Alveolar recruitment versus hyperinflation: a balancing act

PURPOSE OF REVIEW

To address lung recruitment according to pressure/volume curves, along with regional recruitment versus hyperinflation evidence from computed tomography and electrical impedance tomography.

RECENT FINDINGS

Cyclical tidal volume recruitment of atelectatic lung regions causes acute lung injury, as do large breaths during pneumonectomy. Using the lower inflection point on the static pressure/volume inflation curve plus 2 cmH2O as a positive end-expiratory pressure setting limits hyperinflation in acute lung injury, but may not provide enough positive end-expiratory pressure to avoid cyclical recruitment/derecruitment injury in more severe acute lung injury regions. Both computed tomography and electrical impedance tomography can help titrate positive end-expiratory pressure in these regions, thereby assuring an 'open lung' ventilatory pattern. Regional pressure/volume curves show that adequate positive end-expiratory pressure for severe acute lung injury regions may not be reliably determined from whole lung pressure/volume curves. Balancing positive end-expiratory pressure requires both arterial PO2 and PCO2 values to determine at what level hyperinflated regions become seriously underperfused (develop very high ventilation-perfusion ratios), adding to the hypercarbia from increased deadspace.

SUMMARY

Positive end-expiratory pressure levels must be high enough to minimize recruitment/derecruitment cycling. Balancing recruitment versus overdistension may require thoracic tomography, to assure sufficient improvement in oxygenation while limiting hypercarbia.

Changes in HRCT findings in patients with respiratory bronchiolitis-associated interstitial lung disease after smoking cessation

High-resolution computed tomography (HRCT) findings in patients with respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) are varied and nonspecific. There is no known report of changes in HRCT findings and respiratory function test results for RB-ILD patients following the cessation of smoking. Five patients with RB-ILD, confirmed by surgical lung biopsy, were retrospectively studied. Each stopped cigarette smoking and did not receive corticosteroid therapy after diagnosis. The clinical symptoms, respiratory function test results and HRCT findings obtained at the final observation were compared with those from the time of diagnosis. Ground-glass opacity and centrilobular nodules corresponding to pathological respiratory bronchiolitis, as well as intralobular fine linear-reticular opacity corresponding to fibrosis involving the subpleural alveolar septa, showed computed tomography-pathological correlations. Both clinical symptoms and the diffusing capacity of the lungs for carbon monoxide improved significantly following smoking cessation, as did ground-glass opacity and centrilobular nodules seen during the initial HRCT examination. Centrilobular nodules and ground-glass opacity, which are the main features of high-resolution computed tomography of respiratory bronchiolitis-associated interstitial lung disease patients and represent pathological respiratory bronchiolitis, can be improved by smoking cessation. The diffusing capacity of the lung for carbon monoxide in respiratory function tests can be also improved.

Mutations in the SLC34A2 gene are associated with pulmonary alveolar microlithiasis

RATIONALE

Pulmonary alveolar microlithiasis is an autosomal recessive disorder in which microliths are formed in the alveolar space.

OBJECTIVES

To identify the responsible gene that causes pulmonary alveolar microlithiasis.

METHODS

By means of a genomewide single-nucleotide polymorphism analysis using DNA from three patients, we have narrowed the region in which the candidate gene is located. From this region, we have identified a gene that has mutations in all patients with pulmonary alveolar microlithiasis.

MEASUREMENTS AND MAIN RESULTS

We identified a candidate gene, SLC34A2, that encodes a type IIb sodium phosphate cotransporter and that is mutated in six of six patients investigated. SLC34A2 is specifically expressed in type II alveolar cells, and the mutations abolished the normal gene function.

CONCLUSION

Mutations in the SLC34A2 gene that abolish normal gene function cause pulmonary alveolar microlithiasis.

