Fractal properties of pulmonary blood flow: characterization of spatial heterogeneity

Glenny, Robb W.; Robertson, H. Thomas

doi:10.1152/jappl.1990.69.2.532

Cited by 178 publications

(153 citation statements)

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“…Inspired by a demonstration of scale-dependent heterogeneity of cardiac blood flow (5, 37), a high-resolution study of lung perfusion distribution confirmed that the spatial heterogeneity of regional blood flow increased in a similar predictable fashion as resolution was enhanced (25). This scale dependence of measured regional blood flow heterogeneity can be understood as a consequence of the progressive branching of the pulmonary arterial tree, where flows will be heterogeneous but locally correlated.…”

Section: Scale-dependent Heterogeneity Of Lung Blood Flowmentioning

confidence: 83%

“…Nicolaysen et al (45) used circumferentially cut sections from partially inflated and frozen RMS-labeled lungs to refute the existence of a significant radial gradient of flow in the lung. After intravenous injection of a flow label, Glenny and Robertson (25) employed in situ supine tissue fixation and acquired gamma camera images of transverse slices of the fixed lung. Regardless of the approach to fixation, sectioning, and counting, the regional flow heterogeneity attained by these studies revealed coefficients of variation ranging between 20 and 45%.…”

Section: Methods To Create Microsphere Maps Of Flowmentioning

confidence: 99%

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Microsphere maps of regional blood flow and regional ventilation

Robertson

Hlastala²

2007

Journal of Applied Physiology

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Robertson HT, Hlastala MP. Microsphere maps of regional blood flow and regional ventilation. J Appl Physiol 102: [1265][1266][1267][1268][1269][1270][1271][1272] 2007. First published December 7, 2006; doi:10.1152/japplphysiol.00756.2006.-Systematically mapped samples cut from lungs previously labeled with intravascular and aerosol microspheres can be used to create high-resolution maps of regional perfusion and regional ventilation. With multiple radioactive or fluorescent microsphere labels available, this methodology can compare regional flow responses to different interventions without partial volume effects or registration errors that complicate interpretation of in vivo imaging measurements. Microsphere blood flow maps examined at different levels of spatial resolution have revealed that regional flow heterogeneity increases progressively down to an acinar level of scale. This pattern of scale-dependent heterogeneity is characteristic of a fractal distribution network, and it suggests that the anatomic configuration of the pulmonary vascular tree is the primary determinant of high-resolution regional flow heterogeneity. At ϳ2-cm 3 resolution, the large-scale gravitational gradients of blood flow per unit weight of alveolar tissue account for Ͻ5% of the overall flow heterogeneity. Furthermore, regional blood flow per gram of alveolar tissue remains relatively constant with different body positions, gravitational stresses, and exercise. Regional alveolar ventilation is accurately represented by the deposition of inhaled 1.0-m fluorescent microsphere aerosols, at least down to the ϳ2-cm 3 level of scale. Analysis of these ventilation maps has revealed the same scale-dependent property of regional alveolar ventilation heterogeneity, with a strong correlation between ventilation and blood flow maintained at all levels of scale. The ventilation-perfusion (V A/Q ) distributions obtained from microsphere flow maps of normal animals agree with simultaneously acquired multiple inert-gas elimination technique V A/Q distributions, but they underestimate gas-exchange impairment in diffuse lung injury.ventilation-perfusion ratio; radioactive microspheres; fluorescent microspheres; aerosol IN VIVO PULMONARY IMAGES OF intravenously injected radionuclide-labeled microspheres and radionuclide-labeled aerosol have been part of the clinical diagnostic armamentarium for over 40 years. The resolution of the old in vivo planar gamma camera images was relatively weak, and lung flow mapping techniques using experimental animals were subsequently developed to gain enhanced spatial resolution. The microsphere mapping approach involves in vivo administration of intravascularly injected and/or aerosol labels, followed by fixation of the lung, systematic cutting and mapping of the cut pieces, and measurement of label concentrations in each piece. The spatial perfusion and/or ventilation maps that are reconstructed from these data have been employed in a wide range of experimental studies. This review will address the advantages and lim...

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Section: Scale-dependent Heterogeneity Of Lung Blood Flowmentioning

confidence: 83%

Section: Methods To Create Microsphere Maps Of Flowmentioning

confidence: 99%

Microsphere maps of regional blood flow and regional ventilation

Robertson

Hlastala²

2007

Journal of Applied Physiology

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“…In the pulmonary circulation literature, these slopes are described in terms of fractal dimensions because a fractal system can be described by using multiscale analysis (7). The fractal dimension is equal to one minus the slope of the regression line (5). Thus a slope of Ϫ0.5 has a fractal dimension of 1.5, which corresponds to a condition in spatial statistics known as complete spatial randomness (CSR; Ref.…”

Section: Analysis Of Particle Distributionmentioning

confidence: 99%

“…Glenny and Robertson considered this question and predicted how the CV of blood flow should behave as the tissue subdivision volume approached what they described as "the anatomic limit of the capillary" (5). At such a volume, they predicted that blood flow would become uniform among lung units, producing a fractal plot that was horizontal (fractal dimension 1.0) as it extended leftward through smaller and smaller tissue subdivision volumes.…”

