A new technique for measurement of pharyngeal pH: normal values and discriminating pH threshold.

INTRODUCTION: Identifying gastroesophageal reflux disease as the cause of respiratory and laryngeal complaints is difficult and depends largely on the measurements of increased acid exposure in the upper esophagus or ideally the pharynx. The current method of measuring pharyngeal pH environment is inaccurate and problematic due to artifacts. A newly designed pharyngeal pH probe to avoid these artifacts has been introduced. The aim of this study was to use this probe to measure the pharyngeal pH environment in normal subjects and establish pH thresholds to identify abnormality.

METHODS: Asymptomatic volunteers were studied to define the normal pharyngeal pH environment. All subjects underwent esophagram, esophageal manometry, upper and lower esophageal pH monitoring with a dual-channel pH catheter and pharyngeal pH monitoring with the new probe. Analyses were performed at 0.5 pH intervals between pH 4 and 6.5 to identify the best discriminating pH threshold and calculate a composite pH score to identify an abnormal pH environment.

RESULTS: The study population consisted of 55 normal subjects. The pattern of pharyngeal pH environment was significantly different in the upright and supine periods and required different thresholds. The calculated discriminatory pH threshold was 5.5 for upright and 5.0 for supine periods. The 95th percentile values for the composite score were 9.4 for upright and 6.8 for supine.

CONCLUSION: A new pharyngeal pH probe which detects aerosolized and liquid acid overcomes the artifacts that occur in measuring pharyngeal pH with existing catheters. Discriminating pH thresholds were selected and normal values defined to identify patients with an abnormal pharyngeal pH environment.