The effects of water temperature on cerebral blood flow during aquatic exercise.

PURPOSE: Recent studies suggest that episodic increases in cerebral blood flow (CBF) may contribute to the improvement in brain health associated with exercise training. Optimising CBF during exercise may enhance this benefit. Water immersion in ~ 30-32 °C augments CBF at rest and during exercise; however, the impact of water temperature on the CBF response has not been investigated. We hypothesised that cycle ergometry in water would increase CBF compared to land-based exercise, and that warm water would attenuate the CBF benefits. METHODS: Eleven young heathy participants (nine males; 23.8 ± 3.1 yrs) completed 30 min of resistance-matched cycle exercise in three separate conditions; non-immersion (Land), 32 °C and 38 °C water immersion up to the level of the waist. Middle cerebral artery velocity (MCAv), blood pressure, and respiratory measures were assessed throughout the exercise bouts. RESULTS: Core temperature was significantly higher in the 38 °C immersion than 32 °C (+ 0.84 ± 0.24 vs + 0.04 ± 0.16, P < 0.001), whilst mean arterial pressure was lower during 38 °C exercise compared to Land (84 ± 8 vs 100 ± 14 mmHg, P < 0.001) and 32 °C (92 ± 9, P = 0.03). MCAv was higher in 32 °C immersion compared to the Land and 38 °C conditions throughout the exercise bout (68 ± 10 vs 64 ± 11 vs 62 ± 12 cm/s, P = 0.03 and P = 0.02, respectively). CONCLUSION: Our findings suggest that cycle exercise in warm water attenuates the beneficial impact of water immersion on CBF velocity due to redistribution of blood flow to subserve thermoregulatory demand. Our findings suggest that, whilst water-based exercise can have beneficial effects on cerebrovascular function, water temperature is a key determinant of this benefit.

Effects of exercise during water immersion on arterial function in humans.

Flow-mediated dilation (FMD) provides a valid bioassay of vascular function in humans. Although water immersion induces hemodynamic effects that modify brachial artery shear stress, it is unclear whether water-based exercise modifies FMD. We hypothesized that exercise in 32°C water would decrease brachial artery shear and FMD relative to land-based exercise, whereas exercise in 38°C would increase brachial shear and FMD. Ten healthy participants (8 males; 23.9 ± 3.3 yr) completed 30 min of resistance-matched cycle exercise in three separate conditions: on land and in 32°C and 38°C water. Brachial artery shear rate area under the curve (SRAUC) was measured throughout each condition, with FMD measured pre- and postexercise. Brachial SRAUC increased during exercise in all conditions and was highest across the 38°C condition compared with Land and 32°C conditions (38°C: 27,507 ± 8,350 vs. Land: 9,908 ± 4,738 vs. 32°C: 13,840 ± 5,861 1/s, P < 0.001). Retrograde diastolic shear was greater during 32°C than both Land and 38°C conditions (32°C:-3,869 ± 2,198 vs. Land:-1,602 ± 1,334 vs. 32°C:-1,036 ± 1,754, P < 0.01). FMD increased as a result of 38°C (6.2 ± 1.9 vs. 8.5 ± 2.7%, P = 0.03), with no change in the Land exercise (6.3 ± 2.4 vs. 7.7 ± 2.4%, P = 0.10) or 32°C condition (6.4 ± 3.2 vs. 6.7 ± 3.2%, P = 0.99). Our findings indicate that cycle exercise in hot water attenuates retrograde shear, increases antegrade shear, and FMD. Exercise in 32°C water induces central hemodynamic changes relative to land-based exercise, but these do not translate to increases in FMD in either condition, likely due to the impact of increased retrograde shear. Our findings indicate that modification of shear has direct acute impacts on endothelial function in humans.

Impact of Oxygen Supplementation on Brachial Artery Hemodynamics and Vascular Function During Ascent to 5,050 m.

