No abstract

Pressurized metered dose inhalers (pMDI) produce large numbers of droplets with smaller sizes than 5 mm to treat asthma and other pulmonary diseases. The mechanism responsible for droplet generation from bulk propellant liquid is poorly understood, mainly because the small length scales and short time scales make it difficult to characterize transient spray formation events. This article describes the development and findings of a numerical atomization model to predict droplet size of pharmaceutical propellants from first principles. In this model, the velocity difference between propellant vapor and liquid phase inside spray orifice leads to formation of wave-like instabilities on the liquid surface. Two variants of the aerodynamic atomization model are presented based on assumed liquid precursor geometry: (1) cylindrical jet-shaped liquid ligaments surrounded by vapor annulus; (2) annular liquid film with vapor flow in the core. The growth of instabilities on the liquid precursor surfaces and the size of the subsequently formed droplets are predicted by numerical solutions of dispersion equations. The droplet size predictions were compared with phase doppler anemometry (PDA) data and the predictions were in good agreement with the number mean diameter D 10 , which is representative of the respirable droplets. The temporal behavior of droplet size production was captured consistently well during the period of the first 95% of the propellant mass emission. The outcome of our modeling activities also suggests that, in addition to saturated vapor pressure of the propellant, its viscosity and surface tension are also key properties that govern pMDI droplet size. EDITORWarren Finlay

This article reports the extension to binary propellant/excipient mixtures of the multiphase model of transient internal flow and atomization in pressurized metered dose inhalers (pMDIs) of Gavtash and colleagues for propellant-only flows. The work considers different accounts of the effect of less volatile ethanol on the saturated vapor pressure (SVP), viscosity and surface tension of HFA-based pMDI formulations. Representation of the SVP of HFA/ethanol mixtures by Raoult's law is compared with the empirical model developed by Gavtash and colleagues as well as different theoretical mixing rules for surface tension and viscosity. For initial ethanol contents ranging from 0 to 20% by mass, the temperature, pressure and spray velocity were predicted to be almost independent of ethanol concentration when using the empirical SVP model of Gavtash and colleagues. The predicted aerosol droplet size increases with increasing concentration of ethanol. These model predictions compare favorably with phase Doppler anemometry (PDA) measurements of pMDI sprays. Exploration of model predictions with different mixing rules suggest that variations of the dynamic viscosity could result in 0.7 mm droplet size change, and different surface tension models yield around 1.5 mm droplet size change. The findings of this work challenge the view that the increase of droplet size is caused by the low volatility of excipients such as ethanol. Instead, attention is focused on composition-dependent viscosity and surface tension as potential controlling parameters with significant effect on the droplet size of HFA/ethanol sprays.

No abstract

Background: Caffeine is a kind of methylxanthine whose consumption can promote the cognitive and executive functions of the human brain. Objectives: In this study, we seek to investigate the effect of drinking coffee on the period of the eye movement fixation component. Materials and Methods:The research was of the quasi-experimental type. 60 subjects were randomly divided into two groups of thirty. The subjects in one group drank coffee before the experiment was conducted. The other group, which is the control group, did not. Both groups would then read a text, and the eye movement tracking device would record the fixation periods of the subjects' eyes while reading. Results:The results of the independent t-test comparing the mean fixation time in the two groups demonstrated that the difference was significant at the 0.001 level, where the group that drank coffee before studying had significantly less fixation time than the control group. Additionally, Cohen's d index of 4.29 determined that the difference lies in the maximum effect size range. Conclusion: It can be concluded that drinking a cup of coffee before studying can lead to decrease in eye movement fixation period and increase in information encoding and processing speed.