Attenuated Cardiac Autonomic Function in Response to Hand Grip Exercise Among Individuals with Intellectual Disability

Abstract

Individuals with intellectual disability (ID) are at a greater risk for co-occurring health conditions, such as cardiovascular disease (CVD). Previous research has indicated autonomic dysfunction, an important contributor to CVD risk, to be present in individuals with ID. However, autonomic dysfunction and its potential impact on work capacity has not been thoroughly investigated in individuals with ID. PURPOSE: To assess cardiac autonomic function between individuals with ID and a matched control group during isometric handgrip (HG) exercise. METHODS: Individuals with (n=13; 30±7yrs, 27.0±6.9kg/m2) and without ID (n=19; 28±7yrs, 25.5±3.7kg/m2) had cardiac autonomic function assessed via heart rate variability (HRV) in two-minute sections, before, during, and after seated isometric HG exercise at 30% of maximal voluntary contraction. ECG recordings were acquired and analyzed in the time (root mean square of successive differences (RMSSD) and percentage of RR intervals differing by <50ms (PNN50)), and frequency domains (low and high frequency (LF, HF), and LF/HF ratio). Data were log-transformed in the case of non-normal distribution, but raw data are presented below. RESULTS: HG exercise elicited a decrease in RMSSD, LF, and HF (p<0.05) in both groups that returned to baseline values during recovery. Controls reduced pNN50 during HG and recovered to values higher than seated, however, no changes were observed in ID (interaction, p=0.03). LF/HF ratio did not change in either group. CONCLUSION: Individuals with ID appear to have attenuated cardiac autonomic responses (i.e., depressed sympathetic tone or incomplete vagal withdrawal) to a sympathoexcitatory task, such as isometric HG exercise. These data suggest that autonomic dysfunction likely exists among individuals with ID even during submaximal intensities and may contribute to the low work capacity in this population. However, a greater sample size is required to fully elucidate these findings.