Esophageal Motility: Manometry Principles

0:00Welcome to Board Pearls. This is episode one of four of the Esophageal Motility chapter, in the Esophageal Disorders module. This episode is manometry from first principles, and the whole thing rests on one simple idea: on every swallow the esophagus has two jobs, and the test exists to check whether each one happened. The sphincter at the bottom has to open so the food can pass, and the muscle of the body has to squeeze in a top-to-bottom wave that carries the food down. Every number manometry reports is measuring one of those two jobs, and every diagnosis is just a statement about which job failed and how. Hold that, and everything else is detail.

0:38There's also an order to it, and the order matters as much as the numbers. You always ask about the sphincter first, before you look at the body at all, because whether the sphincter relaxed is the highest-stakes question and it decides which half of the differential you're even in. So that's how we'll go: what the sphincter is doing, then what the body is doing, and only in that order.

1:00The measurement itself is a catheter sitting from the throat down into the stomach, reading pressure at points all along the esophagus, and the software paints those pressures as a color picture of where and when the squeeze happens. The standard study is ten swallows lying down and five sitting up, and the reason you care about the position is that a couple of the diagnoses depend on the sphincter pressure behaving differently supine versus upright, so a study that skipped the upright swallows literally can't finish the job. Two extra maneuvers fill in gaps: a run of quick swallows in a row to test whether the muscle has any reserve, and a fast two-hundred-milliliter drink through a straw to stress the sphincter when you suspect it isn't opening.

1:41Now the first number, and it's the one that runs the whole test, the integrated relaxation pressure, the IRP. It's worth being precise about what it actually measures, because the name hides it. It is not the resting tightness of the sphincter. It's how completely the sphincter lets go in the seconds after you swallow. The software finds the lowest sustained pressure across the junction during the relaxation window and reports that. So a high IRP means one specific thing: the sphincter failed to open when it was told to. And that is exactly why you read it first, because the answer splits every remaining diagnosis in two. If the IRP is high, the sphincter is the problem and you're looking at achalasia or outflow obstruction. If the IRP is normal, the sphincter is fine and whatever is wrong lives in the body of the esophagus. You don't even ask about the body until you've answered this. On the usual system, normal is under fifteen lying down and under twelve sitting up.

2:40The second number describes the body's squeeze, the distal contractile integral, the DCI, and the cleanest way to think about it is as the total force of the contraction, how strong, how long, over how much of the esophagus. What you actually use are the bands it falls into, because each band is a different kind of failure. Under a hundred is a failed swallow, essentially no squeeze at all. A hundred to about four hundred fifty is a weak one. Four hundred fifty to eight thousand is normal. Over eight thousand is a contraction that's too strong. And one particular reading carries more weight than any other: every single swallow failing, no squeeze anywhere across all of them. That finding is load-bearing precisely because of the first number. If the IRP is normal, a totally silent body means absent contractility, a body that has simply died. If the IRP is high, that same silent body means achalasia, because now the sphincter is stuck shut and the muscle has quit. Same body picture, two completely different diseases, and the only thing that tells them apart is the sphincter you already checked.

3:43The third number catches a contraction that fires too early, the distal latency. It's the time from the swallow starting to the contraction arriving near the bottom of the esophagus, and normal is four and a half seconds or more. Shorter than that, and the squeeze reached the end too soon, before the wave had a chance to travel down in order. That premature squeeze is what a spasm is on the tracing. And one more pattern, fragmentation, is a squeeze with a big gap broken into its middle, which along with a lot of weak or failed swallows is how you land on ineffective motility.

4:16So the short version is that manometry only ever tells you two things at once, and it tells them in order. First, does the sphincter relax on a swallow, which is the IRP, and that single number decides whether you're dealing with a sphincter problem or a body problem. Second, if the sphincter is fine, what is the body doing, which the DCI, the distal latency, and the presence or absence of a whole wave describe: a silent body, a body that squeezes too hard, a body that fires too early, or a body that squeezes weakly and in pieces. Every diagnosis in this chapter is just a specific pairing of those two answers, and the recurring trap is reading the body picture without first checking the sphincter, because the same body tracing can belong to two opposite diseases depending on that first number.

5:04With the three numbers in hand, the next episode builds the disease they point to most often, achalasia, entirely from its mechanism: the sphincter that won't open, the body that loses its wave, the three subtypes that name the three ways a body behaves once it can't make a proper wave, the treatments that all do the same one thing, and the two patients who break the whole framework.

5:27For the full chapter, the practice vignettes, and the topic-tagged question bank, head to board pearls dot com. You'll find the rest of the series on Apple Podcasts, Spotify, or wherever you listen to podcasts. That brings us to the end of episode one of four of chapter two, and I'll see you in the next one.