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Biomedical subjects

K K Cheng

Publications and source records attributed to K K Cheng.

At least 109 records · Page 6Linked to original sources
PubMed1987

Postoperative deep vein thrombosis in the Taiwanese Chinese population.

Reports of the incidence of postoperative deep vein thrombosis in the Chinese population of Taiwan are few in the literature. Over a 3 year period, the fibrinogen degradation products test, the pulse volume recorder, and venography were used to study 220 patients undergoing major operations at the Veterans General Hospital in Taipei, Taiwan. Deep vein thrombosis was found in 17 patients (7.7 percent). A comparison of the three diagnostic methods showed that the sensitivities of the fibrinogen degradation products test and the pulse volume recorder were 56.3 percent and 93.7 percent, respectively; the specificities, 97.4 percent and 95.7 percent, respectively; and the accuracies, 85.5 percent and 95.5 percent, respectively. These results support the combined use of the fibrinogen degradation products test and the pulse volume recorder for screening and diagnosing deep vein thrombosis.

Female↗
PubMed1987

Arrhythmogenic effects of theophylline in human atrial tissue.

We studied the effects of theophylline on the transmembrane action potential and the contractile force of human atrial fibers obtained from the hearts of 15 patients, undergoing corrective open-heart surgery. Atrial fibers were perfused with Tyrode solution and driven electrically at a constant rate of 60 beats per min. Theophylline (0.1-1 mM) steepened the diastolic depolarization, increased the amplitude of oscillatory potential during diastole and facilitated the development of spontaneous slow response action potentials. These arrhythmogenic effects of theophylline were suppressed after diltiazem (0.1-0.3 microM) pretreatment. The present findings provide the electrophysiologic evidence that abnormal atrial automaticity as a result of triggered activity may be the underlying cause for atrial ectopic activity and multifocal atrial tachycardia in patients taking theophylline.

Adult↗
PubMed1987

Somatostatin effects in isolated human atrial fibres.

Effects of hypothalamic hormone somatostatin on the action potential and contractile force of 54 human atrial preparations obtained at cardiac surgery were studied with standard microelectrode techniques. In the atrial fibres responding to electrical stimuli with fast response action potentials in 4 mM [K]0 Tyrode solution (maximum rate of phase 0 depolarization greater than 50 V/s), somatostatin (10(-7) to 10(-6) M) reduced slightly the duration of action potential and decreased twitch force dose-dependently. In spontaneously active atrial fibres, somatostatin (10(-7) to 10(-6) M) abolished the action potentials in the preparations with low maximal diastolic potential (MDP, -48 +/- 2.8 mV), but induced only mild suppressive effect in the preparations with high MDP (-70 +/- 2.4 mV). When the fibres were depolarized in 27 mM [K]0 Tyrode solution, somatostatin decreased the maximum rate of depolarization and amplitude of the slow response action potentials induced by electrical stimuli. The delayed afterdepolarizations or triggered action potentials induced by high-frequency electrical drive in the presence of epinephrine were also suppressed by somatostatin. The above findings suggest that somatostatin may suppress the abnormal automaticity and the triggered activity in human atrial fibres through a reduction of cellular calcium.

Action Potentials↗
PubMed1986

Electrophysiological effects of low pH in human atrial fibres.

In the studies of the electrophysiological properties of human atrial fibres obtained at cardiac surgery, it has often been reported that the diastolic potential, the maximum upstroke velocity of the phase 0 depolarization (Vmax) and the amplitude of action potential are relatively low. The same findings were also obtained in our previous study when the tissue preparations were perfused with a Tyrode solution which, as usually described in literatures on cardiac cell studies had a NaHCO3 concentration of 12 mM and was aerated with a gas mixture of 95% O2-5% CO2 at 37 degrees C. Recently we found that the relatively poor electrical activities of the human atrial fibres were related to the low pH value (around 7.06) of the perfusate used. Raising the pH value of the perfusate either by increasing the NaHCO3 concentration or by reducing the CO2 in the bubbling gas mixture significantly improved the electrical activities of the fibres. There is evidence that the suppressive effect of low pH on the electrical activities is due to the hindering action of H+ on the transportation of other cations across the plasma membrane.

Cardiac Surgical Procedures↗
PubMed1985

Electromechanical effects of caffeine in isolated human atrial fibres.

