Autonomic Neuroscience: Basic and Clinical, Dec 1, 2016
Primary graft dysfunction (PGD) is one of the most common complications after lung transplant and... more Primary graft dysfunction (PGD) is one of the most common complications after lung transplant and is associated with significant early and late morbidity and mortality. The cause of primary graft dysfunction is often multifactorial involving patient, donor, and operational factors. Diastolic dysfunction is increasingly recognized as an important risk factor for development of PGD after lung transplant and here we examine recent evidence on the topic. Patients with end-stage lung disease are more likely to suffer from cardiovascular disease including diastolic dysfunction. PGD as result of ischemia-reperfusion injury after lung transplant is exacerbated by increased left atrial pressure and pulmonary venous congestion impacted by diastolic dysfunction. Recent studies on relationship between diastolic dysfunction and PGD after lung transplant show that patients with diastolic dysfunction are more likely to develop PGD with worse survival outcome and complicated hospital course. Patients with diastolic dysfunction is more likely to suffer from PGD after lung transplant. From the lung transplant candidate selection to perioperative and posttransplant care, thorough evaluation and documentation diastolic dysfunction to guide patient care are imperative.
A volumetric solar receiver receives the concentrated radiation generated by a large number of he... more A volumetric solar receiver receives the concentrated radiation generated by a large number of heliostats. Heat transfer takes place from the receiver solid phase to the air as it passes through the porous receiver. Such combined heat transfer within the receiver, associated radiation, convection and conduction, are investigated using a local thermal nonequilibrium model. The Rosseland approximation is applied to account for the radiative heat transfer through the solar receiver, while the low Mach approximation is exploited to investigate the compressible flow through the receiver. Analytic solutions are obtained for the developments of air and ceramic temperatures as well as the pressure along the flow direction. The results show that the pore diameter must be larger than its critical value to achieve high receiver efficiency. Subsequently, there exists an optimal pore diameter for achieving the maximum receiver efficiency under the equal pumping power. The solutions serve as a us...
The cardiovascular and respiratory effects of exercise have been widely studied, as have the auto... more The cardiovascular and respiratory effects of exercise have been widely studied, as have the autonomic effects of imagined and observed exercise. However, the effects of observed exercise in the first person have not been documented, nor have direct recordings of muscle sympathetic nerve activity (MSNA) been obtained during observed or imagined exercise. The aim of the current study was to measure blood pressure, heart rate, respiration, skin blood flow, sweat release, and MSNA (via microelectrodes inserted into the common peroneal nerve), during observation of exercise from the first person point of view. It was hypothesized that the moving stimuli would produce robust compensatory increases in the above-mentioned parameters as effectively as those generated by mental imagery and-to a lesser extent-actual exercise. Nine subjects watched a first-person running video, allowing them to view the action from the perspective of the runner rather than viewing someone else perform the exercise. On average, statistically significant increases from baseline during the running phase were seen in heart rate, respiratory rate, skin blood flow, and burst amplitude of MSNA. These results suggest that observation of exercise in the first person is a strong enough stimulus to evoke "physiologically appropriate" autonomic responses that have a purely psychogenic origin.
American Journal of Physiology-Heart and Circulatory Physiology, 2009
The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsi... more The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsiveness of SNA to changes in blood pressure. In a slightly different analysis, the baroreflex threshold measures the probability of whether a sympathetic burst will occur at a given diastolic blood pressure. We hypothesized that baroreflex threshold analysis could be used to estimate the sensitivity of the sympathetic baroreflex measured by the pharmacological modified Oxford test. We compared four measures of sympathetic baroreflex sensitivity in 25 young healthy participants: the “gold standard” modified Oxford analysis (nitroprusside and phenylephrine), nonbinned spontaneous baroreflex analysis, binned spontaneous baroreflex analysis, and threshold analysis. The latter three were performed during a quiet baseline period before pharmacological intervention. The modified Oxford baroreflex sensitivity was significantly related to the threshold slope ( r = 0.71, P < 0.05) but not to the...
