Impact of acute dynamic exercise on vascular stiffness in the retinal arteriole in healthy subjects.

Acute exercise can improve vascular stiffness in the conduit artery, but its effect on the retinal arterioles is unknown. The present study investigated the effects of acute dynamic exercise on retinal vascular stiffness. In experiment 1, we measured the cardio-ankle vascular index (CAVI), carotid artery intima-media thickness (carotid IMT), and retinal blood velocity by laser speckle flowgraphy in 28 healthy old and 28 young men (69 ± 3 and 23 ± 3 yr, respectively). Pulse waveform variables, which were used as an index of retinal vascular stiffness, were assessed by retinal blood flow velocity profile analysis. In experiment 2, 18 healthy old and 18 young men (69 ± 3 and 23 ± 3 yr, respectively) underwent assessment of pulse waveform variables after a 30-min bout of moderate cycling exercise at an intensity of 60% heart rate reserve. There was a significant difference in the baseline pulse waveform variables between the old and young groups. Pulse waveform variables in the retinal arteriole did not significantly change after acute dynamic exercise, whereas CAVI significantly decreased. These findings suggest that retinal vascular stiffness does not change by acute exercise. The effect of exercise on vascular stiffness in the retinal arterioles might be different from that in the conduit artery.NEW & NOTEWORTHY Acute dynamic exercise is well known to improve vascular stiffness in the conduit artery while its effect on the retinal arterioles has been unknown. This study showed that an acute dynamic exercise does not change vascular stiffness in the retinal arteriole in healthy humans. Different responses to acute dynamic exercise in vascular stiffness in retinal arterioles and conduit arteries are suggested.

The Effects of Beverage Intake after Exhaustive Exercise on Organ Damage, Inflammation and Oxidative Stress in Healthy Males.

Strenuous exercise induces organ damage, inflammation and oxidative stress. To prevent exercise-induced organ damage, inflammation and oxidative stress, rehydrating may be an effective strategy. In the present study, we aimed to examine whether beverage intake after exhaustive exercise to recover from dehydration prevents such disorders. Thirteen male volunteers performed incremental cycling exercise until exhaustion. Immediately after exercise, the subjects drank an electrolyte containing water (rehydrate trial: REH) or did not drink any beverage (control trial: CON). Blood samples were collected before (Pre), immediately (Post), 1 h and 2 h after exercise. Urine samples were also collected before (Pre) and 2 h after exercise. We measured biomarkers of organ damage, inflammation and oxidative stress in blood and urine. Biomarkers of muscle, renal and intestinal damage and inflammation increased in the blood and urine after exercise. However, changes in biomarkers of organ damage and inflammation did not differ between trials (p > 0.05). The biomarker of oxidative stress, thiobarbituric acid reactive substances (TBARS), in plasma, showed different changes between trials (p = 0.027). One hour after exercise, plasma TBARS concentration in REH had a higher trend than that in CON (p = 0.052), but there were no significant differences between Pre and the other time points in each trial. These results suggest that beverage intake after exercise does not attenuate exercise-induced organ damage, inflammation or oxidative stress in healthy males. However, rehydration restores exercise-induced oxidative stress more quickly.

Facial Blood Flow Responses to Dynamic Exercise.

We reported previously that a static handgrip exercise evoked regional differences in the facial blood flow. The present study examined whether regional differences in facial blood flow are also evoked during dynamic exercise. Facial blood flow was measured by laser speckle flowgraphy during 15 min of cycling exercise at heart rates of 120 bpm, 140 bpm and 160 bpm in 12 subjects. The facial vascular conductance index was calculated from the blood flow and mean arterial pressure. The regional blood flow and conductance index values were determined in the forehead, eyelid, nose, cheek, ear and lip. One-way ANOVA and Tukey's post-hoc test were used to examine effects of exercise intensity and target regions. The blood flow and conductance index in skin areas increased significantly with the exercise intensity. The blood flow and conductance index in the lip increased significantly at 120 bpm and 140 bpm compared to the control, while the values in the lip at 160 bpm did not change from the control values. These results suggest that the blood flow in facial skin areas, not in the lip, responds similarly to dynamic exercise, in contrast to the responses to static exercise.

Aging decreases CO2 reactivity in the retinal artery, but not in the ocular choroidal vessels; a cross-sectional study.

