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Biomedical subjects

L M Liu

Publications and source records attributed to L M Liu.

At least 73 records · Page 4Linked to original sources
PubMed1988

Effects of 2.45-GHz microwave and 100-MHz radiofrequency radiation on liposome permeability at the phase transition temperature.

Large unilamellar dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) liposomes loaded with an aqueous chemotherapeutic drug, cytosine arabinofuranoside (ARA-C), were exposed for 30 min to 60 W/kg continuous-wave (CW) 100-MHz or 2.45-GHz radiation in vitro at temperatures between 37 degrees C and 43 degrees C. Liposomes were exposed in HEPES buffer or in HEPES buffer supplemented with 44% by volume fetal calf serum (FCS). Characteristic phase transition responses were detected in the range of 39 degrees C to 40 degrees C with the presence of FCS, increasing maximum % release of 3H-ARA-C by 20% relative to HEPES suspension. Neither frequency of electromagnetic radiation had any detectable effect on liposome permeability or the location of the phase transition in the presence or absence of FCS.

Cytarabine↗
PubMed1988

Evidence for a role of basic fibroblast growth factor in rat embryonic growth and differentiation.

The possibility that basic fibroblast growth factor (FGF) plays a role in the regulation of mammalian embryogenesis was investigated. When transplanted under the renal capsule of syngeneic juvenile hosts, 10-day-old rat embryos grow rapidly, and tissue differentiation occurs in an essentially normal manner. Infusion of antiserum to bovine FGF into the renal artery of kidneys bearing such transplants significantly retarded their growth, and differentiation of all tissues of endodermal and some of those of mesodermal origin was completely suppressed; differentiation of other tissues of mesodermal origin was partially inhibited. Infusion of nonimmune serum had no such effects. Infusion of recombinant bovine FGF into the renal artery stimulated growth of embryo transplants on the infused kidney, but not of those under the renal capsule of the contralateral kidney, and it did not affect growth of the infused kidney itself. These results suggest that FGF may be important for growth and differentiation of endodermal and some mesodermal tissues of mammalian embryos.

Animals↗
PubMed1986

Intraoperative events diagnosed by expired carbon dioxide monitoring in children.

Expired carbon dioxide measurements (PeCO2) were used (1) to assess the adequacy of initial alveolar ventilation, and (2) to document intraoperative airway events and metabolic trends. Three hundred and thirty-one children were studied. Thirty-five intraoperative events were diagnosed by continuous PeCO2 monitoring; 20 were potentially life-threatening problems (malignant hyperthermia, circuit disconnection or leak, equipment failure, accidental extubation, endobronchial intubation, or kinked tube); only two of these were also diagnosed clinically. The duration of anaesthesia may be a factor: 3.9 hours for cases with events vs. 2.5 hours for cases without events (p less than 0.002). There was a higher incidence of hypercarbia (peak expired PeCO2 greater than or equal to 50) in children who were not intubated (29 per cent) compared to those who had an endotracheal tube in place (12 per cent) (p = 0.0001). Hypocarbia (peak expired PeCO2 less than or equal to 30) was more frequent in intubated cases (11 per cent) than in unintubated cases (three per cent) (p = 0.03). There was a high incidence of hypocarbia in infants less than one year of age (p = 0.02). We conclude: (1) life-threatening airway problems are common during anaesthesia in paediatric patients; (2) quantitative measurement of PeCO2 provides an early warning of potentially catastrophic anaesthetic mishaps; (3) the incidence of events increases with duration of anaesthesia.

Anesthesia↗
PubMed1986

Histamine release during the administration of atracurium or vecuronium in children.

The histamine releasing potential of equivalent bolus doses of atracurium 0.6 mg kg-1 or vecuronium 0.12 mg kg-1 was evaluated in 20 children anaesthetized with halothane. Blood samples were obtained before, and at 2 and 5 min after the administration of the neuromuscular blocker. The twitch response to 0.15 Hz was also evaluated. None of the 10 patients receiving vecuronium had a significant increase in plasma histamine concentration. In two of the 10 children receiving atracurium, the plasma histamine concentration increased markedly, but without any apparent clinical manifestations. Recovery of neuromuscular function (to 95% twitch height) after vecuronium 0.12 mg kg-1 was faster than after atracurium 0.6 mg kg-1 (P less than 0.02).

