Regional hypoxic pulmonary vasoconstriction in prone pigs.

Hypoxic pulmonary vasoconstriction (HPV) is known to affect regional pulmonary blood flow distribution. It is unknown whether lungs with well-matched ventilation (V)/perfusion (Q) have regional differences in the HPV response. Five prone pigs were anesthetized and mechanically ventilated (positive end-expiratory pressure = 2 cmH2O). Two hypoxic preconditions [inspired oxygen fraction (FI(O2)) = 0.13] were completed to stabilize the animal's hypoxic response. Regional pulmonary blood Q and V distribution was determined at various FI(O2) (0.21, 0.15, 0.13, 0.11, 0.09) using the fluorescent microsphere technique. Q and V in the lungs were quantified within 2-cm3 lung pieces. Pieces were grouped, or clustered, based on the changes in blood flow when subjected to increasing hypoxia. Unique patterns of Q response to hypoxia were seen within and across animals. The three main patterns (clusters) showed little initial difference in V/Q matching at room air where the mean V/Q range was 0.92-1.06. The clusters were spatially located in cranial, central, and caudal portions of the lung. With decreasing FI(O2), blood flow shifted from the cranial to caudal regions. We determined that pulmonary blood flow changes, caused by HPV, produced distinct response patterns that were seen in similar regions across our prone porcine model.

Nonsteroidal anti-inflammatory drug-associated pulmonary infiltrates with eosinophilia. Review of the literature and Food and Drug Administration Adverse Drug Reaction reports.

OBJECTIVE: The purpose of this study was to detail the clinical and pathologic presentation of pulmonary infiltrates with eosinophilia (PIE) associated with nonsteroidal anti-inflammatory drug use. METHODS: We reviewed case reports and Food and Drug Administration Adverse Drug Reaction Spontaneous Reporting Program reports. RESULTS: A case of pulmonary infiltrates with eosinophilia related to naproxen use was studied. Six similar cases from the medical literature and 22 reports from the Food and Drug Administration were reviewed. Four cases of PIE associated with ibuprofen, obtained from the Food and Drug Administration, and single literature reports of PIE associated with fenoprofen and sulindac detailed similar clinical presentations. The clinical presentation of PIE syndrome associated with nonsteroidal anti-inflammatory drugs included fever, cough, dyspnea, infiltrates on chest roentgenogram, and an absolute peripheral eosinophilia. Pathologic examination revealed poorly defined granulomas with infiltrating eosinophils. CONCLUSIONS: Naproxen and other nonsteroidal anti-inflammatory drugs can elicit the PIE syndrome. The prevalence of this side effect is likely underestimated, given the extensive use of these drugs and the relatively benign course of PIE syndrome.

Developments in non-radioactive microsphere techniques for blood flow measurement.

Considerable progress is being made in the development of non-radioactive microsphere methods. Validation studies of the three commercially available non-radioactive microspheres are promising. In most experimental conditions the use of non-radioactive microspheres saves money. Avoiding the use of radioactivity facilitates the use of microspheres in chronic animal experiments and when blood flow and chemical measurements are performed in the same sample. Moreover, using histological techniques, distributions of coloured or fluorescent microspheres in subunits of organs could be quantified, opening new scientific possibilities. Currently, the fluorescent microsphere technique seems to be the most promising non-radioactive microsphere method. Due to the high sensitivity and good spectral separation, the number of microspheres injected can be as small as that used, for radioactive microspheres, at least six labels can be used, and the relatively large volume in which fluorescence is measured (approximately 1-3 ml) enables the use of time saving microsphere isolation techniques. Development of these methods and further automation of the quantification process (using either automised spectrometry or FACS analysis) will considerably increase interest in the non-radioactive microsphere techniques. To accelerate these developments, investigators are encouraged to share their experiences.

Successful treatment of severe hepatitis C-associated pulmonary vasculitis in a liver transplant recipient.

