Biomedical subjects

G Scheuch

Publications and source records attributed to G Scheuch.

41 records · Page 3Linked to original sources

PubMedDate not supplied

Deposition and dispersion of aerosols in the airways of the human respiratory tract: the effect of particle size.

Small volumes of aerosols (boluses) were inspired predominantly into the conducting airways of human lungs with a fast operating valve system, injecting preselected aerosol volumes near the end of a clean air inhalation. Particle recovery and bolus dispersion in the exhaled air after various periods of breathholding were investigated by measuring aerosol number concentration directly in front of the mouth with a laser photometer. Inspired and expired flow rates were measured with a pneumotachograph. The effect of particle size on these measurements has been investigated using aerosol particles with aerodynamic diameters (dae) between 0.9 and 5 microns. For aerosol particles smaller than 2 microns, bolus dispersion increases with increasing periods of breathholding (tb). After reaching a maximum, dispersion decreases with even longer tb. An increase in particle size yields a smaller increase in dispersion during the first seconds of breathholding while it is not changed significantly without breathhold. Particle losses during inhalation and exhalation increases with particle size. However, with increasing periods of breathholding, the losses of the smaller particles (less than 1.5 microns) were found to be much higher than expected theoretically, implying particle losses by sedimentation in the same airway structures. The small aerosol particles are deposited in smaller airways than bigger particles. These observations can be explained by cardiogenic mixing during periods of breathholding by pulsatile flow oscillations and confirm measurements with enhanced heart rate as described in an earlier paper. Small particles with restricted settling velocities remained longer in an airborne state in the airways and this leads to a more efficient cardiogenic mixing.

Administration, Inhalation↗

PubMedDate not supplied

Dispersion of aerosol particles in an airway cast of a dog.

Aerosol bolus dispersion was measured in the first branching generations of a replicate hollow cast. The cast was made from a solid cast of a beagle-dog tracheobronchial tree. The dispersion was measured after penetration of boluses into different volumetric depths, with different particle sizes and flow rates into the cast. An enhanced flow rate led to a decreasing dispersion in the cast. Particle size up to about 4 microns has no significant effect on dispersion.

Aerosols↗

PubMedDate not supplied

Effect of flow rate on aerosol bolus penetration in a hollow canine lung airway cast.

A cast of dog tracheobronchial airways, which is complete to airways of 1 mm in diameter, was used for experimental studies of the effect of flow rate on aerosol bolus penetration during a tidal breath. Aerosol boli of 35 cm3 were injected during a 1-L inhalation of air. The recoveries of aerosol particles in expired air were measured after various breathholding times. The results show that the penetration depth of an aerosol bolus increases with decreasing flow rate, especially for flow in transition from a flat profile to a parabolic profile.

Aerosols↗

PubMedDate not supplied

Retention of particles inhaled in boli with and without induced bronchoconstriction.

Large lung retentions (up to 50%) of particles < or = 4 microns inhaled with a bolus technique at a penetration depth less than dead space have been reported to occur after 24 h. This retention may be due to retarded clearance of particles deposited in the airways of the tracheobronchial tract; an alternative explanation could be that particles are deposited in the alveolar region. The purpose of the present study was to confirm the occurrence of retained fractions and to study the influence of a cholinergic drug, which is assumed to give a more central particle deposition, on these retentions in human lungs after shallow aerosol bolus inhalation. Twelve healthy subjects inhaled, with a bolus technique, monodisperse Teflon particles (2.4 microns geometric diameter, 3.5 microns aerodynamic diameter), labeled with 111In. The volumetric lung depth of the inspired bolus was around 60 mL and flow rate was about 300 mL/s. Six subjects inhaled the test particles after a provocation with a cholinergic aerosol, which induced a threefold increase in airway resistance. The other six subjects inhaled a cholinergic aerosol after inhalation of the test particles or inhaled no cholinergic aerosol at all. Radioactivity in the body was measured after 0.5, 24, 48, and 72 h with a whole-body scanner with three 127 x 101-mm Nal detectors. The investigation confirmed results obtained earlier by a group in Frankfurt claiming that great retentions occur after 24 h. The retentions tended to be lower in the group receiving a bronchoconstricting drug before the bolus inhalations. There was a significant lung clearance of particles between 24 and 72 h, in contrast to the findings in earlier studies in healthy subjects and asthmatics who inhaled Teflon particles in large volumes. On the other hand, the clearance agreed well with the clearance in healthy subjects with extensive deposition of Teflon particles in the small ciliated airways, obtained by means of an extremely low inhalation flow rate. The results suggest that a considerable fraction of the particles in the bolus inhalation have been deposited in small ciliated airways in which the mucociliary transport is less efficient or in the alveolar region.

Administration, Inhalation↗

PubMedDate not supplied

Deposition pattern of droplets from medical nebulizers in the human respiratory tract.

Total and regional deposition data for aerosol particles in the human respiratory tract measured in normal mouth-breathing subjects are applied to aerosols from medical nebulizers. From deposition data as a function of particle size and respiratory parameters and from the droplet size distributions of various jet and ultrasonic nebulizers, integral mass depositions as a fraction of the aerosol entering the mouthpiece are determined for the total respiratory tract, the extrathoracic airways, the tracheobronchial tree and the alveolar region. Since the aim of inhalation therapy is the deposition of particles in that part of the respiratory tract which is to be treated, the results of this study may also be useful in finding out optimum conditions in cases of therapeutic applications.

Aerosols↗