Oxygen permeability of soft contact lenses in different pH, osmolality and buffering solution

AIM: To determine the effect of pH, osmolality, and buffering system on the oxygen permeability (Dk) of soft contact lenses.METHODS: Two hydrogel lenses (nelfilcon A and etafilcon A) and 2 silicone hydrogel lenses (lotrafilcon A and balafilcon A) were used in the study. These lenses were incubated in phosphate-buffered saline (PBS) and borate-buffered saline (BBS) solutions adjusted by 0.8 pH increments to a pH in the range of 5.8-9.0 or in hypotonic (280 mOsmol/kg), isotonic (310 mOsmol/kg) and hypertonic (380 mOsmol/kg) PBS solutions. Polarographic method was used for measuring the Dk and lenses were stacked as 4 layers to correct the boundary effect.RESULTS: Dk values of all contact lenses measured in BBS solutions were more stable than those in PBS solutions. Especially the etafilcon A lens showed a relative big change compared with other types of contact lenses at the same conditions. When the osmolality of PBS solution increased from hypotonic to hypertonic, Dk of all contact lenses decreased. Variations in Dk existed depending on lens materials, etafilcon A lens was the most affected and nelfilcon A was the least affected by osmolality.CONCLUSION:From the result obtained, it is revealed that Dk of contact lenses is changed by the pH, osmolality, and buffering condition of tear. Thus, Dk of contact lens can be varied by the lens wearers' physiological and/or pathological conditions.     

Early compensatory adaptations in maternal undernourished pregnancies in rats: role of the aquaporins

Objective.?To investigate the effect of maternal undernutrition (MUN) during pregnancy on fetal and placental weight, amniotic fluid (AF) volume, AF osmolality and ion concentrations at gestational ages E16 and E20. We also quantified protein expression of water channels (aquaporins; AQPs).

Methods.?Pregnant rat dams were fed an ad libitum diet (AdLib; n?=?6) or were 50% MUN (n?=?6) beginning at E10 of gestation. At E16 and E20, we assessed the effect of MUN on fetal and placental weights, AF volume and osmolality, and placental expression of AQP1, 8 and 9. We focused on two uterine positions (proximal and mid-horns) with the extremes of nutrient/oxygen supply. We also separately studied the basal zone (hormone production) and the labyrinth zone (feto-maternal exchange).

Results.?We showed that at E16, MUN fetal, and placental weights were unchanged and that, similarly, MUN AF volume, osmolality were comparable to AdLib. At E20, however, MUN fetal and placental zonal weights were significantly decreased. Inversely, due to MUN, maternal and fetal plasma osmolality and Na+ concentrations were significantly increased. Further, MUN AF volume was significantly reduced, while AF osmolality and Na+ concentration were increased at E20.

Conclusion.?Placental basal zone showed variable changes in AQP expression unrelated to position in the uterus or the gestational age (and thus severity of the fetal/placental growth restriction). In the labyrinth zone, MUN placental AQP1 was significantly decreased, whereas AQP8 and 9 expressions were significantly increased at E16 and E20. Dysregulation of AQPs' expression prior to the occurrence of oligohydramnios may represent a compensatory mechanism under conditions of early MUN.     

Determination of the renal concentration capacity following intravenous administration of dDAVP in healthy humans

The synthetic AVP analogue 1-desamino-8-d-arginine-vasopressin (dDAVP) is used for treatment of polyuric disorders. Lack of commercially available assays limits the usefulness of dDAVP as a diagnostic tool in the assessment of renal concentrating capacity. We aimed to develop a specific radioimmunoassay (RIA) for determination of plasma dDAVP (pdDAVP) in order to investigate the relationship between pdDAVP levels and urine osmolality (Uosm). Further, we aimed to determine the onset, duration, and maximum concentrating capacity following intravenous (i.v.) bolus dDAVP injection. The dDAVP assay was based on a well-established RIA for measurements of AVP. Fourteen healthy subjects (aged 15–18 years) participated. Blood and urine samples were collected prior to and after i.v. bolus of 0.03?µg/kg dDAVP. Diuresis and Uosm was measured for nine hours following dDAVP administration. PdDAVP and Uosm were analyzed.We established a specific RIA for the measurement of pdDAVP. All subjects reached maximal pdDAVP concentration (C_max) 30 minutes following infusion, and a rise in Uosm after 60 minutes. Maximal Uosm varied between subjects, with no direct correlation to the achieved pdDAVP levels. We found no significant intra-individual variation between two dDAVP infusions and the effect was reproducible in terms of C_max and maximal Uosm. We characterized the relationship between pdDAVP and Uosm after dDAVP bolus injection in healthy adolescents using our dDAVP assay. Maximal Uosm achieved correlated with the baseline Uosm levels and seemed unrelated to achieved pdDAVP levels. The urine concentrating response was maintained at least eight hours.     

