| 1. |
- Shepley, Brooke R, et al.
(författare)
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Negligible influence of moderate to severe hyperthermia on blood-brain barrier permeability and neuronal parenchymal integrity in healthy men.
- 2021
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 130:3, s. 792-800
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Tidskriftsartikel (refereegranskat)abstract
- With growing use for hyperthermia as a cardiovascular therapeutic, there is surprisingly little information regarding the acute effects it may have on the integrity of the neurovascular unit (NVU). Indeed, relying on animal data would suggest hyperthermia comparable to levels attained in thermal therapy will disrupt the blood-brain barrier (BBB) and damage the cerebral parenchymal cells. We sought to address the hypothesis that controlled passive hyperthermia is not sufficient to damage the NVU in healthy humans. Young men (n = 11) underwent acute passive heating until +2°C or absolute esophageal temperature of 39.5°C. The presence of BBB opening was determined by trans-cerebral exchange kinetics (radial-arterial and jugular venous cannulation) of S100B. Neuronal parenchymal damage was determined by the trans-cerebral exchange of tau protein, neuron-specific enolase (NSE), and neurofilament-light protein (NF-L). Cerebral blood flow to calculate exchange kinetics was measured by duplex ultrasound of the right internal carotid and left vertebral artery. Passive heating was performed via a warm-water perfused suit. In hyperthermia, there was no increase in the cerebral exchange of S100B (P = 0.327), tau protein (P = 0.626), NF-L (P = 0.447), or NSE (P = 0.908) suggesting the +2°C core temperature is not sufficient to acutely stress the NVU in healthy men. However, there was a significant condition effect (P = 0.028) of NSE, corresponding to a significant increase in arterial (P = 0.023) but not venous (P = 0.173) concentrations in hyperthermia, potentially indicating extra-cerebral release of NSE. Collectively, results from the present study support the notion that in young men there is little concern for NVU damage with acute hyperthermia of +2°C.NEW & NOTEWORTHY The acute effects of passive whole-body hyperthermia on the integrity of the neurovascular unit (NVU) in humans have remained unclear. We demonstrate that passive heating for ∼1 h until an increase of +2°C esophageal temperature in healthy men does not increase the cerebral release of neuronal parenchymal stress biomarkers, suggesting the NVU integrity is maintained. This preliminary study indicates passive heating is safe for the brain, at least in young healthy men.
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| 2. |
- Speakman, John R., et al.
(författare)
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Total daily energy expenditure has declined over the past three decades due to declining basal expenditure, not reduced activity expenditure
- 2023
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Ingår i: Nature Metabolism. - : NATURE PORTFOLIO. - 2522-5812. ; 5:4, s. 579-588
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Obesity is caused by a prolonged positive energy balance(1,2). Whether reduced energy expenditure stemming from reduced activity levels contributes is debated(3,4). Here we show that in both sexes, total energy expenditure (TEE) adjusted for body composition and age declined since the late 1980s, while adjusted activity energy expenditure increased over time. We use the International Atomic Energy Agency Doubly Labelled Water database on energy expenditure of adults in the United States and Europe (n = 4,799) to explore patterns in total (TEE: n = 4,799), basal (BEE: n = 1,432) and physical activity energy expenditure (n = 1,432) over time. In males, adjusted BEE decreased significantly, but in females this did not reach significance. A larger dataset of basal metabolic rate (equivalent to BEE) measurements of 9,912 adults across 163 studies spanning 100 years replicates the decline in BEE in both sexes. We conclude that increasing obesity in the United States/Europe has probably not been fuelled by reduced physical activity leading to lowered TEE. We identify here a decline in adjusted BEE as a previously unrecognized factor.
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| 3. |
- Tymko, Michael M., et al.
