Neural respiratory drive as a physiological biomarker to monitor change during acute exacerbations of COPD

Abstract

Background Acute exacerbations of chronic obstructive pulmonary disease have a significant negative impact on both patients and healthcare systems. Currently, there are no physiological biomarkers that effectively monitor clinical change or predict respiratory readmission. Acute exacerbations impose a change in the respiratory muscle load-capacity-drive relationship. It was hypothesised that lack of a fall in neural respiratory drive would identify patients at risk of treatment failure and early hospital readmission. Methods An observational study was performed at two UK teaching hospitals. Routine clinical physiological parameters and neural respiratory drive index (NRDI), calculated as the product of second intercostal space parasternal electromyography (EMG) activity normalised to the peak EMG activity during a maximum inspiratory sniff manoeuvre and respiratory rate, were recorded daily from admission to discharge. Results 30 acutely unwell patients of mean (SD) age 72 (10) years, forced expiratory volume in 1 s 0.60 (1.65) l, NRDI 455 (263) AU and median length of stay 6 days were studied. Changes in NRDI correlated with changes in Borg score (r¼+0.60; p<0.001), discriminated between patients deemed to have clinically improved rather than deteriorated (mean difference 339 AU; 95% CI 234 to 444; p<0.001) and identified those patients readmitted within 14 days (mean difference 203 AU; 95% CI 39 to 366; p¼0.017). Conclusions NRDI is a feasible clinical physiological parameter in patients with an acute exacerbation of chronic obstructive pulmonary disease and can provide useful information on treatment response and risk of readmission.

Measurement of neural respiratory drive via parasternal intercostal electromyography in healthy adult subjects

“…It is likely that the effect of lung and chest wall pathology on the respiratory load-capacity balance may be of greater significance than the relatively subtle influences affecting NRD in healthy subjects in the current study. Variability of up to 4µV or 5% of maximum represents a much smaller proportion of the resting signal in patients with significant lung disease (Murphy et al, 2011;Reilly et al, 2011;Steier et al, 2011) compared to the healthy subjects studied here. Of note, however, is the slightly higher within-than between-session variability, with higher first measurements within the same testing session.…”

“…Previous studies (Murphy et al, 2011;Reilly et al, 2011;Steier et al, 2011) including measurements of EMGpara in healthy individuals have recruited relatively small numbers of subjects from staff and students of respiratory physiology departments.…”

“…EMGpara was expressed both as a raw RMS value in microvolts (µV) termed"EMGpara" and as a percentage of the highest RMS EMGpara value recorded during the maximal inspiratory efforts ("EMGpara%max"). The neural respiratory drive index (NRDI, expressed in %.breaths/min (%.BPM)) was also calculated as the product of EMGpara%max and respiratory rate (Murphy et al, 2011).…”

“…Reproducibility of EMGpara%max measurements has been demonstrated (Murphy et al, 2011;Reilly et al, 2011), but these studies have mainly been undertaken in small groups of healthy individuals experienced in respiratory manoeuvres. It is not known whether naïve subjects are as able to reliably perform such maximal respiratory efforts reproducibly.…”

Acute monitoring of patients with chronic respiratory disease during hospital admission

“…These may be clinically useful in the future as an automated strategy to monitor patients during acute illness. 21 …”