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Biomedical subjects

M B Smith

Publications and source records attributed to M B Smith.

At least 73 records · Page 4Linked to original sources
PubMed1997

Augmented sympathetic tone alters muscle metabolism with exercise: lack of evidence for functional sympatholysis.

It is unclear whether sympathetic tone opposes dilator influences in exercising skeletal muscle. We examined high levels of sympathetic tone, evoked by lower body negative pressure (LBNP, -60 mmHg) on intramuscular pH and phosphocreatine (PCr) levels (31P-nuclear magnetic resonance spectroscopy) during graded rhythmic handgrip (30 contractions/min; approximately 17, 34, 52 and 69% maximal voluntary contraction). Exercise was performed with LBNP and without LBNP (Control). At the end of exercise, LBNP caused lower levels of muscle pH (6.59 +/- 0.09) compared with Control (6.78 +/- 0.05; P < 0.05). PCr recovery, an index of mitochondrial respiration, was less during the recovery phase of the LBNP trial. Exercise mean arterial pressure was not altered by LBNP. The protocols were repeated with measurements of forearm blood flow velocity and deep venous samples (active forearm) of hemoglobin (Hb) saturation, pH, and lactate. With LBNP, mean blood velocity was reduced at rest, during exercise, and during recovery compared with Control (P < 0.05). Also, venous Hb saturation and pH levels during exercise and recovery were lower with LBNP and lactate was higher compared with Control (P < 0.05). We conclude that LBNP enhanced sympathetic tone and reduced oxygen transport. At high workloads, there was a greater reliance on nonoxidative metabolism. In other words, sympatholysis did not occur.

Adult↗
PubMed1997

Modest hypothermia preserves cerebral energy metabolism during hypoxia-ischemia and correlates with brain damage: a 31P nuclear magnetic resonance study in unanesthetized neonatal rats.

Recent studies have shown that mild to moderate (modest) hypothermia decreases the damage resulting from hypoxic-ischemic insult (HI) in the immature rat. To determine whether suppression of oxidative metabolism during HI is central to the mechanism of neuroprotection, 31P nuclear magnetic resonance (NMR) spectroscopy was used to measure high energy metabolites in 7-d postnatal rats under conditions of modest hypothermia during the HI. The rats underwent unilateral common carotid artery ligation followed by exposure to hypoxia in 8% oxygen for 3 h. Environmental temperature was decreased by 3 or 6 degrees C from the control temperature, 37 degrees C, which reliably produces hemispheric damage in over 90% of pups. The metabolite parameters and tissue swelling (edema) at 42 h recovery varied very significantly with the three temperatures. Tissue swelling was 26.9, 5.3, and 0.3% at 37, 34, and 31 degrees C, respectively. Core temperature and swelling were also measured, with similar results, in parallel experiments in glass jars. Multislice magnetic resonance imaging, histology, and triphenyltetrazolium chloride staining confirmed the fairly uniform damage, confined to the hemisphere ipsilateral to the ligation. The NMR metabolite levels were integrated over the last 2.0 h out of 3.0 h of HI, and were normalized to their baseline for all surviving animals (n = 25). ATP was 47.9, 69.0, and 83.0% of normal, whereas the estimator of phosphorylation potential (phosphocreatinine/inorganic phosphorus) was 16.9, 27.8, and 42.6% of normal at 37, 34, and 31 degrees C, respectively. There was a significant correlation of both phosphocreatinine/inorganic phosphorus (p < 0.0001) and ATP levels (p < 0.0001) with brain swelling. Abnormal brain swelling and thus damage can be reliably predicted from a threshold of these metabolite levels (p < 0.0001). Thus for all three temperatures, a large change in integrated high energy metabolism during HI is a prerequisite for brain damage. With a moderate hypothermia change of 6 degrees C, where there is an insufficient change in metabolites, there is no subsequent HI brain damage. In general, treatment for HI in our 7-d-old rat model should be aimed at preserving energy metabolism.

Analysis of Variance↗
PubMed1996

Three-dimensional mapping of the static magnetic field inside the human head.

Finite element analysis was used to calculate the static magnetic field within the three-dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of the human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 x 2 x 0.5 cm may have frequency differences of more than 2.0 ppm. The linewidth of a single voxel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.