BACKGROUND: The CO2 reactivity is often used to assess vascular function, but it is still unclear whether this reactivity is affected by aging. OBJECTIVE: To investigate the effects of aging on the CO2 reactivity in ocular and cerebral vessels, both of which are highly sensitive to hypercapnia, we compared the CO2 reactivity in the retinal artery (RA), retinal and choroidal vessels (RCV), optic nerve head (ONH), and middle cerebral artery (MCA) between young and middle-aged subjects. METHODS: We measured the CO2 reactivity in 14 young and 11 middle-aged males using laser-speckle flowgraphy during a 3-min inhalation of CO2-rich air. RESULTS: The CO2 reactivity in the RA and ONH were lower in the middle-aged group than in the young group, but no significant effect of age was observed in the RCV or MCA. The CO2 reactivity in the RA and ONH were correlated significantly with age, whereas those in the RCV or MCA were not. CONCLUSIONS: These findings suggest that there are regional differences in the effect of age on the CO2 reactivity among not only ocular and cerebral vessels, but also the retinal and choroidal vessels, even though these vessels are in neighboring areas.

Fluid intake restores retinal blood flow early after exhaustive exercise in healthy subjects.

PURPOSE: It remains unclear whether rehydration restores retinal blood flow reduced by exhaustive exercise. We investigated the effect of fluid intake on retinal blood flow after exhaustive exercise. METHODS: Blood flow in the inferior (ITRA) and superior temporal retinal arterioles (STRA) was measured before and after incremental cycling exercise until exhaustion in 13 healthy males. After the exercise, the subjects rested without drinking (control condition: CON) or with drinking an electrolyte containing water (rehydrate condition: REH) and were followed up for a period of 120 min. To assess the hydration state, the body mass was measured, and venous blood samples were collected and plasma volume (PV) was calculated. RESULTS: Body mass decreased in CON after the trial [- 1.1 ± 0.1% (mean ± SE), p < 0.05]. PV was lower in CON than in REH during recovery. The ITRA and STRA blood flows decreased immediately after exercise from the resting baseline (ITRA; - 23 ± 4% in REH and - 30 ± 4% in CON, p < 0.05). The ITRA blood flow recovered baseline level at 15 min of recovery in REH (- 9 ± 3%, p = 0.5), but it remained reduced in CON (-14 ± 3%, p < 0.05). The STRA blood flow was higher in REH than in CON at 15 min (2 ± 3 vs. - 5 ± 3%, p < 0.05). CONCLUSIONS: The results of this study suggest that the reduction in retinal blood flow induced by exhaustive exercise can be recovered early by rehydration.

Exhaustive exercise attenuates the neurovascular coupling by blunting the pressor response to visual stimulation.

Neurovascular coupling (NVC) is assessed as an increase response to visual stimulation, and is monitored by blood flow of the posterior cerebral artery (PCA). To investigate whether exhaustive exercise modifies NVC, and more specifically, the relative contributions of vasodilatation in the downstream of PCA and the pressor response on NVC, we measured blood flow velocity in the PCA (PCAv) in 13 males using transcranial Doppler ultrasound flowmetry during a leg-cycle exercise at 75% of maximal heart rate until exhaustion. NVC was estimated as the relative change in PCAv from the mean value obtained during 20-s with the eyes closed to the peak value obtained during 40-s of visual stimulation involving looking at a reversed checkerboard. Conductance index (CI) was calculated by dividing PCAv by mean arterial pressure (MAP) to evaluate the vasodilatation. At exhaustion, PCAv was significantly decreased relative to baseline measurements, and the PCAv response to visual stimulation significantly decreased. Compared to baseline, exhaustive exercise significantly suppressed the increase in MAP to visual stimulation, while the CI response did not significantly change by the exercise. These results suggest that exhaustive exercise attenuates the magnitude of NVC by blunting the pressor response to visual stimulation.

Inner ocular blood flow responses to an acute decrease in blood pressure in resting humans.

