Search PubMed⌕ Search

Biomedical subjects

D A Merton

Publications and source records attributed to D A Merton.

At least 37 records · Page 2Linked to original sources
PubMed1996

Color amplitude imaging: preliminary results using vascular sonographic contrast agents.

Conventional (mean Doppler frequency shift) color Doppler imaging and a new method of displaying blood flow in color that uses the amplitude of the Doppler signal were utilized to evaluate three vascular sonographic contrast agents. To compare the two color flow detection modalities, a total of 20 pairs of contrast agent injections were performed while imaging a variety of abdominal organs and tumors in experimental animal models. The 20 paired injections were scored independently to indicate whether color amplitude imaging better demonstrated the effects of contrast enhancement (n = 14), both techniques were equivalent in demonstrating the effects of contrast enhancement (n = 4), or color Doppler imaging better demonstrated the effects of contrast enhancement (n = 2). These results indicate that compared to color Doppler imaging, color amplitude imaging improved visualization of both normal and abnormal blood flow in 70% of these cases (P < 0.0001). Specifically, with contrast enhancement of the Doppler signals, organ vascularity and regional differences in parenchymal blood flow were better demonstrated with color amplitude imaging than with color Doppler imaging. In addition, since color amplitude imaging is nondirectional and less angle dependent than color Doppler imaging, it was possible to visualize vessel continuity more completely and to demonstrate vessel branching more clearly with this modality. However, owing to the lack of directivity and poor temporal resolution, information obtained with color amplitude imaging appears to be complementary to that of color Doppler imaging. In conclusion, color amplitude imaging is a reliable method of determining the effectiveness of vascular sonographic contrast agents and should be considered one of the primary flow imaging modalities used for the assessment of these agents.

Animals↗
PubMed1996

Laparoscopic liver sonography: preliminary experience in liver metastases compared with CT portography.

This study evaluated the ability of laparoscopic ultrasonography to detect, localize, and characterize focal liver masses. Laparoscopic ultrasonography and CT portography of the liver were performed in 13 patients with known or suspected malignancy. Laparoscopic ultrasonography directly influenced surgical management in four (31%) cases; three by detection of small focal masses and one by exclusion of masses suspected on CT portography. Laparoscopic ultrasonography provided guidance for biopsy or added important anatomic information in three cases. Laparoscopic ultrasonography was complementary to CT portography but added no additional information in three cases, and it failed to provide any information in two cases. Laparoscopic ultrasonography was falsely negative in one case. In this preliminary series, laparoscopic ultrasonography assisted surgeons in critical decision-making by either providing important new information, clarifying questionable areas, or complementing CT portography.

Adult↗
PubMed1996

Effects of hypocarbia on the development of cystic periventricular leukomalacia in premature infants treated with high-frequency jet ventilation.

BACKGROUND AND OBJECTIVE: Previous data from our institution indicate that mechanically ventilated premature infants are at increased risk for cystic periventricular leukomalacia (CPVL), particularly if hypocapnia occurs. High-frequency jet ventilation (HFJV) may produce substantial hypocapnia. We sought to investigate whether hypocapnia during HFJV is associated with the development of CPVL. METHODS: Sixty-seven premature infants (mean gestational age, 27.2 weeks; mean birth weight, 1001 g) underwent HFJV for a mean of 44 (range, 8 to 70) hours during the first 3 days of life. All infants were followed with serial neurosonograms at least weekly until 6 to 8 weeks of age and every 2 to 4 weeks thereafter until discharge. To assess the cumulative effects of hypotension, acidosis, hypoxemia, and hypocarbia during the first 3 days of life on the development of PVL, we developed a quantitative assessment in which we assigned threshold levels at particular critical values of these parameters (such as a mean PaCO2 of 20 mm Hg) and calculated an area above the curve between longitudinally connected values of these parameters and the threshold levels. RESULTS: Nine of the 67 infants died before 21 days of life. Of the 58 who survived beyond 21 days, large CPVL (> 5 mm in size) developed in 18 infants. Infants with cysts were similar in birth weight, gestational age, and virtually all other antepartum, intrapartum, and postpartum parameters compared with the 40 neonates in whom CPVL did not develop. However, infants with CPVL were significantly more likely to have moderate or severe periventricular echodensities preceding development of CPVL and periventricular echodensities that persisted for a longer period. We did not find an effect of hypotension, acidosis, or hypoxemia on the development of CPVL. There were no differences in the mean PaCO2, the absolute low PaCO2 values, the ranges of low PaCO2 between groups, or area above the curve measurements at threshold levels of 15 and 20 mm Hg, respectively. However, logistic regression analysis revealed that infants with CPVL were independently significantly more likely to have greater cumulative hypocarbia below a threshold level of 25 mm Hg during the first day of life (odds ratio, 5.43; 95% confidence interval, 1.33 to 22.2). CONCLUSIONS: Hypocarbia produced by treatment with HFJV during the first 3 days of life is associated with the subsequent development of CPVL. The mechanisms for the development of CPVL among premature infants treated with HFJV need to be established.