To test the effectiveness of centrifuge-induced artificial gravity with ergometric exercise, 12 h... more To test the effectiveness of centrifuge-induced artificial gravity with ergometric exercise, 12 healthy young men (20.7 ± 1.9 yr) were exposed to simulated microgravity for 14 days of -6 • head-down bedrest. Half the subjects were randomly selected and loaded 1.2 G artificial gravity with 60 W (four out of six subjects) or 40 W (two out of six subjects) of ergometric workload on days 1, 2, 11, 12, 13, 14 (CM group). The rest of the subjects served as the control. Anti-G score, defined as the G-load × running time to the endpoint, was significantly elongated by the load of the centrifuge-ergometer. Plasma volume loss was suppressed (-5.0 ± 2.4 vs. -16.4 ± 1.9%), and fluid volume shift was prevented by the countermeasure load. Elevated heart rate and muscle sympathetic nerve activity after bedrest were counteracted, and exaggerated response to head-up tilt was also suppressed. Centrifuge-induced artificial gravity with exercise is effective in preventing cardiovascular deconditioning due to microgravity exposure, however, an effective and appropriate regimen (magnitude of G-load and exercise workload) should be determined in future studies.
International Journal of Biometeorology, Oct 31, 2012
During the past several decades, obesity has been increasing globally. In Japan, obesity is defin... more During the past several decades, obesity has been increasing globally. In Japan, obesity is defined by a BMI of 25 kg/m² or over; 28.6 % of men and 20.6 % of women are obese. Obese people have an increased incidence of developing cardiovascular, renal, and hormonal diseases and sleep disorders. Obese people also have shortened sleep durations. We investigated seasonal differences in melatonin concentrations, heart rates, and heart rate variability during sleep in obese subjects in Japan. Five obese (BMI, 32.0 ± 4.9 kg/m²) and five non-obese (BMI, 23.2 ± 2.9 kg/m²) men participated in this study in the summer and winter. Electrocardiograms were measured continuously overnight in a climatic chamber at 26 °C with a relative humidity of 50 %. Saliva samples for melatonin were collected at 2300 hours, 0200 hours, and 0600 hours. We found that melatonin concentrations during sleep in obese subjects were significantly lower than those in non-obese subjects in the winter. Heart rate during sleep in winter was significantly higher than that in summer in both obese and non-obese subjects. Heart rate variability was not significantly different in the summer and winter in both obese and non-obese subjects. Our results show that decreased nocturnal melatonin concentrations during winter in obese men may be related to higher heart rates, and this may suggest that obese men are at an increased risk of a cardiovascular incident during sleep, especially in the winter.
The benefits of lower body positive pressure (LBPP) are generally accepted for clinical treatment... more The benefits of lower body positive pressure (LBPP) are generally accepted for clinical treatment in medical emergencies caused by massive bleeding to maintain the systemic blood pressure. They are also used by NASA post spaceflight for preventing orthostatic hypotension in the astronauts. However, controversy still exists concerning the mechanisms underlying LBPP benefits. The purpose of this study was to test the hypothesis that the baroreflex-mediated enhancement in sympathetic activity would be attenuated by LBPP during an orthostatic challenge in humans. Specifically, we studied 1) the sympathetic activity responses by the microneurographic technique, using direct intraneural measurement of muscle sympathetic nerve activity (MSNA); and 2) the contributions of preload and afterload to the chances in MSNA response during orthostasis on application of LBPP. To accomplish these issues, MSNA was recorded microneurographically along with noninvasive measurement of the cardiovascular variables in all the subjects during exposure to a 70 degrees HUT with 30-mm Hg LBPP.
