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

<jats:title>Abstract</jats:title><jats:p>In COPD, pulmonary hyperinflation causes decreased stroke volume thereby decreased oxygen pulse (O<jats:sub>2</jats:sub>P). While O<jats:sub>2</jats:sub>P flattening is related to myocardial ischemia in cardiac patients, O<jats:sub>2</jats:sub>P patterns have seldom been explored in COPD. The aims of the study were to investigate O<jats:sub>2</jats:sub>P-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 O<jats:sub>2</jats:sub>P-curve pattern groups. An algorithm to identify O<jats:sub>2</jats:sub>P-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 (<jats:italic>p</jats:italic> = 0.05–<0.0001) compared to the increasing-type group. During exercise, the flattening-type group had a lower operable O<jats:sub>2</jats:sub>P and more hyperventilation and dyspnea (<jats:italic>p</jats:italic> = 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 (<jats:italic>p</jats:italic> < 0.05). In conclusion, O<jats:sub>2</jats:sub>P 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.</jats:p>