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4122. Antihypertensive treatment, myocardial infarction, and nocturnal myocardial ischaemia.
Patients with critical coronary stenoses or hypertrophied ventricles have impaired coronary vasodilator reserve and are at greatest risk of myocardial ischaemia or infarction if subendocardial perfusion pressure falls below the lower threshold of bloodflow autoregulation. During sleep, antihypertensive treatment may cause coronary artery perfusion pressure to fall below these limits in such patients. Unrecognised nocturnal hypotension may be one reason why treatment has not diminished the risk of myocardial infarction in patients with hypertension.
4124. Genetics of classic Alport's syndrome.
41 families with classic Alport's syndrome (hereditary nephritis with sensorineural deafness) were studied. All their pedigrees were compatible with X-linked inheritance. DNA probes were used to investigate genetic linkage in these families. Linkage to probe S21 (DXS17) was confirmed (LOD score = 4.72 at 0 = 0.06), localising the gene for Alport's syndrome to the middle of Xq; thus the disorder is X-chromosomal in nature.
4127. The increment in the anion gap: overextension of a concept?
The calculation of the anion gap is widely used in the diagnosis of metabolic acidosis. It is often taught that the increment in the anion gap will exactly match the fall in serum bicarbonate during a simple metabolic acidosis of the high anion gap type; if the changes in the anion gap and bicarbonate level are not equivalent, a second acid-base disorder should be suspected. The assumptions upon which this formulation is based are largely unsubstantiated. This review critically examines these assumptions and their clinical implications. Discrepancies between the increment in the anion gap and the reduction in serum bicarbonate must be interpreted cautiously.
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