Vizcardo-Galindo, Gustavo A., Connor A. Howe, Ryan L. Hoiland, Howard H. Carter, Christopher K. Willie, Philip N. Ainslie, and Joshua C. Tremblay. Impact of oxygen supplementation on brachial artery hemodynamics and vascular function during ascent to 5,050 m. High Alt Med Biol. 24:27-36, 2023.-High-altitude trekking alters upper limb hemodynamics and reduces brachial artery vascular function in lowlanders. Whether these changes are reversible with the removal of hypoxia is unknown. We investigated the impact of 20 minutes of oxygen supplementation (O2) on brachial artery hemodynamics, reactive hyperemia (RH; microvascular function), and flow-mediated dilation (FMD; endothelial function). Participants (aged 21-42 years) were examined before and with O2 at 3,440 m (n = 7), 4,371 m (n = 7), and 5,050 m (n = 12) using Duplex ultrasound (days 4, 7, and 10 respectively). At 3,440 m, O2 decreased brachial artery diameter (-5% ± 5%; p = 0.04), baseline blood flow (-44% ± 15%; p < 0.001), oxygen delivery (-39 ± 16; p < 0.001), and peak RH (-8% ± 8%; p = 0.02), but not RH normalized for baseline blood flow. Elevated FMD (p = 0.04) with O2 at 3,440 m was attributed to the reduction in baseline diameter. At 5,050 m, a reduction in brachial artery blood flow (-17% ± 22%; p = 0.03), but not oxygen delivery, diameter, RH, or FMD occurred with O2. These findings suggest that during early trekking at high altitude, O2 causes vasoconstriction in the upper limb along the arterial tree (conduit and resistance arteries). With incremental high-altitude exposure, O2 reduces blood flow without compromising oxygen delivery, RH, or FMD, suggesting a differential impact on vascular function modulated by the duration and severity of high-altitude exposure.

Visualising and quantifying microvascular structure and function in patients with heart failure using optical coherence tomography.

Heart failure (HF) is characterised by abnormal conduit and resistance artery function in humans. Microvascular function in HF is less well characterised, due in part to the lack of tools to image these vessels in vivo. The skin microvasculature is a surrogate for systemic microvascular function and health and plays a key role in thermoregulation, which is dysfunctional in HF. We deployed a novel optical coherence tomography (OCT) technique to visualise and quantify microvascular structure and function in 10 subjects with HF and 10 age- and sex-matched controls. OCT images were obtained from the ventral aspect of the forearm, at baseline (33°C) and after 30 min of localised skin heating. At rest, OCT-derived microvascular density (20.3 ± 8.7%, P = 0.004), diameter (35.1 ± 6.0 µm, P = 0.006) and blood flow (82.9 ± 41.1 pl/s, P = 0.021) were significantly lower in HF than CON (27.2 ± 8.0%, 40.4 ± 5.8 µm, 110.8 ± 41.9 pl/s), whilst blood speed was not significantly lower (74.3 ± 11.0 µm/s vs. 81.3 ± 9.9 µm/s, P = 0.069). After local heating, the OCT-based density, diameter, blood speed and blood flow of HF patients were similar (all P > 0.05) to CON. Although abnormalities exist at rest which may reflect microvascular disease status, patients with HF retain the capacity to dilate cutaneous microvessels in response to localised heat stress. This is a novel in vivo human observation of microvascular dysfunction in HF, illustrating the feasibility of OCT to directly visualise and quantify microvascular responses to physiological stimuli in vivo. KEY POINTS: Microvessels in the skin are critical to human thermoregulation, which is compromised in participants with heart failure (HF). We have developed a powerful new non-invasive optical coherence tomography (OCT)-based approach for the study of microvascular structure and function in vivo. Our approach enabled us to observe and quantify abnormal resting microvascular function in participants with HF. Patients with HF were able to dilate skin microvessels in response to local heat stress, arguing against an underlying structural abnormality. This suggests that microvascular functional regulation is the primary abnormality in HF. OCT can be used to directly visualise and quantify microvascular responses to physiological stimuli in vivo.

The impact of age, sex, cardio-respiratory fitness, and cardiovascular disease risk on dynamic cerebral autoregulation and baroreflex sensitivity.

