PubMed Health⌕ Search

Biomedical subjects

Keisho Katayama

Publications and source records attributed to Keisho Katayama.

At least 19 recordsLinked to original sources
PubMed2006

Effect of arterial oxygenation on quadriceps fatigability during isolated muscle exercise.

The effect of various levels of oxygenation on quadriceps muscle fatigability during isolated muscle exercise was assessed in six male subjects. Twitch force (Q(tw)) was assessed using supramaximal magnetic femoral nerve stimulation. In experiment 1, maximal voluntary contraction (MVC) and Q(tw) of resting quadriceps muscle were measured in normoxia [inspired O(2) fraction (Fi(O(2))) = 0.21, percent arterial O(2) saturation (Sp(O(2))) = 98.4%, estimated arterial O(2) content (Ca(O(2))) = 20.8 ml/dl], acute hypoxia (Fi(O(2)) = 0.11, Sp(O(2)) = 74.6%, Ca(O(2)) = 15.7 ml/dl), and acute hyperoxia (Fi(O(2)) = 1.0, Sp(O(2)) = 100%, Ca(O(2)) = 22.6 ml/dl). No significant differences were found for MVC and Q(tw) among the three Fi(O(2)) levels. In experiment 2, the subjects performed three sets of nine, intermittent, isometric, unilateral, submaximal quadriceps contractions (62% MVC followed by 1 MVC in each set) while breathing each Fi(O(2)). Q(tw) was assessed before and after exercise, and myoelectrical activity of the vastus lateralis was obtained during exercise. The percent reduction of twitch force (potentiated Q(tw)) in hypoxia (-27.0%) was significantly (P < 0.05) greater than in normoxia (-21.4%) and hyperoxia (-19.9%), as were the changes in intratwitch measures of contractile properties. The increase in integrated electromyogram over the course of the nine contractions in hypoxia (15.4%) was higher (P < 0.05) than in normoxia (7.2%) or hyperoxia (6.7%). These results demonstrate that quadriceps muscle fatigability during isolated muscle exercise is exacerbated in acute hypoxia, and these effects are independent of the relative exercise intensity.

Adult↗
PubMed2006

Oxygen uptake kinetics following 20 days of unilateral lower limb suspension.

The purpose of the present study was to examine the effect of unilateral lower limb suspension (ULLS) deconditioning on oxygen uptake kinetics. Eight healthy males underwent ULLS for 20 days and performed a series of 6-min square-wave transitions from rest to 60-W single-leg cycling exercises just before and after ULLS. To characterize the kinetics of the oxygen uptake response, a single exponential model was applied to the data until the end of the fast component omitted the first 15 s of the on-transit using a nonlinear least-squares fitting procedure. The following results were found: (i) the time constant of oxygen uptake was unchanged before and after ULLS; (ii) although there was no significant difference in the baseline and the asymptotic amplitude of the fast component, the asymptote, i.e., the absolute asymptotic amplitude of the fast component (the sum of the baseline and the asymptotic amplitude), and the end exercise oxygen uptake were decreased after ULLS; (iii) the contribution of the slow component to the total response of oxygen uptake was unchanged at pre- and post-ULLS. In conclusion, the asymptote in the fast component and the end exercise oxygen uptake were decreased after 20-d ULLS, though the response speed and the amplitude of the slow component of oxygen uptake were not changed. It is suggested that deconditioning as a result of limb disuse affects oxygen uptake response.

Adaptation, Physiological↗
PubMed2006

Ventilatory and circulatory responses at the onset of exercise after eccentric exercise.

