Hypoxic effects on sympathetic vasomotor outflow and blood pressure during exercise with inspiratory resistance

Katayama, Keisho; Yamashita, Shinichi; Ishida, Kōji; Iwamoto, Erika; Koike, Teruhiko; Saito, Mitsuru

doi:10.1152/ajpregu.00489.2012

Cited by 17 publications

(57 citation statements)

References 49 publications

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“…Additionally, we previously showed that MSNA does increase during mild dynamic exercise in acute hypoxic conditions (Katayama et al . , b ). These results suggest that the cardiopulmonary baroreflex during dynamic exercise could be modified in the presence of heightened sympathetic vasomotor activity.…”

Section: Discussionmentioning

confidence: 99%

“…The MSNA bursts were identified from the mean‐voltage neurogram using customized computer program‐assisted inspection (Katayama et al . , b , ), which accounted for the latency from the ECG R wave to the sympathetic burst (Fagius & Wallin, ). The MSNA was quantified as burst frequency (BF, in bursts per minute) and incidence (BI, in bursts per 100 heart beats; Saito et al .…”

Section: Methodsmentioning

confidence: 99%

“…, ; Katayama et al . , b , ). The MSNA burst amplitude, and thereby total activity, could not be calculated, because in most recordings, electromyographic efferent and afferent nerve activities altered the baselines of the integrated neurogram during leg cycling (Saito et al .…”

Section: Methodsmentioning

confidence: 99%

“…Additionally, our previous study showed that MSNA does increase during mild‐intensity dynamic exercise in hypoxic conditions (Katayama et al . , b ). These results suggest that the cardiopulmonary baroreflex during dynamic exercise could be modulated by a powerful sympatho‐excitatory drive from the exercise pressor reflex, central command and/or the arterial chemoreflex (Fadel & Raven, ; Katayama et al .…”

Section: Introductionmentioning

confidence: 99%

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Hypoxia attenuates cardiopulmonary reflex control of sympathetic nerve activity during mild dynamic leg exercise

Katayama

Ishida

Saito

et al. 2016

Experimental Physiology

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New Findings r What is the central question of this study?The cardiopulmonary baroreflex inhibits adjustment of sympathetic vasomotor outflow during mild-intensity dynamic exercise. However, it is unclear how suppression of sympathetic vasomotor outflow by the cardiopulmonary baroreflex is modulated by a powerful sympatho-excitatory drive from the exercise pressor reflex, central command and/or the arterial chemoreflex. r What is the main finding and its importance?Hypoxia-induced heightened sympathetic nerve activity during dynamic exercise attenuated cardiopulmonary baroreflex control of sympathetic vasomotor outflow. This could facilitate the redistribution of blood flow to the active muscles by sympathetically mediated vasoconstriction of inactive muscles.Muscle sympathetic nerve activity (MSNA) does not increase during mild-intensity dynamic leg exercise in normoxic conditions, despite activation of central command and the exercise pressor reflex. Suppression of MSNA could be caused by muscle pump-induced loading of cardiopulmonary baroreceptors. In contrast, MSNA increases during mild dynamic leg exercise in hypoxic conditions. We hypothesized that hypoxic exercise, which induces a powerful sympatho-excitatory drive from the exercise pressor reflex, central command and/or arterial chemoreflex, attenuates cardiopulmonary reflex control of sympathetic vasomotor outflow. To test this hypothesis, MSNA was recorded during leg cycling in hypoxic conditions and with increased central blood volume by increasing the pedalling frequency to change the cardiopulmonary baroreflex. Subjects performed two leg cycle exercises at different pedal cadences of 60 and 80 r.p.m. (60EX and 80EX trials, respectively) in two (haemodynamic and MSNA) measurement conditions while breathing a hypoxic gas mixture (inspired oxygen fraction = 0.12). Thoracic impedance, stroke volume and cardiac output were measured non-invasively using impedance cardiography. During the MSNA test, MSNA was recorded via microneurography at the right median nerve at the elbow. Changes in thoracic impedance, stroke volume and cardiac output during the 80EX trial were greater than those during the 60EX trial. The MSNA burst frequency during hypoxic exercise in the 80EX trial (39 ± 4 bursts min −1 ) did not differ from that during the 60EX trial (39 ± 3 bursts min −1 ). These results suggest that the cardiopulmonary baroreflex of sympathetic vasomotor outflow during dynamic exercise is modulated by heightened hypoxia-induced sympathetic nerve activity.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hypoxia attenuates cardiopulmonary reflex control of sympathetic nerve activity during mild dynamic leg exercise

Katayama

Ishida

Saito

et al. 2016

Experimental Physiology

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“…Respiratory variables were determined by an online system with a mixing chamber, as in our previous studies (Katayama et al . , ). The subjects breathed through a leak‐free nasal mask (5719; Hans Rudolph, Kansas City, MO, USA).…”