BACKGROUND: Humans display an age-related decline in cerebral blood flow and increase in blood pressure (BP), but changes in the underlying control mechanisms across the lifespan are less well understood. We aimed to; (1) examine the impact of age, sex, cardiovascular disease (CVD) risk, and cardio-respiratory fitness on dynamic cerebral autoregulation and cardiac baroreflex sensitivity, and (2) explore the relationships between dynamic cerebral autoregulation (dCA) and cardiac baroreflex sensitivity (cBRS). METHODS: 206 participants aged 18-70 years were stratified into age categories. Cerebral blood flow velocity was measured using transcranial Doppler ultrasound. Repeated squat-stand manoeuvres were performed (0.10 Hz), and transfer function analysis was used to assess dCA and cBRS. Multivariable linear regression was used to examine the influence of age, sex, CVD risk, and cardio-respiratory fitness on dCA and cBRS. Linear models determined the relationship between dCA and cBRS. RESULTS: Age, sex, CVD risk, and cardio-respiratory fitness did not impact dCA normalised gain, phase, or coherence with minimal change in all models (P > 0.05). cBRS gain was attenuated with age when adjusted for sex and CVD risk (young-older; ß = - 2.86 P < 0.001) along with cBRS phase (young-older; ß = - 0.44, P < 0.001). There was no correlation between dCA normalised gain and phase with either parameter of cBRS. CONCLUSION: Ageing was associated with a decreased cBRS, but dCA appears to remain unchanged. Additionally, our data suggest that sex, CVD risk, and cardio-respiratory fitness have little effect.

Resistance, but not endurance exercise training, induces changes in cerebrovascular function in healthy young subjects.

It is generally considered that regular exercise maintains brain health and reduces the risk of cerebrovascular diseases such as stroke and dementia. Since the benefits of different "types" of exercise are unclear, we sought to compare the impacts of endurance and resistance training on cerebrovascular function. In a randomized and crossover design, 68 young healthy adults were recruited to participate in 3 mo of resistance and endurance training. Cerebral hemodynamics through the internal carotid, vertebral, middle and posterior cerebral arteries were measured using Duplex ultrasound and transcranial Doppler at rest and during acute exercise, dynamic autoregulation, and cerebrovascular reactivity (to hypercapnia). Following resistance, but not endurance training, middle cerebral artery velocity and pulsatility index significantly decreased (P < 0.01 and P = 0.02, respectively), whereas mean arterial pressure and indices of cerebrovascular resistance in the middle, posterior, and internal carotid arteries all increased (P < 0.05). Cerebrovascular resistance indices in response to acute exercise and hypercapnia also significantly increased following resistance (P = 0.02), but not endurance training. Our findings, which were consistent across multiple domains of cerebrovascular function, suggest that episodic increases in arterial pressure associated with resistance training may increase cerebrovascular resistance. The implications of long-term resistance training on brain health require future study, especially in populations with pre-existing cerebral hypoperfusion and/or hypotension.NEW & NOTEWORTHY Three months of endurance exercise did not elicit adaptation in any domain of cerebrovascular function in young healthy inactive volunteers. However, resistance training induced decreased pulsatility in the extracranial arteries and increased indices of cerebrovascular resistance in cerebral arteries. This increase in cerebrovascular resistance, apparent at baseline and in response to both hypercapnia and acute exercise, may reflect a protective response in the face of changes in arterial pressure during resistance exercise.

The Impact of 6-Month Land versus Water Walking on Cerebrovascular Function in the Aging Brain.

INTRODUCTION: To examine the hypothesis that exercise training induces adaptation in cerebrovascular function, we recruited 63 older adults (62 ± 7 yr, 46 females) to undertake 24 wk of either land walking or water walking, or participate in a nonexercise control group. This is the first multi-interventional study to perform a comprehensive assessment of cerebrovascular function in response to longer term (6-month) training interventions, including water-based exercise, in older healthy individuals. METHODS: Intracranial blood flow velocities (middle cerebral artery (MCAv) and posterior cerebral artery) were assessed at rest and in response to neurovascular coupling, hypercapnic reactivity, and cerebral autoregulation. RESULTS: We observed no change in resting MCAv in response to either training intervention (pre vs post, mean (95% confidence interval), land walking: 65 (59-70) to 63 (57-68) cm·s-1, P = 0.33; water walking: 63 (58-69) to 61 (55-67) cm·s-1, P = 0.92) compared with controls and no change in neurovascular coupling (land walking: P = 0.18, water walking: P = 0.17). There was a significant but modest improvement in autoregulatory normalized gain after the intervention in the water-walking compared with the land-walking group (P = 0.03). Hypercapnic MCAv reactivity was not different based on exercise group (land: P = 087, water: P = 0.83); however, when data were pooled from the exercise groups, increases in fitness were correlated with decreases in hypercapnic reactivity (r2 = 0.25, P = 0.003). CONCLUSIONS: Although exercise was not associated with systematic changes across multiple domains of cerebrovascular function, our data indicate that exercise may induce modest changes in autoregulation and CO2 reactivity. These findings should encourage further studies of the longer-term implications of exercise training on cerebrovascular health.

