Effects of pulmonary edema on regional pulmonary perfusion in the intact dog lung

Regional pulmonary blood flow was determined in dogs during varying degrees of pulmonary edema induced by infusing 179.2-659.4 ml/kg normal saline over 2-3 h. Pulmonary hemodynamics and regional blood flows were measured during the base-line period and at 30 min postinfusion. The degree of pulmonary edema was determined by the final extravascular lung water-to-bloodless dry lung weight ratio (W/D). In dogs developing gross alveolar edema (W/D of 10.70 +/- 0.88 vs. 3.10 +/- 0.30 in controls), the blood flow was shifted to either upper or dependent lung regions. The shift to the upper regions was associated with an increased (P < 0.05) pulmonary arterial pressure (Ppa), whereas the shift to the dependent lung was not associated with a significant change in Ppa. Breathing 100% O2 did not prevent these shifts, suggesting that they were not due to localized hypoxic pulmonary vasoconstriction. The flow distribution patterns were also not related to regional differences in edema. In contrast to the changes during fulminant edema, blood flow distribution did not change after moderate levels of pulmonary edema (W/D of 6.03 0.69), suggesting that gross alveolar flooding is required for a redistribution of pulmonary blood flow. Flow redistribution to the upper lung during airway flooding may be due to increase in Ppa, whereas the increased flow in the dependent lung during the same degree of edema may be due to "bulging" of alveolar vessels into the air spaces, secondary to a decrease in surface activity.

Effect of defibrinogenation on lung water accumulation after pulmonary microembolism in dogs

We determined the effects of chronic fibrinogen depletion on the development of pulmonary edema after pulmonary microembolization. Dogs were defibrinogenated with a purified fraction of Malayan pitviper venom (ancrod). Studies were made in four groups: control untreated (group I); emboli untreated (group II); control defibrinogenated (group III); and emboli defibrinogenated (group IV). Fibrinogen decreased (P < 0.05) from 570.6 +/- 100.9 to 5.3 +/- 3.1 mg/100 ml in the ancrod-treated groups. Pulmonary arterial pressure was increased to similar levels in both embolized groups after infusion of 100-mug-diam nonsiliconized glass beads into the right atrium. Pulmonary vascular resistance and pulmonary perfusion pressure were initially increased to similar levels in both embolized groups, but by 75 min postembolization (PE) both parameters were higher (P < 0.05) in the defibrinogenated group. The extravascular lung water-to-bloodless dry lung ratio at 75 min PE of 4.53 +/- 0.24 in group II was greater than the control value of 2.84 +/- 0.22 in group I (P < 0.05). In contrast, the extravascular lung water-to-bloodless dry lung ratio of 3.64 +/- 0.09 in group IV was not different from the control value of 3.38 +/- 0.04 in group III, but was less than 4.53 +/- 0.24 in group II (P < 0.05). Therefore, chronic defibrinogenation in dogs prevented the development of pulmonary edema after pulmonary microembolization. The protective effect may be due to inhibition of the increase in lung vascular permeability and to a time-dependent reduction in pulmonary microvascular pressure.

Effect of granulocytopenia on extravascular lung water content after microembolization

We studied granulocyte entrapment in the lung after pulmonary microembolization to see if it contributes to the increase in extravascular water content. The lungs were embolized by intravenous injection of nonsiliconized glass beads (100 micrometers in diameter) in normal dogs and dogs made granulocytopenic by daily injections of hydroxyurea. Hydroxyurea did not significantly alter the platelet and fibrinogen concentrations. Control and treated dogs were embolized to the same degree, which resulted in similar increases in pulmonary arterial pressure and pulmonary vascular resistance. The extravascular lung water content/bloodless dry lung weight (W/D) ratios in the control and treated groups after embolization were compared with the W/D ratios in the control and treated nonembolized groups, respectively. The W/D ratio increased from the value of 2.84 +/- 0.22 ml/g in the control group to 4.54 +/- 0.19 ml/g at 75 min after embolization (60% increase) (p < 0.05). However, the W/D ratio in the control-granulocytopenic group of 3.54 +/- 0.19 ml/g was not significantly different from the value of 4.09 +/- 0.27 ml/g in the granulocytopenic group after embolization. Because embolization after granulocytopenia produced only a 16% increase in the extravascular lung water content, compared with a 60% increase in the treated group after the same degree of embolization, the results suggested that granulocyte entrapment in the lung after microembolization contributes to the development of pulmonary edema.

