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Biomedical subjects

M Wood

Publications and source records attributed to M Wood.

At least 235 records · Page 13Linked to original sources
PubMed1990

Correlation of an invasive measure of right ventricular pressure and mean arterial pressure.

Recently, cardiac pacemakers have been introduced which increase heart rate during exercise. Current rate responsive pacemakers achieve this objective by monitoring minute ventilation via a transvenous impedance measurement and provides a proportional heart rate increase with increases in minute ventilation. These devices are independent of hemodynamic parameters. Therefore, the potential exists for a sufficiently high rate which results in decreased cardiac output by virtue of Starling's Principle. An invasive measure of right ventricular (RV) pressure is compatible with the power and complexity of contemporary implantable pacemakers. In addition, mean arterial pressure is accepted as a diagnostic indicator of left ventricular hemodynamic compromise. Therefore, a correlation of right ventricular pressure and mean arterial pressure was undertaken. Twenty-six patients were studied during normal sinus rhythm and ventricular tachycardia during routine electrophysiology examination. A beat to beat measure of peak to peak RV pressure resulted in a correlation coefficient of 0.68 with mean arterial pressure.

Blood Pressure↗
PubMed1989

The Epstein-Barr virus:host balance in acute infectious mononucleosis patients receiving acyclovir anti-viral therapy.

This report describes the first of 2 investigations studying mechanisms of Epstein-Barr virus (EBV) persistence in the infected host; specifically, we wish to determine the extent to which virus carriage within the B-cell system is dependent upon continued replication of the virus in permissive oropharyngeal epithelium. Levels of EBV infection at these 2 sites have been monitored in 21 acute infectious mononucleosis (IM) patients before, during and after treatment with high doses of acyclovir (ACV). Twelve patients received oral ACV for 10 days and 9 patients received i.v. ACV for 5 days before the 10-day oral course; all were followed prospectively for 28 days. Infectious EBV, detectable at high initial levels in the patients' throat washings, disappeared almost completely during ACV treatment, then returned again to high levels post treatment. In contrast, levels of virus-infected B cells in the blood showed no reduction linked to the period of ACV treatment nor any increase with resumption of EBV shedding. During IM, therefore, maintenance of high levels of virus carriage within the B-cell pool is not dependent upon the continual recruitment of newly infected B cells. This might reflect an inability of the immune T-cell response in acute IM patients to prevent continued expansion of the existing EBV-infected B-cell pool. Alternatively, it raises the possibility that EBV carriage in B cells in vivo is maintained through a virus:cell interaction which is not sensitive to virus-specific T-cell surveillance.

Acyclovir↗
PubMed1989

Epstein-Barr virus-infected B cells persist in the circulation of acyclovir-treated virus carriers.

In this study, infectious Epstein-Barr virus (EBV) shedding in the oropharynx and numbers of virus-infected B cells in the blood have been monitored in long-term virus carriers receiving acyclovir (ACV) therapy for herpes zoster. Eleven patients on oral ACV were followed prospectively before, during and for 2 weeks after treatment. As expected, the low levels of EBV shedding in these virus carriers (measured as cord-blood lymphocyte transforming activity in throat washings) were eliminated during the period of ACV treatment and returned at later times. Over the same period, however, the frequency of virus-infected B cells in the blood (measured by spontaneous transformation in limiting dilution assay) remained completely unchanged. Regression assays showed that these same patients had normal levels of EBV-specific cytotoxic T-cell immunity, so that the in vivo persistence of virus-infected B cells could not be ascribed to a defect in T-cell surveillance. We infer that the in vivo half-life of the virus-infected B-cell pool in long-term virus carriers is measured in months rather than days. We further suggest that such persistence requires a novel form of virus:B-cell interaction distinct from the type of "latent" infection displayed by in vitro-transformed cells.

Acyclovir↗
PubMed1989

Heart transplantation during the first 12 years of life. Loma Linda University Pediatric Heart Transplant Group.

