Baroreflex activity was assessed in 10 fetal lambs at 85-145 days of gestation. ECG leads sewn to the fetal chest wall, vinyl catheters in brachial artery and femoral vein, and a balloon catheter in the descending aorta were exteriorized through the ewe's flank. After at least 36 hours, the reflex bradycardia, in response to increased blood pressure by balloon inflation, was measured. Baroreflex sensitivity was expressed as the slope of the beat-to-beat relationship between systolic (S.P.) or pulse (P.P.) pressure and the subsequent R-R interval or instantaneous heart rate (H.R.). Baroreflex activity was considered absent if the slope did not differ significandy from zero or if the correlation coefficient was less than 0.7. Throughout gestation baroreceptors could respond to pressure elevation, but the proportion of positive responses increased with age. Baroreflex sensitivity increased up to term when either S.P. or P.P. were plotted against the next R-R interval. Regression analysis of S.P. or P.P. vs. R-R interval, or of P.P. vs. H.R showed increasing baroreflex sensitivity with maturation Analysis of S.P. vs. H.R. showed no significant increase in response with advancing gestation; however, this type of analysis does not take into account the slower resting heart rates of older animals. KEY WORDSAutonomic blocking agents autonomic nervous system blood pressure carotid sinus electrocardiogram heart rate fetal maturation gestation mechanoreceptors vagus nerve• The baroreceptor reflex is a well-known compensatory mechanism for buffering sudden changes in systemic blood pressure in adult animals and man. It is also possible that this baroreflex might participate in the abrupt adaptation that occurs at birth to balance a decreased pulmonary vascular resistance, an increased systemic vascular resistance and a 710variable blood volume. Although other workers have shown that baroreflex responses could be elicited in fetal (1-4) and newborn (1) animals, all previous studies have been conducted in anesthetized animals with the fetus exteriorized. Since it is now well known that cardiovascular function in the fetus may be altered by anesthesia or exterioration (5), we studied fetal lambs in utero while the unsedated ewe stood quietly. The reflex cardiac slowing in response to rapid elevation of blood pressure could then be measured throughout the latter half of gestation. MethodsTen time-dated pregnant ewes (Dorset or Southdown breeds) with fetuses of gestational ages ranging from 85 to 145 days and six neonatal lambs were studied. Food was withheld for 24 hours prior to surgery, and spinal anesthesia was administered to the ewes by intrathecal injection of 2.0 ml of 1% tetracaine hydrochloride (Pontocaine). After insertion of a catheter into the maternal femoral artery, the uterus was exposed French, maximum inflated diameter of 9-12 mm) was inserted into the other fetal femoral artery and was advanced into the descending aorta between the renal arteries and the ductus arteriosus. Using local anesthesia, simi...

Summary Clinical findings and results of treatment in a series of 49 premature infants with birth weights between 850 and 1250 g are presented. The “intensive care” included nursing in incubators with high environmental humidity maintaining skin temperature at 36.5°C, umbilical catheterisation (both arterial and venous), intravenous glucose infusions, correction of metabolic acidosis by rapid sodium bicarbonate infusions, oxygen therapy and finally endotracheal intubation and mechanical ventilation. The series was divided into 3 categories according to the severity of respiratory symptoms. There was only one survivor out of 12 cases in the category of severe RD, whereas 14 of 21 with moderate RD and 9 of 16 with slight or no RD survived. The overall survival rate was 45%. The correlation between clinical findings, arterial blood gases and pH, chest X‐rays, response to treatment and outcome in each of the 3 categories is discussed. The preliminary data from our follow‐up studies indicate that there are only a few cases showing signs of permanent brain injury at the age of two years.

S 425than 120 days gestation; (3) reflex bradycardia was blocked by atropine but not influenced by propranolol; (4) in fetuses the regression coefficients of SP or PP vs. R-R increased with gestational age, but not when SP or PP was correlated with HR because of the lower initial HR in older fetuses; (5) Sympathetic and parasympathetic activity have been studied in exteriorized fetal lambs but not in intact fetuses in utero. We placed vinyl catheters in a systemic artery and hindlimb vein in 20 fetuses from 92 days of gestation to term and also in 3 newborn lambs. The animals were allowed to recover from surgery for 2-3 days and then studied daily for several weeks. Maternal and fetal pH, PCO 3 and PO 2 were normal in all experiments. The blood pressure (BP) and heart rate (HR) responses to selective intravenous injection of propranolol (1 mg/kg), practolol (1-2 mg/ kg), atropine (1.0 mg/kg), phentolamine (0.1 mg/kg), phenoxybenzamine (5 mg/kg) and tyramine (0.25 mg/kg) were recorded. The adequacy of autonomic blockade was confirmed by absence of response to acetylcholine (5-15 /ig/kg), isoproterenol (0.1 /ig/kg) or methoxamine (50 ^g/kg). Changes in HR from resting levels without significant BP change were observed as follows: propranolol 5-25% decrease, practolol 8-22% decrease and atropine 0-64% increase. Response to beta-adrenergic blockade did not vary significantly with gestational age. Phentolamine and phenoxybenzamine decreased systolic BP 2-14 and diastolic BP 2-12 mm Hg in 19/21 animals and tyramine increased systolic BP 7-60 and diastolic BP 10-46 mm Hg in 7/7 animals. No significant difference in sympathetic responses were observed in fetal and newborn lambs, indicating HR and BP to be under similar autonomic control at all ages studied.Catecholamine uptake and storage of the newborn rat heart during post-natal development. GERALD F. ATWOOD and NORMAN KIRSHNER (Intr. by Madison S. Spach). Duke Univ. Med. Ctr., Durham, N. C. The ability of atria, removed from Sprague-Dawley rats at ages 1-21 days, to take up and store catecholamines was studied to correlate this activity with the previously observed physiologic immaturity of the cardiac sympathetic nervous system in the neonate. The cardiac tissue was incubated in Krebs-Henseleit bicarbonate buffer containing 10' 5 M iproniazid and 10" 7 M H 3 -norepinephrine (H S NE). Total uptake and subcellular distribution at 1, 4, 7, 14, and 21 days were determined at various time intervals between 5 and 30 minutes. Uptakes at O°C. served as controls.Uptake rates were expressed on a per gram wet weight basis. There was a small amount of uptake observed during the first post-natal day (0.515 nanagrams/minute) which increased only slightly by 4 days of age (0.683 ng/min). The most significant change occurred between 4 and 7 days (115%). Uptakes at 7, 14, and 21 days were similar to adult values. Since reserpine effectively blocks uptake of catecholamines into the storage granule, 10 5 M reserpine was added to the incubation media to determine the role of t...

Summary Twenty‐seven deaths in premature infants weighing less than 1 250 g who were treated with intermittent positive pressure respiration are reported. The major pulmonary abnormalities were hyaline membrane formation, infection, and hemorrhage occurring‘ alone or in combination with intraverticular hemorrhage. Hyaline membranes were associated with severe clinical features of respiratory distress, whereas infection was not. Prolonged treatment resulted in “bronchopulmonary dysplasia” in only 1 case where severe clinical respiratory distress was associated with the finding of hyaline membranes at post mortem.