Cardiac Activity Before and After Nocturnal Sleep In Adults with Autism

Background: Poor sleep is a frequent finding in autism and it has been shown to interfere with daytime functioning, using either behavioral (Limoges et al., 2005) or EEG measures (Daoust et al. 2004). Literature in typically developing individuals (TD) shows that sleep also influences the regulation of the autonomic nervous system so that the sympathovagal tone is normally higher in the morning compared to evening values. Studies of electrocardiographic (ECG) recordings suggest that there might be disequilibrium between sympathetic and parasympathetic activity in autism (Ming et al., 2005) but it is not known whether this observation is related to sleep or not.

Objectives: Analyze ECG recordings at bedtime and rise time to evaluate the sympathovagal tone before and after nocturnal sleep in autistic and TD individuals. We expected to see in TD as well as in autistic groups an increased sympathetic and an increased parasympathetic tone in morning values relative to evening values. We also expected to find a higher sympathetic tone in autistic participants compared to the TD group both in the evening and the morning recordings.

Methods: Fifteen men with ASD (seven with high functioning autism, HFA: 21.1 ± 4.0 years; eight with Asperger Syndrome, ASP: 23.9 ± 2.1 years) and 18 typically developing individuals (TD: 21.0 ± 4.2 years) were evaluated over two consecutive nights in a sleep laboratory. All participants were free from medication and all had a normal IQ. Sleep was monitored with standard EEG-EOG-EMG measures and ECG was recorded from evening to morning using bipolar sub-clavicular electrodes. ECG samples were taken for 5 minutes at bedtime and just before final rise time in the morning. Spectral analysis of the ECG signal was performed using a commercial software and the following four variables were extracted: total spectral power, low frequency power (LF: sympathetic tone), absolute values of high frequency spectral power (HF: parasympathetic tone), normalized values of high frequency spectral power (HFnu). Groups were compared with Student’s t-tests.

Results: Significant differences between evening and morning values were found only in the TD group, with lower evening values for total spectral power (p=0.008), LF (p=0.007) and HF (p=0.040) were all lower in the evening compared to morning. In the morning, significantly lower HF (p=0.043) and HFnu (p=0.027) values were found in ASD vs. TD groups. When the HFA and ASP subgroups were separately compared to the TD group, the latter showed significantly higher HFnu values in the evening compared to ASP (p=0.043) and HFA (p=0.038). In the morning, results showed that HF values were significantly lower in HFA (p=0.033) compared to TD group and HFnu values were significantly lower in ASP (p=0.034) than TD group.

Conclusions: These results suggest that the effect of nocturnal sleep differs in TD and ASD individuals and that the parasympathetic tone may be lower in ASD. Further analyses will focus on ECG activity during sleep, for each of the sleep stages.