Functional diameters of alveolar microvessels  at high lung volume in zone II

Conhaim, Robert L.; Rodenkirch, Lance A.

doi:10.1152/jappl.1998.85.1.47

Cited by 24 publications

(11 citation statements)

References 15 publications

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“…We showed previously that these particles are trapped mainly in interalveolar corner vessels (1). Furthermore, our trapping data suggest that more than 91% of the infused particles were trapped within the pulmonary microcirculation.…”

Section: Effect Of Parenchyma On Particle Distributionsupporting

confidence: 62%

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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Section: Effect Of Parenchyma On Particle Distributionsupporting

confidence: 62%

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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“…Most issues related to the use of microspheres for the measurement of regional blood flow in small animals have been discussed in the literature (9,10,13,14,20). Assessments of regional PBF were achieved by measuring trapped radionuclide-labeled microspheres in the arterial pulmonary circulation with PET (3,32).…”

Section: Methodological Issues and Critique Of The Techniquementioning

confidence: 99%

Effects of posture on regional pulmonary blood flow in rats as measured by PET

Richter

Bergmann

Pietzsch

et al. 2010

Journal of Applied Physiology

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Using small animal PET with 68 Ga-radiolabeled human albumin microspheres (Ga-68-microspheres), we investigated the effect of posture on regional pulmonary blood flow (PBF) in normal rats. This in vivo method is noninvasive and quantitative, and it allows for repeated longitudinal measurements. The purpose of the experiment was to quantify spatial differences in PBF in small animals in different postures. Two studies were performed in anesthetized, spontaneously breathing Wistar rats. Study 1 was designed to determine PBF in the prone and supine positions. Ga-68-microspheres were given to five prone and eight supine animals. We found that PBF increased in dorsal regions of supine animals (0.75) more than in prone animals (0.70; P ϭ 0.037), according to a steeper vertical gradient of flow in supine than in prone animals. No differences in spatial heterogeneity were detected. Study 2 was designed to determine the effects of tissue distribution on PBF measurements. Because microspheres remained fixed in the lung, PET was performed on animals in the position in which they received Ga-68-microsphere injections and thereafter in the opposite posture. The distribution of PBF showed a preference for dorsal regions in both positions, but the distribution was dependent on the position during administration of the microspheres. We conclude that PET using Ga-68-microspheres can detect and quantify regional PBF in animals as small as the rat. PBF distributions differed between the prone and supine postures and were influenced by the distribution of lung tissue within the thorax. pulmonary blood flow; positron emission tomography;68 Ga radiolabel; human serum albumin microspheres; prone position; supine position; small animal COLORED OR FLUORESCENT MICROSPHERES have primarily been used for blood flow measurements in small animals. Intravenously administered microspheres larger than 10 m are predicted to become trapped in the pulmonary capillaries. Their spatial distribution therefore reflects pulmonary blood flow (PBF; Refs. 11,13,14,20,32,38). Data analysis for colored or fluorescent microspheres requires lung excision and post mortem processing. In contrast, by using radiolabeled microspheres, data for the blood flow distribution could be achieved noninvasively and in vivo (22,35). A major advantage of positron emission tomography (PET) is its high sensitivity and the ability to quantify the concentration of radiotracers in the lung (24). The use of a dedicated small animal PET could allow this method to be translated to rodents. Therefore, we tested the feasibility of measuring PBF in rats using biodegradable, 68 Ga-radiolabeled human serum microspheres (Ga-68-microspheres) and micro-PET.Subsequently, and with a variety of radiotracers, positional changes in regional blood flow from upper to lower regions have been found in large animals and humans (4,15,23,25,33,36). However, to the best of our knowledge there are no data regarding the influence of posture (prone and supine) on regional pulmonary blood flow in small a...

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“…Alveolar corner vessels, which have diameters of 4 to 5 m, might be capable of vasoconstriction. 6,11 This is the vessel population in which we believe the 4-m diameter particles became trapped. 6,12 Vasomotion by such vessels could explain the perfusion heterogeneity we measured after 30% blood loss.…”

Section: Discussionmentioning

confidence: 99%

“…6,11 This is the vessel population in which we believe the 4-m diameter particles became trapped. 6,12 Vasomotion by such vessels could explain the perfusion heterogeneity we measured after 30% blood loss. If endothelial cells in these vessels altered their thickness, it would affect the ability of latex particles (or red cells) to flow down the lumen of those vessels.…”

Section: Discussionmentioning

confidence: 99%

“…Because these particles trap mainly within alveolar corner vessels, their trapping pattern is a measure of perfusion distribution among alveoli. 5,6 To determine the effects of hemorrhage on perfusion distribution, we quantified these patterns in anesthetized rats after removing from up to 30% of their calculated blood volume. Our results showed that interalveolar perfusion was significantly maldistributed after 30% blood volume removal, and suggested that the maldistribution included tissue volumes as small as five alveoli.…”

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