Bronchovascular adjustments after pulmonary embolism

We determined the time course of bronchial blood flow alterations after pulmonary microembolization. Embolization was induced by injecting 100-micrometers-diam glass beads into the right atrium so as to increase pulmonary arterial pressure from 13.8 +/- 1.8 to 35.7 +/- 2.6 Torr in 14 dogs. The increase in pulmonary vascular resistance averaged threefold after embolization (PE). The bronchial blood flow (Qb) was measured using the reference sample method with the 15 +/- 5-micrometers-diam labeled microspheres injected into the left atrium. Simultaneous blood reference samples were collected at constant rates from a femoral artery and the pulmonary artery. The pulmonary arterial reference sample was used to quantify the contribution of peripheral arteriovenous shunts to the total pulmonary activity, and the femoral arterial reference blood was used to quantify Qb. The Qb was decreased to one-third of its base-line value at 60-min PE (P less than 0.05) but not at 5 min PE. Qb was increased 300% at 2 wk PE. The decrease in flow was associated with an increased bronchovascular resistance, whereas the increase in flow was associated with a decreased resistance. The decrease in Qb at 60 min PE may be due to release of peripheral vasoconstrictor substances associated with pulmonary embolism. The finding that bronchial perfusion increased gradually after pulmonary vascular obstruction suggests that increased flow is due to neovascularization.

Regional coronary perfusion and bioenergetics in experimental atherosclerosis

The effects of experimental coronary atherosclerosis on myocardial high energy phosphates and regional coronary perfusion and oxygen delivery were studied. Hypercholesterolemic (HC) New Zealand white rabbits developed mild to moderate coronary vascular disease in 4 months when serum cholesterol levels were maintained at 1500--2000 mg/dl. Resting left ventricular levels of creatine phosphate, adenosine triphosphate (ATP), and the cellular energy charge were unaltered after 2 months of diet but were decreased after 4 and 6 months. Tissue lactate and the lactate/pyruvate ratio were increased after 4 months, suggesting mild tissue ischemia. The regional blood flow rate was measured in rabbits given pentobarbital after 6 months of diet using labeled microspheres, and the response to stress was tested after 5 minutes of hypoxic ventilation (5% O2/N2). The percentage of cardiac output to subendocardium (endo) and subepicardium (epi) in HC rabbits and that in control animals were similar at rest, but unlike that of control animals, the endo perfusion did not increase significantly in HC animals during hypoxic stress. Baseline regional left ventricular oxygen deliveries were similar between groups, but the baseline endo/epi oxygen delivery ratio was reduced in HC rabbits. In control rabbits hypoxia did not alter total O2 delivery, and the endo/epi oxygen delivery ratio was constant, whereas hypoxia in HC animals produced a decrease in total oxygen delivery and a further decrease in the endo/epi oxygen delivery ratio. Thus, moderate long-term coronary occlusive disease produced alterations in the distribution of coronary perfusion that are similar to those after acute partial occlusion, ie, selective reductions in blood flow and oxygen delivery to subendocardium. These results may relate to the pathogenesis of subendocardial infarction in man, which often occurs in the absence of complete coronary occlusion.

Pulmonary transvascular fluid dynamics in sheep during hemorrhage

The effects of hemorrhage on pulmonary hemodynamics and lung transvascular fluid dynamics were studied in sheep. We found that 2 hr of hemorrhage caused a fall in lung lymph flow (p less than 0.05) and no significant change in lymph protein concentration. The fall in lymph flow was not due to decreased vascular surface area since the regional distribution of pulmonary perfusion was not altered during hemorrhage; however, the decrease in lymph flow was associated with decrease (p less than 0.05) in the calculated pulmonary microvascular pressure. The extravascular lung water lung content per g bloodless dry lung was increased (p less than 0.05) in the hemorrhaged sheep from the control values. Pulmonary edema was not due to increased lung vascular endothelial permeability since the net transvascular protein flux was not increased. The finding that pulmonary edema occurred despite the consistent decreases in lymph flow suggests that edema may be due to hemorrhage-induced lymphatic "failure" or that edema fluid is sequestered in spaces (e.g., endothelial cells) where if cannot be drained by the lymphatics.

