Which of the following statements about esophageal motility is/are true?

B. The primary peristaltic wave normally propels the swallowed bolus through the esophagus in 4 to 8 seconds.

D. Secondary peristalsis is initiated when the entire swallowed bolus of food fails to empty from the esophagus into the stomach.

DISCUSSION: Swallowing initiates UES relaxation, which lasts only 0.5 to 1.0 second, considerably less than the 4 to 8 seconds required for a swallowed bolus to pass through the esophagus and into the stomach. A progressive peristaltic contraction normally follows 97% of all swallows. If the swallowed bolus does not empty completely into the stomach, distention of the esophagus initiates secondary peristalsis, which is progressive and sequential and persists until the retained intraesophageal contents have passed into the stomach. Tertiary contractions are simultaneous, nonprogressive, incoordinated contractions of the esophageal smooth muscle that produce the contraction rings responsible for the corkscrew esophagus of diffuse esophageal spasm on barium esophagography.