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Biomedical subjects

G Johnson

Publications and source records attributed to G Johnson.

At least 451 records · Page 25Linked to original sources
PubMed1986

Magnetic resonance imaging in clinically isolated lesions of the brain stem.

Twenty-seven patients with an isolated brain stem syndrome, thought to be due to demyelination, were examined by magnetic resonance imaging (MRI). A brain stem lesion was identified in 25, and clinically silent lesions outside the brain stem were demonstrated in 20. MRI was more sensitive than evoked potentials in detecting brain stem and other lesions. The scan findings were compared with those in 23 patients with multiple sclerosis, who had chronic brain stem dysfunction, with particular reference to the distribution of abnormalities and the MRI characteristics of the lesions. The relaxation times, T1 and T2, of the lesions were measured by MRI. These values were seen to fall in serial studies of acute lesions, but remained unchanged in the chronic lesions. MRI may therefore allow the age of lesions to be assessed.

Adolescent↗
PubMed1986

Relaxation times of apparently normal cerebral white matter in multiple sclerosis.

The magnetic resonance imaging (MRI) characteristics of the apparently normal cerebral white matter were studied in a group of 35 patients with clinically definite multiple sclerosis (MS). The proton relaxation times were compared with those in normal control subjects and patients with clinically isolated neurologic lesions of a type common in MS. Significant differences were found between all the patient groups and the control subjects. Changes in the cerebral white matter may be an early feature of MS.

Brain↗
PubMed1986

Measurement of NMR relaxation times using the minimum number of scans.

NMR relaxation time measurements derived from a set of three multi-slice sequences (which can examine the whole brain in 30 min) have been investigated. T1 and T2 values are 5% and 20% too short, respectively. Noise in the measurements was less than 2%. Temporal instability was negligible. Spatial non-uniformity was 1% (T1) and 3% (T2) within a single slice but 4% (T1) and 14% (T2) from slice to slice. Variations in cerebral tissue measurements have also been investigated: T1 varies by 6% and T2 by 12% over a population of normal controls. There can be significant patient-patient and topographical variations.

Brain↗
PubMed1986

The NMR signal decay characteristics of cerebral oedema.

Quantitative magnetic resonance (MR) imaging has been used to characterize vasogenic and triethyltin-induced cytotoxic cerebral oedema in cats, and the findings have been compared with the ultrastructural features of the lesions. Both normal and oedematous white matter yield non-linear T2 signal decay curves. The derived biexponential functions comprised a short T2 component representing intracellular water, and a long T2 component representing oedema fluid whose T2 was increased by an increase in free water of these tissue compartments. The relative sizes of the long T2 components were compatible with the sizes of the oedema spaces as determined ultrastructurally. Quantitative MR imaging can provide information which reflects the size and relaxation behaviour of the major tissue water compartments.

Animals↗
PubMed1986

Frequency of low values of stimulated saliva flow rate, Dentobuff and Dentocult in routine use.

The traditional reference values for salivary tests are derived from special populations using other methods than the screening tests used nowadays in general practice. In order to study the distribution of test results when the "new" methods were used in a routine way on a population seeking care at the Dental School in Huddinge an examination of 753 adults was carried out. Of special interest were the values which in the literature are associated with caries risk. Stimulated salivary flow rate, buffer capacity and lactobacillus counts were determined using the methods taught at the Dental School, which are also used by many dentists in Sweden. Analysis of the frequency distribution of test results show that women had low flow rates (less than or equal to 0.7 ml/min) of stimulated whole saliva considerably more often (10.7%) than men (5.4%). According to the traditional test of buffer capacity, a final pH 4.0 and below is very low. When using Dentobuff almost half of the women (45%) had such low values. About one fifth of the patients had high numbers of lactobacilli, according to the Dentocult test. This examination of the distribution of salivary parameters has led to more critical application of the traditional reference values when assessing caries risk.

