Biomedical subjects

David L Levin

Publications and source records attributed to David L Levin.

16 recordsLinked to original sources

PubMed2006

Advances in magnetic resonance imaging of lung physiology.

This review presents an overview of some recent magnetic resonance imaging (MRI) techniques for measuring aspects of local physiology in the lung. MRI is noninvasive, relatively high resolution, and does not expose subjects to ionizing radiation. Conventional MRI of the lung suffers from low signal intensity caused by the low proton density and the large degree of microscopic field inhomogeneity that degrades the magnetic resonance signal and interferes with image acquisition. However, in recent years, there have been rapid advances in both hardware and software design, allowing these difficulties to be minimized. This review focuses on some newer techniques that measure regional perfusion, ventilation, gas diffusion, ventilation-to-perfusion ratio, partial pressure of oxygen, and lung water. These techniques include contrast-enhanced and arterial spin-labeling techniques for measuring perfusion, hyperpolarized gas techniques for measuring regional ventilation, and apparent diffusion coefficient and multiecho and gradient echo techniques for measuring proton density and lung water. Some of the major advantages and disadvantages of each technique are discussed. In addition, some of the physiological issues associated with making measurements are discussed, along with strategies for understanding large and complex data sets.

Helium↗

PubMed2006

Steep head-down tilt has persisting effects on the distribution of pulmonary blood flow.

Head-down tilt has been shown to increase lung water content in animals and alter the distribution of ventilation in humans; however, its effects on the distribution of pulmonary blood flow in humans are unknown. We hypothesized that head-down tilt would increase the heterogeneity of pulmonary blood flow in humans, an effect analogous to the changes seen in the distribution of ventilation, by increasing capillary hydrostatic pressure and fluid efflux in the lung. To test this, we evaluated changes in the distribution of pulmonary blood flow in seven normal subjects before and after 1 h of 30 degrees head-down tilt using the magnetic resonance imaging technique of arterial spin labeling. Data were acquired in triplicate before tilt and at 10-min intervals for 1 h after tilt. Pulmonary blood flow heterogeneity was quantified by the relative dispersion (standard deviation/mean) of signal intensity for all voxels within the right lung. Relative dispersion was significantly increased by 29% after tilt and remained elevated during the 1 h of measurements after tilt (0.84 +/- 0.06 pretilt, 1.09 +/- 0.09 calculated for all time points posttilt, P < 0.05). We speculate that the mechanism most likely responsible for our findings is that increased pulmonary capillary pressures and fluid efflux in the lung resulting from head-down tilt alters regional blood flow distribution.

Adult↗

PubMed2006

Prostate volume and prostate-specific antigen levels in men enrolled in a large screening trial.

OBJECTIVES: Prostate volume correlates both with prostate-specific antigen (PSA) values and with the presence of benign prostatic hyperplasia (BPH). Here we examine the relationship between prostate volume and PSA level in a large, geographically diverse sample of men undergoing prostate cancer screening. METHODS: We followed 35,323 men enrolled in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Each man was screened with digital rectal examination (DRE) and PSA levels for up to 4 years. Prostate volume was estimated by DRE performed by trained examiners at the PLCO sites. Linear and logistic regression was used to assess the effect of prostate volume and age on PSA levels. Regression coefficients were adjusted for the effect of prostate volume measurement error. RESULTS: Prostate volume estimated by DRE showed considerable measurement error. Averaging volume over screening visits and accounting for examiner bias greatly reduced this error. Linear regression analysis showed a slope of 0.030/cm3 of log PSA on prostate volume when correcting for measurement error (95% confidence interval [CI], 0.029 to 0.031). Age was independently associated with (log) PSA, with a slope of 0.022 per year. Logistic regression analysis of the risk of having an elevated PSA value (exceeding 4 ng/mL) showed an odds ratio of 1.9 (95% CI, 1.8 to 2.0) associated with a 10 cm3 increase in prostate volume. The correlation of log PSA and prostate volume was 0.37. Prostate volume was not correlated with body mass index and showed weak correlation (r = 0.14) with age. CONCLUSIONS: Prostate volume and age are independently associated with increased PSA levels in a population of men undergoing screening.

Aged↗

PubMed2006

Prostate specific antigen changes as related to the initial prostate specific antigen: data from the prostate, lung, colorectal and ovarian cancer screening trial.

