Oxygen is used as an acceptable therapeutic option. One way of oxygen-therapy is application of humidifier, but unfortunately contamination of humidifiers may infect patients. Survey of microbial contamination of oxygen humidifier reservoirs in selected hospitals of Tehran was the purpose of this study.One hundred and thirty samples of water in humidifiers from three general hospitals in Tehran were collected. Prevalence of microbial contamination and its severity was assessed by colony count. These samples were from internal medicine, ICU and CCU wards. All samples were inoculated on Brain-Heart Infusion agar and colony counts were performed. The pure colonies were subcultured and isolated strains were determined by microbiological methods.Results showed that the rate of contamination was 90%. Mixed microbial contamination was evident in 56.5% of the samples. The contamination rate was varied from 63.6% to 100% in different wards. Colony counts were changed in the range of 100 to more than 105 CFU/ml. There were more than 105 CFU/ml in 23.2% of samples. The most common isolated strains were Staphylococcus saprophyticus, Proteus spp, Acinetobacter spp, E.coli, S.aureus, Diphteroid spp, Fungi, and Pseudomonas aeruginosa.According to the high incidence of contamination in humidifiers, especial attention is needed to prevent transmission of infection by these instruments.

IntroductionThe weaning procedure of mechanical ventilation in many patients is a difficult and long process and increases the time of mechanical ventilation. There are numerous ways to achieve this goal. One common way is using Continuous positive airway pressure (CPAP) ventilator. Considering the lower price of Blender-Humidifier compared to CPAP of ventilator and the limited number of studies in this field, this study was aimed to compare these two procedures.Materials and Methods102 patients in Pediatric intensive care unit (PICU) were allocated randomly in one group: CPAP-ventilator and Blender-Humidifier. Duration of hospital and PICU stay, the number of days of mechanichal ventilation, the frequency of re-intubation, and the mortality of the patients were recorded.ResultsThe study was conducted on 66 male and 36 female patients (64.7% and 35.3% respectively). The average age was (22.5 ± 4.5) months. The most frequent complaint of the patients at the time of visit was coughing (35%), hyperventilation and respiratory distress (21.6%). Hospital stay was (23±14) and (20±12) days in humidifier and cpap groups respectively (p=0.52). PICU stay was (15±11) and (20±11) days in humidifier and cpap groups respectively (p=0.18). Re- intubation rate was 16.2% and 33.5% in humidifier and cpap groups respectively (p=0.15). Mortality rate 8.4% and 21.5% in humidifier and cpap groups respectively (p=0.06).ConclusionAlthough there was no statistically significant difference between two groups, considering the differences in mortality rate, the need for re-intubation, rate of hospital and PICU stay, and at the same time, with easy availability and low prices, using Blender- Humidifier is recommended.

Dear Editor-in-Chief:South Korea had a rapid industrialization after 1960s.81.5 % of the country’s population lives in urban are-as (1). A study shows 37.2 % of citizen use a humidi-fier and half of them employ humidifier disinfectants (2). It is very popular among urban citizen because of closed dry atmosphere in winter season.

In the membrane humidifier, the characteristics of the membrane as the heart of the humidifier and the selection of Nafion as the most common membrane for use in the process of separating two wet and dry streams have a great impact on its performance. In this study, a numerical and three-dimensional investigation of a flat membrane humidifier including the dry flow channels, membrane, wet flow channels and plates on the two sides of the membrane has been investigated by Ansys Fluent software and the effect of membrane characteristics including: thickness, permeability and porosity coefficient on the mass (water) and heat transfer through the membrane and as a result the performance of the humidifier has been investigated. The results show that the use of Nafion 111 due to its lower thickness compared to Nafion 115, 117 and 211, leads to improved heat and mass transfer and therefore improves the performance of the membrane humidifier. Considering the dew point which shows the simultaneous effect of mass and heat transfer; increasing the permeability coefficient of the membrane from 10-15 to 10-21 square meters, the dew point temperature at the outlet of the dry side increases by about 3.5K. In the common limits of the porosity coefficient of common commercial membranes, the change of the porosity coefficient does not have much effect on the performance of the membrane humidifier.

An optimum humidification of the reactant gases of proton exchange membrane (PEM) fuel cell extremely affects its performance. Here, an analytic model of a membrane humidifier for PEM fuel cell is proposed where the effect of mass flow rates, inlet temperatures and pressures are investigated. The governing equations: water transfer equation and the law of conservation of energy in whole humidifier are written, which form a Non-linear system of equations, solved through FORTRAN software. At each stage, the outlet temperatures, the water transfer rate, relative humidity and the dew point at dry side outlet are calculated and discussed. The closer the dry side outlet dew point to the wet side inlet dew point, leads to the better humidifier performance. The results show that an increase in mass flow rate at dry side inlet leads to the weaker humidifier performance; while, an increase in mass flow rate at wet side inlet leads to the better performance. An increase in the pressure at dry side inlet enhances humidifier performance; while, the pressure at wet side inlet does not affect significantly on humidifier performance. Here, preheating the dry gas is not essential and use the cooler wet gas is recommended.

Fuel cell is a type of electrochemical energy converter that converts chemical energy stored in fuel into electrical energy. Nonlinear structure, time-varying dynamics and uncertain physical parameters are the challenges of working with polymer electrolyte membrane (PEM) fuel cells. In this paper, grey box modeling and system identification of flow-through H2/O2 PEM fuel cell with three cells and integrated humidifier is investigated. First, zero-dimensional nonlinear fluidic, thermodynamic and electrochemical modeling of PEM fuel cell is performed. The fuel cell model presented in this research is Multi-Input-Single-Output type. In the following, constant parameters of the studied fuel cell are determined. The system identification process as a multi-input-single-output system is done based on the Prediction-Error minimization, using the method of Trust-Region Reflective Newton. Finally, validation of the obtained model is done with experimental data that not used in modeling. The considered PEM fuel cell was tested under different conditions of temperature, reactant gas inlet pressure and stack current, and 329,420 experimental data were obtained. According to test conditions, data was classified into 189 different modes. The results show that the average voltage error of the identified model compared to the experimental data is equal to 1.03%. Moreover, the correlation between voltage and identified model parameters has been investigated, and the results showed that correlation between voltage and the contact resistance equivalent is higher than coefficients of orifices.