Search PubMed⌕ Search

Biomedical subjects

D Powell

Publications and source records attributed to D Powell.

At least 163 records · Page 9Linked to original sources
PubMed1978

Effects of fentanyl on intracranial pressure and cerebral perfusion pressure during hypocapnia.

Ten patients presenting for carniotomy were studied. Each was anaesthetized with thiopentone or Althesin followed by tubocurarine and the lungs were hyperventilated with nitrous oxide in oxygen. Fentanyl 0.2 mg was administered i.v. and the intracranial pressure (i.c.p.) and mean arterial pressure were recorded continuously for 10 min. At the time of administration of fentanyl nine of the 10 patients were hypocapnic (PaCO2 less than 4 kPa). The changes in i.c.p. were small. Cerebral perfusion pressures less than 50 mm Hg were observed in two patients who had moderate hypotension before the drug was given. We conclude that fentanyl is a valuable agent in the hyperventilation technique in patients with intracranial space-occupying lesions, provided that hypotension is absent.

Adult↗
PubMed1978

Ectopic insulin and Occam's razor: reappraisal of the riddle of tumour hypoglycaemia.

The concept of ectopic insulin production is challenged on the basis of a review of 120 cases from the literature on extrapancreatic tumours associated with hypoglycaemia in which insulin or insulin-like activity were measured. No case met two or more of five criteria of ectopic hormone production. The evidence indicates that hypoglycaemia of extrapancreatic tumours cannot be attributed to insulin. In those rare cases in which plasma insulin was reported as high, pancreatic beta-cells could not be excluded as the source of insulin. Interestingly, many of these dubious cases had carcinoid histology. The review also points out a close association between some spindle-cell tumours and carcinoid tumours which may be relevant to discussion on the disputed origin of some "mesothelial" tumours. Nonsuppressible insulin-like activity (NSILA) consists of a number of factors mimicking insulin activity which compete with insulin or proinsulin for membrane receptors and may crossreact in bioassays, immunoassays, and receptor assays. The question of whether one or several of these substances may be responsible for extrapancreatic hypoglycaemia remains to be elucidated.

Carcinoid Tumor↗
PubMed1978

Humoral hypercalcaemia in a patient with renal-cell carcinoma.

In a patient with hypercalcaemia secondary to a renal-cell carcinoma, a concentration gradient of bioactivity was detected between the tumour effluent vein and the peripheral venous blood that was capable of stimulating adenylate cyclase in bone cells. Immuno-reactive PTH was undetectable in the tumour effluent and in the peripheral blood. It is concluded that a non-parathyroid humoral factor whose action involved cyclic AMP stimulation was responsible for the hypercalcaemia.

Adenocarcinoma↗
PubMed1978

Early effects of parathyroid hormone on rat calvarian bone alkaline phosphatase.

Using a quantitative cytochemical method, explanted calvaria of 1- to 6-day-old male rats were used for the measurement of the in situ effect of parathyroid hormone (PTH) on the activity of alkaline phosphatase (AP) in the calcifying bone. The earliest effect of PTH was observed at 4--7 min. The direction and magnitude of the response of AP was dependent on the age of the animal and on the dose of PTH (50 fg-500 pg/ml). The calvaria of younger animals (2-days old) showed a decrease in AP activity, whereas in 5-day-old rats, AP activity was stimulated by PTH. In 5-day-old animals, the linear dependence of ATP stimulation on the PTH dose in the concentration range 50 fg-50 pg/ml could serve as the basis for a bioassay of a high sensitivity. The age-dependent response of AP to PTH may reflect the difference between the early and late stages of the calcification process. Our observations may reconcile conflicting reports on the effect of PTH on bone AP.

Aging↗
PubMed1977

Apparent improvement of antisera for radioimmunoassay by treatment with sodium iodide.

The concept that antisera for radioimmunoassay can be improved by treatment with NaI and dialysis is challenged. Some antisera are little affected by NaI. Even when NaI does dissociate endogenous antigenic material from crude antiserum, in the subsequent dialysis NaI is dialysed at a much faster rate than antigen, allowing reassociation to occur. The reported improvement of antisera by the NaI method cannot be attributed to the effect of NaI but can be explained by the dilution which occurs during dialysis.

Animals↗
PubMed1977

Intracranial pressure changes in neurosurgical patients during hypotension induced with sodium nitroprusside or trimetaphan.

Intracranial pressure has been measured in 45 patients undergoing neurosurgery during the induction of deliberate hypotension using either sodium nitroprusside or trimetaphan. A statistically significant increase in intracranial pressure (ICP) occurred during the early stages of the infusion of nitroprusside in normocapnic patients. A non-significant increase in ICP was obtained in hypocapnic patients. The mean ICP increased from 6.3 mm Hg to 11.7 mm Hg when the arterial pressure was reduced slightly, but the response in individual patients varied widely (range -1.6 mm Hg to +20.9 mm Hg). When the arterial pressure (BP) had decreased to 70% of the value existing before infusion of nitroprusside, mean ICP returned to control values and thereafter decreased with further reductions in BP. In patients rendered hypotensive with trimetaphan, there was no change in mean ICP but two patients showed moderate increases (+9.3 mm Hg and +5.7 mm Hg). The mechanism of the increase in ICP with nitroprusside is thought to be expansion of the intracranial blood volume as a result of cerebral vasodilatation. Trimetaphan does not usually produce ICP changes except when intracranial compression is severe, for in these circumstances a small change in intracranial blood volume consequent upon autoregulation may trigger an increase in ICP.

Blood Pressure↗
PubMed1976

Idiopathic pulmonary hemosiderosis: ultrastructural studies and responses to azathioprine.

Two boys are presented who fulfilled criteria for a diagnosis of idiopathic pulmonary hemosiderosis. A lung biopsy specimen from the first patient showed alveolar-capillary basement membrane abnormalities, together with abnormalities of capillary endothelial cells and hemosiderin-laden macrophages. A lung biopsy specimen from the second patient showed mainly capillary endothelial abnnormalities and interestitial fibrosis. Both patients had a noticeable improvement in symptoms and relative stabilization of their roentgenographic and pulmonary function abnormalities following azathioprine therapy.

Anemia, Hypochromic↗
PubMed1975

Stimulation of brain adenylate cyclase activity by the undecapeptide substance P and its modulation by the calcium ion.

Synthetic substance P stimulated adenylate cyclase activity in particulate preparations from rat and human brain. The concentration of substance P for half maximal stimulation in rat brain was 1.8-10-minus 7 M. The stimulatory effect of substance P on the rat brain adenylate cyclase activity was 88% compared with 48% by noradrenalin, 163% by prostaglandin E1 and 184% by prostaglandin E2. Both the basal and substance P-stimulated adenylate cyclase activity in rat brain were inhibited by concentration of Ca-2+ above 10-minus 6 M. The chelating agent ethyleneglycol-bis-(beta-aminoethylether)-N, N'-tetraacetic acid at a concentration of 0.1 mM reduced the basal adenylate cyclase activity by 64% and eliminated the substance P-stimulated activity. The inhibition by ethyleneglycol-bis-(beta-aminoethylether)-N, N'-tetraacetic acid was completely reversed by increasing concentrations of Ca-2+.

Adenylyl Cyclase Inhibitors↗