Site of pulmonary edema after unilateral microembolization

The effect of unilateral pulmonary microembolization on regional lung extravascular fluid accumulation was determined in dogs. Embolization was produced by injecting 100-micrometer-diam glass beads (0.25 g/kg) into the right pulmonary artery. After embolization of one lung, pulmonary arterial pressure (Ppa) and pulmonary vascular resistance increased (P less than 0.05) from base-line values of 11.7 +/- 1.3 to 17.9 +/- 1.3 Torr and of 3.4 +/- 0.5 to 5.5 +/- 0.5 Torr/(1/min). Blood flow to embolized lung measured with labeled microspheres decreased from 104.2 +/- 24.9 to 35.2 +/- 9.2 ml/min.g bloodless lung after embolization, whereas flow to the normal lung increased from 43.1 +/- 5.6 to 71.2 +/- 19.2 ml/min.g bloodless lung. Extravascular lung water-to-bloodless dry lung weight ratio (W/D) of 4.97 +/- 0.32 was greater (P less than 0.001) in the embolized lung than the value of 3.34 +/- 0.15 in nonembolized lung. In six dogs pretreated with 500 U/kg of heparin, a similar degree of duration of embolization and similar hemodynamic changes did not result in significant differences in W/D (3.88 +/- 0.18 in right lung vs. 3.02 +/- 0.53 in the left lung), and the right lung ratio was less (P less than 0.05) than the value in the heparinized dogs, suggesting that humoral mechanisms contribute to the genesis of pulmonary edema after regional embolization. Therefore, unilateral embolization leads to a greater increase in extravascular content in the embolized lung than in the nonembolized lung. Because Ppa was in the normal range after embolization, regional pulmonary edema may be due partly to the local release of factors that increase lung vascular permeability.

Cardiac function, coronary flow and MVO2 in hypertrophy induced by pressure and volume overloading

Myocardial function, flow and O2 consumption were compared in cardiac hypertrophy induced by pressure-loading (P) and by volume overloading (V). Increases in LV-to-body weight ratios in P and V hypertrophied hearts were comparable. Indices of LV function such as cardiac output, stroke volume, stroke work, minute work, peak LV dP/dt, ratio of peak LV dP/dt-to-isovolumic pressure and -to-LVEDP, and Vmax were significantly reduced from normal only in hypertrophy induced by V. Left ventricular coronary flow was reduced from 167.1 +/- 27.2 in normal dogs to 146.2 +/- 17.1 cm3/min-100 g-1 in P hypertrophy, and was reduced further to 82.5 +/- 8.2 cm3/min-100 g-1 in V hypertrophy. Flows decreased similarly in epicardium and endocardium in both hypertrophied hearts. Cardiac O2 extraction in P and V hearts was greater than in control hearts. Myocardial O2 consumption was maintained at control values in P hypertrophy, and decreased by 54 +/- 3% in V hypertrophy. These findings indicate that LV function is impaired at rest in hypertrophy induced by V and is normal in hypertrophy induced by P.

Respiratory influence on the total and regional cerebral blood flow responses to intracranial hypertension

The effect of respiration on the cerebrovascular response to elevated intracranial pressure (ICP) was studied in anesthetized dogs. Total and regional cerebral blood flows were measured using labelled microspheres. In spontaneously breathing dogs total and regional cerebral blood flows increased when cerebral perfusion pressure was reduced to 20 mm Hg. The increase in regional flows was greater in the infratentorial areas than in the supratentorial areas. The increase in cerebral flow in spontaneously breathing dogs was associated with the development of hypoxemia and respiratory acidosis secondary to depression of ventilation. Elevation in ICP while regulating PO2, PCO2, and pH by controlled ventilation resulted in decrease in the total and regional cerebral blood flows. The decrease in regional flows was greater in the supratentorial areas. Induction of respiratory acidosis during elevated ICP in the controlled ventilated dogs with a 5% CO2 in air gas mixture, reversed the decrease in cerebral flows. The results suggest that the increase in cerebral blood flow during elevated ICP in spontaneously breathing dogs is secondary to the development of hypoxemia and respiratory acidosis since cerebral vessels retain responsiveness to increased PaCO2 when the vessels are dilated due to elevated ICP. The results also indicate that the regional cerebrovascular response to elevated ICP is non-uniform.

