Resting Heart Rate Variability May Predict Reactivity to Tactile Stimuli, Study Suggests

Resting heart rate variability may be used to predict reactivity to tactile stimuli in people with Rett syndrome, a study suggests.

This approach may help to better understand sensory function in these patients.

The study, “Preliminary Evidence That Resting State Heart Rate Variability Predicts Reactivity to Tactile Stimuli in Rett Syndrome,” was published in the Journal of Child Neurology.

Preclinical and clinical data suggest that people with Rett syndrome have decreased pain sensitivity. However, their sensitivity to specific types of stimuli remains unexplored.

Researchers note that the assessment of pain perception and response in people with Rett cannot rely on self-reporting, given the patients’ severe communication impairments. Thus, there is an unmet need to identify other objective measures of pain response.

Heart rate variability — the variation in the number of heart beats per minute — is used as a measure to quantify the adaptation of the autonomic nervous system to environmental events, such as pain. The autonomic nervous system controls visceral functions such as heart rate, respiratory rate, and digestion.

Previous studies have shown that resting heart rate variability is associated with self-reported pain experiences, suggesting that they are regulated, to some extent, by the autonomic nervous system.

Rett patients’ characteristic reduced heart rate variability suggests a reduced adaptive ability to environmental events and an increased risk of additional health problems.

With this in mind, the researchers set out to evaluate whether resting heart rate variability could predict sensory reactivity in people with Rett syndrome.

The study involved 17 girls and women with Rett, recruited at two International Rett Syndrome Foundation family meetings. The team analyzed the patients’ resting heart rate variability and pain-related behavioral responses during a modified version of the Quantitative Sensory Test (mQST).

Six stimuli were applied to the back of each hand and top of each foot in a fixed order: light touch (von Frey test with weaker force), pinprick, cool, 4 lb of pressure, repeated touch (von Frey test with stronger force), and heat (50 ºC).

The von Frey test uses von fray fibers — small pieces of nylon rod of varying diameters that provide different calibrated forces to a portion of the body — to test a person’s sensitivity to a mechanical stimulus.

Behavioral responses were based on a coding system that included vocalizations such as moaning or crying, upper and lower facial expressions — including a brow furrow or opening of the mouth — motor responses such as flinching, and physiological signs, including gasping.

Repeated touch with von Frey fibers resulted in the highest scores of behavioral responses, followed by light touch, cool, heat, pressure, and pinprick.

Patients with higher resting heart rate variability had significantly higher behavioral response scores to repeated touch. This showed that resting heart rate variability may be used to predict Rett patients’ sensitivity to tactile or mechanical stimulation.

The lack of an association with other types of stimuli may be due to “the repeated von Frey stimuli, which have a longer application time than other stimuli and thus a long enough time to register a change in [heart] signal,” the researchers said.

They also noted that the combination of autonomic (heart rate) and sensory function assessment “may help overcome the issue of absent self-report in Rett syndrome without relying on proxy report in its place, which is a common practice in this and other populations with limited verbal abilities.”

“In addition to the possible utility as outcome measures, it is possible that these measures may serve as predictive or diagnostic biomarkers, as both heart rate variability and traditional quantitative sensory testing have been used to predict health outcomes in other populations,” the researchers concluded.

The team noted that future studies on a more representative population of girls and women with Rett syndrome are required to confirm these findings, to assess whether the lack of behavioral responses were due to short stimuli or to real alterations in sensory processes, and to evaluate how heart rate variability changes in response to each stimulus.