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Biomedical subjects

K J Dennis

Publications and source records attributed to K J Dennis.

At least 19 recordsLinked to original sources
PubMed1998

A paradox of cerebral hyperperfusion in the face of cerebral hypotension: the effect of perfusion pressure on cerebral blood flow and metabolism during normothermic cardiopulmonary bypass.

BACKGROUND: The purpose of this study was to determine the impact of perfusion pressure on cerebral blood flow (CBF) and metabolism during normothermic cardiopulmonary bypass (CPB) and after weaning. MATERIALS AND METHODS: Two groups of mongrel dogs were studied (Group A, CPB perfusion at 50 mm Hg, n = 6; and Group B, CPB perfusion at 100 mm Hg, n = 6). All animals underwent 2 h of normothermic bypass at cardiac indexes >2.1 L/min/m2 and were weaned from pump, maintained at pressures >75 mm Hg, and followed for an additional 2 h. RESULTS: In both groups CBF increased over 85% from baseline, in proportion to the hemodilution during the initiation of CPB. Intracranial pressure increased moderately in both groups during CPB, compromising CBF at 1 h in Group A, but not in Group B. The Group A cerebral metabolic rate for oxygen (CMRO2), however, remained unchanged as the percentage of oxygen extraction increased to compensate for the decreased CBF. During recovery, temperature, mean arterial pressure, and cerebral perfusion pressure were not significantly different between the two groups. However, the CBF, percentage of oxygen extracted, and CMRO2 were significantly lower in Group A. CONCLUSIONS: Normothermic CPB initiated with a crystalloid prime and performed at the lower end of a 50-70 mm Hg perfusion window resulted in a highly significant increase in CBF in order to compensate for hemodilution, while at the same time reduced the perfusion pressure available to supply the increased CBF. Together, these two events create a hemodynamic paradox of hyperperfusion in the face of hypotension. The reduction in CMRO2 in Group A is yet to be explained but seems to remain coupled to CBF and could represent a previously undescribed protective mechanism of hibernating cerebral tissue, similar to the phenomena of ischemic preconditioning in the heart, where cerebral tissue is stimulated to lower metabolism in response to inadequate CBF.

Animals↗
PubMed1995

Variability in measurement of central retinal artery velocity using color Doppler imaging.

The purpose of our study was to test the reproducibility of the central retinal artery velocity measurements as made by color Doppler imaging and pulsed Doppler spectral tracings and to define the optimal location for placement of the sample volume. We used the Siemens Quantum (Q 2000) with a 7.5 MHz linear array transducer to identify the central retinal artery and record its velocity. Eleven eyes from 11 normal subjects were evaluated for the peak systolic central retinal artery velocity in two positions, the first posteriorly in the optic nerve at an average of 3.56 mm from the surface of the optic disc and the second at an average of 1.76 mm from the surface of the optic disc. We then used a color-flow threshold to identify and record the point of maximal velocity. The range of systolic velocities in the 11 eyes was from 5.85 to 22.51 cm/sec. The peak systolic velocity posteriorly in the optic nerve averaged 8.16 cm/sec, whereas near the surface of the optic disc the velocity averaged 13.89 cm/sec (70.2% higher). Using the color flow threshold method, the maximal velocity was located at an average of 1.98 mm from the surface of the optic disc. Our data show that large differences exist in measured central retinal artery velocity that depend on the location of the measurement, and that color-flow thresholding is valuable in locating the optimal location for pulsed Doppler spectral recording.

Blood Flow Velocity↗
PubMed1990

Gas chromatographic analysis of reactive carbonyl compounds formed from lipids upon UV-irradiation.

