Influence of Rehabilitation on Oxygen Uptake Kinetics during High Intensity Exercise in Patients with Idiopathic Pulmonary Fibrosis

Abstract

Idiopathic Pulmonary Fibrosis (IPF) is a chronic, progressive and life-limiting condition of unknown cause with no curative treatment. The impact of IPF on a patient’s quality of life is devastating and palliative treatment such as pulmonary rehabilitation programmes are used to improve quality of life among these individuals, yet relatively little attention has been made to access the effectiveness of rehabilitation programs aimed designed for these patients. There are large gaps in our knowledge on the cardiorespiratory response to exercise and rehabilitation among IPF patients and this study aims to fill this gap in a physiological prospective. We quantified the effects of an eight-week pulmonary rehabilitation program for IPF patients, conducted at Morriston Hospital, Swansea. Fifteen individuals (13 with Idiopathic Pulmonary Fibrosis and two with Pulmonary Fibrosis associated with Rheumatoid Disease) underwent physical and physiological assessments during a three-day testing protocol: 1) On Day 1, physical function (six-minute walk test) and ventilatory function (spirometry) were measured; 2) On Day 2, patients’ cardio-respiratory responses to slowly-increasing, wide-ranging metabolic challenge (using a protocol consisting of periods of rest, incremental bicycle exercise to maximal effort, and post-exercise recovery) were assessed via respiratory gas analysis and ECG recording; 3) On Day 3, patients’ cardio-respiratory responses to rapid-onset, high-workload metabolic challenge were assessed (using a protocol including a rapid-onset, constant workload bicycle exercise) by modelling dynamic respiratory oxygen and heart rate responses. Respiratory gas analysis was used to measure the rate of oxygen uptake ( V O2 ) and oxygen uptake efficiency (OUES). All assessments were performed before and after participants completed the pulmonary rehabilitation programme. A Holter ECG recorder (Pathfinder/Lifecard Digital CF system; Spacelabs Medical Ltd., UK) provided continuous ECG data throughout each exercise test, from which heart rate was derived. Following the rehabilitation programme, heart rate was elevated by 11% - 18% during exercise and recovery states. Post-rehabilitation V O2 was significantly increased (p = 0.01 - 0.03) during the first two minutes of heavy-intensity exercise, whilst HR was reduced (p = 0.04) during this period. OUES and standard measures of respiratory performance (minute ventilation, peak 2 V O ) were unchanged following rehabilitation, whilst peak HR and work rates were significantly reduced during incremental exercise only (p < 10−3). Pulmonary rehabilitation improved the rate of oxygen uptake during heavy-intensity exercise, despite substantially lower heart rates. This suggests that the rehabilitation programme increased systemic arterial-tissue oxygen exchange and/or influenced cardiovascular function to improve systemic oxygen delivery. We might therefore expect that individuals with IPF would find it easier to perform the activities of daily life, including those requiring substantial metabolic demands, following rehabilitation.