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Biomedical subjects

M A Chiong

Publications and source records attributed to M A Chiong.

At least 19 recordsLinked to original sources

Lesch-Nyhan disease in a 20-year- old man incorrectly described as developing 'cerebral palsy' after general anaesthesia in infancy.

Lesch-Nyhan disease (LND) is a rare X-linked recessive genetic disorder caused by a deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) enzyme. The classic clinical condition is characterized by cognitive impairment, hypotonia at rest, choreoathetosis, hyperuricaemia and the hallmark symptom of severe and involuntary self-mutilation. We describe a man with LND who was initially thought to have suffered from a dyskinetic cerebral palsy after an uncomplicated inguinal herniorrhaphy under general anaesthesia at 5 1/2 months of age. In the absence of overt self-injurious behaviour, the diagnosis was not considered for nearly two decades. The diagnosis of LND was established at 20 years of age through clinical review, biochemical examinations and molecular analysis. HPRT haemolysate activity was 7.6% of the normal control, suggesting that he had a milder variant of the disease. Mutation analysis of the HPRT gene revealed a novel missense mutation, c.449T > G in exon 6 (p.V150G). Cascade testing of family members revealed that the mother was heterozygous for the mutation but two siblings (a brother and a sister) did not carry the sequence mutation. Whether the onset of neurological abnormalities in this particular case can be attributed to the general anaesthesia is discussed.

Adult↗

Influence of low extracellular Ca2+ ions on the cardiac function changes induced by verapamil in the perfused rabbit heart.

We tested the hypothesis that the myocardial effects of verapamil (VER) could be enhanced by decreasing the extracellular Ca2+ concentration ([Ca2+]o) in the isolated rabbit heart at 37 degrees C. After perfusion with standard Krebs - bicarbonate solution containing 1.27 mM Ca2+, for a 30-min period of stabilization and 15 min of control, groups of hearts were perfused for an additional 60 min with solutions containing one of the following: 1.27 mM Ca2+ (control group), 0.23 mM Ca2+ (low [Ca2+]o group), 1.27 mM Ca2+ plus 10(-7) M VER (VER group), or 0.23 mM Ca2+ plus 10(-7) M VER (combination, CBN group). These concentrations of [Ca2+]o and VER produce submaximal responses in our preparation. We found that the heart rate - LV pressure product (RPP) in the CBN group fell rapidly to 0 in the first 2-3 min of perfusion, this response being significantly lower than in the other two groups for the first 15 min. Electromechanical dissociation (EMD) appeared in one of six hearts at 60 min and in four of six hearts at 30 min in the low [Ca2+]o and VER groups, respectively, whereas it occurred in the CBN group in all hearts at 3 min. Depolarization rate (DR) fell by 10% in the low [Ca2+]o and VER groups versus a reduction of 45% in the CBN group (P less than 0.05) during the last 45 min of perfusion. The PR interval increased by 300% in the CBN group, a much greater and significant change (P less than 0.05) than in the hearts exposed to VER or low [Ca2+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Low extracellular Ca2+ and enzyme release in the perfused rabbit heart.

Previous studies have shown that the well-oxygenated perfused rabbit heart releases creatine kinase when treated with the calcium antagonist drug verapamil (VER) in a dose-related manner. It is possible that this effect is related to Ca2+ ion deprivation of the sarcolemma. This possibility was explored by perfusing hearts with low Ca2+ (0.5, 0.23, 0.15, and 0 mM) versus a control group (1.27 mM Ca2+) for 60 min. Low Ca2+ perfusion was associated with reduction in the heart rate--left ventricular systolic pressure product and O2 consumption, tendency for the coronary sinus flow to increase, electromechanical dissociation, prolongation of atrioventricular conduction and QT interval, and decrease in myocardial glycogen. Lower total adenosine nucleotides were found only in the 0 mM Ca2+ group. As the Ca2+ concentration was reduced, the hearts lost increasing amounts of creatine kinase, aspartate aminotransferase, and lactate dehydrogenase. These results confirm the importance of Ca2+ ions in contractile and electrical cardiac functions and show that decreased availability of this cation leads to increasing enzyme leakage resembling that seen in VER-treated hearts.

Animals↗

Ventricular fibrillation induced prior to cardioplegic arrest in hypertrophied pig hearts.