Radiology of Severe Acute Respiratory Syndrome (SARS)

Severe acute respiratory distress syndrome (SARS) caused by SARS-associated coronavirus (SARS-CoV) is a systemic infection that clinically manifests as progressive pneumonia. During the initial phases of infection the virus causes pauci-inflammatory alveolar and interstitial edema that result in imaging abnormalities dominated by ground glass opacities (GGO). Severe SARS cases can develop radiologic and pathologic findings of diffuse alveolar damage. Although radiologic evidence of acute bronchiolitis is absent, SARS-CoV also infects ciliated airway epithelium, probably accounting for respiratory transmissibility of the virus. Radiologic recovery from SARS can be complete, but computed tomography images often show persistent GGO and reticular opacities, some of which reflect pathologic findings of fibrosis. Long-term follow-up imaging of survivors shows gradual decrease of GGO and reticulation with persistent air trapping in some patients. The latter is evidence of small airway disease that is not radiologically evident at the onset of the disease.

Cytokine gene polymorphisms and high-resolution-computed tomography score in idiopathic pulmonary fibrosis

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a serious disease with unknown cause and the influence of cytokine gene polymorphisms is presumed in the etiology and pathogenesis of the disease. We used high-resolution computed tomography (HRCT) as a marker of disease stage and progression and compared the alveolar and interstitial score with IL-1, IL-4, IL-12, IL-1RA and IL-4RA cytokine gene polymorphisms.

SUBJECTS AND METHODS

The IPF patients were all Caucasians from the Czech Republic and consisted of 20 females and 10 males, with a mean age of 65 years, range 36-85. The HRCT results were evaluated by an experienced viewer using the interstitial and alveolar score scales, which were based on the IPF HRCT description system from Gay SE, Kazerooni EA, Tows GB, Lynch JP, Gross BH, Cascade PN, et al. [Idiopathic pulmonary fibrosis. Predicting response to therapy and survival. Am J Respir Crit Care Med 1998;157:1063-72]. We evaluated the polymorphisms of cytokine genes utilizing a PCR with sequence-specific primers method.

RESULTS

The HRCT alveolar score was more pronounced in IL-4 RA (+1902) AG heterozygotes. The HRCT interstitial score was less severe in the IL-12 (-1188) AA homozygotes. According to progression of the HRCT interstitial score, the CC homozygosity at IL-1 RA (mspa 111100), the AA homozygosity at IL-4 RA (+1902) and CC homozygosity at IL-4(+33) positions were more frequent in patients with stable disease compared to those with progressive disease.

CONCLUSIONS

We assume from our data that the polymorphisms of IL-4, IL-4RA, IL-1RA and IL-12 genes (genes of cytokines with regulatory activity) might influence the phenotype of IPF as shown by measurable changes in HRCT investigations.

Visualizing lung function with positron emission tomography

Positron emission tomography (PET) provides three-dimensional images of the distributions of radionuclides that have been inhaled or injected into the lungs. By using radionuclides with short half-lives, the radiation exposure of the subject can be kept small. By following the evolution of the distributions of radionuclides in gases or compounds that participate in lung function, information about such diverse lung functions as regional ventilation, perfusion, shunt, gas fraction, capillary permeability, inflammation, and gene expression can be inferred. Thus PET has the potential to provide information about the links between cellular function and whole lung function in vivo. In this paper, recent advancements in PET methodology and techniques and information about lung function that have been obtained with these techniques are reviewed.

Diffuse alveolar damage: uncommon manifestation of pulmonary involvement in patients with connective tissue diseases

BACKGROUND

Diffuse alveolar damage (DAD) is a relatively common finding on surgical lung biopsy and can result from a variety of causes.

METHODS

We studied nine consecutive patients with connective tissue disease (CTD) and DAD diagnosed on surgical lung biopsy to examine this association and clinical implications.

RESULTS

The median age was 63 years (range, 35 to 76 years), and seven of the patients were women (78%). Underlying CTDs included rheumatoid arthritis in five patients, polymyositis in two patients, and one patient each with systemic sclerosis and mixed CTD. In seven patients (78%), CTD had been diagnosed before the onset of DAD; six of these patients had a preexisting interstitial lung disease (ILD) related to their CTD. DAD was the presenting manifestation leading to a new CTD diagnosis in two patients (22%). CT of the chest revealed ground-glass opacities and/or consolidation bilaterally with or without honeycombing. In all patients, surgical lung biopsy revealed DAD for which no cause could be identified other than the underlying CTD. Seven patients (78%) were receiving mechanical ventilatory support at the time of the surgical lung biopsy. Four patients (44%) survived to hospital discharge and included one patient with preexisting ILD and all three patients without chronic ILD.