Section: Methodsmentioning

confidence: 99%

Responses of sex steroid hormones to different intensities of exercise in endurance athletes

Sato

Iemitsu

Katayama

et al. 2015

Experimental Physiology

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New Findings r What is the central question of this study?What is the effect of different exercise intensities on sex steroid hormone concentrations in individuals with different degrees of physical fitness? r What is the main finding and its importance?In endurance athletes, serum concentrations of sex steroid hormones increased only with high-intensity exercise. Moreover, different responses of sex steroid hormone secretions were induced by different exercise intensities in individuals with low and high levels of physical fitness.Previous studies have shown that acute exercise elevates sex steroid hormone concentrations in rodents and that sprint exercise increases circulating testosterone in healthy young men. However, the effect of different exercise intensities on sex steroid hormone responses at different levels of physical fitness is still unclear. In this study, we compared circulating sex steroid hormone responses at different exercise intensities in athletes and non-athletes. Eight male endurance athletes and 11 non-athletes performed two 15 min sessions of submaximal exercise at 40 and 70% peak oxygen uptake (V O 2 peak ), respectively, and exercised at 90%V O 2 peak until exhaustion. Venous blood samples were collected during the last minute of each submaximal exercise session and immediately after exhaustion. Acute exercise at 40, 70 and 90%V O 2 peak induced significant increases in serum dehydroepiandrosterone (DHEA) and free testosterone concentrations in non-athletes. On the contrary, only 90%V O 2 peak exercise led to an increase in serum DHEA and free testosterone concentrations in athletes. Serum 5α-dihydrotestosterone concentrations increased with 90%V O 2 peak exercise in both athletes and non-athletes. Additionally, serum estradiol concentrations were significantly increased at moderate and high exercise intensities in both athletes and non-athletes. These results indicate that in endurance athletes, serum sex steroid hormone concentrations, especially serum DHEA and 5α-dihydrotestosterone concentrations, increased only with high-intensity exercise, suggesting that different responses of sex steroid hormone secretion are induced by different exercise intensities in individuals with low and high levels of physical fitness. In athletes, therefore, high-intensity exercise may be required to increase circulating sex steroid hormone concentrations.

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Load carriage physiology in normoxia and hypoxia

Baur,

Buchanan

et al. 2023

Eur J Appl Physiol

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Purpose To determine the effects of load carriage in normoxia and normobaric hypoxia on ventilatory responses, hemodynamics, tissue oxygenation, and metabolism. Methods Healthy males (n = 12) completed 3 randomly ordered baseline graded exercise tests in the following conditions: (1) unloaded normoxic (U: FIO2 = 20.93%), (2) loaded (~ 30 kg) normoxic (LN), and (3) loaded hypoxic simulating ~ 3650 m (LH: FIO2 = ~ 13%). Thereafter, experimental exercise trials were completed in quasi-randomized order (i.e., U completed first) consisting of 3 × 10 min of walking (separated by 5 min seated rest) with stages matched with the U condition (in ascending order) for relative intensity, absolute oxygen consumption ([VO2]; 1.7 L min−1), and walking speed (1.45 ± 0.15 m s−1). Results Load carriage increased perceived exertion and reduced VO2max (LN: − 7%; LH: − 32%; p < 0.05). At matched VO2, stroke volume and tidal volume were reduced and maintained with LN and LH vs. U, respectively (p < 0.05). Increases in cardiac output and minute ventilation at matched VO2 (with LH) and speed (with LN and LH), were primarily accomplished via increases in heart rate and breathing frequency (p < 0.05). Cerebral oxygenated hemoglobin (O2HHb) was increased at all intensities with LN, but deoxygenated hemoglobin and total hemoglobin were increased with LH (p < 0.05). Muscle oxygen kinetics and substrate utilization were similar between LN and U, but LH increased CHO dependence and reduced muscle O2HHb at matched speed (p < 0.05). Conclusion Load carriage reduces cardiorespiratory efficiency and increases physiological strain, particularly in hypoxic environments. Potential load carriage-induced alterations in cerebral blood flow may increase the risk for altitude illnesses and requires further study.

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Hypoxic effects on sympathetic vasomotor outflow and blood pressure during exercise with inspiratory resistance

Cited by 17 publications

References 49 publications

Hypoxia attenuates cardiopulmonary reflex control of sympathetic nerve activity during mild dynamic leg exercise

Hypoxia attenuates cardiopulmonary reflex control of sympathetic nerve activity during mild dynamic leg exercise

Responses of sex steroid hormones to different intensities of exercise in endurance athletes

Load carriage physiology in normoxia and hypoxia

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