Abstract
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.
Highlights
In non-invasive cardiopulmonary exercise testing (CPET), oxygen pulse (O2P) is defined as oxygen uptake (V O2) divided by heart rate
A reduced O2P has been reported in patients with chronic obstructive pulmonary disease (COPD), and this has been associated with swings in intrathoracic pressure resulting from deranged ventilatory mechanics[13] or dynamic hyperinflation[14]
Twenty patients (44%) with an increasing O2P pattern initially followed by a flattening pattern were classified in the plateau-type group, 16 patients (36%) with an increasing pattern during loaded exercise were classified in the increasing-type group, and nine patients (20%) with a decreasing pattern during the last few minutes were classified in the decreasing-type group
Summary
In non-invasive cardiopulmonary exercise testing (CPET), oxygen pulse (O2P) is defined as oxygen uptake (V O2) divided by heart rate It indicates the capability of oxygen consumption in all body tissues per heart beat, and is a function of stroke volume and oxygen extraction by cells. A reduced O2P has been reported in patients with chronic obstructive pulmonary disease (COPD), and this has been associated with swings in intrathoracic pressure resulting from deranged ventilatory mechanics[13] or dynamic hyperinflation[14] This reduction in O2P has been shown to be partly reversed in patients with emphysema after pharmacological[15] or surgical lung volume reduction[16,17,18]. These findings may affect the currently-used algorithm for reporting CPET and provide insight into the mechanisms that determine O2P curve patterns
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