Influence of long-term oxygen therapy on cardiac acceleration and deceleration capacity in hypoxic patients with chronic obstructive pulmonary disease

Background: There is increasing interest in cardiovascular co‐morbidities of chronic obstructive pulmonary disease (COPD). Heart rate turbulence (HRT) and phase‐rectified signal averaging (PRSA) techniques quantify the heart’s acceleration/deceleration capacities. We postulated that these methods can help assess the integrity of cardiac control in hypoxic COPD. Methods: Eight hypoxic stable COPD patients, nine healthy age‐matched older adults and eight healthy young adults underwent ECG monitoring for 24 h. Patients with COPD were also monitored following 4 weeks of standardized oxygen therapy. HRT measures turbulence onset (TO), turbulence slope (TS)] and PRSA‐derived acceleration/deceleration (AC, DC) indices were quantified within 6‐h blocks to assess circadian variation. Results: There were between‐group differences for variables TS, DC and AC (P<0·0005, η² = 0·54–0·65), attributable solely to differences between healthy young and COPD subjects. Only HR (P<0·0005) and DC index (P = 0·008) showed circadian variation. A significant interaction ‘trend’ effect for HR (F_9,87 = 2·52, P = 0·015, η² = 0·21) reflected the strong influence of COPD on HR circadian variation (afternoon and night values being different to those in healthy subjects). Conclusions: As expected, heart rate dynamics were substantially diminished in older (healthy and COPD) groups compared with healthy young controls. Patients with COPD showed similar heart rate dynamics compared with age‐matched controls, both before and after hypoxia correction. However, there was a suggestion of diminished DC in COPD compared with age‐matched controls (P = 0·059) that was absent following oxygen therapy. TS, DC and AC indices were altered by similar degrees in older subjects, apparently indicating equivalent tonic dysfunction of sympathetic/parasympathetic systems with ageing.