Whether inner ocular vessels have an autoregulatory response to acute fluctuations in blood pressure is unclear. We tried to examine the validity of acute hypotension elicited by thigh-cuff release as to assess the dynamic autoregulation in the ocular circulation. Blood flow velocity in the superior nasal and inferior temporal retinal arterioles, and in the retinal and choroidal vasculature were measured with the aid of laser speckle flowgraphy before and immediately after an acute decrease in blood pressure in 20 healthy subjects. Acute hypotension was induced by a rapid release of bilateral thigh occlusion cuffs that had been inflated to 220 mmHg for 2 min. The ratio of the relative change in retinal and choroidal blood flow velocity to the relative change in mean arterial blood pressure (MAP) was calculated. Immediately after cuff release, the MAP and blood flows in the all ocular target vessels decreased significantly from the baseline values obtained before thigh-cuff release. The ratio of the relative change in inner ocular blood flow velocity to that in the MAP exceeded 1% / %mmHg. An explicit dynamic autoregulation in inner ocular vessels cannot be demonstrated in response to an acute hypotension induced by the thigh-cuff release technique.

Effects of vasodilatation and pressor response on neurovascular coupling during dynamic exercise.

PURPOSE: Visual stimulation increases the blood flow in the posterior cerebral artery (PCA), which supplies blood to the visual cortex by neurovascular coupling (NVC). Relative contributions of vasodilatation and pressor response on NVC during dynamic exercise are still unknown. METHODS: We measured the blood flow velocity in the PCA (PCAv) by transcranial Doppler ultrasound flowmetry during rest and exercise in 14 healthy males while they performed 12-min submaximal leg-cycle exercises at mild-, moderate-, and high-intensity, which corresponded to heart rates of 120, 140, and 160 bpm, respectively. NVC was estimated as the relative change in PCAv from 20 s eye-closing to the peak response during 40 s looking at a reversed checkerboard. Conductance index was calculated for evaluating vasodilatation as pressure divided by blood flow. RESULTS: In response to visual stimulation, a magnitude of vasodilatation was significantly decreased under the moderate-intensity, while pressor response was significantly suppressed under the high-intensity exercises, compared with the control condition. Conversely, peak response to visual stimulation in PCAv was not affected by exercise intensity though relative and absolute responses were significantly lower in the moderate- and high-intensity exercises than the control. CONCLUSION: It is suggested that the contributions of pressor response and vasodilatation were modified by exercise intensity, partly playing a role for stabilizing the peak response of PCAv with visual stimulation during dynamic exercise.

Effects of heat stress on ocular blood flow during exhaustive exercise.

The hypothesis that heat stress reduces the ocular blood flow response to exhaustive exercise was tested by measuring ocular blood flow, blood pressure, and end- tidal carbon dioxide partial pressure (PETCO2) in 12 healthy males while they performed cycle ergometer exercise at 75% of the maximal heart rate at ambient temperatures of 20°C (control condition) and 35°C (heat condition), until exhaustion. The blood flows in the retinal and choroidal vasculature (RCV), the superior temporal retinal arteriole (STRA) and the superior nasal retinal arteriole (SNRA) were recorded at rest and at 6 and 16 min after the start of exercise period and at exhaustion [after 16 ± 2 min (mean ± SE) and 24 ± 3 min of exercise in the heat and control condition, respectively]. The mean arterial pressure at exhaustion was significantly lower in the heat condition than in the control condition at both 16 min and exhaustion. The degree of PETCO2 reduction did not differ significantly between the two thermal conditions at either 16 min or exhaustion. The blood flow velocity in the RCV significantly increased from the resting baseline value at 6 min in both thermal conditions (32 ± 6% and 25 ± 5% at 20°C and 35°C, respectively). However, at 16 min the increase in RCV blood flow velocity had returned to the resting baseline level only in the heat condition. At exhaustion, the blood flows in the STRA and SNRA had decreased significantly from the resting baseline value in the heat condition (STRA: -19 ± 5% and SNRA: -30 ± 6%), and SNRA blood flow was lower than that in the control condition (-14 ± 6% vs -30 ± 6% at 20°C and 35°C, respectively), despite the finding that both thermal conditions induced the same reductions in PETCO2 and vascular conductance. These findings suggested that the heat condition decreases or suppresses ocular blood flow via attenuation of pressor response during exhaustive exercise. Key PointsThe ocular (retinal and choroidal) blood flow response to exhaustive exercise with heat stress is unknown.We hypothesized that the heat stress decreases ocular blood flow response to exhaustive exercise, since cerebral flow, which is regulated similarly to ocular flow, was reported to decrease during heat stress.To test this hypothesis, ocular blood flow was measured during exhaustive exercise at 20°C (control condition) and 35°C (heat condition).At exhaustion in the heat condition, the ocular flow response was suppressed or decreased with an attenuated pressor response.It is suggested that the heat condition decreases or suppresses the ocular blood flow to exhaustive exercise via attenuation of pressor response.