This study aimed to clarify how muscle sympathetic nerve activity (MSNA) in humans, which plays a... more This study aimed to clarify how muscle sympathetic nerve activity (MSNA) in humans, which plays an important role in blood pressure control against gravity, is altered under microgravity (microG) conditions, and how the MSNA change is modified by breathing maneuvers. Ten subjects seated themselves in a jet aircraft with their knees extended. MSNA was recorded microneurographically from the left tibial nerve with simultaneous monitoring of ECG, blood pressure, respiration, and intrathoracic blood volume estimated by the impedance method during parabolic flight in a jet aircraft. In half of the parabolas, their respiration was controlled at 0.25 Hz by a metronome. Results: MSNA was enhanced under hypergravity just before microG entry, and immediately suppressed by microG induced by parabolic flight. The suppression was more marked with controlled than with uncontrolled respiration (51.6 +/- 7.2 vs 82.8 +/- 2.5%, mean +/- SE, 1G=100%). MSNA changes during microG correlated significantly to changes in blood pressure and intrathoracic blood volume. The blood pressure fall 10 to 15 sec after microG entry was less prominent with controlled than with uncontrolled respiration. We conclude that changes in arterial blood pressure and intrathoracic blood volume modulate MSNA during microG induced by parabolic flight, depending largely on breathing maneuvers.
Both lower body positive pressure (LBPP) and head-down tilt (HDT) can induce fluid shifts from th... more Both lower body positive pressure (LBPP) and head-down tilt (HDT) can induce fluid shifts from the lower body to the thorax and result in a loading of cardiopulmonary baroreceptors. The aim of this study was to compare the effects of LBPP and HDT on cardiovascular responses in humans. To accomplish this, a graded LBPP test of 10, 20 and 30 mmHg, as well as a 6 degrees HDT was applied. It has been suggested that <20 mmHg LBPP and <30 degrees HDT load the cardiopulmonary baroreceptors by translocation of blood volume from the lower body to the thorax, while >20 mmHg LBPP activates the intramuscular pressure-sensitive receptors.
Advances in Experimental Medicine and Biology, Dec 28, 2009
In order to elucidate the effects of deconditioning (inactivity) on the ventilatory and circulato... more In order to elucidate the effects of deconditioning (inactivity) on the ventilatory and circulatory responses at the onset of exercise within 20 s, we initiated head-down bed rest and unilateral lower limb suspension experiments, and measured these responses to dynamic voluntary leg exercise and passive movements. Initial ventilatory and heart rate responses to voluntary exercise were attenuated after bed rest but showed no change after suspension or during passive movements, suggesting the minimal role of peripheral neural reflex.
To clarify the role of autonomic nervous functions in cardiovascular adaptation to microgravity, ... more To clarify the role of autonomic nervous functions in cardiovascular adaptation to microgravity, heart rate variability (HRV) and blood pressure variability (BPV) were evaluated during thermoneutral head-out water immersion (HOI) of eight healthy young subjects 23 to 31 yr of age. The very low-frequency (VLF; 0.00-0.04 Hz) component of BPV tended to increase during HOI, whereas the low-frequency (LF; 0.04-0.15 Hz) component of BPV and the ratio of LF power to high-frequency (HF; 0.15-0.40 Hz) component (LF/HF ratio) of HRV decreased. The HF component of HRV increased in all the subjects during immersion up to the shoulder. Concomitantly, we found a decrease in heart rate and increases in stroke volume and cardiac output with no significant changes in BP and respiration rate during HOI. These results suggest that both vasomotor and cardiac sympathetic activities are suppressed and that the parasympathetic (vagal) activity is enhanced during HOI.
Medicine and Science in Sports and Exercise, May 1, 2018
metabolic and ventilatory parameters, and perceptual responses were measured throughout each TT. ... more metabolic and ventilatory parameters, and perceptual responses were measured throughout each TT. Statistical differences between TT DS and TT C were tested each 20% interval of the TT using Student's paired t-tests. Data are expressed as means ± SD. RESULTS: Subjects displayed normal pulmonary function upon study entry. Time to completion was greater in TT DS compared with TT C (536±34 vs. 489±34 s, p<0.05) as a result of reduced power at 40-100% of TT DS completion compared with TT C (Δ=-10.2±8.7%). Additionally, minute ventilation (V ̇E) was similar at 40-100% of TT DS completion compared with TT C (Δ=0.9±11.0%). However, integrated inspiratory mouth pressure (∫P m ) was greater throughout TT DS compared with TT C (p<0.05), and arterial pulse saturation (SpO 2 ) fell at a greater rate throughout TT DS compared with TT C (-2.2±0.8 vs. -1.3±0.4 % per interval, p<0.01). Rating of perceived breathlessness (RPB) was significantly greater at 20% and 40% of TT DS compared with TT C , but was not different during the remaining intervals. CONCLUSION: Power output during a cycling time trial is reduced in response to increased ventilatory stress in an effort to balance the additional ventilatory work and potential impact to blood gas tensions. Additionally, the fact that V ̇E and RPB were largely similar between conditions suggests that these parameters may play an important role in the determination of self-selected work rates.
