Effects of respiratory muscle unloading on leg muscle oxygenation and blood volume during high-intensity exercise in chronic heart failure.
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 ([O2Hb]), tissue oxygenation index, and total Hb ([HbTOT], 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 O2 saturation by pulse oximetry (SpO2). 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 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[O2Hb]% and Delta[HbTOT]%, 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.
Borghi-Silva
Audrey
A
Pulmonary Function and Clinical Exercise Physiology Unit, Division of Respiratory Diseases, Federal University of Sao Paulo, São Paulo, São Paulo, Brazil.
Carrascosa
Cláudia
C
Oliveira
Cristino Carneiro
CC
Barroco
Adriano C
AC
Berton
Danilo C
DC
Vilaça
Debora
D
Lira-Filho
Edgar B
EB
Ribeiro
Dirceu
D
Nery
Luiz Eduardo
LE
Neder
J Alberto
JA
D000328:Adult; D001810:Blood Volume; D002302:Cardiac Output; D002307:Cardiography, Impedance; D002908:Chronic Disease; D015444:Exercise; D017079:Exercise Tolerance; D006333:Heart Failure / Q000378:metabolism / Q000503:physiopathology*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010101:Oxygen Consumption; D011446:Prospective Studies; D012123:Pulmonary Ventilation; D052097:Quadriceps Muscle / Q000098:blood supply / Q000378:metabolism / Q000503:physiopathology*; D012039:Regional Blood Flow; D012107:Research Design; D012132:Respiratory Muscles / Q000098:blood supply / Q000378:metabolism / Q000503:physiopathology*; D019265:Spectroscopy, Near-Infrared
D006454:Hemoglobins; D019344:Lactic Acid