Cell origins and diagnostic accuracy of interleukin 27 in pleural effusions

The objective of the present study was to investigate the presence of interleukin (IL)-27 in pleural effusions and to evaluate the diagnostic significance of pleural IL-27. The concentrations of IL-27 were determined in pleural fluids and sera from 68 patients with tuberculous pleural effusion, 63 malignant pleural effusion, 22 infectious pleural effusion, and 21 transudative pleural effusion. Flow cytometry was used to identify which pleural cell types expressed IL-27. It was found that the concentrations of pleural IL-27 in tuberculous group were significantly higher than those in malignant, infectious, and transudative groups, respectively. Pleural CD4(+) T cells, CD8(+) T cells, NK cells, NKT cells, B cells, monocytes, macrophages, and mesothelial cells might be the cell sources for IL-27. IL-27 levels could be used for diagnostic purpose for tuberculous pleural effusion, with the cut off value of 1,007 ng/L, IL-27 had a sensitivity of 92.7% and specificity of 99.1% for differential diagnosing tuberculous pleural effusion from non-tuberculous pleural effusions. Therefore, compared to non-tuberculous pleural effusions, IL-27 appeared to be increased in tuberculous pleural effusion. IL-27 in pleural fluid is a sensitive and specific biomarker for the differential diagnosing tuberculous pleural effusion from pleural effusions with the other causes.     

Vascular endothelial growth factor in malignant pleural effusion associated with lung cancer

The presence of vascular endothelial growth factor (VEGF) was examined by enzyme immunoassay in 60 cytology-documented malignant pleural effusions associated with primary lung cancer and 51 other benign and malignant pleural effusions. Exudative pleural effusions contained significantly higher amounts of VEGF than transudative pleural effusions. Among exudative pleural effusions, levels of VEGF in malignant pleural effusions associated with lung cancer were significantly higher than those of benign exudative pleural effusions. There was no significant difference in pleural VEGF in patients with different histological types or clinical stages of lung cancer. Serial measurement of pleural VEGF levels was performed in six lung cancer patients treated with intrapleural instillation of recombinant interferon γ, and reduction of pleural effusion was associated with decreasing pleural VEGF levels. These findings suggest that VEGF has a role in the accumulation of exudative pleural effusions, especially that of malignant pleural effusion associated with lung cancer. Received: 14 April 1999 / Accepted: 10 June 1999     

Diagnostic imaging of small amounts of pleural fluid: pleural effusion vs. physiologic pleural fluid

The aim of this article is to present an overview of our 10 years clinical research work and early clinical experience with small pleural effusions. Small amounts of pleural fluid are severely difficult to identify with imaging methods (chest x-rays and ultrasound). Nevertheless, it may be an important finding, sometimes leading to a definitive diagnosis of pleural carcinomatosis, infection or other pathologic condition. Chest x-rays were used for many years for the diagnosis of small pleural effusions. Lateral decubitus chest radiographs represented a gold standard for imaging of small amounts of plural fluid for more than 80 years. In the last two decades, ultrasonography of pleural space became a leading real-time method for demonstrating small pleural effusions. Furthermore, the advent of sonographic technology actually enables detection of physiologic pleural fluid in some otherwise healthy individuals. In conclusion, new definitions of the key terms in the field of diagnostic imaging of small amounts of pleural fluid seem to be justified. We suggest that the term pleural fluid should determine physiologic pleural space condition while the term pleural effusion should only be used in the cases of pleural involvement or pleural illness.     

