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B S Block

Publications and source records attributed to B S Block.

26 records · Page 2Linked to original sources
PubMed1985

Validity of mathematical methods of quantitating fetal heart rate variability.

Twenty-two mathematical formulas purporting to quantitate fetal heart rate variability, 13 for short-term and nine for long-term variability, were examined by using artificially generated numbers representing either short-term variability or long-term variability. Numbers representing short-term variability consisted of alternating beats, and those representing long-term variability were sine waves of differing amplitude or frequency spanning the generally accepted clinical range of fetal heart rate variability. The validity of the indices was determined by applying certain selected criteria. The results showed that 11 of the 13 short-term variability indices validly measured short-term variability, whereas only one of the nine long-term variability indices did so. The two major defects in the long-term variability indices were that there was an increase in the long-term variability index as the short-term variability increased, and the long-term variability indices did not increase linearly with increasing frequency of long-term variability complexes. This study suggests that short-term variability is relatively easy to quantify, but there is little relationship between the long-term variability indices and what is clinically regarded as long-term variability.

Female↗
PubMed1984

Preterm delivery is not predicted by serial plasma estradiol or progesterone concentration measurements.

Previous studies suggest that plasma estradiol-17 beta and progesterone concentration values differ between patients who deliver before term and those who deliver at term. To determine if these values would aid in preterm delivery risk prediction, we measured plasma estradiol-17 beta and progesterone concentrations serially in 90 patients at high risk for preterm delivery. Measurements from 17 patients who developed documented preterm labor and/or were delivered before term were compared to the tenth and ninetieth percentiles of 42 patients who were delivered at term. The sensitivity of these measurements to predict preterm delivery was very low. Also, the mean plasma estradiol-17 beta and progesterone concentrations in patients with preterm labor who had term deliveries and in patients with preterm labor that progressed to preterm delivery were not different from each other or from patients delivering at term. No change in plasma estradiol-17 beta or progesterone concentration was noted preceding labor. We conclude that serial measurements of plasma estradiol-17 beta and progesterone concentrations do not improve preterm delivery risk prediction.

Adolescent↗
PubMed1984

Continuous measurement of oxygen consumption in fetal sheep.

A microcomputer-based system has been developed to measure oxygen consumption continuously in fetal sheep. The system includes an umbilical artery electromagnetic blood flow transducer and two fiberoptic catheter oximeters for measuring umbilical artery and vein oxyhemoglobin saturation in vivo. The electrical signals from these instruments are digitized and sampled by a microcomputer. Fetal oxygen consumption is calculated from the Fick principle by use of the digitized signals and hemoglobin concentrations. The latter is measured intermittently and updated if necessary. System validation required that artifacts in oxyhemoglobin recordings could be avoided and that the catheter readings agreed with values from intermittent samples. Continuous heparin infusion and careful catheter placement facilitated attainment of these requirements. The system can be used to obtain continuous recordings of fetal oxygen consumption during rapidly occurring physiologic events.

Animals↗
PubMed1984

Responses of the growth-retarded fetus to acute hypoxemia.

Growth retardation in the human fetus associated with maternal cardiovascular disease is frequently accompanied by birth asphyxia and perinatal mortality. We have investigated the cardiovascular responses to acute hypoxemia in the fetal lamb with growth retardation secondary to embolization of the uteroplacental vascular bed. In the basal period, fetal arterial P02 and umbilical perfusion were significantly lower, and perfusion of the adrenal glands, brain, and heart was significantly higher, in embolized than in control fetal lambs. During imposed acute hypoxemia there was preferential perfusion of vital organs, the adrenal glands, brain, and heart in control and embolized fetuses. This preferential perfusion to the vital organs during hypoxemia was significantly more pronounced in embolized animals. Because of the increased compensation during acute hypoxemia, as reflected by the increased preferential perfusion of vital organs, the growth-retarded fetuses would probably decompensate sooner if the hypoxemia was prolonged.

