Pulmonary Adaptive Responses to HIIT in COPD

Patients with Chronic obstructive pulmonary disease (COPD) suffer from a progressive loss of lung function that leads to poor quality of life, and often invalidity and early death. Regular exercise is considered the most effective non-pharmacological intervention for improving quality of life in these patients. However, its use is halted by the lack of understanding of the mechanism of exercise-induced improvement in COPD, and is widely thought not to have any effect on lung function in the clinical setting. Exercise is thus mainly considered a way to alleviate symptoms, primarily by improving skeletal muscle function, but without the potential to reverse the disease. Therefore, relatively short and low-intensity exercise interventions are typically prescribed and are often not pursued in patients with the greatest symptom burden.

The reasoning for not prescribing exercise more widely in COPD is based on two assumptions: 1) new tissue cannot be formed in the adult lung, and 2) no consistent exercise training-induced changes in lung function have previously been documented.

However, de novo tissue formation has repeatedly been demonstrated in the adult lung, both in animals and humans, primarily in response to prolonged hypoxia and pneumonectomy. It has recently been reported that interval-based training counteracts the progressive loss of lung tissue in animal models of experimental COPD. The most likely stimulus is the mechanical strain, and if any measurable changes are to be induced by training, a high-intensity interval training (HIIT) scheme is preferable to be initiated in pulmonary rehabilitation.

On this basis, this study aim to conduct a prospective randomised trial, in which the impact of HIIT on lung weight (assessed by CT), rest-to-exercise diffusion capacity, 3-dimensional distribution of pulmonary perfusion measured by single photon emission computed tomography (SPECT)-low dose CT are addressed. Indeed, the latter is an especially useful clinical tool for the pathophysiological classification of COPD patients, and rest-to-exercise SPECT has the potential as a diagnostic tool that 'pinpoints' the exact cause of dyspnoea in the individual COPD patient, but has not yet been validated for this purpose. While all the methods are established, there is a need for more information regarding COPD-associated changes in lung tissue mass ('lung weight') and rest-to-exercise pulmonary diffusion changes compared to the healthy state. An assessment of the feasibility of an extended HIIT-trial using these methods in COPD patients as well as estimates of the in-study changes in the resultant physiological estimates (for the purpose of sample size estimations) is warranted.