BACKGROUND: We report the clinical course of a patient who developed fever, hypoxia, and bilateral pulmonary infiltrates two and a half years after orthotopic liver transplantation (OLT) for cirrhosis due to hepatitis C. The patient had a history of hepatitis C-associated vasculitis manifested by purpuric skin rashes, renal abnormalities, and elevated cryoglobulins, and was receiving interferon-alpha at the time of presentation. RESULTS: The results of bronchoscopy with bronchoalveolar lavage were unrevealing, and open lung biopsy revealed active small vessel vasculitis. The patient responded dramatically to plasmapheresis and the addition of high-dose corticosteroids with resolution of hypoxia, pulmonary infiltrates, and glomerulonephritis. This is, to our knowledge, the first report of the successful treatment of hepatitis C-associated pulmonary vasculitis after OLT. CONCLUSIONS: We conclude that hepatitis C-associated pulmonary vasculitis should be included in the differential diagnosis of a patient presenting with fever, hypoxia, and pulmonary infiltrates after OLT for hepatitis C. Treatment with plasmapheresis and high-dose corticosteroids may be effective in patients with this disorder.

Occult spontaneous esophageal perforation. Unusual clinical and radiographic presentation.

We report a unique presentation of spontaneous esophageal perforation or Boerhaave's syndrome. Our patient had no risk factors predisposing her to barogenic rupture of the esophagus, and she had none of the "classic" presenting signs. She was asymptomatic, and her clinical course appeared to be chronic. Her chest roentgenogram demonstrated bilateral thick-walled cavities with air-fluid levels. Computerized axial tomography of the chest and swallow of meglumine diatrizoate (Gastrografin) showed the cavities and esophagus to communicate. This patient's presentation and radiographic studies extend the reported description of Boerhaave's syndrome.

Spatial correlation of regional pulmonary perfusion.

Despite the heterogeneous distribution of pulmonary blood flow, perfusion appears to be spatially ordered, with neighboring regions of lung having similar magnitudes of flow. This premise was tested by determining the spatial correlation of regional flow [rho(d)] as a function of distance (d) between regions. Regional pulmonary perfusion was measured in both supine and prone positions in seven anesthetized mechanically ventilated dogs with radiolabeled microspheres. After excision and drying, the lungs were cubed into pieces 1.2 cm on a side, with a three-dimensional coordinate assigned to each piece. The microsphere-determined flow to each piece was measured by radioactive counts, and rho(d) was calculated for all paired pieces within the same lobe. rho(d) was greatest for adjacent pieces (d = 1.2 cm) and decreased with increasing d, becoming negative at large distances in all dogs and positions. The spatial correlation of flow between adjacent pieces, rho(1.2 cm), was greater in the supine than in the prone position (0.66 vs. 0.72, P less than 0.05). The observations for each dog and position were fit to the equation rho(d) = d(a)+b.d+c, and the coefficients were used to compare rho(d) in the supine and prone positions. rho(d) differed in the two positions (P less than 0.05), with rho(d) falling off more rapidly with distance in the supine position. When trends in flow due to gravity were mathematically removed, differences between supine and prone positions were no longer observed. The spatial correlation of regional pulmonary perfusion was anisotropic in both supine and prone positions. The observation that regional pulmonary perfusion is highly correlated over large spatial distances has important implications for models of flow distribution.

Fractal modeling of pulmonary blood flow heterogeneity.

The heterogeneity of pulmonary blood flow is not adequately described by gravitational forces alone. We investigated the flow distributions predicted by two fractally branching vascular models to determine how well such networks could explain the observed heterogeneity. The distribution of flow was modeled with a dichotomously branching tree in which the fraction of blood flow from the parent to the daughter branches was gamma and 1-gamma repeatedly at each generation. In one model gamma was held constant throughout the network, and in the other model gamma varied about a mean of 0.5 with a standard deviation of sigma. Both gamma and sigma were optimized in each model for the best fit to pulmonary blood flow data from experimental animals. The predicted relative dispersion of flow from the two model fractal networks produced an excellent fit to the observed data. These fractally branching models relate structure and function of the pulmonary vascular tree and provide a mechanism to describe the spatially correlated distribution of flow and the gravity-independent heterogeneity of blood flow.