CONCLUSION

We conclude that DAD can complicate the clinical course of patients with CTD-related chronic ILD, or can occasionally occur as a presenting manifestation of CTDs. When DAD occurs in patients with CTDs, the outcome appears to be worse for those with preexisting chronic ILD compared to those without ILD.

[Evaluation of the characteristic of alveolar recruitment and derecruitment with the static pressure-volume curve in rabbits with acute respiratory distress syndrome]

OBJECTIVE

To evaluate the value of static pressure-volume (P-V) curve during alveolar recruitment and derecruitment in mechanical ventilated rabbits with acute respiratory distress syndrome (ARDS), and to explore the lung protective ventilation strategies.

METHODS

The ARDS rabbit model was duplicated by warm-saline alveolar lavage. Dynamic CT scan was implemented to monitor the intrapulmonary gas volume and distribution during alveolar recruitment and derecruitment gradually. Static P-V curve was measured to reflect the features of alveolar recruitment and derecruitment.

RESULTS

Four aeration regions including nonaeration, insufficient aeration, normal aeration and overinflation regions, varied following airway pressure variation (t = 2.477 - 9.794, all P < 0.05). Recruitment of insufficient aeration region was found. Alveolar recruitment was divided two parts, alveolar open at nonaeration region and recruitment at insufficient aeration region. And alveolar derecruitment was divided two parts, alveolar close at nonaeration region and derecruitment at insufficient aeration region. Distribution frequency of alveolar open was different from inspiratory (r = 0.219, P = 0.220). And distribution frequency of alveolar close was different from expiratory (r = 0.094, P = 0.593). The compliance of P-V curve was only positively correlated with the volume of insufficient aeration region (inspiration r = 0.827, P = 0.006; expiration r = 0.792, P = 0.011). The airway pressure with the maximal compliance at inspiratory P-V curve [(16.2 +/- 3.5) cm H2O, 1 cm H2O = 0.098 kPa] was positively correlated with the alveolar opening pressure [(16.4 +/- 3.4) cm H2O, r = 0.900, P = 0.002], and the airway pressure with the maximal compliance at expiratory P-V curve [(11.9 +/- 2.4) cm H2O] was positively correlated with the alveolar closing pressure [(11.3 +/- 2.5) cm H2O, r = 0.887, P = 0.003].

CONCLUSIONS

During inspiration, alveolar recruitment takes place with alveolar overinflation. The compliance of P-V curve is correlated with insufficient region volume, and reflects the potential of lung recruitment, and can predict the alveolar opening pressure and closing pressure.

Evaluation of pulmonary alveolo-capillary permeability in Type 2 diabetes mellitus: using technetium 99mTc-DTPA aerosol scintigraphy and carbon monoxide diffusion capacity

The thickening of alveolar basement membrane is found in autopsies, along with microvascular pathologies, in Type 1 and 2 diabetes mellitus (DM). To detect the function and permeability of alveolar basement membrane, carbon monoxide diffusion capacity (DLCO) and technetium 99m-diethyltriaminepentaaceticacid ((99m)Tc-DTPA) aerosol scintigraphy methods can be used. The aim of this study was to determine alveolar basement membrane damage using these two methods. Nineteen women and 6 men, nonsmoking, Type 2 DM cases, without any lung and/or heart disease and who had neither anemia nor obesity, made up the patient group. They were compared with six female and nine male healthy cases who had the same characteristics with the diabetes cases. All of the cases DLCO were measured by single-breath method and (99m)Tc-DTPA aerosol scintigraphy was performed. DLCO showed no difference between the two groups. Aerosol scintigraphy was significantly decreased in the diabetic group (P=.01). In cases with >5 years of diabetic duration (P<.01), in cases with glycolized hemoglobin (HbA(1c)) </=8% (P<.05) and >8% (P<.05), and in microangiopathic cases (P<.01), alveolo-capillary permeability was significantly decreased than in the control group. Among the same groups, no significant difference could be detected for DLCO. The permeability of alveolar basement membrane can reduce in respect to diabetes duration and poor metabolic control. According to our investigation, (99m)Tc-DTPA aerosol scintigraphy method is more sensitive than DLCO method for determining these pathologies.

