Texas Health Presbyterian Hospital Denton

Heat waves are associated with increased fatalities from adverse cardiovascular events attributed to the negative effects of heat on cardiac function. However, scientific understanding of acute cardiac adjustments to heat has come primarily from laboratory experiments employing insulated and encapsulated heating modalities, most commonly water-perfused suits. We evaluated whether findings from those studies reflect cardiac responses during more natural exposures to hot ambient conditions simulated in climate-controlled chambers by synthesizing the findings from over 400 laboratory-based heat exposure studies (6858 participant-exposures) published between 1961-2024. Among all included studies, median (interquartile range) elevations in core temperature and heart rate from baseline to end-exposure were 0.9 (0.5-1.3)°C and 27 (15-40) beats/min. Multilevel mixed-effects meta-analyses revealed exacerbated elevations in heart rate, cardiac output, and rate pressure product (estimate of cardiac workload) and blunted falls in systolic pressure in participants heated via encapsulated modalities. Leveraging the large dataset, we also provide empirical estimates of body temperature and cardiovascular responses to a wide range of conditions experienced during heat waves. With rising global temperatures, ecologically-minded physiological research is needed to improve understanding of the effects of heat stress on cardiac responses and further the development of robust climate health models and evidence-based heat-health guidance.

We tested the hypothesis that skin wetting would attenuate, whereas electric fans would increase, thermal and cardiac strain in older adults exposed to very hot and dry heat. Twenty-three older adults (66-84 yr) were exposed (randomized) to 3 h of ambient heating (47°C and 15% relative humidity) with water spray, fan use, water spray + fan use, or no cooling intervention. We assessed thermal, cardiovascular, and cardiac responses. Compared with control, water spray reduced the increase in core temperature by -0.24°C [95% CI: -0.42, -0.06] (P = 0.007), ending skin temperature by -2.1°C [-2.6, -1.5] (P < 0.001), sweat rate by -0.12 L/h [-0.15, -0.09] (P < 0.001), ending heart rate by -5 beats/min [-8, -1] (P = 0.004), and ending rate pressure product by -1,027 beats/min·mmHg [-1,733, -321] (P = 0.004). Fan use augmented the increase in core temperature by 0.60°C [0.36, 0.84] (P < 0.001), ending skin temperature by 1.5°C [0.9, 2.1] (P < 0.001), sweat rate by 0.17 L/h [0.13, 0.20] (P < 0.001), ending heart rate by 15 beats/min [8, 23] (P < 0.001), and ending rate pressure product by 2,326 beats/min·mmHg [780, 3,872] (P = 0.003). Water spray + fan had no effect on core temperature (P = 0.308) or skin temperature (P = 0.114). However, sweat rate (0.07 L/h [0.001, 0.13]; P = 0.031) and ending heart rate (8 beats/min [1, 15]; P = 0.046) were higher with water spray + fan. Water spray attenuates, whereas fans increase, thermal and cardiac strain in older adults exposed to very hot and dry conditions. Thus, electric fans are not advised as a cooling intervention under the assessed conditions. Water spray offers some cooling benefits when access to energy is unavailable.NEW & NOTEWORTHY Extreme heat increases morbidity and mortality, particularly among older adults. Air conditioning can mitigate heat strain but may be inaccessible; thus, there is a need to identify nonair conditioning-dependent cooling strategies. We show that water spray attenuates, whereas fans increase, thermal and cardiac strain in older adults exposed to very hot and dry conditions. Importantly, our findings highlight that water spray offers the greatest benefit for individuals who are vulnerable to hyperthermia and tachycardia associated with heat stress.

