Venous hydrostatic indifference point as a marker of postnatal adaptation to orthostasis in swine.

The postulate that venous adaptation assists postural baroreflex regulation by shifting the hydrostatic indifference point (HIP) toward the heart was investigated in eight midazolam-sedated newborn piglets. Whole body head-up (+15, +30, and +45 degrees ) and head-down (-15 and -30 degrees ) tilt provided a physiological range of orthostatic strain. HIP for all positive tilts shifted toward the heart (P < 0.05), +45 degrees HIP shifted most [6.7 +/- 0.3, 5.9 +/- 0.5, and 3.6 +/- 0.3 (SE) cm caudal to right atrium on days 1, 3, and 6, respectively]. HIP for negative tilts (3.0 +/- 0.2 cm caudal to right atrium) did not shift with postnatal age. Euthanasia on day 6 caused 2.1 +/- 0.3-cm caudal displacement of HIP for positive and negative tilts (P < 0.05). HIP proximity to right atrium was not altered by alpha-, beta-adrenoceptor and cholinoceptor blockade on day 5. It is concluded that early HIP migration reflects enhancement of venous pressure control to head-up orthostatic strain. The effect is independent of baroreflex-mediated adrenoceptor and cholinoceptor mechanisms.

Haemophilus influenzae type B invasive disease in urban and rural children: immunization patterns and prevalence of disease.

To examine the impact of the introduction of Haemophilus influenzae type b (Hib) conjugate vaccine, we reviewed the incidence of Hib invasive disease in the state of Florida from 1984 to 1992. We analyzed the incidence of disease in two populations of children, one residing in an urban area and the other in a rural area. This study was designed to compare incidence rates prior to and following the introduction of Hib vaccine for children. Our data show a > 80% decrease in the incidence of Hib invasive disease in the state of Florida and a similar decrease in both the urban and rural populations examined. Analysis of the data revealed that the majority of children contracting Haemophilus influenzae type b invasive disease in both populations were either not immunized or were only partially immunized.

Characterization of the neonatal heart rate baroreflex during and after ECMO.

Prolonged continuous blood pressure (BP) and heart rate (HR) recordings from neonates of 35 to 42 weeks gestation were studied during and after ECMO. Data segments with significant deviation of BP were extracted for further analysis. The simultaneous changes in BP and HR were compared and the slope of the regression determined baroreflex sensitivity (BRS). Of 464 BP deviations, 98% produced curves with a negative slope consistent with the presence of a baroreflex. The average BRS was -1.0 +/- 0.8 bpm/mmHg (mean +/- S.D.) and curves were steeper during rising BP than falling BP (-1.1 +/- 0.9 beats/min per mmHg versus -0.9 +/- 0.6, P = 0.001). The baroreflex was more sensitive during ECMO than after ECMO to both rising BP (-1.0 +/- 0.5 beats/min per mmHg versus -0.7 +/- 0.5, P = 0.004) and falling BP (-1.0 +/- 0.6 beats/min/mmHg versus -0.7 +/- 0.5, P = 0.04). HR response curves obtained during different BP fluctuations on the same recording had varying threshold, consistent with acute resetting. One infant demonstrated chronic baroreceptor resetting over 3 days to a rise in resting BP. The near-term, critically ill neonate has an active baroreflex which is capable of resetting. ECMO was associated with accentuation of the baroreflex response.

Effect of short-term muscle relaxation on neonatal plasma volume.

OBJECTIVES: To study the effect of pancuronium-induced muscle relaxation on circulating plasma volume. DESIGN: A prospective, controlled study. Consecutive infants who were paralyzed with pancuronium and a comparative group who were not paralyzed during mechanical ventilation were studied. SETTING: Neonatal ICU of a regional referral university-affiliated hospital. PATIENTS: Newborn infants weighing greater than 1700 g who required respiratory assistance within 24 hrs of birth and who were free of congenital heart disease, sepsis, or blood loss were eligible for entry into the study. Infants who received colloid infusions during the study period were excluded. A total of 17 consecutive infants (nine paralyzed and eight nonparalyzed control infants) were studied. Four paralyzed infants and one nonparalyzed infant received colloid infusions before the completion of the study and were excluded from the final analysis. MEASUREMENTS: Plasma volume was measured three times in the paralyzed infants: a) immediately before the first dose of pancuronium, b) after 12 to 24 hrs, and c) greater than or equal to 12 hrs after the return of muscle activity, but before extubation. Plasma volume in the nonparalyzed, control infants was measured at the time of intubation, 12 to 24 hrs after commencing mechanical ventilation, and 12 hrs after extubation. Plasma volume was measured using the Evans blue dye dilution technique. RESULTS: There were no changes in the plasma volume or blood volume in the three measurements among both the paralyzed and nonparalyzed infants. CONCLUSION: Pancuronium-induced muscle relaxation in mechanically ventilated newborn infants weighing greater than 1700 g did not alter circulating plasma volume in 24 hrs.

Tracheal occlusion in the newborn piglet. Effects of sleep state and occlusion timing on arousal and respiratory responses.

Twelve piglets of 3-5 days of age were instrumented for determination of sleep state and performance of midtracheal occlusions. After spontaneously occurring sleep the occlusions were performed either at end-inspiration or end-expiration in quiet and active sleep. The time from occlusion to arousal differed significantly between quiet and active sleep. Arousal from quiet sleep following end-expiratory occlusions occurred after a mean of 3.1 s. After similar, end-expiratory occlusions in quiet sleep were commonly followed by apneas, presumably a manifestation of the Hering-Breuer reflex. Such apneas were rare in active sleep (P less than 0.01). The arousal response to midtracheal occlusions in the newborn piglet is qualitatively similar to that previously described in the newborn lamb, but occurs more rapidly. Our results suggest that the response to vaguely mediated information from pulmonary stretch receptors is impaired inactive sleep.

Cellulose phosphate and chlorothiazide in childhood idiopathic hypercalciuria.

A calcium loading test performed on seven of eight children with idiopathic hypercalciuria identified the hyperabsorptive form of hypercalciuria in five and renal hypercalciuria in one. The type of hypercalciuria was not identified in the other patient. Three children presented with hematuria without calculus formation. Chlorothiazide reduced the urinary calcium excretion level in two of six patients to the normal range. The addition of cellulose phosphate to chlorothiazide reduced the urinary calcium excretion level to the normal range in those four patients who showed an incomplete response to chlorothiazide alone. There was clinical improvement with cellulose phosphate in another child whose symptoms did not disappear after chlorothiazide had reduced urinary calcium level to the normal range. Cellulose phosphate is effective in children with recurrent stone formation who have shown inadequate response to chlorothiazide.