Computer Simulation↗
PubMed1996

Double-sampled echo-planar imaging at 3 tesla.

A persistent artifact in the images acquired by the echo-planar imaging (EPI) method is the Nyquist or N/2 ghost which interferes with the image and reduces the signal-to-noise ratio (SNR). The Nyquist ghost is the result of the time-reversal asymmetry between the even and odd echoes. To eliminate this artifact, the authors present a double-sampled EPI (DSEPI) method in which echoes from each even and odd echo pair are equally phase encoded. The even and odd echoes are separately reconstructed into two distinct images which are then added together. The DSEPI method has been applied to human brain at 3.0 T and shown to be a simple and effective way to eliminate the Nyquist ghost and restore image SNR loss.

Brain↗
PubMed1996

A telecommunications system for monitoring and counseling patients with hypertension. Impact on medication adherence and blood pressure control.

This study was conducted to evaluate the effect of automated telephone patient monitoring and counseling on patient adherence to antihypertensive medications and on blood pressure control. A randomized controlled trial was conducted in 29 greater Boston communities. The study subjects were 267 patients recruited from community sites who were >or= 60 years of age, on antihypertensive medication, with a systolic blood pressure (SBP) of >or= 160 mm Hg and/or a diastolic blood pressure (DBP) of >or= 90 mm Hg. The study compared subjects who received usual medical care with those who used a computer-controlled telephone system in addition to their usual medical care during a period of 6 months. Weekly, subjects in the telephone group reported self-measured blood pressures, knowledge and adherence to antihypertensive medication regimens, and medication side-effects. This information was sent to their physicians regularly. The main study outcome measures were change in antihypertensive medication adherence, SBP and DBP during 6 months, satisfaction of patient users, perceived utility for physicians, and cost-effectiveness. The mean age of the study population was 76.0 years; 77% were women; 11% were black. Mean antihypertensive medication adherence improved 17.7% for telephone system users and 11.7% for controls (P = .03). Mean DBP decreased 5.2 mm Hg in users compared to 0.8 mm Hg in controls (P = .02). Among nonadherent subjects, mean DBP decreased 6.0 mm Hg for telephone users, but increased 2.8 mm Hg for controls (P = .01). For telephone system users, mean DBP decreased more if their medication adherence improved (P = .03). The majority of telephone system users were satisfied with the system. Most physicians integrated it into their practices. The system was cost-effective, especially for nonadherent patient users. Therefore, weekly use of an automated telephone system improved medication adherence and blood pressure control in hypertension patients. This system can be used to monitor patients with hypertension or with other chronic diseases, and is likely to improve health outcomes and reduce health services utilization and costs.

Aged↗
PubMed1996

Specificity of DNA alkylation by 1-(2-chloroethyl)-3-alkyl-3-acyltriazenes depends on the structure of the acyl group: kinetic and product studies.

The reactions of calf thymus DNA with ten 1-(2-chloroethyl)-3-alkyl-3-acyltriazenes of varying acyl side chain structure were studied alone, or in the presence of porcine liver esterase in pH 7.0 phosphate buffer. In several of the key triazenes, the acyl substituent contained a free carboxylic acid group. With esterase present in the reaction mixture, the resultant levels of DNA alkylation could be correlated with the kinetic rates of decomposition of the triazenes. Under these conditions, the predominant pathway of decomposition involved deacylation of the parent triazene and eventual production of an alkanediazonium ion. This intermediate subsequently alkylated DNA--guanine to give 7-alkylguanine as the principal reaction product. In the absence of esterase, the order of DNA alkylation for all of the acyltriazenes did not correlate with their respective rates of decomposition, leading to the conclusion that the triazenes did not decompose by the expected mode of uncatalyzed N(2)-N(3) heterolyic cleavage. The major DNA alkylation product from the N(3)-methyltriazenes was 7-methylguanine, instead of the expected 7-(chloroethyl)- and 7-(hydroxyethyl)guanine products, which suggested that the acyl group was being hydrolyzed. However, acyltriazenes with an N(3)-benzyl group rather than a methyl in this position produced very little 7-benzylguanine product, contrary to prediction. An alternative mechanism involving internally assisted hydrolysis of the side chain ester is proposed to explain these results. NMR product analysis and computational studies were carried out to lend support to the postulated mechanism.