Clinical probability and alveolar dead space measurement for suspected pulmonary embolism in patients with an abnormal D-dimer test result

BACKGROUND

Most patients with suspected pulmonary embolism (PE) have a positive D-dimer test and undergo diagnostic imaging. Additional non-invasive bedside tests are required to reduce the need for further diagnostic tests.

OBJECTIVES

We aimed to determine whether a combination of clinical probability assessment and alveolar dead space fraction measurement can confirm or exclude PE in patients with an abnormal D-dimer test.

METHODS

We assessed clinical probability of PE and alveolar dead space fraction in 270 consecutive in- and outpatients with suspected PE and positive D-dimer. An alveolar dead space fraction < 0.15 was considered normal. PE was subsequently excluded or confirmed by venous compression ultrasonography, spiral computed tomography and a 3-month follow-up. Radiologists were unaware of the results of clinical probability and capnography.

RESULTS

PE was confirmed in 108 patients (40%). Capnography had a sensitivity of 68.5% (95% confidence interval [CI]: 58.9-77.1%) and a specificity of 81.5% (95% CI: 74.6-87.1%) for PE. Forty-five patients (16.6%) had both a low clinical probability and normal capnography (sensitivity: 99.1%, 95% CI: 94.9-100%) and 34 patients (12.6%) had both a high clinical probability and abnormal capnography (specificity: 100%, 95% CI: 97.7-100%).

CONCLUSION

Capnography alone does not exclude PE accurately. The combination of clinical probability and capnography accurately excludes or confirms PE and avoids further testing in up to 30% of patients.

Measurement of alveolar derecruitment in patients with acute lung injury: computerized tomography versus pressure-volume curve

INTRODUCTION

Positive end-expiratory pressure (PEEP)-induced lung derecruitment can be assessed by a pressure-volume (P-V) curve method or by lung computed tomography (CT). However, only the first method can be used at the bedside. The aim of the study was to compare both methods for assessing alveolar derecruitment after the removal of PEEP in patients with acute lung injury or acute respiratory distress syndrome.

METHODS

P-V curves (constant-flow method) and spiral CT scans of the whole lung were performed at PEEPs of 15 and 0 cmH2O in 19 patients with acute lung injury or acute respiratory distress syndrome. Alveolar derecruitment was defined as the difference in lung volume measured at an airway pressure of 15 cmH2O on P-V curves performed at PEEPs of 15 and 0 cmH2O, and as the difference in the CT volume of gas present in poorly aerated and nonaerated lung regions at PEEPs of 15 and 0 cmH2O.

RESULTS

Alveolar derecruitments measured by the CT and P-V curve methods were 373 +/- 250 and 345 +/- 208 ml (p = 0.14), respectively. Measurements by both methods were tightly correlated (R = 0.82, p < 0.0001). The derecruited volume measured by the P-V curve method had a bias of -14 ml and limits of agreement of between -158 and +130 ml in comparison with the average derecruited volume of the CT and P-V curve methods.

CONCLUSION

Alveolar derecruitment measured by the CT and P-V curve methods are tightly correlated. However, the large limits of agreement indicate that the P-V curve and the CT method are not interchangeable.

Pulmonary nodules in osteosarcoma patients: differential diagnosis of central venous catheter-related infections in the lungs

PURPOSE

The purpose of this study was to evaluate the differential diagnosis of pulmonary nodules by conventional radiography and computed tomography (CT) in osteosarcoma patients with central venous catheter.

