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Papers by Manabu Shibasaki
The journal of physiological sciences : JPS, 2020
We investigated that the effects of hypercapnia-induced elevations in cerebral perfusion during a... more We investigated that the effects of hypercapnia-induced elevations in cerebral perfusion during a heat stress on global cerebrovascular responses to an orthostatic challenge. Seven volunteers completed a progressive lower-body negative pressure (LBNP) challenge to presyncope during heat stress, with or without breathing a hypercapnic gas mixture. Administration of the hypercapnic gas mixture increased the partial pressure of end-tidal CO 2 greater than pre-heat stress alone, and increased both internal carotid artery (ICA) and vertebral artery (VA) blood flows ( P < 0.05). During LBNP, both ICA and VA blood flows with the hypercapnic gas mixture remained elevated relative to the control trial ( P < 0.05). However, at the end of LBNP due to pre-syncopal symptoms, both ICA and VA blood flows decreased to similar levels between trials. These findings suggest that hypercapnia-induced cerebral vasodilation is insufficient to maintain cerebral perfusion at the end of LBNP due to p...
Journal of Applied Physiology, 2001
The dependence of O2 uptake (V˙o 2) kinetics on the muscle mass recruited under conditions when f... more The dependence of O2 uptake (V˙o 2) kinetics on the muscle mass recruited under conditions when fiber and muscle recruitment patterns are similar following the onset of exercise has not been determined. We developed a motorized cycle ergometer that facilitated one-leg (1L) cycling in which the electromyographic (EMG) profile of the active muscles was not discernibly altered from that during two-leg (2L) cycling. Six subjects performed 1L and 2L exercise transitions from unloaded cycling to moderate [VT) exercise. The 1L condition yielded kinetics that was unchanged from the 2L condition [the phase 2 time constants (τ1, in s) for 0.05; for >VT: 1L = 26.8 ± 12.0; 2L = 27.8 ± 16.1, P > 0.05]. The overall V˙o 2 kinetics (mean response time) was not significantly different for the two exercise conditions. However, the gain of the fast component (the amplitude/work rate) during the 1L exercise was significantly higher than that for the 2L exercise for both moderate and heavy work ra...
Journal of Applied Physiology, 2000
To investigate how the sweating response to a sustained handgrip exercise depends on changes in t... more To investigate how the sweating response to a sustained handgrip exercise depends on changes in the exercise intensity, the sweating response to exercise was measured in eight healthy male subjects. Each subject lay in the supine position in a climatic chamber (35°C and 50% relative humidity) for ∼60 min. This exposure caused sudomotor activation by increasing skin temperature without a marked change in internal temperature. After this period, each subject performed isometric handgrip exercise [15, 30, 45, and 60% maximal voluntary contraction (MVC)] for 60 s. Although esophageal and mean skin temperatures did not change with a rise in exercise intensity and were similar at all exercise intensities, the sweating rate (SR) on the forearm increased significantly ( P < 0.05) from baseline (0.094 ± 0.021 mg ⋅ cm−2 ⋅ min−1at 30% MVC, 0.102 ± 0.022 mg ⋅ cm−2 ⋅ min−1at 45% MVC, 0.059 ± 0.009 mg ⋅ cm−2 ⋅ min−1at 60% MVC) in parallel with exercise intensity above exercise intensity at 30%...
Journal of Applied Physiology, 2001
The purpose of this study was to identify the pattern of change in the density of activated sweat... more The purpose of this study was to identify the pattern of change in the density of activated sweat glands (ASG) and sweat output per gland (SGO) during dynamic constant-workload exercise and passive heat stress. Eight male subjects (22.8 ± 0.9 yr) exercised at a constant workload (117.5 ± 4.8 W) and were also passively heated by lower-leg immersion into hot water of 42°C under an ambient temperature of 25°C and relative humidity of 50%. Esophageal temperature, mean skin temperature, sweating rate (SR), and heart rate were measured continuously during both trials. The number of ASG was determined every 4 min after the onset of sweating, whereas SGO was calculated by dividing SR by ASG. During both exercise and passive heating, SR increased abruptly during the first 8 min after onset of sweating, followed by a slower increase. Similarly for both protocols, the number of ASG increased rapidly during the first 8 min after the onset of sweating and then ceased to increase further ( P >...