Alkylating Agents↗
PubMed1996

A prospective evaluation of an endoscopic ultrasonic probe to detect intraparenchymal malignancy at pediatric thoracoscopy.

Thoracoscopy has been proposed as the procedure of choice for the evaluation of focal, suspected malignant pulmonary lesions in children. One drawback with this approach, however, is the concern that intraparenchymal lesions may go undetected. We prospectively evaluated the ability of an endoscopic ultrasonic probe to detect intraparenchymal nodules. The handheld probe contains a piezoelectric ultrasound emitter and receiver that operates at 7.5 MHz. The axial resolution of the probe is 1.1 cm. Two different probe tips were used. One is a forward viewing tip and the other is angled at 45 degrees relative to the axis of the probe shaft. Both probes image 90 degrees sectors. Twelve thoracoscopies on nine patients were performed using the ultrasound probe. Of seven patients with confirmed metastatic disease, six had thoracoscopy converted to open thoracotomy to assure that no lesion had been missed. The probe was able to accurately assess surrounding bronchovascular structures and the presence and location of previously placed surgical clips. Although deep structures were readily visualized with the probe, lesions within 1.5 cm of the surface of the lung were poorly visualized. No complications occurred. This ultrasound system allows for the distinction of dense lesions from the surrounding pulmonary parenchyma except for those lying near the surface of the lung, which are usually easy to see directly. Furthermore, the images define the broncho vascular structures adjacent to the lesion. This device may enhance thoracoscopy by facilitating the detection of, and ability to resect, pulmonary intraparenchymal lesions.

Endoscopes↗
PubMed1996

Early impact of new health care legislation on the pediatric surgical experience of surgical residents.

On January 1, 1994, Tennessee implemented TennCare, an insurance program for the state's medically uninsured and those who were previously covered by Medicaid. To determine how this change has affected the pediatric surgical experience of residents in training, we reviewed our institution's operative case logs from the first quarter of 1994 and compared them with logs for the first quarter of the years 1990 through 1993. Cases were classified according to urgency and necessity of surgical procedures. No significant change was noted in the number of patients having operations for the most necessary or urgent conditions, such as solid tumors or appendicitis. In contrast, the number of elective operations, principally for hernias, decreased significantly during the same period. While Tennessee's legislative change apparently has not affected the volume of urgent surgical cases, it has significantly decreased surgical residents' elective pediatric surgical experience.

Appendicitis↗
PubMed1996

Influences of gender on sympathetic nerve responses to static exercise.

We compared reflex responses to static handgrip at 30% maximal voluntary contraction (MVC) in 26 untrained men (mean age 35 +/- 3 yr) and 23 untrained women (mean age 39 +/- 4 yr). Women demonstrated attenuated increases in blood pressure and muscle sympathetic nerve activity (MSNA; by microneurography) compared with men. This difference was also observed during a period of posthandgrip circulatory arrest. 31P-nuclear magnetic resonance (NMR) spectroscopy studies demonstrated attenuations in the production of diprotonated phosphate and the development of cellular acidosis in women compared with men. Subjects also performed ischemic handgrip to fatigue. During this paradigm, MSNA responses were similar in the two groups, suggesting that freely perfused conditions are necessary for the full expression of the gender effect. Finally, we examined MSNA responses to adductor pollicus exercise in 7 men (26 +/- 1 yr) and 6 women (25 +/- 2 yr). MVC values and times to fatigue were similar in the two groups (MVC: men, 4.3 +/- 0.4 kg; women, 4.0 +/- 0.3 kg; not significant. Time to fatigue: men, 209 +/- 16 s; women, 287 +/- 50 s; not significant). At periods of end exercise and postexercise circulatory arrest, MSNA responses were attenuated in the women compared with the men. We conclude that, during nonischemic static exercise, sympathetic neural outflow is less in women compared with men. This response is due to an attenuated metaboreflex in women. Finally, on the basis of the adductor pollicus experiments, this effect appears independent of muscle mass, workload, and the level of training.

Acidosis↗
PubMed1996

Trial by jury; a pilot study of juror perception of mental health professional testimony in NGRI pleas for first degree international homicide.