腺苷脱氨酶在结核性胸膜炎和恶性胸腔积液的对比临床分析

目的：探究腺苷脱氨酶在结核性胸腔积液和恶性胸腔积液中的含量规律。方法：回顾分析自2010年3月至2012年5月于本院胸心外科住院的胸腔积液患者,对穿刺获得的胸腔积液,用比色法测定胸腔积液中腺苷脱氨酶的水平。测量血中腺苷脱氨酶的水平进行对比。结果：结核性胸膜炎组患者胸腔积液ADA测定值为89．67±47．85IU／L,癌性胸腔积液组水平为24．56±11．491U／L,胸腔积液ADA水平在结核性胸膜炎与癌性胸腔积液组之间存在显著性差异（P〈0．05）;以ADA〉45IU／L诊断结核性胸膜炎：则敏感性为（48／51）94．1,特异性为（48／52）88．9％,以ADA〈45IU／L一诊断恶性胸腔积水：则敏感性（（51／55）89．4％,特异性为（51／54）94．4％;结核性胸膜炎中胸腔积液ADA／血清中ADA比值为2．25±0．72,癌性胸腔积液组水平0．43＋0．1,结核性胸膜炎与癌性胸腔积液组之间存在显著性差异（P〈0．05）;以胸腔积液ADA／血清中ADA比值〉1．0为界诊断结核性胸膜炎：则敏感性为（46／51）90．1,特异性为（45／55）81．8．％,以胸腔积液ADA／血清中ADA比值〈1．0诊断恶性胸腔积水：则敏感性（47／57）82．4％,特异性为（47／53）88．7％。结论：腺苷脱氨酶在结核性胸膜炎和恶性胸腔积液中的含量有明显差异。     

Evaluation of Cepheid's Xpert MTB/RIF Test on Pleural Fluid in the Diagnosis of Pleural Tuberculosis in a High Prevalence HIV/TB Setting

Background

Diagnosis of pleural tuberculosis (TB) using routinely available diagnostic methods is challenging due to the paucibacillary nature of the disease. Histopathology and pleural tissue TB culture involves an invasive procedure which requires expertise and appropriate equipment, both often unavailable in many health units. Xpert MTB/Rif test has been widely evaluated in sputum specimens but data on its performance in pleural TB is scarce. We evaluated the accuracy of Cepheid''s Xpert MTB/Rif test on pleural fluid in the diagnosis of pleural TB in Uganda.

Methods

Consenting adult patients with exudative pleural effusions underwent pleural biopsy and the tissue obtained subjected to Lowenstein-Jensen and mycobacterial growth indicator tube MTB cultures and histopathology. Pleural fluid for Xpert MTB/Rif testing was also collected. Data on socio-demographic characteristics, clinical symptoms, HIV status and CD4 count were also collected. Sensitivity, specificity, positive and negative predictive values of Xpert MTB/Rif test on pleural fluid in pleural TB diagnosis were calculated using pleural tissue MTB culture and/or histopathology as the reference standard.

Results

Of the 116 participants [female 50%, mean age 34 (SD ±13], 87/116 (75%) had pleural TB confirmed on pleural tissue culture and/or histopathology. The Xpert MTB/Rif test identified 25 (28.7%) of the 87 confirmed pleural TB cases. The sensitivity and specificity of Xpert MTB/Rif test were 28.7% and 96.6% respectively while the positive and negative predictive values were 96.1% and 31.1% respectively.

Conclusion

Xpert MTB/Rif test on pleural fluid does not accurately diagnose pleural TB and therefore cannot be used as an initial evaluation test in patients with suspected pleural TB. New, rapid and accurate tests for the diagnosis of pleural TB are still warranted.     

Fine needle aspiration of follicular variant of papillary thyroid carcinoma presenting with pleural effusion: a case report

BACKGROUND: Malignant pleural effusion in association with mesothelioma, bronchogenic carcinoma and breast carcinoma is common, although less frequently reported with other malignancies. We report a follicular variant of papillary thyroid carcinoma (FVPTC), diagnosed on fine needle aspiration cytology (FNAC) of thyroid and lymph nodes and subsequently proved to have metastasized to the pleural cavity. CASE: A 46-year-old man presented with history of breathlessness, thyroid swelling, pleural effusion and bilateral cervical lymphadenopathy. FNAC of the thyroid swelling and the lymph nodes showed features of FVPTC with cervical lymph node metastasis. Pleural fluid examination led to suspicion of pleural involvement by metastatic deposit, confirmed by subsequent pleural biopsy. CONCLUSION: Thyroid malignancies presenting with pleural effusion are rare. In this case, although pleural fluid cytology suggested involvement of pleura, a definitive diagnosis could be rendered only on pleural biopsy. An ancillary aid, such as immunocytochemistry, could have helped establish pleural involvement on routine pleural fluid cytology alone. This case emphasizes the possible existence of rare cases of FVPTC that may be associated with a dismal prognosis. In our case, initial diagnosis of FVPTC could be made only on correlating FNA features of thyroid aspirate with those of lymph node aspirate.     