(författare)
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UBC-Nepal Expedition : acute alterations in sympathetic nervous activity do not influence brachial artery endothelial function at sea level and high altitude
- 2017
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 123:5, s. 1386-1396
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Tidskriftsartikel (refereegranskat)abstract
- Evidence indicates that increases in sympathetic nervous activity (SNA), and acclimatization to high altitude (HA), may reduce endothelial function as assessed by brachial artery flow-mediated dilatation (FMD); however, it is unclear whether such changes in FMD are due to direct vascular constraint, or consequential altered hemodynamics (e.g., shear stress) associated with increased SNA as a consequence of exposure to HA. We hypothesized that 1) at rest, SNA would be elevated and FMD would be reduced at HA compared with sea-level (SL);and 2) at SL and HA, FMD would be reduced when SNA was acutely increased, and elevated when SNA was acutely decreased. Using a novel, randomized experimental design, brachial artery FMD was assessed at SL (344 m) and HA (5,050 m) in 14 participants during mild lower-body negative pressure (LBNP; -10 mmHg) and lower-body positive pressure (LBPP; -10 mmHg). Blood pressure (finger photoplethysmography), heart rate (electrocardiogram), oxygen saturation (pulse oximetry), and brachial artery blood flow and shear rate (Duplex ultrasound) were recorded during LBNP, control, and LBPP trials. Muscle SNA was recorded (via microneurography) in a subset of participants (n = 5). Our findings were 1) at rest, SNA was elevated (P < 0.01), and absolute FMD was reduced (P = 0.024), but relative FMD remained unaltered (P = 0.061), at HA compared with SL; and 2) despite significantly altering SNA with LBNP (+60.3 +/- 25.5%) and LBPP (-37.2 +/- 12.7%) (P < 0.01), FMD was unaltered at SL (P = 0.448) and HA (P = 0.537). These data indicate that acute and mild changes in SNA do not directly influence brachial artery FMD at SL or HA.
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| 4. |
- Wheeler, Michael J., et al.
(författare)
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Morning exercise mitigates the impact of prolonged sitting on cerebral blood flow in older adults
- 2019
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Ingår i: Journal of applied physiology. - Rockville : American Physiological Society. - 8750-7587 .- 1522-1601. ; 126:4, s. 1049-1055
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Tidskriftsartikel (refereegranskat)abstract
- Preventing declines in cerebral blood flow is important for maintaining optimal brain health with aging. We compared the effects of a morning bout of moderate-intensity exercise, with and without subsequent light-intensity walking breaks from sitting, on cerebral blood velocity over 8 h in older adults. In a randomized crossover trial, overweight/obese older adults (n = 12, 70 +/- 7 yr; 30.4 +/- 4.3 kg/m2), completed three acute conditions (6-day washout); SIT: prolonged sitting (8 h, control); EX + SIT: sitting (1 h), moderate-intensity walking (30 min), followed by uninterrupted sitting (6.5 h); and EX + BR: sitting (1 h), moderate-intensity walking (30 min), followed by sitting (6.5 h) interrupted with 3 min of light-intensity walking every 30 min. Bilateral middle cerebral artery velocities (MCAv) were determined using transcranial Doppler at 13 time points across the day. The temporal pattern and average MCAv over 8 h was determined. The pattern of MCAv over 8 h was a negative linear trend in SIT (P < 0.001), but a positive quadratic trend in EX + SIT (P < 0.001) and EX + BR (P < 0.01). Afternoon time points in SIT were lower than baseline within condition (P <= 0.001 for all). A morning dip in MCAv was observed in EX + SIT and EX + BR (P < 0.05 relative to baseline), but afternoon time points were not significantly lower than baseline. The average MCAv over 8 h was higher in EX + SIT than SIT (P = 0.007) or EX + BR (P = 0.024). Uninterrupted sitting should be avoided, and moderate-intensity exercise should be encouraged for the daily maintenance of cerebral blood flow in older adults. The clinical implications of maintaining adequate cerebral blood flow include the delivery of vital oxygen and nutrients to the brain.NEW & NOTEWORTHY: This is the first study to measure the combined effects of an exercise bout with breaks in sitting on cerebral blood velocity in older adults. Using frequent recordings over an 8-h period, we have performed a novel analysis of the pattern of cerebral blood velocity, adjusting for concurrent measures of mean arterial pressure and other potential confounders in a linear mixed effects regression. Copyright © 2019 the American Physiological Society.
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