Heart Rate Variability (HRV; the rhythmic beat-to-beat change in heart rate) has been used as an indicator of emotional regulation and psychological adjustment in numerous studies (Beauchaine, 2001). It has recently been used to better understand the social deficits seen in ASD. The polyvagal theory (Porges, 1998, 2011) describes a neural social engagement system, and the functioning of this system can be measured by assessing the action of the vagal nerve on the heart, which manifests as HRV. Higher HRV indicates more parasympathetic activity, which in turn reflects better emotional regulation and a readiness to engage in social interaction. The polyvagal theory predicts that individuals with ASD would have lower HRV during reciprocal social interactions.
The first aim of this study was to compare HRV for individuals with ASD to neurotypical controls (TDC) across the conditions of resting baseline, a live socially demanding task (i.e., conversation task from the ADOS), and a cognitively demanding task (i.e., Matrices subtest from the DAS-II). The second aim of the study was to investigate the relationship between HRV and parent-report measures of emotional regulation (i.e., Emotional Control subtest of the BRIEF), anxiety (i.e., the SCARED), and socialization skills (i.e., the Socialization subtest of the VABS-II).
The groups included 18 individuals with ASD and 20 control individuals (TDC) that were matched for age and overall IQ. The diagnosis of ASD was confirmed using the ADI-R and ADOS, and IQ was assessed using the DAS-II. The Biopac MP150 system and BioNomadix Respiration & ECG Modules were used at a sampling rate of 1000 Hz. ECG data were collected using a standard Lead-II configuration with disposable electrodes, and respiration was measured via a small belt (strain gauge) fastened lightly around the sternum. After placement of the electrodes and respiration belt, participants were seated at a table across from the examiner. The task presentation was counterbalanced and included baseline, socially demanding task, baseline, cognitively demanding task, and baseline, with each task lasting for 6 minutes.
There were no significant differences in age between the ASD (M= 11.77, SD=3.00) and TDC (M=13.18, SD=3.15) groups; t(36)=-1.40, p=.168. Additionally, there were no significant differences in overall IQ between the ASD (M=104.28, SD=20.70) and TDC (M=105.45, SD=10.40) groups; t(36)=-.22, p=.824. HRV data were analyzed using power spectral analysis of the high frequency range of .12-1.0 Hz. Preliminary analyses of the HRV data indicated significant group differences for the initial baseline condition. Additional analyses are ongoing.
A strength of this study is the assessment of HRV during a live social interaction, which enhances the ecological validity of the findings. Although data analysis is in preliminary stages, the identification of emotional arousal (lower HRV) during social interactions for individuals with ASD may have important treatment implications since most interventions involve a social component. Including strategies to increase HRV (e.g., stimulating and exercising the neural pathways of the social engagement system) may allow individuals with ASD to profit more from the interventions they are receiving.
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