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Biomedical subjects

D Larson

Publications and source records attributed to D Larson.

At least 91 records · Page 5Linked to original sources
PubMed1983

The effect of variations of pulsed Doppler sampling site on calculation of cardiac output: an experimental study in open-chest dogs.

We measured aortic flow by two-dimensional Doppler echocardiography in an open-chest dog model to examine how variations in Doppler sample volume length and position influence aortic hemodynamic flow calculations. Fourteen dogs underwent right-heart bypass, in which venous return from the venae cavae drained by gravity to a reservoir. A variable-speed roller pump returned the blood to the pulmonary artery, fixing left-sided cardiac input and output. Echo Doppler measurements were performed using a 3.5 MHz transducer placed directly on the aortic arch to determine internal aortic cross-sectional area. The transducer was then directed to image the aortic arch for Doppler velocity measurements and the various sampling sites were investigated. Doppler cardiac output could then be determined for each of the various sample volumes over a range of known roller pump settings. Doppler velocity was analyzed using fast Fourier transform spectral analysis. Mean velocity over the cardiac cycle was obtained by planimetry of the area under the Doppler velocity curve with a minicomputer. Doppler-derived determinations of cardiac output achieved a correlation of r = 0.98-0.99 to values obtained by the roller pump over a range of cardiac outputs from 0.75-5 l/min. The standard error of the estimate was 0.21/min. In this laminar flow model, there was no difference between the predictive accuracy of any of the sampling sites over the range of roller pump flows. Our study shows that Doppler velocity measurements can be used to quantify aortic flow over a clinically useful range and that variations of sample length and position did not produce significant differences in calculated flows.

Animals↗
PubMed1983

The mitral valve orifice method for noninvasive two-dimensional echo Doppler determinations of cardiac output.

We developed and validated a mitral valve orifice method for Doppler cardiac output determination. In 15 open-chest dogs, cardiac output was controlled and measured by a roller pump interposed between the right atrium and pulmonary artery as a right-heart bypass. Left heart flows were measured in the open-chest dog model by Doppler measurements at the mitral valve orifice and compared not only to volume flow measured by the roller pump, but to electromagnetic flow meters as well. The maximum mitral valve orifice area was measured off short-axis two-dimensional echocardiographic views by planimetry. The maximal orifice was then adjusted for its diastolic variation in size by calculating a ratio of mean-to-maximal mitral valve separation on a derived M-mode echocardiogram. Flow was sampled parallel to mitral valve inflow in a four-chamber plane. The multiplication of mean flow throughout the cardiac cycle by the mean mitral valve area after correction for diastolic size variation yielded a cardiac output determination that could be compared to the roller pump measurement. Fifty-two cardiac output determinations over roller pump values of 1-5 l/min yielded a high correlation between roller pump flows and Doppler (r = 0.97 +/- 0.23 l/min). Our study shows that the mitral valve orifice provides an accurate site for Doppler cardiac output measurements.

Animals↗
PubMed1983

A longitudinal study of speech fluency in aphasia: CT correlates of recovery and persistent nonfluency.

The anatomic correlates of speech fluency were studied in 54 right-handed patients with aphasia due to stroke. Speech fluency was assessed at 1 month postonset and then monthly for 5 months. CTs obtained at 5 months postonset were used for lesion localization and volume determination. Persistent nonfluency was associated with lesions in the rolandic cortical region and underlying white matter. Recovery from nonfluency occurred in 6 of 27 patients. Lesions in these six patients were less extensive than lesions in patients with persistent nonfluency. Patients who were fluent by 1 month lacked extensive rolandic lesions.

Adult↗
PubMed1982

Computed tomography and EEG in patients without focal neurologic findings.

We studied 136 patients without focal neurologic findings by EEG and computed tomographic (CT) scanning. Six patients (4.4%) had focal CT lesions. All six had abnormal EEGs, and in four the EEG findings were focal. The initial complaint did not influence the yield of focal CT lesions. The findings suggest that neurologic examination and EEG can be used to screen for focal CT abnormalities.

Adult↗
PubMed1980

5' flanking sequence signals are required for activity of silkworm alanine tRNA genes in homologous in vitro transcription systems.

We have used homologous in vitro transcription to examine the nucleotide sequences required for activity of cloned Bombyx mori tRNA2Ala genes. We have compared the transcriptional properties of an intact gene and a truncated derivative of the same gene lacking all but 11 nucleotides of normal 5' flanking DNA, and we find that at least two regions of DNA are required for accurate transcription of tRNA2Ala genes by homologous B. mori extracts. One of these sites is retained in the truncated gene and may be within the tRNA coding sequence. Competition experiments with intact and truncated genes indicate that this site probably acts by binding a factor necessary for specificity in polymerase III-catalyzed transcription. The second required site is removed by the Hind III cleavage used to produce shortened genes and thus must be 11 nucleotides or more upstream from the transcription initiation point. Possible roles for this site are discussed.

