Attacking the disease spiral in chronic obstructive pulmonary disease: an update

Abstract

In chronic obstructive pulmonary disease (COPD) a pathophysiological cycle occurs such that locomotor muscle weakness and fatiguabilty exist, which in turn limit exercise performance both because of leg discomfort and also because anaerobic metabolism leads to lactic acid production. Since the lactic acid is buffered by bicarbonate there is consequent carbon dioxide (CO2) production. Patients with advanced COPD are flow limited and cannot excrete the CO2 by raising ventilation and thus these patients experience breathlessness which discourages exercise and, in turn, prompts further deconditioning. Structured exercise, termed pulmonary rehabilitation is at the core of reversing the cycle but novel strategies should be employed for patients with advanced disease and alternative therapeutic opportunities may soon be available to improve pulmonary mechanics.

Fig 1.

Prevalence of quadriceps weakness in chronic obstructive pulmonary disease according to GOLD stage. Dark bars = participants with quadriceps less than the lower limit of normal; light bars = participants with quadriceps strength in the normal range. Adapted with permission of the European Respiratory Society ©.

Fig 2.

Transplant free survival as a function quadriceps strength. Data from reference 9.

Fig 3.

Quadriceps myostatin RNA expression in chronic obstructive pulmonary disease patients as a function of (a) strength, (b) six-minute walk, (c) endurance time and (d) physical activity measured using triaxial accelerometry. Reproduced with permission of the European Respiratory Society ©.