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This Article Full Text Full Text (PDF) All Versions of this Article: 294/6/H2465    most recent 91520.2007v1 Alert me when this article is cited 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 Google Scholar Google Scholar Articles by Borghi-Silva, A. Articles by Neder, J. A. Search for Related Content PubMed PubMed Citation Articles by Borghi-Silva, A. Articles by Neder, J. A.

Effects of respiratory muscle unloading on leg muscle oxygenation and blood volume during high-intensity exercise in chronic heart failure

¹Pulmonary Function and Clinical Exercise Physiology Unit, Division of Respiratory Diseases and ³Division of Cardiology, Department of Medicine, Federal University of Sao Paulo, São Paulo, São Paulo, Brazil; and ²Cardiopulmonary Laboratory, Nucleus of Research in Physical Exercise, Federal University of São Carlos, São Paulo, Brazil

Submitted 26 December 2007 ; accepted in final form 24 March 2008

Blood flow requirements of the respiratory muscles (RM) increase markedly during exercise in chronic heart failure (CHF). We reasoned that if the RM could subtract a fraction of the limited cardiac output (Q_T) from the peripheral muscles, RM unloading would improve locomotor muscle perfusion. Nine patients with CHF (left ventricle ejection fraction = 26 ± 7%) undertook constant-work rate tests (70-80% peak) receiving proportional assisted ventilation (PAV) or sham ventilation. Relative changes (%) in deoxy-hemoglobyn, oxi-Hb ([O₂Hb]), tissue oxygenation index, and total Hb ([Hb_TOT], an index of local blood volume) in the vastus lateralis were measured by near infrared spectroscopy. In addition, Q_T was monitored by impedance cardiography and arterial O₂ saturation by pulse oximetry (Sp_O2). There were significant improvements in exercise tolerance (Tlim) with PAV. Blood lactate, leg effort/Tlim and dyspnea/Tlim were lower with PAV compared with sham ventilation (P < 0.05). There were no significant effects of RM unloading on systemic O₂ delivery as Q_T and Sp_O2 at submaximal exercise and at Tlim did not differ between PAV and sham ventilation (P > 0.05). Unloaded breathing, however, was related to enhanced leg muscle oxygenation and local blood volume compared with sham, i.e., higher [O₂Hb]% and [Hb_TOT]%, respectively (P < 0.05). We conclude that RM unloading had beneficial effects on the oxygenation status and blood volume of the exercising muscles at similar systemic O₂ delivery in patients with advanced CHF. These data suggest that blood flow was redistributed from respiratory to locomotor muscles during unloaded breathing.

blood flow; cardiac failure; cardiovascular physiology; hemodynamics; muscle; oxygen consumption