Robert D. Meade

University of Ottawa · School of Human Kinetics

Aging is associated with an elevated risk of heat-related mortality and morbidity, attributed, in part, to declines in thermoregulation. However, comparisons between young and older adults have been limited to brief exposures (1-4 hours), which may not adequately reflect the duration or severity of the heat stress experienced during heat waves. We...

With rising global temperatures, heat-related mortality is increasing, particularly among older adults. While this is often attributed to declines in thermoregulatory function, little is known regarding the effect of age on the cellular processes associated with mitigating heat-induced cytotoxicity. We compared key components of the cellular stress...

Background: Health agencies, including the U.S. Centers for Disease Control and Prevention and the World Health Organization, recommend that heat-vulnerable older adults without home air-conditioning should visit cooling centers or other air-conditioned locations (e.g., a shopping mall) during heat waves. However, experimental evidence supporting...

More frequent and intense periods of extreme heat (heatwaves) represent the most direct challenge to human health posed by climate change. Older adults are particularly vulnerable, especially those with common age-associated chronic health conditions (e.g., cardiovascular disease, hypertension, obesity, type 2 diabetes, chronic kidney disease). In...

The heat-related health burden is expected to persist and worsen in the coming years due to an ageing global population and climate change. Defining the breadth and depth of our understanding of age-related changes in thermoregulation can identify underlying causes and strategies to protect vulnerable individuals from heat. We conducted the first s...

Heat waves can cause dangerous elevations in body temperature that can compromise cellular function and increase the risk of heat stroke and major cardiovascular events. Visiting a cooling center or other air-conditioned location is commonly recommended by health agencies to protect heat-vulnerable older persons but the associated cellular effects...

Unlabelled: Public health agencies recommend that older adults without home air-conditioning visit cooling centres to mitigate indoor overheating during heat waves. However, there is little evidence regarding their influence on self-reported environmental symptoms and mood-state after returning to the heat. Methods: Forty adults (64-79 years) un...

Most heat-related deaths occur due to major adverse cardiovascular events. While recent studies have evaluated resting cardiovascular responses to peak outdoor conditions experienced during heat waves, heat-related deaths occur most often in the home, where conditions can differ substantially from the outdoors. In this randomized trial (ClinicalTri...

New findings: What is the central question of this study? Is the impairment in heat dissipation during exercise observed in men with type 2 diabetes related to glycaemic control (indexed by glycated haemoglobin; haemoglobin A1c )? What is the main finding and its importance? No association was found between haemoglobin A1c (range: 5.1-9.1%) and wh...

Adverse Childhood Experiences (ACEs) are known to contribute to later mental health. Conversely, Benevolent Childhood Experiences (BCEs) may buffer against mental health difficulties. The importance of ACEs and BCEs for mental health of both parents and children may be most obvious during periods of stress, with potential consequences for functioni...

Introduction: Hormonal intrauterine devices (IUDs) contain the progestin levonorgestrel, which may impair sweating and skin vasodilation. However, whether these alterations translate to reductions in whole-body heat loss (WBHL) is unknown. We evaluated the hypothesis that WBHL would be attenuated in IUD-users compared to non-users during exercise i...

The mid-luteal phase of the menstrual cycle is characterized by an upward shift in basal body core temperature secondary to elevated circulating estradiol and progesterone levels as compared to the early-follicular phase. This elevation in body core temperature, perhaps together with increased estradiol-mediated cutaneous vasodilation, may increase...

Most heat-related deaths and hospitalizations occur in older adults, who spend the majority of their time in the home. However, recent studies aimed at improving our understanding of the physiological challenge posed by extreme heat events (EHE) have exposed participants to peak outdoor conditions, which differ markedly from those occurring indoors...

New findings: What is the central question of this study? Does acute intradermal administration of the antioxidant ascorbate augment local forearm cutaneous vasodilatation and sweating via nitric oxide synthase (NOS)-dependent mechanisms during exercise-heat stress in older adults with uncomplicated controlled hypertension? What is the main findin...

Aging is associated with attenuated sweat gland function, which has been suggested to occur in a peripheral-to-central manner. However, evidence supporting this hypothesis remains equivocal. We revisited this hypothesis by evaluating the sweat rate across the limbs and trunk in young and older men during whole-body, passive heating. A water-perfuse...

Heat-stress induced dehydration is associated with extracellular hyperosmolality. To counteract the associated stress, cells employ cytoprotective mechanisms, including autophagy, however, the autophagic response to hyperosmotic stress has yet to be evaluated in humans. Thus, we investigated autophagy and associated cellular stress pathways (the he...

