The oesophageal acid clearance time was evaluated in 10 healthy volunteers of 'small' boluses of 0·5 and 1 ml and 'minute' boluses of 0·05 and 0·1 ml 0·1 N HCl, as well as 0·1 and 1 ml 0·01 and 0·001 N HCl. Swallow rate was normalised at q 60 seconds. For 0·1 ml 0·1 N HCl, acid clearance time was also measured for swallow intervals of q 30 and 120 seconds. Acid clearance time to restore pH to 4·0 was significantly longer (p<0·01) for the 0·5 and 1 ml 0·1 N HCl (210 and 273 seconds, respectively) than for the 0·05 and 0-01 ml acid boluses (83 and 94 seconds, respectively). The minimum acid clearance time was 18 seconds (0·05 ml 0·1 N HCl). Acid clearance time for 0·1 N HCl was less than one minute on only two occasions. The acid clearance times were comparable when the subjects sat upright. A longer interswallow interval - that is, 120 seconds, resulted in a significantly longer acid clearance time than shorter swallow intervals (p<0·05). Oesophageal acid clearance time for small acid volumes averaged more than three minutes and for minute acid volumes was generally more than one minute; and acid clearance times were comparable for the supine and upright postures, while gastrooesophageal reflux episodes causing pH drops to 3-4 may last for <15 seconds, substantial oesophageal pH drops to ≤ 1·5 that persists <15 seconds are difficult to be attributed to true gastrooesophageal reflux.
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