Are the “critical” inspiratory constraints actually decisive to limit exercise tolerance in COPD?

Physiological effects of nasal high flow therapy during exercise in patients with chronic obstructive pulmonary disease: A crossover randomised controlled trial

BACKGROUND

Nasal high flow (NHF) has been proposed to sustain high intensity exercise in people with COPD, but we have a poor understanding of its physiological effects in this clinical setting.

RESEARCH QUESTION

What is the effect of NHF during exercise on dynamic respiratory muscle function and activation, cardiorespiratory parameters, endurance capacity, dyspnoea and leg fatigue as compared to control intervention.

STUDY DESIGN AND METHODS

Randomized single-blind crossover trial including COPD patients. Two constant workload exercise testing were performed at 75% of peak power with NHF (30L/min, 34°C) or with control intervention. Pressure time product of the transdiaphragmatic pressure (PTPdi/min) and other physiological measurements were continuously monitored. Dyspnoea and lower limb fatigue were assessed using the 10-Borg scale.

RESULTS

14 patients with severe obstruction (median FEV1: 40 (IQR 28 to 52) %) were included. Their median age was 70 (IQR 57 to 72) years. At isotime, NHF had little to no effect on PTPdi/min (MD -15cmH2O.s/min, 95% CI -62 to 33) but increased tidal volume (MD 77mL, 95% CI 21 to 133). NHF also improved endurance capacity (MD 20s, 95% CI 2 to 40) and dyspnoea at isotime (MD -1.1, 95% CI -2.1 to -0.1). NHF had no or uncertain effect on other outcomes.

CONCLUSION

NHF has little to no effect on dynamic respiratory muscle function and activation but improves Vt. It leads to a trivially small increase in endurance capacity but a worthwhile improvement in dyspnoea. NHF may be beneficial for individuals experiencing critical inspiratory constraints and significant dyspnoea.

Diaphragm dome height on chest radiography as a predictor of dynamic lung hyperinflation in COPD

Background and objective

Dynamic lung hyperinflation (DLH) can play a central role in exertional dyspnoea in patients with COPD. Chest radiography is the basic tool for assessing static lung hyperinflation in COPD. However, the predictive capacity of DLH using chest radiography remains unknown. This study was conducted to determine whether DLH can be predicted by measuring the height of the right diaphragm (dome height) on chest radiography.

Methods

This single-centre, retrospective cohort study included patients with stable COPD with pulmonary function test, cardiopulmonary exercise test, constant load test and pulmonary images. They were divided into two groups according to the median of changes of inspiratory capacity (ΔIC=IC lowest - IC at rest). The right diaphragm dome height and lung height were measured on plain chest radiography.

Results

Of the 48 patients included, 24 were classified as having higher DLH (ΔIC ≤-0.59 L from rest; -0.59 L, median of all) and 24 as having lower DLH. Dome height correlated with ΔIC (r=0.66, p<0.001). Multivariate analysis revealed that dome height was associated with higher DLH independent of % low attenuation area on chest computed tomography and forced expiratory volume in 1 s (FEV₁) % predicted. Furthermore, the area under the receiver operating characteristic curve of dome height to predict higher DLH was 0.86, with sensitivity and specificity of 83% and 75%, respectively, at a cut-off of 20.5 mm. Lung height was unrelated to ΔIC.

Conclusion

Diaphragm dome height on chest radiography may adequately predict higher DLH in patients with COPD.

The Exercising Brain: An Overlooked Factor Limiting the Tolerance to Physical Exertion in Major Cardiorespiratory Diseases?

“Exercise starts and ends in the brain”: this was the title of a review article authored by Dr. Bengt Kayser back in 2003. In this piece of work, the author highlights that pioneer studies have primarily focused on the cardiorespiratory-muscle axis to set the human limits to whole-body exercise tolerance. In some circumstances, however, exercise cessation may not be solely attributable to these players: the central nervous system is thought to hold a relevant role as the ultimate site of exercise termination. In fact, there has been a growing interest relative to the “brain” response to exercise in chronic cardiorespiratory diseases, and its potential implication in limiting the tolerance to physical exertion in patients. To reach these overarching goals, non-invasive techniques, such as near-infrared spectroscopy and transcranial magnetic stimulation, have been successfully applied to get insights into the underlying mechanisms of exercise limitation in clinical populations. This review provides an up-to-date outline of the rationale for the “brain” as the organ limiting the tolerance to physical exertion in patients with cardiorespiratory diseases. We first outline some key methodological aspects of neuromuscular function and cerebral hemodynamics assessment in response to different exercise paradigms. We then review the most prominent studies, which explored the influence of major cardiorespiratory diseases on these outcomes. After a balanced summary of existing evidence, we finalize by detailing the rationale for investigating the “brain” contribution to exercise limitation in hitherto unexplored cardiorespiratory diseases, an endeavor that might lead to innovative lines of applied physiological research.