A computer simulation of pulmonary perfusion in three dimensions.

Pulmonary perfusion is spatially correlated with neighboring regions of lung having similar magnitudes of flow and distant pieces exhibiting negative correlation. Although local correlation has been noted in a wide variety of natural processes, negative correlation has not and it may be unique to organ blood flow. We investigate the regional perfusion predicted by a three-dimensional branching vascular model to determine whether such a model can create negative correlation of perfusion. The distribution of flows is modeled by a dichotomously branching tree in which the fraction of flow from parent to daughter branches is gamma and 1-gamma at each bifurcation. The flow asymmetry parameter (gamma) is randomly chosen for each bifurcation from a normal distribution with a mean of 0.5 with an SD of sigma. The branches branch along one of three orthogonal directions to assure a space-filling structure. This model produces flow distributions similar to those observed in experimental animals, with perfusion being positively correlated locally and negatively correlated at distance. The model is refined by incorporating an effect of gravity, which redirects a fraction (delta), of the flow against gravity to the companion daughter branch in the gravitational direction. A flow bias in the "dorsal" direction is also introduced to account for differences in supine-prone perfusion gradients. In its final form, this three-dimensional branching model accounts for previously observed 1) spatial correlation of regional perfusion with negative correlation over distance, 2) isogravitational perfusion heterogeneity, 3) differences in supine and prone perfusion gradients, 4) positive correlation of flows between supine and prone postures, 5) relatively small contributions of gravity to perfusion heterogeneity, and 6) fractal distributions of flow. This three-dimensional branching vascular model relates the function and structure of the pulmonary vascular tree, offering an explanation for both heterogeneous and spatially correlated regional flows.

Fractal properties of pulmonary blood flow: characterization of spatial heterogeneity.

The heterogeneity of pulmonary blood flow was examined using a fractal analytic procedure, and the results were compared with the traditional gravitational model of flow distribution. 99mTc-labeled macroaggregate was injected intravenously at functional residual capacity in six supine anesthetized dogs. The lungs were fixed in situ and sliced in transverse sections. The slices were imaged on a planar gamma camera, and a three-dimensional array of blood flow measurements was reconstructed for each lung. Fractal analysis was used to examine the spatial heterogeneity or RDs (relative dispersion = SD/mean) as a function of the number of pieces into which the flow array was subdivided. RDs was fractal and could be characterized by a fractal dimension (Ds) of 1.09 +/- 0.02, where a Ds of 1.0 reflects homogeneous flow and 1.5 indicates a random flow distribution. The data fit the fractal model exceptionally well with an average r = 0.98. RDs was examined in gravitational and isogravitational planes and as expected was greatest in the gravitational direction. However, the difference was small, suggesting that gravitation plays a secondary role to an underlying process producing heterogeneity. Within the limits of resolution attained by this study (piece volumes greater than 0.25 cm3), the heterogeneity of pulmonary blood flow is well characterized by a fractal model.

Relative contribution of gravity to pulmonary perfusion heterogeneity.