To clarify the mechanism of postprandial hypotension (PPH), we made microneurographic analyses of... more To clarify the mechanism of postprandial hypotension (PPH), we made microneurographic analyses of patients with PPH and 10 healthy controls by recording multi-unit vasoconstrictive impulses of muscle sympathetic nerve activity (MSNA) directly from the tibial nerve fascicles during a glucose tolerance test. Oral intake of 75 grams glucose in 225 ml of water produced significant and prolonged hypotension in all patients and an increase in MSNA in all healthy subjects. Insulin and glucose responses were not significantly correlated with arterial blood pressure reduction. PPH was prevented by an infusion of vasopressin (0.3 U/min) given before glucose intake. These results suggest that PPH is caused by the lack of sympathetic compensation for the systemic hypotensive stress of splanchnic blood pooling that occurs after food ingestion, and that prior treatment with vasopressin reduces the portal venous flow by constricting the splanchnic vessels in patients with PPH.
The mechanism of cardiovascular deconditioning, such as an orthostatic intolerance after space fl... more The mechanism of cardiovascular deconditioning, such as an orthostatic intolerance after space flight, has not been well clarified. Several studies to investigate that mechanism have focused mainly on hemodynamic changes including heart rate, arterial blood pressure, cardiac output, etc., but no studies have yielded a direct insight into changes in the sympathetic nervous system. Among ground-based experiments, parabolic flight is the only maneuver to expose human subjects to actual microgravity although it lasts for only a short duration of approx. 20 sec. Using microneurography, the present study aimed to analyze the involvement of the sympathetic nervous system in regulating the acute effects of fluid shift induced by parabolic flight during the transitional changes from 1 G to hypergravity, hypergravity to microgravity, and microgravity to hypergravity by direct measurement of sympathetic outflow to the muscles. Some parts of the study were published elsewhere. We also investigated how the sympathetic outflow to muscle is modified during microgravity with elimination of the breathing effect by comparing the cardiovascular parameters under controlled and uncontrolled respiration.
Mist sauna is a style of bathing in which hot water vapor is sprayed into a bathroom, establishin... more Mist sauna is a style of bathing in which hot water vapor is sprayed into a bathroom, establishing an air temperature of 40°C with saturated humidity. Bath heater and dryer equipment with mist sauna function was released onto the Japanese market in 2004. After their introduction, various studies investigated the effects of mist sauna bathing, and it has been demonstrated that mist sauna bathing has various effects and efficacies, not only hyperthermic effects but also other effects including on physical appearance. Mist sauna bathing occurs in a bathroom, usually without a toilet, in which the room temperature is approximately 40°C with 100% relative humidity. It has been shown that the mist sauna causes little hemodynamic change, which ensures its safety during bathing. Therefore, we can enjoy safer physiological bathing in a mist sauna than in traditional hot water immersion bathing. In addition, the mist sauna elicits benefits such as improved skin condition, heat acclimation, and autonomic balance. Since mist sauna bathing does not involve immersion of the body in bathtub water, it is less likely to result in an accident during bathing because of the low impact of hemodynamic changes. Recently, mist sauna bathing has drawn attention in the field of nursing care as a bathing style for the hospitalized elderly that can reduce the burden on care-giving personnel during bathing. It is expected that mist sauna will be adopted by homes and various facilities as a useful approach for various purposes, regardless of the user's age or gender.
American Journal of Physiology-regulatory Integrative and Comparative Physiology, Aug 1, 1999
thetic outflow to muscle in humans during short periods of microgravity produced by parabolic fli... more thetic outflow to muscle in humans during short periods of microgravity produced by parabolic flight.
