Breathlessness in Patients with Chronic Airflow Limitation: Anaerobic Threshold
However, reduction of Ve by altering the anaerobic threshold is less consistently achieved in patients with CAL with more advanced disease, where modest improvements in ventilatory reserve are more likely to be attributable to enhanced mechanical efficiency following training. Controlled studies that have examined the impact of supervised multimodality exercise training on breathlessness have shown consistent benefit even in patients with severe disease fully buy antibiotics. Although much of this improvement may be explained by behavioral factors, ie, densensitization to breathlessness, physiologic improvements may also contribute. In a recent study, we examined possible contributing factors to relieve breathlessness after exercise training in 23 patients with severe CAL. Reduced VE/workrate slopes emerged as the only independently significant (albeit weak) predictor of change in Borg ratings (r=0.47, p<0.025). In a second study, we found that significant posttraining reductions in Ve/MBC occurred in the absence of significant changes in base excess measurements, suggesting that factors other than improved aerobic metabolism are important.46 We attributed the reduced ventilatory demand to enhanced mechanical efficiency.
Oxygen Therapy: Supplemental oxygen (O2) has been shown to relieve exertional breathlessness and to improve exercise tolerance in most patients with CAL when compared with compressed air. The mechanisms of relief are still debated, but in hypoxemic patients they are likely related, in part, to reduced ventilatory demand secondary to blunted peripheral chemoreceptor sensitivity. However, central effects of O2 on perceived discomfort at a given level of ventilation cannot be ruled out.23 Symptomatic relief may be linked to enhanced O2 delivery (or utilization) to exercising limb and ventilatory muscles which results in delayed lactate accumulation, reduced VCO2, and reduced Ve at a given work rate.
In association with reduced Ve, we have found in a recent controlled study that O2 therapy improves ventilatory mechanics during exercise: significant reductions in acute DH occurred in patients receiving 60 percent O2 when compared with compressed air 50 Reduced DH correlated significantly (p<0.05) with reduced Borg ratings after accounting for the change in Ve. Thus, O2 relieves breathlessness not only by reducing motor output but also by improving neur о ventilator у coupling. It is noteworthy that the beneficial effects of supplemental O2 on breathlessness and exercise tolerance are observed in patients with CAL who do not meet current American Thoracic Society criteria for long-term O2 therapy.’
Category: Respiratory Symptoms
Tags: breathlessness, chronic airflow limitation, copd, dynamic compression, dynamic hyperinflation, exercise