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The impact of exercise and thermal training interventions on thermoregulatory and cardiovascular function in young and post-menopausal females

Bailey, TG (2014) The impact of exercise and thermal training interventions on thermoregulatory and cardiovascular function in young and post-menopausal females. Doctoral thesis, Liverpool John Moores University.

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The female reproductive hormone oestrogen influences cardiovascular and thermoregulatory control. A dramatic decline in oestrogen during the menopause causes cardiovascular and thermoregulatory dysfunction resulting in hot flushes (HFs). HFs consist of feelings of intense heat with rapid increases in cutaneous vasodilation and sweating that severely affect quality of life and increase cardiovascular disease risk. Treatment using hormone replacement therapy for HFs is contraindicated in some symptomatic females meaning an alternative strategy is warranted. Exercise training may reduce HFs; however no study to date has examined the physiological mechanisms that cause changes in the frequency and severity of HFs following a period of exercise training. Exercise training is known to enhance thermoregulatory efficiency via an earlier core temperature onset for cutaneous vasodilation and sweating in pre-menopausal females. Exercise training is also known to positively impact vascular function in the conduit, cutaneous and cerebral vessels and thus can also decrease cardiovascular risk in symptomatic post-menopausal females. Heat acclimation interventions target the same thermoregulatory and cardiovascular physiological mechanisms, and may also be beneficial. The primary aim of this thesis was to (i) examine whether exercise training reduces objectively measured HFs via improving cardiovascular and thermoregulatory dysfunction in symptomatic post-menopausal females, and to (ii) assess the efficacy of an exercise-independent stimulus in improving thermoregulatory and cardiovascular function in pre-menopausal females.Twenty-one symptomatic post-menopausal females completed a 16-week exercise training intervention (n=14, 52±4y, 29±6 kg/m2) or a no-exercise control intervention (n=7, 52±6y, 30±7 kg/m2). Cardiorespiratory fitness (VO2peak) and brachial artery endothelial function was assessed using flow-mediated dilation (FMD). Participants underwent a passive heat stress in a water-perfused suit (~48ºC) to obtain core temperature thresholds and sensitivities for cutaneous vascular conductance (CVC) and sweat rate at two sites (chest and forearm). Middle cerebral artery velocity (MCAv) was measured at rest and throughout the heat stress. All measurements were repeated following the intervention period. HFs reduced by 39 HF•wk (95% CI= 31, 47) following exercise training compared to no change in control. HF-severity reduced by 101 (AU) (95% CI= 80, 121) following exercise training compared to no change in control. VO2peak and FMD improved (P<0.05), along with a lower core temperature following exercise training [0.14ºC (95% CI=0.03, 0.20; P=0.04)]. Sweat rate and CVC body/core temperature thresholds occurred ~0.22ºC earlier alongside an increase in sweating sensitivity, at both sites, following exercise training. Resting MCAv was 3.12 cm/s (95% CI, 1.20, 5.01; P=0.03) higher, with decreases in MCAv attenuated during heat stress, following exercise training.HFs recorded in symptomatic females during the passive heat stress prior to and following the exercise training (n=9) or no-exercise control (n=6) intervention were used to assess changes in thermoregulatory and (cerebro)vascular responses during an acute HF. HFs were objectively identified and divided into eight equal segments, with each segment representing 12.5% of HF duration, for analysis. Exercise training decreased HF duration by 63s (95% CI, 14, 113; P=0.08) compared to a negligible decrease of 17s (95% CI, -43, 66) following control. Chest sweat rate decreased by 0.04 mg•cm2•min-1 (95% CI, 0.02, 0.06; P=0.01) during HFs after exercise training compared to no change in control (P>0.05). This was accompanied by a reduction in chest skin blood flow of 26 AU (95% CI, 21, 30; P=0.01) during HFs following exercise training compared to no change in control (P=0.10). MCAv was attenuated by 3.4 cm/s (95% CI, 0.7, 5.1; P<0.001) during a HF following exercise training compared to control [0.6 cm/s (95% CI, -0.7, 1.8; P=0.93)].Eighteen pre-menopausal females (25±8y) were assigned to 3x30-min of cycling exercise (70% HRmax) or warm water immersion (42ºC) to the level of the sternum for 8-weeks. FMD (P=0.003) and VO2peak (P<0.001) improved following both interventions. Core body temperature reduced by 0.14ºC (95% CI, 0.04, 0.23; P=0.004) following both interventions. Sweat rate mean body temperature thresholds at the chest and forearm occurred 0.10ºC (95% CI=-0.14, 0.33, P<0.001) and 0.19ºC (0.12, 0.23ºC, P<0.001) earlier following the interventions, alongside an increase in sweat rate sensitivity of 1.18 mg•cm2•min-1 (95% CI= 0.68, 1.67; P<0.001) following water immersion compared to 0.28 mg•cm2•min-1 (95% CI= 0.23, 0.78) following exercise training. CVC core temperature thresholds occurred ~0.20ºC earlier at the chest and forearm (P<0.001). Resting MCAv was 2.30 cm/s (95% CI=1.20, 3.34; P<0.001) higher, with decreases in MCAv attenuated during heat stress, following both interventions.The findings from this thesis suggest that reductions in the frequency and severity of HFs with exercise training are mediated by improvements in thermoregulatory function, alongside cerebral, conduit and cutaneous adaptation. This coincided with objective reductions in HF severity following exercise training, with attenuation in the physiological perturbations observed during an acute HF. Consequently, interventions that target thermoregulatory function may be useful in reducing post-menopausal HFs. In keeping with the exercise mediated physiological changes, warm water immersion training also elicits similar favourable thermoregulatory, conduit- and cerebrovascular adaptations to a period of moderate intensity exercise training in pre-menopausal females. Immersion therapy may therefore be applicable to HF-symptomatic post-menopausal females.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Post-menopausal females; Hot flushes; Warm water immersion; Exercise training; Vascular function; Thermoregulatory function
Subjects: R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions: Sport & Exercise Sciences
Date Deposited: 07 Nov 2016 14:16
Last Modified: 07 Nov 2016 14:16
Supervisors: Jones, Helen and Low, David and Cable, Tim
URI: http://researchonline.ljmu.ac.uk/id/eprint/4394

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