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Expiratory threshold loading impairs cardiovascular function in health and chronic heart failure during submaximal exercise

University of Wisconsin-Madison, John Rankin Laboratory of Pulmonary Medicine, Madison, Wisconsin

Submitted 17 July 2005 ; accepted in final form 10 March 2006

We determined the effects of augmented expiratory intrathoracic pressure (P_ITP) production on cardiac output (Q_TOT) and blood flow distribution in healthy dogs and dogs with chronic heart failure (CHF). From a control expiratory P_ITP excursion of 7 ± 2 cmH₂O, the application of 5, 10, or 15 cmH₂O expiratory threshold loads increased the expiratory P_ITP excursion by 47 ± 23, 67 ± 32, and 118 ± 18% (P < 0.05 for all). Stroke volume (SV) rapidly decreased (onset <10 s) with increases in the expiratory P_ITP excursion (–2.1 ± 0.5%, –2.4 ± 0.9%, and –3.6 ± 0.7%, P < 0.05), with slightly smaller reductions in Q_TOT (0.8 ± 0.6, 1.0 ± 1.1, and 1.8 ± 0.8%, P < 0.05) owing to small increases in heart rate. Both Q_TOT and SV were restored to control levels when the inspiratory P_ITP excursion was augmented by the addition of an inspiratory resistive load during 15 cmH₂O expiratory threshold loading. The highest level of expiratory loading significantly reduced hindlimb blood flow by –5 ± 2% owing to significant reductions in vascular conductance (–7 ± 2%). After the induction of CHF by 6 wk of rapid cardiac pacing at 210 beats/min, the expiratory P_ITP excursions during nonloaded breathing were not significantly changed (8 ± 2 cmH₂O), and the application of 5, 10, and 15 cmH₂O expiratory threshold loads increased the expiratory P_ITP excursion by 15 ± 7, 23 ± 7, and 31 ± 7%, respectively (P < 0.05 for all). Both 10 and 15 cmH₂O expiratory threshold loads significantly reduced SV (–3.5 ± 0.7 and –4.2 ± 0.7%, respectively) and Q_TOT (–1.7 ± 0.4 and –2.5 ± 0.4%, P < 0.05) after the induction of CHF, with the reductions in SV predominantly occurring during inspiration. However, the augmentation of the inspiratory P_ITP excursion now elicited further decreases in SV and Q_TOT. Only the highest level of expiratory loading significantly reduced hindlimb blood flow (–4 ± 2%) as a result of significant reductions in vascular conductance (–5 ± 2%). We conclude that increases in expiratory P_ITP production-similar to those observed during severe expiratory flow limitation-reduce cardiac output and hindlimb blood flow during submaximal exercise in health and CHF.

cardiac output; blood flow distribution; exercise; expiratory flow limitation; heart failure

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