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Biomedical subjects

L M Liu

Publications and source records attributed to L M Liu.

At least 91 records · Page 5Linked to original sources
PubMed1983

Correlation of myoelectric activity and muscle force during selected cat treadmill locomotion.

The purpose of this investigation was to associate the force produced by the cat medial gastrocnemius (MG) during unrestrained treadmill locomotion with the corresponding myoelectric signals (MES's). An intervention analysis based on the autoregressive-integrated moving average (ARIMA) process was performed on records obtained at treadmill speeds of 0.67 ms-1 and 2.24 ms-1. Results indicate that the pattern of MG myoelectric activity during a single step cycle may be divided into two parts. The primary burst (E1 burst) of activity occurs before foot contact and represents an energy build up which is related to a major part of the MG force monitored at the tendon. During stance, a second burst of activity is depicted by an almost critically damped second order system, and is responsible for the residual tension observed. Thus in vivo forces can be linked to MES's provided that phase differences between electrical and mechanical responses are taken into account.

Animals↗
PubMed1983

Metocurine requirements and plasma concentrations in burned paediatric patients.

A cumulative dose-response study for metocurine was performed on 11 burned and 11 non-burned children during thiopentone, nitrous oxide in oxygen and narcotic anaesthesia. Burned children required a significantly (P less than 0.001) greater dose (three-fold) of metocurine to achieve a given degree of neuromuscular blockade compared with non-burned children. For the same degree of twitch depression, burned children required twice the plasma concentration of metocurine. Despite the larger dose, the recovery time for the twitch was not significantly different in the two groups. It is speculated that there may be fundamental changes at the neuromuscular junction of burned children to account for their resistance to the effect of non-depolarizing neuromuscular blockers.

Anesthesia, General↗
PubMed1983

Life-threatening apnea in infants recovering from anesthesia.

To determine whether prematurely born infants with a history of idiopathic apneic episodes are more prone than other infants to life-threatening apnea during recovery from anesthesia, the authors prospectively studied 214 infants (173 full term, 41 premature) who received anesthesia. Fifteen premature infants had a preanesthetic history of idiopathic apnea. Six of these required mechanical ventilation because of idiopathic apneic episodes during emergence from anesthesia. Two were ventilated for other reasons, and seven recovered normally. Infants ventilated for apnea were younger (postnatal age 1.6 +/- 1.2 months, mean +/- SD; conceptual age 38.6 +/- 3.0 weeks) than those who recovered normally (postnatal age 5.6 +/- 2.7 months; conceptual age 55.1 +/- 11.3 weeks) (P less than 0.01). No other premature or full-term infant was ventilated because of postoperative apneic episodes. The authors conclude that anesthetics may unmask a defect in ventilatory control of prematurely born infants younger than 41-46 weeks conceptual age who have a preanesthetic history of idiopathic apnea.

Anesthesia↗
PubMed1983

Safety and efficacy of vecuronium in adolescents and children.

The neuromuscular and cardiovascular effects of vecuronium (Norcuron, ORG NC45) were studied in 40 adolescents (10-17 yr) and children (2-9 yr) anesthetized with 1.5% inspired halothane. Ten adolescents and ten children were given 20 micrograms/kg incremental doses of vecuronium to establish a cumulative dose-response curve during train-of-four stimulation. The ED95 dose was 56 micrograms/kg in children and 40 micrograms/kg in adolescents, children being significantly (P less than 0.01) more resistant to the neuromuscular effects of vecuronium than adolescents. Another group of 10 children and 10 adolescents received a bolus dose of 80 micrograms/kg. This dose provided satisfactory conditions for endotracheal intubation with complete suppression of train-of-four response in all adolescents and children within 2 min. Thereafter, the twitch tension recovered to 5% of control twitch height in 18.5 +/- 1.5 min, to 25% in 24.4 +/- 1.6 min, and to 95% in 43.3 +/- 2.1 min. Vecuronium (20-80 micrograms/kg) did not significantly alter the heart rate or blood pressure nor did it affect kidney or liver function as assessed by routine clinical laboratory tests. Vecuronium is a useful nondepolarizing neuromuscular blocking agent with a short to intermediate duration of action, which can be used safely in children and adolescents.

Adolescent↗
PubMed1982

Investigation of the effects of continuous-wave, pulse- and amplitude-modulated microwaves on single excitable cells of Chara corallina.

Single internodal excitable cells of Chara corallina were exposed to CW, pulse-modulated and sinusoidally modulated S-band microwave fields in a temperature-controlled waveguide exposure chamber. All electrical measurements were made external to the waveguide (ie, under no impressed microwave field). The dependent variables measured before, during, and after exposure to the S-band microwave fields included: resting potential, amplitude of the action potential, rise and decay time of the action potential, conduction velocity, and excitability. Cells maintained at 22 +/- 0.1 degrees C during exposure showed no consistent or statistically significant microwave-dependent alterations in any of the dependent variables.

