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Biomedical subjects

R W Martin

Publications and source records attributed to R W Martin.

At least 199 records · Page 11Linked to original sources
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High speed solution of 2nd order curves with special application to planar sections of blood vessels.

Rapid determination of the areas of planar sections through a blood vessel are required in an on-line blood flow measurement system which utilizes an intravascular ultrasonic catheter. Vessel areas are determined by: (1) using a fast algorithm to fit an ellipse to 6 data points of the vessel wall's location measured with the ultrasonic catheter; (2) computing the area of the determined ellipse. The program is implemented in a general purpose computer with a hardware floating point processor, using 3320 of 16 bit words of memory for storing variables, data, look-up tables, and computation instructions. The program executes in 3 ms, which, when combined with the other computations and timing requirements of the system, allows instantaneous flow computation every 7.3 ms. The system is fast enough to follow pulsatile blood flow. The algorithm applies in other areas which also require fast quantitative measurement; for example, in determining organ or tissue structural contours describable with a 2nd order equation.

Animals↗
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An endoscopic Doppler probe for assessing intestinal vasculature.

Flexible fiberoptic endoscopes permit the physician to inspect the mucosal surface of the upper gastrointestinal tract and colon. However, this visual inspection provides little information about the underlying vascular supply to the intestinal wall. We tested the hypothesis that a Doppler probe could be constructed small enough to pass through the biopsy channel of a fiber endoscope and be used with it while performing endoscopy. The purpose would be to determine the location of patent arteries or veins, determine the magnitude and waveforms of the velocity in them, and estimate their contribution or potential contribution to intestinal bleeding. For this purpose, a miniature catheter probe (1.8 mm O.D. and 2 m in length) and an electronic range limited pulsed Doppler unit were developed. This probe and unit were studied in a series of 13 dogs to determine efficacy of detecting arterial and venous flow and to test the safety of the device. The duodenum was surgically exposed and opened in the region of the common bile duct (CBD). Arteries and veins surrounding the CBD were studied. Particular attention was directed to arterial structures which clinically pose a risk of bleeding when performing endoscopic papillotomy, a therapeutic technique in which the papilla of Vater is cut to release bile duct stones. The results of the study revealed that the probe could indeed detect arterial and venous structures accurately. There was no evidence that the probe produced any injury to the common bile duct or pancreas by histological or serum amylase studies and the device was determined safe and suitable for clinical evaluation.

Animals↗
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An endoscopic Doppler probe: preliminary clinical evaluation.

A new pulsed Doppler catheter has been developed for use during gastrointestinal fiberendoscopy. Modern gastrointestinal endoscopy allows inspection of the wall of the entire esophagus, stomach, duodenum, and colon. Diagnosis is performed by inspecting the surface of the mucosa, biopsy, and cytology. However, it is not possible to determine the characteristics of the blood vessels of the wall beneath the mucosa with available techniques. We have developed a Doppler system which is miniature and can be passed down the biopsy channel of standard fiberendoscopes. This 8 MHz device incorporates range limiting to select the depth of interrogation by Doppler. The length of the probe is 2 m, and the diameter is 1.8 mm. This device has been tested in animal studies for efficacy and safety and is now being tested clinically in patients. The probe has been tested for two indications: the detection of the retroduodenal artery prior to endoscopic papillotomy for retained bile duct stones (90 patients); and the detection of flow in esophageal varices before and after endoscopic sclerotherapy (33 patients). Preliminary results are encouraging and suggest that this device can give information about submucosal blood vessels which cannot be detected using other methods.

Ampulla of Vater↗
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Endoscopic ultrasound probes.

Ultrasound probes are being developed as alternatives to dedicated ultrasound endoscopes. These probes have been designed to pass through the instrument channel of ordinary fiberoptic or video endoscopes. We have developed a 20-MHz mechanical linear probe for use within the upper gastrointestinal tract, pancreatic duct, biliary tree, and colon. Rotational mechanical sector scanning probes as well as phased array probes are also being developed. Ultrasound probes are best used for high resolution imaging of focal endoscopically visible lesions. Endoscopic visualization enables direction of the probe to the lesion of interest. Unlike dedicated ultrasound endoscopes, ultrasound probes do not screen large areas of tissue and do not have deep penetration. Ongoing research will help define the indications for use of these probes and should lead to further refinements in their design.