The purpose of this study was to clarify whether delayed onset muscle soreness (DOMS) and muscle damage after eccentric exercise (ECC) could affect the ventilatory and circulatory responses at the onset of exercise, and whether those effects would continue after the disappearance of DOMS. Ten males participated in this study. We measured ventilatory and circulatory responses at the onset of exercise, for the first 20 s, during knee extension-relaxation voluntary exercise (VOL) and passive movement (PAS), which was achieved by the experimenter alternatively pulling ropes connected to the subjects' ankles for the same period and frequency as during VOL. VOL and PAS were performed before, 2 days after, and 7 days after ECC. The following results were found: (1) the gain of minute ventilation at the onset of VOL at 2 days after ECC was significantly larger than that of before ECC; (2) the gain of minute ventilation at 7 days after ECC during both VOL and PAS was also enhanced significantly as compared to that of before ECC; and (3) heart rate and blood pressure responses were unchanged throughout the experimental period. In conclusion, ventilatory response at the onset of exercise is augmented during DOMS and EIMD after ECC and the enhanced ventilatory response continued after the disappearance of DOMS. It is suggested that enhanced ventilatory response during exercise after ECC is attributed to at least the changes in neural factors and that the mechanisms inducing these augmented ventilatory responses should be different during the period after ECC.

Adult↗
PubMed2005

Changes in ventilatory responses to hypercapnia and hypoxia after intermittent hypoxia in humans.

The purpose of this study was to clarify the changes in hypercapnic and hypoxic ventilatory responses (HCVR and HVR) after intermittent hypoxia and following the cessation of hypoxic exposure. Twenty-nine males were assigned to one of four groups, i.e., a hypoxic (EX1-H, n=7) or a control (EX1-C, n=7) group in Experiment 1, and a hypoxic (EX2-H, n=8) or a control (EX2-C, n=7) group in Experiment 2. In each experiment, the hypoxic tent system was utilized for intermittent hypoxia, and the oxygen levels in the tent were maintained at 12.3+/-0.2%. In Experiment 1, the EX1-H group spent 3 h/day in the hypoxic tent for 1 week. HCVR and HVR were determined before and after 1 week of intermittent hypoxia, and again 1 and 2 week after the cessation of hypoxic exposure. In Experiment 2, the subjects in the EX2-H group performed 3 h/day for 2 weeks in intermittent hypoxia. HCVR and HVR tests were carried out before and after intermittent hypoxia, and were repeated again after 2 weeks of the cessation of hypoxic exposure. The slope of the HCVR in the EX1-H group did not show a significant increase after 1 week of intermittent hypoxia, while HCVR in the EX2-H group increased significantly after 2 weeks of intermittent hypoxia. The HCVR intercept was unchanged following 1 or 2 weeks of intermittent hypoxia. There was a significant increase in the slope of the HVR after 1 and 2 weeks of intermittent hypoxia. The increased HCVR and HVR returned to pre-hypoxic levels after 2 weeks of the cessation of hypoxia. These results suggest that 3 h/day for 2 weeks of intermittent hypoxia leads to an increase in central hypercapnic ventilatory chemosensitivity, which is not accompanied by a re-setting of the central chemoreceptors, and that the increased hypercapnic and hypoxic chemosensitivities are restored within 2 weeks after the cessation of hypoxia.

Adaptation, Physiological↗
PubMed2005

Effect of a repeated series of intermittent hypoxic exposures on ventilatory response in humans.

The purpose of this study was to elucidate the magnitude and the time course of ventilatory changes resulting from a repeated series of hypoxic exposures. Eight healthy males participated in the present study. The subjects spent 1 h/day in normobaric hypoxia (12% inspired oxygen). Inspired minute ventilation (V(I)), end-tidal partial pressure of carbon dioxide (P(ET(CO2))), and arterial oxygen saturation (SaO2) were measured in a hypoxic tent. These measurements were taken for 10 consecutive days (series 1), and were taken again after the subjects had been away from hypoxic exposure for 1 month (series 2). P(ET(CO2)) decreased and SaO2 increased progressively in the hypoxic tent during the 10 days of intermittent hypoxia in series 1. At the onset of series 2 (days 1 to 3), P(ET(CO2)) was significantly lower and SaO2 was significantly higher than those on day 1 during series 1. These results suggest that humans who have had previous hypoxic exposure adapt sooner to hypoxic condition due to an increase in the magnitude of hyperventilation in the first few days of a series of reexposures to hypoxia.

Acclimatization↗
PubMed2005

Vestibulo-cardiorespiratory responses at the onset of chair rotation in endurance runners.