Section: Particle Distribution Analysismentioning

confidence: 99%

“…Glenny and Robertson's requirement for a conspicuous flattening of the fractal plot might be too strong a condition for observance of uniformity of flow (5). By definition, latex particle distribution is more uniform than CSR whenever DI Ͻ 1, which, in terms of a log CV plot (fractal plot), translates into the condition log CV Ͻ Ϫ1/2log v Ϫ 1/2log .…”

Section: Particle Distribution Analysismentioning

confidence: 99%

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Perfusion heterogeneity in rat lungs assessed from the distribution of 4-μm-diameter latex particles

Conhaim

Watson

Heisey

et al. 2003

Journal of Applied Physiology

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sion heterogeneity in rat lungs assessed from the distribution of 4-m-diameter latex particles. J Appl Physiol 94: 420-428, 2003. First published October 11, 2002 10.1152/japplphysiol. 00700.2002.-Pulmonary vascular perfusion has been shown to follow a fractal distribution down to a resolution of 0.5 cm 3 (5E11 m 3 ). We wanted to know whether this distribution continued down to tissue volumes equivalent to that of an alveolus (2E5 m 3 ). To investigate this, we used confocal microscopy to analyze the spatial distribution of 4-m-diameter fluorescent latex particles trapped within rat lung microvessels. Particle distributions were analyzed in tissue volumes that ranged from 1.7E2 to 2.8E8 m 3 . The analysis resulted in fractal plots that consisted of two slopes. The left slope, encompassing tissue volumes less than 7E5 m 3 , had a fractal dimension of 1.50 Ϯ 0.03 (random distribution). The right slope, encompassing tissue volumes greater than 7E5 m 3 , had a fractal dimension of 1.29 Ϯ 0.04 (nonrandom distribution). The break point at 7E5 m 3 corresponds closely to a tissue volume equivalent to that of one alveolus. We conclude that perfusion distribution is random at tissue volumes less than that of an alveolus and nonrandom at tissue volumes greater than that of an alveolus. alveolar perfusion; fluorescent microspheres; fractal analysis; pulmonary blood flow FRACTAL ANALYSIS HAS BEEN used extensively to analyze the distribution of perfusion throughout the lung (3). The method is to infuse 15-m-diameter fluorescent latex particles into the pulmonary circulation and then count the number of trapped particles in blocks of frozen or air-dried lungs (15). The blocks, which range in size from 0.5 mm 3 to 2 cm 3 , are grouped mathematically to allow particle counts to be obtained in successive volumes of tissue that range from single tissue blocks up to groups of blocks on the scale of the whole lung (4). For groups of each volume, the mean and SD of the particle counts are calculated for the blocks that compose the group. A fractal plot is assembled by plotting the log of the coefficient of variation (CV; SD/mean) of the group count against the log of the group tissue volume. When this is done for groups of all volumes, it produces a linear plot that shows that the CV of the particle count increases as the group tissue volume decreases. The linearity of such plots is considered to be evidence of a fractal system, which means that perfusion distribution within the lung follows a fractal pattern. Fractals are complex geometric shapes that exhibit a scale-independent property of self-similarity such that the smallest part, no matter how highly magnified, resembles the whole (11). Using this approach, Glenny and colleagues (4) showed that pulmonary perfusion distribution remained fractal down to a tissue volume of 0.5 cm 3 (5E11 m 3 ).It is interesting to speculate whether or not this pattern continues down to the level of the alveolus. An alveolus with a diameter of 75 m has a volume of 2.2E5 m 3 , but present methods...

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Pulmonary Function in Space

West

Elliott²,

Guy³

et al. 1997

JAMA

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The lung is exquisitely sensitive to gravity, and so it is of interest to know how its function is altered in the weightlessness of space. Studies on National Aeronautics and Space Administration (NASA) Spacelabs during the last 4 years have provided the first comprehensive data on the extensive changes in pulmonary function that occur in sustained microgravity. Measurements of pulmonary function were made on astronauts during space shuttle flights lasting 9 and 14 days and were compared with extensive ground-based measurements before and after the flights. Compared with preflight measurements, cardiac output increased by 18% during space flight, and stroke volume increased by 46%. Paradoxically, the increase in stroke volume occurred in the face of reductions in central venous pressure and circulating blood volume. Diffusing capacity increased by 28%, and the increase in the diffusing capacity of the alveolar membrane was unexpectedly large based on findings in normal gravity. The change in the alveolar membrane may reflect the effects of uniform filling of the pulmonary capillary bed. Distributions of blood flow and ventilation throughout the lung were more uniform in space, but some unevenness remained, indicating the importance of nongravitational factors. A surprising finding was that airway closing volume was approximately the same in microgravity and in normal gravity, emphasizing the importance of mechanical properties of the airways in determining whether they close. Residual volume was unexpectedly reduced by 18% in microgravity, possibly because of uniform alveolar expansion. The findings indicate that pulmonary function is greatly altered in microgravity, but none of the changes observed so far will apparently limit long-term space flight. In addition, the data help to clarify how gravity affects pulmonary function in the normal gravity environment on Earth.

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Fractal properties of pulmonary blood flow: characterization of spatial heterogeneity

Cited by 178 publications

References 0 publications

Microsphere maps of regional blood flow and regional ventilation

Microsphere maps of regional blood flow and regional ventilation

Perfusion heterogeneity in rat lungs assessed from the distribution of 4-μm-diameter latex particles

Pulmonary Function in Space

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