Cardiovascular and respiratory dysfunction in chronic obstructive pulmonary disease complicated by impaired peripheral oxygenation

Abstract

Ming-Lung Chuang,1,2 Shih-Feng Huang,1 Chun-Hung Su2,3 1Division of Pulmonary Medicine and Department of Critical Care Medicine, 2School of Medicine, 3Division of Cardiology and Department of Internal Medicine, Chung Shan Medical University Hospital, Taichung, Taiwan, Republic of China Background: Impaired peripheral oxygenation (IPO)-related variables readily achieved with cardiopulmonary exercise testing (CPET) represent cardiovascular dysfunction. These variables include peak oxygen uptake (VO2) <85% predicted, anaerobic threshold <40%  VO2max predicted, VO2-work rate slope <8.6 mL/watt, oxygen pulse <80% predicted, and ventilatory equivalents for O2 and CO2 at nadir of >31 and >34, respectively. Some of these six variables may be normal while the others are abnormal in patients with chronic obstructive pulmonary disease (COPD). This may result in confusion when using the interpretation algorithm for diagnostic purposes. We therefore hypothesized that patients found to have abnormal values for all six variables would have worse cardiovascular function than patients with abnormal values for none or some of these variables.Methods: In this cross-sectional comparative study, 58 COPD patients attending a university teaching hospital underwent symptom-limited CPET with multiple lactate measurements. Patients with abnormal values in all six IPO-related variables were assigned to an IPO group while those who did not meet the requirements for the IPO group were assigned to a non-IPO group. Cardiovascular function was measured by two-dimensional echocardiography and Δlactate/ΔVO2, and respiratory dynamics were compared between the two groups.Results: Fourteen IPO and 43 non-IPO patients were entered into the study. Both groups were similar with regard to left ventricular ejection fraction and right ventricular morphology (P>0.05 for both). At peak exercise, both groups reached a similar heart rate level and Δlactate/ΔVO2. The IPO patients had an unfavorable dead space to tidal volume ratio, mean inspiratory tidal flow, and shallow breathing (P<0.05–P<0.001).Conclusion: Our IPO and non-IPO patients with COPD had similar cardiovascular performance at rest and at peak exercise, indicating that IPO variables are non-specific for cardiovascular function in these patients. COPD patients with full IPO variables have more deranged ventilatory function. Keywords: dead space ventilation, dynamic hyperinflation, air-trapping, inspiratory tidal flow rate, lung function, cardiovascular function, oxygen pulse