Since November 1985, forty-four heart transplants have been accomplished in 43 infants and children younger than 12 years of age. Indications for transplantation included structural heart disease (31 patients), idiopathic or viral cardiomyopathy (10 patients), and combined structural and myopathic disease (2 patients). Postoperative recipient surveillance was achieved noninvasively during the first year of life; endomyocardial biopsy was employed in children. Maintenance immunosuppression included cyclosporine and azathioprine therapy during the first year after transplantation in young infants, graduating to cyclosporine therapy alone beyond the first year. Azathioprine therapy was continued indefinitely in children. There have been 5 perioperative deaths and 1 late death in this series of recipients. Overall survival was 86%. Growth, development, and psychosocial adjustments generally have been excellent. Donor heart growth has been normal. Coronary artery disease has not yet been observed. Our findings indicate that heart transplantation seems to be effective therapy for selected incurable pediatric cardiac diseases.

Child↗
PubMed1989

Halothane inhibition of propranolol metabolism is stereoselective.

Propranolol, like many drugs, is used clinically as a racemic mixture. The major pharmacodynamic effects of propranolol, however, are mediated by the (-)-isomer, which is 100 times as potent as the (+)-isomer. The two isomers also differ in their pharmacokinetic characteristics. To determine whether halothane anesthesia stereo-selectively inhibits the metabolism of racemic propranolol, eight male mongrel dogs were studied. On the first day of the study, 40 mg racemic propranolol was infused into the portal vein and arterial blood samples were obtained over the following 4 h for the measurements of (+)- and (-)-propranolol concentrations by HPLC. The study was repeated 24 h later during 2 MAC halothane anesthesia, when the intrinsic clearance of total propranolol was decreased by 67.5 +/- 5%, from 6.14 +/- 1.1 1/min to 1.84 +/- 0.4 1/min (P less than 0.05). The decrease in intrinsic clearance was stereoselective, (-)-propranolol being affected to a greater extent than (+)-propranolol; thus, the decrease in the clearance of (-)-propranolol, from 10.96 +/- 2.71/min to 2.6 +/- 0.71/min (73 +/- 5%) was significantly (P less than 0.05) greater than the decrease in the clearance of (+)-propranolol, (62 +/- 3%) from 4.3 +/- 0.8 1/min to 1.5 +/- 0.3 1/min. Furthermore, the ratio of the intrinsic clearance of (-)-propranolol to the intrinsic clearance of (+)-propranolol was significantly (P less than 0.05) reduced by halothane anesthesia, from 2.42 +/- 0.29 to 1.69 +/- 0.11. Stereoselective inhibition of propranolol metabolism results in proportionally higher concentrations of (-)-propranolol during halothane anesthesia than are present in awake dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1989

The effect of advancing age on the sympathetic response to laryngoscopy and tracheal intubation.

The effect of aging on the hemodynamic and sympathetic response to tracheal intubation was evaluated in 27 patients aged 18 to 80 years, ASA Class I and II, given atropine 0.4 mg and diazepam 10 mg as premedication and thiopental, 4.0 mg/kg, and succinylcholine 100 mg for anesthesia induction. Laryngoscopy and tracheal intubation was performed 60 seconds after induction. The elderly had significantly less chronotropic response to intubation 2, 3, 4, and 5 minutes after induction so that the maximum increase in heart rate above awake values was negatively correlated with age (R = -0.66, P less than 0.001). Baseline systolic blood pressure (SBP) and mean BP increased significantly with age (R = 0.81, P less than 0.001 and R = 0.76, P less than 0.001, respectively) but age was not significantly related to increases in SBP and mean BP following intubation. Baseline plasma norepinephrine (NE) levels increased with age ( R = 0.51, P less than 0.01). Following intubation, mean plasma NE concentrations were significantly higher in elderly patients than young patients, despite the diminished heart rate response. Heart rate (HR) per pg/ml of NE, a measure of cardiac sensitivity to beta stimulation, was therefore significantly less 2, 3, and 4 mins after induction in elderly patients than in younger patients. To determine if this alteration in cardiac sensitivity to endogenous catecholamines was reflected by changes in beta receptor function on lymphocytes, beta receptor density and the proportion of receptor binding agonist with high affinity (%RH) were measured. No significant correlation between beta-receptor affinity for agonist, %RH, or receptor density was found with age, HR, or HR per pg/ml NE.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Bradyarrhythmias, emergency pacing, and implantable defibrillation devices.

