Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep.
OBJECTIVE
To examine interactions between positive end-expiratory pressure (PEEP) and posture on regional distribution of ventilation and to compare measurements of regional ventilation with two aerosols: a wet fluorescent microsphere aerosol (FMS, median mass aerodynamic diameter 1.1 microm) and a dry Tc-labeled carbon particle aerosol (Technegas, TG, median mass aerodynamic diameter approximately 0.1 microm).


METHODS
Experimental study.


METHODS
Academic laboratory.


METHODS
: Anesthetized and mechanically ventilated sheep (n = 16).


METHODS
Four conditions were studied: prone or supine posture with or without 10 cm H2O PEEP.


RESULTS
Comparisons of FMS and TG were made in five animals. The median correlation coefficient of the two ventilation tracers was .95 (range, .91-.96). The mean ventilation per unit weight of dry lung for horizontal planes was almost identical whether measured with TG or FMS. The distribution of ventilation was assessed by analyzing deposition of aerosol in about 1,000 lung regions per animal. Distribution of ventilation down the vertical axis was linear in prone (the slope indicated a dorsal-to-ventral three-fold difference in ventilation) but unimodal in supine animals with the mode in the center of the lung. Redistribution of ventilation with 10 PEEP differed between posture, shifting the mode in supine toward dependent lung regions while eliminating the dorsal-to-ventral gradient in prone. The regional heterogeneity in ventilation was greater in supine sheep at both levels of PEEP, and this was due mostly to greater isogravitational heterogeneity in supine than in prone position.


CONCLUSIONS
The wet fluorescent microsphere aerosol was as reliable as Technegas for high-resolution measurements of regional ventilation. The markedly different effects of 10 PEEP in supine and prone sheep may have important implications for gas exchange both in noninjured and injured lungs.
Division of Anesthesiology, Department of Medicine and Care, Faculty of Health Sciences at the University of Linköping, Linköping, Sweden.
Mats J
MJ
Johansson
Andreas
A
Wiklund
Torun
T
Flatebø
Anne
A
Nicolaysen
Gunnar
G
Nicolaysen
Sten M
SM
Walther
D000280:Administration, Inhalation; D000336:Aerosols / Q000008:administration & dosage; D000818:Animals; D005453:Fluorescence; D008863:Microspheres; D023421:Models, Animal; D011175:Positive-Pressure Respiration; D011187:Posture / Q000502:physiology*; D016684:Prone Position / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D012121:Respiration, Artificial; D012756:Sheep; D013670:Sodium Pertechnetate Tc 99m / Q000008:administration & dosage; D016683:Supine Position / Q000502:physiology
D000336:Aerosols; C056708:Technegas; D013670:Sodium Pertechnetate Tc 99m