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.