Echocardiographic changes following active heat acclimation

Abstract

Heat adaption through acclimatisation or acclimation improves cardiovascular stability by maintaining cardiac output due to compensatory increases in stroke volume. The main aim of this study was to assess whether 2D transthoracic echocardiography (TTE) could be used to confirm differences in resting echocardiographic parameters, before and after active heat acclimation (HA). Thirteen male endurance trained cyclists underwent a resting blinded TTE before and after randomisation to either 5 consecutive daily exertional heat exposures of controlled hyperthermia at 32 with 70% relative humidity (RH) (HOT) or 5-days of exercise in temperate (21 with 36% RH) environmental conditions (TEMP). Measures of HA included heart rate, gastrointestinal temperature, skin temperature, sweat loss, total non-urinary fluid loss (TNUFL), plasma volume and participant's ratings of perceived exertion (RPE). Following HA, the HOT group demonstrated increased sweat loss (p = 0.01) and TNUFL (p = 0.01) in comparison to the TEMP group with a significantly decreased RPE (p = 0.01). On TTE, post exposure, there was a significant comparative increase in the HOT group in left ventricular end diastolic volume (p = 0.029), SV (p = 0.009), left atrial volume (p = 0.005), inferior vena cava diameter (p = 0.041), and a significant difference in mean peak diastolic mitral annular velocity (e’) (p = 0.044). Cardiovascular adaptations to HA appear to be predominantly mediated by improvements in increased preload and ventricular compliance. TTE is a useful tool to demonstrate and quantify cardiac HA.

Improvements in orthostatic tolerance with physical training are augmented with heat acclimation; a randomised controlled trial

“…We also did not measure the CONTROL groups training burden on the passive days in the HEAT group however cardiovascular strain was similar between groups. Echocardiography has signi cant inter-observer and intra-observer variability particularly in the measurement of LV volumes [75] which may explain why we were unable to demonstrate a signi cant increase in LVEDV in the HEAT group, in comparison to CONTROL, during this study in comparison to previous [71]. However we used the same echocardiographer to limit interobserver variability, who was blinded to the participants intervention.…”

“…Preliminary echocardiographic data [71]coupled with these data suggests improvements in diastolic function with heat acclimation above that of exercise alone. We know that exercise, regardless of weight loss, reduces occurrence and symptoms of atrial brillation and this is, in part, thought to mediated by improvements in diastolic dysfunction [72].…”

Vascular compliance and left ventricular compliance cross talk: Implications for using long-term heat acclimation in cardiac care

“…Recent human translational studies, using 1) Short-term isothermic heat acclimation achieved by cycling at a 32°C and 70% R.H. (Relative Humidity) at an exercise intensity of 2.0–2.7 W kg-1 for 5 days compared to daily cycling for 90 min, in temperate environmental conditions of 21.5°C and 36% R.H. and 2) Passive heat acclimation (12 d, −48°C, 50 min) ( Parsons et al, 2020 ; Wilson et al, 2020 ) indicated that short-term, active heat acclimation enhances ventricular compliance, along with physiological thermoregulatory responses (e.g., plasma volume expansion, decreased heart rate, altered cardiac filling pressure and increased stroke volume), rather than changes in cellular elasticity. No intrinsic cellular or molecular explanation for these responses were provided.…”

“…The impact of passive LTHA in rats confirms the findings of Horowitz et al (1986a) but differs from the effects of 5 days of passive HA in humans ( Trachsel et al, 2020 ), where minimal adaptive responses were detected in the heart. While Parsons et al (2020) and Trachsel et al (2020) , present pre versus post treatment comparisons within the same group, we performed within and between (namely, comparisons between all stressors employed) group analyses of the long-term impacts of the stressors, when hormonal responses (e.g., reduced thyroxin) leading to myosin phenotype changes take place ( Horowitz, 2003 ). Notably, the impact of seasonal temperatures on slow myosin were reported in Camelus dromedarius ( Abdelhadi et al, 2012 ).…”

Exercise Heat Acclimation With Dehydration Does Not Affect Vascular and Cardiac Volumes or Systemic Hemodynamics During Endurance Exercise

“…For example, exercising Q has been reported to decrease (Wyndham, 1951), remain unchanged (Rowell et al, 1967;Wyndham et al, 1968), or increase (Nielsen et al, 1993) following HA, while data regarding human cardiac volumes, function and systemic blood flow is limited. Recently, passive and active HA regimens were shown to minimally enhance left atrial and ventricular diastolic volumes at rest; however, these responses were not correlated with an increase in BV or lowered HR (Parsons et al, 2020;Wilson et al, 2020). Passive HA with controlled hyperthermia has also failed to induce changes in resting HR, EDV, and SV in thermoneutral conditions (Trachsel et al, 2020).…”