Atracurium↗
PubMed1986

Continuous infusion of atracurium in children.

Atracurium infusion requirements were determined in 28 children anesthetized with N2O:O2 narcotic, N2O:O2 halothane (1% inspired), and N2O:O2 enflurane (2% inspired). When the patient was recovering from a bolus dose of 0.4 mg/kg atracurium, a continuous infusion of atracurium was started and the rate was adjusted to maintain 90-99% muscle twitch depression. Patients receiving enflurane anesthesia required atracurium at an infusion rate of 4.9 +/- 0.3 micrograms X kg-1 X min-1 which was a significantly lower rate (P = 0.0001) than those anesthetized with halothane (8.3 +/- 0.4 micrograms X kg-1 X min-1) or with N2O:O2 and narcotic (9.3 +/- 0.5 micrograms X kg-1 X min-1). At the onset of neuromuscular blockade, the twitch response disappeared faster after train-of-four stimulation repeated every 10 s than after single twitch rates of stimulation at 0.1 Hz. In children, during halothane anesthesia after 0.4 mg/kg atracurium, the response of the adductor of the thumb was ablated in 2.0 +/- 0.3 min with train-of-four stimulation, and in 3.7 +/- 0.4 min with single twitch stimulation. The authors recommend the use of a nerve stimulator during continuous infusion of atracurium because of the marked interpatient differences in infusion-rate requirements.

Anesthesia↗
PubMed1985

Viability and phagocytosis of neutrophils exposed in vitro to 100-MHz radiofrequency radiation.

Rabbit polymorphonuclear leucocytes (PMN, neutrophils) obtained from peritoneal exudate were exposed in vitro for one-half or one hour to continuous wave or amplitude-modulated (20-Hz) 100-MHz RF radiation in a temperature-controlled coaxial exposure chamber at field strengths from 2.5 to 4.1 V/cm (SARs of 120 to 341 W/kg). RF exposure at 37 +/- 0.2 degrees C had no detectable effect on PMN viability or phagocytosis compared to sham-exposed cells simultaneously subjected to the same time-temperature regime. Temperature control studies indicated that at 37 degrees C no effect on PMN viability would be expected but phagocytosis would be reduced by approximately 6%/degrees C temperature increase. The absence of an effect of RF exposure suggests that there was minimal undetected intrasample heating and that phagocytosis was not affected by 100-MHz RF radiation under the conditions of this study.

Animals↗
PubMed1985

Erythrocyte hemolysis by radiofrequency fields.

A field-strength-dependent hemolytic effect of continuous-wave radiofrequency (RF) exposure in vitro has been demonstrated. Erythrocytes in whole heparinized rabbit blood were hemolyzed by a 2-h exposure to 50- or 100-MHz RF fields at field strengths of greater than 4 V/cm. An effect of comparable magnitude resulted from exposure to 10-MHz RF at a field strength of 9 V/cm. Sample temperatures were maintained at 22.5 degrees +/- 0.2 degrees C. There was no apparent involvement of heating or temperature gradients, nor were there any RF exposure effects on cellular K+ or Na+ concentration, nor on pH. The mechanism of the hemolytic effect is not known. Since the percentage of lysed erythrocytes was less than 1% and there was an absence of effects on cellular cation concentrations, RF radiation may have irreversibly altered the plasma membrane permeability of a sensitive subpopulation of red cells (possibly aged cells) leading to osmotic lysis. RF radiation at these frequencies appears to affect red cells in a manner that is qualitatively and quantitatively different from microwave radiation.

Animals↗
PubMed1985

Foetal monitoring in parturients undergoing surgery unrelated to pregnancy.

Foetal heart rate and tocodynamic monitoring of the uterus was performed in five pregnant patients undergoing urgent or emergency surgery unrelated to their pregnancy. All received general anaesthesia with halothane or enflurane and nitrous oxide. The loss of beat-to-beat variation of the foetal heart rate was observed in all patients under general anaesthesia, and is probably normal for the anaesthetized foetus. Since continuous intraoperative monitoring of foetal heart rate in pregnant patients is technically feasible during peripheral surgery and during many intra-abdominal procedures, attempts should be made to monitor foetal heart rate in all anaesthetized parturients to assure that the anaesthetic is not causing foetal insult. Postoperative monitoring of uterine tone is useful in the diagnosis and treatment of postoperative premature labor.

