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  • 1
    ISSN: 1432-1238
    Keywords: Key words Haemoconcentration ; Haemodilution ; Pressure-flow relationship ; Pulmonary circulation ; Pulmonary vascular flow resistance ; Pulmonary vascular hypertension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: Pulmonary vascular flow resistance depends on blood viscosity, mainly due to haematocrit, and on vessel dimensions determining blood volume in this highly compliant vascular bed. We, therefore, evaluated the interaction between haematocrit, blood flow, and transpulmonary vascular pressure gradient under conditions of controlled pulmonary blood volume. Design: Experimental study in isolated zone-III rabbit lungs perfused with autologous blood. Setting: Laboratory for experimental studies. Interventions: Stepwise and independent variation of flow (50, 100, and 200 ml/min), pulmonary blood volume (increments of 2.5 ml and 5 ml imposed by changes of left atrial pressure), and haematocrit (0–50 %) varied by haemodilution (Krebs-Henseleit/albumin) or haemoconcentration (centrifugation). Measurements: Pulmonary arterial, left atrial, and airway pressures as well as reservoir volume (reflecting reciprocal changes of lung blood volume) and lung weight. Results: Haemodilution from the normal haematocrit (32 %) to 10 % at constant pulmonary blood volume and flow decreased flow resistance only slightly, whereas haemoconcentration (50 %) increased flow resistance up to 130 %. At the same time increments of in pulmonary blood volume of 2.5 and 5 ml (approx. 15 and 30 % of normal pulmonary blood volume) at constant haematocrit significantly shifted downwards pressure-flow relationships for all investigated haematocrits (0–50 %). Conclusions: Because of the multiple interrelationships between haematocrit, blood flow and pulmonary blood volume, haematocrit effects on pulmonary flow resistance and pressure-flow relationships in the pulmonary vasculature should be studied at controlled blood volume. While haemodilution only has minor effects, haemoconcentration changes pressure-flow relationships markedly. Pulmonary blood volume has a major impact on slope and position of pressure-flow relationships for all haematocrits investigated.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1238
    Keywords: Key words Isolated rabbit lung ; Haematocrit ; Haemoconcentration ; Haemodilution ; Hypoxic pulmonary vasoconstriction ; Pulmonary blood volume ; Pulmonary circulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: Erythrocytes influence the magnitude of hypoxia-induced pulmonary artery pressure increase. It is, however, unknown to what extent haemoconcentration and haemodilution affect this response and whether intrapulmonary blood volume (and thus vessel dimensions) alters the magnitude of pressure increase. Furthermore, it is unclear whether the haemodilution/haemoconcentration-dependent pressure increase is flow-related, via flow-dependent changes in vasomotor tone or rheologic effects, or can also be observed under no-flow conditions. Design: Experimental study in isolated rabbit lungs (n = 12) perfused with autologous blood at constant flow (100 ml/min) and ventilated with 5 % carbon dioxide in air. Setting: Laboratory for experimental studies. Interventions: Haemoconcentration (centrifugation) and haemodilution (Krebs-Henseleit/albumin) were carried out, resulting in haematocrits between 50 % and 0 %. During hypoxic ventilation, inspiratory oxygen fraction was reduced from 0.20 to 0.03. Measurements and results: Under constant flow conditions, haemodilution (from a Hct of 34–36 % to 0–1 %) decreased hypoxic pulmonary artery pressure response to one-third (from 10.8 ± 2.3 cmH2O to 3.1 ± 1.0 cmH2O, P 〈 0.05), while haemoconcentration did not affect the magnitude of hypoxic response (10.5 ± 2.0 cmH2O). For all haematocrit values an increase in pulmonary blood volume (by 5 ml) decreased the magnitude of pressure response. Hypoxia-induced changes in static vascular filling pressure (double occlusion pressure) and vascular compliance were used to assess the strength of hypoxic vasoconstriction under static conditions. Neither haemoconcentration nor haemodilution altered hypoxia-induced changes in either variable. Conclusions: The magnitude of the acute hypoxic pressure response is not altered by haemoconcentration, but significantly reduced by haemodilution. In contrast, neither haemoconcentration nor haemodilution influenced hypoxia-induced changes in static vascular filling pressure and compliance. This suggests that the degree of hypoxic pulmonary vasoconstriction is not affected under static conditions and that the red blood cell-dependence of the magnitude of hypoxic pressure response is based on flow-related mechanisms.
    Type of Medium: Electronic Resource
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