Respiratory Responses to Graded Isocapnic Expiratory Threshold Loading in Humans

健康受測者對閥性吐氣負載於第二氧化碳下的呼吸反應

王儷穎(Li-Ying Wang) ； Frank J. Cerny

《物理治療》 25卷5期 (2000/09) Pp. 292-303

摘要

研究背景與目的：健康的受測者對閥性吐氣負載(expiratory threshold load；ETL)的典型反應是持續性的過度換氣。實驗假設，當閥性吐氣負載所引起的二氧化碳過低現象（hypocapnia），經由在吸氣端加入二氧化碳矯正至與平靜呼吸「等二氧化碳壓」（isocapnia）後，呼吸及腹肌活動對閥性吐氣負載反應會增強。本研究的另一個目的是測定體位（body position）對閥性吐氣負載反應的影響。研究方法：總共十位受測者參與本實驗。我們分別測試在仰臥（supine）及直立（upright）的體位下，每位受測者對閥性吐氣負載，在加入（ISO）與不加入（CON；即對照組）二氧化碳的狀況下，呼吸及腹肌活動反應。閥性吐氣負載包括四個值，分別為０，５，１５，２５水柱壓。呼吸反應包括吸氣時間(T1)，吐氣時間(TE)，總呼氣時間(TTOT)，潮氣容積(VT)，呼吸率(Fb)，每分鐘換氣量(VE)，平均吸氣氣流率(VT/Tl)，及平均吐氣氣流(VT/TE)的測定。腹肌活動反應由表面電極來測定，包括腹內斜肌（internal oblique muscle；IO）和腹外斜肌（external oblique muscle；IO）的肌電圖。肌電圖的起始（times of onset；onset latencies）和持續時間（duration）由原始肌電圖來測定（raw EMGs）；肌電圖的最高振幅（peak amplitudes）由整合肌電圖（integrated EMGs）來測定。實驗過程中，我們持續監測記錄潮氣末二氧化碳分壓（end-tidal PCO2；PETCO2）。實驗結果：閥性吐氣負載導致潮氣末二氧化碳分壓的下降（CON），並調整為與平靜呼吸等「二氧化碳壓」（ISO）。在仰臥及直立體位下，對於閥性吐氣負載的呼吸反應包括：潮氣容積，每分鐘換氣量，平均吸氣流率，及平均吐氣氣流率在「等二氧化碳壓」的狀態下（ISO）顯著的大於對照組（CON）。內、外腹斜肌對閥性吐氣負載的反應中，肌電振幅大小及持續時間不受潮氣末二氧化碳壓的影響但起始時間時間在「二氧化碳壓」（ISO）的狀況下顯著較短。在直立體位下，潮氣容積，每分鐘換氣量，肌電振幅及持續時間對閥性吐氣負載的反應顯著大於仰臥體位。結論：根據實驗結果，我們推斷閥性吐氣負載所引發的「低二氧化碳壓」是對閥性吐氣負載所加在呼吸系統上的壓迫的一種代償，並藉由此，預防因二氧化碳所可能引起的過度呼吸。

關鍵字

閥性吐氣負載 ； 等二氧化碳壓 ； 體位 ； 呼吸反應 ； 呼吸控制

並列摘要

Background and Purpose：In healthy human subjects, an expiratory threshold load (ELT)induces sustained hyperventilation. We hypothesized that, during ETL breathing, the ventilatory responses and abdominal expiratory activity would be greater if the ETL-related hypocapnia were pre-vented by maintaining the end-tidal PCO2 (PETCO2) isocapnic to near that during quiet breathing. Another purpose was to determine the effect of body position on these ETL responses. Methods：We studied 10 subjects who breathed against ETL without (CON)and with CO2 added(ISO)in both supine and upright positions. ETLs were studied at 0,5,15 and 25 cm H2O Inspiratory (T1), expiratory (TE), and total cycle (TTOT) durations, tidal volume (VT), breathing frequency (Fb), minute ventilation (VE), mean inspiratory flow rate (VT/Tl), and mean expiratory flow rate (VT/TE) were determined from inspiratory flow recordings. Abdominal electromyograms (EMGs) were detected with surface electrodes placed over the internal (IO) and external oblique muscle (EO) regions. Times of onset (onset latencies),and duration of the EMG expiratory bursts were determined from raw EMGs；peak amplitudes of the EMG expiratory bursts were determined from the integrated EMGs.TETCO2 was continuously recorded. Results：In response to ETL,PETCO2 decreased during CON and was maintained isocapnic to quiet breathing(QB) level during ISO. During ISO, VT, VE, VT/Tl, and VT/TE were significantly greater than those during CON in both body positions. Amplitudes and durations of the EMG expiratory bursts from EO and IO abdominal muscles were not different between CON and ISO but the onset latencies of these expiratory bursts during ISO were significantly shorter than those during CON. During either ETL conditions tidal volume (VT), minute ventilation (VE), peak amplitudes and durations of the abdominal EMG expiratory bursts were greater when the subjects were upright than supine. The onset latencies of the EMGs were shorter when the subjects were upright than when supine. Conclusion：We conclude that, during loaded ETL breathing ,developing hypocapnia acts to compensate for this stress by preventing further CO2-induced hyperpnea.

並列關鍵字

Expiratory threshold loading ； ETL ； Isocapnic ； Body position ； Ventilatory responses ； Control of breathing