We hypothesized that by inducing ventricular fibrillation (VF) prior to cardioplegic arrest in nonvented hypertrophied hearts of pigs, the metabolic characteristics of the epicardial and endocardial regions would be compromised compared with animals in which cardioplegic solution was infused while the hearts were in normal sinus rhythm (NSR). These abnormalities would be reflected not only in greater deterioration of myocardial metabolism after reperfusion in the VF group, but they would also be more pronounced in the subendocardial layers of hypertrophied left ventricles. Results obtained in hypothermic hearts (28 degrees C) maintained at 8 degrees to 12 degrees C during cardioplegic arrest demonstrated no major consistent differences in the stores of glycogen, creatine phosphate, adenine nucleotides, and lactate in both groups of hearts, for either layer of the left ventricular myocardium. The only significant difference was slightly lower creatine kinase content in the VF hearts than in the NSR group. It is concluded that induction of VF in hypothermic (28 degrees C), nonvented, hypertrophied hearts prior to infusion of cardioplegic solution does not affect myocardial energy stores compared with hearts in NSR, provided that the period of VF prior to clamping is short (3 minutes) and that the myocardial temperature is lowered to 28 degrees C prior to VF and is maintained at 8 degrees to 12 degrees C during cardioplegic arrest.

Adenine Nucleotides↗

The hemodynamic and metabolic effects of cardioplegic rearrest in the pig.

The hemodynamic and metabolic effects of two consecutive 1-hour periods of cardioplegic arrest with a 20-minute interval of reperfusion or cardioplegic rearrest were evaluated in pig hearts. This model was designed to recreate in the laboratory a situation occasionally encountered during open-heart operation. Results indicate that at the end of 40 minutes of reperfusion following cardioplegic rearrest and 20 minutes after cardiopulmonary bypass (CPB), the stores of glycogen, adenosine triphosphate and total adenine nucleotides were lower than those found in hearts beating under CPB for an identical period of time. These stores were, however, sufficient to permit hemodynamic recovery, and they compared favorably with those found in hearts subjected to a single hour of cardioplegic arrest and reperfusion. The laboratory data and our previous clinical experience suggest that cardioplegic rearrest is a feasible alternative when surgical difficulties demand a second period of aortic cross-clamping after an initial period of cardioplegic arrest and reperfusion.

Adenine Nucleotides↗

Should ventricular fibrillation be induced prior to the infusion of cardioplegic solution?

The present study evaluates the metabolic effects on the left ventricular energy stores of a clinically used cardioplegic solution that was infused into the ascending aorta of pigs while the heart was either fibrillating (induced ventricular fibrillation) or in normal sinus rhythm prior to aortic clamping. Fibrillating hearts had lower stores of glycogen in the epicardium and endocardium compared with hearts in normal sinus rhythm. There was no difference in the stores of creatine phosphate between the hearts for both the epicardium and endocardium, but stores of adenosine triphosphate (ATP) in both layers were lower in fibrillating hearts. These results indicate that for ideal myocardial protection the cardioplegic solution should be infused while the heart is beating under cardiopulmonary bypass, and that ventricular fibrillation induced and maintained prior to cross-clamping may cause myocardial damage.

Adenosine Triphosphate↗

The spectrum of unstable angina: prognostic role of serum creatine kinase determination.

A prospective study of 199 patients with unstable angina pectoris was undertaken to assess whether frequent serial sampling of serum creatine kinase (CK) was useful in predicting prognosis. Nineteen percent of the patients had transient CK elevations suggestive of a small myocardial infarct that was outside the detective ability of conventional electrocardiographic and enzymatic determinations. These patients had a 1 year mortality rate of 16 percent, which was significantly higher than that in the remaining patients (Fisher's exact test p = 0.05). Furthermore, the recurrence rate of myocardial infarction (14 percent) in the patients who had transient CK elevation was significantly greater than that (2 percent) in those who did not have CK elevation (Fisher's exact test p = 0/01). These data suggest that frequent serum CK sampling in the first 48 hours after admission for unstable angina has prognostic value and that persons with CK elevation may warrant a more aggressive approach to investigation and management.

Adult↗

Metabolism of the perfused rabbit heart. V. Verapamil-induced release of creatine kinase.

The effects of verapamil (VER), at concentrations of 0 X 10(-9) X 10(-8) X 10(-7), and 5 X 10(-7) M (or 0, 0.5, 5, 50, and 250 ng/mL) were studied in the isolated rabbit heart during 70 min of aerobic perfusion with a standard Krebs-bicarbonate medium at 37 degrees C. The studied variables were left ventricular performance (RPP, heart rate times left ventricular (LV) systolic pressure), coronary sinus flow (CSF), oxygen uptake (MVO2), rate of creatine kinase (CK) release, and energy stores (glycogen, creatine phosphate (CP), ATP, and total adenine nucleotides (TAN) ). The results show that (i) VER depressed RPP in a dose-related manner: (ii) MVO2 declined as VER concentration increased except in the 5 x 10(-7) M group which showed a paradoxical increase in O2 uptake; (iii) CSF was only slightly decreased by VER with the exception of the 5 x 10(-7) M group, which showed an increase in flow; (iv) VER was associated with increments in the rates of CK release in a dose-related fashion (2, 4, 15, and 29 times the rate observed in the untreated group), and (v) VER was associated with slight decrease in glycogen levels, but no changes in CP or adenine nucleotides. It is concluded that, in our preparation, VER caused marked increases in the rate of CK loss in the absence of depletion of total energy stores. The data suggest that the drug affects the permeability characteristics of the sarcolemma, perhaps via localized depletion of calcium stores.

