Interrelationships between regional blood flow, blood volume, and ventilation in supine humans

Brudin, Lars; Rhodes, C. G.; Valind, Sven; Jones, T.S.; Hughes, J. M. B.

doi:10.1152/jappl.1994.76.3.1205

Cited by 71 publications

(80 citation statements)

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“…In the current study, the absolute values of pulmonary perfusion recorded in normal subjects are comparable to previous estimates obtained in humans using this [4] and other techniques [16,17], and showed (when using a large ROI) a gravitational gradient to perfusion. This is consistent with traditional concepts, which suggest that the distribution of pulmonary perfusion is explained through the interaction of alveolar, pulmonary arterial and venous and interstitial pressures [1,2].…”

Section: Discussionsupporting

confidence: 89%

“…For the purpose of constructing timedensity curves, a rapid multi-section scan acquisition was performed at a single level, immediately prior to, and following the rapid, automated injection (60 mL at 20 mL?s -1 ; Angiomat 6000, Liebal-Flarsheim Company, Cincinnati, OH, USA) of radio-opaque contrast material (Omnipaque 300 mgI?mL -1 , Nycomed, Amersham, UK). In each study [15][16][17][18][19][20]6-mm sections were obtained. The acquisition time for each section was 100 ms.…”

Section: Computed Tomography Protocolmentioning

confidence: 99%

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Quantifying pulmonary perfusion in primary pulmonary hypertension using electron-beam computed tomography

Jones

Hansell²,

Evans

2004

Eur Respir J

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Traditionally, a gravitational distribution of pulmonary perfusion has been described in normal subjects. How this may vary in patients with primary pulmonary hypertension (PPH), which is characterised by vascular obstruction due to intimal thickening, smooth muscle cell proliferation and episodes of thrombosis in small and medium sized pulmonary arteries, is unclear. In this study the potential of electronbeam computed tomography in quantifying the distribution of pulmonary perfusion in patients with PPH was investigated.Contrast-enhanced sections were obtained during inspiration in the supine position at baseline and during administration of the vasodilator adenosine in five healthy subjects and five patients with PPH. Under each experimental condition, regions of interest were placed along the nondependent-to-dependent axis and values for relative perfusion derived.In healthy individuals, a marked nondependent-to-dependent gradient in perfusion was observed. By contrast, in PPH, perfusion values were significantly lower and were uniform across the lung section, although the administration of adenosine resulted in increased perfusion in all regions of interest.Electron-beam computed tomography provides physiological and structural information about the pulmonary circulation in subjects with pulmonary vascular disease. Traditionally, a gravitational distribution of pulmonary perfusion has been described in normal subjects, determined by the interrelationship between hydrostatic, alveolar and interstitial pressures [1,2]. More recently, animal studies, employing techniques with high spatial resolution, have suggested that the influence of gravity is less important than the structure of the pulmonary vascular tree in determining regional blood flow in the lungs [3]. Similar findings in humans have been confirmed by a study employing electronbeam computed tomography (EBCT) to quantify regional pulmonary perfusion [4]. EBCT allows the fast (millisecond) acquisition of the data necessary for cardiac imaging. Pulmonary regional blood flow can be calculated by applying an appropriate model to changes in lung density detected, following the passage of contrast. EBCT has been used previously in both animal and clinical studies of perfusion [5][6][7], the results obtained showed a good correlation with those found from microsphere-based investigations.Primary pulmonary hypertension (PPH) is characterised by the restriction of the pulmonary vascular bed, secondary to a combination of intimal thickening, vascular smooth muscle cell proliferation and episodes of thrombosis, in small-and medium-sized arteries. Studies of pulmonary perfusion patterns in PPH, excluding those aimed at differentiating between PPH and chronic thromboembolic disease, are scarce. However, investigations using computed tomography (CT) have shown that patients with systemic sclerosis and secondary pulmonary hypertension have a reduced density gradient between the dependent and nondependent parts of the lung, compared with similar patients ...

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Section: Discussionsupporting

confidence: 89%

Section: Computed Tomography Protocolmentioning

confidence: 99%

Quantifying pulmonary perfusion in primary pulmonary hypertension using electron-beam computed tomography

Jones

Hansell²,

Evans

2004

Eur Respir J

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“…Absolute measures of pulmonary perfusion are difficult to obtain using currently available techniques. In experimental animals, such values can be obtained using microspheres, and positron emission tomography has been used in humans, and have shown comparable values to those corrected perfusion data reported here [22,23]. Further, data from the current study are in accordance with estimates of pulmonary perfusion acquired using EBCT in experimental animals [16,24].…”

Section: Discussionsupporting

confidence: 83%

Pulmonary perfusion quantified by electron-beam computed tomography: effects of hypoxia and inhaled NO

