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S D Davis

Publications and source records attributed to S D Davis.

At least 37 records · Page 2Linked to original sources
PubMed1999

Forced expiratory maneuvers in very young children. Assessment of flow limitation.

The application of negative expiratory pressure (NEP) to the airway opening during forced expiratory maneuvers has recently been described as a noninvasive method to assess whether flow limitation is achieved in adults. This methodology has great potential for extending the measurement of forced expiratory maneuvers to young children who may not produce maximal efforts as reproducibly as adults. We used NEP to assess flow limitation in 10 children between 3 and 5 yr of age. NEP was well tolerated by all subjects. With the application of NEP, there was not a step increase in flow, a finding consistent with flow limitation for the subjects. In addition to visual inspection, we proposed a method to quantify the change in flow during a short NEP. The flow-volume curves obtained with and without NEP were visually the same, other than the flow transients produced by NEP. The calculated values of FVC and FEF25-75 were not significantly different when measured from flow- volume curves with and without NEP. There was a statistically significant increase in FEV1 with NEP; however, the group mean increase in FEV1 was less than 2%. We conclude that NEP may be a useful technique to determine whether flow limitation has been achieved in young children performing forced expiratory maneuvers.

Child, Preschool↗
PubMed1999

The relationship between xylem conduit diameter and cavitation caused by freezing.

The centrifuge method for measuring the resistance of xylem to cavitation by water stress was modified to also account for any additional cavitation that might occur from a freeze-thaw cycle. A strong correlation was found between cavitation by freezing and mean conduit diameter. On the one extreme, a tracheid-bearing conifer and diffuse-porous angiosperms with small-diameter vessels (mean diameter <30 μm) showed no freezing-induced cavitation under modest water stress (xylem pressure = -0.5 MPa), whereas species with larger diameter vessels (mean >40 μm) were nearly completely cavitated under the same conditions. Species with intermediate mean diameters (30-40 μm) showed partial cavitation by freezing. These results are consistent with a critical diameter of 44 μm at or above which cavitation would occur by a freeze-thaw cycle at -0.5 MPa. As expected, vulnerability to cavitation by freezing was correlated with the hydraulic conductivity per stem transverse area. The results confirm and extend previous reports that small-diameter conduits are relatively resistant to cavitation by freezing. It appears that the centrifuge method, modified to include freeze-thaw cycles, may be useful in separating the interactive effects of xylem pressure and freezing on cavitation.

Journal Article↗
PubMed1998

Web-based digital radiology teaching file: facilitating case input at time of interpretation.

OBJECTIVE: Our goal was to develop a software system that allows easy and rapid input of digital radiology images and text reports, at the time of interpretation, into an easily searchable electronic teaching file database using the Internet and the World-Wide Web protocols, servers, and browsers. CONCLUSION: Using the Internet, the World-Wide Web, and our software system, we can rapidly input digital radiology images and associated text reports into an easily searchable database accessed by privileged users. This inexpensive and simple method for building a digital teaching file database allows cross-platform access for users who have a Web browser.

Computer Communication Networks↗
PubMed1997

Intestinal stem cell division and genetic diversity. A computer and experimental analysis.

Somatic mutations are expected to arise with age. This process is accelerated in mice lacking the DNA mismatch repair gene Pms2. The distributions of microsatellite alleles present in small patches of normal Pms2 -/- intestines revealed a general increase in genetic diversity or the number of mutations with age. However, the patterns were complex with different distributions and variances present within a single mouse. Computer simulations indicate that the experimental data are consistent with mutation rates between 0.0020 and 0.0025 mutations per division, nonrandom cell death, and an effective population size of 20 or fewer cells. Small numbers of cells exacerbate the random accumulation of mutations expected of a stochastic mutation process. The computer simulations and experimental data are consistent with known patterns of intestinal development and renewal by small numbers of stem cells and demonstrate relatively high mutation rates in histologically normal epithelium. These findings provide background for the analysis of microsatellite mutations in normal and tumor tissue lacking mismatch repair and further support the hypothesis that microsatellite loci can function as molecular tumor clocks.

Adenosine Triphosphatases↗
PubMed1996

Needle-tip repositioning during computed-tomography-guided transthoracic needle aspiration biopsy of small deep pulmonary lesions: minor adjustments make a big difference.

The aim of the study was to determine whether a thin-gauge transthoracic biopsy needle would be deflected from a straight path as it passed through lung tissue, and whether partially withdrawing the needle and reinserting it while applying pressure could significantly change the degree of deflection. Using a cadaver lung, we showed that the needle tip was deflected, on average, 2.5 mm from a straight path in a direction opposite to the bevel. The reinsertion technique using pressure caused the average deflection to increase to 6.3 mm, a significant difference from the previous value. We have found this technique to be useful in the performance of transthoracic needle aspiration biopsy of small deep pulmonary nodules where differences in positioning of the needle tip by only a few millimeters can achieve the correct, rather than an indeterminate, diagnosis.

