Airway compliance and flow limitation during forced expiration in dogs

Abstract

Bronchial pressure measured by means of a Pitot static probe, esophageal pressure, and airflow were monitored during forced lung deflations in six anesthetized dogs. Dynamic transmural pressure-cross-sectional area area curves (Ptm-A curves) were constructed for three intrathoracic tracheal positions and one right lower lobal bronchial position. From the Ptm-A curves the maximal possible flow (Vmax) through the airways at each of the four positions was calculated and compared with the overall maximal flow obtained during the same deflation. The peak of the maximal expiratory flow-volume curve (MEFV curve) equaled the calculated Vmax at more than one position in the trachea but did not reach the Vmax calculated for the more peripheral position. During the transition between the peak and the plateau of the MEFV curve, the Ptm-A curve often changed shape, indicating an abrupt change in the "tube law," probably due to changes in axial tension of the airway. During the flow-volume curve plateau, measured flow was near an estimated Vmax at a single point in the trachea. At lower lung volumes where the MEFV curve descends from the plateau, measured flow equaled Vmax calculated for the right lower lobe position. This indicates that after an initial period with no localized choking a "choke point" develops and eventually moves toward the periphery. We conclude that measurement of dynamic Ptm-A curves allows a precise prediction of maximal expiratory flows from the properties of the airways.

Effects of Bronchial Intermittent Constrictions on Explosive Flow during Coughing in the Dogs

“…ratory flow developed. The pattern of explosive flow was consistent with that in a previous report [14]. It consisted of: (1) An ascending part until peak flow was reached, (2) A first descending part, (3) A plateau with a negative slope, (4) A second, steeper descending section, and (5) A final plateau part with small flow.…”

“…Patterns of Paw and V of sham cough were consistent with those reported during human coughing [19][20][21] or simulated coughing [14]. During the stimulation of vagus efferent fibers, the peak explosive flow slightly but significantly decreased and the duration of plateau phase shortened significantly.…”

“…This simulation method has been used by several authors [13,14]. To simulate an inspiratory phase of coughing, positive airway pressure (10 cmH 2 O) was initially applied for 3-5 s, and then the airway pressure was suddenly switched to Ϫ40 cmH 2 O (simulation of explosive phase of coughing).…”

Elastic Properties of the Central Airways in Obstructive Lung Diseases Measured Using Anatomical Optical Coherence Tomography

“…Although the Brackel method (flow across a Pitot-static tube) allows measurements during a dynamic maneuver, the indirect derivation of airway area is prone to inaccuracies (11). HRCT, as used in the Brown and colleagues study, measures airway dimensions directly, but only at fixed volume points, failing to capture the dynamic nature of airway elastic properties (10).…”

“…The light-based imaging technique used in this study confers several advantages in measuring airways over existing direct imaging modalities, such as CT (10,25,26), or indirect techniques, such as measurement of anatomical dead space (2-4) or Pitot tubes (9,11). These include: the ability to perform airway measurements at specific sites within the tracheobronchial tree, allowing localized rather than global mechanical measurements without exposure to ionizing radiation; and the capacity to precisely, directly, and repeatedly measure airway dimensions.…”