Effects of caffeine on the action potential and contractile force of human atrial fibres obtained at cardiac surgery were studied with standard microelectrode technique. In 4 mmol . litre-1 [K]o, the only significant action produced by 0.3 to 3 mmol . litre-1 caffeine on the electro-mechanical activity of relatively normal atrial fibres was a slight shortening of the action potential duration at 50% repolarisation. When the fibres were depolarised in 27 mmol . litre-1 [K]o or in atrial fibres showing slow responses in 4 mmol . litre-1 [K]o, however, caffeine could increase the upstroke of slow response and the force. In 18% of atrial fibres showing slow responses in 4 mmol . litre-1 [K]o, caffeine induced spontaneous discharges and potentiated afterdepolarisations. The positive inotropic and the arrhythmogenic effects of caffeine could be diminished by pretreating the fibres with propranolol or Ca antagonists (diltiazem and verapamil). In fibres beating spontaneously in normal [K]o, caffeine accelerated spontaneous rhythms initially and then depressed them. Propranolol potentiated the later depression but did not block the initial acceleration. The results suggest that caffeine increases the transmembrane Ca influx and enhances the release of Ca from the intracellular stores in human atrial fibres. As a consequence, caffeine could induce arrhythmias in atria from certain individuals.

Action Potentials↗
PubMed1984

Positive inotropic effect of acetylcholine in isolated human atrial fibers.

We studied the effects of acetylcholine on the transmembrane action potential and the contractile force of isolated human atrial fibers obtained at cardiac surgery. In 3 of 12 preparations, 10(-7)-10(-6) M acetylcholine induced a substantial increase in the contractile force following a brief initial decrease. Atropine diminished both the initial negative and the later positive inotropic effects induced by acetylcholine while propranolol abolished only the later effect.

Acetylcholine↗
PubMed1977

Adrenergic mechanisms in the hepatic microcirculation in the rat.

The in vivo hepatic microvascular bed of the rat was observed microscopically in the transilluminated liver and the diameter of the hepatic sinusoids was measured by serial photomicrography. Intraportal infusion of tyramine induced concentration-dependent constriction of the hepatic sinusoids, but also dilatation of the sinusoids when the dose was small. These effects were attributed to the release of endogenous noradrenaline which activated either alpha- or beta-adrenergic receptors and caused constriction, or dilatation, of the sinusoids respectively. Adrenaline and noradrenaline induced similar changes in the hepatic sinusoids as tyramine, while phenoxybenzamine induced dilatation, and propranolol constriction, of the sinusoids. All the above responses were abolished by pretreatment with reserpine. A possible noradrenaline-mediated basal vasomotor tone in the hepatic sinusoids for autonomic control of the blood flow in the sinusoids was postulated.

Animals↗
PubMed1976

Intrahepatic microvascular changes in carbon tetrachloride-induced cirrhotic livers in the rat.

Liver cirrhosis was produced in the rat by combined carbon tetrachloride-phenobarbitone treatment, and the microcirculation in the cirrhotic liver was observed by a quantitative in vivo transillumination technique. The total sinusoidal flow in the observed region of the cirrhotic liver did not differ significantly from that in the normal liver, despite the reduced number of sinusoids and the increased portal venous pressure. The cirrhotic liver also presented a fast-velocity population of portal and hepatic venules and sinusoids in addition to the normal slow-velocity population. The possible mechanism of these "arterialized" microvessels is discussed.

Animals↗
PubMed1976

Effect of the ligation of hepatic artery on the microcirculation in the cirrhotic liver in the rat.

The significance of the hepatic arterial supply in the intrahepatic microcirculation in normal and carbon tetrachloride-induced cirrhotic livers was studied by dye injection method and by ligation of the hepatic artery. The in vivo distribution of dye injected into the hepatic artery evidenced the presence of arterio-venous shunts in the cirrhotic liver. When the hepatic artery of the cirrhotic liver was ligated, the elevated portal venous pressure dropped significantly, and the fast-flowing population of microvessels and sinusoids in the bimodal frequency distribution plot disappeared. The fast-flowing microvessel and sinusoids appeared to be the "arterial" microvessels and sinusoids, and they were converted into the slow-flowing venous channels after hepatic arterial ligation. The transmission of arterial pressure via the A-V shunts may be of greater significance in the pathophysiology of portal hypertension than previously believed.

Animals↗