A diagram showing the Brodie Bellows Tambour used to measure esophageal pressure. It was connected via a U-tube manometer to a 50 cc balloon that was inserted into a subject’s esophagus.

From Payne WW, Poulton EP.  Experiments on visceral sensation.  Part I.  The relation of pain to activity in the human esophagus.  J. Physiol, 1927, volume 63(3), page 217.