Younes Magdy, Ostrowski Michele, Atkar Raj, Laprairie John, Siemens Andrea, Hanly Patrick
Sleep Centre, Foothills Medical Centre, University of Calgary, Calgary, Alberta, Canada.
J Appl Physiol (1985). 2007 Dec;103(6):1929-41. doi: 10.1152/japplphysiol.00561.2007. Epub 2007 Sep 6.
The response to chemical stimuli (chemical responsiveness) and the increases in respiratory drive required for arousal (arousal threshold) and for opening the airway without arousal (effective recruitment threshold) are important determinants of ventilatory instability and, hence, severity of obstructive apnea. We measured these variables in 21 obstructive apnea patients (apnea-hypopnea index 91 +/- 24 h(-1)) while on continuous-positive-airway pressure. During sleep, pressure was intermittently reduced (dial down) to induce severe hypopneas. Dial downs were done on room air and following approximately 30 s of breathing hypercapneic and/or hypoxic mixtures, which induced a range of ventilatory stimulation before dial down. Ventilation just before dial down and flow during dial down were measured. Chemical responsiveness, estimated as the percent increase in ventilation during the 5(th) breath following administration of 6% CO(2) combined with approximately 4% desaturation, was large (187 +/- 117%). Arousal threshold, estimated as the percent increase in ventilation associated with a 50% probability of arousal, ranged from 40% to >268% and was <120% in 12/21 patients, indicating that in many patients arousal occurs with modest changes in chemical drive. Effective recruitment threshold, estimated as percent increase in pre-dial-down ventilation associated with a significant increase in dial-down flow, ranged from zero to >174% and was <110% in 12/21 patients, indicating that in many patients reflex dilatation occurs with modest increases in drive. The two thresholds were not correlated. In most OSA patients, airway patency may be maintained with only modest increases in chemical drive, but instability results because of a low arousal threshold and a brisk increase in drive following brief reduction in alveolar ventilation.
对化学刺激的反应（化学反应性）以及唤醒（唤醒阈值）和在无唤醒情况下打开气道（有效恢复阈值）所需的呼吸驱动增加是通气不稳定的重要决定因素，因此也是阻塞性呼吸暂停严重程度的重要决定因素。我们在21例阻塞性呼吸暂停患者（呼吸暂停低通气指数为91±24 h⁻¹）接受持续气道正压通气时测量了这些变量。在睡眠期间，压力间歇性降低（调低）以诱发严重的呼吸浅慢。调低操作分别在室内空气中进行，以及在呼吸高碳酸血症和/或低氧混合气约30秒后进行，后者在调低之前诱发一系列通气刺激。测量调低之前的通气和调低期间的气流。化学反应性通过给予6%二氧化碳并伴有约4%去饱和后第5次呼吸时通气增加的百分比来估计，数值较大（187±117%）。唤醒阈值通过与50%唤醒概率相关的通气增加百分比来估计，范围为40%至>268%，21例患者中有12例<120%，这表明在许多患者中，化学驱动的适度变化就会引发唤醒。有效恢复阈值通过与调低气流显著增加相关的调低前通气增加百分比来估计，范围从零至>174%，21例患者中有12例<110%，这表明在许多患者中，驱动的适度增加就会引发反射性扩张。这两个阈值不相关。在大多数阻塞性睡眠呼吸暂停患者中，仅化学驱动适度增加可能就能维持气道通畅，但由于唤醒阈值低以及肺泡通气短暂减少后驱动迅速增加，导致通气不稳定。