Stimulation of the vestibular system has been reported to elicit ventilatory and circulatory changes in humans. The purpose of this study was to clarify the characteristics of vestibular-mediated ventilatory and circulatory responses in male endurance runners at the onset of passive chair rotation, which selectively stimulates the semicircular canals. Fourteen runners and 14 male untrained subjects participated. The vestibular stimulus test, which consists of 180 degrees chair rotations (left or right half-turns on an earth-vertical axis) for a duration of 2 s, was carried out on each subject. Inspiratory minute ventilation, tidal volume, respiratory frequency, heart rate, and blood pressure were measured by breath-by-breath and beat-to-beat techniques before, during, and after the chair rotation for a total of 60 s. It was found in this study that (i) the relative change of minute ventilation response in the endurance runners was significantly (P < 0.05) greater than in the untrained subjects during and after the rotation, and that (ii) no significant group differences were observed in heart rate and mean blood pressure responses during and after the rotation. In conclusion, vestibular-mediated ventilatory response, but not circulatory response, at the onset of the chair rotation in the endurance runners was significantly greater than that in the untrained subjects. The results from the present study suggest that an increase in vestibulo-ventilatory response would be attributed to an adaptation to long-term endurance training.

Adaptation, Physiological↗
PubMed2005

Intensive cycle training with artificial gravity maintains muscle size during bed rest.

INTRODUCTION: The present study aimed to investigate the effect of intensive cycle training with short-arm centrifuge-induced hypergravity during bed rest on muscle size and function. METHODS: This study involved 10 healthy men who were divided into 2 groups: a countermeasure group, BR-CM (n = 5); and a control group, BR-Cont (n = 5). The BR-CM subjects partook in intensive cycle training (to 90% of maximum HR) with short-arm centrifuge-induced artificial gravity on alternate days during 20-d bed rest. Muscle volume of the thigh and maximum voluntary contraction (MVC) during isometric knee extensions was measured before and after bed rest. Muscle functional magnetic resonance imaging (mfMRI) and electromyogram (EMG) of the quadriceps femoris were obtained during submaximal knee extension exercises at a load of 30% MVC. RESULTS: The volume of the total thigh muscles was maintained in the BR-CM group (-1%), whereas it was not in the BR-Cont group (-9%, p < 0.05). MVC decreased in the BR-CM (7%) and BR-Cont groups (23%). EMG activity in the BR-CM group after bed rest was significantly lower than that of before; however, no significant change was found in the BR-Cont group. There were no significant changes in the resting and exercised mfMRI signals in either the BR-CM or BR-Cont groups. CONCLUSION: These results suggest that intensive cycle training with hypergravity maintained the size of human skeletal muscles during bed rest.

Adult↗
PubMed2004

Ventilatory and circulatory responses at the onset of voluntary exercise and passive movement in sprinters.

The purpose of this study was to clarify the characteristics of ventilatory and circulatory responses at the onset of voluntary exercise and passive movement in sprinters. Eleven male university sprinters and 11 male untrained subjects participated in the present study. Voluntary exercise consisted of leg extension-flexion movement for 20 s with weights corresponding to 5% of each subject's body mass attached to each ankle. Passive movement was achieved without weights by the experimenter alternately pulling ropes that were connected to the subject's ankles for the same period and frequency as during voluntary exercise. In the present study, the following results were found: (1) the magnitude of relative changes (gain) of minute ventilation at the onset of passive movement in the sprinters was significantly smaller than that in the untrained subjects [mean (SEM) 33.3 (2.9) vs 61.7 (6.4)%, P<0.05]; (2) the time for reaching one-half of the gain (response time) of heart rate at the onset of voluntary exercise and passive movement in the sprinters was significantly slower than that in the untrained subjects [2.5 (0.2) vs 1.7 (0.2) s in voluntary exercise and 3.4 (0.8) vs 1.5 (0.1) s in passive movement, P<0.05]; (3) the gain and response time of mean blood pressure at the onset of voluntary exercise and passive movement showed no significant differences between the two groups. It is concluded that sprinters show slowed heart rate response at the onset of voluntary exercise, and attenuated ventilatory and slowed heart rate responses at the onset of passive movement as compared with untrained subjects.