Animals↗

Is cardioplegic rearrest safe?

In cardiac bypass procedures the use of anoxic arrest or ventricular fibrillation is known to cause severe myocardial damage. The authors have investigated the safety of using cardioplegic rearrest when surgical difficulties are encountered at the end of cardiac bypass procedure after cardioplegic arrest and reperfusion of the myocardium. From their clinical experience with 12 patients and laboratory experience with 13 pigs the authors conclude that although cardioplegic rearrest is not ideal it can be used safely in this situation.

Animals↗

Cardioplegic rearrest: clinical experience with 12 patients.

Myocardial damage due to ischemic arrest occurs during aortic unclamping and early reoxygenation (reperfusion injury). Thus, surgeons may be reluctant to reinfuse cardioplegic agents if a second period of aortic cross-clamping is required at the end of cardiopulmonary bypass. Because of technical difficulties, 12 patients underwent two consecutive periods of cardioplegic arrest with an intervening period of reperfusion of the heart. All survived without complications. Myocardial biopsy specimens from three patients revealed some cellular edema. Serial enzyme levels measured postoperatively compared favourably with those of 12 other patients who had sustained a single period of multidose cardioplegic arrest. Postoperative hemodynamic measurements were similar to preoperative values. Although cardioplegic rearrest may appear safe in the human heart, further studies assessing hemodynamics, morphology and metabolism are necessary in order to delineate fully the changes that occur with this method of myocardial preservation.

Coronary Artery Bypass↗

Metabolism of the perfused rabbit heart. IV. Effects of beta-adrenergic blockade on enzyme release and later energy stores during postanoxic reoxygenation.

The effects of 80 microM dl-propranolol on left ventricular (LV) performance, energy stores, and creatine kinase (CK) release were studied in a modified Langendorff rabbit heart preparation during 75 min of aerobic perfusion and postanoxic reoxygenation. The data showed that this concentration of propranolol, which blocked the effects of beta-adrenergic stimulation without affecting LV performance, coronary sinus flow (CSF), or oxygen consumption (MV O2), was associated with greater stores of glycogen and adenine nucleotides at the end of aerobic perfusion. Similar effects were observed during postanoxic reoxygenation, when recoveries of left ventricular systolic pressure, heart rate, heart rate--left ventricular systolic pressure product, CSF, and MV O2 remained unchanged during propranolol administration, but myocardial concentrations of glycogen, creatine phosphate, and ATP were greater and the ATP:AMP ratio and the energy charge were higher than in untreated hearts. In addition, the rate of CK loss was lower in the blocked postanoxic hearts than in the unblocked group. These results indicate that propranolol had a beneficial effect on cardiac metabolism during postanoxic recovery tending to normalize energy stores and to reduce enzyme loss during reoxygenation or perfused rabbit hearts without affecting mechanical performance, coronary flow, or O2 metabolism.

Animals↗

Cardioplegic arrest in pigs. Effects of glucose-containing solutions.

A clinically used cardioplegic solution was evaluated in the laboratory in an attempt to elucidate the value of glucose in maintaining the glycogen and energy stores of the myocardium during aortic cross-clamping. In one group of animals the cardioplegic solution contained glucose; in the other group it did not. Energy stores were determined in full-thickness biopsies of left ventricular myocardium taken prior to bypass, at 60 minutes of cardioplegic arrest, and after 20 minutes of reperfusion. At the end of cardioplegic arrest, glycogen levels were slightly higher than control values, with no differences between the groups. Creatine phosphate (CP) and adenosine triphosphate (ATP) fell by 69% to 73% and 43% to 55%, respectively, from the control values, but there were no statistical differences between these groups. At the end of reperfusion, glycogen and CP stores had returned to control but ATP concentration remained below control values in both groups. These results indicate that glucose is of no value either to maintain myocardial glycogen or to influence the changes in CP and ATP during cardioplegic arrest. The dissociation between the complete and partial restoration of CP and ATP stores to control levels during reperfusion suggests either that ATP consumption is greater than the energy transfer between CP and ADP:ATP systems or that the energy transfer is defective under these experimental conditions.

Adenosine Triphosphate↗