Heart Rate Variability in Duchenne Muscular Dystrophy During Computer Task

Computational Task in Duchenne Muscular Dystrophy: Involvement of Cardiac Autonomic Regulation.

HRV is attained using a Polar RS800CX. Then, evaluated through linear, non-linear and chaotic global techniques (CGT). Forty-five male subjects were included in the DMD group and age-matched with forty-five in the healthy Typical Development (TD) control group. They were assessed for twenty minutes at rest sitting, and then five minutes whilst performing the maze task on a computer.

This is a cross-sectional study, where HR was recorded beat-to-beat (RR intervals) using the portable Polar RS800CX HR monitor (Polar Electro, Finland). HR was recorded before the onset and at the end of the five minutes of the computer maze paradigm task.

The subjects were seated in a standard chair (walkers, TD group and DMD) or in their own wheelchair (non-walkers, DMD group), the Polar watch was positioned on the wrist. The analysis of HRV was possible through the recording of RR interval in two periods: the period of twenty minutes at seated rest, and then during the computer task for five minutes.

The computer task used a maze paradigm with one correct pathway that could be negotiated and ultimately solved. All participants were positioned comfortably and an evaluator responsible for instruction and annotation of data.

Each individual was instructed to walk the correct path with the digital character pawn (pointed on the screen by the evaluator) to the exit of the maze identified by an "x" (pointed on the screen by the evaluator). It was provided for the subjects, who used the arrow buttons on the keyboard, identified by up, down, right and left, using the dominant hand, with the arrows moving through a 20 x 20 cm maze. Participants were requested to complete the maze as fast as possible.

HRV analysis followed the guidelines published by the Task Force of the European Society of Cardiology and North American Society of Pacing and Electrophysiology. The RR intervals were recorded, and then were downloaded to the Polar Precision Performance program (v.3.0). This software enabled the visualization of HR and the extraction of a cardiac period (RR intervals series; the variation of beat-to-beat interval in milliseconds) file in ".txt" format. For analysis of HRV data at rest, we analyzed 1000 consecutive RR intervals, and for HRV analysis for the computational task, the number of consecutive RR intervals obtained was exactly 256 RR intervals. Digital filtering complemented by manual filtering was performed to eliminate artifacts and only series with greater than 95% of sinus beats were included in the study. HRV analysis was undertaken through linear, non-linear and chaotic global techniques (CGT).

Inclusion Criteria:

• DMD diagnoses was based on molecular methods and/or muscular protein expression.
• TD age-matched with DMD.

Exclusion Criteria:

• subjects with severely dilated myocardium.
• subjects with other associated diseases.
• individuals with inability to understand task instructions.