Autonomic Neuroscience: Basic and Clinical, Dec 1, 2016
Primary graft dysfunction (PGD) is one of the most common complications after lung transplant and... more Primary graft dysfunction (PGD) is one of the most common complications after lung transplant and is associated with significant early and late morbidity and mortality. The cause of primary graft dysfunction is often multifactorial involving patient, donor, and operational factors. Diastolic dysfunction is increasingly recognized as an important risk factor for development of PGD after lung transplant and here we examine recent evidence on the topic. Patients with end-stage lung disease are more likely to suffer from cardiovascular disease including diastolic dysfunction. PGD as result of ischemia-reperfusion injury after lung transplant is exacerbated by increased left atrial pressure and pulmonary venous congestion impacted by diastolic dysfunction. Recent studies on relationship between diastolic dysfunction and PGD after lung transplant show that patients with diastolic dysfunction are more likely to develop PGD with worse survival outcome and complicated hospital course. Patients with diastolic dysfunction is more likely to suffer from PGD after lung transplant. From the lung transplant candidate selection to perioperative and posttransplant care, thorough evaluation and documentation diastolic dysfunction to guide patient care are imperative.
A volumetric solar receiver receives the concentrated radiation generated by a large number of he... more A volumetric solar receiver receives the concentrated radiation generated by a large number of heliostats. Heat transfer takes place from the receiver solid phase to the air as it passes through the porous receiver. Such combined heat transfer within the receiver, associated radiation, convection and conduction, are investigated using a local thermal nonequilibrium model. The Rosseland approximation is applied to account for the radiative heat transfer through the solar receiver, while the low Mach approximation is exploited to investigate the compressible flow through the receiver. Analytic solutions are obtained for the developments of air and ceramic temperatures as well as the pressure along the flow direction. The results show that the pore diameter must be larger than its critical value to achieve high receiver efficiency. Subsequently, there exists an optimal pore diameter for achieving the maximum receiver efficiency under the equal pumping power. The solutions serve as a us...
The cardiovascular and respiratory effects of exercise have been widely studied, as have the auto... more The cardiovascular and respiratory effects of exercise have been widely studied, as have the autonomic effects of imagined and observed exercise. However, the effects of observed exercise in the first person have not been documented, nor have direct recordings of muscle sympathetic nerve activity (MSNA) been obtained during observed or imagined exercise. The aim of the current study was to measure blood pressure, heart rate, respiration, skin blood flow, sweat release, and MSNA (via microelectrodes inserted into the common peroneal nerve), during observation of exercise from the first person point of view. It was hypothesized that the moving stimuli would produce robust compensatory increases in the above-mentioned parameters as effectively as those generated by mental imagery and-to a lesser extent-actual exercise. Nine subjects watched a first-person running video, allowing them to view the action from the perspective of the runner rather than viewing someone else perform the exercise. On average, statistically significant increases from baseline during the running phase were seen in heart rate, respiratory rate, skin blood flow, and burst amplitude of MSNA. These results suggest that observation of exercise in the first person is a strong enough stimulus to evoke "physiologically appropriate" autonomic responses that have a purely psychogenic origin.
American Journal of Physiology-Heart and Circulatory Physiology, 2009
The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsi... more The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsiveness of SNA to changes in blood pressure. In a slightly different analysis, the baroreflex threshold measures the probability of whether a sympathetic burst will occur at a given diastolic blood pressure. We hypothesized that baroreflex threshold analysis could be used to estimate the sensitivity of the sympathetic baroreflex measured by the pharmacological modified Oxford test. We compared four measures of sympathetic baroreflex sensitivity in 25 young healthy participants: the “gold standard” modified Oxford analysis (nitroprusside and phenylephrine), nonbinned spontaneous baroreflex analysis, binned spontaneous baroreflex analysis, and threshold analysis. The latter three were performed during a quiet baseline period before pharmacological intervention. The modified Oxford baroreflex sensitivity was significantly related to the threshold slope ( r = 0.71, P < 0.05) but not to the...