Carbon Dioxide↗
PubMed1996

High-frequency jet ventilation in the early management of respiratory distress syndrome is associated with a greater risk for adverse outcomes.

OBJECTIVE: The objective of this investigation was to determine if high-frequency jet ventilation (HFJV) used early in the treatment of premature infants with respiratory distress syndrome was effective in reducing pulmonary morbidity without increasing the occurrence of adverse neurologic outcomes. STUDY DESIGN: A total of 73 premature infants who met the inclusion criteria (gestational age of less than 33 weeks, birth weight of more than 500 g, age of less than 24 hours, need for assisted ventilation with peak inspiratory pressure of more than 16 and FIO2 more than 0.30, and roentgenographic evidence of respiratory distress syndrome) were randomized to either conventional (n = 36) or to high-frequency jet (n = 37) ventilation. Our goals were to maintain the infants on the assigned ventilator for at least 7 days unless they could either be extubated or meet crossover criteria. Univariate analyses were initially used to compare the two groups. Stepwise logistic regression was subsequently used to assess whether various factors independently influenced adverse outcomes. RESULTS: The two groups of infants were similar in all obstetrical, perinatal, and neonatal demographic characteristics. The mean birth weight and gestational age in the conventional group were 930 g and 26.6 weeks and in the HFJV group, 961 g and 26.9 weeks. The infants were randomized at similar ages (7.1 and 7.3 hours of life, respectively). Their prerandomization ventilator settings and arterial blood gases were nearly identical. There were no differences in pulmonary outcomes (occurrence of air leaks, need for oxygen or ventilation at 36 weeks postconception), and there were no differences in the mean number of days oxygen was required, number of days ventilated, or length of hospital stay. Infants ventilated with HFJV were significantly more likely to develop cystic periventricular leukomalacia (10 vs 2, P = .022) or to have a poor outcome (grade IV hemorrhage, cystic periventricular leukomalacia, or death) (17 vs 7, P = .016). Logistic regression analysis revealed HFJV to be a significant independent predictor of both cystic periventricular leukomalacia and a poor outcome. The presence of hypocarbia was not an independently significant predictor of adverse outcomes. CONCLUSIONS: With the HFJV treatment strategy that we used, use of the high-frequency jet ventilator in the early management of premature infants with respiratory distress syndrome resulted in significantly more adverse outcomes than in those treated with conventional mechanical ventilation.

Blood Pressure↗
PubMed1995

Laparoscopic gray-scale and color Doppler US: preliminary animal and clinical studies.

PURPOSE: To evaluate a semiflexible ultrasound (US) transducer inserted through a laparoscopic port to image abdominal structures. MATERIALS AND METHODS: Laparoscopic US with a 9.6-mm-diameter, 5.0-7.5-MHz semiflexible transducer with gray-scale, color, and spectral Doppler capabilities was performed in three miniature swine and in 25 patients with a variety of abdominal abnormalities. RESULTS: This miniature US probe was used to locate normal structures such as blood vessels, allowing the surgeon to decide the best approach for dissection. Color and spectral Doppler US proved especially useful in differentiating vascular from nonvascular structures. The presence or absence of stones in the gallbladder and common bile duct was readily determined. It was possible to detect masses and to provide guidance for their aspiration or biopsy within abdominal organs. In 10 cases (40%), laparoscopic US helped the surgeon make the decision for clinical management and altered the surgical procedures. CONCLUSION: Laparoscopic US was useful in assisting laparoscopic evaluation of abnormalities in the abdomen.

