Study Highlight — HRV during sleep in autistic children

Content Warning: To help me back-up my points with other sources, I am citing sources that medicalize and pathologize autism and posttraumatic stress injuries. Please read with caution and take good care of yourselves.

The article below is worth archiving. As I am only beginning to hone my fundamentals in the area of autonomics, I am sure I don’t have a complete grasp of what is happening here. But the study felt like some validation for my beliefs that autonomics are a meaningful factor in autistic experience.

I am planning to work on a few primer posts about autonomics and the Polyvagal theory soon. I can’t think of a better way for me to learn than to write and teach about them with intent to introduce others to them. Until then, I still want to share research I am reading to meet my goals of curating specific research I feel is relevant to the intersections of trauma, stress, and autism. However, my ability to translate and make the research accessible will likely shift over time as I hopefully grow more confident in my ability to digest the work fully and report on it accurately.

Here is a link to a full PDF of this article. Hopefully that link will continue to work. If it is not working, please let me know.

Harder, R., Malow, B., Goodpastor R., Fahad, I., Halbower, A., Goldman S., . . . Diedrich A. (2016). Heart rate variability during sleep in children with autism spectrum disorder. Clin Auton Res, 26(6): 423-432. DOI 10.1007/s10286-016-0375-5

The Abstract:

Purpose

Autonomic dysfunction has been reported in

autism spectrum disorders (ASD). Less is known about

autonomic function during sleep in ASD. The objective of

this study is to provide insight into the autonomic cardio-

vascular control during different sleep stages in ASD. We

hypothesized that patients with ASD have lower vagal and

higher sympathetic modulation with elevated heart rate, as

compared to typical developing children (TD).

Methods

We studied 21 children with ASD and 23 TD

children during overnight polysomnography. Heart rate and

spectral parameters were calculated for each vigilance

stage during sleep. Data from the first four sleep cycles

were used to avoid possible effects of different individual

sleep lengths and sleep cycle structures. Linear regression

models were applied to study the effects of age and diag-

nosis (ASD and TD).

Results

In both groups, HR decreased during non-REM

sleep and increased during REM sleep. However, HR was

significantly higher in stages N2, N3 and REM sleep in the

ASD group. Children with ASD showed less high fre-

quency (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. We found an age

effect in LF in REM different in ASD and TD.

Conclusion

Our findings suggest possible deficits in vagal

influence to the heart during sleep, especially during REM

sleep. Children with ASD may have higher sympathetic

dominance during sleep but rather due to decreased vagal

influence.

First, a critical obstacle in performing analysis of HRV is the requirement of stationarity in HR data. This is difficult to achieve, especially in awake children. The

stereotypic behavior and excessive movements found in ASD can furthermore skew HR and HRV [18]. Second, baseline conditions or tasks present a stressful situation for a child with ASD [15]. Third, medications used in ASD can affect HR and HRV. Finally, children with ASD show reduced responsiveness of HRV during challenging tasks [1].

Sleep provides an opportunity to study the child during a

time of decreased stressful psychological inputs and fewer

body movements.

One of the strengths of our work is that by recording during sleep, we were able to minimize the confounding effects of daytime anxiety on autonomic parameters.

My primary takeaways:

1) They found autonomic differences in autistic children as compared to non-autistic peers.

2) The autonomic differences found in autistic children could be the “result of decreased vagal activation, sympathetic activation dominance or both.”

3) Results taken together “sugges[t] that these children may have higher sympathethic [sic] dominance during sleep (e.g., LF to HF ratio) but due to decreased vagal influence.”

4) “[L]ess vagal modulation to the heart during REM sleep. . . has implications for the challenging daytime [experiences of autistic people] as REM sleep has restorative functions, such as information processing of memories between the hippocampus and neo cortex [34].”

5) “Sleep quality affects the performance and autonomic function the next day [35]. We found lower sleep efficiency and higher amount of wakefulness during the sleep period, which could affect the autonomic function during the next day.”

6) Monitoring autonomics during sleep controls for daytime confounding effects of daytime anxiety.

7) “Our data . . . point out the importance of accounting for age in physiological studies of autism. . . .”

8) These results “raise the possibility of a [sic] developmental delay seen in [autism] may extend to the autonomic nervous system.”