The high level of accuracy of EBC pH measurement is in part the result of decades of advances in measurement of this standard chemical property. There are readily available technological capabilities to assess concentrations of hydrogen ions as low as 10 fmol/L (which is equivalent to a very alkaline pH of 14) and as high as 1 mol/L (a very acid pH of 0). Measurement of pH is routinely performed in dilute aqueous fluids such as EBC and even in highly purified water such as used in steam turbines. In EBC, concentrations of hydrogen ions unequivocally are in the useful range of available assays, and the level of assay detection is therefore not a limiting factor. Due to the nature of EBC, the effective pH probe either will be designed specifically for low-ionic-strength fluids, or be proven to work in them by calibrating in low-ionic-strength buffer identically to normal pH buffers, and by stabilizing rapidly in EBC.
It is important to note that these reference data are applicable for the methodology we employed but should be extended to other methodology with some caution. For example, we collected EBC as a liquid, not as an ice. It is possible that collection as an ice may decrease trapping of relevant volatile acids and make the assay less sensitive to airway acidification. We employed a single-use disposable collection system that was never exposed to detergents or other agents that might not be fully removed by rinsing. We make efforts to collect sample only when subjects consumed no food or drink for 1 h prior to collection. These issues should be considered as investigators design studies involving EBC pH. canadian health&care mall
Importantly, consideration should be given to the possibility that a low EBC pH value in a given subject might reflect either laryngopharyngeal acidification or lower airway acidification or both. Longitudinal assessment (multiple samples during a day) will help to distinguish these possibilities.
This work along with previous published data reveal that gas standardized EBC pH is a particularly robust assay that is not systematically affected by patient age or sex, nor by duration or volume of sample collection, nor by presence of methacholine-induced airflow obstruction, nor by extended sample storage. Only alterations in airway pH, at some level, appear to affect the EBC measurement when performed using our methodology.
Given that invasive measures of airway pH are rarely performed and provide only very focal data, EBC pH remains the most readily available method to study the contribution of airway acid stress to respiratory disease. The healthy subject reference data reported in this study should serve as normative data for comparison purposes as others investigate EBC pH, airway acid stress, and laryngopharyngeal acid reflux in patients with diverse respiratory diseases.