Heart rate variability (HRV) in individuals with autism spectrum disorders (ASD) has been investigated in some studies but the procedures and results vary. We conducted a systematic review and meta-analysis to compare HRV in individuals with and without ASD; the influence of different conditions and HRV indices is considered. Baseline HRV and HRV reactivity were analyzed in several ways: parasympathetic indices in hierarchical order (main analysis), total variability, specific parasympathetic indices and respiratory sinus arrhythmia (RSA), etc. The review covered 34 studies for quantitative analysis. Individuals with ASD had a significantly lower baseline HRV for parasympathetic indices in hierarchical order (Hedges'g=-0.5168, p < 0.0001) and RSA (g=-0.5860, p=0.0010). The reactivity of HRV in situations of social stress (g=-0.4647, p = 0.0033) and social debriefing (g=-0.5001, p = 0.0007) was also significantly lower in subjects with ASD. RSA reactivity was significantly lower in ASD group for all situations, with the largest effect size for social stress (g=-0.7246, p < 0.0001). The results support low HRV to be a potential biomarker of ASD, especially RSA reactivity under social stress.
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