Validation of the CO2 rebreathing method for measuring cardiac output in patients with hypertension or heart failure.

The CO2 rebreathing method, a noninvasive indirect Fick procedure, has been previously validated in normal subjects at supine rest and during exercise. In the present study 29 nearly simultaneous measurements of cardiac output were made by CO2 rebreathing and dye dilution in 17 patients with cardiovascular disease, 11 with hypertension, and six with congestive heart failure. Cardiac output at supine rest averaged 5.52 +/- 0.31 L. per minute by CO2 and 5.62 +/- 0.32 L. per minute by dye dilution (r = 0.93). Successive cardiac output measurements by rebreathing varied 6.0 +/- 1.1 per cent (r = 0.96) and by dye dilution, 6.5 +/- 0.9 per cent. Changes in cardiac output during exercise or after beta-adrenergic blockade were reflected by the CO2 method. It is concluded that the CO2 method provides reliable measurements of cardiac output both at rest and during exercise in patients with hypertension or congestive heart failure. Further validation of the method is needed in various disease states before it can be widely applied.