Older individuals are at a greater risk for adverse cardiovascular events during extreme heat exposure. However, detailed characterization of their cardiac responses to environmental heat exposure is lacking. In 20 young (18-39 yr) and 20 older (>65 yr) adults (50% male in both groups), we document the echocardiography-assessed left ventricular responses to a very hot and dry [DRY, 47°C and 15% relative humidity (RH)] and hot humid (HUMID, 41°C and 40% RH) 3-h heat exposure, with intermittent bouts of light physical activity throughout. In both climates and in both age groups, heat stress 1) increased cardiac output by ∼0.7 ± 0.8 L/min, 2) decreased stroke volume by ∼7 ± 10 mL, and 3) augmented diastolic function through increased atrial contribution to filling by 5 ± 5%. In the DRY climate, mitral annular systolic velocity (s') increased to a greater extent in older subjects (Δ 3.3 ± 2.1 vs. Δ 1.5 ± 1.5 cm/s, P = 0.002), with less difference in HUMID (Δ 2.1 ± 1.3 cm/s vs. 1.4 ± 1.3 cm/s, P = 0.096). Despite these adjustments, systolic blood pressure was only maintained in the younger group and fell consistently in older individuals (0 ± 8 mmHg) in DRY (Δ -11 ± 14 mmHg vs. 1 ± 8 mmHg, P = 0.001) and HUMID (Δ -9 ± 15 mmHg vs. -1 ± 8 mmHg, P = 0.030). In summary, older adults rely on a greater augmentation of systolic function during extreme heat exposure, but the magnitude depends on the heat stress severity.NEW & NOTEWORTHY Comparing healthy young and older adults, we assessed left ventricular cardiac function (using echocardiography) during two separate 3-h extreme heat exposures in a very hot and dry or hot humid climate type. Although the augmentation of diastolic function and cardiac output were similar between age groups, older adults showed a greater increase in mitral annular systolic velocity with heat exposure, indicating a stronger reliance on systolic mechanisms to maintain stroke volume.

Recent studies have reported blunted increases in blood pressure (BP) during static handgrip (SHG) in patients with heart failure with preserved ejection fraction (HFpEF), which may be attributed to abnormal sympathetic reactivity during exercise and/or impaired muscle metaboreflex function. However, it is unknown whether the sympathetic neural response to SHG and isolated muscle metaboreflex activation via post-exercise circulatory occlusion (PECO) are attenuated in HFpEF. Thirty-nine patients with HFpEF and 24 age-matched non-HFpEF controls were studied in the supine position. BP, heart rate (HR), and muscle sympathetic nerve activity (MSNA) were measured during SHG at 40

Wakeham, Denis J., Andrew R. Tomlinson, Giorgio Manferdelli, Matthew M. Howrey, Anna K. Geib, Murugappan Ramanathan, Marcus Payne, Renie Guilliod, James Berry, Tony G. Babb, Peter Hackett, Benjamin D. Levine, and Christopher M. Hearon, Jr. The physiological and altitude lowering effects of different supplemental oxygen flow rates at extreme simulated altitude: a pilot study. High Alt Med Biol. 27:143-151, 2026. BACKGROUND:Approximately 80% of high-altitude climbers use supplemental oxygen >8,000 meters, yet optimal dosing strategies have not been established. METHODOLOGY:Therefore, in six unacclimatized individuals (34 ± 8 years; 2 F/4 M), we quantified the effects of supplemental oxygen flow rates (6, 4, 2, 1 and 0 L/min) using the SUMMIT Oxygen mask at 282 mmHg (rest and cycle ergometry: 60 and 120 Watts) and 253 mmHg (rest only) barometric pressure in a hypobaric chamber. We measured oxygen saturation (SpO2) and gas fractions in the mask during 4-minute exposures to each flow rate. RESULTS:Resting at 282 mmHg, SpO2 (6 L/min: 99% ± 0%; 0 L/min: 70% ± 8%, p < 0.001) and mean inspired oxygen fraction decreased (6 L/min: 65.87% ± 14.11%; 0 L/min: 21.50% ± 0.44%, p < 0.001) with lowering of supplemental oxygen. Exercise further decreased SpO2 and oxygen fractions across all flow rates at 282 mmHg. At 253 mmHg, SpO2 followed a similar trend to data collected at 282 mmHg (6 L/min: 96% ± 2%; 4 L/min: 93% ± 3%; 2 L/min: 87% ± 3%; 1 L/min: 71% ± 0%; 0 L/min: 66% ± 9%). Furthermore, at rest at 253 mmHg, 2 L/min of supplemental oxygen lowered the equivalent altitude to 4,489 meters. CONCLUSION:All unacclimatized participants were able to tolerate 253 mmHg at rest on as little as 2 L/min of supplemental oxygen.