Mechanisms of increased maximum expiratory flow during HeO2 breathing in dogs

Abstract

We used the retrograde-catheter technique to investigate the effect of a helium-oxygen gas mixture (HeO2) on resistance to maximum expiratory flow (Vmax) in airways subsegments between alveoli and the equal pressure point (EPP), and between EPP and the flow-limiting segment (FLS). FLS were found at the same site in main-stem bronchi on both air and HeO2 in most dogs studied. Static elastic recoil pressure (Pel = 7 +/- 1 cmH2O) and the lateral pressure at FLS (Ptm' = 11 +/- cmH2O) were not different on the two gases, and delta Vmax averaged 33 +/- 12%. EPP were located on HeO2 in segmental bronchi (7 +/- 2 mm ID), and EPP on air were always located more downstream. There was no density dependence of resistance between alveoli and EPP on HeO2, and delta Vmax was due to the marked density dependence of the pressure losses of convective acceleration in the short airway segment between EPP HeO2 and FLS. Assuming that FLS is the "choke point," these findings are consistent with wave-speed theory of flow limitation modified to account for viscous pressure losses in peripheral airways. These results and conclusions question previous interpretations of delta Vmax as an index of peripheral airways obstruction, and demonstrate the utility of wave-speed theory in explaining complicated mechanisms of expiratory flow limitation.

How does HeO2 increase maximum expiratory flow in human lungs?

“…We will try to integrate our results with the intuitive approaches of Mead et al (4) and Pride et al (5) as well as the mncathemiiatical approaclh described by the wave-speed theorv (6,13). Fturthermore, we will use equations derived from the previouis canine study (3) and apply them to the data found in the excised human lungs. Mllechatnisms of AV,naX.…”

“…This nonuiniform response to HeO2 may indicate that the density dependence of resistance to airflow muist also show wide variability, and the resistance to different flow regimes may contribute to this varied response. To determine the cause of this wide variation, we previously examined and described the mechanisms of lVmax in dogs (3). The latter study was designed within the framework of ouir uniderstanding the mechanism of flow limitation, which included the equal pressture point (EPP) theory of Mead et al (4), and the Starling resistor concept of Pride et al (5).…”

“…The latter study was designed within the framework of ouir uniderstanding the mechanism of flow limitation, which included the equal pressture point (EPP) theory of Mead et al (4), and the Starling resistor concept of Pride et al (5). The pertinent concepts of these approaches have been recently reviewed (3). In the previotus canine experiment, to partition the airway segment relevant to flow limitation, we placed retrograde catheters at the EPP on HeO2 and jtust uipstream from intrathoracic loci where flow became limited (i.e., the flow-limiting segment [FLS] of Pride et al).…”

“…The adcqtiate frequency responise of the apparatus anid the smnall error in lateral pressure measuremeint was described (3).…”

Use of Heliox Delivered via High-Flow Nasal Cannula to Treat an Infant With Coronavirus-Related Respiratory Infection and Severe Acute Air-Flow Obstruction

“…1 The lower density and higher viscosity of heliox relative to nitrogen-oxygen mixtures can significantly reduce airway resistance (R aw ) when an anatomic air-flow obstruction is present and gas flow is turbulent. 2,3 Heliox also reduces R aw in acute asthma in adults and children and in adults with COPD exacerbations. [3][4][5] Heliox may enhance the bronchodilating effects of ␤-agonist administration for acute asthma.…”