A NEW GRAPHICAL METHOD EVALUATING GAS EXCHANGE IN CONGESTIVE HEART FAILURE

Abstract

1714 PURPOSE: To determine 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). METHODS: Forty-three patients' resting, exercise, and recovery GE graphs were evaluated using a graphical method to determine oxygen consumption (VO2), ventilation (VE), ventilatory threshold (VT), and respiratory exchange ratio (RER). Breath by breath data were evaluated using three averaging techniques, average 5 of 7 breaths (5/7), mean of 8 breaths (AVG 8), and 30 second average (30 sec). A repeated measure of ten subjects' graphical data was performed to evaluate intraobserver variability. The graphical method was compared between averaging techniques and also to a commonly used computer evaluation of the same data. RESULTS: In using the graphical method there were no statistically significant differences between averaging techniques during rest, exercise, or recovery at the 0.01 level. However, large differences were noted between computer generated and graphical methods. These differences were statistically significant for resting VO2 (p<0.01). The bias of repeated measures was not statistically or clinically different. VT was in close agreement between all techniques, with one subject whose VT was indeterminate using 30 sec. CONCLUSIONS: In conclusion, the graphical method can be used reliably because it displays a low intraobserver variability and its limits of agreeability are small enough to be used for clinical purposes. Computer generated results must be interpreted with caution because of a tendency to report unsubstantiated data. When incorporating the graphical method the averaging technique chosen has little influence on all measures.