DEVELOPMENT AND TESTING OF A FLEXIBLE PLASTIC HYDROGEN ION-SELECTIVE ELECTRODE FOR IN VIVO pH MEASUREMENTS OF AIRWAY SURFACE LIQUID

Cystic fibrosis (CF) is the most common fatal autosomal recessive genetic disorder among people of Caucasian ancestry. It is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a transepithelial transporter responsible for ion transport and maintaining fluid homeostasis. These mutations impair chloride and bicarbonate transport to the airway lumen, leading to mucus thickening and acidification of the airway surface liquid (ASL). These alterations impair host-defence, making CF patients more prone to recurrent microbial infections in the respiratory tract. This project aimed to develop a pH meter capable of measuring ASL pH in vivo through bronchoscopy, which involved optimizing the construction of long plastic H+-selective electrodes using polyethylene (PE) tubing, assessing their usability, and testing their effectiveness in a tracheostomized piglet model. These advancements are critical for future research on pH levels and fluctuations in the lungs of CF pigs and human patients, enhancing our understanding of pH imbalances in CF patients’ ASL. Using PE tubing is effective for the manufacturing of long and flexible ion-selective electrodes (ISEs), with a success rate between 85% and 90%. Their mean Nernstian slope, adjusted R2 and response time were comparable with similar devices previously reported, maintaining their usability stable for up to two days after manufacture. Shielding the electrodes with a custom-built grounded stainless-steel braid reinforced tubing significantly reduced the noise amplitude in the recordings (p<.001), enabling their introduction and use through an endoscope working channel. The plastic ISE were able to record ASL pH fluctuations in the tracheostomized piglet (mean=0.07 pH units), although the ∆pH and ∆[CO2] were smaller than the ones reported in previous works. ∆pH and the electrodes response time were negatively linearly corelated (p=.003), and the adjusted R2 and minimum and maximum pH were positively linearly corelated (p=.01 and .008, respectively). These results suggest that electrodes with low response times and high adjusted R2 should be used in future assays. The novel plastic ISE design demonstrated satisfactory performance and usability during the tests, making it a promising tool for future in vivo bronchoscopy assays in CF pigs and human subjects.

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