Liquid thickness vs. vertical pressure gradient in a model of the pleural space

In recent studies using relatively noninvasive techniques, the vertical gradient in pleural liquid pressure was 0.2-0.5 cmH2O/cm ht, depending on body position, and pleural liquid pressure closely approximated lung recoil (J. Appl. Physiol. 59: 597-602, 1985). We built a model to discover why the vertical gradient in pleural pressure is less than hydrostatic (1 cmH2O/cm). A long rubber balloon of cylindrical shape was inflated in a plastic cylinder. The "pleural" space between the balloon and cylinder was filled with blue-dyed water. With the cylinder vertical, we measured pleural pressure by a transducer through side taps at 2-cm intervals up the cylinder. The pressure was measured with different amounts of water in the pleural space. With a clear separation between the balloon and the container, the vertical gradient in pleural liquid pressure was hydrostatic. As water was withdrawn from the pleural space, the balloon approached the wall of the container. Over an 8-cm-long midregion of the model where the balloon diameter matched the cylinder diameter, the vertical gradient was not hydrostatic and was virtually absent. In this region, the pleural liquid pressure was uniform and equal to the recoil of the balloon. In this section we could not see any pleural space. By scintillation imaging using 99mTc-diethylenetriamine pentaacetic acid in the water, we estimated the thickness of this flat "costal" pleural space to be approximately 20 microns. Radioactive tracer injected at the top of the pleural space appeared by 24 h at the bottom, which indicated a slow drainage of liquid by gravity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Local and systemic impacts of pleural oxygen exposure in thoracotomy

The pleural cavity is normally in a state of negative pressure and low oxygen tension. It is exposed to the atmosphere during thoracic surgery. However, no reports of pathophysiological investigation of the effects of pleural oxygen exposure involved in thoracotomy are available. In this study, the effects of pleural oxygen exposure on systemic and pleural inflammation were investigated. Male Wistar rats (9 weeks old) were placed on mechanical ventilation and underwent thoracotomy with lipopolysaccharide (LPS) administration, which simulates latent inflammatory condition. The pleural cavity was exposed to nitrogen (N(2) thoracotomy group), air (20% oxygen, air thoracotomy group), or 100% oxygen (O(2) thoracotomy group) under mechanical ventilation for 2 h. Animals were sacrificed 2 h or 8 h after LPS administration, and inflammatory indices (plasma tumor necrosis factor-alpha and interleukin-6, histology) were examined. For examination of inflammatory mediators, pleural effusion was added to cultured RAW264 cells, a murine macrophage cell line, and tumor necrosis factor-alpha levels in supernatant were measured. The capacity of pleural superoxide generation was investigated without LPS administration. Results showed increases in plasma interleukin-6 concentration and lung injury in the air and O(2) thoracotomy groups. Pleural oxygen exposure stimulated pleural superoxide generation, and increased pleural 4-hydroxy-2-nonenal and lung lipid peroxide concentrations. Tumor necrosis factor-alpha levels in cell culture supernatants were increased by the addition of pleural effusion from the air and O(2) thoracotomy groups. In conclusion, pleural oxygen exposure induced pleural oxidative injury and aggravated latent systemic inflammatory response.     

血清和胸水中CA125在结核性和癌性胸水中的表达及临床意义

目的:探讨血清和胸水中CA125在结核性和癌性胸水中的表达及鉴别诊断意义。方法:抽选我院确诊的结核性胸水病人85例(结核组)和癌性胸水病人71例(癌症组),检测两组患者血清和胸水中CA125表达,并以胸水/血清中CA125比值10(p-CA125/s-CA12510)为临界值,观察其对癌性胸水的鉴别特异度、灵敏度及准确性。结果:癌症组胸水中CA125表达及p-CA125/s-CA125比值均显著高于结核组(P0.05);但血清中两组CA125表达比较差异无显著性(P0.05);两组胸水中,以35U/ml为临界值,两组患者阳性率92.9%(79/85)、100%(71/71)比较差异无显著性(X2=7.0718,P=0.0078)。癌症组中p-CA125/sCA125比值10的比率(84.5%VS 17.6%)明显高于结核组(X2=66.6244,P=0.0000);并以其为诊断癌性胸水的临界值,鉴别诊断特异度、灵敏度及准确性分别为82.3%、84.5%、83.3%。结论:血清和胸水中CA125表达对于鉴别结核性或者是癌性胸水的临床意义不大,但是p-CA125/s-CA125比值对于鉴别结核性和癌性胸水具有一定临床价值。     

