OSCILLATORY PRESSURE-FLOW RELATIONSHIPS OF CANINE AIRWAYS - A STEADY-STATE MODEL FOR DIFFERENT GASES

We measured the airway pressure drop (Delta Paw) between the trachea a nd the alveolus in three normal anesthetized paralyzed dogs, together with flow (ii) at the trachea. Alveolar pressure was measured using a closed-chest modification of the standard alveolar capsule technique. Measurements were made during a period of sinusoidal ventilation at 0. 83 Hz with a tidal volume of 35 ml/kg, after a 30-s period of apnea. W e found that the amplitude of the swings in Delta Paw decreased transi ently after onset of sinusoidal ventilation. We established that this decrease was due to a reflex bronchodilatation by making additional me asurements on vagotomized dogs. We developed a mathematical model to a ccount for the steady-state data that included both laminar and turbul ent flow, airway wall elastance, airway gas inertance, and the Bernoul li effect at the site of tracheal pressure measurement. The model accu rately described the data obtained from each dog with four different g as mixtures containing air, helium, neon, and sulfur hexafluoride. We also constructed Moody plots from the measured Delta Paw-V relationshi ps, after removing the estimated contributions of gas inertance and th e Bernoulli effect from Delta Paw, and found evidence of the effects o f changing airway dimensions throughout a breath, ii unsteadiness, and differences between inspiratory and expiratory resistances.