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Biomedical subjects

G Jackson

Publications and source records attributed to G Jackson.

At least 19 recordsLinked to original sources
PubMed1992

Possible blindsight in infants lacking one cerebral hemisphere.

Patients with damage to the striate cortex have a subjectively blind region of the visual field, but may still be able to detect and localize targets within this region. But the relative roles in this 'blindsight' of subcortical neural systems, and of pathways to extra-striate visual areas, have been uncertain. Here we report results on two infants in whom one cerebral hemisphere, including both striate and extra-striate visual cortex, needed surgical removal in their first year. Single conspicuous targets in the half-field contralateral to the lesion could elicit fixations, implying detection and orienting by a subcortical system. In contrast, binocular optokinetic nystagmus (OKN), for which a subcortical pathway has often been thought adequate, showed a marked asymmetry. In normal neonates, fixation shifts and OKN have both been taken to reflect subcortical control; our results are consistent with subcortical control for fixation but not for OKN.

Brain↗
PubMed1992

The Hatle orifice area formula tested in normal bileaflet mechanical mitral prostheses.

The Hatle formula was derived empirically in native mitral stenosis and may not be valid for normal prosthetic valves. Bileaflet mechanical prostheses open fully at low flows and have minimal interindividual variation in orifice area. In these valves effective area and measured manufacturer's area should be similar. We studied 60 patients aged 58 +/- 12 yr at a mean of 5 months after implantation with a CarboMedics prosthesis. There was a coexistent aortic prosthesis in 21. All diastolic measurements were averaged over 5 beats and stroke volume was calculated from the integral of the subaortic velocity trace and the cross-sectional area of the left ventricular outflow tract. For the whole group, area by the Hatle formula was 3.1 +/- 0.7 cm2 and measured area was 2.8 +/- 0.4 cm2. There was no significant correlation between these values (p = 0.329). Pressure half-time was more closely correlated with peak transmitral velocity (p = 0.012), RR interval (p = 0.015), diastolic time interval (p = 0.062) and stroke volume (p = 0.074). We conclude that the Hatle formula should not be applied to normal bileaflet mitral prostheses where pressure half-time reflects nonprosthetic factors more closely than orifice area.

Aged↗
PubMed1992

Continuity equation and Gorlin formula compared with directly observed orifice area in native and prosthetic aortic valves.

Orifice areas calculated by the continuity and Gorlin equations have been shown to correlate well in vivo. The continuity equation, however, gives underestimates compared with the Gorlin formula and it is not clear which is the more accurate. Both equations have therefore been tested against maximal orifice area measured by planimetry in eight prepared native aortic valves and four bioprostheses. A computer controlled, ventricular flow simulator (cycled at 70 beats/min) was used at five different stroke volumes that gave cardiac outputs of 2.8 to 7.0 l/min. The mean difference between measured and estimated orifice area was zero for the continuity equation, but -0.14 cm2 for the conventional Gorlin formula. Thus the Gorlin formula tended to give overestimates compared with both measured area and area estimated by the continuity equation, probably because of the effect of pressure recovery. When predictive equations derived from these data were tested, residual standard deviations were around 0.3 cm2 at all stroke volumes for the continuity equation, around 0.2 cm2 for the invasive Gorlin formula, and between 0.2 and 0.4 cm2 for the modified Gorlin formula. These results suggest that estimates of orifice area in an individual valve as judged by any of the equations tested should be seen as a guide to rather than as a precise measure of actual orific area.

Anthropometry↗
PubMed1992

Percutaneous balloon pericardiotomy in the management of recurrent malignant pericardial effusions.

Two patients with recurrent symptomatic pericardial effusions secondary to malignant disease were successfully treated by percutaneous balloon pericardiotomy. Open surgery was avoided and the procedure was completed under local anaesthesia in less than 40 minutes. The first patient was free of recurrence at nine months but pericardial effusion recurred at two months in the second patient. Percutaneous balloon pericardiotomy offers a potentially important new means of relieving recurrent tamponade and substantially reduces trauma to the patient.

Adult↗
PubMed1992

Prospective study of microalbuminuria as predictor of mortality in NIDDM.

