Patterns of Oxygen Pulse Curve in Response to Incremental Exercise in Patients with Chronic Obstructive Pulmonary Disease - An Observational Study

In COPD, pulmonary hyperinflation causes decreased stroke volume thereby decreased oxygen pulse (O₂P). While O₂P flattening is related to myocardial ischemia in cardiac patients, O₂P patterns have seldom been explored in COPD. The aims of the study were to investigate O₂P-curve patterns and associated factors in COPD. Seventy-five patients with stable COPD were enrolled. The demographics, cardiac size, physiological measurements and stress EKG were compared among O₂P-curve pattern groups. An algorithm to identify O₂P-curve patterns was developed in 28 patients. In the remaining 45 patients after excluding two with poor effort, this algorithm revealed 20 (44%) flattening, 16 (36%) increasing, and nine (20%) decreasing patterns. The flattening-type group had lower body mass, cardiac size, and diffusing capacity, and larger lung volumes (p = 0.05-<0.0001) compared to the increasing-type group. During exercise, the flattening-type group had a lower operable O₂P and more hyperventilation and dyspnea (p = 0.02-<0.01). None had ST-T changes. Most differences were related to body mass and mildly to inspiratory fraction. The decreasing-type group performed higher effort than the increasing-type group (p < 0.05). In conclusion, O₂P flattening was common and was associated with reduced body mass and pulmonary hyperinflation rather than with myocardial ischemia. The decreasing-type may be caused by motivation to exercise.