We designed a series of experiments and analyses to quantify the contribution of gravity to pulmonary perfusion heterogeneity. Regional pulmonary perfusion was measured in five anesthetized and ventilated dogs in both supine and prone positions by use of radiolabeled microspheres injected during apnea at functional residual capacity. Measurements of flow were repeated in each position, and the sequence of positions was prospectively designed to nullify any effect of order. The lungs of each animal were excised, perfused with saline until clear, dried at an inflation pressure of 25 cmH2O, and cut into 1.9-cm3 pieces. Each piece was weighed and the radioactivity determined in a scintillation counter. Measurement errors were minimized by excluding lung pieces that had greater than 25% airway and weighed less than 10 mg or greater than 60 mg. Weight-normalized flows in each position and repetition were determined for each lung piece. An analysis of variance model was used to identify the percentage of variation in regional flow that was due to position (supine vs. prone), to random error and time (measurement and repetition), and to structure, where structure was defined as the component of flow that remained constant across position and replication. The contributions of position, error/time, and structure to the total variability of flow across the five dogs were 7.8 +/- 0.6, 8.4 +/- 8.3, and 83.8 +/- 8.4%, (SD), respectively. Because the contribution of position represents the additive effect of gravity between two opposite positions, the contribution of gravity to perfusion heterogeneity in one position may be as little as 4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Validation of fluorescent-labeled microspheres for measurement of regional organ perfusion.

Estimations of dog lung, pig heart, and pig kidney regional perfusion by use of fluorescent-labeled microspheres were compared with measurements obtained with standard radiolabeled microspheres. Pairs of radio- and fluorescent-labeled microspheres (15 microns diam, 6 colors) were injected into a central vein of a supine anesthetized dog and the left ventricle of three supine anesthetized pigs while reference blood samples were simultaneously withdrawn from a femoral artery in the pigs. The lungs were cubed into approximately 2 cm3 pieces (n = 1,510). Each pig heart and kidney was cubed into approximately 1-g pieces (total n = 192 and 120, respectively). The radioactivity of each organ piece and reference blood sample was determined using a scintillation counter with count rates corrected for decay, background, and spillover. Tissue samples and reference blood samples were digested with KOH and filtered and the fluorescent dye was extracted with a solvent, or the dye was extracted from lung tissue without filtering. The fluorescence of each sample was determined for each color by use of an automated spectrophotometer. Perfusion was calculated for each organ piece from both the radioactivity and fluorescence. Correlation between flow determined by radio- and fluorescent-labeled microspheres was as follows: r = 0.96 +/- 0.01 (SD) (lung, filtered, n = 588), r = 0.99 +/- 0.00 (lung, nonfiltered, n = 710), r = 0.95 +/- 0.02 (heart, filtered), and r = 0.96 +/- 0.02 (kidney, filtered). Compared with colored microspheres, methods for quantitating fluorescent-labeled microspheres are more sensitive, less labor intensive, and less expensive. Fluorescent-labeled microspheres provide a new nonradioactive method for single and repeated measurement of regional organ perfusion.

Fractal nature of regional ventilation distribution.

High-resolution measurements of pulmonary perfusion reveal substantial spatial heterogeneity that is fractally distributed. This observation led to the hypothesis that the vascular tree is the principal determinant of regional blood flow. Recent studies using aerosol deposition show similar ventilation heterogeneity that is closely correlated with perfusion. We hypothesize that ventilation has fractal characteristics similar to blood flow. We measured regional ventilation and perfusion with aerosolized and injected fluorescent microspheres in six anesthetized, mechanically ventilated pigs in both prone and supine postures. Adjacent regions were clustered into progressively larger groups. Coefficients of variation were calculated for each cluster size to determine fractal dimensions. At the smallest size lung piece, local ventilation and perfusion are highly correlated, with no significant difference between ventilation and perfusion heterogeneity. On average, the fractal dimension of ventilation is 1.16 in the prone posture and 1. 09 in the supine posture. Ventilation has fractal properties similar to perfusion. Efficient gas exchange is preserved, despite ventilation and perfusion heterogeneity, through close correlation. One potential explanation is the similar geometry of bronchial and vascular structures.

Correlation between ventilation and perfusion determines VA/Q heterogeneity in endotoxemia.

