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Biomedical subjects

M D Smith

Publications and source records attributed to M D Smith.

At least 361 records · Page 20Linked to original sources
PubMed1992

Postoperative cerebrospinal-fluid fistula associated with erosion of the dura. Findings after anterior resection of ossification of the posterior longitudinal ligament in the cervical spine.

Of twenty-two patients who had had anterior decompression of the spinal canal for ossification of the posterior longitudinal ligament and cervical myelopathy, seven had absence of the dura adjacent to the ossified part of the ligament. The spinal cord and nerve-roots were visible through this defect. Although the arachnoid membrane appeared to be intact and watertight in most patients, a cerebrospinal-fluid fistula developed postoperatively in five, and three had a second operation to repair the defect in the dura. On the basis of this experience, we recommend use of autogenous muscle or fascial dural patches, immediate lumbar subarachnoid shunting, and modification of the usual postoperative regimen, such as limitation of mechanical pulmonary ventilation to the shortest time that is safely possible and use of anti-emetic and antitussive medications to protect the remaining coverings of the spinal cord when the dura is found to be absent adjacent to an ossified portion of the posterior longitudinal ligament in the cervical spine.

Adult↗
PubMed1991

Midventricular obstruction associated with chronic systemic hypertension and severe left ventricular hypertrophy.

Midventricular obstruction is an uncommon finding previously defined by catheterization and angiographic techniques in patients with hypertrophic cardiomyopathy. This study describes the clinical and echocardiographic findings of 10 consecutive patients (mean age 73 years) with severe concentric left ventricular (LV) hypertrophy and the unusual finding of a dynamic systolic obstruction located in the midportion of the left ventricle. All patients were known to have chronic hypertension, and none had a history or family history of hypertrophic cardiomyopathy. In each case, a well-defined, high velocity, turbulent jet was identified by Doppler color flow imaging and subsequently confirmed with conventional Doppler techniques. Septal and posterior wall thickness averaged 1.67 and 1.57 cm, respectively. Mean LV mass index was 199 g/m2 and ejection fraction averaged 78%. Peak systolic velocity obtained by continuous-wave Doppler averaged 2.7 m/s and appeared as either a "late-peaking" or a "spike and dome" configuration. Seven of 10 patients gave a history of syncope or severe presyncope at the time of echocardiographic examination. At a mean follow-up of 1 year, syncope or presyncope had resolved in 5 patients in whom medication was adjusted based on the ultrasound study, but persisted in 2 patients in whom diuretic therapy was continued. It is concluded that obstruction to systolic flow can occur at the mid-LV level in some patients with severe concentric LV hypertrophy and avoidance of medication known to lower LV volume may relieve symptoms of transient inadequate cardiac output.

Aged↗
PubMed1991

Gene expression in Deinococcus radiodurans.

We previously reported that the Escherichia coli drug-resistance determinants aphA (kanamycin-resistance) and cat (chloramphenicol-resistance) could be introduced to Deinococcus radiodurans by transformation methods that produce duplication insertion. However, both determinants appeared to require dramatic chromosomal amplification for expression of resistance. Additional studies described here, confirming this requirement for extensive amplification, led us to the use of promoter-probe plasmids in which the E. coli promoter has been deleted, leaving only coding sequences for the marker gene. We find that the insertion of D. radiodurans sequences immediately upstream from the promoterless drug-resistance determinant produces drug-resistant transformants without significant chromosomal amplification. Furthermore, a series of stable E. coli-D. radiodurans shuttle plasmids was devised by inserting fragments of D. radiodurans plasmid pUE10 in an E. coli plasmid directly upstream from a promoterless cat gene. These constructions replicated in D. radiodurans by virtue of the pUE10 replicon and expressed the cat determinant because of D. radiodurans promoter sequences in the pUE10 fragment. Of three such constructions, none expressed the cat gene in E. coli. Similar results were obtained using a promoterless tet gene. Translational fusions were made between D. radiodurans genes and E. coli 5'-truncated lacZ. Three fusions that produced high levels of beta Gal in D. radiodurans were introduced into E. coli, but beta Gal was produced in only one. The results demonstrate that the E. coli genes cat, tet and lacZ can be efficiently expressed in D. radiodurans if a D. radiodurans promoter is provided, and that D. radiodurans promoters often do not function as promoters in E. coli.

Cloning, Molecular↗
PubMed1991

Value and limitations of Doppler pressure half-time in quantifying mitral stenosis: a comparison with micromanometer catheter recordings.

