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Biomedical subjects

M C Allen

Publications and source records attributed to M C Allen.

At least 73 records · Page 4Linked to original sources
PubMed1986

The evolution of primitive reflexes in extremely premature infants.

A longitudinal study describes the pattern of appearance of eight primitive reflexes in a population of 47 viable extremely premature infants, beginning as early as 25 wk postconceptional age (PCA). Infants were examined weekly, from 1 wk of age until discharge from the neonatal intensive care unit. Primitive reflexes were graded as to completeness and intensity of response. Three patterns emerged: the upper and lower extremity grasp reflexes were present in all premature infants, from 25 wk and beyond, the Moro, asymmetric tonic neck reflex and Galant (lateral trunk incurvature reflex) were present in some premature infants as early as 25 wk PCA, and in the majority by 30 wk PCA, and the lower extremity placing, positive support, and stepping were occasionally present prior to 30 wk PCA, yet were not uniformly present and/or complete even at term. In each case, the primitive reflex became stronger, more complete, more consistently elicited and more prevalent with increasing postconceptional age. The pattern of primitive reflexes in the premature infant at term (40 wk PCA) is similar to that of full-term newborns. Sequential assessment of the primitive reflexes may be a useful method of evaluating extremely premature infants prior to term.

Birth Weight↗
PubMed1986

Medical complications of prematurity.

The improved survival of extremely premature infants has generated intense interest in the quality of life of the survivors. This review focuses on the major long-term complications of prematurity (developmental disability, retinopathy of prematurity, chronic lung disease) and concludes with an overview of the broader spectrum of morbidity. Severe impairment (cerebral palsy, mental retardation, retrolental fibroplasia, severe chronic lung disease) fortunately occurs in a small proportion of survivors. However, the prevalence of the lesser morbidities (minimal cerebral dysfunction/learning disability, poor growth, postneonatal illnesses, rehospitalization) is less clearly defined. These problems all have an impact on families, and on medical and educational services.

Attention Deficit Disorder with Hyperactivity↗
PubMed1985

Renal failure and the use of morphine in intensive care.

Intravenous morphine infusions were given to 20 patients in the intensive-care unit to provide sedation and analgesia. In 10 of the patients renal impairment was already present or developed during intensive care. Plasma morphine concentrations for a given dose of morphine and morphine clearance depended on renal function; dose-related plasma morphine concentrations rose as renal function deteriorated. Reduced morphine clearance leads to increased elimination half-life of the drug, and neurological impairment caused by unrecognised high concentrations of morphine could result in an incorrect diagnosis of cerebral damage in patients in intensive care.

Adult↗
PubMed1985

Use of an emulsion of ICI 35868 (propofol) for the induction and maintenance of anaesthesia.

2,6-Diisopropyl phenol in a fat emulsion formulation (propofol) has been used to supplement 67% nitrous oxide in oxygen anaesthesia in 20 patients premedicated with morphine 0.15 mg kg-1 and atropine 0.6 mg, and undergoing body surface surgery. Following an induction dose of propofol 2.5 mg kg-1, the mean maintenance dose was 73.4 micrograms kg-1 min-1. When compared with 10 patients receiving Althesin to supplement nitrous oxide in oxygen in a similar manner, recovery was considerably faster following propofol. The only major side-effect associated with the use of propofol was pain on injection in nine out of 20 patients. When the patients receiving propofol were compared with a second control group (n = 11) in whom anaesthesia was induced with thiopentone 4 mg kg-1 and maintained with 1% halothane and nitrous oxide in oxygen, the former group showed a significant (P less than 0.01) decrease in the plasma cortisol concentration 30 min after the induction of anaesthesia. However, by 3 h after induction, the cortisol concentration in both groups was not significantly different from the baseline (preinduction) value. The mechanism of this decrease is not known. Investigation of the influence of the fat emulsion on blood coagulation and fibrinolysis revealed no differences when compared with patients receiving Althesin.

Adolescent↗
PubMed1985

Peri-operative endocrine effects of etomidate.

This study investigated the effects of etomidate on endocrine responses to anaesthesia and surgery. Patients undergoing abdominal hysterectomy received standard anaesthetics of either etomidate for induction with etomidate infusion, or thiopentone and halothane. Etomidate suppressed the secretion of cortisol and aldosterone for between 8 and 22 hours after the end of the etomidate infusion; 11-deoxycortisol secretion was not suppressed during the etomidate infusion, but rose postoperatively; 17 alpha-hydroxyprogesterone suppression also lasted only as long as the etomidate infusion. There were no effects on plasma oestradiol, ACTH, or prolactin, but growth hormone concentrations were elevated in the etomidate group. Etomidate was concluded to have influenced adrenocortical function only, where it probably inhibits 11 beta-hydroxylation, 17 alpha-hydroxylation and other intramitochondrial hydroxylation reactions. There were no clinical sequelae attributable to adrenocortical suppression. The relationship of chemical structure of etomidate and other phenylated imidazoles to inhibition of steroidogenesis is discussed.