Adaptation, Physiological↗
PubMed2004

Effect of intermittent hypoxia on oxygen uptake during submaximal exercise in endurance athletes.

The purpose of the present study was to clarify the following: (1) whether steady state oxygen uptake (VO(2)) during exercise decreases after short-term intermittent hypoxia during a resting state in trained athletes and (2) whether the change in VO(2) during submaximal exercise is correlated to the change in endurance performance after intermittent hypoxia. Fifteen trained male endurance runners volunteered to participate in this study. Each subject was assigned to either a hypoxic group (n=8) or a control group (n=7). The hypoxic group spent 3 h per day for 14 consecutive days in normobaric hypoxia [12.3 (0.2)% inspired oxygen]. The maximal and submaximal exercise tests, a 3,000-m time trial, and resting hematology assessments at sea level were conducted before and after intermittent normobaric hypoxia. The athletes in both groups continued their normal training in normoxia throughout the experiment. VO(2) during submaximal exercise in the hypoxic group decreased significantly (P<0.05) following intermittent hypoxia. In the hypoxic group, the 3,000-m running time tended to improve (P=0.06) after intermittent hypoxia, but not in the control group. Neither peak VO(2) nor resting hematological parameters were changed in either group. There were significant (P<0.05) relationships between the change in the 3,000-m running time and the change in VO(2) during submaximal exercise after intermittent hypoxia. The results from the present study suggest that the enhanced running economy resulting from intermittent hypoxia could, in part, contribute to improved endurance performance in trained athletes.

Adaptation, Physiological↗
PubMed2004

Ventilatory and heart rate responses at the onset of chair rotation in man.

In the present study, we attempted to confirm whether pulmonary ventilation and heart rate increased immediately after passive chair rotation in man. Inspiratory minute volume (V(I)), tidal volume (V(T)), respiratory frequency (f), and heart rate (HR) were determined by breath-by-breath and beat-by-beat techniques before, during, and after rotation for a total of 45 s. It was found that V(I) significantly increased immediately after chair rotation, but HR remained almost constant. These results suggest that the activation of horizontal semicircular canals is one causal factor of ventilatory response at the onset of exercise with rotational movement in healthy subjects, but heart rate response is not.

Adult↗
PubMed2004

Ventilatory and cardiovascular responses to hypercapnia after 20 days of head-down bed rest.

INTRODUCTION: Few studies have attempted to investigate the influence of prolonged head-down bed rest (HDBR) on hypercapnic ventilatory chemosensitivity, and there are no data available regarding associated changes in arterial BP and heart rate (HR). The aim of this study was to clarify the influence of prolonged HDBR on ventilatory and cardiovascular responses to hypercapnia. METHODS: There were five healthy men who participated in this study. Resting ventilatory and cardiovascular responses to hypercapnia were measured by means of Read's CO2 rebreathing method 4 d before and on the 19th day of HDBR. Measured variables included systolic and diastolic BP (SBP and DBP, respectively), inspired minute ventilation (VI), and end-tidal partial pressure of CO2 (PETCO2). RESULTS: Ventilatory response to hyperoxic hypercapnia (deltaVI/ deltaPETCO2) decreased significantly on the 19th day of HDBR (1.42 +/- 0.65 to 0.90 +/- 0.41 L x min(-1) x torr(-1), p < 0.05). On the other hand, SBP, DBP, and HR responses (deltaSBP/deltaPETCO2, deltaDBP/deltaPETCO2, and deltaHR/deltaPETCO2) were unchanged. DISCUSSION: The results from this study suggest that prolonged HDBR leads to diminished central hypercapnic ventilatory chemosensitivity.

Adult↗
PubMed2004

Acceleration with exercise during head-down bed rest preserves upright exercise responses.

