Alastair A. Hutchison

Decreased imposed work with a new nasal continuous positive airway pressure device

This model study compared the imposed work of two nasal continuous positive airway pressure (NCPAP) devices for very low birthweight (VLBW) babies; a new NCPAP device, designed by Moa et al., (Crit Care Med 16:1238, 1988), and a conventional NCPAP device. In addition, the variabilities in the pressures of a simulated airway were compared. A continuous flow (8 L/min) was used to generate CPAP. A Harvard ventilator was used to simulate breathing at a fixed volume (12.1 mL) and rate (45 breaths/min). The pressure drop across and the flow rate through each device were measured, thus allowing the determination of imposed work, i.e., the work of breathing done by the patient to overcome frictional losses due to the NCPAP device. In addition, the pressure fluctuations in the simulated airway were measured. The data presented are averages of 36 breaths using the new device and 34 breaths using the conventional device. The means of the imposed work in the new device and in the conventional device were 0.135 (95% Cl ± 0.004) mJ/breath and 0.510 (95% Cl ± 0.004) mJ/breath (P < 0.01) respectively. The coefficients of variation for pressure in the simulated airway were: new 6.8% and conventional 15.3%. We conclude that the imposed work of the new NCPAP device for the VLBW baby is approximately one‐fourth of that of the conventional device. The airway pressure generated by the VLBW size of the new NCPAP device shows less variability during simulated breathing than that found with the conventional device. The findings support the clinical use of the new NCPAP device in the very low birthweight baby. Pediatr Pulmonol. 1996; 22:188–194.

Nonimmune Hydrops fetalis: Fetal and Neonatal Outcome during 1983–1992

Prognostic factors for survival of 62 fetuses and neonates with nonimmune hydrops fetalis (NIHF) were studied retrospectively. Twenty-eight infants survived ≥28 days which is 45% for all fetuses and newborns diagnosed with NIHF and 61% for liveborns with unresolved NIHF. Univariate analysis identified that mortality was associated with the presence of ≥2 serous cavity effusions and a need for chest compressions at birth. Multivariate logistic regression analysis confirmed that the presence of ≥2 serous cavity effusions was significantly associated with mortality from NIHF <28 days after birth [OR = 48.2 (CI 3.6, 662.9) (p < 0.004)]. We conclude that, compared to published cases from the 1970s and early 1980s, survival of liveborns with NIHF seems improved. The decrease in stillbirths is more notable. The severity of hydrops at birth is the key determinant for survival.

Effects of cochlear ablation on local cerebral glucose utilization in fetal sheep.

Local cerebral glucose utilization was measured by the [14C]-deoxyglucose method in five near-term fetal sheep in whom bilateral ablation of the cochleae had been accomplished aseptically 5 to 8 days earlier. The tympanic membrane and ossicles were removed and all turns of each cochlea were unroofed with destruction carried to the modiolus. Mean local cerebral glucose utilization of 33 of 34 gray matter structures and four of four white matter structures in operated animals were significantly lower (p less than 0.05) than that in unoperated control fetuses. The depression in local cerebral glucose utilization was greatest (p less than 0.002) in brain stem auditory nuclei, in which the mean rate of glucose utilization was approximately 25% of the levels in unoperated fetuses. The pattern of glucose utilization in these structures was clearly altered, with a reversal of the normal distribution in density of the inferior colliculus. Tonotopic bands of high local cerebral glucose utilization frequently seen in autoradiographs of inferior colliculus in unoperated fetuses were not observed in operated fetuses. These results show that the glucose utilization of the brain, and by implication the normal growth and maturation of the brain, depends on an intact auditory system during prenatal life.

Effect of high-intensity sound on local cerebral glucose utilization in fetal sheep

The effects of external noise on fetal sheep cerebral glucose utilization were determined with the [14C]deoxyglucose method. Seventeen animals were prepared at 130 days gestation with catheters and electrodes for assessing fetal behavioral state. Five to 7 days later, 7 animals were studied under normal laboratory sound conditions (65-70 dB), 5 animals were exposed to 105-120 dB broadband noise levels produced by two earphones applied to the abdomen of the ewe, and 5 fetuses were stimulated with an electronic artificial larynx (EAL), positioned on the abdomen directly over the fetal head. There were no significant differences between local cerebral glucose utilization in controls and earphone ewes, and no obvious alteration in behavioral states. However, there were marked, significant differences in glucose utilization along the central auditory pathway during EAL stimulation. These autoradiographs revealed isofrequency-like bands in medial geniculate body and irregular darkening of cortex of the temporal lobe. Total time spent in clearly defined high and low voltage electrocortical activity did not change during EAL stimulation.

