Acute Effects of Oxygen Administration on Neuromuscular Fatigue in Chronic Obstructive Pulmonary Disease Patients With Chronic Respiratory Failure and Long-term Oxygen Therapy

Advanced Chronic Obstructive Pulmonary Disease (COPD) with Chronic Respiratory Failure (CRF) and long-term oxygen therapy (LTOT) need is a condition with a poor prognosis that causes symptoms such as dyspnea and fatigue that dramatically reduce the quality of life of the person with COPD. Typically, the advanced phase of COPD is characterized by a fluctuating pattern with recurrent hospitalizations, and a vicious cycle in which dyspnea increases and exercise tolerance and physical activity are reduced, which in turn lead to depression, social isolation, and low quality of life and increased risk of death.

Muscle dysfunction in these patients contributes, together with dynamic hyperinflation, to the increase of fatigue and dyspnea during exercise, leading to the early cessation of effort and the decrease of maximum aerobic capacity. In patients with CRF, the increase of arterial oxygenation could have a beneficial result through the direct inhibition of the stimulation of the carotid body receptors by reducing ventilation and respiratory rate.

The increase in arterial oxygenation could also promote the increase in muscle oxygenation by i) reducing the production of lactates during efforts at iso-work and ii) increasing the pulmonary vasodilation and consequently the cardiac output and therefore oxygen delivery to the exercising muscle. Interestingly, the increase in muscle oxygenation is likely delaying the onset of diaphragm fatigue.

In the clinical setting, studies have shown the acute administration of oxygen to be useful in reducing the ventilatory demand of the COPD patient by reducing minute ventilation and respiratory rate and improving exercise tolerance. In COPD patients with and without chronic respiratory failure, acute oxygen administration appears to improve endurance capacity, maximal exercise capacity, dyspnea, and minute ventilation. In patients with moderate/severe non-hypoxic COPD at rest and during exercise, training with oxygen supplementation provides greater benefit to exercise tolerance and respiratory pattern. Instead, in patients with normoxia at rest and exercise-induced desaturation, the exercise tolerance evaluated with the six-minute walking test progressively improves with the addition of oxygen, although there is enormous variability within the individual groups.

In this population, the addition of oxygen during exercise leads to marginal effects linked only to a slight benefit on dyspnea. Therefore, to date, this treatment regimen only aims at patients with exercise-induced desaturation with associated severe dyspnea. Therefore, there is little support from the literature in offering oxygen therapy extensively during physical training to patients with COPD. Besides, there is a lack of solid studies that lead to firm conclusions on the use of oxygen therapy with particular reference to the benefits on functional outcomes, symptoms and quality of life.