The relationship between physical function and experience of fatigue in patients with chronic obstructive pulmonary disease

Background Chronic Obstructive Pulmonary Disease (COPD) is increasing throughout the world and most rapidly among women. COPD is characterized by a progressive loss of physical functions. The reason for this is multi-factorial and include not only lung related deficiencies but also several systemic consequences and symptoms of which several are potential restrictors of physical function. The relationship between physical function and symptoms are not clear, especially not among women with COPD. Aim The overall aim of this thesis was to illuminate the relationship between two dimensions of physical function (physical activity and physical capacity) and experience of fatigue. The specific aims were to explore factors associated with low physical activity and to examine experience of fatigue and its relationship to physical capacity and disease severity in men and women with COPD. Methods A cross-sectional study was conducted including 121 patients (67 women) with stable COPD and mean age of 67 (+/-7) years. Physical activity was measured with the International Physical Activity Questionnaire short form. Physical capacity included assessment of lung function (dynamic spirometry), exercise capacity (the 6-minute walk distance [perceived dyspnoea and leg fatigue in connection to the test]) and muscle strength (the Timed Stands Test and grip strength). Fatigue was assessed with structured questions covering the frequency, duration and severity of fatigue the previous month and patients were categorized as those with no fatigue, moderate fatigue or severe fatigue. Data about other symptoms (dyspnoea, anxiety and depression), symptom burden (Memorial Symptom Assessment Scale), fat and fat free mass (bio-impedance analysis) and smoking history was collected. Results Forty-two percent of the patients reported a low physical activity level. A majority of the patients reported experience of fatigue the previous month, 52% moderate fatigue and 25% severe fatigue. Low physical activity was associated with severe fatigue, worse exercise capacity and a higher amount of smoking. There were no differences in experience of fatigue between men and women. Men with fatigue had worse physical capacity and disease severity compared to men without fatigue. Women with fatigue had comparable physical capacity and disease severity to women without fatigue except for a higher perceived leg fatigue after the exercise capacity test. Multiple logistic regression analysis showed that exercise capacity and disease severity were associated with fatigue in both men and women but in women, leg fatigue was also strongly associated with the presence of fatigue. Conclusions Severe fatigue, worse exercise capacity and a higher amount of smoking were independently associated with low PA. This result suggests that patients with severe fatigue might need specific strategies to become more physically active. Presence of fatigue was associated with exercise capacity and disease severity in both men and women. In addition, in women leg fatigue was strongly associated with fatigue. Muscle endurance training might be extra important in the rehabilitation of women with COPD experiencing fatigue. However the association between fatigue and exercised induced leg fatigue among the women warrant further investigation