A growing body of research has suggested heart rate variability (HRV) may be reduced in autism spectrum disorder (ASD) in comparison to neurotypical cohorts. While there have been several studies investigating HRV in children diagnosed with ASD, few studies have been conducted in adults. The objective of the current study was to investigate autonomic nervous system activity as assessed by HRV in adults diagnosed with ASD. We hypothesized that adults with ASD would show a reduction in HRV compared to neurotypical participants. Participants diagnosed with ASD (n = 55) were recruited from the Autism Clinic for Translational Research at the Brain and Mind Centre (University of Sydney) between 2013 and 2017. Neurotypical participants were recruited from advertisements and online media. Resting state heart rate was measured for 5 min while participants sat in an upright position. Results showed there was an overall significant difference in resting-state HRV between adults diagnosed with ASD compared to the neurotypical control group. Logarithmically transformed high frequency (HF) and root mean square of successive differences were particularly decreased in the ASD group, suggesting lower parasympathetic activity. The use of psychotropic medications and comorbidities were associated with reductions in low frequency of HRV. Our data suggest an overall dysregulation in resting autonomic activity in adults with ASD. This may represent an important physiological mechanism leading to potential cardiovascular risk in ASD, which warrants further investigation. Autism Res 2019, 12: 922-930.Lay Summary: ASD is commonly associated with a range of physical and mental health comorbidities. Autonomic disruptions underlying reductions in heart rate variability (HRV) have been linked to a range of mental and physical health conditions. We assessed resting-state HRV in adults diagnosed with ASD in comparison to healthy individuals. Our results showed reduced heart rate variability in people diagnosed with ASD compared to adults without ASD. These findings implicate a role for autonomic activity as a potentially modifiable risk factor for ASD.

Decreased heart rate variability (HRV) is considered a common marker of autonomic dysfunction that contributes to poor health outcomes. While some studies have suggested that children with autism spectrum disorder (ASD) show reduced HRV, research is yet to consider whether this may be associated with medication use and symptom severity. This study examined the relationship between resting state HRV, medication use and symptom severity in children diagnosed with ASD. Children with ASD (N = 86), aged between 3 and 12 years (M = 8.09), were compared to 44 neurotypical children of similar age (M = 7.15). Laboratory assessment of HRV involved 5 min of non‐invasive baseline electrocardiogram assessments while participants viewed an age‐appropriate non‐verbal animated video. Time‐domain and frequency‐domain HRV measures were analyzed. ASD symptom severity was assessed using the Autism Diagnostic Observation Schedule‐Second Edition (ADOS‐2) and Social Responsiveness Scale (SRS‐2). Results indicated that children with ASD exhibited reduced resting HRV relative to neurotypical children. Subsequent analyses within the ASD group suggested that this group difference was greater in children who were taking psychotropic medication (N = 36). Our data also provides tentative evidence of a relationship between HRV and social impairment symptoms in children with ASD, with more severe repetitive behaviors (as measured by the ADOS‐2) associated with decreased resting HRV. Overall, these findings suggest that HRV may be atypical in children with ASD and suggest the importance of exploring HRV as a risk factor for cardiovascular health in this group. Lay Summary Cardiac activity, such as heart rate variability (HRV), can provide insight into the autonomic nervous system. This study reports on the association between resting‐state HRV and autonomic nervous system activity in young children with autism spectrum disorder (ASD) compared to neurotypical children. These results may help us understand what underlies autonomic nervous system dysfunction and the potential pathophysiological mechanisms leading to increased cardiovascular risk in ASD.

Early supports to enhance social development in children with autism are widely promoted. While oxytocin has a crucial role in mammalian social development, its potential role as a medication to enhance social development in humans remains unclear. We investigated the efficacy, tolerability, and safety of intranasal oxytocin in young children with autism using a double-blind, randomized, placebo-controlled, clinical trial, following a placebo lead-in phase. A total of 87 children (aged between 3 and 12 years) with autism received 16 International Units (IU) of oxytocin (n = 45) or placebo (n = 42) nasal spray, morning and night (32 IU per day) for twelve weeks, following a 3-week placebo lead-in phase. Overall, there was no effect of oxytocin treatment over time on the caregiver-rated Social Responsiveness Scale (SRS-2) (p = 0.686). However, a significant interaction with age (p = 0.028) showed that for younger children, aged 3–5 years, there was some indication of a treatment effect. Younger children who received oxytocin showed improvement on caregiver-rated social responsiveness ( SRS-2). There was no other evidence of benefit in the sample as a whole, or in the younger age group, on the clinician-rated Clinical Global Improvement Scale (CGI-S), or any secondary measure. Importantly, placebo effects in the lead-in phase were evident and there was support for washout of the placebo response in the randomised phase. Oxytocin was well tolerated, with more adverse side effects reported in the placebo group. This study suggests the need for further clinical trials to test the benefits of oxytocin treatment in younger populations with autism.Trial registration www.anzctr.org.au (ACTRN12617000441314).