Gravity is a minor determinant of pulmonary blood flow distribution

Glenny, R. W.; Lamm, Wayne J. E.; Albert, Richard K.; Robertson, H. Thomas

doi:10.1152/jappl.1991.71.2.620

Cited by 328 publications

(268 citation statements)

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“…This is not in line with the fact that the pulmonary blood flow continues to prevail in the dorsal regions in the prone position, as observed in many animal studies [8].…”

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confidence: 64%

Assessment of oxygenation response to prone position ventilation in ARDS by lung ultrasonography

Guérin

Gattinoni

2016

Intensive Care Med

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Acute respiratory distress syndrome (ARDS) is of major concern for the intensivist, as ARDS can only be treated in the intensive care unit (ICU). A cornerstone treatment is mechanical ventilation in order to buy time while the disease leading to ARDS can be cured. Therefore, the first aim of mechanical ventilation is to maintain a viable gas exchange. Over the years we realized that the cost of mechanical ventilation, as measured by the occurrence of ventilator-induced lung injury (VILI) [1], was too high if the target of the mechanical ventilation was normal blood gases. From there, permissive hypercapnia and oxygen saturation between 85 and 90 % were accepted to decrease the risk of VILI.To better tailor the ventilator settings, particularly to avoid potentially dangerous intratidal collapse and decollapse, increased attention was devoted to the characterization of the pathology underlying ARDS. To date, lung CT scan is the gold standard to assess the distribution of strain and from there to make inferences to minimize the occurrence of VILI. It should be mentioned, however, that no study demonstrated that patient outcome can be influenced from lung CT scan findings, essentially because no study has been done with this objective. Since ARDS lung characteristics cannot be monitored using CT imaging, methods feasible at the bedside are very attractive and lung ultrasound (US) is one of them [2]. One limitation of lung US is that the measurements do not quantify physical findings. Even though an aeration score has been developed, it is not quantitative as the Hounsfield units are for CT [3]. This US aeration score has been shown to correlate with PEEP-induced recruited lung volume obtained from the pressure-volume curve [4] and with weaning failure during spontaneous breathing trial [5]. Recently, however, it was shown that recruitment measured by CT scan (as re-inflation of previously not inflated regions) is not correlated with recruitment measured by the pressure-volume curve [6]. This last method and, by inference the US method, actually measure together both the aeration of previously non-aerated regions and a better inflation of lung regions already aerated. The regional hyperinflation, however, cannot be measured accurately either with CT (because of the mass increase of the ARDS lung) or lung US.Haddam et al.[7] performed a multicenter study in 51 ARDS patients with the aim to predict the oxygenation response to the prone position session from using lung US aeration score. The patients included suffered equally from either primary or secondary lung injury and received appropriate lung-protective mechanical ventilation. The authors found that changes in PaO 2 /F I O 2 ratio and lung aeration score did not correlate in either early or late stage of prone position regardless of the focal or nonfocal nature of ARDS. The same was true for changes in PaCO 2 . For the oxygenation to increase, and for the PaCO 2 to decrease, from increased regional lung aeration the blood should continue to flow towards those rea...

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“…This is not in line with the fact that the pulmonary blood flow continues to prevail in the dorsal regions in the prone position, as observed in many animal studies [8].…”

mentioning

confidence: 64%

Assessment of oxygenation response to prone position ventilation in ARDS by lung ultrasonography

Guérin

Gattinoni

2016

Intensive Care Med

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“…The classic description of blood flow distribution is therefore gravitationally dependent, with lung tissue in the non-dependent region (apices of the upright lung) receiving proportionately less of the cardiac output than tissue in the dependent region (base of the upright lung). More recent studies have highlighted irreversibility of the flow gradient with reversal of posture [70], and large iso-gravitational heterogeneity of flow [71], both of which somewhat contradict the gravitational theory for flow distribution. Clark et al [15] showed that postural differences in perfusion gradients can be explained by the combined effect of tissue deformation and extra-acinar blood vessel resistance to flow in the dependent tissue.…”

Section: (B) Distribution Of Embolimentioning

confidence: 96%

Pulmonary embolism: predicting disease severity

Burrowes

Clark

Marcinkowski

et al. 2011

Phil. Trans. R. Soc. A.

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Pulmonary embolism (PE) is the most common cause of acute pulmonary hypertension, yet it is commonly undiagnosed, with risk of death if not recognized promptly and managed accordingly. Patients typically present with hypoxemia and hypocapnia, although the presentation varies greatly, being confounded by co-mordidities such as preexisting cardio-respiratory disease. Previous studies have demonstrated variable patient outcomes in spite of similar extent and distribution of pulmonary vascular occlusion, but the pathophysiological determinants of outcome remain unclear. Computational models enable exact control over many of the compounding factors leading to functional outcomes and therefore provide a useful tool to understand and assess these mechanisms. We review the current state of pulmonary blood flow models. We present a pilot study within 10 patients presenting with acute PE, where patient-derived vascular occlusions are imposed onto an existing model of the pulmonary circulation enabling predictions of resultant haemodynamics after embolus occlusion. Results show that mechanical obstruction alone is not sufficient to cause pulmonary arterial hypertension, even when up to 65 per cent of lung tissue is occluded. Blood flow is found to preferentially redistribute to the gravitationally non-dependent regions. The presence of an additional downstream occlusion is found to significantly increase pressures.

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“…Such a system would permit orientationally dependent studies that are impossible by clinical MRI scanners, where subjects can only be imaged in the supine position. This research is driven by current interest in the pulmonary physiology community, where the effect of gravity, posture, and body orientation on pulmonary ventilation and perfusion is a subject under much debate (15,16,17). A major limitation in this area is the lack of a method to obtain quantitative, high-resolution maps of lung ventilation and perfusion with the subject in different orientations.…”

Section: Introductionmentioning

confidence: 99%

A system for open‐access ³He human lung imaging at very low field

Ruset¹,

Tsai²,

Mair³

et al. 2006

Concepts Magn Reson

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We describe a prototype system built to allow open-access very-low-field MRI of human lungs using laser-polarized 3 He gas. The system employs an open four-coil electromagnet with an operational B 0 field of 4 mT, and planar gradient coils that generate gradient fields up to 0.18 G/cm in the x and y direction and 0.41 G/cm in the z direction. This system was used to obtain 1 H and 3 He phantom images and supine and upright 3 He images of human lungs. We include discussion on challenges unique to imaging at 50 -200 kHz, including noise filtering and compensation for narrow-bandwidth coils.

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Gravity is a minor determinant of pulmonary blood flow distribution

Cited by 328 publications

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Assessment of oxygenation response to prone position ventilation in ARDS by lung ultrasonography

Assessment of oxygenation response to prone position ventilation in ARDS by lung ultrasonography

Pulmonary embolism: predicting disease severity

A system for open‐access ³He human lung imaging at very low field

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Gravity is a minor determinant of pulmonary blood flow distribution

Cited by 328 publications

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Assessment of oxygenation response to prone position ventilation in ARDS by lung ultrasonography

Assessment of oxygenation response to prone position ventilation in ARDS by lung ultrasonography

Pulmonary embolism: predicting disease severity

A system for open‐access 3He human lung imaging at very low field

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Product

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A system for open‐access ³He human lung imaging at very low field