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Biomedical subjects

D C Cheng

Publications and source records attributed to D C Cheng.

50 records · Page 3Linked to original sources
PubMed1992

Dose-response relationship of isoflurane and halothane versus coronary perfusion pressures. Effects on flow redistribution in a collateralized chronic swine model.

The authors studied the redistribution of myocardial blood flow in a collateral-dependent (CD) zone as a function of coronary perfusion pressure (CPP) during isoflurane and halothane anesthesia. A swine model with CD myocardium distal to a chronically occluded left anterior descending coronary artery was developed and studied. Sixteen piglets were allowed to grow for 8-10 weeks after banding of the left anterior descending coronary artery. They were randomly anesthetized with either isoflurane (n = 8) or halothane (n = 8) as the sole anesthetic, which was used to regulate specific CPP. The resultant regional myocardial blood flows were measured using radiolabeled microspheres. Four randomly allocated CPPs, of 30, 40, 45, and 55 mmHg, were studied in each animal. Four additional collateralized animals were anesthetized with alpha-chloralose, and the same CPPs were obtained using an intravenous adenosine infusion (1-5 microM kg-1) to validate this model. There was a proportional decrease in heart rate and blood pressure in both the isoflurane and and the halothane group with CPP. Cardiac output was significantly decreased in the halothane group at 30 mmHg when compared to 55-mmHg CPP, but it was maintained in the isoflurane group. Systemic vascular resistance was significantly lower in the isoflurane group at 30 and 40 mmHg when compared to 55-mmHg CPP. Both the isoflurane and the halothane group showed a proportional and significant decrease in endo-, mid-, and epicardial blood flows at 30-mmHg CPP when compared to baseline. In both CD and normal perfusion zones, isoflurane consistently sustained a higher endocardial blood flow than halothane (5.7-41.1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Analgesic and pulmonary effects of continuous intercostal nerve block following thoracotomy.

This study examined the beneficial effects and potential systemic toxicity from continuous intercostal nerve block by repeated bolus injections of bupivacaine. In this double-blind, randomized study, 20 post-thoracotomy patients were assigned to receive four doses of either: 20 ml 0.5% bupivacaine with epinephrine 5 micrograms.ml-1 (bupivacaine group, n = 10), or 20 ml preservative-free saline (placebo group, n = 10) through two indwelling intercostal catheters every six hours. Patients receiving intercostal bupivacaine injections had greater decreases in visual analogue pain scores (VAS) (P less than 0.05) and lower 24 hr morphine requirements, 16.6 +/- 4.6 mg vs 35.8 +/- 7.2 mg, than patients in the placebo group (P less than 0.05). Higher post-injection values of forced expiratory volume in one second, forced vital capacity and peaked expiratory flow rate were also observed in the bupivacaine group (P less than 0.01). Repeated intercostal bupivacaine administration did lead to systemic accumulation, but the peak bupivacaine level after 400 mg was low at 1.2 +/- 0.2 microgram.ml-1. Thus, the technique of continuous intercostal nerve block described in this study is an effective treatment for the control of post-thoracotomy pain.

Adult↗
PubMed1990

Low-dose sufentanil and lidocaine supplementation of general anaesthesia.

This randomized double-blind study compared the effects of: (1) saline infusion (C); (2) sufentanil alone (1.0 micrograms.kg-1) (S); and (3) low-dose sufentanil (0.5 micrograms.kg-1) in combination with lidocaine (1.5 mg.kg-1) (LS): on the cardiovascular responses to tracheal intubation and on postoperative ventilation as monitored by respiratory inductive plethysmography in day-care surgical procedures of approximately 60 min duration. Thirty healthy, unpremedicated patients were studied. Thiopentone requirements were reduced by 40 and 28 per cent in the S and LS groups respectively compared with control (P less than 0.001). Both treatments suppressed HR and BP responses (P less than 0.005) to intubation. Postoperatively, PaCO2 was elevated (P less than 0.05) in group S. Dose-related respiratory depression was observed. The incidence of postoperative apnoea was significantly higher in both S and LS groups than compared with control (P less than 0.05). However, only patients in group S showed higher apnoea index and mean apnoea duration over the initial 10-20 min after surgery compared with control (P less than 0.005). In addition, group S showed slower respiratory frequency and prolonged expiratory time (P less than 0.005). In conclusion, an induction dose of sufentanil (1 microgram.kg-1) used in balanced anaesthesia of less than 70 min duration was associated with significant respiratory depression, particularly during the initial 10-20 min after surgery, whereas low-dose sufentanil (0.5 micrograms.kg-1) with lidocaine (1.5 mg.kg-1) had minimal postoperative respiratory depression and comparable attenuation of pressor responses to intubation.