Respiratory muscle activities after birth in asphyxiated preterm lambs

Laryngeal and pump muscle activities are important in the establishment and maintenance of functional residual capacity (FRC) after birth. The aim of this study was to determine the expiratory mechanisms by which laryngeal and diaphragmatic activities achieve the increments in FRC postnatally. Wire electrodes were placed in: the laryngeal abductor, a major laryngeal adductor, the inferior pharyngeal constrictor and the diaphragm of six fetal sheep. The lambs were delivered prematurely by cesarean section and a face mask with a pneumotachograph applied. A grunting respiratory pattern was characterized by severe expiratory airflow retardation, associated with laryngeal adductor activity. In grunting breaths, minimal volume loss at end‐expiration and incremental increases in FRC occurred when the onset of diaphragmatic activity preceded the onset of laryngeal muscle activities associated with laryngeal opening. Thus the timing order of laryngeal and diaphragmatic muscle activities near end‐expiration is a determinant of increments in FRC.

Plasma 6-keto prostaglandin F1α and thromboxane B2 in sick preterm neonates

To determined if vascular abnormalities in preterm neonates might be related to vasoactive prostaglandins, stable prostacyclin(6-KPGF1α)andthromboxaneA2(TxB2) metabolites in arterial blood were measured at < 6 hours after birth and at 24, 48, and 72 hours using a radioimmunoassay. Neonates of <32 weeks gestation (N=26) were diagnosed as having either the idiopathic respiratory distress syndrome (IRDS, N=15) or pulmonary edema (PE, N=11), and were also grouped according to the presence or absence of intracranial hemorrhage (ICH, N=11) or patent ductus arteriosus (PDA, N=10). Initial plasma 6-KPGFla was greater in neonates with ICH (0.23 ± 0.04 ng/ml, mean + SE) than without ICH (0.11 ± 0.04, p < 0.05). Neonates with both ICH and IRDS (N=8)had significantly elevated TxB2 at all sampling times compared to neonates with IRDS and no ICH (N=7). Both TxB2 and 6-KPGFla increased with time in those with major ICH. Among neonates without ICH, 7 with IRDS had higher initial 6-KPGFla (0.19 + 0.07 ng/ml) and lower TxB2(0.15 + 0.04 ng/ml) than 8 with PE (0.04 +0.01 and 0.37 + 0.09 ng/ml, respectively).The initial 6-KPGFlα (0.024 + 0.003 ng/ml), measured in neonates with PE and without PDA or ICH (N=6), was significantly less than the corresponding value in the other neonates (0.201 + 0.036 ng/ml) (N=20).

Local cerebral blood flow is increased in rapid-eye-movement sleep in fetal sheep

Behavioral state-induced changes in fetal cerebral blood flow were continuously monitored with a simple thermal dilution method. Thermojunctions were heated 1.5 degrees C above reference thermojunctions implanted contralaterally in various cerebral cortical and subcortical structures of four near-term fetal sheep. Temperature difference in rapid-eye-movement sleep was lower than in non-rapid-eye-movement sleep (p = 0.014), reflecting convective heat loss from increased blood flow. Temperature difference also varied significantly with the locus of placement in the brain (p = 0.003), reflecting, in part, regional differences in cerebral blood flow. The thermocouple method gives qualitative, continuous information on local cerebral blood flow that could be useful in monitoring the vascular response to changing functional activity during prenatal brain development.

Local cerebral glucose utilization in fetal sheep exposed to noise

Rate of local cerebral glucose utilization in fetal sheep was measured in conditions of normal laboratory ambient sound (65 to 70 dB sound pressure levels) and broadband noise (105 and 120 dB sound pressure levels) delivered by two earphones situated on the abdominal surface of the ewe. Broadband noise had neither a visible effect on the ewe nor specific effects on the fetal arterial pH, PaO2, PaCO2, and plasma glucose concentration. However, glucose utilization of many cerebral structures was elevated in noise-exposed fetuses.

Local cerebral glucose utilization in normoxemic and hypoxemic newborn lambs

To determine if hypoxemia altered local cerebral glucose utilization (LCGU) in newborn lambs, and where these alterations occurred, we measured LCGU using the 2-[14C]deoxyglucose [( 14C]DG) autoradiographic technique in lambs made hypoxemic by gradual reduction in inspired oxygen concentration. In 5 normoxemic control lambs, aged 3 days. LCGU of the cerebral cortex and white matter was higher than published values of LCGU in similar structures in near term normal fetuses and 2-4 times higher than reported values in normoxemic puppies. LCGU was highest in vestibular nuclei and auditory structures, followed by cerebellar nuclei, cerebral subcortical structures, and white matter. In 6 hypoxemic newborn lambs (paO2 14-18 torr) consistent increases in LCGU were noted only in the corona radiata compared to the values obtained in the normoxemic control lambs (36.5 +/- 8.1 vs. 23.9 +/- 1.7 mumol/100 per min, mean +/- S.D., P less than 0.02). This increase in LCGU in white matter was clearly noted in autoradiographs in which thin dark central regions within white matter often reached high into the gyri. In the hypoxic group. LCGU of the corona radiata superseded the value in many gray matter structures. In addition, patchy increases of [14C]DG utilization were present in the cerebral cortex of two hypoxemic lambs. Acute hypoxemia increases glucose utilization of the corona radiata to values equivalent to many gray matter structures, and leads to heterogeneous glucose metabolism in the cerebral cortex, but does not alter LCGU in other gray matter structures of newborn sheep.