PURPOSE: Annual screening with PSA, although of unproven benefit, is currently used for prostate cancer early detection. A large fraction of screened men have low (less than 2 ng/ml) initial PSA. The yield over time of positive PSA screens (ie more than 4 ng/ml) in these men has not been well characterized in large cohorts in the United States. MATERIALS AND METHODS: Men in the screening arm of the PLCO received baseline PSA and annual tests for 5 years. 30,495 of these men had baseline PSA 4 ng/ml or less. We estimated the cumulative probability of converting to PSA greater than 4 at years 1 through 5 as a function of baseline PSA. RESULTS: Among men with baseline PSA less than 1 ng/ml, 1.5% converted by year 5 (95% CI 1.2-1.7). Among men with baseline PSA of 1.0 to 1.99 ng/ml, 1.2% (95% CI 0.9-1.3) and 7.4% (95% CI 6.8-8.1) converted by year 1 and 5, respectively. A total of 33.5% and 79% of men with initial PSA of 2.0 to 2.99 and 3.0 to 4.0, respectively, converted by year 5. Of men with baseline PSA less than 1 ng/ml converting to PSA more than 4 ng/ml, 8% were diagnosed with cancer within 2 years of conversion. About 10% of men with baseline PSA less than 1 ng/ml and negative baseline DRE had a positive DRE within 3 years. CONCLUSIONS: For men choosing PSA screening, screening every 5 years for baseline PSA less than 1 ng/ml and every 2 years for PSA 1 to 2 ng/ml could result in a 50% reduction in PSA tests and in less than 1.5% of men missing earlier positive screens, but with an unknown effect on prostate cancer mortality.

Aged↗

PubMed2006

Acute schistosomiasis in nonimmune travelers: chest CT findings in 10 patients.

OBJECTIVE: We describe the findings of unenhanced chest CT in 10 patients with acute schistosomiasis. CONCLUSION: Despite the absence of pulmonary symptoms in four individuals, all patients had parenchymal abnormalities. Small pulmonary nodules were the most common finding, identified in nine patients. These nodules ranged in size from 2 to 5 mm in five patients, with larger nodules ranging up to 15 mm seen in four patients. In one patient, the only parenchymal abnormality was a single 5-mm focus of ground-glass attenuation. No relationship was seen between either the presence of pulmonary symptoms or the presence of peripheral eosinophilia and the severity of parenchymal disease. No additional significant findings were identified.

Acute Disease↗

PubMed2005

Heterogeneous pulmonary blood flow in response to hypoxia: a risk factor for high altitude pulmonary edema?

High altitude pulmonary edema (HAPE) is a rapidly reversible hydrostatic edema that occurs in individuals who travel to high altitude. The difficulties associated with making physiologic measurements in humans who are ill or at high altitude, along with the idiosyncratic nature of the disease and lack of appropriate animal models, has meant that our understanding of the mechanism of HAPE is incomplete, despite considerable effort. Bronchoalveolar lavage studies at altitude in HAPE-susceptible subjects have shown that mechanical stress-related damage to the pulmonary blood gas barrier likely precedes the development of edema. Although HAPE-susceptible individuals have increased pulmonary arterial pressure in hypoxia, how this high pressure is transmitted to the capillaries has been uncertain. Using functional magnetic resonance imaging of pulmonary blood flow, we have been able to show that regional pulmonary blood flow in HAPE-susceptible subjects becomes more heterogeneous when they are exposed to normobaric hypoxia. This is not observed in individuals who have not had HAPE, providing novel data supporting earlier suggestions by Hultgren that uneven hypoxic pulmonary vasoconstriction is an important feature of those who develop HAPE. This brief review discusses how uneven hypoxic pulmonary vasoconstriction increases regional pulmonary capillary pressure leading to stress failure of pulmonary capillaries and HAPE. We hypothesize that, in addition to the well-documented increase in pulmonary vascular pressure in HAPE-susceptible individuals, increased perfusion heterogeneity in hypoxia results in lung regions that are vulnerable to increased mechanical stress.

Altitude Sickness↗

PubMed2005

Baseline chest radiograph for lung cancer detection in the randomized Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial.

