Whitelaw W A, Derenne J, Noble S, McBride B
Department of Medicine, University of Calgary, Alberta, Canada.
Respir Physiol. 1988 May;72(2):151-61. doi: 10.1016/0034-5687(88)90002-3.
Breath-holding subjects often exhibit involuntary contractions of respiratory muscles which are much stronger and faster than the efforts they would make during unrestricted breathing at the same level of CO2 and O2. To gain a better understanding of the genesis of these contractions, we compared them with the respiratory response to external elastic loading. Normal men rebreathed a mixture of 8% CO2 in oxygen against no load, elastic loads of 25 and 75 cm H2O/L, and held their breath, equivalent to an elastic load of 226 cm H2O/L. At iso-CO2, increasing loads led to progressively smaller tidal volumes, inspiratory flow rates and ventilation. However, respiratory muscles were progressively activated by the loads, as indicated by increasing occlusion pressure, so that inspiratory flow rate and ventilation were defended much better than could be expected if no neural compensation occurred. The pattern of respiratory muscle activity in breath-holding was qualitatively similar to that in elastic loading, and seemed quantitatively to be an extreme form of reaction to a large load. The reduction in inspiratory time and therefore of peak inspiratory pressure and ratio of inspiratory to total time with very large loads could be viewed as an adaptive response to limit respiratory muscle fatigue.
屏气的受试者常常表现出呼吸肌的不自主收缩，这些收缩比他们在相同二氧化碳和氧气水平下自由呼吸时所做的努力更强、更快。为了更好地理解这些收缩的起源，我们将它们与对外部弹性负荷的呼吸反应进行了比较。正常男性在无负荷、25 cmH₂O/L和75 cmH₂O/L的弹性负荷下，对含8%二氧化碳的氧气混合气进行再呼吸，并屏气，相当于226 cmH₂O/L的弹性负荷。在等二氧化碳条件下，负荷增加导致潮气量、吸气流量和通气量逐渐减小。然而，如闭塞压增加所示，呼吸肌被负荷逐渐激活，因此吸气流量和通气量得到了比无神经代偿时预期更好的维持。屏气时呼吸肌活动的模式在质量上与弹性负荷时相似，在数量上似乎是对大负荷反应的一种极端形式。吸气时间的缩短以及因此在非常大的负荷下吸气峰值压力和吸气与总时间比值的降低，可以被视为一种限制呼吸肌疲劳的适应性反应。