Abdomen↗
PubMed1995

Normal renal artery spectral Doppler waveform: a closer look.

PURPOSE: To characterize the spectral Doppler tracing of the normal renal artery. MATERIALS AND METHODS: Doppler tracings were obtained from a phantom of a vessel with variable compliance and from the kidneys of 15 healthy volunteers. RESULTS: In the phantom, vascular compliance had the following effects on systolic flow velocity patterns: low compliance, little change in the sharp appearance of the systolic component of the transmitted pulse; mildly increased compliance, down-stream dampening of early systolic acceleration (ESA) with the appearance of a sharp early systolic transmitted peak and of a more rounded late systolic compliance peak; high compliance, delayed and diminished transmitted peak that eventually disappeared within the enlarging down-stream compliance peak. Healthy subjects with compliant vessels had greater ESA and more frequently visualized early systolic peaks in the renal hilum than in the renal sinus. CONCLUSION: Absence of a discrete early systolic peak is a normal finding in young patients, especially in the more distal interlobar arteries. Loss of the early systolic peak may be explained on the basis of vascular compliance.

Acceleration↗
PubMed1995

Parenchymal enhancement and tumor visualization using a new sonographic contrast agent.

The purpose of this study was to assess the ability of a sonographic contrast agent to increase parenchymal echogenicity and improve tumor visibility. The agent is an emulsion that changes at body temperature from nonechogenic submicrometer liquid droplets to echogenic 1 to 5 microns microbubbles, capable of transversing the pulmonary and capillary circulations. Peripheral venous injections (dosages of 0.05 to 0.8 ml/kg) were administered to five woodchucks (three with multiple hepatomas), 12 rabbits (with renal VX-2 tumors), and four dogs. Ultrasonograms were acquired from kidney, liver, tumors (including tumor vessels) and normal vessels. Uptake and washout curves were generated via videodensitometry. Finally, Doppler shifts from a cuff transducer around the celiac trunk were analyzed to provide an in vivo dose-response curve. Vascular enhancement, including hepatoma and VX-2 tumor vessels, was seen for 2 to 3 min. Maximum enhancement was 18.7 dB for a 0.6 ml/kg dose. Enhancement of normal liver and kidney parenchyma was observed in all three species for up to 20 min. Small hepatomas became more echogenic centrally, but larger tumors showed no increase in central echogenicity. In conclusion, improved tumor visibility and parenchymal enhancement was demonstrated in animals.

Animals↗
PubMed1994

Electroencephalographic, neuroradiologic, and neurodevelopmental studies in infants with subclavian steal during ECMO.

Color Doppler imaging revealed a subclavian steal--retrograde flow in the right vertebral artery which shunted blood from the brain's posterior circulation to the right arm via the subclavian artery--in 17 of 54 infants (31%) during extracorporeal membrane oxygenation (ECMO); right vertebral artery flow returned to antegrade after ECMO and removal of the right common carotid arterial cannula. When subjects with and without a subclavian steal were compared, there were no statistically significant differences in mortality; in the results of neonatal electroencephalograms, cranial ultrasound studies, or computed tomography studies; or in early neurological development. Blood flow patterns and peak systolic velocities in the circle of Willis, middle cerebral arteries, internal carotid arteries, and basilar artery were similar in both groups during ECMO; blood flow velocity in the middle cerebral arteries was slightly but significantly lower on the right than the left in both groups. Our results indicate that increased flow in the left vertebral artery adequately compensated for the effect of a subclavian steal on the basilar and cerebral circulation. The moderate to marked neonatal electroencephalographic abnormalities commonly occurring during ECMO and the approximately 20% incidence of neurodevelopmental deficits among ECMO survivors remain largely unexplained.

Blood Flow Velocity↗
PubMed1994

Right common carotid artery reconstruction after extracorporeal membrane oxygenation: vascular imaging, cerebral circulation, electroencephalographic, and neurodevelopmental correlates to recovery.