The authors present a pilot statistical study of the way in which jurors perceived psychiatric/psychological expert testimony in ten court trials for first degree intentional homicide in which a plea of not guilty by reason of mental disease or defect had been entered. The reader is offered a short history of the insanity defense, of the trial by jury, and a discussion of the desired professional and personality prerequisites looked for in choosing a mental health expert. The study is based on a detailed protocol devised by two of the authors--a forensic psychiatrist and a psychologist--assessing various parameters of the professionality and demeanor of the experts on the basis of a statistically valid number of juror responses to the questionnaire. The results show that the jurors perceived the expert testimony as a useful, but not determinant factor when reaching their verdict. This is consonant with the definition of the rationale for using expert testimony as given by the Federal Rules of Evidence.

Adult↗
PubMed1995

Application of the accurate assessment of intracellular magnesium and pH from the 31P shifts of ATP to cerebral hypoxia-ischemia in neonatal rat.

The authors present a high field in vivo demonstration of our 2-dimensional calibration methods for determining magnesium ion concentration ([Mg]), under conditions of fluctuating pH, from the three 31P NMR chemical shift differences of ATP. The effect of 3 h of hypoxic-ischemic insult (HI) on intracellular brain [Mg] was evaluated by using a well established 7-day-old rat model of cerebral HI. During the final hour of HI, there was a significant increase (P < 0.001) in free magnesium as well as in the ratio of total [Mg]/[ATP]. The normal, HI, and early (1-2 h) recovery values of free [Mg] were 0.336 +/- 0.015, 0.519 +/- 0.104, and 0.337 +/- 0.071 mM, respectively. These results are consistent with the temporal changes in [ATP]. Our assessment of [Mg] and pH for this high error measurement is general for most in vivo applications and may be routinely implemented.

Adenosine Triphosphate↗
PubMed1995

A computer simulation of the static magnetic field distribution in the human head.

Distortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air-filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.

Air↗
PubMed1995

Malignant solid tumors in neonates: a 40-year review.

To evaluate the outcome of neonatal malignant solid tumors, we reviewed the records of 222 infants under the age of 1 year with malignant disease who were treated at the University of Texas M.D. Anderson Cancer Center over a 40-year period. Forty-five cases of neonatal (< 30 days old at the time of presentation) malignancies were found. Thirty-two infants had solid tumors and form the basis of this report. Diagnoses included soft tissue sarcoma (13), brain tumor (5), neuroblastoma (6), retinoblastoma (3), malignant melanoma (2), hemangiopericytoma (2), and nephroblastoma (1). The mean age at which initial signs and symptoms were noted was 9 days of life. Fifty-nine percent (19) presented within the first week of life, and 47% (15) presented at birth. The mean age at histological diagnosis was 54 days. The head and neck region was the most common site (18), followed by trunk (9), and extremities (5). Thirty-one patients underwent surgical resection of the primary tumor. Thirteen of those neonates received no additional chemotherapy and/or radiation therapy, whereas 18 received some combination of surgery plus perioperative chemotherapy and/or radiation therapy. Overall survival was 78% (25 of 32) with an average follow-up of 8 years (range, 2 months to 29 years). There were no survivors among those patients with distant metastatic disease at the time of diagnosis. Despite delays, prognosis is excellent in the absence of distant metastatic disease, particularly for extracranial tumors.

Brain Neoplasms↗
PubMed1995

Adolescent treatment. Implications for assessment, practice guidelines, and outcome management.

Treatment for adolescent substance abuse does work. Not only are there clear improvements in substance use frequency and in the number of substances used 1 year after treatment, but also sharp reductions in school and legal problems are observed. Improvements in treatment and the continuum of care can be made however. Substance abuse treatment cannot end with the formal treatment episode. Continuing attendance at support groups, family support, and proactive re-entry plans at school all help to ensure continued recovery after treatment. Many adolescents receive a large amount of medical care in the year prior to admission; however, very few adolescents or their parents list physicians as referral sources at admission. Adolescent substance abuse should be identified by physicians and thereby treated sooner. Through the use of a three-item screen, physicians can reliably identify high-risk adolescents and confidently refer them for a formal chemical dependency evaluation. The use of FIRM has provided a means of understanding how the interactions of certain pretreatment characteristics best predict treatment outcome. Based on such analyses, patient needs can be identified, and practice guidelines can be empirically derived through an iterative process of implementation and evaluation. As the variability of treatment elements increases, treatment process data will become richer. This trend will enable providers to further refine the patient-treatment match by determining the amounts of exposure to specific treatment elements that are most predictive of a positive outcome for a particular group of patients. Efforts have been made to classify chemically dependent patients through the use of factor and cluster analytic techniques. By first identifying discrete types of patients and then measuring how the many services in the treatment experience interact to produce favorable outcomes, optimal treatment guidelines could potentially be derived for each patient type. Further research in this area would further strengthen the bridge between the domains of clinical assessment, practice guidelines, and treatment outcome, setting the stage for even more effective patient-treatment matching and improved outcomes.