Endotoxin increases ventilation-to-perfusion ratio (VA/Q) heterogeneity in the lung, but the precise changes in alveolar ventilation (VA) and perfusion that lead to VA/Q heterogeneity are unknown. The purpose of this study was to determine how endotoxin affects the distributions of ventilation and perfusion and the impact of these changes on VA/Q heterogeneity. Seven anesthetized, mechanically ventilated juvenile pigs were given E. coli endotoxin intravenously, and regional ventilation and perfusion were measured simultaneously by using aerosolized and injected fluorescent microspheres. Endotoxemia significantly decreased the correlation between regional ventilation and perfusion, increased perfusion heterogeneity, and redistributed perfusion between lung regions. In contrast, ventilation heterogeneity did not change, and redistribution of ventilation was modest. The decrease in correlation between regional ventilation and perfusion was responsible for significantly more VA/Q heterogeneity than were changes in ventilation or perfusion heterogeneity. We conclude that VA/Q heterogeneity increases during endotoxemia primarily as a result of the decrease in correlation between regional ventilation and perfusion, which is in turn determined primarily by changes in perfusion.

Spatial pattern of pulmonary blood flow distribution is stable over days.

Despite the heterogeneous distribution of regional pulmonary perfusion over space, local perfusion remains stable over short time periods (20-100 min). The purpose of this study was to determine whether the spatial distribution of pulmonary perfusion remains stable over longer time periods (1-5 days). Regional blood flow was measured each day for 5 days in five awake standing dogs. Fluorescent microspheres of different colors were injected into a limb vein over 30 s on each day. After the last microsphere injection, the dogs were killed, and lungs were flushed free of blood, excised, dried at total lung capacity, and diced into approximately 2-cm3 pieces (n = 1,296-1,487 per dog). Relative blood flow to each piece on each day was determined by extracting the fluorescent dyes and determining the concentrations of each color. We established that blood flow is spatially heterogeneous with a coefficient of variation of 29.5 +/- 2%. Blood flow to each piece is highly correlated with flow to the same piece on all days (r = 0.930 +/- 0.006). The temporal heterogeneity of regional perfusion as measured by the coefficient of variation is 6.9 +/- 0.7% over the 5 days and is nonrandom. The magnitude of spatial and temporal variation is significantly less than previously reported in a study in which anesthetized and mechanically ventilated dogs were used. We conclude that spatial distribution of pulmonary blood flow remains stable over days and we speculate that in the normal awake dog regional perfusion is determined primarily by a fixed structure such as the geometry of the pulmonary vascular tree rather than by local vasoactive regulators. Anesthesia and/or mechanical ventilation may increase the temporal variability in regional perfusion.

Hemodynamic effects of 15-microm-diameter microspheres on the rat pulmonary circulation.

The microsphere method has been used extensively to measure regional blood flow in large laboratory animals. A fundamental premise of the method is that microspheres do not alter regional flow or vascular tone. Whereas this assumption is accepted in large animals, it may not be valid in the pulmonary circulation of smaller animals. Three studies were performed to determine the hemodynamic effects of microspheres on the rat pulmonary circulation. Increasing numbers of 15-microm-diameter microspheres were injected into a fully dilated, isolated-lung preparation. Vascular resistance increased 0.8% for every 100,000 microspheres injected. Microspheres were also injected into an isolated-lung preparation in which vascular tone was increased with hypoxia. Microspheres did not induce vasodilatation, as reported in other vascular beds. Fluorescent microspheres were injected via tail veins into awake rats, and the spatial locations of the microspheres were determined. Regional distributions remained highly correlated when microspheres of one color were injected after microspheres of another color. This indicates that the initial injection did not alter regional perfusion. We conclude that, when used in appropriate numbers, 15-microm-diameter microspheres do not alter regional flow or vascular tone in the rat pulmonary circulation.

Pulmonary blood flow remains fractal down to the level of gas exchange.