The purpose of this study was to compare the Doppler and catheterization pressure half-time methods of estimating mitral valve area with valve areas obtained by the Gorlin equation in a group of patients with clinically significant mitral stenosis. Data were analyzed from 67 consecutive patients who were undergoing continuous-wave Doppler examination and catheterization with micromanometer catheters. Doppler pressure half-time was calculated as the interval between peak transmitral velocity and velocity divided by the square root of 2, as measured from the outer border of the spectral envelope. Doppler mitral valve area (MVA) was obtained with the equation: MVA = 220 divided by pressure half-time. For catheterization data, the pressure half-time was measured directly from simultaneously recorded left ventricular and left atrial pressure (18 patients) or pulmonary capillary wedge pressure (49 patients). The catheterization half-time was taken as the time required for the peak pressure gradient to fall to one half of the initial value. Calculations of the mitral valve area at catheterization were obtained by the Gorlin equation with pressure gradient and cardiac output determinations. Mitral valve area as determined by the Gorlin equation for all cases ranged from 0.4 to 2.0 (mean = 1.03 +/- 0.37) cm2. Linear regression analysis that compared cardiac catheterization and Doppler half-times yielded r = 0.68. For the subgroup of patients with sinus rhythm, the correlation improved to r = 0.76.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Fibrillation↗
PubMed1991

Fusion of the upper cervical spine in children and adolescents. An analysis of 17 patients.

A retrospective review of 17 immature patients who underwent posterior spinal fusion of C1-C2 or C1-C3 was performed to establish the efficacy of the procedure, to determine the incidence of complications, and to identify those at high risk for complications. All had radiographic C1-C2 instability or dislocation. Etiologies included os odontoideum, fixed rotatory subluxation, atlantoaxial subluxation, type II dens fracture nonunion, and nonunion of a Hangman's fracture. Before surgery, 10 patients were neurologically intact, and seven had neurologic findings. Associated diagnosis included Down's syndrome in three and Ehler-Danhlos in one. Follow-up averaged 25 months. One neurologically intact patient had a C2 radiculopathy that resolved by 1 year. Three patients with Down's syndrome had complications: one with a preoperative Brown-Sequard syndrome had transient worsening in the immediate postoperative period, one with a preoperative myelopathy developed a late recurrence of a severe myelopathy that required odontectomy, and another sustained an intraoperative spinal cord contusion followed by postoperative quadriplegia and death due to respiratory failure. Of seven reporting neurologic symptoms before surgery, two had residual deficit in the late postoperative period. These two represented preventable technical errors. There were two nonunions, one of which required occiput to C2 fusion. In general, posterior spinal fusion of the upper cervical spine was found to be a reliable, safe, and predictable procedure, but extra caution should be employed when considering arthrodesis in patients with ongoing spinal cord compression, fixed dislocations, and inherited ligamentous laxity.

Adolescent↗
PubMed1991

Complications of fusion to the upper cervical spine.

Forty-seven operations for posterior fusion of the upper cervical spine were reviewed for complications. Alarmingly, only 11 patients had an entirely uncomplicated course. Most complications were minor, but there were four nonunions, one requiring reoperation. Although seven patients had increased neurologic deficits after surgery, only one was permanent. There was one death due to technical error. Patients with significant instability, myelopathy, prior failed fusions, or unreducible dislocations are at high risk for perioperative neurologic complications.

Adult↗
PubMed1991

Heterozygosity and instability of amplified chromosomal insertions in the radioresistant bacterium Deinococcus radiodurans.

Natural transformation, duplication insertion, and plasmid transformation in Deinococcus radiodurans, a bacterium that contains 4 to 10 chromosomes per cell, were studied. Duplication insertions were often heterozygous, with some chromosomes containing highly amplified insertions and others containing no insertions. Large amplified regions were apparently deleted by intrachromosomal recombination, generating as by-products extrachromosomal circles consisting of multiple tandem repeats of the amplified sequence. The circles were of heterogenous integer sizes, containing as many as 10 or more amplification units. Two strains that are defective in natural transformation and sensitive to DNA-damaging agents were further characterized. Both strains were defective in duplication insertion. While on strain was normal for plasmid transformation, the other was totally defective in this regard, suggesting that plasmid transfer in D. radiodurans may require recombinational functions.

Chromosomes, Bacterial↗
PubMed1991

Regurgitant jet size by transesophageal compared with transthoracic Doppler color flow imaging.

