Biomedical subjects

Donald W McRobbie

Publications and source records attributed to Donald W McRobbie.

4 recordsLinked to original sources

PubMed2005

Studies of the human oropharyngeal airspaces using magnetic resonance imaging. III. The effects of device resistance with forced maneuver and tidal breathing on upper airway geometry.

The anatomical geometry of the upper airways of five healthy volunteers were studied using three-dimensional inhalation-gated magnetic resonance imaging (MRI) for two dummy inhalation devices of varying airflow resistances (0.049(0.5) and 0.004(0.5) kPa(0.5)(L/min)(1)) using a forced maneuver (sharp inhalation) and tidal breathing. The range of maximum inspiratory pressures (MIP) was 0.02-6 kPa. Significant airway expansion occurred for the lower resistance device with forced maneuver compared with tidal breathing. The mean upper airway volume for forced maneuver through a low-resistance device was 60 (SD 15) cm(3) compared with 38 (SD 9) cm(3) for tidal breathing through the same device. Regionally, these increases occurred in the oropharynx (factor of three increase) and the laryngo-pharynx (factor of two increase). Significant changes did not occur for the buccal and laryngeal regions. No significant airway volume change occurred between the two breathing modes using the high-resistance device. In contrast to an earlier study using tidal breathing, device-related volume changes occurred with forced maneuvers in the oropharynx and laryngopharynx. For the low resistance device, significant differences for the minimum airway equivalent radius at the epiglottis occurred between forced maneuver (8.0 mm) and tidal breathing (5.2 mm), and for the maximum airway diameter in the laryngo-pharynx (12.4 mm vs 9.1 mm). For forced maneuvers, significant differences in maximum airway diameter in the oropharynx were also apparent between the devices (12.6 mm low vs. 9.1 mm high) and also in the laryngopharynx (12.4 mm low vs. 9.4 mm high). The minimum radius at the epiglottis varied significantly between devices under forced maneuver breathing (8.0 mm low vs. 8.3 mm high). There was no correlation between airway expansion or contraction and MIP. A linear relationship was found between airway volume changes and maximum calculated volumetric airflow. This work has implication for the modeling of inhaled aerosol dynamics and in vitro particle impaction studies.

Adult↗

PubMed2004

Studies of the human oropharyngeal airspaces using magnetic resonance imaging. II. The use of three-dimensional gated MRI to determine the influence of mouthpiece diameter and resistance of inhalation devices on the oropharyngeal airspace geometry.

The anatomical geometry of the upper airways of 20 volunteers has been studied using three-dimensional (3D)inhalation-gated magnetic resonance imaging (MRI)for four separate dummy inhalation devices of varying diameters and resistances. The only anatomical parameters showing a consistent dependence upon device characteristics were the total airway and buccal volumes between large and small mouthpieces and the distance from the back of the teeth to the first solid obstacle encountered. Individual subjects showed varied device dependent changes: 45% having an increase in regional airway volumes, particularly in the nasopharynx (+46% volume increase)and laryngo-pharynx (+36% volume increase)for the high-resistance devices compared with the low-resistance ones. However, 30% of subjects showed the opposite behavior, a reduction in naso-pharynx volume (-17%), laryngo-pharynx volume (-17%), and laryngeal cavity (-11%). 25% showed no significant difference in airway volume between high- and low-resistance devices. There was a correlation between maximum inspiratory pressure (MIP)and change in airway volume for high-resistance devices, with those exhibiting expansion having generally lower MIP than the group showing contraction (with the non-responders intermediate). Mean airway minimum and maximum cross-sectional areas and radii were not influenced by device. The geometric mean radius at the epiglottis was 5.1 mm (standard deviation [SD] 1.1) and 5.7 mm (SD 1.1) at the vocal cords. Significant differences observed between males and females included MIP for high-resistance devices, the volume and minimum and maximum radii of the laryngeal and laryngeo-pharynx regions, and total airway volume. A cadaver cast exhibited a number of striking differences in comparison with the in vivo data, most notably a significantly greater total volume.

Administration, Inhalation↗

PubMed2003

Changes in brain morphology associated with obstructive sleep apnea.

OBJECTIVE: Obstructive sleep apnea (OSA) causes hypoxemia and fragmented sleep, which lead to neurocognitive deficits. We hypothesised that focal loss of cortical gray matter generally within areas associated with memory processing and learning and specifically within the hippocampus would occur in OSA. METHODS: Voxel-based morphometry, an automated processing technique for magnetic resonance images, was used to characterise structural changes in gray matter in seven right handed, male patients with newly diagnosed OSA and seven non-apneic, male controls matched for handedness and age. RESULTS: The analysis revealed a significantly lower gray matter concentration within the left hippocampus (p=0.004) in the apneic patients. No further significant focal gray matter differences were seen in the right hippocampus and in other brain regions. There was no difference in total gray matter volume between apneics and controls. CONCLUSION: This preliminary report indicates changes in brain morphology in OSA, in the hippocampus, a key area for cognitive processing.

Brain↗

PubMed2003

Studies of the human oropharyngeal airspaces using magnetic resonance imaging. I. Validation of a three-dimensional MRI method for producing ex vivo virtual and physical casts of the oropharyngeal airways during inspiration.

The oropharyngeal region of the human airways has been scanned using 3D MRI and the data used to produce a model cast. The scanning method used a triggering device, which enabled data collection at the same pressure drop in each breathing cycle to produce clear images free of motion-related artefacts. A comparison between two differing MR acquisition strategies was made in a single subject, multi-session study. 3D FISP MR imaging was found to produce the most reliable data. Excluding the buccal cavity, where tongue position was critical, the reproducibility of measured airway volumes and cross sectional areas between sessions was demonstrated. Inter-session total airway volume (excluding the mouth) reproducibility was of the order of 5% and for minimum cross sectional areas at the epiglottis and vocal cords was 10%. The production of a physical cast from the images led to a 5% increase in airway volume compared with the anatomical images but with some loss of fine detail. The data demonstrated the robustness of an ex-vivo means of studying oropharyngeal dimensions and dynamics which may contribute to advancements in the understanding of aerosol delivery of therapeutic agents.

Aerosols↗