Noninvasive Magnetogastrography Detects Erythromycin-Induced Effects on the Gastric Slow Wave

Abstract

Objective: The prokinetic action of erythromycin is clinically useful under conditions associated with gastrointestinal hypomotility. Although erythromycin is known to affect the electrogastrogram, no studies have examined the effects that erythromycin has on gastric slow wave magnetic fields.

Methods: In this study, gastric slow wave activity was assessed simultaneously using noninvasive magnetogastrogram (MGG), electrogastrogram, and mucosal electromyogram recordings. Recordings were obtained for 30 min prior to and 60 min after intravenous administration of erythromycin at dosages of 3 and 6 mg/kg.

Results: MGG recordings showed significant changes in the percentage power distribution of gastric signal after infusion of both 3 and 6 mg/kg erythromycin at t = 1-5 min that persisted for t = 30-40 min after infusion. These changes agree with the changes observed in the electromyogram. We did not observe any statistically significant difference in MGG amplitude before or after injection of either 3 or 6 mg/kg erythromycin. Both 3 and 6 mg/kg erythromycin infusion showed retrograde propagation with a statistically significant decrease in slow wave propagation velocity 11-20 min after infusion. Propagation velocity started returning toward baseline values after approximately 21-30 min for the 3 mg/kg dosage and after 31-40 min for a dosage of 6 mg/kg.

Conclusion: Our results showed that the magnetic signatures were sensitive to disruptions in normal slow wave activity induced by pharmacological and prokinetic agents such as erythromycin.

Significance: This study shows that repeatable noninvasive bio-electro-magnetic techniques can objectively characterize gastric dysrhythmias and may quantify treatment efficacy in patients with functional gastric disorders.

Figure 1

(a): Experimental setup to measure MGG using a SQUID magnetometer, EGG with cutaneous electrodes, and EMG with NG electrode catheter in normal controls. The SQUID sensor array shown in the inset consists of 19 normal-component (z) sensors and five vector channels (marked with x) that also sample x and y magnetic field components (18) ; 1(b) : X-ray showing the placement of NG tube in the stomach and the location of 8 electrodes (15).

Figure 2:

(a) Raw MGG signals from 17 sensors in the SQUID magnetometer during baseline in a normal subject. (b) Seven SOBI components classified as gastric with (c) associated power spectra. (d) Reconstructed SOBI-MGG with (e) power spectra. The reconstructed SOBI-MGG is largely free of interference from respiratory, cardiac, and other noise contributions to the signals.

Figure 3:

(a-d) Representative SOBI-MGG/ SOBI-EGG signals and corresponding power spectra at successive time intervals before and after erythromycin (3mg/kg) administration. (e-f) Mucosal EMG signals with corresponding power spectra before and after erythromycin administration are shown for comparison. Abnormal gastric activity evident immediately after administration of erythromycin eventually returned towards normal activity 30 minutes post-administration in MGG, EGG, and EMG.

Figure 4:

Percent power distributed (PPD) in brady-, normo-, and tachygastric frequency ranges for EMG, MGG and EGG recordings in normal human subjects at successive times both before and after erythromycin administration (3 mg/kg and 6 mg/kg). Statistically significant post-erythromycin PPD changes were denoted by *.

Figure 5:

MGG propagation pattern maps during (a) baseline, (b) t = 5 min post-administration, and (c) t = 25 min post-administration of erythromycin (3 mg/kg) in a typical subject. Each row shows 5 maps of magnetic field activity at two-second intervals in a single subject. During baseline, anterograde propagation is evident as the pattern maxima moves towards the left side of the map, corresponding to the subject’s right side. Retrograde patterns were observed at t = 5 min post erythromycin administration. However at t = 25 min post-administration, the SOBI-MGG propagation pattern returns to normal anterograde propagation.