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Biomedical subjects

J L Lehr

Publications and source records attributed to J L Lehr.

At least 37 records · Page 2Linked to original sources
PubMed1987

Inspiratory aerodynamic valving in goose lungs depends on gas density and velocity.

The non-reversing gas flow pattern in the avian lung has been attributed to 'aerodynamic valves'. A fundamental property of all aerodynamic valves is their dependence on inertial forces in the gas stream: sufficient reduction of inertial forces will cause aerodynamic valves to fail. If valving in the avian lung is aerodynamic, it should fail when gas stream momentum is reduced. We tested the dependence of the inspiratory valves in the goose lung on gas density and gas flow velocity. A bolus of tracer gas was placed in the tracheal cannula during an end-expiratory pause. Tracer gas appearance in a cranial air sac during the following inspiration and pause was used to deduce failure of the 'inspiratory valve' in cyclically ventilated geese. Little or no tracer entered the sac under control conditions, which approximated resting breathing, indicating highly effective valving. Lower flow rate or lower gas density caused increased tracer appearance, indicating valve failure. These results demonstrate the importance of gas inertial forces to normal valve function, and are direct evidence for the aerodynamic nature of the avian inspiratory valve.

Animals↗
PubMed1987

Longitudinal elastic wave propagation in pulmonary parenchyma.

Consideration of the lung as an elastic continuum led us to investigate the possible propagation of elastic waves. Here the relevant stiffness and density are given by the Lamé constants and density of the parenchyma. To test this hypothesis, we measured propagation velocities (c) in dog lobes by recording transit times of a velocity impulse on one side of the lobe and the subsequent arrival on the other side. We compared our measured values of c with elastic longitudinal wave velocities (c long) predicted by values of elastic moduli given by Lai-Fook et al. (J. Appl. Physiol. 40: 508-513, 1976) as a function of translobar pressure (PL) and our measured densities. Good agreement was found between c and c long. Typical values of c ranged from 250-1,500 cm/s as PL ranged from 2-20 cmH2O. No systematic difference in the c-c long relation was found between inflation and deflation, suggesting that the elastic moduli of lungs are essentially a function of pressure. No significant effect was observed by changing the physical properties of the gas within the lobe [air vs. He vs. sulfur hexafluoride (SF6)], suggesting that indeed we were observing waves associated with the coupling of parenchymal density to parenchymal stiffness.

Animals↗
PubMed1987

The radiology information system: its evolution and current status.

Radiology information systems (RIS) have developed over the past 20 years as a specialized area of medical informatics. Although an increasing number of radiology departments utilize such systems, the majority do not. Perhaps this is because no commercially available system has yet demonstrated its ability to provide cost-effective solutions to the diverse problems of different departments. This review begins with a brief history of RIS to point out some approaches that have proven successful and some that have not. Learning about the historical development of RIS also helps understand many of the features that are found in current systems. The bulk of the article is devoted to a detailed discussion of the functional modules found in RIS, including patient registration and data base management, examination scheduling, process control, film file management, diagnostic reporting, financial packages, and management statistics. These discussions emphasize the wide range of activities and problems found in different radiology departments and the wide range of techniques utilized by RIS. General issues of designing or selecting, installing, operating, and optimizing a RIS are discussed briefly. A final section points out areas for future development and expansion of RIS, giving special attention to the incorporation of digital image information into overall radiology systems.

Appointments and Schedules↗
PubMed1986

Nonuniformity of canine lung washout by high-frequency ventilation.

Ethane washout during low tidal volume (25-100 ml) high-frequency (3-40 Hz) ventilation (HFV) was studied in seven excised dog lungs. The lungs were initially equilibrated with 1% ethane, and then the concentration of ethane was monitored by mass spectrometry from multiple anatomic sites along the tracheobronchial tree during washout. We observed that the lung changed from a uniform distribution of ethane concentrations to a nonuniform distribution by a three-phase process. The first phase was nearly complete within the first 15 s and probably corresponds to concentration gradients being established in the central airways. During the second phase of washout, which lasted for several minutes, the concentrations in the various alveolar regions diverged. In the final phase, the regional concentrations remained at fixed ratios, and washout from all sites in the lung was at a constant fractional rate. These data are consistent with a model in which the duration of the second phase and the magnitude of the regional concentration differences established in this phase are dependent on both the magnitude of differences between regional transport paths and the nature of regional coupling by a common transport path to the airway opening.

Animals↗
PubMed1985

Histogram equalization of CT images.