Biopsy, Needle↗
PubMed1996

Pitfalls in CT-guided transthoracic needle biopsy of pulmonary nodules.

Successful performance of transthoracic needle biopsy of pulmonary nodules under computed tomographic (CT) guidance requires both accurate placement of the needle tip within the nodule and withdrawal of an adequate sample from the lesion. Failure to complete the biopsy procedure or to establish a definitive tissue diagnosis may be due to a number of factors. Potential pitfalls in transthoracic needle biopsy include technical factors related to the patient, CT scanning, or the biopsy needle; factors related to the size, location, or internal characteristics of the nodule or to an abnormality within adjacent parenchyma; and complications that may occur during transthoracic needle biopsy, such as pneumothorax or parenchymal hemorrhage. Awareness of how these pitfalls may be avoided or minimized should help expedite the performance of transthoracic needle biopsy and increase the likelihood of a diagnostic result.

Biopsy, Needle↗
PubMed1996

Juxtaphrenic peak in upper and middle lobe volume loss: assessment with CT.

PURPOSE: To investigate the anatomic basis for the juxtaphrenic peak (JP) in upper and/or middle lobe volume loss through radiographic and computed tomographic (CT) correlation. MATERIALS AND METHODS: Chest radiographs and CT scans were reviewed in 32 patients with upper or middle lobe volume loss. The study included 33 cases of volume loss: 12 affected the left upper lobe; 12, the right upper lobe; five, the right upper and middle lobes; and four, the middle lobe. JPs and linear opacities identified on chest radiographs were correlated with juxtadiaphragmatic structures on CT scans. RESULTS: A JP was identified in 22 of 33 (67%) cases, including nine of 12 (75%) with left upper lobe volume loss and eight of 12 (67%) with right upper lobe, four of five (80%) with combined upper and middle lobe, and one of four (25%) with middle lobe volume loss. The JP was due to an inferior accessory fissure in 14 of 22 (64%) cases. Other causes included a medial septum and an accessory fissure other than the inferior accessory fissure. CONCLUSION: The JP sign is seen in the majority of cases with upper lobe or combined upper and middle lobe volume loss. The sign is most commonly related to an inferior accessory fissure.

Adolescent↗
PubMed1996

Aspiration of a large pneumothorax resulting from transthoracic needle biopsy.

PURPOSE: To determine whether simple aspiration of air from the pleural space could obviate chest tube placement in patients with a large pneumothorax after transthoracic needle biopsy. MATERIALS AND METHODS: Seventeen patients, who developed a large pneumothorax (> 30%) during computed tomographic (CT)-guided transthoracic needle biopsy and otherwise would have required chest tube placement, underwent percutaneous aspiration of the pneumothorax while on the CT scanner table. Air was aspirated from the pleural space by using an 18-gauge intravenous catheter attached to a three-way stopcock and a 50-mL syringe. The patients were positioned with the puncture site down after aspiration of the pneumothoraces and oxygen was administered both during and after the procedure. RESULTS: The pneumothorax was almost completely aspirated in all 17 patients. Twelve (70%) patients did not require chest tube placement. Follow-up chest radiographs obtained 2 and 4 hours after the procedure revealed complete or almost complete resolution of the pneumothorax in eight (47%) patients and partial recurrence of a small, stable pneumothorax in four (24%) patients. The remaining five (29%) patients had recurrence of their pneumothorax, which ultimately required chest tube placement. CONCLUSION: Percutaneous catheter aspiration of a large biopsy-induced pneumothorax is safe and easy to perform and may obviate chest tube placement.

Adult↗
PubMed1996

Accuracy and efficacy of chest radiography in the intensive care unit.

In summary, the chest radiograph has only moderate accuracy in visualizing opacification caused by cardiopulmonary abnormalities and may be quite nonspecific as to etiology, whereas it has high diagnostic accuracy for detecting malpositioning of tubes and lines. While focal parenchymal abnormalities are usually visualized on chest radiographs, identification of concomitant abnormalities when ARDS or PE already exist is more difficult. Atelectasis, aspiration, pneumonia, pulmonary hemorrhage, pulmonary thromboembolism, atypical cardiogenic edema, asymmetric ARDS, and neoplasms may be indistinguishable. Repeat chest radiographs and different views may be helpful, as the progression and time course of various etiologies can be quite different. On the other hand, Winer-Muram et al found that review of prior radiographs and clinical data did not improve the diagnostic accuracy for either ARDS or pneumonia. Pleural effusions may even be difficult to distinguish from parenchymal processes, particularly when the patient is in the supine position. Additional views with the patient in a different position--semi-erect, decubitus, or cross-table lateral--may be of assistance. In most cases, pneumothorax is readily detected. Additional studies such as the decubitus view occasionally may be necessary for further evaluation when there is uncertainty about the findings. Subcutaneous air is readily visualized radiographically. Pneumomediastinum and interstitial pulmonary emphysema may be more difficult to see. It is well known that CT allows visualization of much smaller abnormal air collections than radiography. Despite this lack of sensitivity and specificity of chest films, studies have shown that up to 65% of daily films in the ICU reveal significant and/or unsuspected abnormalities that may change the patient's diagnosis or management. Based on these results, the consensus opinion of the ACR Expert Panel found that daily chest radiographs are indicated on patients with acute cardiopulmonary problems and those receiving mechanical ventilation. Patients who require cardiac monitoring but are otherwise stable require only an initial admission film. Additional radiographs are indicated only when a new device is placed or when there is a specific question regarding cardiopulmonary status. It is also noteworthy that despite the chest film being the most commonly ordered radiologic examination for inpatients, there are no comprehensive studies evaluating its cost-effectiveness. Although several studies have done a very limited cost accounting of the potential savings by eliminating routine films in the evaluation of specific subsets of patients, overall impact on patient outcome has not been investigated. Thus, a true assessment of cost-effectiveness has yet to be determined.

