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Title: Effects of respiratory muscle unloading on leg muscle oxygenation and blood volume during high-intensity exercise in chronic heart failure
Authors: Borghi-Silva, Audrey [UNIFESP]
Carrascosa, Claudia [UNIFESP]
Oliveira, Cristino Carneiro [UNIFESP]
Barroco, Adriano C. [UNIFESP]
Berton, Danilo C. [UNIFESP]
Vilaca, Debora [UNIFESP]
Lira-Filho, Edgar B. [UNIFESP]
Ribeiro, Dirceu [UNIFESP]
Nery, Luiz Eduardo [UNIFESP]
Neder, J. Alberto [UNIFESP]
Universidade Federal de São Paulo (UNIFESP)
Keywords: blood flow
cardiac failure
cardiovascular physiology
oxygen consumption
Issue Date: 1-Jun-2008
Publisher: Amer Physiological Soc
Citation: American Journal of Physiology-heart and Circulatory Physiology. Bethesda: Amer Physiological Soc, v. 294, n. 6, p. H2465-H2472, 2008.
Abstract: 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 (QT) 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 (Delta%) in deoxy-hemoglobyn, oxi-Hb ([O(2)Hb]), 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, QT was monitored by impedance cardiography and arterial O-2 saturation by pulse oximetry (SpO(2)). 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 O-2 delivery as QT and SpO2 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 Delta[O(2)Hb]% and Delta[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 O-2 delivery in patients with advanced CHF. These data suggest that blood flow was redistributed from respiratory to locomotor muscles during unloaded breathing.
ISSN: 0363-6135
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