Effect of breathing pattern on gas mixing in a model with asymmetrical alveolar ducts

Abstract

A model of the pulmonary airways was used to study three single-breath indices of gas mixing, dead space (VD), slope of the alveolar plateau, and alveolar mixing inefficiency (AMI). In the model, discrete elements of airway volume were represented by nodes. Using a finite difference technique the differential equation for simultaneous convection and diffusion was solved for the nodal network. Conducting airways and respiratory bronchioles were modeled symmetrically, but alveolar ducts asymmetrically, permitting interaction between convection and diffusion. VD, alveolar slope, and AMI increased with increasing flow. Similar trends were seen with inspired volume, although slope decreased at high inspired volumes with constant flow. VD was affected most by inspiratory flow and AMI and alveolar slope by expiratory time. VD fell approximately exponentially with time of breath holding. Eight different breathing patterns were compared. They had a small effect on alveolar slope and AMI and a greater effect on VD. The model shows how series and parallel inhomogeneity occur together and interact in asymmetrical systems: the old argument as to which is the more important should be abandoned.

Surfactant Improves Gas Mixing and Alveolar Ventilation in Preterm Lambs

“…Also, there is the possibility that, by extending the washout course to very low nitrogen concentration values beyond the end tidal concentration of 2%, we could have detected slowly ventilated compartments of the lung. However, the analysis of the multiple breath nitrogen washout course in terms of separate exponential curves representing separate lung compartments has been questioned (26,34). Model analysis has revealed a complex interaction between convective and diffusive forces in gas mixing during breathing, making predictions about lung compartments due to disease processes difficult (26).…”

A prolonged postinspiratory pause enhances CO2 elimination by reducing airway dead space

“…The effect of a longer T P on V Daw indicates a movement in the proximal direction of the ‘distal boundary of dead space’ (Bowes et al. , 1985).…”

Hypoxic ventilatory response in successful extreme altitude climbers

“…A common underlying factor could be the breathing rate, which was markedly lower in the ''summiters without oxygen'' group during acclimatisation (table 3). Breathing slowly and/or deeply may improve gas exchange at sea level [6,8,[10][11][12][13][14], at altitude [15] and in experimental models [16], and, in addition, slower breathing reduces the HVR [17,18]. The lower respiratory rate in the ''summiters without oxygen'' group was not an artefact caused by the mouthpiece [7].…”