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Biomedical subjects

M Hom

Publications and source records attributed to M Hom.

8 recordsLinked to original sources
PubMed1997

Time course of lysophosphatidylcholine release from ischemic human myocardium parallels the time course of early ischemic ventricular arrhythmia.

BACKGROUND: We determined the kinetics of the release of lysophosphatidylcholine (LPC) into the coronary sinus of patients undergoing stress tests after coronary artery bypass grafting. The kinetics were consistent with a role for this amphiphile in the pathogenesis of ischemic ventricular arrhythmia, a major cause of sudden death. METHODS: Stress testing was initiated in the operating suite by pacing at a rate of 160 beats/min for 2 min. Ischemia was then induced by clamping the bypass grafts to the anterior wall for a maximal time of 4 min. RESULTS: The pacing procedure induced a prompt but reversible increase in coronary sinus LPC concentration from a baseline of 60.9 +/- 2.5 to 83.8 +/- 5.0 mumol/l via pacing alone, and a further increase to 101.8 +/- 6.7 mumol/l when the grafts were clamped for 2 min (P < 0.01). Six minutes after the cessation of pacing, LPC concentration returned to 67.5 +/- 4.4 mumol/l. CONCLUSIONS: These results demonstrate that severe myocardial ischemia is an agonist for rapid release of LPC from the myocardium. Kinetics of this release paralleled the time-course of early onset of electrophysiologic changes in isolated myocytes and perfused heart preparations in vitro. These results indicate that LPC may have an important role in the pathogenesis of ischemic ventricular arrhythmia in patients.

Aged↗
PubMed1993

Lysophosphatidylcholine accumulation in ischemic human myocardium.

Lysophosphatidylcholine accumulates in the coronary sinus during pacing-induced myocardial ischemia in humans. This amphiphile accelerates Ca++ flux leading to cell injury in cultured cardiac myocytes, but it is not known whether lysophosphatidylcholine accumulation is injurious to human myocardium. In this study, we measured lysophosphatidylcholine in normal human myocardium obtained during cardiac surgery and exposed to ischemic conditions in vitro. Total lysophosphatidylcholine concentration (sum of lysophosphatidylcholine remaining in tissue and lysophosphatidylcholine released into the buffer) increased from 0.73 +/- 0.08 nmol/mg protein at baseline to 1.83 +/- 0.45 nmol/mg protein after 5 minutes of ischemia (p < 0.001), and was associated with evidence of cell injury (26% depletion of tissue lactate dehydrogenase). Significant lysophosphatidylcholine release into the incubation buffer (0.41 +/- 0.11 nmol/mg protein) also occurred after 5 minutes of ischemia. In contrast, there was no lysophosphatidylcholine accumulation or release and no lactate dehydrogenase depletion in oxygenated and perfused controls. Attenuation of lysophosphatidylcholine accumulation by incubation with lysophospholipase did not prevent cell injury. Lysoplasmalogen was not detected in ischemic tissue. We conclude that lysophosphatidylcholine accumulation is a marker of myocardial ischemia in humans.

Coronary Disease↗
PubMed1992

Traumatic mediastinal lymphocele mimicking other thoracic injuries: case report.

Thoracic duct injury and chylothorax are rare consequences of blunt thoracic trauma. A contained mediastinal lymph collection (ie, lymphocele) is rarer still. The article describes a case of posttraumatic mediastinal widening resulting from a high-speed motor vehicle accident. During the patient's radiologic assessment aortic rupture, paraspinal hematoma, esophageal injury, mediastinal tumor, and pseudomeningocele were sought and subsequently excluded. At this point a traumatic lymphocele was suggested, and the diagnosis was confirmed by computed tomography-guided percutaneous needle aspiration. The anatomy and physiology of the thoracic duct are reviewed.

Adult↗
PubMed1991

Evaluation of umbilical catheter and tube placement in premature infants.

Umbilical arterial and venous catheters, endotracheal tubes, and nasogastric tubes are routinely used in treating premature infants, and radiologists play a critical role in evaluating proper catheter and tube placement and recognizing potential complications. Ideally, an umbilical venous catheter should be positioned in the right atrium; an umbilical arterial catheter, between T-6 and T-10 (high position) or between L-3 and L-5 (low position); an endotracheal tube, 1.5 cm above the carina, with the infant's head in a neutral position; and a nasogastric tube, in the body of the stomach. Catheters and tubes can be malpositioned in a variety of vessels and the main stem bronchi, respectively. Complications include extraluminal placement of catheters (which can result in death), thrombi in the aorta and pulmonary artery, aortic aneurysm, subglottic stenosis, intubation granuloma, and perforation of the esophagus and stomach.

Catheterization, Peripheral↗
PubMed1991

Dynamics of adaptation for vision with a stabilized image.

The addition of a uniform increment of light to a high-contrast image that has been stabilized on the retina reveals marked perceptual nonlinearities. When the increment is small, the pattern appears in its original phase (OP), large increments produce an apparent phase reversal (APR), and intermediate increments may yield an apparently blank field or an oscillation of the apparent phase. In the present series of studies the threshold values used to produce a stable OP and APR were determined as a function of adaptation time before the application of the increment. The stabilized target had a luminance profile consisting of the difference of two Gaussians. A model of detection incorporating a multiplicative gain controlled by a filtered version of the stimulus was used to account for the occurrence of the OP and the APR and the transitory phenomena following the uniform increment. It is argued that the midpoint of the transition zone between the OP and APR, corresponding to blanking, enables us to estimate the shape of the step response function of the gain filter independently of the subsequent detection processes.

Adaptation, Ocular↗
PubMed1987

Apparent phase reversal during stabilized image fading.

A pattern with a horizontal luminance profile described by the difference of Gaussians (DOG) was viewed under conditions of retinal image stabilization. When a uniform increment was applied after the image had disappeared, the pattern reappeared, but with the reversed phase. This phenomenon of apparent phase reversal (APR) is indicative of changes in local sensitivity. It was studied as a function of the time at which the increment was applied and the space constant of the DOG pattern. It was found that the threshold increment necessary to evoke an APR was an exponential function of time. A slight dependence on the spatial dimensions of the stimulus was also demonstrated. The data were examined according to a model of spatial vision that includes a gain that is inversely proportional to a spatially and temporally filtered version of the stimulus. The data provided estimates of the time constant and the spatial extent of the gain mechanism.

Humans↗
PubMed1979

Distribution and consequences of cell suspensions following intralymphatic infusion.

The fate and consequences of intralymphatic injections of cells was investigated in dogs. The distribution of intact radiolabeled cells was determined in vivo by whole body gamma scanning. Comparison of distributions resulting from intralymphatic, subcutaneous, intradermal and intravenous routes of administration showed that the distribution and duration of radiolabel in various organs varied with the route of administration. Following intralymphatic injection, radiolabel was concentrated in first echelon lymph nodes draining the site of injection and was retained in these nodes for over 4 weeks. Histologic studies showed intense cortical and paracortical lymphopoiesis to be associated with the retention of intralymphatically injected tumor cells by first echelon lymph nodes. Serial histologic examination of lymph nodes from intralymphatically injected inbred beagles revealed that the consequent lymphopoiesis persisted for 5 weeks. In vitro evaluation of peripheral blood and lymph node lymphocyte cytotoxicity to the injected cells indicated that retention and nodal lymphopoiesis was associated with the development of direct lymphocyte cytotoxicity. The effects of concommitant tumor burden, cytotoxic drugs and ionizing radiation were also investigated and suggest that the therapeutic potential for use of the intralymphatic route has not yet been realized.

Animals↗