This article reviews new developments in the field of cardiac pacing. Special emphasis is placed on dual chamber temporary pacing, external transthoracic cardiac pacing, and antitachycardia pacing. The role of the automatic implantable cardioverter defibrillator (AICD) in patients with sudden cardiac death is also explored with emphasis on the presentation of such patients to intensive care units.

Bradycardia↗
PubMed1989

Lack of effect of spinal anesthesia on drug metabolism.

The effect of spinal anesthesia on drug disposition was determined in six dogs with chronically implanted vascular catheters using propranolol as a model compound. On the first study day, 40 mg of unlabeled propranolol and 200 microCi of [3H]propranolol were injected into the portal and femoral veins respectively. Arterial blood samples were taken for 4 hr for measurement of plasma concentrations of labeled and unlabeled propranolol by high-pressure liquid chromatography (HPLC) and of [3H]propranolol by liquid scintillation counting of the HPLC eluant corresponding to each propranolol peak. Twenty-four hr later, spinal anesthesia was induced with tetracaine (mean dose 20.7 +/- 0.6 mg) with low sacral to midthoracic levels and the propranolol infusions and sampling were then repeated. Spinal anesthesia had no significant effect on either the intrinsic clearance of propranolol (2.01 +/- 0.75 L/min before and 1.9 +/- 0.7 L/min during spinal anesthesia), or on mean hepatic plasma flow (2.01 +/- 0.5 L/min before and 1.93 +/- 0.5 L/min during spinal anesthesia). The systemic clearance and elimination half-life of propranolol were also unchanged by spinal anesthesia (0.9 +/- 0.23 L/min on the first day, 0.7 +/- 0.1 L/min during spinal anesthesia; and 101 +/- 21 min on the first day, 115 +/- 16 min during spinal anesthesia, respectively). The volume of distribution (Vd) of propranolol was similarly unaffected by spinal anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Spinal↗
PubMed1988

Campylobacter infection in a closed dog breeding colony.

Most dogs in a closed breeding unit were shown to be asymptomatic excretors of campylobacter organisms by eight weeks old. Increasing serum antibody levels, which were correlated with the excretion of organisms, were demonstrated in the puppies and serum antibodies were also demonstrated in adult dogs. The significance of these findings with respect to the pathogenicity of campylobacter in dogs and their zoonotic implications are discussed.

Animals↗
PubMed1988

Interaction of nucleophilic compounds with complement component C4.

Drugs which induce systemic lupus erythematosus as a toxic side effect have been shown to inhibit the covalent binding of C4, which is an important event in immune complex clearance in normal individuals. Human C4 is encoded at two polymorphic loci, C4A and C4B within the Major Histocompatibility Complex and patients with idiopathic SLE are more likely to have a non-functional (null) C4A gene. The C4A and C4B gene products differ in reactivity with C4A being more reactive with nitrogen nucleophiles, including hydralazine and isoniazid (drugs which induce SLE), than with oxygen nucleophiles. We have established an assay system which allows the effect of nucleophiles on C4 in animal sera to be investigated. It has been found that in comparing reactivity of guinea-pig C4 with human C4A and human C4B that guinea-pig C4 is like human C4A and shows greater reactivity towards nitrogen nucleophiles than towards oxygen nucleophiles. This suggests that the guinea-pig should be a good animal model for drug-induced SLE.

