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Biomedical subjects

L Johns

Publications and source records attributed to L Johns.

50 records · Page 3Linked to original sources
PubMed1984

Cerebral blood flow in sickle cell cerebrovascular disease.

Cerebral blood flow (CBF) has been studied by the xenon-133 (133Xe) inhalation method in 16 children with suspected sickle cell cerebrovascular disease. Abnormalities consisting of decreases in total, hemispheral, or regional CBF were found in 17 of 26 studies. Eleven studies performed immediately after stroke, transient ischemic attack, or depression of state of alertness showed abnormalities. In addition to confirming regional cerebrovascular insufficiency in children with stroke due to major cerebral artery occlusion, the method detected diffuse decrease in CBF in children with stupor, coma, and seizures who had normal angiographic findings. In contrast, six of seven studies obtained after exchange transfusion or during maintenance on hypertransfusion therapy showed normal findings. The difference between results in patients with acute neurologic disturbances and those receiving transfusion therapy was statistically significant (P less than .005). The data indicate that the 133Xe method reliably demonstrates cerebrovascular impairment in sickle cell disease. They also suggest that CBF changes in patients with sickle cell disease can be reversed by exchange transfusion and by hypertransfusion therapy. The 133Xe CBF method may be useful for following up children with sickle cell disease who are at high risk for recurrent stroke.

Adolescent↗
PubMed1981

Cooling the burn wound to maintain microcirculation.

To evaluate the effect which cooling of burn wounds has upon dermal microvascular circulation, standard 10% BSA dorsal guinea-pig scald burns were created. In treated animals, the dorsal burned region was immersed in a circulating ice-water bath (0-3 degrees C) for 30 minutes at various time intervals postburn (10,20,30, and 60 minutes after scald). India-ink perfusion was used to determine the level of dermal vessel patency at 2, 4, 8, 24, 72, and 96 hours after burning. By 96 hours, significant differences could be seen in animals cooled 10, 20, or 30 minutes after burning. Those not treated until 60 minutes after burning had dermal perfusion essentially the same as control animals. 133Xe dermal washout studies were performed at 8 and 24 hours and corroborated these findings. Grossly, burn wounds cooled by 30 minutes after burn had markedly better healing than control animals and animals cooled 60 minutes after burning. We believe these data support the early use of cold water treatment of partial-thickness burn wounds, as demonstrated in this experimental study.

Animals↗
PubMed1981

Increased cerebral blood flow after external carotid artery revascularization.

Ten patients with symptoms of cerebral ischemia were found to have totally occluded internal carotid arteries with significant external carotid artery stenosis or occlusion. Eight patients underwent external carotid endarterectomy, and two patients underwent saphenous vein bypass to the external carotid artery from the subclavian artery. Cerebral blood flow was measured with 133Xe in six patients preoperatively and in five postoperatively. Four of the six patients had diminished mean flow on the affected side, and three had diminished flow in the contralateral side. All patients had abnormalities in regional cerebral blood flow. Postoperatively, all patients had significant improvement in mean blood flow on the side treated with operation (15% to 39%), and four had improvement of blood flow on the contralateral side (12% to 52%). All had improvement in regional cerebral blood flow. Nine of the 10 patients were relieved of their symptoms. One patient, despite improvement in cerebral blood flow, continued to have diminished cerebral flow and symptoms postoperatively. Subsequent extracranial-intracranial bypass relieved his symptoms and his cerebral blood flow returned to normal. Thus external carotid artery revascularization is effective in increasing total and regional cerebral blood flow and in relieving symptoms of internal carotid artery occlusion and external carotid stenosis. Cerebral blood flow measurement with 133Xe is useful in preoperative patient selection and objective assessment of operative results.

Adult↗
PubMed1979

Detailed monitoring of the effects of mannitol following experimental head injury.

The experimental model of a cerebral missile injury developed by Crockard was used in three groups of Rhesus monkeys treated with mannitol. One group received mannitol 15 minutes after being injured with a BB pellet at 90 m/sec impact. Another group was wounded identically, but mannitol treatment was delayed until 1 hour after injury. The last group was wounded with the missile traveling at 180 m/sec, and mannitol was started 15 minutes after trauma. The data were contrasted with the results from the original model. After receiving mannitol, all groups showed marked improvement in mean blood pressure, cerebral perfusion pressure, cerebral blood flow, and cerebral metabolic rate of oxygen consumption out of proportion to the degree of reduction in intracranial pressure (ICP). The authors conclude that the therapeutic value of mannitol may, in some injuries, be directly related to its effects on blood flow and metabolism, as well as to its better known effects upon ICP.

Animals↗
PubMed1979

Morphological and physiological study of the effect of histamine on the isolated perfused rabbit lung.

Histamine causes interstitial pulmonary edema, but whether this is the result of an increased permeability of the pulmonary circulation or only of the bronchial circulation remains to be determined. In order to selectively study the effect of histamine on the pulmonary circulation, we used an isolated perfused rabbit lung preparation because in this species, the bronchial circulation is poorly developed. Edema formation was assessed by continuously monitoring the weight of the lung perfused at constant pressure. These studies were supplemented by electron microscopic observations using hemoglobin as an ultrastructural tracer for microvascular permeability. We found that histamine (8.0 microgram base/100 ml of perfusate) did not cause lung weight to increase. Ultrastructural studies showed that histamine, at this dosage, did not cause a greater leakage of hemoglobin that occurred in the control lungs. Thus, we have concluded that histamine does not increase the permeability of the pulmonary microcirculation in the isolated perfused rabbit lung.

Animals↗
PubMed1977

Economic impact analysis: a theoretical approach.

Where the traditional focus of local planning has been on access to health services, recent legislation and policy reflect an equally prominent concern for costs. Appropriate methodologies for collection and analysis of financial and economic data have been lacking. A particularly difficult problem, both theoretically and practically, is the economic impact of a capital investment by one provider on the rest of the local service system. In order to focus the attention of health service planners, economists and others on this issue, a preliminary theory of "economic impact analysis" is outlined here. Scope of concern and conditions of application ("ripple" and "spigot" models) are defined. Existing analytical tools are reviewed, and related philosophical issues raised.

Capital Expenditures↗
PubMed1975

Preimbursement: a new concept for HMO planning.

Federal endorsement of the HMO concept has resulted in broad understanding of a number of concepts unknown in fee-for-service medicine. As the concepts are adapted to particular circumstances, refinement can be expected. One such refinement, applicable to financial arrangements between the HMO and contracting providers, is discussed here.

Alaska↗