Influence of Mixed Venous Oxygen Tension (PVO2) on Blood Flow to Atelectatic Lung

Domino, Karen B.; Wetstein, Lewis; Glasser, Steven A.; Lindgren, L.; Marshall, Carol Lynn; Harken, Alden H.; Marshall, Bryan E.

doi:10.1097/00000542-198311000-00012

Cited by 104 publications

(43 citation statements)

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“…This finding challenges the concept that during unsupported SB the main mechanism of pulmonary blood flow redistribution is HPV; as in that case, the HPV should have been less effective at higher PvO 2 . 6 The PvO 2 -dependent HPV was either less important for the redistribution of pulmonary blood flow during SB (irrespective of the magnitude of the shunt) or a complementary, yet unidentified mechanism redistributing pulmonary blood flow independent of HPV was active during SB. The negative intrapleural pressure generated during SB might have a role in pulmonary blood flow redistribution, as negative-pressure ventilation has been recently shown to increase oxygenation and decrease pulmonary shunt compared with MV in surfactant-depleted rabbits 24 and in humans with acute respiratory distress syndrome.…”

Section: Discussionmentioning

confidence: 96%

“…Raising CO increases mixed-venous oxygen tension (PvO 2 ), and this results in higher oxygen tension at the HPV sensor site, attenuating the hypoxic vasoconstrictor response. [6][7][8] Moreover, a rising CO increases pulmonary artery pressures, which then distend/recruit pulmonary vessels perfusing nonaerated regions. 9 However, the effect of CO on shunt has not been examined during SB.…”

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confidence: 99%

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Pulmonary Shunt Is Independent of Decrease in Cardiac Output during Unsupported Spontaneous Breathing in the Pig

et al. 2013

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Background: During mechanical ventilation (MV), pulmonary shunt is cardiac output (CO) dependent; however, whether this relationship is valid during unsupported spontaneous breathing (SB) is unknown. The CO dependency of the calculated venous admixture was investigated, with both minor and major shunt, during unsupported SB, MV, and SB with continuous positive airway pressure (CPAP). Methods: In seven anesthetized supine piglets breathing 100% oxygen, unsupported SB, MV (with tidal volume and respiratory rate corresponding to SB), and 8 cm H 2 O CPAP (airway pressure corresponding to MV) were applied at random. Venous return and CO were reduced by partial balloon occlusion of the inferior vena cava. Measurements were repeated with the left main bronchus blocked, creating a nonrecruitable pulmonary shunt. Results: CO decreased from 4.2 l/min (95% CI, 3.9-4.5) to 2.5 l/min (95% CI, 2.2-2.7) with partially occluded venous return. Irrespective of whether shunt was minor or major, during unsupported SB, venous admixture was independent of CO (slope: minor shunt, 0.5; major shunt, 1.1%·min −1 ·l −1 ) and mixed venous oxygen tension. During both MV and CPAP, venous admixture was dependent on CO (slope MV: minor shunt, 1.9; major shunt, 3.5; CPAP: minor shunt, 1.3; major shunt, 2.9%·min) and mixedvenous oxygen tension (coefficient of determination 0.61-0.86 for all regressions). Conclusions: In contrast to MV and CPAP, venous admixture was independent of CO during unsupported SB, and was unaffected by mixed-venous oxygen tension, casting doubt on the role of hypoxic pulmonary vasoconstriction in pulmonary blood flow redistribution during unsupported SB.

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Section: Discussionmentioning

confidence: 96%

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confidence: 99%

Pulmonary Shunt Is Independent of Decrease in Cardiac Output during Unsupported Spontaneous Breathing in the Pig

et al. 2013

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“…An increased Q T decreases HPV due to a combination of increases in PvO 2 [29,30], pulmonary artery pressure [31], and pulmonary blood flow [32,33]. All these factors probably contributed to the transient decrease in HPV.…”

Section: Hypercapnic Acidosis and Hpvmentioning

confidence: 99%

Hypercapnic acidosis transiently weakens hypoxic pulmonary vasoconstriction without affecting endogenous pulmonary nitric oxide production

et al. 2012

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“…In the setting of lung injury, however, breathing hypoxic gas does not reduce shunt suggesting either that vasoconstriction in response to alveolar hypoxia is attenuated in injured lung, or that the hypoxic gas may not reach the alveoli (39). In either instance, PvO 2 may become important such that, with decreases in cardiac output and an accompanying increase in oxygen extraction and reduction in PvO 2 , hypoxic vasoconstriction to shunt regions could increase, thereby decreasing perfusion to these unventilated regions (38)(39)(40)(41)(42). Others, however, have found that PEEP decreases shunt even when cardiac output is kept constant, indicating that at least a portion of the shunt reduction occurring with PEEP involves other mechanisms (29,43).…”

Section: Cardiac Output Reductionmentioning

confidence: 99%

Gas Exchange in the Respiratory Distress Syndromes

Albert

Jobe

2012

Comprehensive Physiology

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This article describes the gas exchange abnormalities occurring in the acute respiratory distress syndrome seen in adults and children and in the respiratory distress syndrome that occurs in neonates. Evidence is presented indicating that the major gas exchange abnormality accounting for the hypoxemia in both conditions is shunt, and that approximately 50% of patients also have lungs regions in which low ventilation-to-perfusion ratios contribute to the venous admixture. The various mechanisms by which hypercarbia may develop and by which positive end-expiratory pressure improves gas exchange are reviewed, as are the effects of vascular tone and airway narrowing. The mechanisms by which surfactant abnormalities occur in the two conditions are described, as are the histological findings that have been associated with shunt and low ventilation-to-perfusion.

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Influence of Mixed Venous Oxygen Tension (PVO2) on Blood Flow to Atelectatic Lung

Cited by 104 publications

References 0 publications

Pulmonary Shunt Is Independent of Decrease in Cardiac Output during Unsupported Spontaneous Breathing in the Pig

Pulmonary Shunt Is Independent of Decrease in Cardiac Output during Unsupported Spontaneous Breathing in the Pig

Hypercapnic acidosis transiently weakens hypoxic pulmonary vasoconstriction without affecting endogenous pulmonary nitric oxide production

Gas Exchange in the Respiratory Distress Syndromes

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