Journal of Applied Physiology

Plouffe, Audrey A.; Fischer, Kylah P.; Vranish, Jennifer R.

2023 Journal of Applied Physiology

doi: 10.1152/japplphysiol.00558.2023

Inspiratory muscle strength training (IMST) has shown potential to improve both respiratory and cardiovascular function in health and disease. Less is known about acute hemodynamic responses to a single IMST session, therefore we assessed upper and lower limb blood flow via Doppler ultrasound in the brachial and popliteal arteries, respectively. Mean, anterograde, and retrograde blood flow (BF) and shear rate (SR) were assessed relative to baseline during low-intensity (15% maximal inspiratory pressure - PImax) and high-intensity (75% PImax) IMST. During low-intensity IMST, popliteal BF and SR were reduced by ~10% and brachial BF and SR were reduced by ~40%. During high-intensity IMST, popliteal BF and SR were reduced by ~20% and brachial BF and SR were reduced by ~35%. BF and SR responses were not statistically different between low-intensity and high-intensity training for either blood vessel (P > 0.05). In addition, anterograde BF and SR were significantly decreased in the brachial artery for both low-intensity and high-intensity training (P < 0.05), but not the popliteal artery (P > 0.05). Finally, during IMST retrograde BF and SR were significantly increased in both the upper and lower limbs during low-intensity and high-intensity training (P < 0.05). These data provide novel insight into the acute BF and SR responses to a single bout of IMST, and may enhance our understanding of the mechanism(s) by which IMST imparts its beneficial chronic effects on cardiovascular function.

Howe, Erika E.; Sharma, Tushar; Marrelli, Laura; Nwebube, Chioma; Bent, Leah R.

2023 Journal of Applied Physiology

doi: 10.1152/japplphysiol.00533.2023pmid: 37675471

Cutaneous input is important in postural control and balance. Aging and diabetes impair skin sensitivity and motor control. Heat application can improve skin sensation, but its influence on motor control remains unknown. This study investigated the effects of heating skin of the foot sole on lower limb cutaneous reflexes. Reflexes were evoked in the tibialis anterior muscle of twenty young, healthy adults before and after heating the foot sole to a maximum of 42 °C. While holding a 15% EMGmax isometric dorsiflexion, a filtered white noise (0-50 Hz) vibration, at 10x perceptual threshold was applied to the heel to stimulate cutaneous mechanoreceptors. Reflexes were analyzed in both the time (cumulant density) and frequency (coherence, gain) domain. Heat increased foot skin temperature ~15.4 °C (p<0.001). Cumulant density peak to peak amplitude significantly increased by 44% after heating (p=0.01) while latencies did not vary (p=0.46). Coherence and gain were significantly greater in the 30-40 Hz range following heating (p=0.048; p=0.02). Heating significantly enhances lower limb cutaneous reflexes. This may be due to the increased ability of cutaneous mechanoreceptors to encode in the 30-40 Hz range.

McCormick, James J.; Meade, Robert D.; King, Kelli E.; Notley, Sean R.; Akerman, Ashley P.; Sigal, Ronald J.; Kenny, Glen P.

2023 Journal of Applied Physiology

doi: 10.1152/japplphysiol.00537.2023pmid: 37707866

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 remain underexplored. We evaluated cellular stress responses in peripheral blood mononuclear cells (PBMC) from 19 older adults (71 [SD 2] years; 9 females) before and after a 9-hour heat exposure (40.3°C and 9.3% relative humidity [RH]), with exposure to a cool room (~23°C) for hours 5 and 6 (cooling group). Responses were compared to 17 older adults (72 [4] years; 7 females) who remained in the heat for the entire 9 hours (control group). Changes in proteins associated with autophagy, apoptotic signaling, acute inflammation, and the heat shock response (HSR) were assessed via Western blot. While both groups experienced similar elevations in physiological strain prior to the cooling center intervention, brief cooling resulted in stark albeit transient reductions in core temperature and heart rate. At the end-exposure, autophagy proteins LC3-II and p62 were elevated 1.9-fold [95% CI: 1.2, 2.8] and 2.3-fold [1.4, 3.8], respectively, in the control group relative to cooling group. This was paired with a 2.8-fold [1.6, 4.7] greater rise in apoptotic protein cleaved-caspase-3 in the control group compared to the cooling group. Our findings indicate that 2-hours of ambient cooling midway through a 9-hour simulated heat wave may preserve autophagy and mitigate heat-induced cellular stress in older adults.