To test the effectiveness of centrifuge-induced artificial gravity with ergometric exercise, 12 h... more To test the effectiveness of centrifuge-induced artificial gravity with ergometric exercise, 12 healthy young men (20.7 ± 1.9 yr) were exposed to simulated microgravity for 14 days of -6 • head-down bedrest. Half the subjects were randomly selected and loaded 1.2 G artificial gravity with 60 W (four out of six subjects) or 40 W (two out of six subjects) of ergometric workload on days 1, 2, 11, 12, 13, 14 (CM group). The rest of the subjects served as the control. Anti-G score, defined as the G-load × running time to the endpoint, was significantly elongated by the load of the centrifuge-ergometer. Plasma volume loss was suppressed (-5.0 ± 2.4 vs. -16.4 ± 1.9%), and fluid volume shift was prevented by the countermeasure load. Elevated heart rate and muscle sympathetic nerve activity after bedrest were counteracted, and exaggerated response to head-up tilt was also suppressed. Centrifuge-induced artificial gravity with exercise is effective in preventing cardiovascular deconditioning due to microgravity exposure, however, an effective and appropriate regimen (magnitude of G-load and exercise workload) should be determined in future studies.
International Journal of Biometeorology, Oct 31, 2012
During the past several decades, obesity has been increasing globally. In Japan, obesity is defin... more During the past several decades, obesity has been increasing globally. In Japan, obesity is defined by a BMI of 25 kg/m² or over; 28.6 % of men and 20.6 % of women are obese. Obese people have an increased incidence of developing cardiovascular, renal, and hormonal diseases and sleep disorders. Obese people also have shortened sleep durations. We investigated seasonal differences in melatonin concentrations, heart rates, and heart rate variability during sleep in obese subjects in Japan. Five obese (BMI, 32.0 ± 4.9 kg/m²) and five non-obese (BMI, 23.2 ± 2.9 kg/m²) men participated in this study in the summer and winter. Electrocardiograms were measured continuously overnight in a climatic chamber at 26 °C with a relative humidity of 50 %. Saliva samples for melatonin were collected at 2300 hours, 0200 hours, and 0600 hours. We found that melatonin concentrations during sleep in obese subjects were significantly lower than those in non-obese subjects in the winter. Heart rate during sleep in winter was significantly higher than that in summer in both obese and non-obese subjects. Heart rate variability was not significantly different in the summer and winter in both obese and non-obese subjects. Our results show that decreased nocturnal melatonin concentrations during winter in obese men may be related to higher heart rates, and this may suggest that obese men are at an increased risk of a cardiovascular incident during sleep, especially in the winter.
The benefits of lower body positive pressure (LBPP) are generally accepted for clinical treatment... more The benefits of lower body positive pressure (LBPP) are generally accepted for clinical treatment in medical emergencies caused by massive bleeding to maintain the systemic blood pressure. They are also used by NASA post spaceflight for preventing orthostatic hypotension in the astronauts. However, controversy still exists concerning the mechanisms underlying LBPP benefits. The purpose of this study was to test the hypothesis that the baroreflex-mediated enhancement in sympathetic activity would be attenuated by LBPP during an orthostatic challenge in humans. Specifically, we studied 1) the sympathetic activity responses by the microneurographic technique, using direct intraneural measurement of muscle sympathetic nerve activity (MSNA); and 2) the contributions of preload and afterload to the chances in MSNA response during orthostasis on application of LBPP. To accomplish these issues, MSNA was recorded microneurographically along with noninvasive measurement of the cardiovascular variables in all the subjects during exposure to a 70 degrees HUT with 30-mm Hg LBPP.