Adaptation to Exercise Training in Conduit Arteries and Cutaneous Microvessels in Humans: An Optical Coherence Tomography Study.

INTRODUCTION: Exercise training has antiatherogenic effects on conduit and resistance artery function and structure in humans and induces angiogenic changes in skeletal muscle. However, training-induced adaptation in cutaneous microvessels is poorly understood, partly because of technological limitations. Optical coherence tomography (OCT) is a novel high-resolution imaging technique capable of visualizing cutaneous microvasculature at a resolution of ~30 µm. We utilized OCT to visualize the effects of training on cutaneous microvessels, alongside assessment of conduit artery flow-mediated dilation (FMD). METHODS: We assessed brachial FMD and cutaneous microcirculatory responses at rest and in response to local heating and reactive hyperemia: pretraining and posttraining in eight healthy men compared with age-matched untrained controls (n = 8). Participants in the training group underwent supervised cycling at 80% maximal heart rate three times a week for 8 wk. RESULTS: We found a significant interaction (P = 0.04) whereby an increase in FMD was observed after training (post 9.83% ± 3.27% vs pre 6.97% ± 1.77%, P = 0.01), with this posttraining value higher compared with the control group (6.9% ± 2.87%, P = 0.027). FMD was not altered in the controls (P = 0.894). There was a significant interaction for OCT-derived speed (P = 0.038) whereby a significant decrease in the local disk heating response was observed after training (post 98.6 ± 3.9 µm·s-1 vs pre 102 ± 5 µm·s-1, P = 0.012), whereas no changes were observed for OCT-derived speed in the control group (P = 0.877). Other OCT responses (diameter, flow rate, and density) to local heating and reactive hyperemia were unaffected by training. CONCLUSIONS: Our findings suggest that vascular adaptation to exercise training is not uniform across all levels of the arterial tree; although exercise training improves larger artery function, this was not accompanied by unequivocal evidence for cutaneous microvascular adaptation in young healthy subjects.

Can exercise training enhance the repeated remote ischaemic preconditioning stimulus on peripheral and cerebrovascular function in high-risk individuals?

BACKGROUND: Repeated exposure to remote ischaemic preconditioning (rIPC; short bouts of non-lethal ischaemia) enhances peripheral vascular function within 1 week; whereas, longer periods of rIPC (~ 1 year) may improve cerebral perfusion. Increasing the 'dose' of rIPC may lead to superior effects. Given the similarities between exercise and rIPC, we examined whether adding exercise to the rIPC stimulus leads to greater adaptation in systemic vascular function. METHODS: Nineteen individuals with increased risk for cardiovascular disease (CVD) were randomly allocated to either 8 weeks of rIPC (n = 9) or 8 weeks of rIPC + exercise (rIPC + Ex) (n = 10). rIPC was applied three times per week in both conditions, and exercise consisted of 50 min (70% heart rate max) of cycling 3 times per week. Peripheral endothelial function was assessed using flow-mediated dilation (FMD) before and after ischaemia-reperfusion (IR). Cerebrovascular function was assessed by dynamic cerebral autoregulation (dCA) and cerebrovascular reactivity (CVR), and cardio-respiratory fitness (VO2peak) using a maximal aerobic capacity test. RESULTS: FMD% increased by 1.6% (95% CI, 0.4, 2.8) following rIPC + Ex and by 0.3% (- 1.1, 1.5) in the only rIPC but this did not reach statistical significance (P = 0.65). Neither intervention evoked a change in dCA or in CVR (P > 0.05). VO2peak increased by 2.8 ml/kg/min (1.7, 3.9) following the rIPC + Ex and by 0.1 ml/kg/min (- 1.0, 1.4) following the rIPC only intervention (P = 0.69). CONCLUSION: Combining exercise with rIPC across an 8-week intervention does not lead to superior effects in cerebrovascular and peripheral vascular function compared to a repeated rIPC intervention in individuals at risk of CVD.

Effects of Land versus Water Walking Interventions on Vascular Function in Older Adults.

