Flow limitation in infants assessed by negative expiratory pressure

Forced expiratory flows by the rapid compression technique are often used to assess airway function in infants; however, it remains unclear as to whether flow limitation (FL) is achieved. Studies in adults have used negative expiratory pressure (NEP) at the airway opening as a noninvasive technique to assess whether FL is achieved. An increase in flow with NEP indicates that FL has not been achieved, whereas no increase in flow with NEP indicates FL has been achieved. In the adult studies, the change in flow was assessed by visual inspection of the flow-volume curve. We evaluated whether NEP could be used to assess FL during forced expiration in infants. In addition, we quantified the change in flow secondary to NEP. We applied -5 cm H(2)O NEP to four infants during forced expiratory maneuvers. The step increase in flow with NEP was always less than 5% at high jacket compression pressures and consistent with FL. For one subject, FL was also confirmed from isovolume pressure flow-curves measured with an esophageal catheter. We conclude that NEP can be used in infants to assess FL during forced expiratory maneuvers by the rapid compression technique.

Neurally mediated hypotension in fatigued Gulf War veterans: a preliminary report

BACKGROUND

Many patients with chronic fatigue syndrome (CFS) have neurally mediated hypotension when subjected to head-up tilt, suggesting autonomic nervous system dysfunction. Some Gulf War veterans have symptoms similar to CFS. Whether they also tend to have neurally mediated hypotension is unknown.

METHODS

We performed 3-stage tilt-table testing on 14 Gulf War veterans with chronic fatigue, 13 unfatigued control Gulf War veterans, and 14 unfatigued control subjects who did not serve in the Gulf War. Isoproterenol was used in stages 2 and 3 of the tilt protocol.

RESULTS

More fatigued Gulf War veterans than unfatigued control subjects had hypotensive responses to tilt (P < 0.036). A positive response to the drug-free stage 1 of the tilt was observed in 4 of 14 fatigued Gulf War veterans versus 1 of 27 unfatigued control subjects (P < 0.012). Heart rate and heart rate variation during stage 1 was significantly greater in the fatigued group (P < 0.05).

CONCLUSION

We conclude that more fatigued Gulf War veterans have neurally mediated hypotension than unfatigued control subjects, similar to observations in CFS. Autonomic nervous system dysfunction may be present in some fatigued Gulf War veterans.

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.

Parenchymal and pleural findings in patients with and patients without acute pulmonary embolism detected at spiral CT

PURPOSE

To compare the frequencies of parenchymal abnormalities and pleural effusions in patients with and patients without acute pulmonary embolism (PE) detected at spiral computed tomography (CT).

MATERIALS AND METHODS

Contrast material-enhanced spiral CT scans obtained in 92 patients clinically suspected of having acute PE were retrospectively reviewed. The presence or absence of parenchymal abnormalities and pleural effusions was noted. The presence of filling defects consistent with central or peripheral PE was recorded.

RESULTS

Twenty-eight patients had CT evidence of PE. Central emboli were evident in 27 (96%) of these patients; 23 (82%) had concomitant central and peripheral emboli, and four (14%) had only central emboli. One patient had an isolated subsegmental clot. Parenchymal abnormalities were seen in 24 (86%) patients with PE and 56 (88%) patients without PE. Atelectasis, the most common finding, was present in 20 (71%) patients with PE and 41 (64%) patients without PE. The only parenchymal abnormality significantly associated with PE was peripheral wedge-shaped opacity, which was seen in seven (25%) patients with PE and three (5%) patients without PE (odds ratio, 6.78; 95% CI = 1.60, 28.62). Pleural effusions were seen in 16 (57%) patients with PE and 36 (56%) patients without PE. In 25 (39%) patients without PE, there were additional CT findings that might suggest an alternative explanation for the acute clinical presentation.

CONCLUSION

Parenchymal and pleural findings at CT are of limited value for differentiating patients with PE from those without PE.

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.

Response of chaparral shrubs to below-freezing temperatures: acclimation, ecotypes, seedlings vs. adults

Leaf death due to freezing was examined for four, co-occurring species of chaparral shrubs from the Santa Monica Mountains of southern California, Rhus laurina (= Malosma laurina), R. ovata, Ceanothus megacarpus, and C. spinosus. Measurements were made on seedlings vs. adults for all species, and for Rhus spp. in winter vs. summer, and at a warm vs. a cold site. We used four methods to determine the temperature for 50% change in activity or cell death (LT(50)) of leaves: (1) electrical conductivity (electrolyte leakage into a bathing solution), (2) photosynthetic fluorescent capacity (Fv/Fm), (3) percentage of palisade mesophyll cells stained by fluorescein diacetate vital stain, and (4) visual score of leaf color (Munsell color chart). In all four species seedlings were found to be more sensitive to freezing temperatures than were adults by 1°-3°C. For adults the LT(50) ranged from -5°C for Rhus laurina in the summer to -16°C for Rhus ovata in the winter. The LT(50) of R. ovata located at a colder inland site was 4C lower than R. ovata at the warmer coastal site just 4 km apart, suggesting ecotypic differences between R. ovata at the two sites. Both R. laurina and R. ovata underwent significant winter hardening. At the cold site, R. ovata acclimated by 6°C on average, while R. laurina acclimated by only 3°C. These results were consistent with species distributions and with field observations of differential shoot dieback between these two congeneric species after a natural freeze-thaw event in the Santa Monica Mountains.

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.

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.

Chest radiography in the ICU

Proper positioning and assessment of abnormalities and complications of the above-mentioned devices have a significant impact on the management of critically ill patients in the intensive care unit (ICU). The timely assessment of new or rapidly evolving findings is critical. Optimal radiographic technique, availability of images to the clinicians, and rapid reporting by the radiologist all serve to maximize the efficacy of bedside chest radiography in the ICU. Sometimes, changes in cardiopulmonary status may only be appreciated on chest radiographs (CXRs). Complications from ventilatory assistance, such as barotrauma, occur frequently and must be detected promptly. The position of monitoring devices, an important component of critical care management, is best checked radiographically. Indications for CXRs and the recommended frequency for repeat follow-up CXRs are based on the existing literature and the consensus of an expert panel formed by the American College of Radiology.

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.

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.

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.

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.

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.