17-alpha-Hydroxyprogesterone↗
PubMed1985

Influence of meptazinol on metabolic and hormonal responses following major surgery. A comparison with morphine.

Opioid drugs in high doses can obtund the stress response to major surgery but only at the expense of marked cardiorespiratory depression. The postoperative hormonal response to surgical stress was measured in 20 patients undergoing hysterectomy who were given either meptazinol 100 mg or morphine 15 mg intramuscularly at the end of the surgery. Both drugs at the doses used failed to diminish the stress response. Those patients who received meptazinol showed elevated prolactin levels: this may be an indicator of agonist activity at the mu 1 opioid receptor.

Adult↗
PubMed1985

Systemic availability of oral slow-release morphine in man.

In a within-patient crossover study on twelve patients we investigated plasma morphine concentrations for 48 hours after administration of intravenous morphine sulphate followed 24 hours later by oral MST Continus [MST]. Patients received either 10 mg i.v. morphine followed by 10 mg MST or 20 mg i.v. morphine followed by 2 X 10 mg MST tablets. Systemic clearance of morphine was low, being about 3 ml/min/kg after both intravenous and oral administration. The ratio of the areas under the concentration-time curve for MST relative to that for i.v. morphine was about 1:1 for 20 mg doses, but was significantly greater than 1:1 for 10 mg doses. The results suggest high oral systemic availability for morphine and low hepatic morphine metabolism.

Administration, Oral↗
PubMed1985

Crib-O-Gram vs. auditory brain stem response for infant hearing screening.

As a part of the longitudinal evaluation of a cluster of neonatal hearing screening procedures in a single high risk population, Crib-O-Gram (COG) and auditory brain stem response (ABR) screening have been administered to 190 infants in the NICU. Multiple COG screening showed inconsistent results in 25% of the infants. The COG failure rate was 27.9% with 2 out of 3 pass criterion. In the two-intensity ABR screening (70 dB and 30 dB), 17.9% failed at 30 dB bilaterally and 30.0% failed unilaterally. The repeated ABR screening and behavioral observation audiometry at age 6 months identified one infant with a significant hearing loss in 78 infants. Two thirds of the COG failures and a little more than half of the ABR failures had a problem mainly with the middle ear. Advantages and disadvantages of each procedure are presented.

Acoustic Impedance Tests↗
PubMed1984

A novel form of dependency of hepatic extraction ratio of opioids in vivo upon the portal vein concentration of drug: comparison of morphine, diamorphine, fentanyl, methadone and buprenorphine in the chronically cannulated cow.

In the chronically cannulated cow, the hepatic extraction ratio for intravenous boluses of morphine, diamorphine, fentanyl, methadone and buprenorphine increased towards a plateau value as portal vein drug concentration increased. An extraction ratio close to zero for morphine was observed at a portal vein plasma drug concentration of about 200 nanomol per litre, which is within the range for significant pharmacodynamic effects. The similar concentrations extrapolated for the other narcotics would be of less pharmacodynamic importance. The phenomenon did not depend with morphine on the history of drug delivery to the liver; measurement of hepatic blood flow showed the effect was not an artifact of unrepresentative blood sampling, and was not related to any action of the narcotics on hepatic blood flow. The existence of this novel type of concentration dependent hepatic extraction ratio in vivo can explain a number of anomalous observations on narcotic pharmacokinetics, especially for morphine. Furthermore, similar behaviour may be expected for non-opioid drugs having similar pharmacokinetic properties.

Animals↗
PubMed1984

Plasma morphine concentrations and clinical effects after thoracic extradural morphine or diamorphine.

Twenty-seven patients undergoing thoracotomy received either morphine sulphate 2 mg or diamorphine hydrochloride 2 mg by thoracic extradural injection for postoperative analgesia. Arterial plasma morphine concentrations were measured by specific radioimmunoassay, and the analgesic, respiratory and biochemical effects noted. The plasma morphine concentrations were significantly greater after extradural diamorphine than after extradural morphine in the first 30 min after injection. The maximum increase in plasma morphine concentration was significantly (P less than 0.02) greater after extradural diamorphine, and mean peak values occurred at 5 and 10 min for diamorphine and morphine, respectively. There were significant decreases in respiratory rate and plasma cortisol concentration with maximum effects between 90 and 180 min after the extradural injection. The analgesia produced by these doses was inadequate. The role of lipophilicity is discussed.