Nonmalignant pleural disease in asbestos exposed workers

The review deals with nonmalignant pleural changes related to asbestos: pleural thickenings, calcifications and effusions. The pathology of the pleural changes and their prevalence in asbestos exposed populations is described. The report presents also the ILO radiographic criteria for identification and classification of pleural changes and the correlation of X-ray findings to autopsy ones. The function of the lung in workers with the pleural disease is analyzed in terms of specific respiratory defects such as restriction of lung size and transfer defect. Finally the implication of the diagnosis of nonmalignant pleural disease for clinical practice is discussed with a special regarded to asbestos related occupational lung disease.     

Liquid and protein dynamics using a new minimally invasive pleural catheter in rabbits.

To obtain continuous access to the pleural space without causing injury, we tested a new transdiaphragmatic pleural catheter for its ability 1) to drain the pleural space without injury and 2) to drain liquid at a rate equal to normal pleural liquid production. In 13 anesthetized rabbits, we opened the abdomen and dissected through the diaphragm to insert a flared-tip catheter into the ventral pleural space on one side and then turned the rabbit prone. In 10 of the rabbits (8 for 6 h, 2 for 24 h), we continuously collected draining pleural liquid, and in 3 rabbits (6 h), we did not open the catheter. We injected radiolabeled albumin intravenously as a protein marker. Terminally, we collected pleural liquid from both pleural spaces and lavaged for total radioactivity. In 14 awake control rabbits without catheters, we measured normal pleural liquid production by the rate of equilibration of radiolabeled albumin from plasma to pleural liquid. We found that, although the percentage of neutrophils was increased on the side with the catheter (54 vs. 1% in control rabbits), the pleural liquid volume, protein concentration, specific activity of albumin, and total radioactivity in the pleural space were the same on the side with the catheter as on the opposite side and in the control rabbits. The liquid flow rate through the catheter over 6 h was 53 +/- 23 microliters/h [0.017 +/- 0.008 (SD) ml.kg-1.h-1], which was not significantly different from the computed rate of normal pleural liquid production in the control rabbits, 49 +/- 14 microliters/h (0.016 +/- 0.004 ml.kg-1.h-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Levels of soluble VCAM-1, soluble ICAM-1, and soluble E-selectin in patients with tuberculous pleuritis

Tuberculosis is characterized by the presence of activated mononuclear cells both in the peripheral circulation and in pleural fluid. Expression and up-regulation of adhesion molecules is the basis of cell-cell adhesion in granuloma formation and in leukocyte migration to the inflammatory site. Soluble isoforms of adhesion molecules have been described, and their expression at high levels indicated an activated state. The purpose of this study was to evaluate levels of soluble adhesion molecules in serum and pleural fluid from patients with tuberculous pleural effusions, compared with non-tuberculous pleural effusions. We analysed levels of soluble vascular cell adhesion molecule-1 (s.VCAM-1), soluble intercellular adhesion molecule-1 (s.ICAM-1), and soluble E-selectin (sE-selectin) in serum and pleural fluid from patients with tuberculous pleuritis, by sandwich ELISA. Serum levels of s.ICAM-1 and s.VCAM-1 in patients with tuberculosis were higher than those in healthy controls (p < 0.001). Levels of sE-selectin levels were in the normal range compared with control groups. In pleural fluid, levels of s.VCAM-1 and s.ICAM-1 were increased in pleural effusions. Patients with tuberculous pleural effusion exhibited high levels of s.ICAM-1 compared with patients with neoplastic pleural involvement. Up-regulation of s.VCAM-1 and s.ICAM-1 in serum, along with increased levels of sE-selectin in pleural effusions from tuberculous patients, may result in transmigration of activated inflammatory cells inducing pleural damage, which may contribute to the pathological processes involved.     

