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Biomedical subjects

D Wong

Publications and source records attributed to D Wong.

At least 253 records · Page 14Linked to original sources
PubMed1987

Reduced narcotic requirement by clonidine with improved hemodynamic and adrenergic stability in patients undergoing coronary bypass surgery.

The authors examined the effect of clonidine, a preferential alpha 2-adrenergic agonist, upon narcotic requirements, hemodynamics, and adrenergic responses during the perioperative period in patients undergoing CABG surgery. Anesthesia was provided by sufentanil supplemented with isoflurane; sodium nitroprusside was given as needed for hemodynamic control. Ten patients received oral clonidine preoperatively at the time of premedication, and again intraoperatively by nasogastric tube. Another group of ten untreated patients were otherwise managed identically. Intergroup differences in required anesthetic and vasoactive drug doses and recovery times were measured and evaluated, as well as hemodynamics and plasma catecholamines prior to induction, after intubation, and at intervals intra- and postoperatively. Patients who received clonidine required less diazepam prior to induction, and received 40% less sufentanil during the anesthetic period, than did untreated controls. More control patients required the addition of isoflurane to prevent hypertension. Mean blood pressures and heart rates were elevated at many sampling points in patients not treated with clonidine. Four of the clonidine-treated group required atropine for treatment of bradycardia in the pre-incision period. Plasma catecholamines were significantly lower throughout most of the study period in patients treated with clonidine. After cardiopulmonary bypass and postoperatively, cardiac outputs were significantly higher in the treated group. Patients who had received clonidine were extubated significantly earlier, and fewer of them shivered postoperatively. We conclude that perioperative treatment with clonidine reduced narcotic and anesthetic requirements, improved hemodynamics, reduced plasma catecholamines, and shortened the period of postoperative ventilation in patients undergoing coronary artery surgery.

Anesthetics↗
PubMed1987

Correction of genetic diabetes insipidus by adult hypothalamic grafts.

Brattleboro rats manifest chronic diabetes insipidus as a result of the genetic deficiency of hypothalamic vasopressin. When basal hypothalamic tissue derived from adult F344 rats was implanted as cell suspensions or tissue blocks in the supraoptic regions of these animals, concentration of urine together with reduced urine output and water intake was observed in some animals. Histologic examination of the grafted brains from the responding animals revealed neuronal cells at the implant sites and vasopressin-staining fibers in the median eminence. This study demonstrates the feasibility of the grafting of adult cerebral tissues to correct a genetic hormonal deficiency.

Animals↗
PubMed1986

Patterned stimulation at the theta frequency is optimal for the induction of hippocampal long-term potentiation.

Short, high frequency stimulation bursts (4 pulses at 100 Hz) were applied to Schaffer/commissural projections to the CA1 field of rat hippocampal slices at 0.1, 0.2, 1.0 or 2.0-s intervals to assess their efficacy in eliciting long-term potentiation (LTP). Bursts repeated at 2-s intervals induced very little LTP; shorter repetition intervals reliably elicited LTP, with the 200-ms repetition interval producing the greatest potentiation. A short-term potentiation effect, which was maximal 20 s after the last burst and decayed within 10 min, was affected differently by the stimulation parameters than was LTP, suggesting that the two phenomena are due to different processes. The results indicate that patterns of stimulation resembling spike discharge patterns of hippocampal neurons in animals in exploratory situations are effective in inducing LTP and suggest temporal constraints on the mechanisms involved in triggering synaptic plasticity.

Animals↗
PubMed1986

Clinical trials versus intuition in evaluating the results of laser photocoagulation.

Clinical trials are often used to evaluate the efficacy of a given treatment. The results of clinical trials however do not always agree with a clinician's experience or intuition. The merits and demerits of Clinical Trials versus Intuition are discussed by using the laser photocoagulation trials of Proliferative Diabetic Retinopathy, Central serous retinopathy, Branch Vein Occlusion (treatment for macular oedema), Senile Macular Degeneration, and Pigment Epithelial Detachment. A model based on Intuition is used to explain the discrepancy between the results of the British and American trials of Branch Vein Occlusion and Senile Macular Degeneration. Proposals on the presentation of Clinical Trials and the place of Intuition are made.

Aging↗
PubMed1986

Response properties of FM-FM combination-sensitive neurons in the auditory cortex of the mustached bat.

For echolocation, the mustached bat, Pteronotus parnellii rubiginosus, emits orientation sounds (pulses) and listens to echoes. Each pulse is made up of 8 components, of which 4 are constant frequencies (Cf 1.4) and 4 are frequency-modulated (FM 1-4). Target-range information, conveyed by the time delay of the echo FM from the pulse FM, is processed in this species by specialized neurons in a part of the auditory cortex known as the FM-FM area. These cortical neurons are responsive to pulse-echo pairs at specific echo delays. The essential components in the sound pair include the pulse FM1 followed by an echo FMn (n = 2, 3 or 4). Downward sweeping FM1-FMn sounds that are similar to those the animal naturally hears during echolocation are the most effective in evoking facilitative responses. Most FM-FM neurons, however, still exhibit facilitative responses to stimulus pairs consisting of upward sweeping FM sounds and/or pure tones at frequencies found in FM sweeps. The magnitude of facilitation is altered by changes in echo rather than pulse amplitude. Neurons characterized by shorter best delays (or echoes from closer targets) do not require larger best echo amplitudes for facilitation.

Animals↗
PubMed1986

Identification of DNA damage as a result of exposure of rats to diesel engine exhaust.

