24 HOUR HEART RATE AND EMG MONITORING DURING REST AND NORMAL DAILY ACTIVITY1020

Abstract

Recently, 24 h heart rate variability (HRV) monitoring has gained popularity as a clinical tool that might provide indications of morbidity and mortality in patient populations. However, interpretation has been performed in the absence of information about the effect of different activity patterns on long-term HRV. We monitored 5 healthy young subjects while they were normally active, and while they remained in bed with minimal activity for 24 h. A new 24 h HR monitor (Polar, RR-Recorder) was first evaluated by simultaneous collection with a standard ECG while subjects performed a range of activities for 1 h. A tight one-to-one relationship existed between the methods. Physical activity was quantified over 24 h by a portable EMG unit(MEGA, ME-3000). As anticipated, there was a dramatic reduction in EMG activity in the resting tests. The mean RR-interval over 24 h was significantly less during activity (846±60 ms) than rest (971±66 ms, P<0.05). Total spectral power was markedly greater, especially in the ultra-low frequency range, during activity (26,015±9,262 vs. 16,100±7,111 ms2/Hz, P<0.05). These results indicate that interpretation of HRV data, especially the ultra-low frequency band (e.g. Bigger et al. Circulation 91: 1936-43, 1995), where prognostic value has been implied, must be made with caution in the absence of information on physical activity patterns. Simply resting in bed caused HRV of healthy subjects to be more similar to the pattern of patients with cardiac disease.