Peroxidation of lipids produces carbonyl compounds; some of these, e.g., malonaldehyde and 4-hydroxynonenal, are genotoxic because of their reactivity with biological nucleophiles. Analysis of the reactive carbonyl compounds is often difficult. The methylhydrazine method developed for malonaldehyde analysis was applied to simultaneously measure the products formed from linoleic acid, linolenic acid, arachidonic acid, and squalene upon ultraviolet-irradiation (UV-irradiation). The photoreaction products, saturated monocarbonyl, alpha,beta-unsaturated carbonyls, and beta-dicarbonyls, were derivatized with methylhydrazine to give hydrazones, pyrazolines, and pyrazoles, respectively. The derivatives were analyzed by gas chromatography and gas chromatography-mass spectrometry. Lipid peroxidation products identified included formaldehyde, acetaldehyde, acrolein, malonaldehyde, n-hexanal, and 4-hydroxy-2-nonenal. Malonaldehyde levels formed upon 4 hr of irradiation were 0.06 micrograms/mg from squalene, 2.4 micrograms/mg from linolenic acid, and 5.7 micrograms/mg from arachidonic acid. Significant levels of acrolein (2.5 micrograms/mg) and 4-hydroxy-2-nonenal (0.17 micrograms/mg) were also produced from arachidonic acid upon 4 hr irradiation.

Acetaldehyde↗
PubMed1989

Infection following caesarean section.

In a prospective clinical study of post-operative infection in 124 patients undergoing Caesarean section, 39 (31.5%) patients developed a total of 45 infections. There was no significant difference in infection rates between elective and emergency procedures. Five patients (4%) developed endometritis, wound infection was found in 14 (11.3%) and 18 patients (14.5%) developed a post-operative urinary tract infection. Pre-operative C-reactive protein levels and intraoperative swabs of the uterine cavity were not helpful in the early detection of endometritis. The risk factors predisposing to post-caesarean infection were obesity and low socioeconomic status.

Cesarean Section↗
PubMed1989

Gas chromatographic determination of malonaldehyde formed by lipid peroxidation.

Gas chromatographic (GC) methods for the determination of malonaldehyde (MA) all require formation of a stable derivative of MA since free MA is not suitable for direct GC analysis. Most reported GC methods give a total measure of free MA and its bound forms because their assay conditions are sufficient to hydrolyze or decompose bound MA during sample preparation. In this paper, GC methods that provide a measure of total MA (free plus bound) are reviewed. A recently developed capillary GC method that allows determination of free MA apart from other forms is also discussed. The method involves derivatization of MA to N-methylpyrazole under milder reaction conditions than with other GC methods. The method represents an advantage over existing techniques for free MA determination because capillary GC offers the highest efficiency of separation among chromatographic methods thus allowing a more specific and accurate measure of MA.

Chromatography, Gas↗
PubMed1989

Production of malonaldehyde from squalene, a major skin surface lipid, during UV-irradiation.

Malonaldehyde (MA), a product of lipid peroxidation, is known to have a number of toxicological effects. Among skin surface components, squalene has been suggested as a significant source of MA following UV exposure. Irradiation of squalene coated on the inside surface of glass tubes served as a simple model to examine skin surface photochemistry. Malonaldehyde produced during UV-irradiation was reacted with methyl hydrazine to form N-methylpyrazole, which was then measured by gas chromatographic analysis. Ultraviolet A-irradiation produced low levels of MA from squalene, with a maximum of 1.0 nmol MA/mumol squalene near 6 h. Malonaldehyde production varied with the energy of irradiation, with levels of 176 nmol/mg squalene and 9 nmol/mg squalene produced after 3 h of irradiation with UVB and UVA, respectively. The thiobarbituric acid (TBA) assay for lipid peroxidation showed large overestimations of MA levels under all irradiation conditions tested. The TBA assay predicted the highest levels of MA with UVC but we did not detect any MA with our assay.

Chromatography, Gas↗
PubMed1988

Reference values for 75 g oral glucose tolerance test in pregnancy.

A 75 g oral glucose tolerance test was performed in 212 pregnant women with no predisposing factors suggesting glucose intolerance to establish the normal pattern of glucose metabolism in pregnancy. Reference values for the test were established for the middle of pregnancy (14-20 weeks, n = 43) and late pregnancy (28-37 weeks, n = 168). One woman was excluded because she had diabetes that required treatment with insulin. There were statistically significant differences between the two groups for samples taken both one and two hours after the glucose load. Reference ranges for the interpretation of the glucose tolerance test in pregnancy should therefore take account of the period of gestation. Arbitrary upper limits of normal (represented by the 97.5 centile) two hours after a 75 g oral glucose load are proposed at 7.5 and 9.6 mmol/l for the second and third trimesters, respectively.