Catheterization, Swan-Ganz↗
PubMed1995

Variability in lesion depth on prone and supine CT scans of the chest: implications for the accuracy of transthoracic needle aspiration biopsy.

Transthoracic needle biopsy of the lung is often performed fluoroscopically in the prone position; nodule depth measurements are made from accompanying computed tomographic (CT) scans performed supine. We evaluated the effect of prone and supine positioning on the effect of nodule depth as measured from the skin surface. Twenty consecutive patients having CT-guided biopsy performed in the prone position were assessed. Nodule depth from posterior skin surface to nodule was compared with prebiopsy supine CT scan. Nodules above the carina showed minimal change in depth. Those below the carina showed considerable variability, with depth changes < or = 4.0 cm. Awareness of the magnitude of the potential effect of patient position on lesion depth should be helpful in reducing the likelihood of false negative results in fluoroscopically guided biopsy.

Biopsy, Needle↗
PubMed1994

Appropriate window and level settings in CT-guided biopsies.

The purpose of this study was to investigate the factors that help determine the needle tip location during computed tomographic (CT)-guided thin needle aspirations. We devised a model using a bottle filled with air, mineral oil, and water into which we could insert a needle. We then obtained CT images using both 5- and 10-mm slice thicknesses and determined the Hounsfield units (HUs) in regions of interest surrounding the needle shaft and some distance away from the needle shaft. We demonstrated that the presence of the needle increases the average HUs of the background both in the same region of interest and in the region of interest some distance from the needle. This effect is seen in air, fat, and water and thus occurs regardless of the attenuation of the background medium. A decrease in slice thickness causes this effect to be even more marked. These experimental results coincided with the theoretical results obtained from an equation that approximates the HUs of the pixels.

Artifacts↗
PubMed1993

Percutaneous CT biopsy of chest lesions: an in vitro analysis of the effect of partial volume averaging on needle positioning.

OBJECTIVE: Accurate needle biopsy of chest lesions requires knowledge of both the direction of the needle and the exact location of the tip of the needle. The purpose of this study was to analyze and illustrate the relationships between the location of the nodule, the size of the nodule, the CT slice thickness, and the needle length. An understanding of these relationships should minimize localization errors due to partial volume averaging and thus increase the accuracy of biopsies. MATERIALS AND METHODS: Geometric principles were used to determine mathematical relationships between the size of the nodule, the CT slice thickness, the length of the needle, and the direction of the needle. A styrofoam model simulating the patient and the lesion to be sampled was developed so that radiographs and CT scans of the model could be obtained with different needle placements to illustrate the phenomenon of partial volume averaging. RESULTS: The accuracy of the CT-guided biopsy can be increased by reducing the CT slice thickness, using longer needles, minimizing the distance to be traversed within the patient, and maximizing the portion of the lesion contained in the CT section used for needle tip localization. Mathematical equations developed from the in vitro model can be used to select the most appropriate CT section and the best length and angle of the needle. CT scans of the model illustrate the use of these equations. CONCLUSION: We found these principles helpful in improving the accuracy of CT needle biopsies, particularly when the lesions are very small and when an angled approach is required. Ideally, the smallest possible CT slice thickness and the longest possible needles should be used, but some practical limitations exist.

Biopsy, Needle↗
PubMed1992

Radiology of congenital abnormalities of the chest.

Radiologic imaging plays a critical role in the management of congenital abnormalities affecting the tracheobronchial tree, lung parenchyma, pulmonary vessels, and the mediastinum. Although procedures such as bronchoscopy, bronchography, and angiography may at times still be required, diagnosis is now usually established noninvasively using ultrasound, CT, MR imaging, or radionuclide imaging techniques. Earlier diagnosis, even in the antenatal period, is possible, thus allowing more prompt and effective treatment. Patients with congenital abnormalities that were previously fatal in infancy and childhood are surviving into adulthood. Clinicians and radiologists alike must now be able to recognize congenital disorders in patients who may have minimal or absent symptoms.

Bronchi↗