Alveolar pressure-airflow characteristics in humans breathing air, He-O2, and SF6-O2

Abstract

In a system of rigid tubes under steady flow conditions, the coefficient of friction [CF = 2 delta P/(rho V2/A2)] (where delta P is pressure drop, rho is density, V is flow, and A is cross-sectional area) should be a unique function of Reynolds' number (Re). Recently it has been shown that at any given Re, the value of CF using transpulmonary pressure (PL) was lower when breathing He-O2 compared with air (Lisboa et al., J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 48: 878-885, 1980). One explanation for this discontinuity is that PL includes the pressure drop due to tissue viscance, which is independent of V, and thus would lead to an overestimate of CF on air compared with He-O2 at any Re. We tested this hypothesis by measuring V related to alveolar pressure, rather than PL, in normal subjects breathing air, He-O2, and SF6-O2. In each subject, for a given Re, CF was greatest breathing SF6-O2 and lowest breathing He-O2, similar to results using PL. Thus tissue viscance is not the sole cause of the discontinuous plot of CF vs. Re, and this phenomenon must be due to other factors, such as changing geometry or nonsteady behavior.

Use of Heliox in the Management of Neonates with Meconium Aspiration Syndrome

“…This trend for an increase in V T and V E values can be attributed to the fact that heliox ventilation allows to deliver equal volume of gas with lower driving pressures as compared to air-oxygen [20,21] . V T improvement during heliox was also found in an animal model of bronchospasm [22] .…”

Heliox for mechanically ventilated newborns with bronchopulmonary dysplasia

“…The improvement in gas exchange may also be related to the observed increase in V TE and VE while on helium–oxygen 16 25. V TE increased with helium–oxygen ventilation because it is possible to deliver equal gas volumes using a lower driving pressure than with air–oxygen mixtures 26 27. PIP significantly decreased during helium–oxygen MV of very low birthweight (VLBW) infants with fixed tidal volume 16.…”

Laughing out loud

“…Based on the results of [Slutsky et al 1981] we approximate this turbulent flow as where ∆P = P lung − Patm to account for atmospheric pressure and k is set to 8.2 × 10 −4 atm · s 2 /liter 2 to match the pressureflow curve described by Slutsky et al…”