Pulmonary vascular response to increase in intracranial pressure: role of sympathetic mechanisms

The pulmonary vascular response to intracranial hypertension was studied in anesthetized controlled ventilated dogs in which intracranial pressure (ICP) was elevated to 20 Torr below the mean arterial pressure for a 20-min period, and regulated at this level. Pulmonary vascular resistance (PVR) increased from control value of 2.7 +/- 0.30 to 8.3 +/- 0.51 Torr-l-1-min at the end of 20-min increase in ICP. The increase in PVR was associated with marked increase (P less than 0.001) in pulmonary arterial pressure from 14.4 +/- 1.3 to 35.4 +/- 4.0 Torr, small increase in left atrial pressure from 5.4 +/- 1.2 to 7.9 +/- 1.9 Torr, and no significant change in pulmonary blood flow. The increase in PVR occurred independently of changes in the arterial pressure. The increase in PVR induced by elevated ICP was correlated with increases in lung water, physiological shunt (Qs/Qt), alveolar dead space (VD), and with hypoxemia. Pretreatment with propranolol (1.5 mg-kg-1) attenuated the increase in PVR during elevation in ICP; the smaller increase in PVR was associated with a marked increase in left atrial pressure and a smaller increase in pulmonary perfusion pressure than in the control group. The propranolol-treated dogs also developed increases in lung water, Qs/Qt, VD, and hypoxemia. In contrast, pretreatment with phenoxybenzamine (1.5 mg-kg-1) inhibited the increases in pulmonary perfusion pressure and PVR induced by ICP elevation as well as the associated increases in lung water, Qs/Qt, VD, and hypoxemia. Therefore, a sustained elevation in ICP at a level below the mean arterial pressure in the intact dog evokes pulmonary vasoconstriction which is mediated by alpha-adrenergic mechanisms. The neurogenic pulmonary vasoconstriction results in the increases in lung water, Qs/Qt, VD, and in the hypoxemia.

Retinal blood flow derived from dye dilution curves: Televised fluorescein angiography

A television system was used to record retinal fluorescein dilution curves. In pigs, fluorescein was injected intravenously (IV), into the left ventricle (ILV), and ILV during bilateral carotid occlusion (ILVco). Dye dilution curves from points on a retinal-artery-vein pair, from two points on a single artery, and from two points on a single vein were recorded by a storage oscilloscope, using two photodetectors positioned over the television image of the vessels. Dye curves were less dispersed following ILV than following IV injections, and were irregular following ILVco injection. The dye appearance time was shortest after injection with ILV and progressively longer with ILVco and IV. The artery-vein mean transit time was greatest during carotid occlusion. Retinal blood flow in a venous segment was calculated to be 0.149 +/- 0.037 mi/min. This value was reproducible following both IV and ILV injections but could not be obtained following ILVco due to irregularity of the curves. It was in the same range as that found (0.095 +/- 0.011 ml/min), using the radioactively labeled microsphere technique. The system was subsequently tested in humans and was found to give reproducible dye curves. The usefulness of the system as a clinical tool is presently being explored.

Effects of isoproterenol and norepinephrine on regional ocular blood flows

The effects of norepinephrine and isoproterenol on regional ocular blood flows were studied by the labeled microspheres using the reference sample method in pigs. Total and regional ocular flows increased in response to norepinephrine and isoproterenol infusions. Increase in flows during norepinephrine infusion may be due to increased ocular perfusion pressure induced by the drug, thereby masking its reported direct vasoconstrictor effect in isolated perfused ocular vessels. Increase in flows during isoproterenol infusion occurred despite a decrease in arterial pressure suggesting the existence of vasodilatory beta-adrenergic receptors in the ocular circulation of the pig.