Animals↗
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The effects of applied pressure on the thickness, layers, and echogenicity of gastrointestinal wall ultrasound images.

Endoscopic ultrasound imaging of the gastrointestinal wall can be performed through intraluminal fluid or by direct transducer contact with the wall. We tested the hypothesis that the ultrasound appearance of the gastrointestinal wall is influenced by the amount of pressure applied when the transducer is in contact with the tissue. Fresh autopsy specimens from the porcine gastrointestinal tract were examined in vitro using an 8.5-MHz linear array ultrasound system. As transducer pressure against the wall was increased from 0 to 10 KPa, changes were seen on the images in wall thickness, tissue echogenicity, and the number of layers. The stomach and rectum were more resistant to compression than the esophagus, duodenum, and colon. Wall echogenicity increased with increasing degrees of applied pressure and some layers were obliterated by this pressure. The second ultrasound layer, or deep mucosa, appeared to be the most susceptible to compression. Endoscopic ultrasound imaging artifacts should be reduced by limiting the amount of pressure applied to the wall with the transducer.

Animals↗
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Changes in esophageal wall layers during motility: measurements with a new miniature ultrasound suction device.

We have developed a miniaturized ultrasound device that attaches to the gastrointestinal mucosa by suction and produces high-resolution (+/- 0.1 mm) images of the layers of the intestinal wall. The esophageal wall layers in a single sheep were measured during 20 occlusive contractions observed with simultaneous endoscopy, which revealed thickening of the inner circular muscle layer from 1.2 +/- 0.2 mm to 2.2 +/- 0.4 mm (p < 0.01), and during 20 dilations demonstrating thinning of the full thickness of the esophageal wall from 3.6 +/- 0.3 mm to 2.9 +/- 0.3 mm (p < 0.01). Safety experiments performed in two canine stomachs demonstrated no erosions or ulceration at any level of suction. Our investigations indicate that the M-mode suction ultrasound device can safely assess changes occurring in the layers of the esophageal wall during contractions and dilations and should be evaluated for the study of human intestinal motility.

Animals↗
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How positionally stable is a transesophageal echocardiographic probe? Implications for three-dimensional reconstruction.

Three-dimensional (3D) reconstruction from a single esophageal scanning position requires a stable relationship between the probe and the heart. The purpose of this study was to examine the movement of a transesophageal echocardiographic probe during 3D image acquisition. A new dual-axis multiplane probe was used that includes a miniature (6 x 6 x 9 mm) magnetic sensor in the tip. The sensor identifies the probe's 3D position and 3D orientation in space with respect to the location of a magnetic field generator placed beneath the subject. In vivo 3D scanning was performed in five anesthetized, ventilated dogs, with positional determinations acquired every 66 msec. Probe movement was estimated by computing the deviations of each x, y, and z position and orientation determination, compared with the average values during each 3D scan or cardiac cycle. Ten 3D scans were analyzed, involving 263 cardiac cycles and 2328 determinations. The range and SD of the translational movement of the transducer were 2.3 and 0.8 mm, 1.7 and 0.5 mm, and 2.4 and 0.7 mm in x, y, and z directions, respectively, during 3D scanning. Translational movement was more dominant than was rotational movement. Misregistration of three-dimensional reconstructions may be due to subtle probe movement. The ability to monitor probe movement may be helpful in optimizing 3D data sets.

Animals↗
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Segmentation of sequences of echocardiographic images using a simplified 3D active contour model with region-based external forces.

A method of segmenting echocardiography images based on three dimensional (two spatial and one time) surface was developed and tested on transcutaneous images from 38 patients and a four-dimensional (three spatial and one time) transesophageal scan of one patient. Active contour models with finite elements representing the curves in the imaging planes and finite difference description linking curves from time frame to time frame were employed. Region-based external forces were incorporated into the framework of the model and an analytical procedure for estimating the values of most of the model parameters was developed and used.

Algorithms↗
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Headaches from chemical exposures.

