In surgery for airway obstruction, the anesthetist and the ear-nose-throat surgeon share the approach to the airway and jet ventilation (JV) is a mutually convenient ventilation technique for both parties. As a consequence of the open system jet ventilation is applied in, bedside measurements of lung volumes are cumbersome to perform and thus, there is a lack of studies comparing different modes of JV or investigating the influence of ventilator settings on lung volumes and gas exchange. In this thesis, single frequency jet ventilation and superimposed high frequency jet ventilation (SHFJV) at different frequencies are systematically compared with respect to lung volume changes, underlying airway pressure variations and the resulting gas exchange. We compared three single-frequency JV modalities with SHFJV in patients. Moreover, we performed a systematic investigation of single frequency JV and SHFJV in a porcine model. Single frequency JV and SHFJV were compared frequency-wise in intact airways and in a newly developed model of tracheal obstruction. This model was also used to assess the influence of variable airway diameter on ventilation effectiveness during SHFJV. We measured chest wall volume variations with opto-electronic plethysmography and obtained airway pressures as well as gas exchange parameters. In unobstructed airways, both single-frequency JV and SHFJV provided adequate oxygenation, despite differences in lung volumes. Carbon dioxide removal was most effective using single frequency JV at a frequency of 150 min-1. During SHFJV, for both intact and obstructed airways, the choice of frequency for the high frequency component had little influence on lung volumes, airway pressures and gas exchange. With decreasing airway diameter and SHFJV, we observed air trapping and lower tidal volumes and acceptable oxygenation. Carbon dioxide removal, however, was insufficient at the narrowest airway diameter. In single frequency JV, very high frequencies resulted in negligible tidal volume and inacceptable gas exchange. Airway obstruction potentiated this frequency dependence. In conclusion, in intact airways, single frequency JV at sufficiently low frequencies provided adequate oxygenation and better CO2 removal than SHFJV. With decreasing airway diameter, SHFJV provided better oxygenation and CO2 removal and may therefore be the mode of choice in more complicated cases.

A method of providing ventilation using impinging jets (IJV) utilizes stratification while delivering air at a high velocity. As a result of this attribute and the simplicity of its terminal construction, IJV offers an advantage over the well-known Displacement Ventilation (DV) system. The corner IJV system was used during this investigation to construct the Computational Fluid Dynamics (CFD) simulation protocol. To verify the suitability of the turbulence model used in the CFD simulation, numerical values derived from several turbulence models were compared to full-scale experiment data. The results of this study demonstrate that turbulent models are the most important factors when using CFD for the study of the velocity field generated by IJVs terminals. A parametric study was conducted after the models were created and verified using the CFD software COMSOL to determine which is the most suitable arrangement for occupants' ventilation and draught avoidance in a square room. Calculations using computational methods were conducted to characterize the rooms' performance under different operating conditions and cross-sections of the air supply terminals. Among the findings of the research is that increasing the cross-section of the supply terminal reduces the sensation of local discomfort, but decreases air velocity speeds. Furthermore, placing the supply terminal on the same side of a room block improves occupant satisfaction, whereas placing the supply terminal on opposite sides enhances ventilation efficiency.

Laparoscopic liver surgery is complicated due to the structure of this organ with open sinusoids. A serious disadvantage is the risk of gas embolism (GE) due to CO2 pneumoperitoneum. CO2 can enter the vascular system through a wounded vein. A common opinion is that gas fluxes along a pressure gradient, e.g. CVP-intra abdominal pressure (IAP). The occurrence of GE could also be eased by entrainment, a ‘Venturi-like’ effect, due to cyclic differences in thoracic pressure and blood flow caused by mechanical ventilation at normal frequency. The aims of these studies were to survey, in a porcine model, the influence on respiratory and haemodynamic variables by GE, to determine at what frequency, severity and duration GE occurs during laparoscopic liver resection (LLR) and whether there are methods to influence the occurrence or severity of GE. Pulmonary and circulatory variables were monitored and measured as well as continuous blood gas monitoring. Transoesophageal echocardiogram was used to identify GE and, according to the amount of bubbles in the right outflow tract of the heart, GE was graded as 0, 1 and 2. Pneumoperitoneum was created by using CO2and IAP was set to 16 mm Hg. A single bolus dose of CO2 influenced respiratory and haemodynamic variables for at least 4 h. During LLR GE occurred in 65-70% of the animals, of which the more serious caused negative influence on cardiopulmonary variables. Elevated PEEP (15 cm H2O) increased CVP but GE occurred irrespective if CVP was lower than or exceeded IAP. In two last studies, a hepatic vein was cut and left open for 3 m before it was clipped. Interestingly, no signs of GE were seen despite an open vein and IAP > CVP in 8 of 20 animals. In the last study high frequency jet ventilation was used in order to minimise the risk of entrainment. The duration of GE was shortened. The occurrence of GE seemed to be influenced by several different factors. The physiological reaction of a GE is impossible to predict for a specific patient, and depends among other factors on comorbidity, and amount, site and entrance rate of GE.