PURPOSE: Endothelial dysfunction is an early and integral atherogenic event. Interventions that improve endothelial function also reduce cardiovascular risk. Due largely to the direct hemodynamic effects of repetitive exercise on the artery wall, exercise training has shown to enhance endothelial function. Land walking (LW) and water walking (WW) induce distinct hemodynamic responses, so the comparison of their effects provides an approach to study shear stress effects on endothelial function. We hypothesized that LW and WW training would have different effects on peripheral artery endothelial function. METHODS: Fifty-one sedentary, older (age = 61.9 ± 6.6 yr, 23.5% male) individuals were randomized into one of three groups: control (n = 16), or one of two exercise groups consisting of 3 × 50 min supervised and individually tailored walking sessions per week for 24 consecutive weeks, performed either on LW (n = 17) or on WW (n = 18). Brachial artery endothelial function (flow-mediated dilation) and smooth muscle cell function (glyceryl trinitrate administration) were tested in all participants before (week 0) and after (week 24) the intervention. RESULTS: Differences were apparent in flow-mediated dilation change between the LW group (week 0, 5.39% ± 0.71%, to week 24, 7.77% ± 0.78%; P = 0.009) and the control group (week 0, 5.87% ± 0.73%, to week 24, 5.78% ± 0.78%). No differences in artery dilation response were found after glyceryl trinitrate administration (all P > 0.05). CONCLUSION: This study suggests that 6-month center-based LW may be superior to WW in terms of improvement in arterial endothelial function in older sedentary individuals.

Visualizing and quantifying cutaneous microvascular reactivity in humans by use of optical coherence tomography: impaired dilator function in diabetes.

The pathophysiology and time course of impairment in cutaneous microcirculatory function and structure remain poorly understood in people with diabetes, partly due to the lack of investigational tools capable of directly imaging and quantifying the microvasculature in vivo. We applied a new optical coherence tomography (OCT) technique, at rest and during reactive hyperemia (RH), to assess the skin microvasculature in people with diabetes with foot ulcers (DFU, n = 13), those with diabetes without ulcers (DNU, n = 9), and matched healthy controls (CON, n = 13). OCT images were obtained from the dorsal part of the foot at rest and following 5 min of local ischemia induced by inflating a cuff around the thigh at suprasystolic level (220 mmHg). One-way ANOVA was used to compare the OCT-derived parameters (diameter, speed, flow rate, and density) at rest and in response to RH, with repeated-measures two-way ANOVA performed to analyze main and interaction effects between groups. Data are means ± SD. At rest, microvascular diameter in the DFU (84.89 ± 14.84 µm) group was higher than CON (71.25 ± 7.6 µm, P = 0.012) and DNU (71.33 ± 12.04 µm, P = 0.019) group. Speed in DFU (65.56 ± 4.80 µm/s, P = 0.002) and DNU (63.22 ± 4.35 µm/s, P = 0.050) were higher than CON (59.58 ± 3.02 µm/s). Microvascular density in DFU (22.23 ± 13.8%) was higher than in CON (9.83 ± 2.94%, P = 0.008), but not than in the DNU group (14.8 ± 10.98%, P = 0.119). All OCT-derived parameters were significantly increased in response to RH in the CON group (all P < 0.01) and DNU group (all P < 0.05). Significant increase in the DFU group was observed in speed (P = 0.031) and density (P = 0.018). The change in density was lowest in the DFU group (44 ± 34.1%) compared with CON (199.2 ± 117.5%, P = 0.005) and DNU (148.1 ± 98.4, P = 0.054). This study proves that noninvasive OCT microvascular imaging is feasible in people with diabetes, provides powerful new physiological insights, and can distinguish between healthy individuals and patients with diabetes with distinct disease severity.

Optical coherence tomography: a novel imaging approach to visualize and quantify cutaneous microvascular structure and function in patients with diabetes.

