Association of peripheral muscle function with pulmonary function, quality of life and serum vitamin d levels in patients with chronic obstructive pulmonary disease

Abstract

Introduction: Chronic obstructive pulmonary disease (COPD) is a common disease characterized by airflow limitation and manifests initially through dyspnea, cough, and secretion. It is among the leading causes of mortality and morbidity at the global level and represents a high economic and social impact that tends to grow. Historically, there has been a greater prevalence of COPD among men; however, in the last two decades, the number of women with COPD has been increasing in most age groups. Stages of the disease are defined as spirometric indexes associated with the evaluation of symptoms or the presence of dyspnea and the risk of exacerbations. Systemic effects occur from worsening of the disease, such as respiratory and peripheral muscle dysfunction, nutritional changes, anxiety and depression, which are usually associated with other comorbidities, causing a decrease in the quality of life (QoL) and, consequently, increase of the mortality rate. The study of the relation between the peripheral muscular function measured by the isokinetic dynamometry of the knee of men and women together with handgrip strength, QoL measurements and serum levels of vitamin D is of the interest to the field of Rehabilitation Sciences, once which may direct the development of new strategies employed in the treatment of these patients. Objective: To evaluate the strength and resistance of the quadriceps and hamstrings according to gender and to verify the association of lower limb muscle function with health-related quality of life (HRQL), pulmonary function and levels of 25-hydroxyvitamin D3 (25(OH)D3) in COPD patients. Methods: This cross-sectional study included 42 patients with COPD (21 men and 21 women) and 42 healthy controls. The HRQL was evaluated by the COPD Assessment Test (CAT), 36-Item Short-Form Health Survey (SF-36) and Saint George's Respiratory Questionnaire (SGRQ). All patients underwent lung function tests and serum 25(OH)D3. Muscle function was assessed by means of the handgrip strength and the isokinetic dynamometer of the knee. Results: Most isokinetic parameters showed differences between men and women and their respective controls, and the greatest differences were observed among women with COPD and healthy controls. The strongest correlations occurred between the isokinetic parameters with SF36 - physical component summary (PCS), SGRQ and pulmonary function, especially at the 240º/s angular velocity. At this rate, the agonist/antagonist relationship was positively correlated with SF36 PCS (r = 0.65), 25(OH)D3 (r = 0.76) and forced expiratory volume in one second (FEV1) (r = 0.65), and negatively with CAT (r = -0.53) and SGRQ (r = -0.64), all with P < 0.001. Conclusion: COPD patients have decreased muscle strength and endurance, being more evident in women. The relationships between muscle function, lung function, HRQoL and 25(OH)D3 are most striking when resistance and hamstring/quadriceps ratio are tested.