Adjuvants, Anesthesia↗
PubMed1990

A randomized comparison of midazolam and diazepam injectable emulsion in cataract surgery.

The purpose of this study was to compare the psychomotor recovery of patients sedated with either midazolam or Diazemuls using the digit symbol substitution test and the Trieger test. Sixty patients were allocated in random double-blind fashion to receive either midazolam or diazepam in oil emulsion (Diazemuls) as intravenous sedation for cataract surgery. Both groups received fentanyl 0.5 micrograms.kg-1 IV. Tests of cognition were performed by the patients prior to sedation and at half-hourly intervals for three hours after cataract surgery. In a dose ratio of 1:4, midazolam was found to produce better sedation but more prolonged recovery than Diazemuls. Anterograde amnesia was comparable in the two groups, while more patients in the Diazemuls group developed episodes of apnoea and venous irritation.

Aged↗
PubMed1990

Differential effect of oncotic pressure on cerebral and extracerebral water content during cardiopulmonary bypass in rabbits.

To study the effect of oncotic pressure on brain water content during cardiopulmonary bypass (CPB), 14 anesthetized New Zealand White rabbits underwent 60 min of nonpulsatile CPB at normothermia. Animals were grouped according to the composition of the circuit priming fluid. Group 1 animals (n = 7) received a priming fluid (6.5% hydroxyethyl starch in 0.72 N NaCl; 323 +/- 13 mOsm/kg [mean +/- SD]) that maintained normal colloid oncotic pressure (COP) during CPB (19.0 +/- 1.5 mmHg). Group 2 animals (n = 7) received a priming fluid (0.9 N NaCl; 324 +/- 23 mOsm/kg) that led to a hypooncotic state (COP = 6.2 +/- 1.2 mmHg). Blood chemistries and hemodynamics were recorded every 15 min during CPB. Animals were given additional priming fluid and sodium bicarbonate during CPB to maintain a circuit flow of 85 ml.kg-1.min-1 and arterial pH greater than 7.35. There were no significant differences between groups 1 and 2 with respect to temperature, central venous pressure, mean arterial pressure, PaO2, PaCO2, plasma sodium concentration, or osmolality at any time during CPB, although osmolality increased in both groups. After 60 min of bypass, animals were killed and organ water contents were determined by wet/dry weight ratios. A separate group of nine similarly prepared and anesthetized animals that did not undergo cannulation or CPB also underwent measurement of plasma chemistries and tissue water contents and served as nonbypass controls (group 3). Brain and kidney water contents were unaffected by oncotic pressure, whereas duodenum and skeletal muscle had significantly greater water content (P = 0.003 and P = 0.008, respectively) after hypooncotic CPB.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Postoperative myocardial infarction documented by technetium pyrophosphate scan using single-photon emission computed tomography: significance of intraoperative myocardial ischemia and hemodynamic control.