Retrospective studies of patients with non-insulin-dependent diabetes mellitus (NIDDM) have suggested that microalbuminuria predicts early all-cause (mainly cardiovascular) mortality independently of arterial blood pressure. These findings have not been confirmed in prospective studies, and it is not known whether the predictive power of microalbuminuria is independent of other major cardiovascular risk factors. During 1985-1987, we examined a representative group of 141 nonproteinuric patients with NIDDM for the prevalence of coronary heart disease and several of its established and putative risk factors, including raised urinary albumin excretion (UAE) rate. Thirty-six patients had microalbuminuria (UAE 20-200 micrograms/min), and 105 had normal UAE (less than 20 micrograms/min). At follow-up, an average of 3.4 yr later, 14 patients had died. There was a highly significant excess mortality (chiefly from cardiovascular disease) among those with microalbuminuria (28%) compared to those without microalbuminuria (4%, P less than 0.001). In univariate survival analysis, significant predictors of all-cause mortality included microalbuminuria (P less than 0.001), hypercholesterolemia (P less than 0.01), hypertriglyceridemia (P less than 0.05), and preexisting coronary heart disease (P less than 0.05). The predictive power of microalbuminuria persisted after adjustment for the effects of other major risk factors (P less than 0.05). We conclude that microalbuminuria is a significant risk marker for mortality in NIDDM, independent of the other risk factors examined. Its presence can be regarded as an index of increased cardiovascular vulnerability and a signal for vigorous efforts at correction of known risk factors.

Albuminuria↗
PubMed1991

A mild outbreak of bovine mastitis associated with Mycoplasma bovigenitalium.

Mycoplasma bovigenitalium was isolated from milk samples from 16 of 99 cows on one farm during a 15-week period in the summer of 1986. One cow was severely affected, four cows had relatively mild signs of mastitis, and three had only altered dry-cow udder secretions. Eleven of the infected cows were dry and three had been calved less than 48 hours. The abrupt method of drying-off and improvements in cleaning of the milking equipment were introduced, but no other control measures were instituted to eradicate the mycoplasma infections. After this mild outbreak of mastitis the herd was monitored for the next 17 months. In total 19 cows had a mycoplasma isolated from udder secretions. Acholeplasmas were isolated from 14 cows but were not associated with clinical mastitis. The udder infections with mycoplasmas apparently resolved without resorting to the segregation and culling of infected animals.

Animals↗
PubMed1991

Efficacy of nifedipine and isosorbide mononitrate in combination with atenolol in stable angina.

Many patients with angina pectoris whose symptoms are not completely controlled by beta-blockers are treated with several types of drugs, but it is not clear whether addition of a calcium-channel antagonist and/or a nitrate confers any advantage over beta-blockade alone. 18 patients receiving atenolol for stable angina pectoris completed a double-blind, randomised, crossover trial of atenolol treatment plus placebo, isosorbide mononitrate, nifedipine, and mononitrate and nifedipine (triple therapy). The patients were assessed subjectively and by treadmill exercise testing and 24 h ambulatory electrocardiographic recordings at the end of each 4-week treatment period. There were no significant differences among the treatment periods in angina attack rates, glyceryl trinitrate consumption, exercise duration to onset of angina or 1 mm ST depression, or duration of symptomless ischaemia. Total exercise duration was longer on atenolol plus mononitrate than on atenolol alone (mean difference 46 [95% confidence interval 18-88] s; p = 0.005), atenolol plus nifedipine (36 [2-71] s; p = 0.04), or triple therapy (28 [6-61] s; not significant). In 12 patients the exercise time was shorter on triple therapy than on atenolol plus mononitrate alone. Although "maximum" antianginal treatment with two or three drugs is commonly accepted, this approach confers no substantial advantage over optimum beta-blockade as monotherapy. If a second drug is needed, there is a slight advantage in favour of isosorbide mononitrate, but if this is not effective, treatment should be changed rather than added. Many patients with angina pectoris seem to be pharmacologically overtreated.

Aged↗
PubMed1991

Intestinal stasis and rupture in rabbits.

During one year 23 of 110 New Zealand white, adult male laboratory rabbits died. The pathological findings included intestinal stasis, intestinal blockage, acute intestinal rupture and intestinal rupture with peritonitis. These changes were considered to represent stages in an intestinal stasis and rupture syndrome. Another group of 20 comparable rabbits remained unaffected.

Animals↗