A well-functioning, energy-efficient ventilation system is of vital importance to offices, not only to provide the kind of comfortable, healthy indoor environment necessary for the well-being and productive work performance of occupants, but also to reduce energy use in buildings and the associated impact of CO2 emissions on the environment. To achieve these goals impinging jet ventilation has been developed as an innovative ventilation concept. In an impinging jet ventilation system, a high momentum of air jet is discharged downwards, strikes the floor and spreads over it, thus distributing the fresh air along the floor in the form of a very thin shear layer. This system retains advantages of mixing and stratification from conventional air distribution methods, while capable of overcoming their shortcomings. The aim of this thesis is to reach a thorough understanding of impinging jet ventilation for providing a good thermal environment for an office, by using Computational Fluid Dynamics (CFD) supported by detailed measurements. The full-field measurements were carried out in two test rooms located in a large enclosure giving relatively stable climate conditions. This study has been divided into three parts where the first focuses on validation of numerical investigations against measurements, the second addresses impacts of a number of design parameters on the impinging jet flow field and thermal comfort level, and the third compares ventilation performance of the impinging jet supply device with other air supply devices intended for mixing, wall confluent jets and displacement ventilation, under specific room conditions. In the first part, velocity and temperature distributions of the impinging jet flow field predicted by different turbulence models are compared with detailed measurements. Results from the non-isothermal validation studies show that the accuracy of the simulation results is to a great extent dependent on the complexity of the turbulence models, due to complicated flow phenomena related to jet impingement, such as recirculation, curvature and instability. The v2-f turbulence model shows the best performance with measurements, which is slightly better than the SST k-ω model but much better than the RNG k-ε model. The difference is assumed to be essentially related to the magnitude of turbulent kinetic energy predicted in the vicinity of the stagnation region. Results from the isothermal study show that both the SST k-ω and RNG k-ε models predict similar wall jet behaviours of the impinging jet flow. In the second part, three sets of parametric studies were carried out by using validated CFD models. The first parametric study shows that the geometry of the air supply system has the most significant impact on the flow field. The rectangular air supply device, especially the one with larger aspect ratio, provides a longer penetration distance to the room, which is suitable for industrial ventilation. The second study reveals that the interaction effect of cooling ceiling, heat sources and impinging jet ventilation results in complex flow phenomena but with a notable feature of air circulation, which consequently decreases thermal stratification in the room and increases draught discomfort at the foot level. The third study demonstrates the advantage of using response surface methodology to study simultaneous effects on changes in four parameters, i.e. shape of air supply device, jet discharge height, supply airflow rate and supply air temperature. Analysis of the flow field reveals that at a low discharge height, the shape of air supply device has a major impact on the flow pattern in the vicinity of the supply device. Correlations between the studied parameters and local thermal discomfort indices were derived. Supply airflow rates and temperatures are shown to be the most important parameter for draught and stratification discomfort, respectively. In the third part, the impinging jet supply device was shown to provide a better overall performance than other air supply devices used for mixing, wall confluent jets and displacement ventilation, with respect to thermal comfort, heat removal effectiveness, air exchange efficiency and energy-saving potential related to fan power.

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A CFD validation study was made using corner supplied impinging jet ventilation operating in cooling mode. The air distribution system has two equilateral triangle shaped inlets placed 80cm above the floor at the two that share a common wall. The supply air was introduced at 2.26m/s. The temperature of the supply air at one of the inlets was slightly higher than the other. The room air velocity and temperature profiles were studied using realizable k-e, RNG k-e, k-e SST and v2-f turbulence models and compared with experimental values. Generally, the agreement between the experimental measurement data of the room air temperatures and velocities and the CFD results was very good in all turbulence models. However, the RNG k-e turbulence model showed better correlation with average errors of 1.9% and 2.8% in predicting temperature and velocity respectively. Possibility of local thermal discomfort with the indoor air were investigated using the Fanger’s thermal comfort indices and draught rate while the air quality was evaluated by the mean age of air and the diffusion coefficient. The thermal comfort indices were computed using a user-defined function and the mean age of air was computed by user- defined scalar that solves a partial differential equation that uses the source diffusivity and calculate the residence time of air in the room. The results show that there is a higher risk of draft at the ankle level (close to 20%) and the room air is freshest near the lower region at the centre of the room. The room air is oldest at the region close to the ceiling in the area between the two mannequins. The study concludes that a satisfactory prediction of thermal stratification and velocity fields can made for evaluating the indoor thermal comfort and air quality using RANS based turbulence models.