During combined radiographic and manometric studies Keet et al. Two Type II pressure waves of pyloric sphincteric cylinder. Simultaneous radiography showed typical contraction of cylinder during both waves.
Base line indicates intraluminal pressure in absence of radiologically visible motor activity.
Compound waves are usually ascribed to additional increases in tone. Contractions of the cylinder in the full stomach are usually quite regular, tending to occur at a rate of 3 per minute. The fact that pressure waves occurred irregularly in this investigation, might have been due to the fact that a small volume of liquid barium was used. No attempt was made by Keet et al. McShane et al.