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This Article Full Text Free Full Text (PDF) Free Supplementary Date All Versions of this Article: 99/5/1802    most recent 00278.2005v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Miller, J. D. Articles by Dempsey, J. A. Search for Related Content PubMed PubMed Citation Articles by Miller, J. D. Articles by Dempsey, J. A.

Effects of augmented respiratory muscle pressure production on locomotor limb venous return during calf contraction exercise

John Rankin Laboratory of Pulmonary Medicine, Medical Sciences Center, University of Wisconsin-Madison, Madison, Wisconsin

Submitted 8 March 2005 ; accepted in final form 12 July 2005

We determined effects of augmented inspiratory and expiratory intrathoracic pressure or abdominal pressure (Pab) excursions on within-breath changes in steady-state femoral venous blood flow (_fv) and net _fv during tightly controlled (total breath time = 4 s, duty cycle = 0.5) accessory muscle/"rib cage" (Pab <2 cmH₂O) or diaphragmatic (Pab >5 cmH₂O) breathing. Selectively augmenting inspiratory intrathoracic pressure excursion during rib cage breathing augmented inspiratory facilitation of _fv from the resting limb (69% and 89% of all flow occurred during nonloaded and loaded inspiration, respectively); however, net _fv in the steady state was not altered because of slight reductions in femoral venous return during the ensuing expiratory phase of the breath. Selectively augmenting inspiratory esophageal pressure excursion during a predominantly diaphragmatic breath at rest did not alter within-breath changes in _fv relative to nonloaded conditions (net retrograde flow = –9 ± 12% and –4 ± 9% during nonloaded and loaded inspiration, respectively), supporting the notion that the inferior vena cava is completely collapsed by relatively small increases in gastric pressure. Addition of inspiratory + expiratory loading to diaphragmatic breathing at rest resulted in reversal of within-breath changes in _fv, such that >90% of all anterograde _fv occurred during inspiration. Inspiratory + expiratory loading also reduced steady-state _fv during mild- and moderate-intensity calf contractions compared with inspiratory loading alone. We conclude that 1) exaggerated inspiratory pressure excursions may augment within-breath changes in femoral venous return but do not increase net _fv in the steady state and 2) active expiration during diaphragmatic breathing reduces the steady-state hyperemic response to dynamic exercise by mechanically impeding venous return from the locomotor limb, which may contribute to exercise limitation in health and disease.

blood flow; breathing mechanics; expiratory flow limitation; Starling resistor

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