INTRODUCTION: The pathophysiology of microvascular disease is poorly understood, partly due to the lack of tools to directly image microvessels in vivo. RESEARCH DESIGN AND METHODS: In this study, we deployed a novel optical coherence tomography (OCT) technique during local skin heating to assess microvascular structure and function in diabetics with (DFU group, n=13) and without (DNU group, n=10) foot ulceration, and healthy controls (CON group, n=13). OCT images were obtained from the dorsal foot, at baseline (33°C) and 30 min following skin heating. RESULTS: At baseline, microvascular density was higher in DFU compared with CON (21.9%±11.5% vs 14.3%±5.6%, p=0.048). Local heating induced significant increases in diameter, speed, flow rate and density in all groups (all p<0.001), with smaller changes in diameter for the DFU group (94.3±13.4 µm), compared with CON group (115.5±11.7 µm, p<0.001) and DNU group (106.7±12.1 µm, p=0.014). Heating-induced flow rate was lower in the DFU group (584.3±217.0 pL/s) compared with the CON group (908.8±228.2 pL/s, p<0.001) and DNU group (768.8±198.4 pL/s, p=0.014), with changes in density also lower in the DFU group than CON group (44.7%±15.0% vs 56.5%±9.1%, p=0.005). CONCLUSIONS: This proof of principle study indicates that it is feasible to directly visualize and quantify microvascular function in people with diabetes; and distinguish microvascular disease severity between patients.

Land-walking vs. water-walking interventions in older adults: Effects on aerobic fitness.

BACKGROUND: Low cardiorespiratory fitness is an independent predictor of all-cause and cardiovascular mortality, and interventions that increase fitness reduce risk. Water-walking decreases musculoskeletal impact and risk of falls in older individuals, but it is unclear whether water-walking improves aerobic fitness in the same way as weight-dependent land-walking. This randomized controlled trial involved 3 intervention groups-a no-exercise control group (CG), a land-walking (LW) group, and a water-walking (WW) group-to investigate the comparative impacts of LW and WW to CG on fitness. METHODS: Both exercise groups attended individually tailored, center-based, intensity-matched 3 × weekly sessions for 24 weeks, which progressed to 150 min of exercise per week. This was followed by a 24-week no-intervention period. Maximal graded exercise tests were performed on a treadmill at Weeks 0, 24, and 48. RESULTS: Maximal oxygen uptake increased from Week 0 to Week 24 in both exercise groups (0.57 ± 0.62 mL/kg/min, 0.03 ± 0.04 L/min for LW; 0.93 ± 0.75 mL/kg/min, 0.06 ± 0.06 L/min for WW, mean ± SE) compared to the CG (-1.75 ± 0.78 mL/kg/min, -0.16 ± 0.05 L/min) (group × time, p < 0.05). Time to exhaustion increased significantly following LW only (123.4 ± 25.5 s), which was significantly greater (p = 0.001) than the CG (24.3 ± 18.5 s). By Week 48, the training-induced adaptations in the exercise groups returned to near baseline levels. CONCLUSION: Our study supports current physical-activity recommendations that 150 min/week of moderate-intensity exercise produces improvements in fitness in previously sedentary older individuals. Also, LW and WW elicit similar improvements in fitness if conducted at the same relative intensities. Exercise-naïve older individuals can benefit from the lower impact forces and decreased risk of falls associated with WW without compromising improvements in cardiorespiratory fitness.

Effects of Acute Exercise on Cutaneous Thermal Sensation.

The aim of this study was to assess the effect of exercise intensity on the thermal sensory function of active and inactive limbs. In a randomised and counterbalanced manner, 13 healthy young male participants (25 ± 6 years, 1.8 ± 0.1 m, 77 ± 6 kg) conducted: (1) 30-min low-intensity (50% heart rate maximum, HRmax; LOW) and (2) 30-min high-intensity (80% HRmax; HIGH) cycling exercises, and (3) 30 min of seated rest (CONTROL). Before, immediately after, and 1 h after, each intervention, thermal sensory functions of the non-dominant dorsal forearm and posterior calf were examined by increasing local skin temperature (1 °C/s) to assess perceptual heat sensitivity and pain thresholds. Relative to pre-exercise, forearm heat sensitivity thresholds were increased immediately and 1 hr after HIGH, but there were no changes after LOW exercise or during CONTROL (main effect of trial; p = 0.017). Relative to pre-exercise, calf heat sensitivity thresholds were not changed after LOW or HIGH exercise or during CONTROL (main effect of trial; p = 0.629). There were no changes in calf (main effect of trial; p = 0.528) or forearm (main effect of trial; p = 0.088) heat pain thresholds after exercise in either LOW or HIGH or CONTROL. These results suggest that cutaneous thermal sensitivity function of an inactive limb is only reduced after higher intensity exercise but is not changed in a previously active limb after exercise. Exercise does not affect heat pain sensitivity in either active or inactive limbs.

