Correlates of habitual physical activity in chronic haemodialysis patients.

BACKGROUND Results of physical performance tests may not reflect the level of habitual physical activity and health status of the dialysis patients. The aim of our study was to assess interdialytic spontaneous physical activity in chronic haemodialysis (HD) patients in relation to their nutritional status, severity of anaemia, inflammation and dialysis adequacy. METHODS Sixty HD patients [27 female, 33 male; mean age 60+/-13 years, time on dialysis 46.2+/-62.1 months and body mass index (BMI) 25.1+/-4.7 kg/m2] without physical and neurological disabilities and 16 healthy individuals (10 female, six male, mean age 56+/-6 years, BMI 26.6+/-4.9 kg/m2) were enrolled into the study. In all patients, spontaneous daily physical activity was measured during 48 h between mid-week dialysis sessions by pedometers. Nutritional status was estimated by anthropometric methods (BMI and mid-arm muscle circumference) and serum albumin concentration. Additionally, body composition was estimated using a multifrequency phase-sensitive bioimpedance analysis (BIA). Severity of anaemia was determined by blood haemoglobin level and haematocrit value, and the presence of inflammatory state was determined by high sensitivity plasma C-reactive (CRP) protein measurements. RESULTS The total number of steps during daily activities in dialysis patients and in healthy individuals was 6896+/-2357 vs 14 181+/-5383 per 48 h, respectively (P<0.001). Dialysis patients showed typical signs of malnutrition in the BIA, i.e. high extracellular mass/body cell mass index (1.17+/-0.28 in dialysis patients vs 0.97+/-0.1 in controls; P<0.001), low percentage cell mass (46.7+/-5.6 and 51.0+/-3.6, respectively; P = 0.002) and low phase angle (5.1+/-0.9 and 5.8+/-0.7, respectively; P = 0.006). Dialysis patients also showed lower serum albumin and blood haemoglobin and higher serum CRP levels than healthy controls. In dialysis patients, the number of steps taken positively correlated with body water (R = 0.28, P = 0.03), fat mass (r = 0.29, P = 0.04), BMI (R = 0.25, P = 0.04), lean body mass (R = 0.26, P = 0.04), intracellular water (r = 0.30, P<0.01), phase angle (R = 0.40, P = 0.002), serum albumin (R = 0.32, P = 0.01), haematocrit (R = 0.46, P = 0.001) and haemoglobin (R = 0.44, P = 0.001). Furthermore, the number of steps taken correlated significantly with mid-arm muscle circumference (r = 0.35, P = 0.006). A negative correlation was found between the number of steps and extracellular mass/body cell mass index (R = -0.37; P = 0.004). No significant relationships were found between the measures of physical activity and high sensitivity CRP or adequacy of dialysis. Multiple regression analysis revealed the independent associations between the number of steps taken by the patients and haemoglobin concentration, age, total body water, extracellular mass/body cell mass index and phase angle. CONCLUSIONS Low habitual physical activity assessed in HD patients with simple portable pedometers is strongly related to several factors of major clinical importance in this population.