heat intolerance because it noninvasively characterizes the efficiency of an individual's thermoregulatory mechanism and hints that an impaired CV reserve might underlie heat intolerance. The CVRI provides a noninvasive measurement of thermoregulation, which has been long awaited to enable on-field studies and dynamic monitoring of heat-exposed task forces.

Cardiovascular and thermal consequences of protective clothing: a comparison of clothed and unclothed states

We have undertaken a laboratory-based examination of the cardiovascular and thermal impact of wearing thermal (heat) protective clothing during fatiguing exercise in the heat. Seven males completed semi-recumbent, intermittent cycling (39.6 degrees C, 45% relative humidity) wearing either protective clothing or shorts (control). Mean core and skin temperatures, cardiac frequency (f(c)), stroke volume (Q), cardiac output (Q), arterial pressure, forearm blood flow (Q(f)), plasma volume change, and sweat rates were measured. In the clothed trials, subjects experienced significantly shorter times to fatigue (52.5 vs. 58.9 min), at lower peak work rates (204.3 vs. 277.4 W), and with higher core (37.9 degrees vs. 37.5 degrees C) and mean skin temperatures (37.3 degrees vs. 36.9 degrees C). There was a significant interaction between time and clothing on f(c), such that, over time, the clothing effect became more powerful. Clothing had a significant main affect on Q, but not Q, indicating the higher Q was chronotropically driven. Despite a greater sweat loss when clothed (923.0 vs. 547.1 g.m(-2) x h(-1); P<0.05), Q(f) and plasma volume change remained equivalent. Protective clothing reduced exercise tolerance, but did not affect overall cardiovascular function, at the point of volitional fatigue. It was concluded that, during moderately heavy, semi-recumbent exercise under hot, dry conditions, the strain on the unclothed body was already high, such that the additional stress imparted by the clothing ensemble represented a negligible, further impact upon cardiovascular stability.

Thermoregulatory responses in post-coronary artery bypass surgery and healthy males during moderate exercise in warm and cool environments

PURPOSE

The purpose of this study was to determine and compare the thermoregulatory and hemodynamic responses to moderate intensity exercise (60% of peak oxygen consumption [.VO(2peak)]) in warm (35 degrees C, 45% relative humidity) and cool (18 degrees C, 65% relative humidity) environments in men who had previously undergone coronary artery bypass graft (CABG) surgery and healthy control subjects, matched for age and body composition.

METHODS

Fourteen post-CABG men and 16 healthy control subjects were recruited and walked 40 minutes at a moderate intensity, in randomized order, in warm and cool environments (on separate days). Measures of heart rate, systolic and diastolic blood pressures, rating of perceived exertion, core (rectal)(T(c)) and mean skin temperatures (T(sk)), oxygen consumption (.VO(2peak)), sweat rate, and blood lactate were taken.

RESULTS

Both groups showed a larger increase (P <.05) in T(c) and rate-pressure product during exercise in the warm compared with the cool environment. However, T(c) and rate pressure product were significantly lower (P <.05), and systolic blood pressure decreased slightly with exercise duration (P <.05) in the CABG group compared with the control group in the warm environment. Heart rate, T(sk), percent .VO(2peak), blood lactate, sweat rate, and rating of perceived exertion did not differ significantly between the groups in either climate and no subject had ischemia or arrhythmia during test procedures.

CONCLUSIONS

These results indicate that clinically stable men with revascularized coronary artery disease are able to cope as well as healthy controls with the thermoregulatory and cardiovascular demands of 40 minutes of moderate intensity exercise in warm and cool environments.