Rationale: Acetylene rebreathing is an accepted method of measuring cardiac output during exercise. However, the reproducibility of the single breath acetylene uptake technique during upper body exercise is unknown.
Purpose: To test the hypothesis that acetylene rebreathing produces reliable measures of cardiac output during different intensities of upper body exercise.
Subjects: Twelve healthy college-age females (age 23.9 +/- 2.1 years) performed upper body ergometry on 2 separate days approximately 1 week apart.
Methods: Cardiac output was measured (SensorMedics, Yorba Linda, CA) using the single breath acetylene technique at rest, 20 and 40 W while exercising using an upper body ergometer. Two values of cardiac output, oxygen consumption, and heart rate were obtained when steady state was achieved and the values for each variable were compared within each intensity to determine reliability. Paired relationships were determined by linear regression. Intraclass correlation coefficients (ICC) were used to describe the reliability of the cardiac output values within each day.
Results: The single breath acetylene uptake technique during upper body exercise had excellent reliability. The resting standard error of measurement (SEM) = 0.33 L/min, coefficient of variation (CV) for cardiac output values were 13% at rest; 10% at 20 W; 4% at 40 W. Test-retest correlations were highly reproducible (r = 0.98, P < .0001, r2 = 0.94) for all values between day 1 vs day 2. No significant differences were found for within trials (at each work load) or between days (paired t tests, P > .05). The intraclass correlation coefficient (ICC) for the single breath acetylene technique was 0.96.
Conclusion: These results demonstrate that the single breath acetylene uptake method provides reliable measurements of cardiac output during rest and exercise at low- and moderate-intensity with an upper body ergometer in female students.
Clinical relevance: Cardiac output is an important part of understanding regulation of cardiovascular and metabolic functions in health and disease. Determining cardiac output through noninvasive measures would minimize the discomfort and overall risk to the patient.