Day-to-day variation of 24-hour intragastric acidity.

Twenty-four-hour intragastric acidity was measured continuously using an intragastric electrode in 13 normal volunteers studied four times. Subjects were studied twice in the hospital and twice as outpatients. The dietary conditions were strictly controlled and the replicate studies were compared to assess the variability of such recordings of acidity. The accuracy of the technique was assessed, and a detection limit for differences was calculated for commonly used time periods. Over 24 h, during the night, during the day, and during the evening the technique is able to detect consistent changes of pH of greater than 0.1 units. During separate 5-min periods the limits of detection were considerably greater. This study demonstrates the variability of 24-h intragastric acidity and confirms that continuous monitoring is able to detect important changes of acidity under both hospitalized and ambulant conditions.