Acute Disease↗
PubMed1984

Effects of beta-adrenergic blockade on blood flow distribution during hypoxaemia in fetal sheep.

Hypoxaemia in fetal sheep causes a decrease in vascular resistance of the heart, brain and adrenal gland which results in increased blood flow to these organs. Placental blood flow is maintained. To investigate whether increased beta-adrenergic activity during hypoxaemia is involved in these changes, the effects of propranolol on organ blood flows (using the microsphere method) and other cardiovascular variables were studied during fetal hypoxaemia (50% reduction of fetal haemoglobin saturation) in 5 chronically catheterized fetal sheep at 126 to 130 days of gestation. Beta-blockade during hypoxaemia caused a fetal bradycardia and a 30% drop in cardiac output. Placental and myocardial blood flows fell by 39% and 37% respectively. Total peripheral resistance increased by 35% mainly due to increased fetal placental vascular resistance. Heart and lung vascular resistances increased following propranolol. In 3 similarly catheterized animals, propranolol administered in the absence of hypoxaemia led to a 9% drop in cardiac output and placental blood flow but no redistribution of blood flow to fetal organs. It is concluded that the increased beta-adrenergic activity associated with fetal hypoxaemia limits the negative chronotropic effects of concomitantly increased vagal activity, maintains placental blood flow through its inotropic and chronotropic activity as well as by maintenance of placental vasodilatation and may be one of several factors which increase myocardial blood flow during hypoxaemia.

Adrenal Glands↗
PubMed1979

False-positive amniotic fluid cytology in a parturient with active genital herpes infection at term.

A patient who developed genital herpes infection diagnosed at 37 weeks' gestation is presented. Amniocentesis performed at 38 weeks' gestation revealed herpetic changes in fetal cells. Subsequent amniotic fluid viral culture was negative. The infant was delivered by elective primary cesarean section at 39 weeks' gestation, demonstrated no evidence of herpetic infection, and was well at a 3-month follow-up examination. Positive cytologic changes seen in epithelial cells obtained by amniocentesis do not necessarily indicate intrauterine infection of the fetus. Cytologic changes alone are inadequate, and viral isolation by culture or by immunofluorescence should be required before prophylactic cesarean section is abandoned in the treatment of the parturient with active genital herpes infection near term.

Adult↗
PubMed1977

Human splanchnic metabolism during diabetic ketoacidosis.

Splanchnic exchange rates of glucose, acetoacetate, beta-hydroxybutyrate, lactate, pyruvate, glycerol, alanine, glutamine, glutamate, free fatty acids, and triglycerides were measured in eight patients during moderate to severe diabetic ketoacidosis. Their arterial glucose concentration was 20.68 (9.80-52.79) mumole/liter and tic glucose release was 0.77 (0.09-2.44) mmole/min. Gluconeogenesis accounted for about one-half of net splanchnic glucose release, assuming quantitative conversion of net splanchnic extracted lactate, pyruvate, glycerol, alanine, and alpha-ketoglutarate equivalents to glucose. Net splanchnic free fatty acid extraction was 0.24 (0.09-0.52) mmole/min. There was a positive correlation between free fatty acid uptake and ketone-body release. Net splanchnic acetoacetate release was 0.50 (0.05-0.92) mmole/min and beta-hydroxybutyrate release was 0.35 (-0.16 to 0.84) mmole/min. Total ketone-body release was 0.84 (0.37-1.61) mmole/min. The wide ranges of net splanchnic glucose and ketone-body production rates show the heterogeneous characteristics of the diabetic patient in ketoacidosis. It is concluded that the hyperglycemia and hyperketonemia of diabetic ketoacidosis is due to the lack of reciprocity among rates of hepatic glycogenlysis, gluconeogenesis, and ketogenesis resulting in inappropriate net splanchnic release of glucose and ketone bodies.

Alanine↗