Adolescent↗
PubMed1995

The development and reliability of the Recovery Attitude and Treatment Evaluator-Questionnaire I (RAATE-QI).

A reliability study was performed on a new 94-item true-false report instrument called the Recovery Attitude And Treatment Evaluator-Questionnaire I (RAATE-QI). The RAATE-QI consists of five dimensions which assess a patient's status in five clinically relevant areas for making admission assessment, treatment placement/matching and planning decisions, and discharge/follow-up outcome assessments. The five dimensions measure: resistance to treatment (treatment motivation and denial), resistance to continuing care (long-term denial), biomedical acuity, psychiatric/psychological acuity, and social/family environmental support status. Data on 143 inpatients who completed the RAATE-QI from a public sector chemical dependency/dual diagnosis treatment unit demonstrated test-retest reliabilities in the range from .73 to .87, and internal consistency reliabilities in the range from .63 to .78 across the five dimensions. These preliminary data suggest that the RAATE-QI may be a clinically reliable assessment/placement tool.

Adolescent↗
PubMed1994

Cerebral energy metabolism during hypoxia-ischemia correlates with brain damage: a 31P NMR study in unanesthetized immature rats.

The association between the ultimate brain damage resulting from unilateral hypoxic-ischemic insult (HI) and the changes in high-energy metabolites, measured by noninvasive phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy during the insult, was evaluated in 7-day postnatal rats. When the NMR metabolite levels were integrated over the last 1.5 h out of 2.5 h of HI, there was a significant correlation of both the estimator of phosphorylation potential (P < 0.001) and ATP levels (P < 0.01) with histologic score of damage and area morphometry. In particular, the development of cerebral infarction could be predicted from the NMR evaluation (P < 0.005). These findings suggest that a large disturbance in cellular energy metabolism is a prerequisite for the subsequent neuropathological alterations in this model.

Adenosine Triphosphate↗
PubMed1994

Fine-needle aspiration cytology of hepatic leiomyosarcoma.

Hepatic leiomyosarcoma is a rare malignancy to involve the liver, occurring as a primary liver sarcoma in patients without an underlying medical disorder, as a metastatic malignancy, and with increasing incidence, as a primary tumor in AIDS patients. A series of hepatic leiomyosarcomas diagnosed by FNA biopsy, including the first reported case in an adult AIDS patient, were reviewed with respect to cytomorphologic features. The series consisted of five men and two women ranging from 24 to 72 years of age. One case was a primary hepatic lesion in a 24-yr-old man with AIDS and six were metastatic from a number of sites (stomach, small bowel, retroperitoneum, vena cava, and seminal vesicle). Two cytologic patterns were identified. Aspirates of spindle-cell leiomyosarcomas (six cases) generally produced hypocellular smears composed primarily of small irregular clusters of cells with blunt-ended, uniform, overlapping nuclei. The differential diagnosis included benign reactive processes and other benign and malignant spindle-cell neoplasms. The aspirate of an epithelioid leiomyosarcoma (one case) revealed a second pattern characterized by highly cellular smears with many single polygonal cells having eccentric, malignant nuclei and a characteristic clear quality to the cytoplasm in Papanicolaou-stained material. This epithelial appearance generated a differential diagnosis that included hepatocellular carcinoma, metastatic carcinoma, and melanoma. Careful integration of clinical information, cytomorphologic features, and ancillary studies will allow specific FNA diagnosis of hepatic leiomyosarcoma in most cases.

Acquired Immunodeficiency Syndrome↗