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Biomedical subjects

N Newby

Publications and source records attributed to N Newby.

8 recordsLinked to original sources
PubMed1995

Analysis of heroin drug seizures by Micellar Electrokinetic Capillary Chromatography (MECC).

A rapid procedure using Micellar Electrokinetic Capillary Chromatography (MECC) is presented for the quantitation of illicit heroin samples. This analytical system resolves heroin from accompanying impurities and adulterants enabling accurate quantitation via the use of an internal standard. An aqueous run buffer consisting of 40 mmol sodium dodecyl sulfate, 8.5 mmol sodium phosphate, 8.5 mmol sodium borate and 15% acetonitrile is used with a 27 cm x 50 microns fused silica capillary column. Linearity, accuracy and reproducibility studies of heroin using this method are established. Comparisons to a commonly used gas chromatographic method show excellent correlation. Due to its high resolution and speed, this MECC system also serves as a screening procedure to detect impurities and adulterants present in heroin samples. Relative migration times of various opiates and adulterants are reported. With minor exceptions, complete separation of numerous compounds is achieved within five minutes, including compounds that are difficult to analyze by gas chromatography such as morphine, O6-acetylmorphine, aspirin and salicylic acid.

Chromatography, Gas↗
PubMed1980

Phenytoin hypersensitivity presenting as postoperative fever.

One of the most catastrophic complications of intracranial surgery is infection. These infections present frequently as postoperative fever and a change in sensorium. Phenytoin is used frequently in conjunction with intracranial operation to prevent seizures. We report two patients in whom, although the full phenytoin sensitivity syndrome ultimately developed, the presenting sign was postoperative fever. The phenytoin sensitivity syndrome is reviewed with emphasis on the fact that all components of the syndrome are not always present initially. The clinical significance of the presentation of phenytoin hypersensitivity as postoperative fever is discussed.

Adult↗
PubMed1977

Sources of error in measuring cerebrospinal fluid formation by ventriculocisternal perfusion.

Ventriculocisternal perfusion is regarded as a precise method of measuring the rate of formation of cerebrospinal fluid (CSF) but it possesses inherent potential sources of error. Using the technique to measure CSF formation rate in the rhesus monkey, we have observed rate changes when none were expected. Most puzzling has been the steady decline of CSF formation rate at 4 percent each hour during the final five hours of a seven hour perfusion although variables known to affect CSF formation remained stable. In addition, alterations in rate caused by artefacts were observed in experiments in which craniospinal blood volume was changed by sudden changes of either PCO2 or central venous pressure. Mobilisation or sequestration of incompletely equilibrated CSF is believed responsible. In other experiments, a small increase of intracranial pressure produced by increasing outflow resistance was quickly followed by an apparent reduction of CSF formation. We have concluded that to assess accurately the effect a variable has on the rate of CSF formation, one must control perfusion time and craniospinal blood volume as well as intracranial pressure.

Animals↗
PubMed1976

PCO(2) and rate of formation of cerebrospinal fluid in the monkey.

Changes in cerebrospinal fluid formation rate (VF) with hypocapnia were measured by the ventriculocisternal perfusion technique in 24 rhesus monkeys anesthetized with nitrous oxide. In addition cerebral blood flow (CBF) was measured by the hydrogen clearence methods, Vf in control animals declined at a mean rate of 2.3 mul/min each hour during the last 4.5 h of a 7-h perfusion although variables known to effect Vf remained stable. Three hours after perfusion began, Vf of normocapnic controls was 41.4 mul/min +/- 5.4; CBF, 59P ML/100 G PER MIN. When Pco(2) was reduced to half of control, Vf fell to 35.6 mul/min +/- 6.3 and CBF fell by 27%. When Pco(2) was doubled, Vf fell to 33.1 mul/min +/- 5.3 and CBF increased threefold. The difference in Vf id significant only for the hypercapnic group (p=0.01). When animals were used as their own controls, three were no significant differences in Vf with hypercapnia compared to normocapnia. These results indicated that in the monkey variations of Pco(2) within broad physiologic limits, which are sufficient to cause large changes in CBF, have little effect of Vf.

Acidosis↗
PubMed1976

Effect of intracisternal phentolamine on cerebral blood flow after subarachnoid injection of blood.

The hydrogen clearance method was used to measure total and focal cerebral blood flow (CBF) in the monkey before and for 5 hours after a simulated subarachnoid hemorrhage (SAH). Some monkeys also received 0.2 to 1.0 mg/kg phentolamine intracisternally 3 hours after SAH. Results show that SAH did not change cerebrovascular resistance, but as cerebral perfusion pressure decreased, CBF fell transiently. Phentolamine injected intracisternally 3 hours after SAH produced a significant fall in arterial blood pressure; cerebrovascular resistance did not change but CBF decreased significantly. These data indicate that intracisternal phentolamine cannot be considered potentially useful to treat ischemic encephalopathy after SAH.

Animals↗
PubMed1976

Preserved autoregulation in the rhesus spinal cord after high cervical cord section.

The authors studied the effect of high cervical cord section on the phenomenon of autoregulation in the rhesus monkey with the hydrogen clearance method to measure focal spinal cord blood flow (SCBF). Laminectomies were performed at T7-11 and C1-2. The spinal cord was completely severed at C1-2. Under normocapnic conditions, SCBF was then measured in the thoracic spinal cord over a wide range of blood pressures (MAP). The MAP was either lowered by bleeding or raised by the intravenous infusion of angiotensin. Autoregulation was found to be intact between 50 and 125 mm Hg, following a pattern similar to the one observed in the intact animal.

Animals↗
PubMedDate not supplied

The effect of a simulated subarachnoid hemorrhage on cerebral blood flow in the monkey.

The hydrogen clearance method was used to measure local and total cerebral blood flow (CBF) in the rhesus monkey before and for five hours after a simulated subarachnoid hemorrhage (SAH). CBF remained stable after SAH unless SAH was associated with a fall in cerebral perfusion pressure. In addition, cerebrovascular resistance did not increase after SAH. These results suggest that vasoactive agents in fresh whole blood, and the arterial spasm they produce when added to cerebrospinal fluid (CSF), play only a limited role in the pathogenesis of ischemic encephalopathy that follows an SAH.

Animals↗