Adult↗
PubMed1986

Blindness and visual impairment in southern Malawi.

There is a paucity of reliable information on the prevalence and causes of blindness in sub-Saharan Africa, and this produces problems in designing and evaluating blindness prevention programmes. To address this problem and to provide baseline data for the evaluation of such programmes, the government of Malawi, in conjunction with a number of agencies, conducted a population-based prevalence survey of ocular disease in the Lower Shire River Valley in southern Malawi, an area where blindness is common. The prevalence of bilateral blindness found (1.27%) is similar to that in other developing countries and represents a significant public health problem. At least 60% of this blindness is preventable or easily reversible.

Adult↗
PubMed1986

Protective effect of physical training on cardiovascular responses to hemorrhagic hypotension and shock.

The primary objective of this study was to determine if a measurable degree of protective cardiovascular adaptation to hypovolemic shock is developed in response to aerobic training. Twelve rats were trained (T) by running on a rodent treadmill 60 min/day, 5 days/wk at 30 m/min on a 5 degree incline for a period of 13-17 weeks. Elevated levels of SDH activity in the vastus intermedius muscles of the trained group (T) verified physiological training. Each T rat was weight matched with a sedentary untrained (UT) control, anesthetized with sodium pentobarbital, and subjected to a modified Wiggers hemorrhagic shock protocol. The parameters monitored were the maximum reduction in vascular capacitance (ie, maximum blood shed) when MAP was lowered to 30 mm Hg by hemorrhage; the time necessary to achieve maximum blood loss at 30 mm Hg (compensation time); and the time between maximum and 20% uptake of the shed volume from the reservoir (decompensation time). The data show that the initial MAPs for the UT group were significantly higher than the T group (133 +/- 3 mm Hg vs 121 +/- 4 mm Hg). The maximum blood loss normalized to body weight and pressure drop was .268 +/- .012 ml/kg/mm Hg for UT and .343 +/- .02 ml/kg/mm Hg for T (P less than .001), suggesting that T had a better ability to reduce total vascular capacitance. Also, both the compensation and decompensation times were greater in the T than UT groups. These data suggest that treadmill exercise-conditioned rats have a greater inherent cardiovascular compensatory ability than untrained rats.

Animals↗
PubMed1986

Lower extremity amputation: the control series.

Although various techniques to determine amputation level have become available, obvious clinical factors may yet identify patients in whom a major amputation is unlikely to heal. We have analyzed the association of multiple clinical factors with the morbidity of 1028 consecutive amputations performed in 786 patients during a 13-year period. The overall operative mortality rate was 7% (57 of 786 patients). Cardiac complications were the leading cause of death (43%). In the 729 patients surviving operation, 345 above-knee amputations (AKAs) and 626 below-knee amputations (BKAs) were performed. After operation, 15.4% of these amputations failed to heal and required proximal revision. The AKA failure rate was 9% and the BKA failure rate was 19%. Significantly higher failure rates were noted in whites, nondiabetics, and those patients with heart disease. It is concluded that major amputation continues to be associated with significant morbidity and mortality rates despite changes in perioperative care and surgical technique. Common clinical characteristics indicate high-risk patients in whom a BKA is unlikely to heal and who may benefit from prospective attempts to determine amputation level.

Amputation, Surgical↗
PubMed1986

Retinal angiomatosis: the ocular manifestations of von Hippel-Lindau disease.

The ocular manifestations of a large von Hippel-Lindau pedigree are presented. Of 24 persons with retinal angiomas, 18 are living and are the basis of this report. Nineteen of their 28 affected eyes were asymptomatic with 2 to 4 small tumours per eye. Nine eyes had lost vision secondary to exudative detachment. Seven of these had peripheral disease with rapid recurrences. Two had untreated disc tumours. Tumours less than 1 disc diameter (DD) in size were easily treated with photocoagulation. Multiple treatments of cryotherapy were required for larger tumours. Scleral buckle and early vitrectomy are recommended for vitreous traction. Tumour in a 4-year-old and a de-novo tumour in a 42-year-old lead us to recommend life-time surveillance of patients at risk. Many patients had false negative family histories. A review of the literature leads us to suspect that the majority of retinal angiomas are familial. We emphasize the ophthalmologist's responsibility to investigate such patients.