MATERIALS AND METHODS

Between March 1997 and December 2001 at our Department of Musculoskeletal Oncology, 231 patients with peripheral osteosarcoma received a central venous catheter to allow infusion therapy and blood sampling. The mean age of these patients was 16 years (range 4-63), and 90 were aged 15 years or younger. All patients underwent radiological investigation for tumour staging and comparison with the following study in accordance with the protocol in place at our Department of Oncology and Division of Diagnostic Imaging.

RESULTS

Of a total of 231 patients, 13 (5.6%) developed an infection of the central venous line, with fever that was very high in some cases. In ten cases (4.3%), radiology showed damage to the alveolar interstitium typical of inflammatory forms, whereas in the remaining three (1.3%) it depicted nodular opacities, which required differentiation between lung metastases and septic emboli. After appropriate antibiotic and replacement of the central venous line, CT demonstrated disappearance of the lung nodules in all three patients, enabling a diagnosis of nodular septic embolism.

CONCLUSIONS

Placement of a central venous catheter for infusion therapy, chemotherapy and blood sampling has improved the quality of life of cancer patients. The most common complications of the use of central venous catheters include infection and venous thrombosis whereas pulmonary septic emboli are rare.

Squamous Cell Carcinoma of the Lung Spreading Along the Alveolar Walls With a Bubblelike Appearance on HRCT

On health examination, a nodular opacity of size of 25 mm was detected in a 54-year-old man. High-resolution computed tomography scans showed irregular-shaped ground glass opacity with bubble-like appearance in the right lung. The low-magnified histological findings after right upper lobectomy demonstrated squamous cell carcinoma that progressed along the alveolar septum and resembled the growing pattern of bronchioloalveolar carcinoma. As the mechanism of the formation of air density on computed tomography, the presence of check valve phenomenon was estimated. Squamous cell carcinoma of the lung that multiplies along alveolar walls shows localized ground glass opacity including air density areas similar to those in bronchioloalveolar carcinoma on high-resolution computed tomography.

Patrón alveolar nodular como forma de presentación de la toxicidad pulmonar por amiodarona

Amiodarone is a triiodinated antiarrhythmic drug that accumulates in alveolar macrophages. Its use is limited by its high rate of associated pulmonary toxicity, estimated at 5-7%. Radiologic findings for pulmonary toxicity caused by amiodarone are unspecific and varied. The most common finding is subpleural reticular-type interstitial thickening, predominately in the bases of the lungs. However, the presence of parenchymal nodules is an uncommon presentation. We report the case of a woman treated with amiodarone that presented multiple nodular lesions at plain-film radiography and high-resolution CT that were compatible with pulmonary toxicity caused by amiodarone at pathologic examination.

Refraction-enhanced tomography of mouse and rabbit lungs

In order to evaluate the effectiveness of edge enhancement by refraction in computed tomography, images of a cross section of a euthanized mouse thorax were recorded at low (20 keV) and high (72 keV) x-ray energies at a spatial resolution of about 40 microm. Compared with the images obtained with the detector at 30 cm from an object, when the object was located at 113 cm from the detector, the contrast between tissues and air was improved at both energies. The improvement was more pronounced at 72 keV where the absorption contrast was weaker. This effect was due to refraction at the surfaces of alveolar membranes and small airways which creates areas with apparently high and low linear attenuation coefficients within tissues. The edge enhancement by refraction was also effective in images of a euthanized rabbit thorax at x-ray energies of 40 and 70 keV at a spatial resolution of about 0.15 mm. These results raise the possibility that the refraction contrast may be utilized to obtain a high-resolution tomographic image of human lung and bone with low dose.

Hemorrhage Causes Interalveolar Perfusion Maldistribution in the Lungs of Anesthetized Rats

BACKGROUND

Lung injury often occurs following hemorrhage and we hypothesized that this might be due to the effects of hemorrhage on perfusion distribution among alveoli. To test this, we measured interalveolar perfusion distribution in anesthetized, spontaneously breathing rats subjected to blood losses of 0%, 10%, 20%, or 30% of calculated blood volume.

