Heart rate and spectral EEG changes accompanying periodic and isolated leg movements during sleep.

CEDE both the leg movements and the associated electroen-cephalogram (EEG) changes by as much as 6 seconds. They also reported that the heart-rate changes were greater when occurring with periodic leg movements in sleep (PLMS) than with either isolated (ILMS) or respiratory-related leg movements. We 2 and others 3 have previously reported essentially opposite findings, i.e., that heart-rate changes associated with ILMS are greater than those with PLMS. In our study, the spectral EEG changes were also greater for ILMS than for PLMS. This discrepancy in leg movement-related heart-rate changes was not addressed by Guggisberg et al. 1 Careful consideration of the 2 works reveals methodologic differences that might account for these discrepancies. In our previous study, 2 we analyzed only PLMS that were separated by at least 30 seconds, as opposed to the 10 seconds used by Guggisberg et al. 1 Our selection of 30 seconds was derived from a preliminary analysis that revealed that leg movement-related heart-rate changes usually persist up to 15 seconds after the onset of the movement. Our choice of a minimum interval of 30 seconds comfortably avoided the potential confounding effects of persisting heart-rate changes from a leg movement preceding the one under analysis. Our heart-rate analyses, extended from 20 seconds before to 30 seconds after each leg movement, with the first 10 seconds used as baseline. This allowed us to be comfortable that the baseline heart rate was not affected by a recent leg movement. Guggis-berg et al 1 included PLMS separated by only 10 seconds in their analysis, and their baseline heart rate was therefore determined by a period that was within 10 seconds of the prior movement and would likely include the relative bradycardia occurring after the prior movement. This methodologic problem negatively impacts their results in 2 important ways. First, the simple return to baseline from the natural bradycardia that follows a preceding leg movement has been misinterpreted as part of an increase in heart rate associated with the subsequent leg movement. Second, this artifactual difference would occur for frequent PLMS spaced closely together but not for ILMS that are spaced, by definition, further apart. As an example, the Figure depicts the heart-rate changes accompanying 2 consecutive leg movements during sleep, separated by approximately 15 seconds , the first of which is not preceded by another leg movement ; in this example, it is clear that heart-rate values preceding the …