The impact of acute remote ischaemic preconditioning on cerebrovascular function.

PURPOSE: Remote ischaemic preconditioning (RIPC) refers to the protection conferred to tissues and organs via brief periods of ischaemia in a remote vascular territory, including the brain. Recent studies in humans report that RIPC provides neuroprotection against recurrent (ischaemic) stroke. To better understand the ability of RIPC to improve brain health, the present study explored the potential for RIPC to acutely improve cerebrovascular function. METHODS: Eleven young healthy (females n = 6, age; 28.1 ± 3.7 years) and 9 older individuals (females n = 4, age 52.5 ± 6.7 years) at increased risk for stroke (cardiovascular disease risk factors) underwent assessments of cerebrovascular function, assessed by carbon dioxide (CO2) reactivity and cerebral autoregulation during normo- and hypercapnia (5% CO2) following 40 mins of bilateral arm RIPC or a sham condition. Squat-to-stand manoeuvres were performed to induce changes in blood pressure to assess cerebral autoregulation (0.10 Hz) and analysed via transfer function. RESULTS: We found no change in middle cerebral artery velocity or blood pressure across 40 mins of RIPC. Application of RIPC resulted in no change in CO2 reactivity slopes (sham vs RIPC, 1.97 ± 0.88 vs 2.06 ± 0.69 cm/s/mmHg P = 0.61) or parameters of cerebral autoregulation during normocapnia (sham vs RIPC, normalised gain%, 1.27 ± 0.25 vs 1.22 ± 0.35, P = 0.46). CONCLUSION: This study demonstrates that a single bout of RIPC does not influence cerebrovascular function acutely in healthy individuals, or those at increased cardiovascular risk. Given the previously reported protective role of RIPC on stroke recurrence in humans, it is possible that repeated bouts of RIPC may be necessary to impart beneficial effects on cerebrovascular function.

Land- versus water-walking interventions in older adults: Effects on body composition.

OBJECTIVES: Increasing physical activity is a priority worldwide, including for older adults who may have difficulty performing traditional forms of exercise, and for whom retention of muscle mass is an important consideration. Water-based exercise may provide an alternative if benefits are comparable. We compared the impact on body composition of 24-week water- versus land-walking interventions in healthy but inactive older adults. DESIGN: Randomised, controlled trial. METHODS: 72 participants (62.5±6.8yr) were randomised to a land-walking (LW), water-walking (WW) or control (C) group in a supervised centre-based program. The exercise groups trained 3 times/week at matched intensity (%HRR), increasing from 40-45% to 55-65% heart rate reserve (HRR). Height, weight, body mass index (BMI), waist and hip girths were recorded; dual X-ray absorptiometry (DXA) provided fat and lean tissue masses. Participants were re-assessed 24 weeks after completion of the intervention. RESULTS: There were no significant changes in body mass or BMI following either exercise protocol, however central adiposity was reduced in both exercise groups, and the WW group increased lower limb lean mass. These benefits did not persist over the follow-up period. CONCLUSIONS: Exercise can confer beneficial effects on body composition which are not evident when examining weight or BMI. Both WW and LW improved body composition. Water walking can be recommended as an exercise strategy for this age group due to its beneficial effects on body composition which are similar to, or exceed, those associated with land-walking. For benefits to persist, it appears that exercise needs to be maintained.

Assessment of the human cutaneous microvasculature using optical coherence tomography: Proving Harvey's proof.

William Harvey proved the circulation of blood 400 years ago using a combination of ligature application and astute observation that presaged the existence of capillaries. Here we report findings, based on our development of a novel application of optical coherence tomography (OCT), that directly confirm the impact of cuff inflation on microvessels as small as ~30µm. By emulating Harvey's proofs, using cuff inflation at low pressure in the presence and absence of skin heating, we have imaged and quantified significant effects on microvascular diameter and density in humans in vivo. The application of cuff pressure significantly increased microvascular diameter (40.5 ± 4.6 vs 47.1 ± 3.9 µm, P = .01) and density (8.33 ± 4.3 vs 15.1 ± 4.9%, P < .01). These impacts were reversed by cuff deflation. Our study also showed the profound impacts of skin heating on microvessel diameter (46.7 ± 5.8 vs 70.6 ± 7.8 µm, P < .01) and density (14.2 ± 6.5 vs 43.2 ± 9%, P < .01) in vivo, which were further exacerbated by cuff inflation. Our approach to the direct visualization of the human skin microvasculature is non-invasive, safe, and easily applied. Future experiments might be directed at questions of microvascular physiology and pathophysiology, such as how different mammals thermoregulate and what impacts cardiovascular disease and diabetes have on microvascular structure and function.

