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, eta(2) = 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,F-87 = 2.52, P = 0.015, eta(2) = 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 (health), 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.