Table 5 Autonomic nervous system deregulation in ASD

Anderson et al. [62]

Study 1: ASD group (N = 12, M = 11, F = 1, mean age = 50.25 months, range = 30–69 months), down syndrome (DS) group (N = 9, M = 7, F = 2, mean age = 48.67 months, range = 20–73 months), TD group (N = 11, M = 10, F = 1, mean age = 51.73 months, range = 34–69 months)

Study 2: ASD group (N = 18, mean age = 57.78 months, range = 39–73 months), TD group (N = 19, mean age = 52.26 months, range = 33–79 months)

Tonic pupil size, saliva sample collection

ASD showed larger pupil size and lower sAA levels than controls; sAA was strongly correlated with tonic pupil size; typical controls showed a linear increase in sAA during the day

Limitations: small sample size, disproportioned M/F ratio in groups of the first study, not stratification in the second study for males and females

Strengths: two different studies, presence of two a control groups (healthy individuals and down syndrome)

Pace et al. [64]

ASD group (N = 19, mean age = 10.7 ± 1.2 years), control group (N = 19, mean age = 9.9 ± 1.6 years)

Questionnaire, actigraphy; nocturnal recordings; HRV analysis

Lower mean HR values were found during sleep with respect to those registered during wakefulness; however, the ASD group showed a lower decrease in HR during deep sleep despite the presence of a higher parasympathetic tone

Limitations: small sample size, not stratification in males and females

Strengths: presence of a control group

Harder et al. [65]

ASD children (N = 21, all males, mean age = 7.8 ± 1.8 years) and typically developed children (N = 23, M = 18, F = 5, mean age = 8.0 ± 1.9 years)

Polysomnography, HR and HRV

In both groups, HR decreased during non-REM sleep and increased during REM sleep; HR was significantly higher in stages N2, N3 and REM sleep in the ASD group; ASD children showed less HF modulation during N3 and REM sleep; LF/HF ratio was higher during REM; heart rate decreases with age at the same level in ASD and in TD. LF was influenced by age

Limitations: small sample size, ASD children were composed only by males

Strengths: controlled study

Tessier et al. [66]

ASD children (N = 13, range 7–12 years, mean age = 10.2 ± 2.1), ASD adults (N = 16, range = 16–27 years, mean age = 22.0 ± 3.8 years), TD children (N = 13, range = 6–13 years, mean age = 10.5 ± 1.8 years), TD adults (N = 17, range = 16–27 years, mean age = 21.1 ± 4.0 years)

Sleep laboratory measures, ECG recordings

Results show that ASD adults had lower HFnu in the morning than TD adults. During REM sleep, adults had higher LF/HF ratio than children, regardless of their clinical status

Limitations: high number of males, ASD participants were medicine-free; LH/FH ratio significance has been largely questioned

Strengths: four different equally subdivided groups (children and adults with or without ASD)

Bharath et al. [8]

ASD children (N = 40, M = 24, F = 16, range = 5.25–12 years, mean age = 10 years), TD controls (N = 40, M = 26, F = 14, range = 7.25–11.75 years, mean age = 9 years)

Autonomic index was assessed by the analysis of short term HRV; urinary levels of VMA estimation was used as a biochemical autonomic index

ASD children exhibit lower cardio-vagal activity as measured by HRV and increased sympathetic activity as assessed by urinary VMA compared to that of TD children

Limitations: small sample size, difference in M/F ratio

Strengths: presence of a control group similar to ASD ones (same number of participants)

Sheinkopf et al. [59]

Infants later diagnosed with ASD (N = 12, M = 12, F = 0) and controls non-later ASD (N = 106, M = 58, F = 48) range: 1–72 months

HR and RSA

Both groups showed an expected age-related decrease in HR and increase in RSA, without difference in rate of HR decrease over time; ASD infants demonstrated a smaller linear increase in RSA, indicating slower growth in RSA over time in comparison to controls, thus suggesting that differences in physiological regulation may develop with age in ASD

Limitations: small sample size; participants were drawn from a high-risk cohort designed to investigate the developmental effects of prenatal drug exposure, which could have effects on RSA at one moth of age; disproportion between two groups composition

Strengths: controlled study

Thapa et al. [61]

ASD group (N = 55, M = 74.5%, F = 25.5%, mean age = 23.11 ± 5.98 years) control group (N = 55, M = 80%, F = 20%, mean age = 22.00 ± 5.24 years)

HRV

Difference in resting-state HRV between adults diagnosed with ASD compared to the neurotypical control group, with lower parasympathetic activity in ASD

Limitations: ASD group had psychiatric comorbidities, whose effect was difficult to determine due to small sample size; two different devices were used to determine HRV; majority of patients were males

Strengths: presence of a control group

Mohd et al. [60]

ASD children (N = 6), TD controls (N = 14)

HRV derived from PPG

HRV response can differentiate between ASD and TD children and could contribute to the detection of ASD to facilitate the children getting the best intervention at the earliest possible time

Strengths: controlled study

Limitations: small sample size, not stratification in age and sex

Chong et al. [67]

ASD children (N = 13) divided in: dysregulated sleep group (N = 7, M = 63%, F = 37%, mean age = 7.53 ± 1.35 years)

Regulate sleep group (N = 6, M = 80%, F = 20%, mean age = 4.46 ± 1.28 years)

Actigraphy for sleep measure, EDA (which included NSSCR and SCL, SCQ for ASD symptoms core, VABS-II for adaptive behavior

Children in the dysregulated sleep group had fewer NSSCRs and lower SCL in the afternoon

Limitations: small and heterogeneous sample; prevalence of males in both groups; absence of a control group

Strengths: subdivision in two groups based on facility/difficulty in sleeping