2 resultados para control cerebral

em DigitalCommons@The Texas Medical Center


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The rheoencephalogram (REG) is the change in the electrical impedance of the head that occurs with each heart beat. Without knowledge of the relationship between cerebral blood flow (Q) and the REG, the utility of the REG in the study of the cerebral vasculature is greatly limited. The hypothesis is that the relationship between the REG and Q when venous outflow is nonpulsatile is^ (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)^ where K is a proportionality constant and Q is the mean Q.^ Pulsatile CBF was measured in the goat via a chronically implanted electromagnetic flowmeter. Electrodes were implanted in the ipsilateral cerebral hemisphere, and the REG was measured with a two electrode impedance plethysmograph. Measurements were made with the animal's head elevated so that venous flow pulsations were not transmitted from the heart to the cerebral veins. Measurements were made under conditions of varied cerebrovascular resistance induced by altering blood CO(,2) levels and under conditions of high and low cerebrospinal fluid pressures. There was a high correlation (r = .922-.983) between the REG calculated from the hypothesized relationship and the measured REG under all conditions.^ Other investigators have proposed that the REG results from linear changes in blood resistivity proportional to blood velocity. There was little to no correlation between the measured REG and the flow velocity ( r = .022-.306). A linear combination of the flow velocity and the hypothesized relationship between the REG and Q did not predict the measured REG significantly better than the hypothesized relationship alone in 37 out of 50 experiments.^ Jacquy proposed an index (F) of cerebral blood flow calculated from amplitudes and latencies of the REG. The F index was highly correlated (r = .929) with measured cerebral blood flow under control and hypercapnic conditions, but was not as highly correlated under conditions of hypocapnia (r = .723) and arterial hypotension (r = .681).^ The results demonstrate that the REG is not determined by mean cerebral blood flow, but by the pulsatile flow only. Thus, the utility of the REG in the determination of mean cerebral blood flow is limited. ^

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Objective. To study the risk factors for eclampsia, a rare but significant complication of pregnancy.^ Target population. All deliveries at or after the 20th week of gestation that took place between January 1, 1977 and March 1992, and between January 1990 and April 1992 at two hospitals in Houston, Texas, respectively.^ Study population. Sixty-six confirmed cases of eclampsia, and 2 groups of randomly selected controls: Non-preeclamptic and preeclamptic deliveries matched to cases on hospital and month of delivery on a 1:4 ratio.^ Exclusions. Women with chronic hypertension, gestational epilepsy, a previous history of epilepsy, and convulsions attributed to encephalitis, meningitis, cerebral tumor, and intracerebral bleeding, and women without a definite diagnosis of preeclampsia/eclampsia.^ Results. Eclampsia developed in 0.52-0.93/1000 deliveries. Fifty-six percent of seizures occurred in the antepartum period, 2% as early as 20 weeks of gestation and 39% between 37 and 42 weeks. Twenty-nine percent and 15% occurred in the postpartum and late postpartum periods, respectively, 8% as late as one week postpartum. A different set of risk factors was involved in the development of eclampsia in non-preeclamptic women than in the progression from preeclampsia to eclampsia. Factors involved in the development of eclampsia included, in addition to twin pregnancy and family history of pregnancy-induced hypertension, fewer than 3 prenatal care visits, urinary tract infections, primigravidity, obesity, black ethnicity, diabetes mellitus, and age $\le$20 years. Risk factors involved in the progression from preeclampsia to eclampsia included fewer than 3 of prenatal care visits, and age $\le$20 years. Protective factors were magnesium sulfate administration prior to seizure, history of abortions and longer gestational age. Having less than 3 prenatal care visits and being less than or equal to 20 years of age were predictors of eclampsia, whether of its development or progression from preeclampsia. Once preeclampsia is diagnosed, primigravid, diabetic, black, or obese women and those with urinary tract infections did not appear to exhibit any increased risk for the progression to eclampsia. The administration of magnesium sulfate was especially protective, followed by a positive history of abortions, 3 or more prenatal care visits, and longer gestational age. The protective effect of MgSO$\sb4$ was only slightly diminished when cases were restricted to the 65% who had a diagnosis of preeclampsia. The progression from preeclampsia to eclampsia may be largely preventable through adequate prenatal care and presumably the administration of magnesium sulfate. (Abstract shortened by UMI.) ^