The spatial distribution of pulmonary blood flow is increasingly heterogeneous as progressively smaller lung regions are examined. To determine the extent of perfusion heterogeneity at the level of gas exchange, we studied blood flow distributions in rat lungs by using an imaging cryomicrotome. Approximately 150,000 fluorescent 15-microm-diameter microspheres were injected into tail veins of five awake rats. The rats were heavily anesthetized; the lungs were removed, filled with an optimal cutting tissue compound, and frozen; and the spatial location of every microsphere was determined. The data were mathematically dissected with the use of an unbiased random sampling method. The coefficients of variation of microsphere distributions were determined at varying sampling volumes. Perfusion heterogeneity increased linearly on a log-log plot of coefficient of variation vs. volume, down to the smallest sampling size of 0.53 mm(3). The average fractal dimension, a scale-independent measure of perfusion distribution, was 1.2. This value is similar to that of other larger species such as dogs, pigs, and horses. Pulmonary perfusion heterogeneity increases continuously and remains fractal down to the acinar level. Despite the large degree of perfusion heterogeneity at the acinar level, gases are efficiently exchanged.

Vasomotor tone does not affect perfusion heterogeneity and gas exchange in normal primate lungs during normoxia.

To determine whether vasoregulation is an important cause of pulmonary perfusion heterogeneity, we measured regional blood flow and gas exchange before and after giving prostacyclin (PGI(2)) to baboons. Four animals were anesthetized with ketamine and mechanically ventilated. Fluorescent microspheres were used to mark regional perfusion before and after PGI(2) infusion. The lungs were subsequently excised, dried inflated, and diced into approximately 2-cm(3) pieces (n = 1,208-1,629 per animal) with the spatial coordinates recorded for each piece. Blood flow to each piece was determined for each condition from the fluorescent signals. Blood flow heterogeneity did not change with PGI(2) infusion. Two other measures of spatial blood flow distribution, the fractal dimension and the spatial correlation, did not change with PGI(2) infusion. Alveolar-arterial O(2) differences did not change with PGI(2) infusion. We conclude that, in normal primate lungs during normoxia, vasomotor tone is not a significant cause of perfusion heterogeneity. Despite the heterogeneous distribution of blood flow, active regulation of regional perfusion is not required for efficient gas exchange.

Applications of fractal analysis to physiology.

This review describes approaches to the analysis of fractal properties of physiological observations. Fractals are useful to describe the natural irregularity of physiological systems because their irregularity is not truly random and can be demonstrated to have spatial or temporal correlation. The concepts of fractal analysis are introduced from intuitive, visual, and mathematical perspectives. The regional heterogeneities of pulmonary and myocardial flows are discussed as applications of spatial fractal analysis, and methods for estimating a fractal dimension from physiological data are presented. Although the methods used for fractal analyses of physiological data are still under development and will require additional validation, they appear to have great potential for the study of physiology at scales of resolution ranging from the microcirculation to the intact organism.

Temporal heterogeneity of regional pulmonary perfusion is spatially clustered.

This study investigates temporal changes in regional pulmonary perfusion. Five dogs were studied with five or six different radiolabeled microspheres being injected via a central vein over 30 s every 20 min. The lungs of each animal were cubed into 1.9 cm3 pieces with spatial coordinates noted for each piece. Within individual pieces, the coefficient of variation of regional perfusion over time was 17.2 +/- 6.8% (SD) and across dogs accounted for 7.26 +/- 5.7% of total perfusion heterogeneity. Temporal variability or "twinkling" was not random. When lung pieces with similar temporal flow patterns were grouped together (regardless of spatial location), groups were more tightly clustered in space than expected by chance. Statistical clustering methods revealed regulation of blood flow on a large scale (lobar arteries), and fractal analyses suggested regulation existed on a smaller scale (arterioles). We conclude that regional pulmonary perfusion is heterogeneous over time in a nonrandom pattern and that pieces clustered by temporal patterns of perfusion are neighbors in the spatial domain.