Journal of Applied Physiology, 2001
ACh is the neurotransmitter responsible for increasing sweat rate (SR) in humans. Because ACh is ... more ACh is the neurotransmitter responsible for increasing sweat rate (SR) in humans. Because ACh is rapidly hydrolyzed by acetylcholinesterase (AChE), it is possible that AChE contributes to the modulation of SR. Thus the primary purpose of this project was to identify whether AChE around human sweat glands is capable of modulating SR during local application of various concentrations of ACh in vivo, as well as during a heat stress. In seven subjects, two microdialysis probes were placed in the intradermal space of the forearm. One probe was perfused with the AChE inhibitor neostigmine (10 μM); the adjacent membrane was perfused with the vehicle (Ringer solution). SR over both membranes was monitored via capacitance hygrometry during microdialysis administration of various concentrations of ACh (1 × 10−7–2 M) and during whole body heating. SR was significantly greater at the neostigmine-treated site than at the control site during administration of lower concentrations of ACh (1 × 10−7...
Journal of Applied Physiology, 1999
It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V˙o 2) kinet... more It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V˙o 2) kinetics would be altered by body posture during heavy exercise [i.e., above the lactate threshold (LT)]. Nine subjects performed transitions from unloaded cycling to work rates representing moderate (below the estimated LT) and heavy exercise (V˙o 2 equal to 50% of the difference between LT and peakV˙o 2) under conditions of upright and supine positions. During moderate exercise, the steady-state increase in V˙o 2was similar in the two positions, butV˙o 2 kinetics were slower in the supine position. During heavy exercise, the rate of adjustment ofV˙o 2 to the 6-min value was also slower in the supine position but was characterized by a significant reduction in the amplitude of the fast component ofV˙o 2, without a significant slowing of the phase 2 time constant. However, the amplitude of the slow component was significantly increased, such that the end-exerciseV˙o 2 was the same in the two ...
Journal of applied physiology (Bethesda, Md. : 1985), 2018
Changes in cerebral blood flow (CBF) subsequent to alterations in the partial pressures of oxygen... more Changes in cerebral blood flow (CBF) subsequent to alterations in the partial pressures of oxygen and carbon dioxide can modify dynamic cerebral autoregulation (CA). While cognitive activity increases CBF, the extent to which it impacts CA remains to be established. In the present study we determined whether dynamic CA would decrease during a cognitive task and whether hypoxia would further compound impairment. Fourteen young healthy subjects performed a simple Go/No-go task during normoxia and hypoxia (inspired O fraction = 12%), and the corresponding relationship between mean arterial pressure (MAP) and mean middle cerebral artery blood velocity (MCA V) was examined. Dynamic CA and steady-state changes in MCA V in relation to changes in arterial pressure were evaluated with transfer function analysis. While MCA V increased during the cognitive activity ( P < 0.001), hypoxia did not cause any additional changes ( P = 0.804 vs. normoxia). Cognitive performance was also unaffected...
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2017
We herein investigated the effects of face/head and whole body cooling during passive heat stress... more We herein investigated the effects of face/head and whole body cooling during passive heat stress on human somatosensory processing recorded by somatosensory-evoked potentials (SEPs) at C4′ and Fz electrodes. Fourteen healthy subjects received a median nerve stimulation at the left wrist. SEPs were recorded at normothermic baseline (Rest), when esophageal temperature had increased by ~1.2°C (heat stress: HS) during passive heating, face/head cooling during passive heating (face/head cooling: FHC), and after HS (whole body cooling: WBC). The latencies and amplitudes of P14, N20, P25, N35, P45, and N60 at C4′ and P14, N18, P22, and N30 at Fz were evaluated. Latency indicated speed of the subcortical and cortical somatosensory processing, while amplitude reflected the strength of neural activity. Blood flow in the internal and common carotid arteries (ICA and CCA, respectively) and psychological comfort were recorded in each session. Increases in esophageal temperature due to HS signif...
American Journal of Physiology - Heart and Circulatory Physiology, 2017
The effect of acute increases in cardiac contractility on cerebral blood flow (CBF) remains unkno... more The effect of acute increases in cardiac contractility on cerebral blood flow (CBF) remains unknown. We hypothesized that the external carotid artery (ECA) downstream vasculature modifies the direct influence of acute increases in heart rate and cardiac function on CBF regulation. Twelve healthy subjects received two infusions of dobutamine [first a low dose (5 μg·kg−1·min−1) and then a high dose (15 μg·kg−1·min−1)] for 12 min each. Cardiac output, blood flow through the internal carotid artery (ICA) and ECA, and echocardiographic measurements were performed during dobutamine infusions. Despite increases in cardiac contractility, cardiac output, and arterial pressure with dobutamine, ICA blood flow and conductance slightly decreased from resting baseline during both low- and high-dose infusions. In contrast, ECA blood flow and conductance increased appreciably during both low- and high-dose infusions. Greater ECA vascular conductance and corresponding increases in blood flow may pro...