Adolescent↗
PubMed1986

Intrinsic versus extrinsic regional vascular control during hemorrhagic hypotension and shock.

An analysis of both intrinsic (eg, autoregulatory) and extrinsic adrenoreceptor regulation of the vascular smooth muscle within skeletal muscle (SM), cutaneous (C), and mesenteric (M) tissues obtained during local tissue hypotension (LH), hemorrhagic hypotension (HH), and shock (S) is presented. A series of pressure/conductance curves show that the intrinsic regulation of vascular tone remains down to LH values of 40 mm Hg in M to 60 mm Hg in SM and does not occur in C; all three vascular beds respond to HH by exhibiting strong extrinsic vasoconstriction, the elevated tone persists throughout HH in C but lasts only a few minutes in M while SM vasoconstriction may last up to 45 min; and during the terminal phase of S, vascular tone was best maintained in C. In vitro studies suggest that the prehemorrhage alpha 1 adrenoreceptor control is greatest in M and least in SM. During compensatory and early decompensatory HH, alpha 1 receptors are depressed in SM. M vessels show this alpha 1 receptor hyposensitivity only during compensatory HH. All vessels show strong responsiveness to NE during all stages of HH and S, yet M vessels demonstrate a progressive increase in the NE concentrations required to elicit and ED50, suggesting some degree of adrenoreceptor desensitization or down regulation. This is in contrast to the adrenoreceptor hypersensitivity noted in SM during both compensatory and decompensatory stages. C vessels show this pattern in all stages except S. These data verify that each vascular bed has its own unique set of vascular control mechanisms that can act independently during HH and S.

Animals↗
PubMed1985

The effects of cytoskeletal inhibitors on intestinal iron absorption in the rat.

An established and validated method using loops of intestine in vivo in rats was used to study the effects of cytoskeletal inhibitors on iron absorption. Radioactive iron instilled into the loop of intestine pretreated with test substance was monitored in the blood and, after death, ferritin loading with radioactive iron was measured on density gradients of mucosal cell homogenates and absorbed iron in the carcass was determined. Colchicine, vincristine and cytochalasin B all caused dose- and time-dependent inhibition of iron absorption, and the effects of cytochalasin B were reversible within 1 h. It is not known which cellular component is the vehicle for the transcellular movement of iron from the intestinal lumen onto plasma transferrin; however, this study showed that the uptake of iron by ferritin in an iron-absorbing loop of intestine paralleled the actual absorption of iron into the carcass. This phenomenon did not occur in non-iron-absorbing intestinal and was inhibited by the action of the cytoskeletal inhibitors in the iron-absorbing region. Previously we had shown that iron uptake into cells and onto cellular transferrin was virtually the same throughout the small intestine, irrespective of the iron-absorbing capacity of the region. The results of this study therefore suggest that iron absorption depends on an intact cytoskeletal system and that ferritin in the iron-absorbing cell is able to load from the pool of iron committed to transcellular movement onto plasma transferrin.

Animals↗
PubMed1985

The influence of hypertension upon the normal cardiovascular responses to hemorrhagic hypotension and shock.

The data suggest that rats genetically inbred to be hypertensive (SHR) are less able to compensate for hemorrhage and shock than their normotensive controls (WKY). Two reasons for this genetic dysfunction are: 1) SHRs seem to depend more on innervated alpha 1 than noninnervated alpha 2 adrenoreceptors for vasoconstriction; and 2) the vascular smooth muscle hypertrophy noted in SHRs may interfere with effective vasoconstriction.

Animals↗