Abstract
We performed multiple-breath N2 washouts (MBNW) with tidal volumes of 1 liter at 8-16 breaths/min and constant flow rates in six normal subjects. For each breath we computed the slope of the alveolar plateau, normalized by the mean expired N2 concentration (Sn), the Bohr dead space (VDB), an index analogous to the Fowler dead space (V50), and the normalized slope of phase II (S2). In four subjects helium (He) and sulfur hexafluoride (SF6) were washed out after equilibration with a 5% gas mixture of each tracer. The Sn for He and SF6 increased in consecutive breaths, but the difference (delta Sn) increased only over the first five breaths, remaining constant thereafter. In all six subjects Sn, VDB, and V50 increased progressively in consecutive breaths of the MBNW, the increase in Sn being the greatest, approximately 290% from the first to the 23-25th breath. In contrast, S2 was unchanged initially and decreased after the sixth breath. The results indicate that after the fifth breath the increase in Sn during a MBNW is diffusion independent and may constitute a sensitive index of convection-dependent inhomogeneity (CDI). Subtraction of this component from the first breath suggests that Sn in a single-breath washout is largely due to a diffusion-dependent mechanism. The latter may reflect an interaction of convection and diffusion within the lung periphery, whereas CDI may comprise ventilation inequality among larger units, subtended by more centrally located branch points.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: Journal of applied physiology (Bethesda, Md. : 1985)
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.