We've updated our privacy policy.

mrueschman

mrueschman
Joined Oct 2013
Bio

NSRR staff

Boston, MA

0000-0002-0506-8368

mrueschman
Joined Oct 2013
Bio

NSRR staff

Boston, MA

0000-0002-0506-8368

I received a response from the analyst. Posted below.

Does this have to do with artefacts?

Yes.

Why did you decide exactly for 0.35, 2.5, 180 and 1000? Are these set empirically by you or based on a paper?

They were set empirically.

These thresholds were set empirically with the objective of removing artifacts.

Even though automated QRS annotations were corrected as appropriate by a trained technician, a residual number of beats could have been incorrectly annotated. NN intervals < 0.35 s are artifact because they fall on the refractory period of the heart. There is also a very high chance that NN intervals > 2.5 s (heart rate less than 24 bpm) are misdetections rather then long pauses. These thresholds were meant to exclude misdetections and mislabeled beats.

“180”: 180 beats in 5 minutes corresponds to a heart rate of 36 bpm. If a 5-min window did not have at least 180 beats most likely that was due to artifact and/or the presence of non-sinus beats. For some perspective, the population median [25th and 75th percentiles] of the average NN interval was 939 [859 – 1033] ms, which in terms of heart rate corresponds to 63.9 [58 – 69.8] bpm.

Note that HRV is a technique that only applies to NN interval time series. Furthermore, there is no consensus on how to perform frequency analysis of “discontinuous” (due to the deletion of non-sinus beats) time series. Thus we wanted to limit the number of these windows.

“1000”: Participants with less than 1000 NN intervals (~15 mins) over the full night were immediately excluded. Either they were not in sinus rhythm or signal quality was an issue. Criteria for analyzing participants with at least 2h of combined N1, N2, N3-N4, REM was based on the idea that if we wanted to compare HRV for different sleep stages we needed a minimum amount of data. In addition, for the generation of full night (from sleep onset to sleep termination) summary statistics we wanted to avoid putting together those who spend most of the sleep period awake with those who slept “much more”.