Background: There is increasing interest in the cardiovascular pathology independently associated with chronic obstructive pulmonary disease (COPD). We examined the influence of long-term oxygen therapy (LTOT) on heart rate (RR) and QT time-series in COPD.
Methods: Ten hypoxic stable COPD patients underwent Holter ECG monitoring for 24 h and physical activity/energy expenditure monitoring for 5 days before and after LTOT. Variability of RR and QT time-series was quantified using standard statistics and their structural (correlation/scaling) properties were assessed using multifractal analysis. Pre- and post-LTOT cardiac/activity parameters were compared to examine the influence of oxygen therapy and circadian variation.
Results: PaO(2) increased (P = 0.0004) whilst PaCO(2) was unchanged (P = 0.56) following LTOT. Activity/energy expenditure estimates were also unchanged following LTOT (P = 0.64-0.99), but RR variability was increased during the morning (P < 0.05) and night (P < 0.1, trend only). Multifractality of RR and QT time-series was not significantly changed following LTOT, although QT multifractality showed some time-dependent fluctuations. Trends in RR and QT time-series over 24-h were similar pre- and post-LTOT, indicating a generally normal circadian response.
Conclusions: An increase in HRV following LTOT (but notably in the absence of altered activity levels) provides tentative evidence that LTOT has a direct effect on heart rate control in COPD. This beneficial influence was expressed mainly during the morning, and the relevance of this diurnal variation in response requires further investigation. It was also confirmed that both RR and (to a lesser degree) QT time-series in COPD have a multifractal structure, and this is not affected appreciably by LTOT.