Ocular blood flow decreases during passive heat stress in resting humans.

BACKGROUND: Heat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow. FINDINGS: Ocular blood flow, end-tidal carbon dioxide (P(ET)CO2) and blood pressure were measured for 12 healthy subjects wearing water-perfused tube-lined suits under two conditions of water circulation: (1) at 35 °C (normothermia) for 30 min and (2) at 50 °C for 90 min (passive heat stress). The blood-flow velocities in the superior temporal retinal arteriole (STRA), superior nasal retinal arteriole (SNRA), and the retinal and choroidal vessels (RCV) were measured using laser-speckle flowgraphy. Blood flow in the STRA and SNRA was calculated from the integral of a cross-sectional map of blood velocity. PETCO2 was clamped at the normothermia level by adding 5% CO2 to the inspired gas. Passive heat stress had no effect on the subjects' blood pressures. The blood-flow velocity in the RCV was significantly lower after 30, 60 and 90 min of passive heat stress than the normothermic level, with a peak decrease of 18 ± 3% (mean ± SE) at 90 min. Blood flow in the STRA and SNRA decreased significantly after 90 min of passive heat stress conditions, with peak decreases of 14 ± 3% and 14 ± 4%, respectively. CONCLUSION: The findings of this study suggest that passive heat stress decreases ocular blood flow irrespective of the blood pressure or arterial partial pressure of CO2.

Regional differences in facial skin blood flow responses to the cold pressor and static handgrip tests.

We have previously reported the unique regional responses of facial skin blood flow (SkBF) to oral application of the basic tastes without simultaneous systemic circulatory changes. In the present study, we determined whether a systemic circulatory challenge due to sympathetic activation induces regional differences in facial SkBF by observing the responses in facial SkBF and blood pressure to a 2-min cold pressor test (CPT) and static handgrip exercise (HG) by right hand in 20 healthy subjects. The CPT significantly increased SkBF in the forehead, eyelid, cheek, upper lip and lower lip by 6 ± 2 to 8 ± 2 % (mean ± SEM) as compared to resting baseline, with a significant simultaneous increase (13 ± 2 %) in mean arterial pressure (MAP), whereas it significantly decreased the SkBF in the nose by 5 ± 2 %. The HG significantly increased SkBF in the forehead, cheek and lower lip by 6 ± 3 to 10 ± 3 %, with a significant simultaneous increase in MAP (13 ± 2 %), while it induced no significant change in the other regions. Increases in SkBF were greater in the right than left cheek during CPT. These results demonstrate that a systemic circulatory challenge via sympathetic activation elicits regional differences in the facial SkBF response.

Effect of preceding exercise on cerebral and splanchnic vascular responses to mental task.

BACKGROUND: To investigate the effect of preceding acute exercise on the peripheral vascular response to a mental task, we measured splanchnic and cerebral blood flow responses to performing a mental task after exercise and resting. METHODS: In the exercise trial, 11 males exercised for 30 min on a cycle ergometer with a workload set at 70% of the age-predicted maximal heart rate for each individual. After a 15-min recovery period, the subjects rested for 5 min for pre-task baseline measurement and then performed mental arithmetic for 5 min followed by 5 min of post-task measurement. In the resting trial, they rested for 45 min and pre-task baseline data was obtained for 5 min. Then mental arithmetic was performed for 5 min followed by post-task measurement. We measured the mean blood velocity in the middle cerebral artery and superior mesenteric artery and the mean arterial pressure. RESULTS: Mean arterial pressure and mean blood velocity in the middle cerebral artery were significantly higher than the baseline during mental arithmetic in both exercise and resting trials. Mean blood velocity in the middle cerebral artery during mental arithmetic was greater in the control trial than the exercise trial. Mean blood velocity in the superior mesenteric artery showed no significant change during mental arithmetic from baseline in both trials. CONCLUSION: These results suggest that acute exercise can moderate the increase in cerebral blood flow induced by a mental task.

Ocular circulatory responses to exhaustive exercise in humans.

