BARD, R. L. and J. M. NICKLAS. New graphical method for evaluating gas exchange in congestive heart failure. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 870–876, 2000.
Purpose: 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).
Methods: Fifty patients’ resting, exercise, and recovery GE graphs were evaluated using a new graphical method to determine oxygen consumption (V̇O2), ventilation (V̇E), 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.
Results: 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.
Conclusion: 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.
Gas exchange (GE) data are key components in the evaluation of patients with congestive heart failure (CHF). Cardiopulmonary exercise testing is routinely used to estimate prognosis, assess the severity of disability, and triage patients for possible cardiac transplantation (8,15,20). However, there is no accepted standard for evaluating and reporting GE data from computer-assisted systems. In a recent review, Howley et al. (11) raise concerns regarding the lack of guidelines and the need for consistent terminology. Howley et al. (11) suggested a few guidelines regarding exercise testing, but there are no specific guidelines regarding the evaluation and reporting of GE data.
The distinction between CHF patients and others is not trivial because of the significant differences in GE kinetics. Patients with a cardiomyopathy display an oscillating pattern of oxygen consumption (V̇O2), carbon dioxide production, and minute ventilation (V̇E) during exercise testing (25). This physiologic phenomenon combined with nonphysiologic artifacts commonly complicate the measurement of GE (14) and makes the reporting of results difficult. Assessments of GE in patients with CHF frequently require examination of a graphical display of the data.
Data can be presented by averaged time intervals, rolling time intervals, averaging of a number of breaths, and rolling averages of breaths. In the literature, research is often presented without the sampling interval mentioned or with descriptions that are vague. Although previous investigators have evaluated different averaging techniques (2,12,14,16,23), only one study (12) has addressed patients with CHF. Studies involving CHF and GE have used a variety of averaging techniques. Some studies use a time average of 30 s (15), whereas some textbooks present cardiomyopathy cases using a rolling average of eight breaths (25).
Previous studies have evaluated averaging techniques during exercise, but without evaluations of resting and recovery data. In the text Exercise Gas Exchange in Heart Disease, Kraemer (13) devotes an entire chapter to the use of GE in recovery and concludes that recovery GE may ultimately provide a more accurate gauge of patient symptoms. Kraemer (13) also states that there are few published studies in this area. One CHF study (18) used a graphical analysis of steady state and graded exercise GE data similar to that of the current study. Additionally, Myers (22) recommends collecting 1 to 5 min of resting GE to ascertain that the cardiopulmonary exercise test begins with the patient in a relaxed state. This resting data is clinically useful because it can identify patients who exhibit periodic breathing. Periodic breathing is known to be associated with increased mortality risk (1,6,9,10,19) and elevated pulmonary capillary wedge pressures (1,7,19). One author has expressed the need for standardization of sampling intervals for exercise testing (23) and has since recommended using 30-s averages printed every 10 s (21,22). This “rolling time average” (RTA) is unique and is not commonly available on automated systems. In the review by Howley et al. (11), a 30-s time interval is suggested for exercise testing.
The purpose of this study was to determine the usefulness of a new graphical method for evaluating GE as applied to three common averaging techniques during rest, exercise, and recovery in patients with CHF.
University of Michigan Medical Center, Congestive Heart Failure and Transplant Program, Ann Arbor, MI
Submitted for publication September 1998.
Accepted for publication May 1999.
Address for correspondence: Robert L. Bard, University of Michigan Medical Center, 1500 E. Medical Center Drive, L3119 Womens, Box 0273, Ann Arbor, MI 48109-0273. E-mail: firstname.lastname@example.org.