BACKGROUND: The Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial was initiated in 1992 to examine cause-specific mortality reduction from screening for these four cancers in men and women. We report lung cancer detection results of the baseline screening round. METHODS: Of the 154,942 participants enrolled, who were aged 55-74 years with no history of PLCO cancers, 77,465 were randomly assigned to the intervention arm. Current or former smokers and never smokers in this arm received an initial single-view posterior-anterior chest radiograph. RESULTS: In the initial screen, 5991 (8.9%, 95% confidence interval [CI] = 8.7% to 9.2%) of radiographs were suspicious for lung cancer: 8.2% (95% CI = 7.9% to 8.5%) for women and 9.6% (95% CI = 9.3% to 10.0%) for men. Rates were highest for older age groups and for smokers. Among those 5991 participants with a positive screen, 206 (3.4%, 95% CI = 3.0% to 3.9%) underwent biopsy examination, 126 (61.2%, 95% CI = 54.5% to 67.8%) of whom were diagnosed with lung cancer within 12 months of the screen (59 in women and 67 in men). The positive predictive value was 2.1% (95% CI = 1.7% to 2.5%), and 1.9 lung cancers were detected per 1000 screens. Among these cancers, 44% (95% CI = 35% to 52%) were stage I non-small-cell lung cancer. High rates of lung cancer were found in current smokers (6.3 per 1000 screens) and in former smokers who had smoked within the past 15 years (4.9 per 1000 screens). The lung cancer detection rate among never smokers was 0.4 per 1000 screens; this group accounted for 11% (95% CI = 5.6% to 16.6%) of the cancers identified. CONCLUSIONS: In the baseline screen, nearly half the cancers were stage I. Whether this experience results in a reduction in lung cancer mortality is yet to be seen.

Adenocarcinoma↗

PubMed2005

Whole-body CT screening: spectrum of findings and recommendations in 1192 patients.

PURPOSE: To retrospectively determine the frequency and spectrum of findings and recommendations reported with whole-body computed tomographic (CT) screening at a community screening center. MATERIALS AND METHODS: This HIPAA-compliant study received institutional review board approval, with waiver of informed consent. The radiologic reports of 1192 consecutive patients who underwent whole-body CT screening of the chest, abdomen, and pelvis at an outpatient imaging center from January to June 2000 were reviewed. Scans were obtained with electron-beam CT without oral or intravenous contrast material. Reported imaging findings and recommendations were retrospectively tabulated and assigned scores. Descriptive statistics were used (means, standard deviations, and percentages); comparisons between subgroups were performed with univariate analysis of variance and chi(2) or Fisher exact tests. RESULTS: Screening was performed in 1192 patients (mean age, 54 years). Sixty-five percent (774 of 1192) were men and 35% (418 of 1192) were women. Nine hundred three (76%) of 1192 patients were self referred, and 1030 (86%) of 1192 subjects had at least one abnormal finding described in the whole-body CT screening report. There were a total of 3361 findings, with a mean of 2.8 per patient. Findings were described most frequently in the spine (1065 [32%] of 3361), abdominal blood vessels (561 [17%] of 3361), lungs (461 [14%] of 3361), kidneys (353 [11%] of 3361), and liver (183 [5%] of 3361). Four hundred forty-five (37%) patients received at least one recommendation for further evaluation. The most common recommendations were for additional imaging of the lungs or the kidneys. CONCLUSION: With whole-body CT screening, findings were detected in a large number of subjects, and most findings were benign by description and required no further evaluation. Thirty-seven percent of patients had findings that elicited recommendations for additional evaluation, but further research is required to determine the clinical importance of these findings and the effect on patient care.

Adult↗

PubMed2005

Prostate Cancer Screening in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial: findings from the initial screening round of a randomized trial.

