Interrupter resistance elucidated by alveolar pressure measurement in open-chest normal dogs

Abstract

The interrupter method for measuring respiratory system resistance involves rapidly interrupting flow at the mouth while measuring the pressure just distal to the point of interruption. The pressure signal observed invariably exhibits two distinct phases. The first phase is a very rapid jump, designated delta Pinit, which occurs immediately on interruption of flow. The second phase is designated delta Pdif and is a further pressure change in the same direction as delta Pinit but evolving over several seconds. The physiological interpretations of delta Pinit and delta Pdif have been somewhat unclear. Delta Pinit has been taken to equal the pressure drop across the pulmonary airways, possibly with a contribution from the tissues of the respiratory system. Delta Pdif can arise, in principle, from two sources: gas redistribution throughout the lung after interruption of flow and stress recovery within the tissues. To resolve these issues we performed interruption experiments on anesthetized paralyzed, tracheotomized, open-chest normal dogs during passive expiration while measuring alveolar pressures at three sites with alveolar capsules. We found that, in the absence of the chest wall, delta Pinit reflects only the resistance of the airways and that delta Pdif can be ascribed almost entirely to the stress recovery properties of lung tissues.

Pulmonary morphofunctional effects of acute myocardial infarction

“…In addition, surfactant action may have been thwarted by intra-alveolar fluid accumulation, resulting in elevated EL,st. The reasons for the increase in DP2L also pertain to DEL, since both reflect pulmonary viscoelastic/inhomogeneous behaviour [19,20]. In group IP EL,st was also increased, although no physiological/ morphological correlation could be found.…”

“…RL,int represents airway resistance [19]. The increase in RL,int was probably influenced by bronchial intraluminal oedema ( fig.…”

“…Pulmonary mechanics were measured using end-inspiratory occlusions after constant flow inflations [16,18,19]. In an open chest preparation, Ptr reflects transpulmonary pressure (PL).…”

“…1). DP1L selectively reflects pressure dissipated against airway resistance in normal animals and humans [18,19], and DP2L reflects the viscoelastic properties (stress relaxation) and/or inhomogeneities of lung tissues [19], together with a tiny contribution of pendelluft in normal situations [18,20]. The total pressure drop (DPL,tot) is equal to the sum of DP1L and DP2L.…”

Respiratory mechanics and morphometric changes during pneumoperitoneum in normal rats

“…Respiratory mechanics were measured from end-inspiratory occlusions after constant flow inflations [14]. Although this method has been used for a long time, the significance of the variables measured has only recently been clarified [13,[15][16][17][18]. After end-inspiratory occlusion, there is an initial fast drop in tracheal pressure (∆P1,rs) from the preocclusion value down to an inflection point (Pi,rs), followed by a slow pressure decay (∆P2,rs), until a plateau is reached.…”