Headaches are a common complaint after work place or environmental exposures. A striking index case led to a literature review which uncovered only limited information. We then performed a retrospective descriptive study of 50 subjects referred to University Clinics with the complaint of headaches associated with chemical exposures at their work place. Our data suggest a different headache may exist depending on whether the chemical exposure is routine and limited versus accidental and extensive. Low level work place chemical exposures appear to cause headaches that abate soon after cessation of the exposure. A single accidental and extensive exposure may lead to patient complaints of a new headache syndrome that may last from several months to years. The characteristics associated with the onset of a new headache syndrome from accidental chemical exposures includes: 1) An acute large quantity of exposure. 2) A short latency of onset of the heralding headache. 3) A severe intensity and long duration of the heralding headache. 4) New recurring headaches that were not experienced before the acute exposure. We suggest a possible term for this high exposure syndrome i.e. Chemical Headache Exposure Syndrome (CHES).

Adult↗
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Biomechanics of the human epiglottis.

The mechanism that folds the epiglottis down over the closed larynx in the course of swallowing has been unclear. Measurements of the force needed to fold the epiglottis in cadaver specimens exceed the estimated force available from the aryepiglottic muscle. Frame-by-frame analysis of cinefluorograms reveals that deglutitional epiglottic downfolding occurs at the time of maximal elongation of the hyoepiglottic ligament. The observations lead us to propose a conical model of epiglottic downfolding which also explains the conical shape of the epiglottis usual in early infancy. The infant shape may be part of a protective partially closed entrance adaptive to suckling, while maturational widening of the opening adapts to the growing respiratory demands of increasing physical exertion.

Adult↗
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Malignant melanoma presenting as nasal obstruction.

Mucosal melanomas arising in the nasal cavity are rare tumors comprising less than 1 percent of all melanomas. Often, the common clinical symptom is nasal obstruction. Grossly, they may or may not be pigmented and frequently attain large sizes. Histologic diagnosis of these tumors may be difficult, requiring immunohistochemical or electron microscopic confirmation. Aggressive surgical management is the treatment of choice in clinical stage I disease. Subsequent surveillance for recurrence is mandatory. Markers such as 5-S-cysteinyldopa may prove useful in staging, prognosticating, and postoperative surveillance for early recurrence, but their exact role has yet to be delineated. Ultimate prognosis is poor.

Aged↗
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Hemorrhage associated with cesarean delivery: when is transfusion needed?

Our objective was to determine the incidence of blood administration after cesarean delivery and whether such transfusions are always beneficial. In this retrospective study 1610 women underwent cesarean delivery during a 2-year period and 127 of these patients had hemorrhage during or after operation. Of these subjects 103 received blood because of intraoperative hemorrhage, a reduction in the hematocrit of more than 10 points, or because the postoperative hematocrit was < 24%. These subjects were compared with the remaining women (n = 24) who met the same criteria for hemorrhage but did not receive transfusion. The maternal age, race, and parity were similar in both groups. The estimated blood loss (873 +/- 484 ml) and the preoperative hematocrit (33.4% +/- 6.4%) in the women who did not receive transfusion were not significantly different from those of patients who received packed red blood cells (854 +/- 576 ml and 30.0% +/- 5.4%, respectively). The postdelivery hematocrit was similar in both groups: 25.9% +/- 4.3% in the nontransfused group and 24.5% +/- 5.6% in the transfused group. Patients in the transfused group received a mean of 3.8 +/- 4.9 units of packed red blood cells, with a range of 1 to 40 units. The mean equilibrated (stable) hematocrit after transfusion was 28.4% +/- 5.4%, which was significantly greater than the mean equilibrated postoperative hematocrit of 22.7% +/- 4.6% in patients who did not receive transfusion (p < 0.0001). Nonetheless, the hospital stay, incidence of postoperative infection, and incidence of wound complications were similar in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
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Obstetric challenges of massive obesity complicating pregnancy.

This study examined the effects of massive maternal obesity on medical complications, mode of delivery, postpartum complications, and hospital confinement. In this retrospective case control study, women weighing > 300 pounds delivering from January 1, 1986, to November 1, 1991, were matched for age, race, parity, and height with lean parturient women (mean weight 160 +/- 21 pounds). Among massively obese women there was a greater incidence of chronic hypertension (p < 0.05) and diabetes (p < 0.05) than in the control group. Primary cesarean section was more frequent (p < 0.05), as was the postoperative complication of endometritis when obese patients were compared with lean women (p < 0.05). Cephalopelvic disproportion was the only indication for primary cesarean section, which occurred with greater frequency in the obese group. The postpartum hospital confinement was also significantly longer in the obese study group (p < 0.05). The gestation of a massively obese parturient woman is more frequently complicated by chronic hypertension and diabetes. Abdominal delivery for cephalopelvic disproportion is more likely, and this mode of birth is more often followed by endometritis, which results in longer hospital stays.

