New graphical method for evaluating gas exchange in congestive heart failure

The purpose of this study was to determine the usefulness of a new graphical method for evaluating gas exchange (GE), as applied to three common averaging techniques used during rest, exercise, and recovery in patients with congestive heart failure (CHF).

Fifty patients' resting, exercise, and recovery GE graphs were evaluated using a new graphical method to determine oxygen consumption (VO2), ventilation (VE), and respiratory exchange ratio (RER). Precision of the new method was evaluated by repeated measures using the same investigator, an additional investigator, and an untrained student. A 1-min rolling time average (RTA) updated every 20 s was used as the reference to the graphical method and the metabolic cart's computer analysis. Breath-by-breath data were evaluated using three averaging techniques, average 5 of 7 breaths (5/7), average of 8 breaths (AVG 8), and 30-s average (30-s). Differences between the computer and the graphical method were assessed by two-sided t-tests; ANOVA was used between the three investigators and also between the three averaging techniques.

There were no significant differences of repeated measures between trained and untrained investigators. The graphical method results were significantly different than the computer results. The only difference with RTA involved computer resting values, which were also different than the graphical method.

In conclusion, the graphical method may be used to standardize GE evaluation because it displays excellent intrainvestigator precision and good interinvestigator precision between experienced and inexperienced investigators. Averaging techniques less than 30 s have greater bias when using computer-derived values, although when incorporating the graphical method the averaging technique chosen has little influence on all measures.