OBJECTIVE: Right common carotid artery (RCCA) ligation after extracorporeal membrane oxygenation by venoarterial bypass may contribute to lateralized cerebral injury. Reconstruction of this artery after extracorporeal membrane oxygenation has proved feasible but has not been evaluated for neurologic outcome in any substantial series of infants. METHODS: We evaluated RCCA reconstruction in 47 infants treated with ECMO and compared their cerebrovascular and neuroanatomic imaging findings, electroencephalograms, and developmental outcomes with those of 93 infants who had no reconstruction. SUMMARY RESULTS: Color Doppler blood flow imaging revealed that carotid artery patency was usually obtained after RCCA reconstruction. Right internal carotid and bilateral anterior and middle cerebral arterial blood flow velocities were generally higher, and were more symmetrically distributed in infants with reconstructed RCCA. Electroencephalography did not disclose an increased risk of deterioration or marked abnormalities in infants after reconstruction, nor were neuroimaging findings consistent with an increased number of either focal or generalized abnormalities. Neurodevelopmental follow-up revealed no differences in the incidence of delays between those with a reconstructed RCCA and those with a ligated RCCA during the first year of life. CONCLUSIONS: Reconstruction of the RCCA after extracorporeal membrane oxygenation may facilitate normal distribution of cerebral blood flow through the circle of Willis, and may augment both left and right middle cerebral artery blood flow immediately after decannulation. The long-term consequences of either ligation or reconstruction of the RCCA will require careful scrutiny, however, before either course is recommended routinely.

Blood Flow Velocity↗
PubMed1994

US-assisted bronchoscopy with use of miniature transducer-containing catheters.

PURPOSE: To demonstrate the value of ultrasound (US) guidance during flexible bronchoscopic procedures in a series of patients with known or suspected pulmonary neoplasms. MATERIALS AND METHODS: US-guided bronchoscopy was carried out as an adjunct to conventional bronchoscopy for the diagnosis of mediastinal, hilar, or parenchymal neoplasms in 25 patients with masses previously detected with chest radiography or computed tomography. Miniature transducer-containing catheters were inserted through the biopsy port of the flexible bronchoscope, and cross-sectional real-time US scans of tumors, lymph nodes, and blood vessels were obtained. RESULTS: Among six cases of peripheral masses and 19 cases of central masses, additional information was provided in 18 cases (72%). This information was used to choose the optimal site for transmural biopsy. CONCLUSION: These preliminary results suggest that this US procedure may become an important diagnostic tool during bronchoscopy, due to the ability to identify structures beyond the lumen of the tracheobronchial tree.

Adult↗
PubMed1994

Artifacts in ultrasonic contrast agent studies.

Intravenously injected ultrasonic contrast agents making use of encapsulated gas microbubbles have excellent clinical potential for both color and spectral Doppler studies. However, a number of artifacts are associated with sonographic contrast agent measurements. Three artifacts were identified: (1) color "blooming," (2) increased maximum Doppler shift, and (3) spectral "bubble noise." Experiments have been conducted with Albunex and Levovist. These agents were injected into rabbits and humans to allow the cause of the artifacts to be established. Color blooming occurs soon after the bolus injection and is seen as gray scale pixels changing to color display. This is caused by the increase in flow signal strength. The apparent increase in the maximum Doppler shift frequency is due to the limited dynamic range of the spectral display. Only signals above a certain threshold are visible. As the Doppler signal power is enhanced, the highest frequency visible also increases. Finally, very large excursions can sometimes be seen in the spectral display (bubble noise). These might be due to either the breakdown of microbubbles or individual very large bubbles. The color blooming and bubble noise artifacts are easily identifiable and will not influence diagnostic management. The increase in peak Doppler shifts is more troublesome as it prevents comparison of spectral parameters obtained before and after injection of contrast agent.

Albumins↗
PubMed1994

Influence of biological response modifiers: measurement of tumor blood flow and temperature.

Human recombinant interferon-alpha-2b (IFN) is known to inhibit growth of both normal and tumor cells and to stimulate immune effector cell function. We have previously shown that IFN and other biological response modifiers augment accumulation of radiolabeled antibodies in tumors. This investigation demonstrates that 30 min post i.m. administration of IFN significantly (p < 0.01) enhances tumor perfusion in tumor-bearing mice and persists for a much longer time than in normal tissue, which, in part, may contribute to the enhanced tumor uptake of radiolabeled monoclonal antibodies within 1.5 h of their administration. Histological examinations of tumors obtained from animals receiving IFN 72 h previously did not show changes in inflammatory cells. Our investigation shows that laser Doppler flowmetry and color Doppler imaging can provide an excellent means of measuring tumor perfusion changes in small living animals where radioactive tracers cannot be used.

