Effects of altered left atrial pressure on pulmonary vascular pressure-flow relationships

The pulmonary circulation in acute lung injury: a review of some recent advances

1. According to the Starling resistor model of the pulmonary circulation, the pulmonary hypertension of oleic acid lung injury, an experimental model close to the early stage of clinical ARDS, primarily results from an increased vascular closing pressure which exceeds Pla and becomes the effective outflow pressure of the pulmonary circulation. Therefore, calculated pulmonary vascular resistance should be interpreted cautiously during haemodynamic investigations in patients with ARDS. 2. Part of this increased vascular closing pressure is functional. During acute lung injury pulmonary vasomotor tone can be reduced by vasodilators, or increased by cyclooxygenase inhibitors and almitrine. 3. Pulmonary vasodilation due to infused vasodilators usually impairs gas exchange in ARDS. 4. There is evidence that HPV is altered during ARDS. Drugs capable of enhancing the efficacy of HPV could improve gas exchange. If proven safe in the future, cyclooxygenase inhibitors and almitrine are interesting compounds to be tested in ARDS.

Recombinant tissue-type plasminogen activator in canine embolic pulmonary hypertension. Effects of bolus versus short-term administration on dynamics of thrombolysis and on pulmonary vascular pressure-flow characteristics

We used a canine model of embolic pulmonary hypertension, induced by injection of autologous radioactive blood clots, to investigate effects of recombinant tissue-type plasminogen activator (rt-PA) on dynamics of thrombolysis and on pulmonary pressure-flow (PQ) characteristics. Over 5 (rt-PA5) or 15 (rt-PA15) minutes, 1 mg/kg rt-PA was infused. Rate and extent of thrombolysis were assessed by counting over both lung fields with a gamma camera. Emboli increased mean pulmonary artery pressure from 14 to 36 mm Hg (p less than 0.005). This change was predominantly due to an increase in the effective outflow pressure (PI) (from 9 to 29 mm Hg, p less than 0.001), obtained by extrapolation from the linear PQ relation. While pulmonary hemodynamics improved with rt-PA5 and rt-PA15, the change was greatest with rt-PA15. For example, the increase in PI that occurred with embolization was abolished with rt-PA15. Also, the decrease in pulmonary artery pressure was greatest with rt-PA15. While not significantly different, extent of total clot lysis tended to be greatest with rt-PA15 (p less than 0.07). Also, while during infusion, the concentration of rt-PA5 was threefold that of rt-PA15, the corresponding rate of thrombolysis was similar with rt-PA5 and rt-PA15. These results indicate that the improvement in pulmonary hemodynamics with rt-PA is primarily explained by a decrease in PI. Furthermore, they suggest an upper limit to the dose-thrombolytic rate relation with rt-PA.