Adult↗
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Neonatal morbidity between 34 and 37 weeks' gestation.

The objective of this study was to determine the risk of significant neonatal morbidity in women with preterm labor who deliver between 34 and 37 weeks' gestation. A total of 101 women between 34 and 37 weeks' gestation with documented preterm labor met inclusion and exclusion criteria; 90 gave informed consent and were randomly assigned to receive either intravenous magnesium tocolysis (treatment group) or conservative management with hydration, sedation, and observation (control group). Of the 90 women entering the study (45 in the treatment group and 45 in the control group), 2 discontinued tocolytic therapy because of gastrointestinal side effects. The gestational age on admission, cervical dilatation at diagnosis of preterm labor, interval to delivery, and birth weight were not significantly different between the treatment and control groups. There were no serious neonatal complications. In each group, three women had transient tachypnea and one had respiratory distress syndrome. We conclude that neonatal morbidity after delivery between 34 and 37 weeks' gestation is unchanged whether or not attempts to arrest labor are unsuccessful. The extra expense and maternal risk of tocolysis are not justified by beneficial results in the infant.

Adult↗
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Intrapartum hydramnios at term and perinatal outcome.

The objective of this study was to compare the intrapartum outcome among laboring patients with hydramnios (amniotic fluid index > or = 24.0 cm) versus those with adequate fluid (amniotic fluid index > 5.0 and < 24.0 cm). Prospectively, during a 2-year period, 341 patients in early labor underwent four-quadrant measurement of amniotic fluid volume. Forty-two patients had intrapartum oligohydramnios (amniotic fluid index < or = 5.0 cm) and were excluded from further analysis. The study compares the outcome between 277 subjects with adequate fluid and 22 with hydramnios. The intrapartum amniotic fluid index, birth weight, incidence of macrosomia (birth weight > or = 4000 gm), shoulder dystocia, cesarean section for fetal distress or cephalopelvic disproportion, Apgar score, and neonatal malformations were noted in each of the 299 subjects. Umbilical arterial blood gas was analyzed in 189 patients. In this study, 22 women with hydramnios had a significantly higher risk of delivering a macrosomic fetus than the 277 patients with a normal index (36.3% vs 13.7%; p = 0.01). There was no significant difference in the incidence of shoulder dystocia, cesarean section for cephalopelvic disproportion, or fetal distress, Apgar scores < 7 at 1 and 5 minutes, fetal acidosis, or neonatal anomalies. We conclude that hydramnios during the intrapartum period in patients at term is significantly associated with delivery of a macrosomic fetus, but not with delivery of a compromised neonate.

Adult↗
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Comparison of intra-amniotic (15S)-15-methyl-PGF2 alpha and intravaginal prostaglandin E2 for second-trimester uterine evacuation.

OBJECTIVE: To compare the efficacy, safety, and side effects of intra-amniotic (15S)-15-methyl prostaglandin F2 alpha (15-M-PGF2 alpha) and intravaginal prostaglandin E2 (PGE2) for midtrimester uterine evacuation. STUDY DESIGN: Ninety-three patients underwent therapeutic midtrimester pregnancy termination by the use of laminaria placement and intra-amniotic injection of 15-M-PGF2 alpha. A matched control group underwent uterine evacuation by laminaria placement and insertion of PGE2 intravaginal suppositories. The main outcomes studied were time to delivery, side effects, and complications. RESULTS: The 15-M-PGF2 alpha group had a shorter time to delivery (12.3 +/- 6.4 hours) compared with the PGE2 group (16.2 +/- 6.6 hours, p < 0.0001). The evacuation rate over time was significantly greater in the 15-M-PGF2 alpha group (p = 0.001). The PGE2 group had a significantly higher incidence of side effects. CONCLUSIONS: The use of intra-amniotic 15-M-PGF2 alpha for therapeutic second-trimester pregnancy termination is safe and is associated with a more rapid evacuation of the uterus and fewer side effects than intravaginal PGF2 suppositories.

Abortifacient Agents, Nonsteroidal↗