Angus Sarah A, Taylor Joshua L, Mann Leah M, Williams Alexandra M, Stöhr Eric J, Au Jason S, Sheel Andrew William, Dominelli Paolo B
Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.
School of Kinesiology, The University of British Columbia, Vancouver, British Columbia, Canada.
J Physiol. 2023 Nov;601(21):4807-4821. doi: 10.1113/JP285101. Epub 2023 Sep 29.
Intrathoracic pressure (ITP) swings that permit spontaneous ventilation have physiological implications for the heart. We sought to determine the effect of respiration on cardiac output ( ) during semi-supine cycle exercise using a proportional assist ventilator to minimize ITP changes and lower the work of breathing (W ). Twenty-four participants (12 females) completed three exercise trials at 30%, 60% and 80% peak power (W ) with unloaded (using a proportional assist ventilator, PAV) and spontaneous breathing. Intrathoracic and intraabdominal pressures were measured with balloon catheters placed in the oesophagus and stomach. Left ventricular (LV) volumes and were determined via echocardiography. Heart rate (HR) was measured with electrocardiogram and a customized metabolic cart measured oxygen uptake ( ). Oesophageal pressure swings decreased from spontaneous to PAV breathing by -2.8 ± 3.1, -4.9 ± 5.7 and -8.1 ± 7.7 cmH O at 30%, 60% and 80% W , respectively (P = 0.01). However, the decreases in W were similar across exercise intensities (27 ± 42 vs. 35 ± 24 vs. 41 ± 22%, respectively, P = 0.156). During PAV breathing compared to spontaneous breathing, decreased by -1.0 ± 1.3 vs. -1.4 ± 1.4 vs. -1.5 ± 1.9 l min (all P < 0.05) and stroke volume decreased during PAV breathing by -11 ± 12 vs. -9 ± 10 vs. -7 ± 11 ml from spontaneous breathing at 30%, 60% and 80% W , respectively (all P < 0.05). HR was lower during PAV breathing by -5 ± 4 beats min at 80% W (P < 0.0001). Oxygen uptake decreased by 100 ml min during PAV breathing compared to spontaneous breathing at 80% W (P < 0.0001). Overall, attenuating ITPs mitigated LV preload and ejection, thereby suggesting that the ITPs associated with spontaneous respiration impact cardiac function during exercise. KEY POINTS: Pulmonary ventilation is accomplished by alterations in intrathoracic pressure (ITP), which have physiological implications on the heart and dynamically influence the loading parameters of the heart. Proportional assist ventilation was used to attenuate ITP changes and decrease the work of breathing during exercise to examine its effects on left ventricular (LV) function. Proportional assist ventilation with progressive exercise intensities (30%, 60% and 80% W ) led to reductions in cardiac output at all intensities, primarily through reductions in stroke volume. Decreases in LV end-diastolic volume (30% and 60% W ) and increases in LV end-systolic volume (80% W ) were responsible for the reduction in stroke volume. The relationship between cardiac output and oxygen uptake is disrupted during respiratory muscle unloading.
允许自主通气的胸内压（ITP）波动对心脏具有生理影响。我们试图使用比例辅助通气机来最小化ITP变化并降低呼吸功（W），从而确定半卧位周期运动期间呼吸对心输出量（ ）的影响。24名参与者（12名女性）在30%、60%和80%峰值功率（W ）下完成了三次运动试验，分别采用无负载（使用比例辅助通气机，PAV）和自主呼吸。通过放置在食管和胃中的气囊导管测量胸内压和腹内压。通过超声心动图测定左心室（LV）容积和 。通过心电图测量心率（HR），并使用定制的代谢推车测量摄氧量（ ）。在30%、60%和80%W 时，食管压力波动从自主呼吸到PAV呼吸分别降低了-2.8±3.1、-4.9±5.7和-8.1±7.7cmH₂O（P = 0.01）。然而，在不同运动强度下W的降低相似（分别为27±42%、35±24%和41±22%，P = 0.156）。与自主呼吸相比，在PAV呼吸期间， 分别降低了-1.0±1.3、-1.4±1.4和-1.5±1.9 l/min（所有P < 0.05），并且在30%、60%和80%W 时，与自主呼吸相比，PAV呼吸期间每搏输出量分别降低了-11±12、-9±10和-7±11 ml（所有P < 0.05）。在80%W 时，PAV呼吸期间HR降低了-5±4次/分钟（P < 0.0001）。在80%W 时，与自主呼吸相比，PAV呼吸期间摄氧量降低了100 ml/min（P < 0.0001）。总体而言，减弱ITP可减轻左心室前负荷和射血，从而表明与自主呼吸相关的ITP在运动期间影响心脏功能。要点：肺通气通过胸内压（ITP）的改变来实现，这对心脏具有生理影响，并动态影响心脏的负荷参数。在运动期间使用比例辅助通气来减弱ITP变化并降低呼吸功，以检查其对左心室（LV）功能的影响。随着运动强度逐渐增加（30%、60%和80%W ）进行比例辅助通气，导致所有强度下心输出量降低，主要是通过每搏输出量降低。左心室舒张末期容积降低（30%和60%W ）以及左心室收缩末期容积增加（80%W ）是每搏输出量降低的原因。在呼吸肌卸载期间，心输出量与摄氧量之间的关系被破坏。