INTRODUCTION: This study was designed to elucidate the effect of short-arm centrifuge-induced artificial gravity with exercise training during ground-based simulated spaceflight, i.e., prolonged head-down bed rest (HDBR), on respiratory and cardiovascular responses to upright exercise. METHODS: There were 10 healthy men who underwent 20 d of -6 degrees HDBR, and were assigned to either a countermeasure (CM) group (n = 5) or a no countermeasure (No-CM) group (n = 5). The subjects in the CM group performed two sessions (20 min each session, 40 min total) of short-arm centrifuge-induced artificial gravity with exercise training in a supine position on alternate days (10 d total) during HDBR. The first session was set at 0.8-1.4 G load at heart level with a constant exercise intensity (60 W), and the second session began with a 0.3 G load at heart level with an interval exercise protocol (40-80% peak oxygen uptake; VO2peak). The measurements of respiratory and cardiovascular responses to incremental exercise were performed pre- and post-HDBR. RESULTS: The 20 d of HDBR increased minute expired ventilation, heart rate, and respiratory exchange ratio and decreased stroke volume during submaximal exercise in the No-CM group, whereas these parameters were unchanged in the CM group. In the No-CM group, VO2peak decreased significantly (47.0 +/- 8.6 to 34.8 +/- 6.8 ml x kg(-1) x min(-1), p < 0.05), whereas VO2peak in the CM group did not show a significant decrease following 20 d of HDBR (47.7 +/- 10.0 to 43.9 +/- 8.9 ml x kg(-1) x min(-1)). These results suggest that short-arm centrifuge-induced artificial gravity with exercise training is effective in maintaining respiratory and cardiovascular responses to upright exercise.

Adolescent↗
PubMed2004

Effect of centrifuge-induced artificial gravity and ergometric exercise on cardiovascular deconditioning, myatrophy, and osteoporosis induced by a -6 degrees head-down bedrest.

We have reported that centrifuge-induced artificial gravity with ergometric exercise could reduce developing cardiovascular deconditioning in humans. In the present study, we examined this load could prevent the myatrophy and osteoporosis induced by head-down bedrest for 20 days. Subjects were ten healthy male volunteers with informed consent. They were requested to lie down at -6 degrees for 20 days, and evaluation for cardiovascular deconditioning, myatrophy, and osteoporosis. As the result, high G-load with low intensity exercise suppressed the orthostatic intolerance and increase in serum osteoporotic marker, whereas low G-load with high intensity ergometric exercise maintained the maximal oxygen intake, heart dimension, and prevented myatrophy. The combination of high/low G-load with low/high intensity exercise will determine the optimal protocol for prevention of cardiovascular deconditioning, myatrophy, and osteoporosis.

Adult↗
PubMed2003

Effect of menstrual cycle and gender on ventilatory and heart rate responses at the onset of exercise.

To clarify the luteal-follicular and male-female differences in ventilatory and heart rate responses at the onset of exercise, seven women and seven men performed voluntary exercise and passive movement for 20 s (brief voluntary exercise and brief passive movement) and voluntary exercise for 3 min (long voluntary exercise) in a sitting position. Voluntary exercise consisted of alternate flexion-extensions of both lower legs with a weight corresponding to about 2.5% of the subjects' body mass attached to each ankle, at a frequency of about 60 times min(-1). Passive movement was carried out without weights by experimenters pulling ropes attached to both of the subjects' ankles, in the same way as voluntary exercise. During these exercises and movements, minute inspiratory ventilation ( V(I)) and heart rate (HR) were continuously measured by breath-by-breath and beat-to-beat techniques. We calculated relative changes of V(I) and HR (Delta V(I) and DeltaHR). Additionally, we averaged Delta V(I) and DeltaHR obtained during the exercise and movement for each subject, and performed a correlation analysis between the averaged Delta V(I) and DeltaHR. It was clarified that: (1) Delta V(I) and DeltaHR in the follicular phase were almost equal to those in the luteal phase; (2) there were no significant male-female differences in these parameters; (3) significant positive correlations were found in both genders only during brief voluntary exercise. We conclude that ventilatory and HR responses at the onset of voluntary exercise and passive movement are not affected by the menstrual cycle or gender.