应用电视胸腔镜诊治病因不明胸腔积液的疗效观察

目的:探讨电视胸腔镜(video-assisted thoracoscopic surgery VATS)在诊治病因不明胸腔积液中的应用价值.方法:回顾分析2005年4月～2011年4月196例病因不明胸腔积液经电视胸腔镜手术的临床资料.均应用电视胸腔镜进行探查,根据病变情况选择切口部位.排净胸腔积液后,分离粘连,进行胸膜活检后恶性患者行胸膜固定术.结果:196例均明确诊断:140例恶性胸腔积液,36例结核胸腔积液,20例炎性胸腔积液.胸腔镜手术178例,胸腔镜辅助胸壁小切口手术18例.手术时间30～75min,平均54 min.出血量10～120mL,平均53 mL.10例出现术后肺漏气,胸腔引流量＜50 mL/24h拔除胸腔引流管,胸管留置时间4～19天,平均9.4天.191例成功控制胸腔积液,全组无院内死亡.22例接受化疗的恶性胸腔积液患者,随访14～34个月,平均23个月,复查胸片显示无胸腔积液、积气.结论:电视胸腔镜安全、有效、微创,便于操作,可作为诊治病因不明胸腔积液的主要方法.     

The differential diagnostic values of cytokine levels in pleural effusions

The aim is to examine whether the changes in pleural fluid interleukin (IL)-1beta, IL-2, IL-6, and IL-8 levels were significant in differential diagnosis of childhood pleural effusions. IL-1beta, IL-2, IL-6, and IL-8 levels in pleural fluids of all 36 patients were measured. The levels of IL-1beta, IL-2, IL-6, and IL-8 in pleural fluids were statistically significantly higher in the transudate group compared with those of the exudate group. The levels of IL-1 beta, IL-6, and IL-8 were also found to be statistically significantly higher in the empyema group compared with both the parapneumonic and the tuberculous pleural effusion groups. The levels of IL-2 and IL-6 were detected to be statistically significantly higher in the tuberculous pleural effusion group in comparison with those of the parapneumonic effusion group. The results showed that pleural fluids IL-1beta, IL-2, IL-6, and IL-8 could be used in pleural fluids exudate and transudate distinction.     

Pleural fluid cytology of invasive thymoma

A case is presented of invasive thymoma with recurrence in the pleura six years after thymectomy. Diagnosis of the pleural recurrence was by pleural fluid cytology and pleural biopsy. The histologic and cytologic features of the primary neoplasm and pleural recurrence are discussed and compared with the cytologic findings of thymomas in fine needle aspirates.     

MMP-2 VEGF在肺腺癌细胞中的表达及其意义

目的研究探讨基质金属蛋白酶2(MMP-2)及血管内皮生长因子(VEGF)在胸腔积液、痰液中肺腺癌细胞的不同表达及二者在肺癌细胞侵袭转移过程中的相互关系。方法选择胸腔积液、痰液共计264例癌性及异型增生细胞标本经免疫细胞化学方法分别检测MMP-2 VEGF的表达情况。结果免疫细胞化学结果显示:MMP-2在胸腔积液中腺癌细胞、异型增生上皮细胞的表达率分别为71.7%(99/138)、16.7%(6/36),在胸膜炎和结核病变典型良性胸腔积液增生上皮细胞中不表达;在痰腺癌细胞中的表达率为39.1%(27/69),统计结果显示MMP-2在恶性胸腔积液腺癌细胞中的表达率明显高于在异型增生的上皮、增生的上皮及痰腺癌细胞的表达率(P均0.05)。VEGF在胸腔积液中腺癌细胞、异型增生上皮细胞的表达率分别为89.1%(123/138)、33.3%(12/36),在胸膜炎和结核病变典型良性胸腔积液增生上皮细胞中不表达;在痰腺癌细胞中的表达率为47.8%(33/69),VEGF在恶性胸腔积液腺癌细胞中表达率明显高于在异型增生的上皮细胞、增生的上皮细胞及痰腺癌细胞的表达率(P均0.05),且MMP-2同VEGF总阳性表达率之间成正相关(r=0.867,P=0.049)。结果 MMP-2 VEGF在胸水腺癌细胞中高表达,可能与肺腺癌的转移、侵袭有关;两者联合做免疫细胞化学检查对肺腺癌细胞病理诊断有辅助意义。     

A comparison of changes in esophageal pressure and regional juxtacardiac pressures