Owing to the concern regarding genotoxic agents which may be present in diesel engine emissions we have studied the effect, with respect to DNA damage, of the exposure of F344 rats to such emissions for approximately 31 months at levels of particulate material of 7.1 mg/m3. Rats were killed and the DNA extracted from the right lung lobe and coded prior to analysis for DNA adducts by the 32P-postlabeling technique. Although a gradation of adduct intensity was found from high levels to none being detectable, distinction could be made between exposed and unexposed groups based upon the intensity of DNA adducts present.

Animals↗
PubMed1986

Activation of plasminogen by tissue plasminogen activator on normal and thrombasthenic platelets: effects on surface proteins and platelet aggregation.

Tissue plasminogen activator (TPA) converts plasminogen to plasmin within the fibrin clot, thus localizing activation of fibrinolysis. To determine the extent to which platelets promote activation of plasminogen by TPA, we studied the interaction of TPA and plasminogen with unstimulated platelets. Normal washed platelets incubated in the presence of physiologic concentrations of plasminogen (180 micrograms/mL) and TPA (20 ng/mL) failed to generate plasmin activity. In contrast, incubation of platelets with TPA concentrations achieved during thrombolytic therapy (40 to 800 ng/mL) produced a tenfold to 50-fold increase in plasmin activity. After exposure to plasminogen and 200 ng/mL of TPA for one hour, platelets failed to agglutinate in the presence of ristocetin. Incubation of platelets suspended in autologous plasma with 400 ng/mL of TPA for one hour also inhibited ristocetin-induced agglutination. Exposure of platelets to plasminogen and increasing concentrations of TPA correlated with a decrease in glycoprotein Ib (GPIb) and an increase in glycocalicin, as shown by immunoblotting. The glycoprotein IIb/IIIa (GPIIb/IIIa) complex and a 250,000-dalton protein also disappeared from washed platelets after incubation with plasminogen and 200 ng/mL of TPA for one hour. These platelets failed to aggregate in the presence of adenosine diphosphate (ADP) or gamma thrombin, although aggregation in response to calcium ionophore A23187 and arachidonic acid remained intact. However, aggregation in response to all four agonists was normal when platelets were incubated with TPA in the presence of autologous plasma. Platelets from a patient with Glanzmann's thrombasthenia also generated plasmin in the presence of TPA. Hydrolysis of GPIb and inhibition of ristocetin-induced agglutination occurred to a lesser extent with these platelets than with control platelets. We conclude that platelets provide a surface for activation of plasminogen by pharmacologic amounts of TPA. Plasmin generation leads to degradation of GPIb and decreased ristocetin-induced agglutination in normal and thrombasthenic platelets, as well as degradation of GPIIb/IIIa in normal washed platelets and inhibition of ADP and gamma thrombin-induced aggregation. These findings suggest that pharmacologic concentrations of TPA may cause platelet dysfunction due to plasmin generation on the platelet surface.

Adenosine Diphosphate↗
PubMed1986

The role of induced choroidal retinal adhesion in retinal detachment surgery.

The use of induced adhesion in retinal and vitreous surgery is considered. A follow-up report on a series of cases of retinal detachment treated with buckling only shows that there is a risk of late re-detachment from the original hole as the buckle height diminishes. Cryotherapy is therefore necessary to prevent redetachment but as it is not necessary for reattachment it is reasonable to confine its application to the immediate vicinity of the retinal hole. An adhesion is advised in most cases of retinal detachment treated by vitrectomy, exceptions being small holes at the posterior pole.

Choroid↗
PubMed1986

Computer automated visual acuity testing for visual screening.

A computer program was designed for automated visual acuity testing, the aim of which was to evaluate the effectiveness of such systems in a busy out-patient department. The time required for explanation and performing the automated test was compared with that taken by nurses measuring visual acuities in the conventional manner using a Snellen's chart. The correlation of the results of the computer system and the manual measurements was tested.

Adolescent↗
PubMed1985

Acquired Bernard-Soulier syndrome. Evidence for the role of a 210,000-molecular weight protein in the interaction of platelets with von Willebrand factor.

A patient with a lymphoproliferative disorder developed bleeding associated with a prolonged bleeding time and a selective defect of platelet aggregation in response to ristocetin. The patient's purified IgG was shown to inhibit aggregation of washed normal platelets by ristocetin and von Willebrand factor (F VIII:vWF). By Western blotting, it was shown that antibody bound specifically to an antigen of Mr 210,000 present on normal platelets but missing on platelets from patients with congenital Bernard-Soulier syndrome (BSS). Binding was effected by the F(ab)2 portion of the IgG, indicating the presence of an autoantibody rather than an immune complex. These results suggest that the 210,000-Mr protein is involved in the interaction of F VIII:vWF with platelets. Furthermore, we have demonstrated the apparent absence of an additional protein on congenital BSS platelets. Heat-aggregated IgG was also shown to bind to the 210,000-Mr protein, suggesting that this protein may function as an Fc receptor on platelets. The relationship of the 210,000-Mr protein to glycoprotein Ib and the precise role of this protein in the interaction of platelets with F VIII:vWF need to be characterized.

Adult↗
PubMed1985

Use of calcium channel blockers in hypoxic lung disease.

COPD patients who are hypoxic develop pulmonary hypertension primarily because alveolar hypoxia induces muscular hypertrophy of pulmonary arteries. This muscular hypertrophy will regress in animals if they receive continuous oxygen therapy. Since many COPD patients refuse to use oxygen continuously, calcium channel blockers, which inhibit hypoxic pulmonary vasoconstriction, may be effective adjuvant therapy. Nifedipine lowers pulmonary vascular resistance during rest and exercise in hypoxic COPD patients.

Calcium Channel Blockers↗