Revised spectral metrics for body surface measurements of gastric electrophysiology

Abstract

Background Electrogastrography (EGG) non-invasively evaluates gastric function but has not achieved common clinical adoption due to several technical limitations. Body Surface Gastric Mapping (BSGM) has been introduced to overcome these limitations, but pitfalls in traditional metrics used to analyze spectral data remain unaddressed. This study critically evaluates five traditional EGG metrics and introduces improved BSGM spectral metrics, with validation in a large cohort. Methods Pitfalls in five EGG metrics were assessed (dominant frequency, percentage time normogastria, amplitude, power ratio, and instability coefficient), leading to four revised BSGM spectral metrics. Traditional and revised metrics were compared to validate performance using a 100 BSGM subject database (30 min baseline; 4-hrs postprandial), recorded using Gastric Alimetry (Alimetry, New Zealand). Key Results BMI and amplitude were highly correlated (r=-0.57, p<0.001). We applied a conservative BMI correction to obtain a BMI-adjusted amplitude metric (r=-0.21, p=0.037). Instability coefficient was highly correlated with both dominant frequency (r=-0.44, p<0.001), and percent bradygastria (r=0.85, p<0.001), in part due to conflation of low frequency transients with gastric activity. This was corrected by introducing distinct gastric frequency and stability metrics (Principal Gastric Frequency and Gastric Alimetry Rhythm Index (GA-RI)) that were uncorrelated (r=0.14, p=0.314). Only 28% of subjects showed a maximal averaged amplitude within the first postprandial hour. Calculating Fed:Fasted Amplitude Ratio over a 4-hr postprandial window yielded a median increase of 0.31 (IQR 0-0.64) above the traditional ratio. Conclusions & Inferences The revised metrics resolve critical pitfalls impairing the performance of traditional EGG, and should be applied in future BSGM spectral analyses.

Normative values for body surface gastric mapping evaluations of gastric motility using Gastric Alimetry: spectral analysis

“…18,19 Key physiological features of gastric myoelectrical activity motivated the development of spectral metrics used to establish the BSGM reference interval. 10,[20][21][22] These features and the corresponding metrics were recently described in detail by Schamberg et al, 15 and are briefly outlined below, and depicted in Figure 1. Each metric is reported for the overall test, as well as for the preprandial period, postprandial period, and each 1-hour window postprandially.…”

“…The frequency (cycles per minute; cpm) of gastric slow waves has long been applied as a disease indicator for gastric myoelectrical activity. 20–22 We previously reported that simply computing the maximum of the average spectrum did not reliably identify a gastric frequency consistent with visual assessment, 15 so we developed a novel Principal Gastric Frequency metric, which identifies the gastric frequency based on maximizing the GA-RI (defined below). 15 The Principal Gastric Frequency is not reported where the GA-RI does not identify a stable gastric slow wave, or for time periods with an average amplitude of <10 μV, which is the reliability threshold for the Gastric Alimetry system.…”

“…Measures of stability have previously been proposed to define discoordinated periods of gastric activity, such as instability coefficients of gastric frequency and amplitude/power. 20 We previously reported that the use of instability coefficients may lead to incorrect assumptions about gastric stability, 15 and therefore introduced GA-RI for BSGM, being a measure of the concentration of activity within the gastric frequency band relative to the residual spectrum over time. 15 A high GA-RI occurs in cases where there is a distinct band of activity at a single frequency for an extended period, whereas a low GA-RI is observed in cases demonstrating a high degree of scatter in the spectral plot.…”

“…[9][10][11] Spectral metrics are derived from a spectral plot, and represent a form of HR-EGG, achieving robust improvements over traditional EGG metrics. 8,10,12,15 Spectral metrics are currently the most established form of analytics, with a recent BSGM study principally employing these to identify a distinct subgroup of patients with gastric neuromuscular abnormalities in nausea and vomiting syndromes. 11 The aim of this study was to establish normative reference intervals for spectral BSGM metrics for Gastric Alimetry, encompassing the Principal Gastric Frequency, Gastric Alimetry Rhythm Index (GA-RI), BMI-adjusted amplitude, and the fed:fasted amplitude ratio.…”

“…9–11 Spectral metrics are derived from a spectral plot, and represent a form of HR-EGG, achieving robust improvements over traditional EGG metrics. 8,10,12,15 Spectral metrics are currently the most established form of analytics, with a recent BSGM study principally employing these to identify a distinct subgroup of patients with gastric neuromuscular abnormalities in nausea and vomiting syndromes. 11…”