Numerous studies have reported elevated rates of anxiety symptoms and disorders in people with autism spectrum disorders (ASDs). However, the assessment of anxiety symptoms in this population is hindered by difficulties in acquiring good quality personal reports, which are the usual gold standard. The investigation of the underlying physiology of anxiety in this population is particularly important.
Objectives:
To determine whether people with ASDs show a similar physiological response to psychosocial stress measured by heart rate compared to controls, and if this physiological response relates to anxiety.
Methods:
This study is ongoing but currently includes 28 children with ASDs and 9 typically developing controls. We expect our sample size at presentation to include 50 ASD cases and 25 controls.
Participants were aged 10-16 years with a full-scale IQ ≥ 70 measured using the Wechsler Abbreviated Scale of Intelligence. The ASD sample was recruited from clinical services and controls via public advertisement. We specifically recruited ASD participants with and without anxiety problems.
Anxiety was assessed using the Spence Child Anxiety Scale (SCAS) – parent version. For the present analysis, the ASD group was collapsed and anxiety symptoms treated as an independent measure. Participants underwent a psychosocial stress test (Kirschbaum et al, Neuropsychobiology, 1993) consisting of 40 minutes rest, 20 minutes stress and finally 40 minutes recovery. The stress test comprised a non-verbal drawing task and a public speaking task. Mean heart rate was measured in the resting, stress and recovery stages. A stress responsiveness variable was calculated by deducting the mean heart rate at rest from mean heart rate during the stress stage.
Results:
Mean Heart Rate. A 2x3 ANOVA revealed a significant group difference in the resting phase (F(1, 33)=12.56,p=.001) and the recovery phase (F(1, 33)=5.03, p=.03), but not in the stress phase (F(1, 33)=1.49,p =.23). The basal difference remained significant when anxiety symptoms were accounted for.
Stress responsiveness. The ASD group had a mean heart rate increase of 4.62 beats-per-minute compared to 14.29 in the control group (F(1, 35)=22.63, p ≤ .001).
A regression analysis examined the independent roles of anxiety and participant group on stress responsiveness, revealing a significant SCAS by group interaction (β=-.27, p=.02). In the control group, increasing SCAS scores were positively associated with increased stress reactivity while the opposite relationship was seen in the ASD group.
Conclusions:
Overall, young people with ASDs display a significantly increased resting heart rate compared to controls and a lack of responsiveness when entering a stressful situation. Furthermore the relationship between stress responsiveness and baseline anxiety symptoms appears to differ between groups. It may be that a high resting heart rate allows less flexibility to adapt to stress. Alternative interpretations will be discussed.
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