Lifelong Physical Activity Determines Vascular Function in Late Postmenopausal Women.

INTRODUCTION: The study evaluated the role of lifelong physical activity for leg vascular function in postmenopausal women (61 ± 1 yr). METHOD: The study design was cross-sectional with three different groups based on self-reported physical activity level with regard to intensity and volume over the past decade: inactive (n = 14), moderately active (n = 12), and very active (n = 15). Endothelial-dependent and smooth muscle-dependent leg vascular function were assessed by ultrasound Doppler measurements of the femoral artery during infusion of acetylcholine (Ach), the nitric oxide (NO) donor sodium nitroprusside and the prostacyclin analog epoprostenol. Thigh muscle biopsies, arterial and venous plasma samples were obtained for assessment of vasodilator systems. RESULTS: The very active group was found to have 76% greater responsiveness to Ach compared with the sedentary group accompanied by 200% higher prostacyclin synthesis during Ach infusion. Smooth muscle cell responsiveness to sodium nitroprusside and epoprostenol was not different between groups. The protein amount of endothelial NO synthase and endogenous antioxidant enzymes in muscle tissue was higher in the very active than the inactive group. The moderately active group had a similar endothelial and smooth muscle cell responsiveness as the inactive group. A secondary comparison with a smaller group (n = 5) of habitually active young (24 ± 2 yr) women indicated that smooth muscle cell responsiveness and endothelial responsiveness are affected by age per se. CONCLUSIONS: This study shows that leg vascular function and the potential to form prostacyclin and NO in late postmenopausal women, is influenced by the extent of lifelong physical activity.

Visualizing and quantifying the impact of reactive hyperemia on cutaneous microvessels in humans.

The mechanisms underlying reactive hyperemia (RH) responses in microvessels are poorly understood. Previous assessment tools have not been capable of directly visualizing microvessels during physiological stimulation in humans. Optical coherence tomography (OCT) is capable of imaging and quantifying subcutaneous microvessels as small as ~30 µm. In this study we use OCT to visualize and quantify skin microvascular changes in response to RH for the first time in humans. We also assessed the reproducibility of this technique. OCT and laser Doppler flowmetry (LDF) were used simultaneously to scan cutaneous microvessels in 10 young healthy subjects on 2 days. We applied a speckle decorrelation algorithm to assess OCT images and calculated flow rate, speed, diameter, and density parameters. Measures were obtained at rest (baseline) and 30-s following a 5-min cuff inflation (RH). All data were compared between days. The RH stimulus significantly increased (P < 0.0001) OCT-derived microvascular diameter (37.6 ± 3.4 vs. 44.5 ± 5.2 µm), flow rate (82.4 ± 23.4 vs. 240.1 ± 58.6 pl/s), speed (48 ± 5.7 vs. 101.5 ± 17.1 µm/s), density (5.1 ± 1.7 vs. 14.6 ± 2.6%), and also LDF-derived flux (12.3 ± 5.7 vs. 31.6 ± 9.1 perfusion units). At baseline, OCT-derived diameter (r = 0.55), flow rate (r = 0.64), speed (r = 0.55), and density (r = 0.75) showed significant between-day correlations (P < 0.05), as did LDF results (r = 0.74). In response to RH, OCT-derived diameter (r = 0.63) and density (r = 0.64) showed significant correlations (P < 0.05), whereas flow rate (r = 0.45), speed (r = 0.43), and LDF (r = 0.26) were less reproducible. Our study is novel in that it establishes the feasibility of using OCT to visualize and quantify microvascular structure and function responses to RH in humans.NEW & NOTEWORTHY This study describes the first evidence in humans that optical coherence tomography provides direct visualization and comprehensive quantification of cutaneous microvascular hemodynamics as a response to reactive hyperemia. This imaging technique will greatly improve human cutaneous microvascular assessment in physiological and clinical settings.