It is unclear whether exhaustive dynamic exercise increases ocular blood flow, although we have reported that submaximal exercise increases ocular blood flow. We hypothesized that ocular blood flow decreases at exhaustion, since exhaustion causes hyperventilation, which induces a reduction in PaCO(2). To test this hypothesis, ocular blood flow, blood pressure, and respiratory measurements were made in 12 healthy male subjects during cycle ergometer exercise at 75% of maximal heart rate, until exhaustion. Blood flows in the retinal and choroidal vasculature (RCV), the superior temporal retinal arteriole (STRA), and the superior nasal retinal arteriole (SNRA) were measured with the aid of laser-speckle flowgraphy every 3 min during the exercise. The conductance index (CI) in the ocular vasculature was calculated by dividing the blood flow by the mean arterial pressure (MAP). The mean arterial partial pressure of CO(2) (PaCO(2)) was estimated from tidal volume and end-tidal CO(2) partial pressure. MAP significantly increased from the resting baseline throughout the exercise, while PaCO(2) was significantly decreased at exhaustion and during the recovery period. By 6 min after the onset of exercise, blood flow velocity in the RCV significantly increased by 32 ± 6% (mean ± SD) from the resting baseline value. At exhaustion, blood flow velocity in the RCV did not differ significantly from the resting baseline value, and the STRA blood flow was significantly decreased by 13 ± 4%. The CIs in the RCV, STRA, and SNRA were significantly decreased compared to baseline at exhaustion. These findings suggest that ocular blood flow is increased by submaximal exercise, whereas it is suppressed by the hypocapnia associated with exhaustion.

Autoregulation in the ocular and cerebral arteries during the cold pressor test and handgrip exercise.

The aim of this study was to determine whether autoregulation exerts similar effects in the ocular and cerebral vessels, which are both branches of the internal carotid artery. Ocular blood flow velocities, cerebral blood flow velocity and blood pressure were measured in 11 subjects during a 2-min resting period, static handgrip exercise (HG) and a cold pressor test (CPT). Blood velocity data for the superior and inferior temporal retinal arterioles (STRA and ITRA, respectively) and the retinal and choroidal vasculature (RCV) were obtained for 4 s during the measurement using laser speckle flowmetry. Mean blood flow velocity in the middle cerebral artery (MCAVmean) was measured by transcranial Doppler ultrasound. The conductance index (CI) of each vessel was calculated by dividing blood flow by mean arterial pressure. Blood flow velocity in the RCV increased by 19 ± 9% from resting baseline level during the CPT (P < 0.05), while blood flow in the STRA, ITRA and MCAVmean did not. The CI of the MCA decreased. The RCV blood flow velocity, ITRA blood flow and MCAVmean increased by 8 ± 1, 9 ± 3 and 11 ± 4%, respectively, during the HG (P < 0.05). Conversely, STRA blood flow remained unchanged. The HG did not significantly change the CI in any of the vessels measured. These findings suggest that cerebral blood flow velocity was maintained during the CPT, but autoregulation does not work well in the RCV during the CPT and HG.

Effects of dynamic exercise and its intensity on ocular blood flow in humans.

Visual performance is impaired when the ocular blood flow decreases, indicating that ocular blood flow plays a role in maintaining visual performance during exercise. We examined the ocular blood flow response to incremental cycling exercise to test the hypothesis that ocular blood flow is relatively stable during dynamic exercise because of its autoregulatory nature. The blood flow in the inferior and superior temporal retinal arterioles (ITRA and STRA, respectively) and retinal and choroidal vessels (RCV), mean arterial pressure, and heart rate (HR) were measured at rest and during leg cycling in nine young and healthy subjects (26 ± 5 years, mean ± SD). Ocular blood flow was measured by laser speckle flowmetry. The exercise intensity was incremented by 30 W every 3 min until the subject was unable to maintain a position appropriate for measuring ocular blood flow. Blood flow data obtained during cycling exercise were categorized based on HR as follows: <100, 100-120, and >120 bpm. Blood flow in the RCV increased with the exercise intensity: by 16 ± 8, 32 ± 13, and 40 ± 19% from baseline, respectively. However, blood flow and vascular conductance in the ITRA and STRA did not change significantly with exercise. These findings demonstrate for the first time that ocular blood flow increases in the retina and choroid, but not in the arterioles, with increasing exercise intensity during dynamic exercise.