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Biomedical subjects

C K Ng

Publications and source records attributed to C K Ng.

85 records · Page 5Linked to original sources
PubMed1978

[Prophylaxis of supraventricular paroxysmal tachycardias on the basis of electrophysiologic examinations].

Paroxysmal supraventricular tachycardias (PSVT) were classified with regard to electrophysiologic criteria in 12 cases. In 6 patients the reentry circuit of the PSVT involved a concealed accessory connection, in 6 patients the reentry circuit was confined to the A-V node. Different antiarrhythmic drugs were administered orally over a 4 week period, the frequency of attacks and possible side effects were recorded. In patients with accessory pathway metoprolol (n = 3), ajmalin (n = 3), Aprindine (n = 1) and verapamil (n = 1) prevented the occurrence of PSVT. Verapamil, Ro 11-1781, metoprolol and digitalis were effective in A-V nodal reentry. PSVT could be prevented in all but one patient by at least one drug.

Adult↗
PubMed1977

[The effect of ouabain on sinus node function and intracardiac conduction (author's transl)].

The effect of 0.5 mg Ouabain (O) i.v. on sinus node function and on intracardiac conduction was studied by His bundle electrography and atrial stimulation. 7 patients with normal sinus node function and av conduction (group I), 5 patients with sick sinus syndrome (group II), and 5 patients with av block of changing degree (group III) were examined. 2 additional patients had simultaneous sinus node dysfunction and av block (group II/III). The sinus node recovery time was prolonged in 6 patients, the av block was located proximal to the His bundle in 4 patients and distal to the His bundle in 3 patients. The spontaneous sinus rate decreased in group I and remained unchanged in group II and III after O. The PA interval increased slightly after O in groups II and III, the AH interval during sinus rhythm was prolonged after O in groups II and III and in the whole group together. During atrial pacing, the stimulus-His-time was increased in each group when compared at identical stimulation rates. In 4 of 7 patients av block type Wenckebach appeared at a lower stilmulation rate after O. The HV interval remained unaltered after O, the sinus node recovery time varied after O. Phenytoin had no positive effect on the changes observed after O. Unwanted actions of O such as increased bradycardia or increased av conduction disturbances were not observed. O appears to be reasonably safe in most patients with sick-sinus syndrome and changing av block.

Adult↗
PubMed1977

[The effect of Ro 11-1781, a calciumantagonist, on atrioventricular conduction (author's transl)].

The effect of an intravenous bolus of 1 mg/kg Ro 11-1781, a new calciumantagonist, on sinus node automaticity and intracardiac conduction was studied by His-bundle electrography and atrial stimulation. During sinus rhythm, no significant action of Ro 11-1781 on rate, P-A-interval, A-H interval, and H-V-interval was observed. The sinus node recovery time remained unaltered. On atrial stimulation, the St-H-interval was significantly (p less than 0.001) prolonged after Ro 11-1781. Wenckebach Periods occurred at lower stimulation rates in all patients after Ro 11-1781. It is concluded that Ro 11-1781 prolongs av nodal conduction and may be of therapeutic value in the treatment of supraventricular arrhythmias.

Adult↗
PubMed1976

Increased elastic recoil as a determinant of pulmonary barotrauma in divers.

The elastic and conductive behaviour of the lungs were studied in sixteen divers during an interrupted deflation from total lung capacity (TLC.) The results in six divers, who had suffered pulmonary barotrauma (PBT) during shallow water diving, were compared with the findings in a control group of divers. Conductive behaviour and mean lung volumes were similar in the two groups. Compared with the control group, the PBT group had higher maximum transpulmonary pressures and a lower static pulmonary compliance, and deflated their lungs earlier. In relatively stiff lungs, an even distribution of elastance may increase susceptibility to barotrauma, because the more compliant zones are subjected to a greater strain. Pulmonary barotrauma appears to select from the total population of healthy divers those with lungs of decreased distensibility.

Diving↗
PubMedDate not supplied

Estimating alveolar surface area during life.

Alveolar surface area (Sa) may be derived from measurements of total lung capacity (TLC) and mean linear intercept (Lm), an estimate of average airspace size. Because the index of pulmonary distensibility, K, is a function of Lm, we were able to derive Lm from ln K using their respective age regressions and estimated Sa in 147 healthy subjects. K was obtained from exponential analysis of static pressure-volume data. TLC was measured in a body plethysmograph. As an estimate of airspace size, the value used for Lm was shown to be appropriate for the air-inflated lung at TLC. In 95 men (mean age 40 +/- 16 SD years), Sa was 118 (SD 22) m2 and in 52 women (mean age 38 +/- 17 SD years) it was 91 (SD 18) m2 and Sa decreased with age (P less than 0.001). In a morphometric study, Thurlbeck (Am. Rev. Respir. Dis. 95: 765-773, 1967) obtained smaller values for Sa (owing to the use of a smaller lung volume) and a similar decrease in Sa with age as that found here. Providing a standardised methodology is used for measurement of K, the present method allows a reasonable estimate of Sa to be obtained during life.

Adult↗
PubMedDate not supplied

Tracer kinetic modeling in nuclear cardiology.

