A. K. W. Wood

Heating of guinea-pig fetal brain during exposure to pulsed ultrasound

Ultrasound-induced temperature elevations in fresh and formalin-fixed fetal guinea-pig brains were measured during in vitro insonation, with a stationary beam in a tank containing water at 38 degrees C. The pulsing regimen used 6.25 microseconds pulses, repeated at a frequency of 4 kHz emitted from a focussed transducer operating with a centre frequency of 3.2 MHz. The greatest temperature rise in brain tissue occurred close to bone and correlated with both gestational age and progression in bone development. After a 2 min insonation with a spatial peak temporal average intensity (ISPTA) of 2.9 W/cm2, a mean temperature elevation of 5.2 degrees C was recorded in fetuses of 60 days gestation (dg). The same exposure produced an increase of 2.6 degrees C in the centre of whole brains of 60 dg fetuses when the bony cranium was removed. As most of the heating occurs within 40 s, these findings have implications for the safety of pulsed Doppler examinations where dwell-time may be an important factor.

In vivo heating of the guinea-pig fetal brain by pulsed ultrasound and estimates of thermal index.

Temperature was measured in the brain in live near-term fetal guinea pigs (62-66 d gestational age), during in utero exposure to a fixed beam of pulsed ultrasound at intensity ISPTA 2.82 W/cm2. Mean temperature increases of 4.3 degrees C close to parietal bone and 1.1 degrees C in the mid-brain were recorded after 2-min exposures. These values were lower (12%) than those obtained for ultrasound-induced heating near the bone in dead fetuses insonated in utero. A significant cooling effect of vascular perfusion was observed only when guinea pig fetuses reached late gestation, near term, when the cerebral vessels were well developed. The estimated value for the thermal index (TIB), as used in AIUM/NEMA output display standard, underestimated the measured temperature increase at the bone-brain interface. The ratio of measured temperature to the TIB is 1.3. A modification of the cranial thermal index provided a more reasonable, conservative, estimate of the temperature increase at a biologically significant point of interest at the brain-bone interface.

Ultrasound-induced temperature increase in guinea-pig fetal brain in utero: third-trimester gestation.

Temperature increase was measured at various depths in the brain of living fetal guinea pigs during in utero exposure to unscanned pulsed ultrasound at ISPTA 2.8 W/cm2. Mean temperature increases of 4.9 degrees C close to parietal bone and 1.2 degrees C in the midbrain were recorded after 2-min exposures. When exposures were repeated on the same sites in each fetus after death, the corresponding mean temperature increases were 4.9 degrees C and 1.3 degrees C, respectively. Cerebral blood perfusion had little cooling effect on ultrasound-induced heating in the guinea pig fetus of 57-61 days gestational age.

PHYSIOLOGICAL STUDIES OF GASTRO‐OESOPHAGEAL REFLUX AND AIRWAY PROTECTIVE RESPONSES IN THE YOUNG ANIMAL AND HUMAN INFANT

1. The mechanisms that underlie the Sudden Infant Death Syndrome (SIDS) must explain its two unique features; age at death and death during apparent sleep.

Airway protection following simulated gastro-oesophageal reflux in sedated and sleeping neonatal piglets during active sleep.

1. In infants, promethazine has been implicated in the pathogenesis of sleep apnoea, apparent life threatening events (ALTE) and the Sudden Infant Death syndrome (SIDS). The aim of the present study was to investigate, in a neonatal animal, the effects of a commonly used promethazine‐containing medication on airway protective mechanisms and cardiorespiratory reflexes following simulated gastro‐oesophageal reflux (GER) to different levels in the oesophagus and pharynx.

SEDATION WITH PROMETHAZINE PROFOUNDLY AFFECTS SPONTANEOUS AIRWAY PROTECTION IN SLEEPING NEONATAL PIGLETS

1. Phenothiazine use in infants has been implicated in apparent life‐threatening events, sleep apnoea and Sudden Infant Death Syndrome.

SONOGRAPHIC OBSERVATIONS OF THE GASTRODUODENAL JUNCTION IN NEONATAL PIGLETS

Knowledge of the function of the gastroduodenal junction is important, as changes in its motility are associated with gastrointestinal disorders. Sonographic observations were made of the stomach and duodenum of 19 neonatal piglets, 2-6 d of age. Contractions of the stomach and duodenum were identified clearly; the overall rate of gastric contractions was about 4 min-1. The percentage of contractions in which there was a closure of the terminal pyloric antrum and pyloric canal varied, being 57.2% +/- 4.6% in the first postprandial hour and 43.1% +/- 3.0% in the third. Antegrade flow of digesta principally occurred preceding a closure of the pyloric antrum and canal. During contractions of the pyloric antrum, the torus pyloricus moved caudally to fill the lumen of the pyloric canal. Our sonographic method provided a noninvasive technique for studying the form and function of gastroduodenal motility in the neonate, suitable for investigating factors that alter gastric emptying.

Effects of promethazine on porcine gastroduodenal function : A sonographic study

This sonographic study was aimed at examining the effect of sedation with promethazine (1.5 mg x kg(-1)), on gastroduodenal function in neonatal piglets. On 3 consecutive days, observations of gastroduodenal motility during the first 3 postprandial h were made in 13 animals (3 to 5 days old; 7 sleeping naturally and 6 sedated 2 h prior to feeding). Promethazine significantly reduced both the closures per min of the terminal part of the pyloric antrum and pyloric canal and the percentage of gastric contractions that were followed by closure of the terminal pyloric antrum and canal. Such actions of promethazine on motility of the gastroduodenal junction could lead to a delay in gastric emptying of ingesta with a consequent increased risk of reflux of gastric contents into the esophagus. Because gastroesophageal reflux has been associated with the pathogenesis of sudden infant death syndrome (SIDS), care should be taken if promethazine is to be used as a sedative in neonates.