Harms C A, Wetter T J, McClaran S R, Pegelow D F, Nickele G A, Nelson W B, Hanson P, Dempsey J A
Department of Preventive Medicine, John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin, Madison, Wisconsin 53705, USA.
J Appl Physiol (1985). 1998 Aug;85(2):609-18. doi: 10.1152/jappl.1998.85.2.609.
We have recently demonstrated that changes in the work of breathing during maximal exercise affect leg blood flow and leg vascular conductance (C. A. Harms, M. A. Babcock, S. R. McClaran, D. F. Pegelow, G. A. Nickele, W. B. Nelson, and J. A. Dempsey. J. Appl. Physiol. 82: 1573-1583, 1997). Our present study examined the effects of changes in the work of breathing on cardiac output (CO) during maximal exercise. Eight male cyclists [maximal O2 consumption (VO2 max): 62 +/- 5 ml . kg-1 . min-1] performed repeated 2.5-min bouts of cycle exercise at VO2 max. Inspiratory muscle work was either 1) at control levels [inspiratory esophageal pressure (Pes): -27.8 +/- 0.6 cmH2O], 2) reduced via a proportional-assist ventilator (Pes: -16.3 +/- 0.5 cmH2O), or 3) increased via resistive loads (Pes: -35.6 +/- 0.8 cmH2O). O2 contents measured in arterial and mixed venous blood were used to calculate CO via the direct Fick method. Stroke volume, CO, and pulmonary O2 consumption (VO2) were not different (P > 0.05) between control and loaded trials at VO2 max but were lower (-8, -9, and -7%, respectively) than control with inspiratory muscle unloading at VO2 max. The arterial-mixed venous O2 difference was unchanged with unloading or loading. We combined these findings with our recent study to show that the respiratory muscle work normally expended during maximal exercise has two significant effects on the cardiovascular system: 1) up to 14-16% of the CO is directed to the respiratory muscles; and 2) local reflex vasoconstriction significantly compromises blood flow to leg locomotor muscles.
我们最近证实，最大运动期间呼吸功的变化会影响腿部血流和腿部血管传导率（C.A. 哈姆斯、M.A. 巴布科克、S.R. 麦克拉兰、D.F. 佩格洛、G.A. 尼克勒、W.B. 尼尔森和J.A. 登普西。《应用生理学杂志》82: 1573 - 1583, 1997）。我们目前的研究考察了最大运动期间呼吸功的变化对心输出量（CO）的影响。八名男性自行车运动员[最大耗氧量（VO₂ max）：62 ± 5 ml·kg⁻¹·min⁻¹]在VO₂ max水平进行了多次2.5分钟的自行车运动。吸气肌功分别为：1）处于对照水平[吸气食管压（Pes）：-27.8 ± 0.6 cmH₂O]，2）通过比例辅助通气机降低（Pes：-16.3 ± 0.5 cmH₂O），或3）通过阻力负荷增加（Pes：-35.6 ± 0.8 cmH₂O）。通过直接Fick法，利用动脉血和混合静脉血中测得的氧含量来计算CO。在VO₂ max时，对照试验和负荷试验之间的每搏输出量、CO和肺耗氧量（VO₂）无差异（P > 0.05），但在VO₂ max时吸气肌卸载时比对照值低（分别低-8%、-9%和-7%）。卸载或负荷时动静脉氧差无变化。我们将这些发现与我们最近的研究相结合，以表明最大运动期间正常消耗的呼吸肌功对心血管系统有两个显著影响：1）高达14 - 16%的CO流向呼吸肌；2）局部反射性血管收缩显著损害腿部运动肌的血流。