This study aimed to clarify how muscle sympathetic nerve activity (MSNA) in humans, which plays a... more This study aimed to clarify how muscle sympathetic nerve activity (MSNA) in humans, which plays an important role in blood pressure control against gravity, is altered under microgravity (microG) conditions, and how the MSNA change is modified by breathing maneuvers. Ten subjects seated themselves in a jet aircraft with their knees extended. MSNA was recorded microneurographically from the left tibial nerve with simultaneous monitoring of ECG, blood pressure, respiration, and intrathoracic blood volume estimated by the impedance method during parabolic flight in a jet aircraft. In half of the parabolas, their respiration was controlled at 0.25 Hz by a metronome. Results: MSNA was enhanced under hypergravity just before microG entry, and immediately suppressed by microG induced by parabolic flight. The suppression was more marked with controlled than with uncontrolled respiration (51.6 +/- 7.2 vs 82.8 +/- 2.5%, mean +/- SE, 1G=100%). MSNA changes during microG correlated significantly to changes in blood pressure and intrathoracic blood volume. The blood pressure fall 10 to 15 sec after microG entry was less prominent with controlled than with uncontrolled respiration. We conclude that changes in arterial blood pressure and intrathoracic blood volume modulate MSNA during microG induced by parabolic flight, depending largely on breathing maneuvers.
Both lower body positive pressure (LBPP) and head-down tilt (HDT) can induce fluid shifts from th... more Both lower body positive pressure (LBPP) and head-down tilt (HDT) can induce fluid shifts from the lower body to the thorax and result in a loading of cardiopulmonary baroreceptors. The aim of this study was to compare the effects of LBPP and HDT on cardiovascular responses in humans. To accomplish this, a graded LBPP test of 10, 20 and 30 mmHg, as well as a 6 degrees HDT was applied. It has been suggested that <20 mmHg LBPP and <30 degrees HDT load the cardiopulmonary baroreceptors by translocation of blood volume from the lower body to the thorax, while >20 mmHg LBPP activates the intramuscular pressure-sensitive receptors.
Advances in Experimental Medicine and Biology, Dec 28, 2009
In order to elucidate the effects of deconditioning (inactivity) on the ventilatory and circulato... more In order to elucidate the effects of deconditioning (inactivity) on the ventilatory and circulatory responses at the onset of exercise within 20 s, we initiated head-down bed rest and unilateral lower limb suspension experiments, and measured these responses to dynamic voluntary leg exercise and passive movements. Initial ventilatory and heart rate responses to voluntary exercise were attenuated after bed rest but showed no change after suspension or during passive movements, suggesting the minimal role of peripheral neural reflex.
To clarify the role of autonomic nervous functions in cardiovascular adaptation to microgravity, ... more To clarify the role of autonomic nervous functions in cardiovascular adaptation to microgravity, heart rate variability (HRV) and blood pressure variability (BPV) were evaluated during thermoneutral head-out water immersion (HOI) of eight healthy young subjects 23 to 31 yr of age. The very low-frequency (VLF; 0.00-0.04 Hz) component of BPV tended to increase during HOI, whereas the low-frequency (LF; 0.04-0.15 Hz) component of BPV and the ratio of LF power to high-frequency (HF; 0.15-0.40 Hz) component (LF/HF ratio) of HRV decreased. The HF component of HRV increased in all the subjects during immersion up to the shoulder. Concomitantly, we found a decrease in heart rate and increases in stroke volume and cardiac output with no significant changes in BP and respiration rate during HOI. These results suggest that both vasomotor and cardiac sympathetic activities are suppressed and that the parasympathetic (vagal) activity is enhanced during HOI.
Medicine and Science in Sports and Exercise, May 1, 2018
metabolic and ventilatory parameters, and perceptual responses were measured throughout each TT. ... more metabolic and ventilatory parameters, and perceptual responses were measured throughout each TT. Statistical differences between TT DS and TT C were tested each 20% interval of the TT using Student's paired t-tests. Data are expressed as means ± SD. RESULTS: Subjects displayed normal pulmonary function upon study entry. Time to completion was greater in TT DS compared with TT C (536±34 vs. 489±34 s, p<0.05) as a result of reduced power at 40-100% of TT DS completion compared with TT C (Δ=-10.2±8.7%). Additionally, minute ventilation (V ̇E) was similar at 40-100% of TT DS completion compared with TT C (Δ=0.9±11.0%). However, integrated inspiratory mouth pressure (∫P m ) was greater throughout TT DS compared with TT C (p<0.05), and arterial pulse saturation (SpO 2 ) fell at a greater rate throughout TT DS compared with TT C (-2.2±0.8 vs. -1.3±0.4 % per interval, p<0.01). Rating of perceived breathlessness (RPB) was significantly greater at 20% and 40% of TT DS compared with TT C , but was not different during the remaining intervals. CONCLUSION: Power output during a cycling time trial is reduced in response to increased ventilatory stress in an effort to balance the additional ventilatory work and potential impact to blood gas tensions. Additionally, the fact that V ̇E and RPB were largely similar between conditions suggests that these parameters may play an important role in the determination of self-selected work rates.