Chlorophyta↗
PubMed1982

Effects of X-band microwave exposure on rabbit erythrocytes.

Rabbit erythrocytes were exposed in vitro to continuous wave (CW) and pulse-modulated X-band microwaves in wave guide exposure chambers. Erythrocytes were exposed as whole (heparinized) blood suspensions or as washed cells in 1:1 isotonic buffered K+-free saline suspensions. Statistically significant increases in K+ efflux relative to thermal controls were detected when red cells were exposed in whole blood suspensions to either CW or pulsed 8.42-GHz microwaves at SARs that resulted in equilibrium sample temperatures of approximately 24 degrees C. Under the same exposure conditions, no statistically significant K+ efflux occurred in the case of 1:1 red cell suspensions. Measured differences in sample heating rates and temperature gradients between microwave-exposed and heated control suspensions may account in part for the differential effect of microwave exposure but such effects do not appear to explain the results of this study fully.

Animals↗
PubMed1981

The dose-response effects of oral cimetidine on gastric pH and volume in children.

The effects of preanesthetic oral cimetidine on gastric fluid pH and volume were studied in 97 infants and children. A dose-response curve was constructed using doses of 2.5, 5.0, 7.5, and 10 mg/kg. The ED50 of cimetidine that produces pH values higher than 2.5 was 3.0 mg/kg, and the ED95 was 7.5 mg/kg. Cimetidine exponentially reduced the volume of gastric fluid. Cimetidine was most effective between one and four hours after oral administration. In children who are at high risk of pulmonary aspiration, we recommend that oral cimetidine, 7.5 mg/kg, be given 1-3 hours preoperatively in order to protect the lungs from the accidental aspiration of acidic gastric secretions.

Adolescent↗
PubMed1981

Comparison of equipotent doses of non-depolarizing muscle relaxants in children.

The neuromuscular effects of equipotent doses of non-depolarizing muscle relaxants used for endotracheal intubation were studied in 27 children anesthetized with thiopental, nitrous oxide/oxygen, and narcotic. Equipotent doses of d-tubocurarine (0.8 mg/kg), metocurine (0.5 mg/kg), and pancuronium (0.13 mg/kg) were used. At these doses conditions for intubation were satisfactory in all children and the twitch was completely abolished in 26 of the 27 patients. The twitch height recovered to 5% of control values in 54 +/- 6 minutes, and 29 +/- 2 minutes later recovered to 25% of control values. The time from injection of the drug to maximum effect, the conditions for intubation, and recovery times among the three drugs were not significantly different. Train-of-four values correlated (p less than 0.001) with the twitch heights. When the twitch height at 0.1 Hz was 21% of control values, only three contractions were detected following train-of-stimulation. At 14% of control twitch height, two contractions were detected; at 7% of control twitch height, one contraction was detected. The most frequent reason for administering an incremental dose of relaxant was the beginning of respiratory movements, corresponding to a twitch height of 24% of control values (train-of-four 3%). The second most common reason was unsatisfactory abdominal wall relaxation (twitch height 31% of control values, train-of-four 11%.

Anesthesia↗
PubMed1980

Studies of exposure of rabbits to electromagnetic pulsed fields.

Dutch rabbits were acutely exposed to electromagnetic pulsed (EMP) fields (pulse duration 0.4 mus, field strengths of 1--2 kV/cm and pulse repetition rates in the range of 10 to 38 Hz) for periods of up to two hours. The dependent variables investigated were pentobarbital-induced sleeping time and serum chemistry (including serum triglycerides, creatine phosphokinase (CPK) isoenzymes, and sodium and potassium). Core temperature measured immediately pre-exposure and postexposure revealed no exposure-related alterations. Over the range of field strengths and pulse durations investigated no consistent, statistically significant alterations were found in the end-points investigated.

Animals↗
PubMed1978

Metocurine in infants and children: neuromuscular and clinical effects.

A cumulative dose--response curve for metocurine based on body weight was determined in 30 infants and children during halothane (1.2 per cent inspired), nitrous oxide and oxygen (60/40 per cent) anesthesia. The mean and range of twitch depression and time for recovery from maximal neuromuscular blockade were not significantly different over an age range from newborn to 7 years. Metocurine is twice as potent as d-tubocurarine in children, and their requirement is more than that for adults. The rate of recovery from metocurine in children was the same as that from d-tubocurarine. In another 30 children, use of metocurine at a large dose (0.5 mg/kg) for endotracheal intubation caused no significant change in blood pressure or pulse rate. Cardial arrhythmias were not seen.

Blood Pressure↗