Influence of mild hypoxia on cardiorespiratory responses and muscle oxygenation during incremental exercise

This study investigated the influence of cardiorespiratory responses, blood lactate concentration and muscle oxygenation during incremental exercise tests in normoxia and hypoxia. Seven healthy subjects performed an incremental cycle ergometer exercise test breathing in random order either room air or a 15% O2 gas mixture. Ventilation and pulmonary gas exchange were measured and computed breath-bybreath. Arterial oxygen saturation (SaO2) was estimated continuously via pulse oxymeter. Forearm venous blood for measurement of blood lactate was collected every minute. Continuous-wave near infrared spectroscopy measured peripheral tissue saturation (SO2NIRS) in the vastus lateralis muscle. Significant reduction in oxygen uptake (p<0.01), power output (p<0.01) and SaO2 (p<0.001) was found in peak incremental exercise during hypoxia compared with normoxia. For the same power output in the twoconditions, hypoxia significantly decreased SaO2 (ANOVA: p<0.001) and blood lactate concentration (ANOVA: p<0.05) and increased minute ventilation (ANOVA: p<0.01). In the hypoxic condition, oxygen uptake and SO2NIRS were not found when exercising at the same power output compared with normoxia. This study would suggest that mild hypoxia may be avoided through ventilatory compensation at the alveolar level, and oxygen consumption in alveolar and peripheral tissue oxygenation can be maintained while exercising for the same power output

シセイ ガ セキ ノ サイダイ リュウリョウ (Cough Peak Flow) ト コキキン カツドウ ニ アタエル エイキョウ

【目的】姿勢が咳の最大流量(CPF)や咳嗽時呼気筋活動, 呼吸筋力や肺活量にどのような影響を与えるのかを調査することを目的とした. 【方法】健常成人男性17名を対象に背臥位, ベッドアップ45度, 端座位の3姿勢でCPF, 呼吸筋力, 肺活量を計測し, CPF測定時のみ呼気筋(外腹斜筋, 腹直筋)の活動を記録した. 筋活動の評価は, 事前に最大随意収縮時の筋積分値(最大iEMG)を求め, 咳嗽時筋活動を最大iEMGに対する百分率(%iEMG)として評価した. 【結果】CPF, 肺活量, 外腹斜筋の%iEMGは端座位が最も高く, 次いで45度座位, 背臥位の順であり, 端座位と他の姿勢との間には全て有意差を認めた(P<0.05). 腹直筋の%iEMGは姿勢による変化を認めなかった. 【考察】CPFを始め, ほとんどの項目で端座位が最も高く, 背臥位で最低値となり, 姿勢の影響を受けることが明らかになった. 効果的な咳嗽を行なうには背臥位よりも, できるかぎり端座位に近い姿勢で行なうことが望ましいと考えられた.Purpose: The purpose of this study was to investigate the effect of posture on cough peak flow (CPF), electromyographic (EMG) activity of the abdominal muscles (external abdominal oblique muscles, EO; rectus abdominis muscles, RA), respiratory muscle strength (maximum expiratory and inspiratory pressure, PEmax and PImax), and vital capacity (VC). Methods: Seventeen normal adult men participated in this study. We measured the CPF, EMG activities of the EO and RA during coughing, PEmax, PEmax, and VC in the following 3 postures: supine, 45 degrees head-up, and sitting. The raw EMG data were rectified, and the integrated EMG data were normalized relative to the values obtained during maximum voluntary contractions (%iEMG). Results: CPF, %iEMG of the EO, PImax, PEmax, and VC were higher in the sitting position than in any of the other positions. The %iEMG of the RA did not change with posture. Conclusion: These results suggest that CPF, %iEMG of the EO, PImax, PEmax, and VC are affected by the posture, and that it is preferable to adopt a more head-up position for effective coughing