To clarify the mechanism of postprandial hypotension (PPH), we made microneurographic analyses of... more To clarify the mechanism of postprandial hypotension (PPH), we made microneurographic analyses of patients with PPH and 10 healthy controls by recording multi-unit vasoconstrictive impulses of muscle sympathetic nerve activity (MSNA) directly from the tibial nerve fascicles during a glucose tolerance test. Oral intake of 75 grams glucose in 225 ml of water produced significant and prolonged hypotension in all patients and an increase in MSNA in all healthy subjects. Insulin and glucose responses were not significantly correlated with arterial blood pressure reduction. PPH was prevented by an infusion of vasopressin (0.3 U/min) given before glucose intake. These results suggest that PPH is caused by the lack of sympathetic compensation for the systemic hypotensive stress of splanchnic blood pooling that occurs after food ingestion, and that prior treatment with vasopressin reduces the portal venous flow by constricting the splanchnic vessels in patients with PPH.
The mechanism of cardiovascular deconditioning, such as an orthostatic intolerance after space fl... more The mechanism of cardiovascular deconditioning, such as an orthostatic intolerance after space flight, has not been well clarified. Several studies to investigate that mechanism have focused mainly on hemodynamic changes including heart rate, arterial blood pressure, cardiac output, etc., but no studies have yielded a direct insight into changes in the sympathetic nervous system. Among ground-based experiments, parabolic flight is the only maneuver to expose human subjects to actual microgravity although it lasts for only a short duration of approx. 20 sec. Using microneurography, the present study aimed to analyze the involvement of the sympathetic nervous system in regulating the acute effects of fluid shift induced by parabolic flight during the transitional changes from 1 G to hypergravity, hypergravity to microgravity, and microgravity to hypergravity by direct measurement of sympathetic outflow to the muscles. Some parts of the study were published elsewhere. We also investigated how the sympathetic outflow to muscle is modified during microgravity with elimination of the breathing effect by comparing the cardiovascular parameters under controlled and uncontrolled respiration.
Mist sauna is a style of bathing in which hot water vapor is sprayed into a bathroom, establishin... more Mist sauna is a style of bathing in which hot water vapor is sprayed into a bathroom, establishing an air temperature of 40°C with saturated humidity. Bath heater and dryer equipment with mist sauna function was released onto the Japanese market in 2004. After their introduction, various studies investigated the effects of mist sauna bathing, and it has been demonstrated that mist sauna bathing has various effects and efficacies, not only hyperthermic effects but also other effects including on physical appearance. Mist sauna bathing occurs in a bathroom, usually without a toilet, in which the room temperature is approximately 40°C with 100% relative humidity. It has been shown that the mist sauna causes little hemodynamic change, which ensures its safety during bathing. Therefore, we can enjoy safer physiological bathing in a mist sauna than in traditional hot water immersion bathing. In addition, the mist sauna elicits benefits such as improved skin condition, heat acclimation, and autonomic balance. Since mist sauna bathing does not involve immersion of the body in bathtub water, it is less likely to result in an accident during bathing because of the low impact of hemodynamic changes. Recently, mist sauna bathing has drawn attention in the field of nursing care as a bathing style for the hospitalized elderly that can reduce the burden on care-giving personnel during bathing. It is expected that mist sauna will be adopted by homes and various facilities as a useful approach for various purposes, regardless of the user's age or gender.
American Journal of Physiology-regulatory Integrative and Comparative Physiology, Aug 1, 1999
thetic outflow to muscle in humans during short periods of microgravity produced by parabolic fli... more thetic outflow to muscle in humans during short periods of microgravity produced by parabolic flight.
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Papers by Satoshi Iwase