Adult↗
PubMed1984

Controlled comparison of intrathecal cinchocaine with intrathecal cinchocaine and morphine. Clinical effects and plasma morphine concentrations.

Twenty patients scheduled for elective total hip replacement were given either intrathecal cinchocaine with morphine hydrochloride 2.5 mg or intrathecal cinchocaine alone before general anaesthesia. Arterial plasma morphine concentrations were measured and analgesic, respiratory and biochemical effects compared. Plasma morphine concentrations increased to 19.3 nmol litre-1 at 210 min. PaCO2 concentrations increased significantly only in those patients who received morphine as well as cinchocaine. Patients receiving cinchocaine alone, but not those given cinchocaine and morphine, had significant (P less than 0.01) increases in plasma cortisol concentrations' in the period after operation. Median time to next analgesic in patients receiving cinchocaine with intrathecal morphine was 22 h, significantly (P less than 0.01) longer than in patients receiving intrathecal cinchocaine alone (7.8 h).

Aged↗
PubMed1984

Sensitive and specific morphine radioimmunoassay with iodine label: pharmacokinetics of morphine in man after intravenous administration.

Analysis of morphine in plasma by radioimmunoassay is complicated by interference from morphine metabolites, particularly morphine-3-glucuronide. This interference makes radioimmunoassay a poor technique to study the pharmacokinetics of morphine in man. The method described here is one which uses commercially available anti-morphine antiserum and separating reagent with a simply prepared iodinated morphine derivative. Cross-reactivity to morphine metabolites is negligible and the method correlates well with HPLC. Results obtained for pharmacokinetic parameters after intravenous administration in man are in agreement with published data using GLC or HPLC. The method is inexpensive, simple and rapid; choice of a different antiserum could allow the method to be used for screening for drugs of abuse such as morphine, diamorphine, codeine and dihydrocodeine.

Chromatography, High Pressure Liquid↗
PubMed1983

Comparison of effects of intraoperative and postoperative methadone: acute tolerance to the postoperative dose?

The effects of methadone 10 mg administered in two different clinical contexts, at induction of anaesthesia and following operation, were studied in two groups of patients undergoing elective total hip replacement. The intraoperative group received methadone 10 mg i.v. at induction of anaesthesia as part of a balanced anaesthetic technique. The postoperative group received methadone 10 mg i.v. following operation, extradural bupivacaine being used for the operative period. A demand analgesia system delivering methadone i.v. was used after operation in both groups. Arterial blood-gas tensions, cortisol and glucose concentrations, analgesic effects and plasma methadone concentrations were compared in the two groups. The only major difference between the two groups was in analgesic requirement. At the time of connection to the demand system the two groups had the same plasma methadone concentrations. Subsequently, the postoperative group had a significantly greater analgesic requirement which resulted in significantly greater plasma methadone concentrations the following morning. Thus, the administration of methadone following operation appeared to exert less analgesic effect than the same dose given during operation. The reasons for this are discussed.

Adult↗
PubMed1983

The effect of choline mustard on the rat superior cervical ganglia.

The effect of choline mustard aziridinium ion (ChM) on the isolated superior cervical ganglion of the rat was investigated. In the presence of ChM (22.5 microM), stimulation at 1 Hz resulted in a slowly developing blockade of transmission, which did not occur at a stimulus frequency of 0.1 Hz. Choline (0.1 mM) slowed the onset of the blockade produced by stimulation at 1 Hz in the presence of ChM. The presence of excess thiosulphate ions prevented the action of ChM on the transmission in the superior cervical ganglion. Treatment of the ganglion with ChM (22.5 microM) only slightly inhibited the depolarization produced by carbachol (dose ratio 1.3), suggesting the drug produced a small degree of receptor blockade. [3H]-choline accumulation in the rat superior cervical ganglia displays several components: (a) sodium-dependent high affinity uptake (SDHAU) that can be activated further by preincubation in a high concentration of K+ ions; (b) sodium-dependent low affinity uptake (SILAU); (c) linear diffusional accumulation which does not saturate. Hemicholinium-3 selectively inhibits the activated sodium-dependent high affinity uptake, but is a weak inhibitor of resting sodium-dependent high affinity uptake and sodium-independent low affinity uptake. ChM inhibits both activated and resting sodium-dependent high affinity uptake, but is a very weak inhibitor of sodium-independent low affinity uptake. Homocholine shows similar selectivity. ChM inhibition of activated sodium-dependent high affinity uptake is very much more persistent than that of hemicholinium-3. Hemicholinium-3 and ChM both inhibit [3H]-acetylcholine synthesis.

Animals↗