Applied Human Science Journal of Physiological Anthropology, Mar 1, 1998
The journal of physiological sciences : JPS, 2020
We investigated that the effects of hypercapnia-induced elevations in cerebral perfusion during a... more We investigated that the effects of hypercapnia-induced elevations in cerebral perfusion during a heat stress on global cerebrovascular responses to an orthostatic challenge. Seven volunteers completed a progressive lower-body negative pressure (LBNP) challenge to presyncope during heat stress, with or without breathing a hypercapnic gas mixture. Administration of the hypercapnic gas mixture increased the partial pressure of end-tidal CO 2 greater than pre-heat stress alone, and increased both internal carotid artery (ICA) and vertebral artery (VA) blood flows ( P < 0.05). During LBNP, both ICA and VA blood flows with the hypercapnic gas mixture remained elevated relative to the control trial ( P < 0.05). However, at the end of LBNP due to pre-syncopal symptoms, both ICA and VA blood flows decreased to similar levels between trials. These findings suggest that hypercapnia-induced cerebral vasodilation is insufficient to maintain cerebral perfusion at the end of LBNP due to p...
Journal of Applied Physiology, 2001
The dependence of O2 uptake (V˙o 2) kinetics on the muscle mass recruited under conditions when f... more The dependence of O2 uptake (V˙o 2) kinetics on the muscle mass recruited under conditions when fiber and muscle recruitment patterns are similar following the onset of exercise has not been determined. We developed a motorized cycle ergometer that facilitated one-leg (1L) cycling in which the electromyographic (EMG) profile of the active muscles was not discernibly altered from that during two-leg (2L) cycling. Six subjects performed 1L and 2L exercise transitions from unloaded cycling to moderate [VT) exercise. The 1L condition yielded kinetics that was unchanged from the 2L condition [the phase 2 time constants (τ1, in s) for 0.05; for >VT: 1L = 26.8 ± 12.0; 2L = 27.8 ± 16.1, P > 0.05]. The overall V˙o 2 kinetics (mean response time) was not significantly different for the two exercise conditions. However, the gain of the fast component (the amplitude/work rate) during the 1L exercise was significantly higher than that for the 2L exercise for both moderate and heavy work ra...
Journal of Applied Physiology, 2000
To investigate how the sweating response to a sustained handgrip exercise depends on changes in t... more To investigate how the sweating response to a sustained handgrip exercise depends on changes in the exercise intensity, the sweating response to exercise was measured in eight healthy male subjects. Each subject lay in the supine position in a climatic chamber (35°C and 50% relative humidity) for ∼60 min. This exposure caused sudomotor activation by increasing skin temperature without a marked change in internal temperature. After this period, each subject performed isometric handgrip exercise [15, 30, 45, and 60% maximal voluntary contraction (MVC)] for 60 s. Although esophageal and mean skin temperatures did not change with a rise in exercise intensity and were similar at all exercise intensities, the sweating rate (SR) on the forearm increased significantly ( P < 0.05) from baseline (0.094 ± 0.021 mg ⋅ cm−2 ⋅ min−1at 30% MVC, 0.102 ± 0.022 mg ⋅ cm−2 ⋅ min−1at 45% MVC, 0.059 ± 0.009 mg ⋅ cm−2 ⋅ min−1at 60% MVC) in parallel with exercise intensity above exercise intensity at 30%...
Journal of Applied Physiology, 2001
The purpose of this study was to identify the pattern of change in the density of activated sweat... more The purpose of this study was to identify the pattern of change in the density of activated sweat glands (ASG) and sweat output per gland (SGO) during dynamic constant-workload exercise and passive heat stress. Eight male subjects (22.8 ± 0.9 yr) exercised at a constant workload (117.5 ± 4.8 W) and were also passively heated by lower-leg immersion into hot water of 42°C under an ambient temperature of 25°C and relative humidity of 50%. Esophageal temperature, mean skin temperature, sweating rate (SR), and heart rate were measured continuously during both trials. The number of ASG was determined every 4 min after the onset of sweating, whereas SGO was calculated by dividing SR by ASG. During both exercise and passive heating, SR increased abruptly during the first 8 min after onset of sweating, followed by a slower increase. Similarly for both protocols, the number of ASG increased rapidly during the first 8 min after the onset of sweating and then ceased to increase further ( P >...