Animals↗
PubMed1988

Comparison of the effects of isoflurane or fentanyl-nitrous oxide anaesthesia on propranolol disposition in dogs.

The disposition of propranolol was studied, using dual-route administration, in two groups of six dogs. Each dog was studied on three consecutive days: day 1 awake, day 2 during anaesthesia, and day 3, 24 h after anaesthesia. Anaesthesia was with isoflurane 2.0 MAC (in oxygen) in one group and with a fentanyl-nitrous oxide-atracurium regimen in the other group. In the group receiving fentanyl, anaesthesia caused a significant decrease (63%) in intrinsic clearance from the day 1 value (P less than 0.05) and a 45% decrease in systemic clearance (P less than 0.05). Hepatic plasma flow decreased by 27% (ns). A similar pattern was found with isoflurane: intrinsic clearance decreased by 53% (P less than 0.05) and systemic clearance by 40% (P less than 0.05). Hepatic plasma flow decreased by 40% (ns). In both groups, the values 24 h after anaesthesia were not significantly different from those obtained on day 1. Anaesthesia with either fentanyl-nitrous oxide-atracurium or isoflurane has a marked, but short-lasting effect on the disposition of propranolol, in part as a result of a decrease in intrinsic clearance.

Anesthesia, General↗
PubMed1988

Comparison of propofol and thiopental for the induction of anesthesia.

We compared the safety, efficacy, and side effects of induction of anesthesia with propofol (2.5 mg/kg), a new intravenous agent, and thiopental (4.0 mg/kg) in 62 patients in American Society of Anesthesiologists class I or II. There was no significant difference between induction times for the propofol (40.0 +/- 2.0 sec) and thiopental (44.0 +/- 4.0 sec) groups. Propofol administration produced a significant fall (P less than .05) in systolic blood pressure (SBP), from 134.1 +/- 2.6 mm Hg before injection to 128.3 +/- 2.4, 118.2 +/- 2.7, and 114.4 +/- 2.8 mm Hg one, two, and three minutes after injection, respectively. Diastolic blood pressure (DBP) fell significantly (P less than .05) during the three postinjection periods. Heart rate (HR) rose significantly (P less than .05), from 78.6 +/- 3.1 beats per minute before injection to 89.4 +/- 3.4 beats per minute one minute after injection. In patients given thiopental, SBP fell significantly (P less than .05), from 131.7 +/- 2.7 mm Hg before induction to 126.4 +/- 3.4 and 126.9 +/- 4.0 mm Hg two and three minutes after injection, respectively. The DBP did not change significantly in the thiopental group, but the HR rose significantly (P less than .05), from 73.3 +/- 2.8 beats per minute before injection to 83.9 +/- 3.0, 90.1 +/- 2.3, and 84.2 +/- 2.4 beats per minute one, two, and three minutes after injection, respectively. In 94% of patients given propofol, there were apneic periods of more than 60 seconds, compared to 50% in the thiopental group (P less than .05). There was a significant difference (P less than .05) between groups for the incidence of pain on injection; 31% of the patients receiving propofol had pain, compared to 3% of those receiving thiopental.

Adolescent↗
PubMed1988

Inner city deprivation and medical education: a survey of medical students by medical students.

A total of 330 preclinical and clinical medical students and house officers at St Mary's Hospital were surveyed by questionnaire to assess their knowledge and experience of inner city deprivation and health, and their opinions on the role of the doctor in responding to these problems. The response rate was 87%. Over 75% of the respondents had had no experience of inner city living conditions before coming to medical school, and they gained little experience during the medical course until well into the clinical years. Most preclinical students wanted more contact with the community early in the course; less than one-third of the clinical students wanted this. The differences in knowledge and attitudes between the year groups are discussed and possible reorientation in medical education is considered.

Attitude of Health Personnel↗