Adolescent↗
PubMed1985

Methohexital plasma concentrations in children following rectal administration.

Despite the increasing use of rectal methohexital as a premedicant-induction agent in pediatric anesthesia, there are no data to confirm the assumption that low plasma methohexital concentrations are the cause of inadequate sedation of children and that high concentrations are associated with the loss of consciousness. Plasma methohexital concentrations were determined in 20 ASA Class I children, ages 2-7 yr, after the rectal administration of methohexital (25 mg/kg). Seventeen of the 20 children in this study fell asleep after receiving the drug and achieved peak plasma concentrations greater than 2 micrograms/ml. The maximum plasma methohexital concentration in children that did not fall asleep was less than 2 micrograms/ml. The mean time to the onset of sleep after drug administration was 8.3 min (at which time the mean plasma concentration was 4.4 micrograms/ml). The mean peak plasma concentration and the mean time to peak plasma concentration were 4.7 micrograms/ml and 13.9 min, respectively. Loss of consciousness after rectal administration of methohexital correlates well with the plasma concentration of the drug.

Anesthesia, Inhalation↗
PubMed1984

The dose response effect of long-acting nondepolarizing neuromuscular blocking agents in children.

Cumulative dose-response curves were constructed for pancuronium, metocurine, d-tubocurarine and gallamine in 56 children anaesthetized with thiopentone, N2O/O2 and narcotic. The dose response curves of the four relaxants did not deviate significantly from parallelism. The effective dose causing 95 per cent depression of the twitch at 0.1 Hz was: pancuronium 0.08 mg X kg-1, metocurine 0.34 mg X kg-1, d-tubocurarine 0.6 mg X kg-1, and gallamine 3.4 mg X kg-1. Thus, pancuronium is 40 times more potent than gallamine, while metocurine and d-tubocurarine are seven and four times more potent than gallamine. The recovery of twitch height from 5-25 per cent of control for pancuronium (15.6 +/- 1.7 min) was significantly faster (p less than 0.01) than metocurine (27.3 +/- 1.9 min), d-tubocurarine (32.2 +/- 4.8 min), or gallamine (30 +/- 3.3 min). Compared to studies in adults, the present data indicate that children have a tendency (statistically not significant) to require more relaxant and recover more quickly than adults.

Adult↗
PubMed1984

The neuromuscular response of infants to a continuous infusion of succinylcholine.

The response of the adductor of the thumb to ulnar nerve stimulation (0.1 Hz) was evaluated during continuous infusion of succinylcholine (SCh) in 20 infants anesthetized with halothane (1%) and N2O2/O2. Train-of-four stimulation (2 Hz for 2 s) was used to differentiate between phase I and phase II block. Some infants were very resistant to the neuromuscular effects of SCh. These infants (Group 1) were younger in age, 57 +/- 15 days (mean +/- SE) and required 24.6 +/- 3.3 mg X kg-1h-1 SCh to achieve more than 90% depression of the twitch. Older infants (Group 2), 188 +/- 33 days, required significantly less (P less than 0.001) SCh (8.7 +/- 0.5 mg X kg-1h-1) to achieve the same degree of twitch suppression. Group 1 infants recovered from the effects of SCh very rapidly. After 10 mg/kg SCh, the train-of-four ratio in Group 1 infants recovered to 75% in 4.7 +/- 0.6 min, whereas it took 34 +/- 10 min in Group 2 infants (P less than 0.01). Tachyphylaxis developed in infants after 3.6 +/- 0.3 mg/kg (mean +/- SE) and phase II block after 5.3 +/- 0.7 mg/kg (P less than 0.05) SCh. Combining the data of infants with that of children from a previous study conducted in a similar fashion resulted in significant correlation (P less than 0.001) between the log age and SCh requirement. The rate of administration of a continuous infusion of SCh in infants should be based upon the response of infants and not on a fixed dose (mg X kg-1 X h-1).

Humans↗