Journal of Applied Physiology, 2001
ACh is the neurotransmitter responsible for increasing sweat rate (SR) in humans. Because ACh is ... more ACh is the neurotransmitter responsible for increasing sweat rate (SR) in humans. Because ACh is rapidly hydrolyzed by acetylcholinesterase (AChE), it is possible that AChE contributes to the modulation of SR. Thus the primary purpose of this project was to identify whether AChE around human sweat glands is capable of modulating SR during local application of various concentrations of ACh in vivo, as well as during a heat stress. In seven subjects, two microdialysis probes were placed in the intradermal space of the forearm. One probe was perfused with the AChE inhibitor neostigmine (10 μM); the adjacent membrane was perfused with the vehicle (Ringer solution). SR over both membranes was monitored via capacitance hygrometry during microdialysis administration of various concentrations of ACh (1 × 10−7–2 M) and during whole body heating. SR was significantly greater at the neostigmine-treated site than at the control site during administration of lower concentrations of ACh (1 × 10−7...
Journal of Applied Physiology, 1999
It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V˙o 2) kinet... more It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V˙o 2) kinetics would be altered by body posture during heavy exercise [i.e., above the lactate threshold (LT)]. Nine subjects performed transitions from unloaded cycling to work rates representing moderate (below the estimated LT) and heavy exercise (V˙o 2 equal to 50% of the difference between LT and peakV˙o 2) under conditions of upright and supine positions. During moderate exercise, the steady-state increase in V˙o 2was similar in the two positions, butV˙o 2 kinetics were slower in the supine position. During heavy exercise, the rate of adjustment ofV˙o 2 to the 6-min value was also slower in the supine position but was characterized by a significant reduction in the amplitude of the fast component ofV˙o 2, without a significant slowing of the phase 2 time constant. However, the amplitude of the slow component was significantly increased, such that the end-exerciseV˙o 2 was the same in the two ...
Journal of applied physiology (Bethesda, Md. : 1985), 2018
Changes in cerebral blood flow (CBF) subsequent to alterations in the partial pressures of oxygen... more Changes in cerebral blood flow (CBF) subsequent to alterations in the partial pressures of oxygen and carbon dioxide can modify dynamic cerebral autoregulation (CA). While cognitive activity increases CBF, the extent to which it impacts CA remains to be established. In the present study we determined whether dynamic CA would decrease during a cognitive task and whether hypoxia would further compound impairment. Fourteen young healthy subjects performed a simple Go/No-go task during normoxia and hypoxia (inspired O fraction = 12%), and the corresponding relationship between mean arterial pressure (MAP) and mean middle cerebral artery blood velocity (MCA V) was examined. Dynamic CA and steady-state changes in MCA V in relation to changes in arterial pressure were evaluated with transfer function analysis. While MCA V increased during the cognitive activity ( P < 0.001), hypoxia did not cause any additional changes ( P = 0.804 vs. normoxia). Cognitive performance was also unaffected...
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2017
We herein investigated the effects of face/head and whole body cooling during passive heat stress... more We herein investigated the effects of face/head and whole body cooling during passive heat stress on human somatosensory processing recorded by somatosensory-evoked potentials (SEPs) at C4′ and Fz electrodes. Fourteen healthy subjects received a median nerve stimulation at the left wrist. SEPs were recorded at normothermic baseline (Rest), when esophageal temperature had increased by ~1.2°C (heat stress: HS) during passive heating, face/head cooling during passive heating (face/head cooling: FHC), and after HS (whole body cooling: WBC). The latencies and amplitudes of P14, N20, P25, N35, P45, and N60 at C4′ and P14, N18, P22, and N30 at Fz were evaluated. Latency indicated speed of the subcortical and cortical somatosensory processing, while amplitude reflected the strength of neural activity. Blood flow in the internal and common carotid arteries (ICA and CCA, respectively) and psychological comfort were recorded in each session. Increases in esophageal temperature due to HS signif...
American Journal of Physiology - Heart and Circulatory Physiology, 2017
The effect of acute increases in cardiac contractility on cerebral blood flow (CBF) remains unkno... more The effect of acute increases in cardiac contractility on cerebral blood flow (CBF) remains unknown. We hypothesized that the external carotid artery (ECA) downstream vasculature modifies the direct influence of acute increases in heart rate and cardiac function on CBF regulation. Twelve healthy subjects received two infusions of dobutamine [first a low dose (5 μg·kg−1·min−1) and then a high dose (15 μg·kg−1·min−1)] for 12 min each. Cardiac output, blood flow through the internal carotid artery (ICA) and ECA, and echocardiographic measurements were performed during dobutamine infusions. Despite increases in cardiac contractility, cardiac output, and arterial pressure with dobutamine, ICA blood flow and conductance slightly decreased from resting baseline during both low- and high-dose infusions. In contrast, ECA blood flow and conductance increased appreciably during both low- and high-dose infusions. Greater ECA vascular conductance and corresponding increases in blood flow may pro...
Applied Human Science Journal of Physiological Anthropology, Mar 1, 1998