Adaptation, Physiological↗
PubMed2003

Intermittent hypoxia improves endurance performance and submaximal exercise efficiency.

The purpose of the present study was to elucidate the influence of intermittent hypobaric hypoxia at rest on endurance performance and cardiorespiratory and hematological adaptations in trained endurance athletes. Twelve trained male endurance runners were assigned to either a hypoxic group (n = 6) or a control group (n = 6). The subjects in the hypoxic group were exposed to a simulated altitude of 4500 m for 90 min, three times a week for 3 weeks. The measurements of 3000 m running time, running time to exhaustion, and cardiorespiratory parameters during maximal exercise test and resting hematological status were performed before (Pre) and after 3 weeks of intermittent hypoxic exposure (Post). These measurements were repeated after the cessation of intermittent hypoxia for 3 weeks (Re). In the control group, the same parameters were determined at Pre, Post, and Re for the subjects not exposed to intermittent hypoxia. The athletes in both groups continued their normal training together at sea level throughout the experiment. In the hypoxic group, the 3000 m running time and running time to exhaustion during maximal exercise test improved. Neither cardiorespiratory parameters to maximal exercise nor resting hematological parameters were changed in either group at Post, whereas oxygen uptake (.V(O2)) during submaximal exercise decreased significantly in the hypoxic group. After cessation of intermittent hypoxia for 3 weeks, the improved 3000 m running time and running time to exhaustion tended to decline, and the decreased .V(O2) during submaximal exercise returned to Pre level. These results suggest that intermittent hypoxia at rest could improve endurance performance and submaximal exercise efficiency at sea level in trained endurance athletes, but these improvements are not maintained after the cessation of intermittent hypoxia for 3 weeks.

Adaptation, Physiological↗
PubMed2003

Cardiorespiratory responses to hypoxia and hypercapnia at rest in vocalists.

In order to clarify whether or not ventilatory and circulatory responses to hypoxia and hypercapnia at rest in male vocalists (n = 11) are identical to those of untrained subjects (n = 11), ventilatory responses to hypoxia (HVR) and hypercapnia (HCVR) were estimated as the slope of regression relating .VI to SaO(2) (Delta.VI/DeltaSaO(2)) or the slope factor (A) for the .VI-PETO(2) curve, and as the slope of regression relating .VI to PETCO(2) (Delta.VI/DeltaPETCO(2)), respectively. The respiratory frequency (f), tidal volume (VT), heart rate (HR), and blood pressure (BP) responses to hypoxia and hypercapnia were also estimated as the slope of the line calculated by linear regression related to SaO(2) and PETCO(2). Mean values of Delta.VI/DeltaSaO(2) and A as an index of hypoxic ventilatory response were lower in the vocalist group (0.39 +/- 0.25 l.min(-1).%(-1) and 76.8 +/- 55.7 l.min(-1).torr(-1)) than that in the control group (0.56 +/- 0.46 l.min(-1).%(-1) and 101.6 +/- 85.4 l.min(-1).torr(-1)), and there was no statistically significant difference. The Deltaf/DeltaSaO(2) was significantly (plt;0.05 ) lower in the vocalist group (-0.02 +/- 0.39 breaths.min(-1).%(-1)) than that in the control group (0.43 +/- 0.65 breaths.min(-1).%(-1)). In contrast, mean values of Delta.VI/DeltaPETCO(2) per body mass index were significantly (p<0.05) lower in the vocalist group (0.05 +/- 0.03 l.min(-1).torr(-1)) than those in the control group (0.10 +/- 0.06l.min(-1).torr(-1)). There were also significant differences in DeltaVT/DeltaPETCO(2) and Deltaf/DeltaPETCO(2) between the two groups (p<0.05). However, no significant differences in HR and BP responses to hypoxia and hypercapnia between the two groups were observed. These results suggest that the magnitude of ventilatory response, but not HR and BP, to hypoxia and hypercapnia at rest in vocalists is reduced by chronic vocal training, including breath control and elongation of phonation for long periods.

Adult↗