Blood Glucose↗
PubMed1988

Analysis of free malondialdehyde in photoirradiated corn oil and beef fat via a pyrazole derivative.

Malondialdehyde (MA) formed in linolenic acid, linoleic acid, corn oil and beef fat upon photoirradiation was determined by gas chromatography (GC). The MA produced was reacted with methylhydrazine to give 1-methylpyrazole and was subsequently analyzed on a GC equipped with a nitrogen-phosphorus specific detector and a fused silica capillary column. MA values determined by this method correspond to free or unbound MA levels. Linolenic and linoleic acids produced 867 micrograms MA/g and 106 micrograms MA/g, respectively. Oleic and stearic acids did not produce detectable levels of MA upon photoirradiation. Amounts of MA produced after eight hour irradiations of corn oil and beef fat were 56.24 micrograms/g and 25.01 micrograms/g, respectively. Some photoreaction products in irradiated corn oil also were identified as methylhydrazine derivatives.

Calibration↗
PubMed1988

The OVEIA assay, a simultaneous measurement of oestrone and pregnanediol glucuronides, for studying the treatment of infertility patients.

A new simple assay developed for establishing the limits of the fertile period was evaluated in infertility patients. This assay is a colorimetric method for measuring the oestrone glucuronide/pregnanediol glucuronide ratio. Steroid levels were assayed simultaneously and an index of their ratio was obtained in this dual analyte assay (DAA). Twenty subfertile women, receiving clomiphene citrate for ovulation induction, were monitored for the DAA index using early morning urine samples. Ten of these women were also monitored in a pretreatment cycle. A further 10 patients on an in-vitro fertilization (IVF) programme were assessed with the same assay. DAA ratios were found to correlated with follicular phase serum oestradiol levels. Peak DAA ratios dropped dramatically when significant rises in urinary luteinizing hormone concentrations occurred prior to ovulation. An association between high DAA ratios and adequate luteal phase activity was also established. In addition, the total volume of the three largest ovarian follicles, as measured by ultrasound, in IVF patients was found to correlate with DAA measurements.

Adult↗
PubMed1987

The suppression of ovarian function by the new oral contraceptive--Femodene.

Luteinising hormone, oestradiol and progesterone were measured in 36 women commencing Femodene contraception on the first day of menstruation. Of these subjects, 17 were not on any oral contraception during the preceding cycle, the remaining 19 changing from another oral contraceptive formulation. Full measurements were performed in the cycle preceding and the first cycle on Femodene. In another 3 subjects the measurements were made during only one cycle - the first on Femodene. The results confirm ample suppressive effects of Femodene on pituitary and ovarian function. The clinical side effects experienced by the 39 subjects are described.

Contraceptives, Oral, Combined↗
PubMed1987

A random plasma glucose method for screening for abnormal glucose tolerance in pregnancy.

A method is described for screening all pregnant women for abnormal glucose tolerance. It is based on determining random plasma glucose at 28-30 weeks gestation, having simply noted whether the woman had eaten within the preceding 2 h. If the random plasma glucose level was greater than or equal to 97.5th centile, a 75 g oral glucose tolerance test was performed. This method of screening is cheaper and slightly more efficient than screening based on conventional risk indications.

Blood Glucose↗
PubMed1987

You see what you look for and recognize what you know.

The clinical examination is the cornerstone for all diagnostic and therapeutic decisions. The pertinent components of the history and physical examination as they relate to diabetes are discussed in this article.

Diabetic Angiopathies↗
PubMed1986

Suppression of ovarian function by Microgynon 30 in day 1 and day 5 "starters".

The suppression of ovulation during the first treatment cycle with Microgynon 30 (150 micrograms levonorgestrel and 30 micrograms ethinyl oestradiol) for nine subjects starting the "pill" on day 1 of their cycle and five subjects on day 5 was investigated. Serum oestradiol and progesterone levels throughout the cycle and midcycle urinary LH levels were reliably suppressed in all day 1 "starters". Serum progesterone levels and urinary LH levels were also suppressed in day 5 "starters" but one subject produced oestradiol levels within the normal range of ovulatory cycles. Mean oestradiol levels of day 5 "starters" were found to be significantly higher than those of day 1 "starters" (p less than 0.05).

Adolescent↗