Animals↗
PubMed1994

Internal abdominal hernia: diagnosis with ultrasonography.

The imaging findings associated with internal abdominal hernia have been reported for plain radiography, barium studies, arteriography and computed tomography. The authors present a case in which the ultrasonographic findings indicated left paraduodenal hernia. In the investigation of an abdominal mass, the presence of changing cystic or tubular internal components and a surrounding membrane should arouse suspicion of an internal hernia.

Aged↗
PubMed1993

Sonographically guided laparoscopy and mediastinoscopy using miniature catheter-based transducers.

Miniature ultrasound transducers (12.5 MHz) housed in 9 Fr catheters were passed through a laparoscope or mediastinoscope to image a variety of normal and abnormal structures within the peritoneal cavity and mediastinum in 20 patients. These transducers made it possible to visualize the gallbladder and bile ducts and evaluate for the presence of stones, to detect masses and provide guidance for their aspiration or biopsy, and to image the internal structures of the ovary and fallopian tube. In addition, these miniature transducers were used to locate such normal vital structures as blood vessels, thereby allowing the surgeon to decide on the best approach for dissection during mediastinoscopy. During conventional surgery, the surgeon or gynecologist can palpate an area of abnormality not directly visualized. However, during laparoscopy and mediastinoscopy direct palpation is not possible. Therefore, it is important to find another method to determine what structures lie beneath the visualized surface. These miniature ultrasound transducers appear to offer a means for making such determinations.

Adult↗
PubMed1993

Galactose-based intravenous sonographic contrast agent: experimental studies.

A galactose-based sonographic contrast agent, which produces stable microbubbles capable of traversing the cardiopulmonary circulation, was used to enhance Doppler signals in blood vessels of varying size after intravenous injection. A series of experiments using dogs, rabbits, and woodchucks was conducted to establish the ability of the agent to enhance the reflectivity of normal tissue, tumor tissue, and blood. Although no enhancement was perceptible in tissue on the sonogram, significant enhancement of color and spectral Doppler signals was demonstrated in a variety of vessels. These included the aorta, vena cava, and portal vein as well as such small vessels as those of the retina of the eye, renal cortex, liver parenchyma, and gallbladder wall. Both spectral and color Doppler enhancement was shown in naturally occurring woodchuck hepatomas. Peak Doppler signal enhancement after bolus injection was approximately 10 dB with a dose of 0.01 ml/kg. Recirculation of the agent provided enhancement after intravenous bolus injection for more than 3 min. With a steady intravenous infusion of 0.2 ml/min/kg, Doppler signal enhancement of about 14 dB was maintained continuously for more than 5 min. The results of these animal experiments, in particular in small vessels and with recirculation after intravenous injection, suggest excellent potential for future clinical applications.

Angiography↗
PubMed1992

Right common carotid artery reconstruction in neonates after extracorporeal membrane oxygenation: color Doppler imaging.

Thirty-three neonates treated for reversible respiratory failure underwent reconstruction of their previously ligated right common carotid arteries (RCCAs) immediately after extracorporeal membrane oxygenation (ECMO). Cerebral color Doppler imaging, performed during and repeatedly after ECMO, revealed antegrade flow in the right internal carotid artery (ICA) in all neonates within 6 days after successful RCCA reconstruction. Mean ICA velocity was significantly less in the right artery compared with the left during ECMO and within 1 hour of reconstruction, but there was no difference after 12 hours. In neonates with successful RCCA reconstruction, the flow in the proximal right anterior cerebral artery was antegrade in only 4% of examinations during ECMO but became antegrade in 94% after 6 days. Retrograde flow in the right posterior communicating artery persisted in 50% of examinations performed 1 day after reconstruction. ICA flow become antegrade with symmetric velocities shortly after successful RCCA reconstruction. Collateral flow persists longer but decreases rapidly.

Blood Flow Velocity↗