ISSN:
1432-055X
Keywords:
Schlüsselwörter Pulmonale Zirkulation
;
Regionale Durchblutung
;
Radioaktive Microspheres
;
Beatmung
;
Thorakotomie
;
Ein-Lungenventilation
;
Hypoxische pulmonale Vasokonstriktion
;
Key words Pulmonary circulation
;
Regional blood flow
;
Microspheres
;
radioactive
;
Mechanical ventilation
;
Thoracotomy
;
Hypoxia
;
unilateral
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Description / Table of Contents:
Abstract The physiological pattern of regional pulmonary blood flow is mainly determined by the relationship of pulmonary arterial, venous, and alveolar pressures [12, 32]. Changes in alveolar pressure and pulmonary geometry may therefore be expected to influence regional perfusion, which is a key determinant of pulmonary gas exchange. Unilateral thoracotomy is usually performed with the patient in the lateral decubitus position. The present study examined the influence of mechanical factors on regional pulmonary blood flow distribution in rabbits in the lateral decubitus position during normoxia and unilateral hypoxia. Methods. Anaesthetised white New Zealand rabbits (n=8) weighing 2200–3900 g (x¯=2860 g) received central venous injections of radioactive microspheres while in the left lateral decubitus position during spontaneous breathing (SB) and during mechanical ventilation (two-lung ventilation, 2LV), under closed (2LVC) and open chest (2LVT) conditions, as well as during unilateral hypoxia of the nondependent lung induced by nitrogen inflation (1LVN) or atelectasis (1LVA). The method used for one-lung ventilation (1LV) has been previously described in detail [13]. Arterial, central venous, and pulmonary arterial pressures were recorded continuously. Lungs were excised, dried in the inflated state, and cut into 16 sagittal slices, which were further divided into lobar components, the lower lobes into center and periphery. The radioactivity of each specimen was measured in a gamma-counter; perfusion of the individual tissue specimens was quantified using the software program MIC III [14]. The Friedman test followed by paired comparisons according to Conover [33] was used for statistical analysis of differences between the experimental phases. Perfusion of central and peripheral parts of isogravitational slices was compared by use of the Wilcoxon matched pairs test. Values are given as means±SE; the level of significance was P〈0.05 unless otherwise indicated. Results and discussion. Haemodynamic parameters did not differ significantly between the experimental phases (Table 1). Compared to 2LV, a significant increase in venous admixture (P〈0.05) and a corresponding decrease in PaO2 (P〈0.01) were observed during 1LV. This effect was significantly more pronounced during 1LVA as compared to 1LVN (P〈0.01). Since inspiratory pressure was kept constant thoughout the experiments, moderate respiratory acidosis developed during both phases of 1LV. Regional perfusion (Qr) of the nondependent lung was slightly reduced during 2LVC compared to SB and 2LVT. One-lung ventilation induced a significant decrease in perfusion of the hypoxic lung (P〈0.001 1LVN, 1LVA vs. SB,2LVC,2LVT). In accordance with the data obtained from blood gas analysis and oximetry, this effect was more pronounced during N2 insufflation than during atelectasis (P〈0.01 1LVN vs. 1LVA). Among the factors that may account for this effect, PaCO2 did not differ significantly between both phases of 1LV. During N2 insufflation PO2 at the hypoxia-sensitive site is lower than during atelectasis, where it equals mixed-versus PO2 (Pv¯O2). The difference in local PO2 is unlikely, however, to have caused the changes in regional perfusion between 1LVN and 1LVA, since Pv¯O2 was as low as 40 mmHg during 1LVA and the pulmonary vascular response to hypoxia has been found to reach its maximum in this PO2 range [2, 11]. Enhanced redistribution of regional perfusion during 1LVN as compared to 1LVA is therefore most likely attributed to differences in alveolar pressure and pulmonary geometry. Apart from a radial perfusion gradient in the right lower lobe during 2LVC and 2LVT, no isogravitational Qr gradients were observed. Conclusion. We conclude that controlled mechanical ventilation in the lateral decubitus position causes only minor changes in vertical blood flow distribution. During 1LV inflation of the hypoxic lung by positive airway pressure enhances hypoxia-induced blood flow redistribution, thereby improving arterial oxygenation. Differences in alveolar pressure and lung geometry are the most important factors to account for this effect.
Notes:
Zusammenfassung Die intrapulmonale Perfusionsverteilung wird durch mechanische Faktoren wie Atemwegsdruck und Entfaltung der Lunge beeinflußt. Während Ein-Lungenventilation haben Veränderungen dieser Faktoren in der hypoxischen Lunge unmittelbare Auswirkungen auf die arterielle Oxygenierung. Ziel der vorliegenden Studie war es daher, die intrapulmonale Perfusionsverteilung während Normoxie und unilateraler pulmonaler Hypoxie unter verschiedenen Beatmungsbedingungen zu quantifizieren. Bei anästhesierten weißen Neuseeländer Kaninchen (n=8) wurde in Seitenlage die regionale Lungendurchblutung unter 5 Versuchsbedingungen in jeweils 64 definierten Lungenproben mittels radioaktiv markierter Mikrosphären gemessen: Unter Spontanatmung (SB), während maschineller Beatmung bei geschlossenem Thorax (2LV c ) und nach Thorakotomie (2LV T ) sowie während Ein-Lungenventilation bei entfalteter (N 2 -CPAP, 1LV N ) und bei atelektatischer oberer Lunge (1LV A ). Die regionale Perfusion (Q r ) der oberen Lunge war während 2LV c geringer als unter SB und 2LV T . Ein-Lungenventilation (1LV) verminderte die Durchblutung der hypoxischen Lunge signifikant (p〈0,001 1LV N , 1LV A vs. SB,2LV C ,2LV T ), die Abnahme war bei entfalteter Lunge ausgeprägter als bei Atelektase (p〈0,01 1LV N vs. 1LV A ). Innerhalb gleicher Gravitationsebenen fanden sich nur marginale Unterschiede in der relativen Perfusion. Kontrollierte maschinelle Beatmung in Seitenlage verändert die intrapulmonale Durchblutungsverteilung nur unwesentlich. Während 1LV verstärkt die Entfaltung der hypoxischen Lunge durch positiven Atemwegsdruck die Hypoxie-induzierte Perfusionsumverteilung und trägt dadurch zur Verbesserung der arteriellen Oxygenierung bei.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s001010050159
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