Duranti Roberto, Bonetti Lorenzo, Vivoli Paolo, Benedetti Tommaso, Binazzi Barbara, Laveneziana Pierantonio, Scano Giorgio
Dipartimento di Medicina Interna, Unita Funzionale di Medicina Iperbarica, University of Florence, Firenze, Italy.
Med Sci Sports Exerc. 2006 Nov;38(11):1932-8. doi: 10.1249/01.mss.0000232020.83242.0c.
Length-tension and force-velocity characteristics of respiratory muscles and hyperinflation are the likely determinants of dyspnea in subjects exercising under hyperbaric conditions. We hypothesize that hyperinflation plays a minor role and that the reduced velocity of shortening of the respiratory muscles modulates dyspnea for any given pleural pressure.
We studied five normal subjects who performed an incremental exercise test on a cycloergometer in both normobaric (SL) and hyperbaric (4 ATA) conditions. We measured breathing pattern, inspiratory pleural pressure swing (Pessw), Delta Pes (i.e., the difference between the most and the less negative pleural pressures during tidal breathing), and dyspnea intensity (Borg score). End-expiratory lung volume (EELV) changes were evaluated by measuring changes in inspiratory capacity. Mean inspiratory flow (VT/TI) was used as an index of velocity of shortening of respiratory muscles.
Compared with SL, at 4 ATA, peak exercise ventilation (VE) (84.5 vs 62.2 L x min(-1)) and VT/TI (2.99 vs 2.16 L x s)(-1) were lower, Pessw (30.9 vs 38.6 cm H2O) and Delta Pes (43.8 vs 62.2 cm H2O) were higher, and Borg score was not different (7.60 vs 8.20 au). EELV decreased progressively during exercise but remained higher than at SL. Borg score was greater for a same VE and lower for a same Delta Pes. VT/TI was lower for a same Pessw. The differences in EELV between SL and 4 ATA did not relate with the concurrent changes in Borg score.
The results confirm our hypothesis that during exercise in hyperbaric conditions, decreased velocity of shortening of respiratory muscles modulates pressure-induced increases in dyspnea, with hyperinflation playing a minor role.
呼吸肌的长度 - 张力和力 - 速度特性以及肺过度充气可能是高压环境下运动受试者呼吸困难的决定因素。我们假设肺过度充气起次要作用，并且在任何给定的胸膜压力下，呼吸肌缩短速度的降低会调节呼吸困难。
我们研究了五名正常受试者，他们在常压（SL）和高压（4个绝对大气压）条件下在自行车测力计上进行递增运动试验。我们测量了呼吸模式、吸气胸膜压力摆动（Pessw）、ΔPes（即潮式呼吸期间最负和次负胸膜压力之间的差值）和呼吸困难强度（Borg评分）。通过测量吸气容量的变化来评估呼气末肺容积（EELV）的变化。平均吸气流量（VT/TI）用作呼吸肌缩短速度的指标。
与SL相比，在4个绝对大气压下，运动峰值通气量（VE）（84.5对62.2 L×min⁻¹）和VT/TI（2.99对2.16 L×s⁻¹）较低，Pessw（30.9对38.6 cmH₂O）和ΔPes（43.8对62.2 cmH₂O）较高，且Borg评分无差异（7.60对8.20 au）。运动期间EELV逐渐下降，但仍高于SL时。对于相同的VE，Borg评分更高；对于相同的ΔPes，Borg评分更低。对于相同的Pessw，VT/TI更低。SL和4个绝对大气压之间EELV的差异与Borg评分的同时变化无关。
结果证实了我们的假设，即在高压环境下运动期间，呼吸肌缩短速度的降低调节了压力诱导的呼吸困难增加，而肺过度充气起次要作用。
