In infants, conventional ventilatory assistance often leads to pneumothorax since neonatal lungs are more subject to barotrauma than adult lungs. Because of relatively lower airway pressures in comparison to conventional mechanical ventilation, high frequency jet ventilation (HFJV) has been suggested as one method of assisting this patient population. Unfortunately, HFJV has been reported to lead to new traumatic effects including endothelial erosion due to the high velocity jet impinging on the tracheal endothelial surface, and gradual deterioration in overall gas exchange efficiency. Also, results obtained using HFJV in neonates have been difficult to compare due to the wide range of jet design and operation parameters employed by different clinical groups. Central to all of these problems is a lack of a clear understanding of the physical mechanisms of operation of HFJV in neonates. In order to obtain some of this understanding, research is proposed to investigate the hypothesis that jet nozzle design and location exert a major influence on the overall efficiency of gas exchange and tracheal wall shear rates in high frequency jet ventilation (HFJV) in neonates. We propose to test this hypothesis by using the experimental technique of liquid-bead flow visualization in physical scale models of the neonatal bronchial tree. Flow visualization will be achieved by taking conventional and high speed motion pictures of the oscillating liquid flow produced by the jet operating in the models. The liquid-bead flow in the physical models is made similar to the gas flow occurring during HFJV in neonatal lungs by use of the fluid mechanical principle of dynamic and geometrical similarity. The motion picture frames taken of the flow will be developed and analyzed using an image analyzer. By this analysis we will determine the tidal volume actually injected by the jet; the shearing force exerted by the jet on the tracheal wall; and the overall efficiency of the convective airway gas exchange process for a given set of parameters of jet design, operation and location. Pressures at various locations within the liquid-filled models will also be measured simultaneously and used to predict the corresponding gas pressures in the neonatal airways. The principle investigators have developed the technique of liquid-bead flow visualization in bronchial airway models and have applied it with considerable success to the case of normal respiration and high frequency-piston oscillation ventilation.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL033891-01A1
Application #
3346223
Study Section
Respiratory and Applied Physiology Study Section (RAP)
Project Start
1986-02-01
Project End
1989-01-31
Budget Start
1986-02-01
Budget End
1987-01-31
Support Year
1
Fiscal Year
1986
Total Cost
Indirect Cost
Name
University of Pennsylvania
Department
Type
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Scherer, P W; Neff, J D; Baumgardner, J E et al. (1996) The importance of a source term in modeling multibreath inert gas washout. Respir Physiol 103:99-103
Schwardt, J D; Neufeld, G R; Baumgardner, J E et al. (1994) Noninvasive recovery of acinar anatomic information from CO2 expirograms. Ann Biomed Eng 22:293-306
Schreiner, M S; Leksell, L G; Gobran, S R et al. (1993) Microemboli reduce phase III slopes of CO2 and invert phase III slopes of infused SF6. Respir Physiol 91:137-54
Neufeld, G R; Schwardt, J D; Gobran, S R et al. (1992) Modelling steady state pulmonary elimination of He, SF6 and CO2: effect of morphometry. Respir Physiol 88:257-75
Neufeld, G R; Gobran, S; Baumgardner, J E et al. (1991) Diffusivity, respiratory rate and tidal volume influence inert gas expirograms. Respir Physiol 84:31-47
Schwardt, J D; Gobran, S R; Neufeld, G R et al. (1991) Sensitivity of CO2 washout to changes in acinar structure in a single-path model of lung airways. Ann Biomed Eng 19:679-97
Muller, W J; Hess, G D; Scherer, P W (1990) A model of cigarette smoke particle deposition. Am Ind Hyg Assoc J 51:245-56
Muller, W J; Gerjarusek, S; Scherer, P W (1990) Studies of wall shear and mass transfer in a large scale model of neonatal high-frequency jet ventilation. Ann Biomed Eng 18:69-88
Scherer, P W; Gobran, S; Aukburg, S J et al. (1988) Numerical and experimental study of steady-state CO2 and inert gas washout. J Appl Physiol 64:1022-9