BACKGROUND: The benefit of screening for prostate cancer using prostate-specific antigen (PSA) testing and digital rectal examination (DRE) is uncertain and is under evaluation in a randomized prospective trial, the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Although the final results are several years away, the initial round of screening is complete. We describe the population enrolled in the PLCO trial, their baseline PSA and DRE screening results, and diagnostic follow-up results during the first year of follow-up. METHODS: A total of 38,350 men were randomly assigned to the screening arm of the PLCO trial from November 1993 through June 2001. Men were advised to seek diagnostic follow-up from their primary care provider if their DRE was suspicious for cancer and/or if their serum PSA level was higher than 4 ng/mL. PLCO trial staff obtained records related to diagnostic follow-up. RESULTS: Compliance with both screening tests was high (more than 89%). At screening, 7.5% of men had a positive DRE (i.e., suspicious for cancer) and 7.9% had a PSA level higher than 4 ng/mL. Of the men with positive screening tests, 74.2% underwent additional diagnostic testing, and 31.5% underwent a prostatic biopsy within 1 year. Overall, 1.4% of the men in the screening arm were diagnosed with prostate cancer, the majority of whom had clinically localized cancer. These compliance, biopsy, and cancer detection rates appear to be representative of contemporary practice patterns. CONCLUSION: The PLCO trial is evaluating PSA- and DRE-based screening for prostate cancer in a clinically valid manner. Whether such screening will result in a reduction of prostate cancer mortality cannot be answered until the randomized comparison is completed.

Aged↗

PubMed2004

Pulmonary blood flow heterogeneity during hypoxia and high-altitude pulmonary edema.

Uneven hypoxic pulmonary vasoconstriction has been proposed to expose parts of the pulmonary capillary bed to high pressure and vascular injury in high-altitude pulmonary edema (HAPE). We hypothesized that subjects with a history of HAPE would demonstrate increased heterogeneity of pulmonary blood flow during hypoxia. A functional magnetic resonance imaging technique (arterial spin labeling) was used to quantify spatial pulmonary blood flow heterogeneity in three subject groups: (1) HAPE-susceptible (n = 5), individuals with a history of physician-documented HAPE; (2) HAPE-resistant (n = 6), individuals with repeated high-altitude exposure without illness; and (3) unselected (n = 6), individuals with a minimal history of altitude exposure. Data were collected in normoxia and after 5, 10, 20, and 30 minutes of normobaric hypoxia FI(O(2)) = 0.125. Relative dispersion (SD/mean) of the signal intensity was used as an index of perfusion heterogeneity. Oxygen saturation was not different between groups during hypoxia. Relative dispersion was not different between groups (HAPE-susceptible 0.94 +/- 0.05, HAPE-resistant 0.94 +/- 0.05, unselected 0.87 +/- 0.06; means +/- SEM) during normoxia, but it was increased by hypoxia in HAPE-susceptible (to 1.10 +/- 0.05 after 30 minutes, p < 0.0001) but not in HAPE-resistant (0.91 +/- 0.05) or unselected subjects (0.87 +/- 0.05). HAPE-susceptible individuals have increased pulmonary blood flow heterogeneity in acute hypoxia, consistent with uneven hypoxic pulmonary vasoconstriction.

Adult↗

PubMed2004

Radiology of pulmonary vascular disease.

Diagnostic radiology plays an important role in the evaluation of suspected pulmonary vascular disease. This article discusses the use of various radiographic modalities and the radiographic features of several pulmonary vascular diseases.

Diagnostic Imaging↗

PubMed2004

MR evaluation of pulmonary blood flow.

Pulmonary blood flow is one of the primary determinants of gas exchange. While a number of methods can be used to evaluation pulmonary perfusion, these have substantial limitations. In this paper, we discuss the use of magnetic resonance imaging techniques for the evaluation of pulmonary blood flow. While these methods are not commonly used at present, they have the potential to contribute greatly to the evaluation of suspected pulmonary vascular disease.

Animals↗

PubMed2003

A pig model of high altitude pulmonary edema.

High altitude pulmonary edema (HAPE) affects unacclimatized individuals ascending rapidly to high altitude. The pathogenesis of HAPE is not fully elucidated, and many investigative techniques that could provide valuable information are not suitable for use in humans; thus, an animal model is desirable. Rabbits, sheep, dogs, and ferrets have been shown not to consistently develop HAPE, and studies in rats are limited by the animal's small size and inconsistent response. Pigs develop a marked pulmonary vasoconstrictive response to hypoxia, and preliminary studies of HAPE in pigs have been promising. To determine the suitability of pigs as an animal model of HAPE, we exposed six subadult (20 to 25 kg) pigs to normobaric hypoxia (10% oxygen) for 48 hr. One week before, and immediately after exposure to hypoxia, under anesthesia, arterial blood gases were obtained and bronchoalveolar lavage (BAL) and chest x-ray were performed. Hypoxia increased alveolar-arterial pressure difference for oxygen from 22 +/- 9 to 38 +/- 5 torr, p < 0.01) and red cell (from 12.3 +/- 5.9 to 27.4 +/- 5.3 cells x 10(5)/mL(-1), p < 0.001) and white cell (from 1.59 +/- 0.90 to 7.88 +/- 3.36 cells x 10(5)/mL(-1), p < 0.05) concentrations in BAL in all animals. Total BAL protein concentration increased by 64% and fractional albumin by 38% (both p < 0.05) posthypoxia. One animal had evidence of pulmonary edema on X ray. Some pigs develop findings consistent with early HAPE when exposed to normobaric hypoxia. Increasing the duration of hypoxic exposure or exercising the animals in hypoxia may better model the disease process observed in humans with clinically significant HAPE.

