Noninvasive measurement of cardiac output during 6-minute walk test by inert gas rebreathing to evaluate heart failure.

OBJECTIVE: The objective of this study was to assess the clinical value of cardiac output (CO) measurements using the inert gas rebreathing (IGR) method during the 6-minute walk test (6MWT) in evaluation of chronic heart failure (CHF). METHODS AND
RESULTS: A total of 56 CHF patients in our hospital who conformed to the Framingham CHF diagnostic criteria were recruited to this study from October 2007 to February 2009. Subjects were asked to complete a 6MWT and a bicycle exercise test. The CO was measured during both tests using IGR. B-type natriuretic peptide (BNP) levels and the left ventricular ejection fraction (LVEF) were measured at rest. The 6MWT did not correlate with BNP, LVEF, peak cardiac output (PCO), or CO during the 6MWT (CO6MWT). A negative correlation between CO6MWT and BNP as well as a strong correlation between CO6MWT and PCO was observed. When atrial fibrillation and valvular heart disease patients were excluded, CO6MWT and LVEF became significantly correlated. After grouping patients into tertiles according to their PCO values, the PCO remained correlated with CO6MWT within each group. The mean difference between CO6MWT and PCO decreased with decreases in the mean PCO in each group. No significant differences were found in the third tertile (PCO < 10.1 L/min).
CONCLUSIONS: The IGR method during 6MWT is safe and reliable to evaluate cardiac function in patients with CHF.