Metaboreflex activation augments sweating during mild-to-moderate hyperthermia in euhydrated (isosmotic isovolemic) individuals. Recent work indicates that extracellular hyperosmolality may augment metaboreflex-mediated elevations in sympathetic nervous activity. Our primary objective was therefore to test the hypothesis that extracellular hyperosm...

Background: Transcranial Doppler (TCD) measurements poorly predict vasospasm in patients with aneurysmal subarachnoid hemorrhage (aSAH). Variability descriptors of mean cerebral blood flow velocity (mean-CBFV) may improve this prediction. We assessed the feasibility of generating reliable mean-CBFV variability metrics using extended TCD recordings...

Purpose: Time-weighted averaging is used in occupational heat stress guidelines to estimate the metabolic demands of variable-intensity work. However, compared to constant-intensity work of the same time-weighted average metabolic rate, variable-intensity work may cause decrements in total heat loss (dry + evaporative heat loss) that exacerbate he...

Laser-Doppler flowmetry (LDF) is commonly used to assess cutaneous vasodilatation responses, but its reliability (i.e. consistency) during whole-body passive heating is unknown. We therefore assessed the reliability of LDF-derived indices of cutaneous vasodilatation during incremental whole-body heating. Fourteen young men (age: 24 (SD 5) years) co...

With the increasing threat of climate change and the accompanying rise in the frequency and severity of extreme heat events, there are growing health concerns for heat-vulnerable elderly adults. Elderly adults are at increased risk of developing heat-related injuries, in part due to age-related declines in thermoregulatory and cellular function. Re...

Observed individual variability in cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV) is extensive, especially during exposure to stressors such as heat. A large part of the observed variation may be related to the reliability (consistency) of the measurement. We therefore examined the test-retest reliability of cBRS and HRV mea...

The ventilated capsule technique is widely used to measure time-dependent changes in sweating in humans. However, evaluations of its reliability (consistency) have been restricted to the forearm, despite extensive regional heterogeneity in the sweating response. Given the importance of such information for experimental design, statistical analysis...

Key points: In humans, hypohydration attenuates sweat secretion and attenuates whole-body heat loss, probably to mitigate further fluid losses and thereby support blood pressure regulation. Recently, however, we demonstrated that the hypohydration-mediated reduction in net whole-body heat exchange (evaporative heat loss - dry heat gain) was blunte...

In studies of human thermoregulation, ingestible temperature pills are being increasingly used as a convenient alternative to more clinically relevant indices of deep-body (core) temperature (e.g., rectal temperature). It remains unclear whether the time between pill ingestion and the measurement period influences the validity of telemetry pills as...

Susceptibility to heat illness during physically demanding work in hot environments is greater on the second of two consecutive workdays. While it has been demonstrated that heat storage is exacerbated on the second compared to first workday in older workers (50–65 yr), the effects on heart rate variability (HRV), an established surrogate of cardia...

New findings: What is the central question of this study? Does higher aerobic fitness, indexed by peak oxygen uptake (V̇O2 peak), attenuate the age-related decline in thermoregulatory function during exercise in the heat? What is the main finding and its importance? When assessed in aerobically fit and less fit adults (V̇O2 peak: ∼30 vs. ∼50 mL/kg...

New findings: What is the central question of this study? Repeated heat exposure during the summer months can enhance heat loss in humans (seasonal heat acclimatization), but does the magnitude of that enhancement differ between young and older adults when assessed during passive heat exposure? What is the main finding and its importance? While se...

Prepubertal children (6-12 years) differ from adults in various morphological and physiological factors that may influence thermoregulatory function; however, experimental evidence of meaningful child-adult differences in heat strain during exercise-heat stress is sparse, despite numerous studies. While we appreciate the challenges associated with...

Purpose: Current occupational heat stress guidelines rely on time-weighted averaging to quantify the metabolic demands of variable-intensity work. However, variable-intensity work may be associated with impairments in whole-body total heat loss (dry+evaporative heat loss), especially in older workers, which exacerbate heat strain relative to const...

Lower-limb intermittent sequential pneumatic compression (ISPC) improves circulation and vascular function in elderly adults. We evaluated the hypothesis that ISPC would also augment whole-body heat loss (WBHL) in elderly adults (aged 69 ± 4 years) resting in extreme heat (40 °C). While ISPC increased mean arterial pressure (91 ± 9 mm Hg) relative...

