Spontaneous breathing reduces pulmonary shunt independent of hypoxic vasoconstriction in the lung collapse model
(English)Manuscript (preprint) (Other academic)
Background: Compared with mechanical ventilation (MV), spontaneous breathing (SB) improves oxygenation even without recruiting atelectatic lung areas, probably by redistributing perfusion to well ventilated areas whose alveolar vessels are not compressed by the higher alveolar pressures of MV. We assumed that regional vasoconstriction, presumably hypoxic vasoconstriction (HPV), causes a redistribution of perfusion, and when the vasoconstriction is blocked by sodium nitroprusside (SNP) infusion, pulmonary shunt in the porcine lung collapse model is similar during SB and MV.
Methods: Lung collapse was induced in 8 piglets by negative pressure application. The animals were allowed both to breathe spontaneously or set to MV at settings matched to SB, in random order. Calculated venous admixture (Qva/Qt), a proxy for pulmonary shunt, was measured, and any vasoconstriction was blocked by SNP infusion. For determining vascular tone, venous return was gradually reduced and cardiac output (CO) over pulmonary perfusion pressure (Pppulm) plots were recorded.
Results: With SNP, Qva/Qt increased both during MV (from 7.7 to 20.2%, P=0.009) and SB (from 3.5 to 9%, P=0.013) with similar slopes of the Pppulm over CO plot (~1.5 mmHg*min/L), indicating a similar hypoxic response during both conditions.
Conclusion: Despite attenuating any vasoconstriction, unexpectedly, pulmonary shunt was lower during spontaneous breathing than during MV. This suggests a mechanism active during SB, favorably redistributing pulmonary blood flow and not silenced by SNP.
pulmonary shunt, pulmonary hypoxic vasoconstriction, sodium nitroprusside, mechanical ventilation, spontaneous breathing
Anesthesiology and Intensive Care
Research subject Physiology
IdentifiersURN: urn:nbn:se:uu:diva-182303OAI: oai:DiVA.org:uu-182303DiVA: diva2:559443