Cardiac response to combined moderate heat and exercise in men with coronary artery disease

Effects of Medications on Heat Loss Capacity in Chronic Disease Patients: Health Implications Amidst Global Warming

Pharmacological agents used to treat or manage diseases can modify the level of heat strain experienced by chronically ill and elderly patients via different mechanistic pathways. Human thermoregulation is a crucial homeostatic process that maintains body temperature within a narrow range during heat stress through dry (i.e., increasing skin blood flow) and evaporative (i.e., sweating) heat loss, as well as active inhibition of thermogenesis, which is crucial to avoid overheating. Medications can independently and synergistically interact with aging and chronic disease to alter homeostatic responses to rising body temperature during heat stress. This review focuses on the physiologic changes, with specific emphasis on thermolytic processes, associated with medication use during heat stress. The review begins by providing readers with a background of the global chronic disease burden. Human thermoregulation and aging effects are then summarized to give an understanding of the unique physiologic changes faced by older adults. The effects of common chronic diseases on temperature regulation are outlined in the main sections. Physiologic impacts of common medications used to treat these diseases are reviewed in detail, with emphasis on the mechanisms by which these medications alter thermolysis during heat stress. The review concludes by providing perspectives on the need to understand the effects of medication use in hot environments, as well as a summary table of all clinical considerations and research needs of the medications included in this review. SIGNIFICANCE STATEMENT: Long-term medications modulate thermoregulatory function, resulting in excess physiological strain and predisposing patients to adverse health outcomes during prolonged exposures to extreme heat during rest and physical work (e.g., exercise). Understanding the medication-specific mechanisms of altered thermoregulation has importance in both clinical and research settings, paving the way for work toward refining current medication prescription recommendations and formulating mitigation strategies for adverse drug effects in the heat in chronically ill patients.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Extreme Heat and Cardiovascular Health: What a Cardiovascular Health Professional Should Know

As global temperatures continue to rise, extreme heat events are becoming more frequent and intense. Extreme heat affects cardiovascular health as it is associated with a greater risk of adverse cardiovascular events, especially for adults with preexisting cardiovascular diseases. Nonetheless, the pathophysiology underlying the association between extreme heat and cardiovascular risk remains understudied. Furthermore, specific recommendations to mitigate the effects of extreme heat on cardiovascular health remain limited to guide clinical practice within the context of a warming climate. The overall objective of this review article is to raise awareness that extreme heat poses a risk for cardiovascular health. Specifically, the review discusses why cardiovascular healthcare professionals should care about extreme heat, how extreme heat affects cardiovascular health, and recommendations to minimise the cardiovascular consequences of extreme heat. Future research directions are also provided to further our understating of the cardiovascular health consequences of extreme heat. A better awareness and understanding of the cardiovascular consequences of extreme heat will help cardiovascular health professionals assess the risk and optimise the care of their patients exposed to an increasingly warm climate.

MitoNEET in Perivascular Adipose Tissue Blunts Atherosclerosis under Mild Cold Condition in Mice

Background: Perivascular adipose tissue (PVAT), which surrounds most vessels, is de facto a distinct functional vascular layer actively contributing to vascular function and dysfunction. PVAT contributes to aortic remodeling by producing and releasing a large number of undetermined or less characterized factors that could target endothelial cells and vascular smooth muscle cells, and herein contribute to the maintenance of vessel homeostasis. Loss of PVAT in mice enhances atherosclerosis, but a causal relationship between PVAT and atherosclerosis and the possible underlying mechanisms remain to be addressed. The CDGSH iron sulfur domain 1 protein (referred to as mitoNEET), a mitochondrial outer membrane protein, regulates oxidative capacity and adipose tissue browning. The roles of mitoNEET in PVAT, especially in the development of atherosclerosis, are unknown.

Methods: The brown adipocyte-specific mitoNEET transgenic mice were subjected to cold environmental stimulus. The metabolic rates and PVAT-dependent thermogenesis were investigated. Additionally, the brown adipocyte-specific mitoNEET transgenic mice were cross-bred with ApoE knockout mice. The ensuing mice were subsequently subjected to cold environmental stimulus and high cholesterol diet challenge for 3 months. The development of atherosclerosis was investigated.

Results: Our data show that mitoNEET mRNA was downregulated in PVAT of both peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc1α)- and beta (Pgc1β)-knockout mice which are sensitive to cold. MitoNEET expression was higher in PVAT of wild type mice and increased upon cold stimulus. Transgenic mice with overexpression of mitoNEET in PVAT were cold resistant, and showed increased expression of thermogenic genes. ApoE knockout mice with mitoNEET overexpression in PVAT showed significant downregulation of inflammatory genes and showed reduced atherosclerosis development upon high fat diet feeding when kept in a 16°C environment.

Conclusion: mitoNEET in PVAT is associated with PVAT-dependent thermogenesis and prevents atherosclerosis development. The results of this study provide new insights on PVAT and mitoNEET biology and atherosclerosis in cardiovascular diseases.

Perivascular adipose tissue in vascular function and disease: a review of current research and animal models

Perivascular adipose tissue (PVAT), long assumed to be nothing more than vessel-supporting connective tissue, is now understood to be an important, active component of the vasculature, with integral roles in vascular health and disease. PVAT is an adipose tissue with similarities to both brown and white adipose tissue, although recent evidence suggests that PVAT develops from its own precursors. Like other adipose tissue depots, PVAT secretes numerous biologically active substances that can act in both autocrine and paracrine fashion. PVAT has also proven to be involved in vascular inflammation. Although PVAT can support inflammation during atherosclerosis via macrophage accumulation, emerging evidence suggests that PVAT also has antiatherosclerotic properties related to its abilities to induce nonshivering thermogenesis and metabolize fatty acids. We here discuss the accumulated knowledge of PVAT biology and related research on models of hypertension and atherosclerosis.

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.