Purpose: Sweat-induced fluid loss during prolonged exercise-heat stress can compromise cardiovascular and thermoregulatory function, although its effects on cardiac autonomic modulation remain unclear. We therefore examined heart rate variability (HRV) and recovery (HRRec), as surrogates of cardiac autonomic modulation, during and following prolon...

Blood pressure (BP) is an important physiological marker of human health. It is commonly measured by a cuff-based monitor via either auscultatory or oscillometric methods. Recently, significant research has been conducted to mathematically estimate BP from pulse transit time (PTT) to enable cuffless and continuous BP measurement. In this research,...

Background: Protease-activated receptor 2 (PAR2) exists in the cutaneous vasculature and eccrine sweat glands. We previously showed that in young habitually active men, exogenous PAR2 activation via the agonist SLIGKV-NH2 had no effect on heat loss responses of cutaneous vasodilatation and sweating during rest or exercise in the heat. However, age...

New findings: What is the central question of this study? The aim was to identify the greatest contributor(s) to the variation in whole-body heat exchange, as assessed using direct calorimetry, among young men and women with heterogeneous characteristics during exercise at increasing metabolic heat production rates in dry heat. What is the main fi...

Age-related impairments in cutaneous vascular conductance (CVC) and sweat rate (SR) during exercise may result from increased arginase activity, which can attenuate endogenous nitric oxide (NO) production. We therefore evaluated whether arginase inhibition modulates these heat-loss responses in young (n = 9, 23 ± 3 yr) and older (n = 9, 66 ± 6 yr)...

Aim Aging and hypohydration independently attenuate heat dissipation during exercise; however, the interactive effects of these factors remain unclear. We assessed the hypothesis that aging suppresses hypohydration‐induced reductions in whole‐body heat loss during exercise in the heat. Methods On two occasions, eight young (mean [SD]: 24 [4] years...

We recently reported that the nonselective cyclooxygenase (COX) inhibitor ketorolac attenuated sweating but not cutaneous vasodilation during moderate-intensity exercise in the heat. However, the specific contributions of COX-1 and COX-2 to the sweating response remained to be determined. We tested the hypothesis that COX-1 but not COX-2 contribute...

Workers in many industries (e.g., mining, electric utilities, other) often perform consecutive days of prolonged (~10-12 hours), strenuous work in the heat. These conditions cause considerable heat strain over an entire workday, which can lead to dangerous increases in core temperature [1] that elevate the risk of heat illness and even death. Howev...

Protease-activated receptor 2 (PAR2) exists in the endothelial cells of skin vessels and eccrine sweat glands. We evaluated the hypothesis that exogeneous activation of PAR2 augments cutaneous vasodilatation and sweating during rest and exercise in the heat. In ten young males (23±5 years), cutaneous vascular conductance (CVC) and sweat rate were m...

Purpose: Prolonged work in the heat may exacerbate the rise in core temperature on the next work day, especially in older workers who display impairments in whole-body heat loss that increase body heat storage and core temperature relative to young adults during heat stress. We therefore evaluated whether whole-body heat loss in older adults was i...

Following exercise, mean arterial pressure (MAP) is reduced ~5-10 mmHg from pre-exercise baseline. In non-endurance-trained males, post-exercise hypotension results from peripheral vasodilation not offset by increased cardiac output (CO). By contrast, post-exercise hypotension occurs through a reduction in CO from pre-exercise baseline in endurance...

We assessed the role of purinergic P2 receptors in the regulation of cutaneous vasodilation in young adults at rest and during intermittent moderate-intensity exercise in the heat (35°C). P2 receptor blockade augmented resting cutaneous vasodilation but had no influence during and following exercise. This increase was partly diminished by nitric ox...

New findings: What is the central question of this study? It remains to be determined whether type 2 diabetes attenuates muscarinic and nicotinic cutaneous vasodilatation and sweating as well as purinergic cutaneous vasodilatation. What is the main finding and its importance? We show that type 2 diabetes specifically attenuates purinergic cutaneou...

Purpose: Heat strain is known to be exacerbated on the second of consecutive work days. We therefore evaluated whether prolonged work in the heat would impair whole-body heat loss capacity on the next day. Methods: To evaluate this possibility, we assessed changes in whole-body heat exchange and heat storage in eight young (26 years (SD 4)) male...

The roles of nitric oxide synthase (NOS), reactive oxygen species (ROS) and angiotensin II type 1 receptor (AT1R) activation in regulating cutaneous vasodilation and sweating during prolonged (≥60 min) exercise are currently unclear. Moreover, it remains to be determined whether fluid replacement (FR) modulates the above thermoeffector responses. T...