Combined echocardiography and Doppler color flow mapping from transthoracic imaging windows has become the standard method for the noninvasive assessment of valvular regurgitation. This study compared regurgitant jet areas by Doppler color flow imaging derived from the newer transesophageal approach with measurements obtained from conventional transthoracic apical views. Maximal regurgitant jet area determinations and an overall visual estimate of lesion severity were obtained from 42 patients who underwent color flow examination by both techniques. Seventy-three regurgitant lesions were visualized by transesophageal flow imaging: 34 mitral, 22 aortic, and 17 tricuspid jets. Transthoracic studies in the same patients revealed fewer regurgitant lesions for each valve; 20 mitral, 16 aortic, and 12 tricuspid (p = 0.0009). A comparison of maximal jet areas determined by transesophageal and transthoracic studies showed a good overall correlation (r = 0.85, SEE = 2.8 cm2) and a systematic overestimation by the transesophageal technique (TEE = 0.96 TTX + 2.7). For the subgroup with mitral insufficiency, valve lesions visualized by both techniques were larger by the transesophageal approach (n = 18, 6.0 versus 3.6 cm2, p = 0.008). Semiquantitative visual grading of individual valve lesions by two independent observers revealed a higher grade of regurgitation with more jets classified as mild (38 versus 25), moderate (18 versus 13), and severe (17 versus 10) by esophageal imaging than by transthoracic imaging. Thus, transesophageal color flow mapping techniques yield a higher prevalence of valvular regurgitation than do transthoracic techniques in the same patients. Jet area and the overall estimate of regurgitant lesion severity were also greater by transesophageal color Doppler imaging compared with standard transthoracic imaging.(ABSTRACT TRUNCATED AT 250 WORDS)

Echocardiography, Doppler↗
PubMed1991

Do gamma delta T cells play an important role in autoimmune disease?

A T cell subpopulation using an alternative receptor heterodimer (gamma delta T cells) contributes 0.5-10% to the T cell population in the normal peripheral blood. One subset of gamma delta T cells (V gamma 9+/V delta 2+/ C gamma 1) preferentially recognizes mycobacterial antigens, which are the triggering antigens in the rat adjuvant arthritis (AA), an animal model with some similarities with rheumatoid arthritis (RA). Here we summarize data on the prevalence of gamma delta T cells in peripheral blood, synovial fluid and synovial membranes of RA patients which show that gamma delta T cells, in particular the subset reactive with mycobacterial antigens in normal individuals, are rare in all studied compartments. Furthermore, there was no enrichment of gamma delta T cells in the peripheral blood of patients with ankylosing spondylitis or systemic lupus erythematosus, autoimmune diseases with involvement of the joints. In the AA model depletion of the "conventional" alpha beta T cells completely prevented the induction of the disease and very effectively improved ongoing arthritis even though substantial numbers of gamma delta T cells were present in these animals. Taken together, our data do not support the notion of a significant contribution of gamma delta T cells to chronic joint inflammation in the autoimmune diseases studied or in adjuvant arthritis.

Animals↗
PubMed1991

Thymic squamous cell carcinoma.

In the case described, a 43-year-old man had an asymptomatic mass involving the right hilar and superior mediastinum. At surgery, the tumor was found to have invaded the right middle lobe of the lung and the pericardium. The mass was found to be a thymic squamous cell carcinoma, a rare tumor. Two serum tumor markers--lipid-associated sialic acid and squamous cell carcinoma antigen--were elevated. The patient underwent postoperative radiation therapy and has responded favorably to treatment. He had no clinical evidence of metastasis or recurrence as of 43 months postoperatively.

Adult↗
PubMed1991

Doppler echocardiographic evaluation of diastolic dysfunction.

Recently, considerable effort has been directed toward the application of Doppler methods for detecting diastolic dysfunction. Recordings of transmitral filling velocity as obtained from pulsed-wave Doppler have been extensively investigated as a noninvasive method for determining left ventricular diastolic filling properties. Although Doppler parameters appear to reflect volumetric transmitral flow, close correlations with invasive descriptors of diastolic performance have not been found. Furthermore, Doppler transmitral velocities are sensitive to changes in ventricular preload, afterload, and heart rate. However, at least two distinct Doppler spectral patterns have been identified that are associated with impaired ventricular relaxation and restrictive physiology. Thus, Doppler recordings have proven to be of value in identifying the presence and type of diastolic dysfunction, and in the future they may be helpful in following the response to therapeutic interventions. The purpose of this paper is to review the available information relating Doppler transmitral recordings with catheterization and clinical descriptors of diastolic function. Additionally, the aim is to provide an understanding of the value and limitations of these noninvasive measurements in identifying and treating patients with diastolic abnormalities.

Amyloidosis↗
PubMed1991

Upper-airway obstruction after multilevel cervical corpectomy for myelopathy.

We reviewed the cases of seven patients who had had obstruction of the upper airway immediately after an anterior procedure on the cervical spine and had required reintubation. All patients had had moderate or severe myelopathy preoperatively (average, 3.6 on the Nurick scale), and all had had a multilevel anterior cervical corpectomy for decompression followed by arthrodesis. The early compromise of the upper airway was believed to be due to edema rather than to the formation of a hematoma. Five patients had no sequelae, but two died of complications related to the obstruction. Risk factors common to these patients included moderate or severe myelopathy and multilevel corpectomy. Six patients had a history of heavy smoking and one, of asthma. We believe that extra caution should be used in the postoperative management of the airways when multilevel corpectomy is performed in patients who have these pre-existing conditions.

Aged↗