Leveraging Accelerometry as a Prognostic Indicator for Increase in Opioid Withdrawal Symptoms

Abstract

Treating opioid use disorder (OUD) is a significant healthcare challenge in the United States. Remaining abstinent from opioids is challenging for individuals with OUD due to withdrawal symptoms that include restlessness. However, to our knowledge, studies of acute withdrawal have not quantified restlessness using involuntary movements. We hypothesized that wearable accelerometry placed mid-sternum could be used to detect withdrawal-related restlessness in patients with OUD. To study this, 23 patients with OUD undergoing active withdrawal participated in a protocol involving wearable accelerometry, opioid cues to elicit craving, and non-invasive Vagal Nerve Stimulation (nVNS) to dampen withdrawal symptoms. Using accelerometry signals, we analyzed how movements correlated with changes in acute withdrawal severity, measured by the Clinical Opioid Withdrawal Scale (COWS). Our results revealed that patients demonstrating sinusoidal-i.e., predominantly single-frequency oscillation patterns in their motion almost exclusively demonstrated an increase in the COWS, and a strong relationship between the maximum power spectral density and increased withdrawal over time, measured by the COWS (R = 0.92, p = 0.029). Accelerometry may be used in an ambulatory setting to indicate the increased intensity of a patient's withdrawal symptoms, providing an objective, readily-measurable marker that may be captured ubiquitously.

Keywords: accelerometer; non-invasive therapies; opioid addiction; opioid use disorder; opioid withdrawal; restlessness; spectral analysis; spectrograms; vagal nerve stimulation; wearable.

Figure 1

A sample size of n = 23 patients participated in the protocol. Patients were administered COWS by the clinical staff throughout the protocol while patient movements were tracked via accelerometry. Movement data was monitored by a triaxial accelerometer connected to a 4-channel signal conditioner powering the accelerometer. The entire unit was connected to a laptop. The accelerometer was positioned at the center of the sternum and recorded in real-time.

Figure 2

Spectral analysis of accelerometer waveforms extracted from 10−s windows during the experiment. Patient A represents patients not exhibiting sinusoidal wave patterns and having no increase in their COWS restlessness scores, while Patient B represents patients exhibiting sinusoidal wave patterns and having a four-point increase in their COWS scores. The amplitudes of the electrocardiogram (ECG) and accelerometer signals in the Ax-direction were normalized using z-score normalization as indicated by the y-axes in the figure. All accelerometer waveforms are taken from the craniocaudal direction. The dark red color where the highest energy content is located (and where LBFT is located) is between 0−10 Hz. The other colors such as yellow and blue are low energy noise signals.

Figure 3

Methods used to find significant correlations between the COWS scores and the normalized max PSD, as well as the correlations between the frequency at the max PSD and the normalized max PSD. (A) Accelerometer data were normalized using z-score normalization, where µ = mean and σ = standard deviation. The maximum PSD of a 10−s window was normalized to the summation of all PSD values within the same window. Freq = frequency. (B) Processed data were analyzed by visual inspection for sinusoidal patterns in the accelerometer data lasting ≥5 s in a 10−s window. A patient was labeled a “Sinusoidal Patient” if three or more windows containing the aforementioned pattern were found in the first opioid cue (FOC) or last opioid cue (LOC) of their accelerometer data.

Figure 4

Most patients with OUD classified as “Sinusoidal” had an increase in opioid withdrawal or deterioration over time as measured with the COWS. Patients classified as “Non-Sinusoidal” were as likely to have worsening withdrawal symptoms (deterioration) as no change or an improvement in withdrawal symptoms (no deterioration: no change or a decrease in their overall COWS scores).