Purpose: In this case report, we evaluated physiological strain in electrical utilities workers during consecutive work shifts in hot outdoor conditions. Methods: Four highly experienced electrical utilities workers were monitored during regularly scheduled work performed in hot conditions (∼34˚C) on two consecutive days. Worker hydration (urine...

PURPOSE: The American Conference of Governmental and Industrial Hygienists (ACGIH®) Threshold Limit Values (TLV® guidelines) for work in the heat consist of work-rest (WR) allocations designed to ensure a stable core temperature that does not exceed 38°C. However, the TLV® guidelines have not been validated in older workers. This is an important sh...

Aging and chronic disease such as type 2 diabetes (T2D) are associated with impairments in the body's ability to dissipate heat. To reduce the risk of heat-related injuries in these heat vulnerable individuals, it is necessary to identify interventions that can attenuate this impairment. We evaluated the hypothesis that intradermal administration o...

Purpose: We evaluated physiological responses during exercise at a fixed evaporative requirement for heat balance (Ereq) but varying combinations of metabolic and environmental heat load. Methods: Nine healthy, physically active males (age: 46±8 years) performed four experimental sessions consisting of 75-min of semi-recumbent cycling at various...

We evaluated the association between aerobic power (defined by peak oxygen consumption; VO2peak) and the contribution of nitric oxide synthase (NOS) to the sweating response in young and older individuals during exercise in the heat. Data from 44 young (24 ± 1 years) and 48 older (61 ± 2 years) males with mean VO2peak of 47.8 ± 2.4 (range, 28.0-62....

Na+/K+-ATPase has been shown to regulate the sweating and cutaneous vascular responses during exercise; however, similar studies have not been conducted to assess the roles of the Na-K-2Cl co-transporter (NKCC) and K+ channels. Additionally, it remains to be determined if these mechanisms underpinning the heat loss responses differ with exercise in...

Nitric oxide (NO) increases cutaneous blood flow; however, the underpinning mechanism(s) remains to be elucidated. We hypothesized that the cutaneous blood flow response during intradermal administration of sodium nitroprusside (SNP, a NO donor) is regulated by calcium-activated potassium (KCa) channels and cyclooxygenase (COX) in young adults. We...

Purpose: We evaluated core temperature responses and the change in body heat content ([INCREMENT]H b ) during work performed according to the Threshold Limit Values (TLVs), which are designed to ensure a stable core temperature that does not exceed 38.0°C. Methods: Nine young males performed a 120-min work protocol consisting of cycling at a fix...

Many studies have aimed to identify the controllers of sweating using ventilated capsules with intradermal microdialysis. It is unclear, however, if the surface area covered by the capsule influences the observed response as a result of differences in the number of sweat glands affected by the infused pharmacological agent relative to the total gla...

Key points: Nitric oxide synthase (NOS) contributes to sweating and cutaneous vasodilatation during exercise in the heat. Similarly, reports show that Na(+) /K(+) -ATPase activation can modulate sweating and microvascular circulation. In light of the fact that NO can activate Na(+) /K(+) -ATPase, we evaluated whether there is an interaction betwee...

Nitric oxide synthase (NOS) contributes to sweating and cutaneous vasodilation during exercise in younger adults. We hypothesized that endothelial NOS (eNOS) and neuronal NOS (nNOS) mediate NOS-dependent sweating, whereas eNOS induces NOS-dependent cutaneous vasodilation in younger adults exercising in the heat. Further, aging may upregulate induci...

We assessed the physical demands associated with electrical utilities work in North America and how they influence the level of thermal and cardiovascular strain experienced. Three common job categories were monitored as they are normally performed in thirty-two electrical utility workers: i) Ground Work (n=11), ii) Bucket Work (n=9), and iii) Manu...

Acetylcholine released from cholinergic nerves is a key neurotransmitter contributing to heat stress-induced cutaneous vasodilation and sweating. Given that sympathetic cholinergic nerves also release ATP, ATP may play an important role in modulating cholinergic cutaneous vasodilation and sweating. However, the pattern of response may differ betwee...

Nitric oxide (NO)-dependent cutaneous vasodilation is reportedly diminished during exercise performed at high (700 W) relative to moderate (400 W) rate of metabolic heat production. We evaluated whether this impairment results from increased oxidative stress associated with an accumuluation of reactive oxygen species (ROS) during high intensity exe...

PURPOSE: The purpose of this study was to assess the physiological strain experienced by North American electrical utility workers during the performance of their normal work duties in heat stressed conditions. METHODS: Three common job categories were monitored as they are normally performed in thirty-two electrical utility workers: i) Ground Work...