CIRCADIAN-RHYTHM AND VARIABILITY OF HEART-RATE IN DUCHENNE-TYPE PROGRESSIVE MUSCULAR-DYSTROPHY

Using 24-hour Halter monitoring and time domain and power spectral mea surements, we evaluated the variability of the heart rate and its circ adian rhythm in 55 male patients with Duchenne-type progressive muscul ar dystrophy (DMD) to characterize their autonomic function versus fin dings in 20 normal controls. Comparisons were also made in patients wi th mild, moderate, and severe stages of DMD. The percent difference be tween successive RR intervals that exceeded 50 ms, a measure of parasy mpathetic tone, was significantly lower even in patients with early st age of DMD than in controls (p < 0.01). This trend became marked with disease progression. Power in the high-frequency (HF) range (0.15 to 0 .40 Hz), a measure of parasympathetic tone, was lower (p < 0.01), and the ratio of the power in the low-frequency (LF) range (0.04 to 0.15 H z) and that of HF range (LF/HF ratio), a measure of sympathetic tone, was higher in DMD patients versus controls (p < 0.01). This trend was also marked with disease progression. Patients with mild or moderate d isease had a slight circadian;alteration in HF and LF/HF ratio. Patien ts with severe disease had virtually no circadian rhythm in HF. Their LF/HF ratio was higher at night (p < 0.01), lower in the morning (p < 0.01), and still lower during the day (p < 0.01), the opposite of cont rol findings. The autonomic abnormalities in DMD were thus characteriz ed by a significant increase in sympathetic activity and a significant decrease in parasympathetic activity. Thus, heart rate variability an d circadian rhythm were useful in assessing autonomic dysfunction in D MD.