Objectives: To investigate the association between atypical PLR parameters and non-specific impairments in ANS by measurement of heart rate variability simultaneously with PLR in children with ASD.
Methods: PLR was measured using a two channel binocular apparatus, and HRV was measured using a remote heart rate device. PLR was induced by a 100ms green light pulse and measured in both light adapted (LA) and dark adapted (DA) conditions. Heart rate recording was started five minutes before the PLR test while keeping the participant in a sitting position and ended five minutes after the test. The tests were conducted in 71 children with ASD (age 11.3±3.0 years, 63 males and 8 females) and a typically developing control group of 50 children (age 10.8±2.4 years, 26 males and 24 females). To study medication effects, the ASD group was divided into a medication group (if the participants were taking antipsychotics, ADHD medications, antidepressants, etc.) and a non-medication group. Five basic PLR measurements including resting pupil diameter, relative constriction, latency, constriction velocity and re-dilation velocity were calculated to quantify PLR. To analyze heart rate variability, Fourier transform was applied to calculate the high frequency (0.15 – 0.4 Hz, “HF”) and low frequency (0.04-0.15Hz, “LF”) components of the RR tachogram power spectrum.
Results: Similar to the previous findings, PLR latency was significantly longer in children with an ASD than children of typical development (p < 0.0001). The ASD group with medications had smaller PLR constriction than the typical controls and the non-medication ASD group (p < 0.001). The latency difference between the ASD group with and without medication was not significant. The average heart rate was significantly higher in children with an ASD (p < 0.05). Both the ASD and control groups showed smaller normalized HF power and higher LF/HF ratios during the PLR test than during the resting periods (p < 0.05). However such PLR test associated changes were significantly smaller in the ASD group than in the typically developing control group.
Conclusions: The atypical PLR profiles found in our preliminary study were confirmed in the larger ASD population tested in this study. The observed high average heart rate suggested an increased sympathetic tone in the ASD group. Our results also indicated that PLR testing itself induced less ANS modulation changes in the ASD group than in the typical controls.
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