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 less than 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 less than 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 less than 15 seconds, substantial oesophageal pH drops to less than or equal to 1.5 that persists less than 15 seconds are difficult to be attributed to true gastrooesophageal reflux.
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