METHODS

We measured interalveolar perfusion distribution by analyzing trapping patterns of 4-mum diameter fluorescent latex particles infused into the pulmonary circulation. The particles (2 x 10) were infused 1 hour after each animal had been bled, and the lungs were then removed and air-dried. Using a confocal fluorescence microscope, we collected images of the particles in eight sections of each lung. Each image encompassed 3,360 x 3,360 x 100 microm (approximately 5,000 alveoli), and included 3-4,000 particles. Particle distributions in the images were measured using the method of dispersion index (DI) analysis. A DI value of zero corresponds to a statistically random distribution; the more DI exceeds zero, the more the distribution is clustered or inhomogenous.

RESULTS

The largest DI values for the four groups were: 0%, 0.69 +/- 0.41; 10%, 0.57 +/- 0.58; 20%, 0.72 +/- 0.34; 30%, 1.38 +/- 0.41. The 30% blood loss group had a max DI value approximately twofold greater than those of the other three (p < 0.0001).

CONCLUSIONS

Our results suggest that interalveolar perfusion distribution becomes markedly maldistributed at blood losses of 30%. This contributes to ventilation-perfusion mismatching, and may be a precipitating event for lung injury following hemorrhage.

Acute respiratory distress syndrome: underrecognition by clinicians and diagnostic accuracy of three clinical definitions

OBJECTIVE

To determine and compare the diagnostic accuracy of three clinical definitions of acute respiratory distress syndrome (ARDS): (1) the American-European consensus conference definition; (2) the lung injury score; and (3) a recently developed Delphi definition. A second objective was to determine the accuracy of clinical diagnoses of ARDS made in daily practice.

DESIGN

Independent comparison of autopsy findings with the daily status of clinical definitions, constructed with data abstracted retrospectively from medical records.

SETTING

Tertiary intensive care unit.

PATIENTS

One hundred thirty-eight patients from the period 1995 through 2001 who were autopsied after being mechanically ventilated.

INTERVENTIONS

Clinical ARDS diagnoses were determined daily without knowledge of autopsy results. Charts were reviewed for any mention of ARDS in the clinical notes. Autopsies were reviewed independently by two pathologists for the presence of diffuse alveolar damage. The sensitivity and specificity of the definitions were determined with use of diffuse alveolar damage at autopsy as the reference standard.

MEASUREMENTS AND MAIN RESULTS

Diffuse alveolar damage at autopsy was documented in 42 of 138 cases (30.4%). Only 20 of these 42 patients (47.6%) had any mention of ARDS in their chart. Sensitivities and specificities (95% confidence intervals) were as follows: American-European definition, 0.83 (0.72-0.95), 0.51 (0.41-0.61); lung injury score, 0.74 (0.61-0.87), 0.77 (0.69-0.86); and Delphi definition, 0.69 (0.55-0.83), 0.82 (0.75-0.90). Specificity was significantly higher for both the lung injury score and Delphi definition than for the American-European definition (p < .001 for both), whereas comparisons of sensitivity, which was higher for the American-European definition, were not significantly different (p = .34 and p = .07, respectively).

CONCLUSIONS

Acute respiratory distress syndrome appears underrecognized by clinicians in patients who die with this syndrome. In this population, the specificities of existing clinical definitions vary considerably, which may be problematic for clinical trials.

Morphometric deformations of small airways and alveoli under quasi-static inflation process

Localized morphometric deformations of small airways and alveoli during respiration have many biomedical and physiological implications. We developed fast synchrotron radiation CT system to visualize the small airways and alveoli of an intact mouse lung without fixation and dehydration, and analyzed their localized morphometric deformations between functional residual capacity (FRC) and total lung capacity (TLC). In the diameter behavior, the averaged and range values were significantly larger for smaller airways (68.8%, range: 0.36-0.89) than larger airways (45.2%, range: 0.40-0.57). These results indicated that the airway did not deformed in same manner and that these morphological differences characterized the heterogeneous lung function.