Functional physiology of the human terminal antrum defined by high-resolution electrical mapping and computational modeling

Abstract

High-resolution (HR) mapping has been used to study gastric slow-wave activation; however, the specific characteristics of antral electrophysiology remain poorly defined. This study applied HR mapping and computational modeling to define functional human antral physiology. HR mapping was performed in 10 subjects using flexible electrode arrays (128-192 electrodes; 16-24 cm²) arranged from the pylorus to mid-corpus. Anatomical registration was by photographs and anatomical landmarks. Slow-wave parameters were computed, and resultant data were incorporated into a computational fluid dynamics (CFD) model of gastric flow to calculate impact on gastric mixing. In all subjects, extracellular mapping demonstrated normal aboral slow-wave propagation and a region of increased amplitude and velocity in the prepyloric antrum. On average, the high-velocity region commenced 28 mm proximal to the pylorus, and activation ceased 6 mm from the pylorus. Within this region, velocity increased 0.2 mm/s per mm of tissue, from the mean 3.3 ± 0.1 mm/s to 7.5 ± 0.6 mm/s (P < 0.001), and extracellular amplitude increased from 1.5 ± 0.1 mV to 2.5 ± 0.1 mV (P < 0.001). CFD modeling using representative parameters quantified a marked increase in antral recirculation, resulting in an enhanced gastric mixing, due to the accelerating terminal antral contraction. The extent of gastric mixing increased almost linearly with the maximal velocity of the contraction. In conclusion, the human terminal antral contraction is controlled by a short region of rapid high-amplitude slow-wave activity. Distal antral wave acceleration plays a major role in antral flow and mixing, increasing particle strain and trituration.

Keywords: computational fluid dynamics; electrophysiology; interstitial cell of Cajal; slow wave; stomach.

Fig. 1.

Example of data collection and electrode positioning. A: in vivo placement of four PCB arrays (128 recording channels in total: 16 cm²) on the stomach during data collection. Exact positioning was established using the pyloric ring and angularis incisura as reference points. B: a schematic of the stomach indicating the location of three electrodes in the proximal antrum (A1–A3) and three in the prepyloric antrum (B1–B3) relative to the pyloric ring and angularis incisura.

Fig. 2.

Example of slow-wave signals and their associated electrograms. A: example electrograms of two slow-wave cycles from a single case over a period of 30 s in six electrodes. Channels A1–A3 were located in the proximal antrum where signals display slower propagation and lower amplitude than in the prepyloric antrum (B1–B3) (also refer to Fig.1). Example of three slow-wave cycles from a second (B) and third (C) patient in six electrodes. D–F: activation time (AT), amplitude, and velocity maps with electrode positions marked. The isochronal color bands represent the area of slow-wave propagation per 2-s intervals. Values at recording channels are indicated by arrow plots and show areas of lower velocity (blue) and those of higher velocity (purple), with arrowheads demonstrating propagation direction. Lower-amplitude values are indicated by areas of dark brown, and higher values by regions of light brown. AT maps demonstrate consistent aboral propagation of activity. Areas of high amplitude and high velocity were located in the prepyloric antrum. Differences in the direction of velocity vectors in maps (D–F) can be attributed to slight variation in the positioning of mapping arrays during data collection.

Fig. 3.

Boxplots comparing antral slow-wave amplitudes and velocities. A: comparison of slow-wave amplitude in the prepyloric antrum vs. proximal antrum/distal corpus. B: comparison of slow-wave velocity in the prepyloric antrum vs. proximal antrum/distal corpus.

Fig. 4.

Schematics of the human stomach illustrating the regions of high velocity and amplitude with reference to anatomical landmarks. A: slow-wave velocities in the prepyloric antrum increase significantly 16–40 mm (median 28 mm) from the pyloric sphincter and remain high for a length of 12–32 mm (median 22 mm). The high-velocity region terminates 4–8 mm (median 6 mm) from the pyloric sphincter. B: slow-wave amplitudes in the prepyloric antrum increase significantly 28–44 mm (median 36 mm) from the pyloric sphincter and remain high for a distance of 16–28 mm (median 22 mm). This region of increased amplitude terminates at 12–16 mm (median 14 mm) from the pyloric sphincter.

Fig. 5.

Comparison of instantaneous velocity between reference (A) and acceleration (B) models. While the wave propagation velocity is 2.5 mm/s for the reference model, it increases from 2.5 mm/s to 6.8 mm/s in the acceleration model. Viscosity of the virtual gastric content was 0.1 Pa/s.

Fig. 6.

Mixing efficiency modeled as a function of maximal velocity of peristaltic contraction. Acceleration ranges from 0 to 0.36 mm/s per mm of tissue, corresponding to maximal contractile velocity from 2.5 to 11.1 mm/s.