Pulmonary arterial pressure-flow plots in dogs: effects of isoflurane and nitroprusside

Abstract

We investigated the effects of nitroprusside and isoflurane on multipoint pulmonary arterial pressure (PAP)/cardiac index (Q) plots in pentobarbital sodium-anesthetized dogs ventilated alternatively in hyperoxia (fraction of inspired O2, FIO2, 0.4) and hypoxia (FIO2 0.1). Over the entire range of Q studied, 2-5 l.min-1.m-2, hypoxia increased PAP in 16 dogs ("responders") and did not affect PAP in 16 other dogs ("nonresponders"). A hypoxic pulmonary vasoconstriction (HPV) was restored in the nonresponders by intravenous administration of 1 g of acetylsalicylic acid (ASA). Nitroprusside (5 micrograms.kg-1.min-1) inhibited HPV in responders (n = 8) and nonresponders treated with ASA (n = 8). End-tidal 1.41% isoflurane (a minimal alveolar concentration equal to one for dogs) did not affect HPV in responders (n = 8) and nonresponders treated with ASA (n = 8). In the latter group isoflurane increased PAP at the highest Q studied (3-5 l.min-1.m-2) in hyperoxia and hypoxia. In a final group of eight dogs with Q kept constant, PAP remained unchanged during two consecutive sequences of alternated 30-min periods (maximum time to generate a PAP/Q plot) successively at FIO2 0.4 and 0.1, and the hypoxia-induced increase in PAP was reproducible. Thus the present experimental model appeared suitable for the study of the effects of hypoxia and drugs on pulmonary vascular tone of intact dogs. At the given doses HPV was inhibited by nitroprusside and not affected by isoflurane. Products of arachidonic acid metabolism possibly could be implicated in the pulmonary vascular effects of isoflurane.

Isoflurane and Desflurane Impair Right Ventricular–Pulmonary Arterial Coupling in Dogs

“…21 In previous studies, isoflurane was found to cause some increase or no change in pulmonary vascular tone. 10,17,20,22 Heerdt et al 11 reported that PA resistance and elastance were increased with isoflurane, in contrast with aortic resistance that decreased and aortic elastance that remained unchanged. In the current study, isoflurane and desflurane reduced PA pressure.…”

Role of NO pathway, calcium and potassium channels in the peripheral pulmonary vascular tone in dogs

“…SNP inhibited the hypoxic pulmonary vasoconstriction in anaesthetized dogs [20]. Moreover, the NO donor was an effective vasodilator of all pulmonary vessels with the exception of the smallest arteries in a model of sheep isolated pulmonary arteries and veins [21].…”

Hypertonic Saline Hydroxyethylstarch Restores Right Ventricular-Arterial Coupling after Normovolemic Hemodilution in Piglets

“…Flow-pressure relations better discriminate between passive (flow-induced) changes and active (tone-induced) changes in PA pressure, and allow detection of more subtle changes in vascular tone. 24 Flow-pressure curves here were generated with transient flow reductions (less than 10 s) to prevent cardiovascular responses because of sympathetic activation. 18 Pulmonary vascular impedance allows for the quantification of the three components that oppose blood ejection from the ventricle into the artery, i.e., resistance because of small distal vessels, elastance because of large proximal vessels, and reflected waves that increase pressure and decrease forward flow.…”