Bioimpedance spectroscopy as a measure of physical functioning in nursing home residents

Intracellular resistance (Ri), a raw measure of bioimpedance spectroscopy (BIS), has been suggested for assessment of muscle health. The associations of repeated BIS measurements with functioning and nutritional status were investigated in nursing home residents suffering from poor health and disabilities.

A total of 106 nursing home residents (age 83±8 yrs, 75% women) were recruited. Whole body and calf BIS measures (lean body mass, resistance at 50 kHz, and Ri), height and calf electrode distance (D) were used to calculate six muscle indices. Hand grip and knee extension strengths were measured and data on Activities of Daily Living (ADL), mobility score, and Mini Nutritional Assessment (MNA) collected. Repeated measurements were performed at 3 (BIS) and 6 months (BIS, muscle strength, ADL, mobility, and MNA).

All bioimpedance muscle indices were lower in women than men and associated with MNA. However, the calf skeletal muscle index (SMI=D2/Ri) associated with muscle strength measurements at baseline and consistently with mobility and ADL also at 6-month re-examination. When compared to the highest tertile of SMI percent change (cut point +0.7%), the patients in the lowest tertile (cut point - 11.6%) had a 5.3-fold risk (p=0.004) for mobility decline within the 6-month follow-up. This risk association also remained significant after controlling for age, gender, baseline mobility, and percent change in body weight.

Calf intracellular resistance related to electrode distance is associated with the activities of daily living reflecting mobility in typical nursing home residents and a decrease in this index indicates a markedly increased risk for mobility decline.