Alanine↗
PubMed1979

The primary transcription product of a silkworm alanine tRNA gene: identification of in vitro sites of initiation, termination and processing.

A 13.5 Kb fragment of Bombyx mori DNA containing a single tRNA2Ala gene has been cloned, and transcribed in vitro with Xenopus germinal vesicle extracts. The primary transcription product of the tRNA2Ala gene has been isolated and shown to possess an unprocessed triphosphorylated 5' terminus. Products resulting from processing of this transcript have also been isolated and characterized. Complete nucleotide sequence analysis of this cloned alanine tRNA gene and its primary transcript shows that transcription initiates three nucleotides away from the mature tRNA2Ala 5' end and terminates in a U cluster 22 nucleotides beyond the last encoded 3' nucleotide of the mature species. Sequence determination of the products of in vitro maturation shows that in contrast to the tRNA processing mechanism characteristic of procaryotes, the extra 3'-nucleotides in this silkworm tRNA precursor are removed by a single endonucleolytic cleavage.

Alanine↗
PubMed1979

Early diagnosis of delayed posttraumatic intracerebral hematomas.

Nine cases of delayed posttraumatic intracerebral hematomas (DTICH) were found retrospectively among 656 patients with closed head injuries admitted to the Hennepin County Medical Center in a 12-month period. All cases had severe head injuries sustained with the head in motion. The interval from cranial injury to diagnosis of DTICH by computerized tomography (CT) varied from 8 hours to 13 days. Eight patients were comatose on admission, three had focal seizures, and three had focal findings. The diagnosis was made on repeat CT scans obtained because of the development of focal findings in four cases, lack of improvement in four cases, and general neurological deterioration in one case. Four patients had initially negative CT scans. Four demonstrated only extracerebral hematomas on initial CT scan. One patient showed intracerebral hematoma on the initial scan followed by new hematomas on repeat study. The cases presented are discussed in light of pertinent literature.

Accidents, Traffic↗
PubMed1978

Acute multiple sclerosis with contrast-enhancing plaques.

In a case of clinically fulminant multiple sclerosis (MS), contrast-enhancing lesions were visible by computerized axial tomography (CT). The patient died less than three weeks after the study, making neuropathologic correlation possible. It appears that areas of contrast enhancement correlate in acute MS with early demyelinative lesions, and enhancement is related to breakdown of the blood-brain barrier. That such a disturbance is important in the pathogenesis of demyelination in MS has been suggested by other data as well. The characteristic CT findings of MS must therefore include enhancing lesions that reflect disease activity and that may be the only CT abnormality.

Acute Disease↗
PubMed1978

Radical or modified neck dissection: a therapeutic dilemma.

Three hundred ten evaluable patients received a classic, functional, or spinal accessory-nerve-sparing neck dissection during 1970 to 1975. The functional procedure was at least equal to the classic procedure in the patients in whom it was employed. The spinal accessory-nerve-sparing operation is offered as an alternative to the classic procedure in all patients in whom the nerve is not directly invaded by cancer. If these guidelines are followed, the patient will rarely experience the pain and shoulder dysfunction that result from the loss of the trapezius muscle, while the chances of control of cancer in the neck remain optimal.

Head and Neck Neoplasms↗
PubMed1975

The endogenous reverse transcriptase activity of Gibbon ape lymphoma virus: characterization of the DNA product.

The DNA product of the endogenous reverse transcriptase reaction of Gibbon ape lymphoma virus has been analyzed and characterized. Data show that in simultaneous detection assays in which the type and/or concentration of divalent cation is varied the best yield of rapidly-sedimenting DNA was obtained from reactions containing 1.5 mM Mn2+. This yield is ten-fold better than the yield observed at the optimal Mg2+ concentration (5.0mM). Evidence is presented to show that DNA synthesized at the optimal concentration of either of these cations consists of large pieces varying in size from 4 to 12S. This DNA hybridizes efficiently to homologous viral RNA (greater than 60 percent annealing) and protects at least two-thirds of GALV 70S [32P]RNA from ribonuclease digestion. The hybrids formed with homologous viral RNA are stable as evidenced by their thermal elution patterns from hydroxylapatite columns. In contrast, DNA synthesized in reactions in which the concentration of Mn2+ or Mg2+ was greater than optimal was predominantly 4S or smaller in size and displayed a low level of hybridization (less than 10 percent) to homologous viral RNA.

Animals↗