Background: Multifrequency bioelectrical impedance analysis (MF-BIA) is a technique that measures body impedance (Z) at different frequencies (5, 10, 50, 100, and 250 kHz). Body composition may be estimated using empirical equations, which include BIA variables or, alternatively, raw BIA data may provide direct information on water distribution and muscle quality.
Objectives: To compare raw MF-BIA data between COPD patients and controls and to study their relationship with respiratory and functional parameters in COPD patients.
Methods: MF-BIA was performed (Human Im-Touch analyzer) in 212 COPD patients and 115 age- and BMI-matched controls. Fat-free mass (FFM) and fat mass were estimated from BIA data, and low- to high-frequency (5 kHz/250 kHz) impedance ratio was calculated. Physical fitness, lung function and respiratory muscle strength were also assessed in COPD patients.
Results: After adjusting for age, weight, and body mass index, FFM and the 5/250 impedance ratio were lower in COPD patients (P<0.001) and were negatively affected by disease severity. In both male and female patients, the 5/250 impedance ratio was significantly correlated mainly with age (r=-0.316 and r=-0.346, respectively). Patients with a 5/250 impedance ratio below median value had lower handgrip strength (P<0.001), 6-minute walk distance (P<0.005), respiratory muscle strength (P<0.005), forced expiratory volume in 1 second (P<0.05) and vital capacity (P<0.005). Finally, the 5/250 impedance ratio was reduced (P<0.05) in patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) III and IV (compared to those with GOLD I and II) or a BODE index between 6 and 10 points (compared to those with BODE index between 1 and 5 points).
Conclusion: MF-BIA may be a useful tool for assessing body composition and nutritional status in COPD patients. In particular, the impedance ratio could give valuable information on cellular integrity and muscle quality.
Keywords: impedance ratio; muscle quality; muscle strength.