Reliability and validity of novel methods in the assessment of cold-induced shivering

Introduction: This study assessed the test-retest reliability and validity of four metrics of shivering onset; oxygen uptake (V̇O2), electromyography (EMG), mechanomyography (MMG) and bedside shivering assessment scale (BSAS). Methods: Ten volunteers attended three identical experimental sessions involving passive deep-body cooling via lower-body cold water immersion at 10°C water temperature. V̇O2, EMG and MMG were continuously assessed, while the time elapsed at each BSAS stage was recorded. To determine shivering onset, metrics were graphed as a function of time and rectal temperature (Trec). A baseline was visually identified, followed by two inflection points for intermittent and constant shivering. Inflection points were classified by three independent researchers and the median was used. Results: Shivering was observed across all subjects, with an onset time ranging from 1238 to 3367s across trials and metrics. Time provided a more reliable indicator of shivering onset than Trec (mean Intraclass Correlation [ICC]; time, 0.92; Trec, 0.83 ). MMG presented the most reliable indicator of shivering onset time between trials (ICC; intermittent shivering, 0.94; constant shivering, 0.96), followed by BSAS and V̇O2, while EMG presented the least reliable (ICC; intermittent, 0.84; constant, 0.82). Chronologically, MMG and EMG were similar in detecting onset, whereas a mean lag of 99s or 0.03°C Trec was seen in V̇O2 identification. A 312s or 0.13°C Trec lag was seen in BSAS identification compared to the mean of objective metrics. Signal-noise ratio favoured EMG (SNR, 1.99 ± 1.33), followed by MMG (SNR, 1.68 ± 0.51) and finally V̇O2 (SNR, 1.37 ± 0.24) in the analysis of inflection points. Conclusion: Good to excellent reliability can be seen across all metrics, yet given the observed lag times, SNR’s, along with known advantages/disadvantaged of each metric, it is recommended that no single metric should be used in isolation. These results have been used to develop an integrated multi-modal measure of shivering.