The aim of this prospective study was to document postoperative myocardial infarction (PMI) by technetium pyrophosphate scan using single-photon emission computed tomography (TcPPi-SPECT) in 28 patients undergoing elective coronary bypass grafting (CABG). The relationships of intraoperative electrocardiographic myocardial ischemia, hemodynamic responses, and pharmacological requirements to this incidence of PMI were correlated. Radionuclide cardioangiography and TcPPi-SPECT were performed 24 h preoperatively and 48 h postoperatively. A standard high-dose fentanyl anesthetic protocol was used. Twenty-five percent of elective CABG patients were complicated with PMI, as documented by TcPPi-SPECT with an infarcted mass of 38.0 +/- 5.5 g. No significant difference in demographic, preoperative right and left ventricular function, number of coronary vessels grafted, or aortic cross-clamp time was observed between the PMI and non-PMI groups. The distribution of patients using preoperative beta-adrenergic blocking drugs or calcium channel blocking drugs was found to have no correlation with the outcome of PMI. As well, no significant differences in hemodynamic changes or pharmacological requirements were observed in the PMI and non-PMI groups during prebypass or postbypass periods, indicating careful intraoperative control of hemodynamic indices did not prevent the outcome of PMI in these patients. However, the incidence of prebypass ischemia was 39.3% and significantly correlated with the outcome of positive TcPPi-SPECT, denoting a 3.9-fold increased risk of developing PMI. Prebypass ischemic changes in leads II and V5 were shown to correlate with increased CPK-MB release (P less than 0.05) and tends to occur more frequently with lateral myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Artery Bypass↗
PubMed1988

Silicone polymer uptake method for determination of cholesterol thermodynamic activity in model bile systems.

Cholesterol in bile has been linked to the incidence of gallstone disease through the concept of supersaturation as measured by the cholesterol saturation index (CSI). The latter is a linear function of cholesterol concentration and is based on the assumption that all cholesterol in bile is solubilized and transported in bile salt-lecithin (BS-L) mixed micelles, as well as in bile salt simple micelles. In light of the discovery of the cholesterol-lecithin vesicles as significant cholesterol carriers, there is a need to re-evaluate this old concept. This study examined the feasibility of the silicone polymer uptake method for the direct determination of the cholesterol thermodynamic activity (AT) in model bile systems. In cases of unsaturation and near saturation, a linear relationship was observed between CSP,Eq, the cholesterol concentration in the silicone polymer at equilibrium, and CAq,Eq/Cs,Aq for taurocholate (TC), taurochenodeoxycholate (TCDC), and tauroursodeoxycholate (TUDC) systems either containing or not containing lecithin. Here, CAq,Eq is the cholesterol concentration in the aqueous micellar solution at equilibrium, and Cs,Aq is the cholesterol monohydrate solubility of the same medium. In TC-L solutions supersaturated with cholesterol, the linear relationship continued to hold up to the point where vesicles started to form. Vesicle formation initiated a negative deviation from linearity. At constant lecithin concentration, the CSP,Eq value, or the cholesterol thermodynamic activity at which vesicle formation began, was a function of the TC:L ratio; the larger the TC:L ratio, the higher the cholesterol thermodynamic activity for the onset of vesicle formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile↗
PubMed1988

Calcium channel blockade does not offer adequate protection from perioperative myocardial ischemia.

This study aimed to detect the difference in hemodynamic and electrocardiographic responses during the prebypass period in patients undergoing coronary bypass grafting who were receiving beta-adrenergic blocking drugs, calcium entry blocking drugs, or both beta-adrenergic and calcium entry blocking drugs. Electrocardiographic evidence of myocardial ischemia was noted significantly more frequently in patients receiving calcium entry blocking drugs alone at induction of anesthesia (P less than 0.03), skin incision (P less than 0.05), and sternotomy (P less than 0.002). Heart rate at sternotomy was significantly higher in patients receiving calcium entry blocking drugs (P less than 0.02) as compared to patients receiving beta-adrenergic blocking drugs or the combination of both drugs. In conclusion, patients treated with calcium entry blocking drugs alone had significantly higher incidence of perioperative ischemic ECG changes compared with patients receiving beta-adrenergic blocking drugs alone or in combination with calcium channel blocking drugs.

Adrenergic beta-Antagonists↗
PubMed1988

Isoflurane and primary pulmonary hypertension.

Primary pulmonary hypertension is a rare and fatal disease. These patients represent an anaesthetic challenge because of the high mortality associated with the marked intra-operative increase in pulmonary vascular resistance and right ventricular decompensation. This is a first case report which demonstrates the safe and beneficial effects of isoflurane in lowering pulmonary arterial pressure and pulmonary vascular resistance in such a patient for a short surgical procedure. The anaesthetic considerations in these patients are discussed.