Altitude Sickness↗

PubMed2002

Radiology of pulmonary Mycobacterium avium-intracellulare complex.

Although the radiographic appearance of pulmonary MAC infection in the immunocompetent host can be varied, there are several generalizations that can be made. The classic radiographic appearance is indistinguishable from that of pulmonary tuberculosis. The classic form is seen most commonly in males and is typically associated with other predisposing diseases, especially chronic obstructive pulmonary disease. Most patients have upper lobe disease with associated pleural thickening. Widespread disease is common, as is cavitation. Pleural effusions and adenopathy are uncommon. The Lady Windermere syndrome is a special form of pulmonary MAC seen primarily in middle-aged and elderly women. The radiographic findings are bronchiectasis and small nodules, predominately located within the middle lobe and lingula. The combination of bronchiectasis involving exclusively, or primarily, the right middle lobe and lingula is highly suggestive of pulmonary MAC, even in the face of negative sputum cultures. Pulmonary infection with MAC in the immunocompromised patient generally reflects a widespread systemic disease. As such, the radiographic appearance is highly variable. Diffuse pulmonary opacities and adenopathy are common features. Plain radiographs are frequently normal despite active pulmonary infection. Regardless of the clinical situation, pulmonary MAC infection is often omitted from the radiographic differential even when the appearance is characteristic. In general, when pulmonary abnormalities are identified that are consistent with a granulomatous infection, pulmonary MAC needs to be considered along with tuberculosis and fungal infection. Especially with pulmonary MAC, radiographic stability over several years does not exclude active disease. The radiographic appearance may be suggestive of the diagnosis of pulmonary MAC, but correlation with the clinical and microbiological data is necessary to confirm the diagnosis.

Humans↗

PubMed2002

Cerebral microembolization during radiofrequency ablation of lung malignancies.

Three patients underwent radiofrequency (RF) ablation for treatment of malignant lung tumors. During three of the four RF ablation sessions, duplex ultrasound was used to intermittently sample the carotid arteries for the presence of emboli; microemboli were detected in all three patients. Embolization occurred within 1 minute of "roll-off." The rate of embolization ranged from 2 to 50 per minute. No new neurologic defects were found on examination. No cognitive, memory, or behavioral changes were noted by any of the three patients or their spouses. Microemboli to the cerebral circulation occurred during RF ablation of lung tumors. The clinical significance of these emboli is unknown.

Aged↗

PubMed2002

Nonneoplastic lesions of the tracheobronchial wall: radiologic findings with bronchoscopic correlation.

Nonneoplastic diseases of the central airways are uncommon but can be categorized as either focal or diffuse, although there is some overlap. Focal diseases include postintubation stenosis, postinfectious stenosis, posttransplantation stenosis, and various systemic diseases that may involve the airways and lead to focal stenosis (eg, Crohn disease, sarcoidosis, Behçet syndrome). Diffuse diseases of the central airways include Wegener granulomatosis, relapsing polychondritis, tracheobronchopathia osteochondroplastica, amyloidosis, papillomatosis, and rhinoscleroma. Conventional radiography is often the first step in the evaluation of suspected central airway disease and may be adequate in itself to identify the abnormality. However, computed tomography (CT) improves both the detection and characterization of central airway disease. Bronchoscopy remains the primary procedure for the diagnostic work-up of these disease entities. Nevertheless, a thorough radiologic evaluation with radiography and CT may demonstrate specific imaging findings (eg, calcification) that can help narrow the differential diagnosis and aid in the planning of bronchoscopy or therapeutic intervention.

Amyloidosis↗