Assessing Cardiocirculatory Compensation Capacity In Copd: Impact Of Disease Severity

Background: The functional limitation of patients with COPD results from a respiratory impairment and a reduction in peripheral muscle extraction. Inasmuch as the circulatory system is not a limiting factor, it can serve a useful adaptive role to optimise oxygen transport. Objective: To assess the extent to which compensatory cardiocirculatory adjustments are present when there is reduced oxygen transfer. Methods: Using a subset (N=115) from the Canadian longitudinal COPD cohort study (CanCOLD), we compared results from continuous measurements of ventilation,VO2 and bioimpedance (Physio-Flow®) cardiac output (CO) during peak incremental cycling. Arteriovenous oxygen difference was computed using Fick equation (Da-vO2 = VO2 / CO). Subjects were grouped for disease severity : Gr. A: At Risk,ever smokers (N=51) Gr. B: GOLD1 (N=33) Gr.C:GOLD2 (N=31). There were no group differences in age, body mass index or sex ratio. Results: The figure below shows that the CO vs Da-vO2 relationship with increasing VO2 is not different between groups A and B but the relationship is shifted up and leftward in group C indicating a compensatory increase in CO for VO2 over approximately 1000ml. Conclusion: Severity of COPD, even moderate, negatively impacts peripheral O2 extraction. An elevation in CO is then observed which serves as partial compensation to optimize the O2 transport function.