Osmolality and tear film dynamics

The tear film is a nourishing, lubricating and protecting layer that bathes the ocular surface. It is continuously replenished through cycles of production and elimination via evaporation, absorption and drainage. These processes are often referred to as tear film dynamics. Osmolality is an objective clinical measurement that provides insight into the balance of these complex tear film dynamics. Balanced tear production and elimination is vital for tear film integrity, stability and normal osmolality. Imbalances cause alterations of the tear film structure and composition, ultimately leading to tear film instability and measurable tear film hyperosmolality. Elevated tear film osmolality is considered a core mechanism in dry eye, forming the basis of dry eye symptoms and leading to ocular surface damage. Despite its immense potential in the diagnosis of dry eye, tear film osmolality is not commonly assessed. This review will focus on the current knowledge of tear film dynamics and tear film osmolality.     

Effect of osmolality on mucociliary transportability and rheology of cystic fibrosis and bronchiectasis sputum

OBJECTIVE: Water is the main constituent of mucus, and its concentration is likely to be important in all aspects of mucus function, including ciliary clearance. The objective of this study was to investigate the effect of water content and osmolality of the mucus on mucociliary transportability. METHODOLOGY: Rheology and ciliary transportability of 10 sputum samples that had been subjected to various manipulations were measured using a mucus-depleted bovine trachea model. RESULTS: It was shown that addition of sodium chloride 0.2 Osmoles/kg (0.585% weight for weight) increased the transportability by 41% (P < 0.01). Evaporation of the sputum to 50% of its original weight caused a 118% increase in transportability (P < 0.0006), but iso-osmolal removal of 50% of the liquid with filter cards led to a non-significant, 25% increase in transportability. Parallel plate viscoelasticity was approximately doubled in both the evaporated and liquid-depleted samples, but was not changed by the addition of 0.2 Osmoles/kg of sodium chloride. The correlation between the osmolality of sputum and ciliary transportability (r = 0.54, P= 0.005) was better than the correlations between the viscosity (r = 0.21, P= 0.27) or elasticity (r = 0.23, P= 0.23) and ciliary transportability. CONCLUSIONS: These results suggest that the osmolality of sputum exerts a greater influence on mucociliary clearance than its viscoelastic properties.     

Influence of a new monomeric nonionic radiographic contrast medium (iobitridol-350 versus NaCl) on cutaneous microcirculation: single-center, prospective, randomized, double-blind phase IV study in parallel group design

This single-center, prospective, randomized, double-blind phase IV study with parallel-group design was performed to test whether injection of a newly designed non-ionic monomeric radiographic contrast medium in the axillary artery influences the ipsilateral cutaneous microcirculation. Twenty patients with coronary heart disease or suspected coronary heart disease were investigated. Ten patients received iobitridol and 10 normal saline solution. The confirmatory target variable was the capillary erythrocyte velocity (v(RBC)). The v(RBC) was continuously recorded before and up to 3 min after the injection of iobitridol or normal saline solution and subsequently evaluated off-line. Thirty seconds after injection of 20 ml iobitridol, v(RBC) was reduced by 32% (P < 0.05). This was the strongest reduction, but v(RBC) was reduced at all time points measured up to 180 s following the injection (P < 0.05 up to 180 s). The overall reduction in v(RBC) was also statistically significant (P 0.0446). In contrast, there was a tendency toward an increase in v(RBC) following injection of 20 ml normal saline (P 0.0512). There was also a tendency toward a difference in the time course of changes in v(RBC) following injection of iobitridol compared to normal saline (P 0.0607). The decrease in v(RBC) following iobitridol injection (standardized difference (SD) according to Cohen, 0.67) can be regarded as biometrically weak, and the increase following normal saline injection (SD, 0.24) as very weak. The microcirculatory disturbance induced by iobitridol injection is less severe than that due to comparable high-viscosity contrast media.