Histogram equalization for display of clinical CT images was evaluated. In theory, histogram equalization makes optimal use of an available grey scale to display an image, and its use could circumvent the problem of selecting specific window settings for each image. In several clinical images, the use of a spatially variable histogram equalization technique limited to that portion of the CT image occupied by the patient did appear to increase the visibility of anatomic structures. However, using the technique also increased displayed image noise and artifacts. Although radiologists found this to be objectionable, it did not decrease the detectability of simulated low-contrast liver metastases. Further evaluation of histogram equalization for displaying CT images is being pursued.

Brain↗
PubMed1985

Photographic measurement of pleural surface motion during lung oscillation.

The regional pleural surface expansion of an excised dog lung was measured during high-frequency ventilation (HFV) using synchronized stroboscopic photography to stop lung motion at 20 evenly spaced intervals over a respiratory cycle during ventilation at 1 Hz with a volume of 100 ml, 15 Hz with 100 ml, or 30 Hz with 50 ml. The lungs were also photographed during quasi-static deflation. The pleural surface was marked with ink dots to form 84 approximately square figures. The side lengths and areas of each of the 84 "squares" were measured for each frame of each photo sequence. At 1 Hz and during the quasi-static deflation the lung ventilated nearly synchronously, although minor nonuniformities were noted on both small and large length scales. At 15 and 30 Hz, the lung expanded asynchronously and nonuniformly, with a 78% increase in surface expansion per 100 ml of tracheal tidal volume, as frequency was increased from 1 to 30 Hz. These nonuniformities in expansion suggest marked interregional airflow and elastic wave propagation in the parenchyma during HFV.

Animals↗
PubMed1984

Digital image processing: effect on detectability of simulated low-contrast radiographic patterns.

Detection studies of simulated low-contrast radiographic patterns were performed with a high-quality digital image processing system. The original images, prepared with conventional screen-film systems, were processed digitally to enhance contrast by a "windowing" technique. The detectability of simulated patterns was quantified in terms of the results of observer performance experiments by using the multiple-alternative forced-choice method. The processed images demonstrated a significant increase in observer detection performance over that for the original images. These results are related to the displayed and perceived signal-to-noise ratios derived from signal detection theory. The improvement in detectability is ascribed to a reduction in the relative magnitude of the human observer's "internal" noise after image processing. The measured dependence of threshold signal contrast on object size and noise level is accounted for by a statistical decision theory model that includes internal noise.

Computers↗
PubMed1984

Influence of the endotracheal tube on CO2 transport during high-frequency ventilation.

Low-volume, high-frequency ventilation (HFV) delivered via an endotracheal tube can maintain eucapnia in both humans and animals. Because recent animal studies have suggested that a substantial fraction of the resistance to gas transport during HFV can be attributed to the presence of the endotracheal tube, we evaluated the importance of the endotracheal tube on carbon dioxide elimination (VCO2) during HFV in humans. We compared the effectiveness of delivering the fresh gas bias flow at the proximal and the distal end of an endotracheal tube. For each bias flow position, we ventilated patients using tidal volumes of 60 ml or less and frequencies from 0.5 to 12 Hz. In each case, VCO2 was approximately 50% greater when the fresh gas was introduced at the carinal end of the endotracheal tube. Thus, the endotracheal tube contributed about one third of the resistance to HFV-induced CO2 transport in these patients. These results indicate that the position of the fresh gas source strongly influences the effectiveness of HFV.

Adult↗
PubMed1983

Truncated-view artifacts: clinical importance on CT.

A truncated-view artifact in CT is produced whenever any part of the patient or imaged object is present in some but not all of the views obtained for a slice. The potential to create images with this artifact exists for any CT scanner in which the fan beam (or its equivalent) does not cover the entire gantry aperture. This includes most CT systems currently on the market. Although the artifact may not create a severe visual disturbance in the image, it can alter the CT numbers in a manner that will compromise the accuracy of quantitative analyses. This report describes the nature of the truncated-view artifact and presents simulated examples for both mathematical phantoms and clinical scans. The artifact can be eliminated by assuring that the entire patient and all foreign objects are included in the field of view, or it can be minimized by placing objects that cannot be entirely within the field of view as close to the edge of the gantry aperture as possible.

Humans↗
PubMed1982

Gas exchange during high-frequency ventilation of the chicken.