The relationship between esophageal pressure and juxtacardiac pressures was studied during positive end-expiratory pressure (PEEP) ventilation applied to both lungs or selectively to one lung. The experiments were performed in eight anesthetized dogs with balloon catheters in the esophagus and in the left and right pericardial and overlying pleural cavities and with an open-ended liquid-filled catheter in the pleural cavity. Bilateral PEEP (10, 20, and 30 cmH2O) caused progressive and similar increments in left and right pleural pressure. Selective PEEP, however, increased ipsilateral pleural balloon pressure more than contralateral pressure. The increase in ipsilateral pleural balloon pressure markedly exceeded the increase in esophageal pressure. There was a small increase in pleural open-ended catheter pressure that approximated the increase in esophageal pressure. During selective PEEP, pericardial balloon pressure remained uniform because of a decrease in ipsilateral pericardial transmural pressure. In conclusion, selective PEEP caused nonuniform increments in regional pleural balloon pressure. Left and right pericardial balloon pressure, however, increased uniformly with selective PEEP because of reduced ipsilateral pericardial transmural pressure. The esophageal balloon did not reflect the marked regional increments in pleural balloon pressure with selective PEEP and consistently underestimated the changes in pleural balloon pressure with general PEEP.     

Pleural stress pressure as a force to control liquid accumulation and maintain lung expansion

Total gas pressure in the pleural space is more subatmospheric than that in the alveolar cavity. This pressure difference minus elastic recoil pressure of the lung was termed stress pressure. We investigated the relationship between stress pressure and a force that would hold the lung against the chest wall to prevent accumulation of liquid. The condition was a pleural space with an enlarged pleural surface pressure. Dogs anesthetized with pentobarbital sodium were placed in a box maintained subatmospherically at approximately -30 cmH2O and breathed atmospheric air for 4 h. Liquid volume in the pleural space of the dogs was measured under conditions of thoracotomy. In the normal group, the volume of the pleural liquid was within the normal range of approximately 2.0 ml and the visceral and the parietal pleura made contact. In the pneumothorax group, established by injecting 50 ml of air into the pleural space, the liquid increased significantly in all cases by a mean value of approximately 12 ml. Thus pleural stress pressure seems to be an important force holding the lung against the chest wall and aiding in the control of accumulation of liquid in a more subatmospheric pleural space.     

Clearance of lung edema into the pleural space of volume-loaded anesthetized sheep

To determine whether lung edema leaks into the pleural space, we measured flow rates of visceral pleural liquid from exposed sheep lungs during volume loading and then compared the protein concentration of visceral pleural liquid and lung interstitial liquids (lymph and peribronchovascular cuff liquid). For 4 h, we volume loaded 24 anesthetized ventilated sheep with one side, both sides, or neither side of the chest open. During the experiment, we collected visceral pleural liquid from a bag surrounding the exposed lung and lung lymph; after the experiment, we collected peribronchovascular cuff liquid. We found that during volume loading visceral pleural liquid flow increased significantly by 2 h, and its protein concentration over the final hour was the same as that of lung interstitial liquids. The volume of visceral pleural liquid correlated with excess lung water and wedge pressure elevation. By our estimates, clearance of edema from the lung into the pleural space constituted 23-29% of all edema liquid collected, similar to measured lymph edema clearance. We conclude that edema liquid leaks directly from edematous sheep lungs into the pleural space and that this leakage provides an important additional route of edema clearance.     

Pleural pressure distribution and its relationship to lung volume and interstitial pressure

The mechanics of the pleural space has long been controversial. We summarize recent research pertaining to pleural mechanics within the following conceptual framework, which is still not universally accepted. Pleural pressure, the force acting to inflate the lung within the thorax, is generated by the opposing elastic recoils of the lung and chest wall and the forces generated by respiratory muscles. The spatial variation of pleural pressure is a result of complex force interactions among the lung and other structures that make up the thorax. Gravity contributes one of the forces that act on these structures, and regional lung expansion and pleural pressure distribution change with changes in body orientation. Forces are transmitted directly between the chest wall and the lung through a very thin but continuous pleural liquid space. The pressure in pleural liquid equals the pressure acting to expand the lung. Pleural liquid is not in hydrostatic equilibrium, and viscous flow of pleural liquid is driven by the combined effect of the gravitational force acting on the liquid and the pressure distribution imposed by the surrounding structures. The dynamics of pleural liquid are considered an integral part of a continual microvascular filtration into the pleural space. Similar concepts apply to the pulmonary interstitium. Regional differences in lung volume expansion also result in regional differences in interstitial pressure within the lung parenchyma and thus affect regional lung fluid filtration.