Gas exchange during simulated airway secretion in the anaesthetized rabbit.
We wished to study the effect of airways secretion on gas exchange. Peripheral airway secretion was simulated in 9 rabbits by the continuous inhalation of nebulized isotonic saline, at a droplet size of about 3 microns. Intrapulmonary deposition of saline in the peripheral airways (83% in airways smaller than 0.5 mm) did not alter total inspiratory resistance (mean 5.4 kPa.l-1.s), but led to a decrease in compliance of the total respiratory system from 45.9 to 21.8 ml.kPa-1 after one hour of nebulization. Arterial oxygen tension decreased from 17.8 kPa to 12.1 and 6.9 kPa after 5 and 60 min of nebulization, respectively. PaCO2 was unaffected after 5 min (4.5 kPa) but increased to 7.0 kPa after 60 min of nebulization. Ventilation-perfusion relationships (VA/Q) showed a significant increase in perfusion of areas with low VA/Q ratios (from 0.7 to 6.3% of cardiac output) and in shunt (from 1.4 to 4.3%) after 5 min of nebulization. At the end of the experiment shunt was increased markedly to 29.7% of cardiac output whereas perfusion of low VA/Q regions remained at the same level (7.3%). The results from this animal model indicate that all gas exchange abnormalities known to occur in asthma can be reproduced without measurably increasing the resistance of the respiratory system.
Lagerstrand
L
L
Dept of Clinical Physiology, Huddinge University Hospital, Stockholm, Sweden.
Dahlbäck
M
M
Hedenstierna
G
G
D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D001249:Asthma / Q000503:physiopathology*; D004195:Disease Models, Animal; D007552:Isotonic Solutions; D009330:Nebulizers and Vaporizers; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D011817:Rabbits; D012137:Respiratory System / Q000378:metabolism*; D012965:Sodium Chloride / Q000008:administration & dosage; D014692:Ventilation-Perfusion Ratio / Q000502:physiology
D007552:Isotonic Solutions; D012965:Sodium Chloride