Recent studies have shown that high-frequency ventilation (HFV) at 1-30 Hz is capable of maintaining adequate gas exchange in humans and dogs even when tidal volumes are substantially less than dead space. We evaluated the effectiveness of HFV in roosters by comparing CO2 elimination during various frequencies and tidal volumes of HFV with CO2 elimination during conventional mechanical ventilation. Sinusoidal oscillations were applied at the tracheal cannula. A bias flow provided fresh gas at the top of the tracheal cannula. Three conclusions emerge from the data. 1) HFV enhances gas transport in the chicken as it does in mammals. 2) At low oscillatory flows (amplitude X frequency) CO2 elimination depends on both frequency and tidal volume, whereas at higher flows CO2 elimination depends more strongly on tidal volume. The flow at which this transition occurs is relatively lower than in humans and much lower than in dogs. 3) HFV at volumes below dead space is usually not capable of maintaining adequate gas exchange in the chicken in contrast to results in dogs and humans.

Airway Resistance↗
PubMed1981

Tidal volume and frequency dependence of carbon dioxide elimination by high-frequency ventilation.

Six patients with chronic respiratory failure received mechanical ventilation with tidal volumes less than or equal to the dead-space volume, at frequencies of 30 to 900 breaths per minute. The rate of elimination of carbon dioxide from the ventilator system during a brief trial of high-frequency ventilation accurately predicted the long-term effectiveness of a given combination of frequency and tidal volume. Below frequencies of about 200 breaths per minute, the volume of carbon dioxide eliminated from these patients was most strongly related to the product of frequency and tidal volume; at higher frequencies, carbon dioxide elimination was determined by the tidal volume and was independent of frequency. These results suggest that although the effectiveness of high-frequency ventilation is primarily a function of the product of tidal volume and frequency, above a critical frequency the mechanical characteristics of the lung reduce gas transport by limiting the volume transmitted to the periphery of the lung.

Adolescent↗
PubMed1978

Engineering aspects of ECMO technology.

The primary areas of extracorporeal membrane oxygenation (ECMO) technology with engineering components are: biomaterials, oxygenator design, ECMO physiology and total system design. The evolution of ECMO has been largely empirical, with many innovations introduced directly from clinical experience and observation. Major advances are needed in both materials ans oxygenator design if current hematologic hazards are to be reduced. Optimization of ECMO systems has not been attempted in any systematic way because the basic physiology is not well enough understood to define the rationales for optimum control and management strategies. Once these strategies have been developed and tested, currently available automation technology can be applied to make the ECMO system system simpler and safer for clinical use.

Engineering↗
PubMed1976

Direct measurement of the effect of film miniaturization on diagnostic accuracy.

A method for directly measuring the reduction in diagnostic accuracy incurred by altering original radiographs was applied to evaluate a 35 mm film system. A total of 4,290 readings of 2,145 proved cases were collected. Analysis of the results indicate that the 35 mm system reduced diagnostic accuracy by about 2.3% +/- 2.4% at a 95% confidence level. The same method can be used to evaluate other photographic reduction systems, television displays, enhancement schemes, or even the importance of clinical data in roentgenographic interpretation.

Diagnostic Errors↗
PubMed1975

Retrograde aortic perfusion by partial cardiopulmonary bypass: effect of mixing on measured arterial oxygen tension.

Partial venoarterial bypass with return of oxygenated blood to the femoral artery can produce mixing in the aorta of the blood from the oxygenator and left ventricular sources at flow rates of less than 50% of the total body flow. This was observed in six anesthetized sheep with normal lungs maintained on controlled ventilation on partial cardiopulmonary (venoarterial) bypass. The evidence of mixing increases with the extracorporeal flow rate, reaching the aortic arch in a majority of cases at the higher rates. Management of bypass and the interpretation of its effects depend on definite knowledge of the presence or absence of mixing. Partial bypass will raise the arterial oxygen tension (Pao-2) of the blood continuing to flow through the lungs. This effect is independent of mixing (Pao-2) and may be related either to the addition of oxygen to the blood or to an enhanced pulmonary ventilation-perfusion relationship.

Animals↗
PubMed1975

Pulmonary insufficiency induced by oleic acid in the sheep: a model for investigation of extracorporeal oxygenation.

Most previous studies of the efficiency of bypass techniques for respiratory support have been conducted in hypoxic but otherwise normal animals. However, mechanisms of improved oxygenation by partial venoarterial bypass in the presence of acute respiratory insufficiency can be better studied with an appropriate pathophysiologic model; for this purpose, acute hemorrhagic pulmonary edema was induced in sheep by injection of oleic acid into the right atrium. The model presented a 3 hour period of elevated pulmonary shunting with stable hemodynamics. This preparation is being employed to the study of the mechanisms of extracorporeal oxygenation.

Animals↗