Adult↗
PubMed1985

Changes in blood amino acids account for the insulin and glucagon responses to mixed meals in dogs.

The relationships between changes in the plasma levels of immunoreactive insulin (IRI) and glucagon (IRG) in response to the postprandial increments of circulating amino acids were studied under normal physiological conditions in healthy dogs. In the presence of a unique postprandial physiological euglycemic "glucose clamp" which occurs in these dogs, plasma IRG rose to an earlier peak than IRI and both remained elevated for 16-19 hr. Amino acid (AA) profiles also showed postprandial incremental responses for up to 16 hr. Multiple correlation analyses indicated that only branched chain AAs were significantly correlated with IRI profiles and were devoid of a relationship to IRG. Similarly, only ornithine, lysine and glycine were significantly correlated with IRG profiles and devoid of a relationship to IRI. The significance of individual IRG stimulating effects of alanine and arginine were masked by other amino acid interactions, as significant intercorrelation was found among all 13 amino acids. Two equations were derived from the multiple regression analysis accounting for the postprandial time course of changes in IRI and IRG levels with only 5 amino acid concentrations: (1) (delta IRI) = 0.37 (delta Leu) -0.45(delta His), and (2) (delta IRG) = 0.55(delta Orn) + 0.37(delta Gly) -0.69 (delta Ser). These observations confirm the physiologic role in islet hormone secretion of the postprandial increments in circulating amino acids in the absence of glycemic change.

Amino Acids↗
PubMed1983

Norethindrone acetate inhibition of triglyceride synthesis and release by rat hepatocytes.

The progestin, norethindrone acetate has been widely administered to patients in the form of oral contraceptives; however, its hypolipemic action has received little study. This report describes the effects of conventional doses of norethindrone acetate (100 micrograms/day.kg body weight 0.75) on rat plasma lipid levels in vivo as well as the mechanism of action on triglyceride metabolism in isolated hepatocytes in vitro. Norethindrone acetate administration led to significant and proportional reductions of the concentrations of triglycerides, cholesterol and phospholipids of plasma lipoproteins of density less than 1.006 of rats fed a high carbohydrate diet. Norethindrone acetate (0.1 mM) also significantly inhibited the incorporation of both [9,10(-3)H] palmitate and [U-14C]glycerol into triglycerides of isolated hepatocytes from fed rats, by 11 to 16% (P less than 0.001). Release of labeled triglycerides from the isolated hepatocytes was similarly inhibited, 21% and 46%, respectively (P less than 0.05). At the higher concentration of 1.0 mM, norethindrone acetate inhibited the incorporation of [2(-3)H]glycerol into hepatocytic triglycerides by 35-39% (P less than 0.05). The present findings suggest that inhibition of hepatic triglyceride synthesis can account for the reduction of hepatic triglyceride secretion and for at least part of the lowering of plasma VLDL levels which occurs during administration of norethindrone acetate in the rat.

Animals↗
PubMed1978

A new double-labelling procedure for determination of amino acid composition: application to bacteriorhodopsin.

A new double-labelling procedure for amino acid analysis which requires only routine chromatographic equipment is described. When 1-fluoro-2,4-dinitro[3H]benzene is reacted with a mixture of 14C-labelled amino acids followed by reaction with the same 14C-labelled amino acid mixture diluted with an unlabelled sample of amino acids, the 3H:14C ratio in the resulting 2,4-dinitrophenyl (DNP) amino acid derivatives of the diluted sample will be increased in proportion to the quantity of unlabelled amino acid in the diluted sample. This procedure gave reliable results when applied to the known proteins insulin and lysozyme. The procedure is most advantageous when applied to amino acids which are unstable during acid hydrolysis or present in low molar fractions. When applied to the analysis of the bacteriorhodopsin in Halobacterium cutirubrum, this procedure showed the presence of one histidine residue and four tryptophan residues per mole protein but no cystine or cysteine; in general, the analyses obtained were consistent with those originally reported by Oesterhelt, D. and Stoeckenius, W. (1971) (Nature (London) New Biol. 233, 149-152) for bacteriorhodopsin of H. halobium.

Amino Acids↗