The introduction of tracer kinetic modeling techniques in conjunction with nuclear imaging has allowed the assessment of physiologic processes in the myocardium in a noninvasive and quantitative manner. Alongside the development of novel radiopharmaceuticals for both positron emission tomography and single photon emission computed tomography is the clarification of their pharmacology, pharmacokinetics, and modeling strategies for assessment of physiologic rates from imaging data. Image analysis and tracer kinetic modeling techniques used in nuclear cardiology must address unique considerations related to the heart. The most commonly used tracers and modeling techniques are presently discussed, with particular attention given to methods that allow absolute quantitation of physiologic processes. The applications of these techniques are obvious in research protocols and may find more use in future clinical studies.

Coronary Circulation↗
PubMedDate not supplied

Effect of tiapamil in the Wolff-Parkinson-White syndrome.

The effect of tiapamil was studied in 9 patients with the Wolff-Parkinson-White syndrome using programmed stimulation of the heart. Before the drug, sustained orthodromic tachycardias could be initiated in 7 patients and antidromic tachycardia in 2 by premature atrial and/or ventricular stimulation. An intravenous bolus of tiapamil, 2 mg/kg, terminated the tachycardia in 7 out of 8 cases by a block in the atrioventricular (AV) node. Tiapamil lengthened the effective refractory period of the AV node in the only patient in whom it could be measured and the atrial effective refractory period in 1 out of 9 cases, but the drug had no influence on antegrade or retrograde refractory periods of the accessory pathway or on that of the ventricle. The AV nodal conduction time (A-H interval) was prolonged. Following tiapamil, it was not possible to initiate the tachycardia in 4 cases, in 2 patients the tachycardia zone widened, and in 3 it was unaltered. In the latter cases, the cycle length of the tachycardia was increased. Tiapamil appears to be useful for the termination of tachycardia and also for its prevention in some cases. In others, it may facilitate the inhibition of tachycardia. The delayed AV nodal conduction during sinus rhythm augments the area of ventricular preexcitation, which may facilitate the electrocardiographic localization of the accessory pathway.

Adolescent↗
PubMedDate not supplied

Metoprolol in the treatment and prophylaxis of paroxysmal reentrant supraventricular tachycardia.

The effect of metoprolol on paroxysmal reentrant supraventricular tachycardia was studied in 30 patients. In 16 cases (12 accessory pathway, 4 pure AV nodal reentry) programmed stimulation was performed before and after 0.1 mg/kg intravenous metoprolol. When administered during sustained tachycardia, metoprolol terminated the arrhythmia in 4 out of 12 cases. Metoprolol prolonged the AV nodal functional and effective refractory period and the A-H interval but had no effect on refractory periods and conduction intervals of accessory pathways. Following metoprolol no tachycardia could be initiated in five patients. Premature atrial pacing revealed widened tachycardia zones in 10 cases; premature ventricular pacing showed varying responses to the drug. Twenty two patients (13 accessory pathway, 9 pure AV nodal reentry) received two times 50 to two times 100 mg metoprolol orally per day and were followed for 4 weeks. Five patients did not complete the entire term, four because of frequent tachycardia and one because of side effects. Ten patients were free of arrhythmia, most over several months, and seven continued to have attacks. Plasma levels were higher on oral metoprolol. Intravenous testing had correctly predicted the response to oral metoprolol in seven out of eight patients. Higher plasma concentrations, suppression of premature beats, or the different patient population may explain the more favorable prophylactic action of oral metoprolol.

Administration, Oral↗
PubMedDate not supplied

Effects of delta 1- and delta 6-tetrahydrocannabinol on the adenylate cyclase activity in ventricular tissue of the rat heart.

Adrenaline 1 micrograms markedly elevated the activity of adenylate cyclase in ventricular tissue of rat hearts. delta 1-THC 25, 50 and 100 micrograms significantly reduced the adenylate cyclase activity with the maximum effect observed with the dose of 25 micrograms. Doses below or above this range did not produce any significant effect on the enzyme activity. Neither delta 6-THC 25 and 100 micrograms nor PVP 400 micrograms had any significant action on adenylate cyclase. The delta 1-THC-induced lowering of the cyclic AMP concentration in ventricular tissue of rat hearts can be explained, at least partly, by its ability to reduce the activity of adenylate cyclase in these tissues. It is suggested that this enzyme inhibition underlies the cardiac depressant action of delta 1-THC.

Adenylyl Cyclases↗
PubMedDate not supplied

Pulmonary distensibility and ventilatory function in smokers.

To define the increase in pulmonary distensibility preceding the development of emphysema, we studied 101 cigarette-smoking volunteers, 73 males and 28 females between the ages of 18 yr and 60 yr (mean 42 yr), who were not disabled. A single exponential function fitted to deflation static pressure-volume data gave the exponent K, an index of distensibility. Total lung capacity (TLC) was measured with a body plethysmograph. Values for VC, FEV1 and mid-expiratory flow were only slightly less than values obtained in nonsmokers. K was increased in smokers and increased with age at a greater rate than in nonsmokers, but smokers were unevenly affected. In relation to height, TLC was increased in male smokers and the increase was directly related to the increase in K. The findings show that increased pulmonary distensibility may be identified in smokers without airway obstruction. Because K is directly related to the size of peripheral airspaces, increased pulmonary distensibility in smokers implies an increase in the size of airspaces caused by an action of cigarette smoke, and taking place in asymptomatic subjects.

Adolescent↗