Jones¹,

Hansell²,

Evans³

2003

Eur Respir J

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Patients with acute lung injury may benefit from the manipulation of pulmonary blood flow using inhaled nitric oxide (iNO) to optimise ventilation/perfusion matching. Current techniques for studying changes in regional pulmonary perfusion are difficult to apply clinically. This study therefore investigated the potential of electronbeam computed tomography (EBCT) to quantify the effects of hypoxia and iNO on regional pulmonary perfusion in five healthy subjects.Contrast-enhanced sections were obtained sequentially under conditions of normoxia, hypoxia (fractional concentration of oxygen in inspired gas (FI,O 2 ) 0.12) and hypoxia, with iNO (14.8 parts per million (ppm)) administered during inspiration in the supine position. Regions of interest were placed along the nondependent to dependent axis and values for relative perfusion derived.Under normoxic conditions a vertical gradient of perfusion existed, which became less apparent due to increased perfusion in nondependent regions after the induction of hypoxia (FI,O 2 0.12). Under physiological circumstances, the distribution of pulmonary blood flow is regulated by a local action of alveolar oxygen tension on precapillary pulmonary vessels. Thus, the reflex of hypoxic pulmonary vasoconstriction (HPV) ensures that blood flow is diverted away from areas of damaged lung, thereby preserving the matching of ventilation (V9) and perfusion (Q9) [1,2]. In contrast, patients with acute lung injury (ALI) demonstrate diminished HPV leading to adverse changes in V9/Q9 matching, manifesting clinically as refractory hypoxaemia [3]. The favourable manipulation of V9/Q9 therefore assumes considerable therapeutic significance. In this context, nitric oxide (NO), an endothelially derived vasodilator that modulates vascular tone in health and disease [4], has been demonstrated to be a selective pulmonary vasodilator when administered by inhalation both in experimental animals [5,6] and humans [7], improving physiological variables (specifically pulmonary artery pressure (Ppa) and arterial oxygen tension) in patients with ALI [4]. The effects of NO on HPV in terms of the modulation of changes in regional pulmonary blood flow induced by hypoxaemia are, however, unknown.Although techniques for studying regional pulmonary perfusion have been difficult to apply clinically, a gravitational distribution of pulmonary perfusion has been described in normal subjects, determined by the interrelationship between hydrostatic, alveolar and interstitial pressures [8,9]. Moreover, animal studies employing high spatial-resolution techniques suggest that the influence of gravity is less important than the structure of the pulmonary vascular tree in determining regional blood flow in the lung [10,11]. The authors have recently employed electron-beam computed tomography (EBCT) to quantify regional pulmonary perfusion in normal subjects placed in the supine and prone positions, demonstrating that a gravitational gradient of pulmonary perfusion existed in both supine and prone positions [12]....

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“…Functional differences between prone and supine postures need to be considered; for example, blood flow and V A/Q heterogeneity are more uniform in the prone posture (68). Gravity has an influence on the distribution of pulmonary perfusion, lung density, and alveolar size (11,12,29) that is dependent on posture (51), and the prone and supine postures differ both from one another and also from the upright posture (51). The extent of this gravitationally based influence is the subject of considerable debate (31,32,87).…”

Section: Posturementioning

confidence: 99%

Advances in magnetic resonance imaging of lung physiology

Hopkins

Levin

Emami

et al. 2007

Journal of Applied Physiology

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This review presents an overview of some recent magnetic resonance imaging (MRI) techniques for measuring aspects of local physiology in the lung. MRI is noninvasive, relatively high resolution, and does not expose subjects to ionizing radiation. Conventional MRI of the lung suffers from low signal intensity caused by the low proton density and the large degree of microscopic field inhomogeneity that degrades the magnetic resonance signal and interferes with image acquisition. However, in recent years, there have been rapid advances in both hardware and software design, allowing these difficulties to be minimized. This review focuses on some newer techniques that measure regional perfusion, ventilation, gas diffusion, ventilation-to-perfusion ratio, partial pressure of oxygen, and lung water. These techniques include contrastenhanced and arterial spin-labeling techniques for measuring perfusion, hyperpolarized gas techniques for measuring regional ventilation, and apparent diffusion coefficient and multiecho and gradient echo techniques for measuring proton density and lung water. Some of the major advantages and disadvantages of each technique are discussed. In addition, some of the physiological issues associated with making measurements are discussed, along with strategies for understanding large and complex data sets.hyperpolarized helium-3 magnetic resonance imaging; regional ventilation; regional perfusion; apparent diffusion coefficient; ventilation-perfusion ratio; regional lung water MANY PULMONARY DISORDERS ARE characterized by either an inability to supply fresh air to the exchange membrane (ventilation), an inability to supply blood to the membrane (perfusion), or an abnormality of the membrane itself, which hinders efficient gas diffusion. As one of the primary and most accessible activities of the lung, measurement of ventilation and lung volumes has been the focus of most pulmonary function tests, and spirometry is performed regularly to assess pulmonary integrity. Despite their usefulness, however, these global measures do not ultimately allow adequate characterization of disease heterogeneity; thus sensitivity to early and mild disease is lost, and the clinically relevant information for disease diagnosis and classification, as well as surgical planning, is incomplete. Developments in new imaging technologies in the past few decades have opened up new possibilities in acquiring regional information about the lung function and structure, with promise to address many of the intrinsic limitations of global measurements.Shortly after the first axial X-ray computed tomograph became available in 1971, techniques were described that applied magnetic field gradients in three dimensions to create nuclear magnetic resonance (MR) images. The first images of two tubes of water were published in March 1973 (52). Since conventional MR imaging (MRI) exploits properties of protons in magnetic fields to produce images, the lung has historically presented problems, not only because it contains mostly air, and the...

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Interrelationships between regional blood flow, blood volume, and ventilation in supine humans

Cited by 71 publications

References 0 publications

Quantifying pulmonary perfusion in primary pulmonary hypertension using electron-beam computed tomography

Quantifying pulmonary perfusion in primary pulmonary hypertension using electron-beam computed tomography

Pulmonary perfusion quantified by electron-beam computed tomography: effects of hypoxia and inhaled NO

Advances in magnetic resonance imaging of lung physiology

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