Study of nitrosating potential at the gastro-oesophageal junction and in Barrett's oesophagus

1. A novel technique utilising the microdialysis technique to measure the concentrations of chemicals of nitrosation, nitrite, thiocyanate, ascorbic acid and total vitamin C in the lumen of the human upper gastrointestinal tract was developed and validated in vitro. 2. The recoveries of the chemicals of interest using the microdialysis probes were inversely proportional to the rate of perfusion of the microdialysis probes except for nitrite which was also dependent on the pH of the solution being sampled. We determined the optimal perfusion rate of the microdialysis probes as 0.15mL hr-1 This perfusion rate enabled adequate volumes of microdialysis product to be obtained for subsequent analysis without reducing the recoveries of the chemicals by the microdialysis probe. 3. The microdialysis probe was accurate in sampling the chemicals of interest under dynamic conditions which mimicked the reaction of intermittent delivery of nitrite in swallowed saliva with gastric juice ascorbic acid under both high and low nitrite load. 4. Salivary nitrite in man is derived from the bacterial reduction of dietary nitrate which has undergone entero-salivary recirculation. In the human subjects without gastro-oesophageal reflux, high concentration of nitrite was detected in the saliva and the distal oesophagus following an oral nitrate load. 5. In subjects without gastro-oesophageal reflux, there was an increasing concentration gradient for ascorbic acid and total vitamin C at increasingly distal sites of the upper gastrointestinal tract whereas there was a decreasing concentration gradient for nitrite with virtually no nitrite detectable in the distal stomach. In the acidic stomach, the cardia was the site of greatest ascorbic acid oxidation and also the site of the lowest ascorbic acid to nitrite ratio both before and after an oral nitrate load indicating that the condition for the formation of carcinogenic N-nitrosamines was maximal at this anatomical site in subjects without gastro-oesophageal reflux. 6. Twenty to thirty percent of the nitrate in the saliva is reduced to nitrite by the bacteria within the oral cavity. The nitrate reduction appears to continue within the oesophagus leading to a greater recovery of nitrite to that in the saliva in some subjects. No nitrate reduction was seen within the nasal cavity of healthy subjects. 7. In subjects with Barrett's oesophagus, concentration gradients for ascorbic acid, total vitamin C and nitrite showed a similar pattern to that of the subjects without gastro-oesophgaeal reflux. However, the ascorbic acid to total vitamin C ratio and ascorbic acid to nitrite ratio in the acidic environment were both lowest within the Barrett's segment suggesting that the oxidative stress and the nitrosation potential were greatest within this anatomical site during periods of acid reflux. 8. Within the Barrett's segment the nitrite concentrations fell greatly compared to that of the squamous oesophagus which was attributed to the conversion of acidified nitrite by the gastric juice ascorbic acid to nitric oxide. Using a miniturised nitric oxide sensor and measuring the nitric oxide generation in real-time we were able to demonstrate nitric oxide generation of up to 50muM when saliva came into contact with acidic gastric juice within the Barrett's segment during periods of gastro-oesophageal reflux

A Novel “Slit Side View” Method to Evaluate Fluid Dynamics during Phacoemulsification

Due to recent technical advances in cataract surgeries, there has been a significant improvement in the safety and surgical outcomes of phacoemulsification. However, the corneal endothelium can be damaged during phacoemulsification by multiple factors. Therefore, we used a slit lamp to analyze the fluid dynamics of ophthalmic viscosurgical devices (OVDs) in the anterior chamber during phacoemulsification. In this experimental study, extracted porcine eyes were injected with OVDs stained with fluorescein through a side port of the eye and then fixed on a slit lamp microscope. After inserting a phaco tip, phacoemulsification simulation was then performed on the iris plane. Subsequent movements of OVDs in the anterior chamber were observed during the procedure by using a slit lamp microscope. Aspiration and removal of cohesive OVDs from the inside of the anterior chamber occurred within a few seconds after the ultrasonic vibration. Aspiration of dispersive OVDs occurred gradually, with some of the OVDs remaining on the side of the anterior chamber side in an irregular shape. This shape enabled the OVD to trap the air, thereby preventing the air from directly touching the corneal endothelium. Viscoadaptive OVDs remained inside the anterior chamber as a lump, with the infusion solution flowing between the corneal endothelium and the OVD, thus leading to the eventual aspiration of the OVD. Viscous dispersive OVDs remained as a lump between the corneal endothelium and the phaco tip. However, once the infusion solution flowed between the cornea and the OVD, the OVD detached from the corneal endothelium, indicating that this type would likely be aspirated and removed. This method, termed the “slit side view,” enables viewing of the movement of OVDs during surgery, as well as observation of the fluid dynamics in the anterior chamber

Evaluation of the Utility of Capsular Stabilization Devices in a Zonular Fiber Defect Model with the Slit Side View System

Capsular stabilization devices were evaluated in a zonular fiber defect model using the slit side view (SSV) system to confirm their utility for capsular stabilization during phacoemulsification. A zonular fiber defect model was made by cutting Zinn’s zonule under observation with a slit lamp microscope in a porcine eye. Phacoemulsification was performed, and the movement of the lens capsule and the depth of the anterior chamber were observed using the SSV in three groups: control group: no surgical instruments used, CE group: a capsule expander was inserted, and CTR group: a capsular tension ring was inserted. In the control group, the equator of the lens was unstable and was easily suctioned to the port of the ultrasound handpiece. The lens capsule was stable in both in the CE and CTR groups. In the CTR group, the equator responsible for the zonular rupture also returned and closed true to its original position. The utility of the capsular stabilization devices in this zonular fiber defect model was confirmed with the SSV system