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Biomedical subjects

T R Gunn

Publications and source records attributed to T R Gunn.

At least 19 recordsLinked to original sources
PubMed1995

Perinatal thermogenesis.

The rapid initiation of thermogenesis is crucial for the survival of newborn infants. At birth the fetus must adapt to cooling, increased oxygenation and separation from the placenta. An experimental approach in the chronically instrumental fetal sheep of 'simulated birth in utero' allowed the evaluation of each of these stimuli sequentially. Cooling stimulated shivering, cardiovascular and endocrine responses but not nonshivering thermogenesis (NST). Ventilation of the cooled fetus with oxygen caused only modest NST which was not altered by an infusion of triiodothyronine. Occluding the umbilical cord was followed by a rapid substantial rise in NST which was maintained until the placental circulation was re-established. Thus the placenta is secreting factors into the fetal circulation which inhibit the ability of the brown adipose tissue to respond to either hormonal or neural stimuli. Placental prostaglandin E2 and probably adenosine are tonic inhibitors of thermogenesis in utero. Effective thermogenesis after birth requires the combination of separation from the placental inhibitors of lipolysis, increased oxygenation from breathing and the stimulation of cutaneous cold receptors.

Adenosine↗
PubMed1995

Nasal route for infant resuscitation by mothers.

In infants under 6 months of age air normally enters the trachea by the nose because the tongue fills the oral cavity, and the oral route is open only when the infant is making muscular efforts such as crying or gasping. The present recommendation for infant resuscitation is for the resuscitator's mouth to cover the mouth and nose of the baby. We set out to test whether this recommendation is feasible. We measured the dimensions of the faces of 28 babies aged between 2 and 4 months (the age when resuscitation is most often needed) and of the mouths of 25 of their mothers. Only 2 mothers would have been able to cover with their mouths the nose and closed mouth of 2 babies (not their own). The mannequins often used to teach adults to resuscitate infants are misleading because they present a wide open mouth, thus implying that that is the preferred route. We recommend that the nasal route of air entry be taught to parents for resuscitation of babies who have stopped breathing.

Cardiopulmonary Resuscitation↗
PubMed1995

Family with partial monosomy 10p and trisomy 10p.

We report on a family with an abnormality of 10p. The propositus has monosomy for the distal region of 10p and severe psychomotor delay, growth failure, congenital heart defect, multicystic kidney, grade V vesicoureteric reflux, and neurosensory hearing loss. The mother and the elder brother of the propositus carry a balanced reciprocal translocation (5q;10p)(q35.3;p12.3). A retarded and epileptic maternal aunt was found to have dup(10p). Study of the family history led to the successful obstetric management of a subsequent twin pregnancy in which an affected fetus with dup(10p) was identified and selectively terminated, while the other normal twin was delivered at term without problems.

Abnormalities, Multiple↗
PubMed1995

Antenatal diagnosis of urinary tract abnormalities by ultrasonography after 28 weeks' gestation: incidence and outcome.

OBJECTIVE: The objective was to establish the likelihood that antenatal upper urinary tract dilatation identified after 28 weeks of gestation will progress to significant postnatal uropathy. STUDY DESIGN: In 5 years, 3856 fetuses had ultrasonography after 28 weeks of gestation when the mothers were first seen in advanced pregnancy for delivery appointments or for other obstetric indications. Fetuses with urinary tract anomalies had ultrasonographic surveillance after 6 days and 6 weeks of life with further evaluation as necessary. RESULTS: Renal tract anomalies were identified in 313 fetuses, and 55 infants had significant renal tract abnormalities. There were 7 deaths; 2 infants were anephric and 5 with hydronephrosis had lethal congenital abnormalities. Dilatation of the upper urinary tract was identified in 7.7% of the fetuses (298/3856) but was transient in 216 of them (72%). Follow-up of children with transient renal pelvis dilatation found only one with a history of urinary tract infection. Obstruction occurred in 23 infants (6.0/1000) and 16 required surgical correction. Vesicoureteric reflux was identified in 14 infants (3.6/1000) and resolved by age 2 years in 64%. Unilateral multicystic renal dysplasia occurred in 8 and posterior urethral valves occurred in 3 infants. CONCLUSION: Antenatal ultrasonography after 28 weeks' gestation identified significant renal tract abnormalities with a frequency of 14.3 per 1000 births, permitting early treatment of the asymptomatic newborn and reducing later renal damage.

Female↗
PubMed1995

A potential role for adenosine in the inhibition of nonshivering thermogenesis in the fetal sheep.

Adenosine is released by the placenta into the fetal circulation and has potent antilipolytic properties in vitro. Nonshivering thermogenesis cannot be demonstrated by cooling fetal sheep in utero but can be induced by supplemental oxygenation and umbilical cord occlusion; this suggests the presence of inhibitor(s) of placental origin. To test whether circulating adenosine could be such an inhibitor, a series of experiments was carried out in nine fetal sheep at 136-145 d gestation. Birth was simulated in utero by sequentially cooling the fetus 2.49 +/- 0.23 degrees C with no change in the low levels of plasma FFA or glycerol; ventilating with O2 via an exteriorized tracheostomy tube and umbilical cord occlusion. Thermogenic indices rose markedly, and plasma FFA and glycerol concentrations peaked at 725 +/- 88 microEq/L (p < 0.01) and 771 +/- 154 mumol/L, (p < 0.001), respectively, O2 consumption rose to 20 +/- 2 mL/min/kg, and temperature increased 1.99 +/- 0.35 degrees C. The long-acting adenosine analog N6-(L-2-phenylisopropyl)-adenosine (PIA) was then infused (90 micrograms/kg bolus, then 300 micrograms/kg/h for 30 min); plasma FFA and glycerol decreased to 265 +/- 56 microEq/L (p < 0.003) and 477 +/- 102 mumol/L (p < 0.04), respectively; O2 consumption fell rapidly to 4.5 +/- 0.3 mL/min/kg (p < 0.01); temperature decreased 1.89 +/- 0.39 degrees C (p < 0.001); and fetal arterial BP decreased to 38 +/- 5 mm Hg (p < 0.004) in 30 min. A stepped dose-response study was performed in three fetal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1992

Cot death.

Explore the source record for details and available documents.

Humans↗
PubMed1992

Modulation of growth hormone secretion by thermogenically derived free fatty acids in the perinatal lamb.

To evaluate the hypothesis that the rapid fall in circulating GH concentrations at birth is secondary to the initiation of nonshivering thermogenesis and the consequent rise in FFA levels, a series of experiments was performed in late-gestation fetal sheep. By sequentially cooling the fetus by means of a coil placed around the fetal thorax, ventilating with oxygen via an exteriorized tracheostomy tube, and separating the fetus from the placenta by occluding the umbilical cord, nonshivering thermogenesis could be induced in utero. In the first protocol (n = 6) cooling alone had no effect on fetal plasma FFA levels, oxygenation elevated FFAs slightly from 64 +/- 7 mu Eq/liter to 183 +/- 29 mu Eq/liter, and cord occlusion caused a further marked rise (P less than 0.005) to 635 +/- 69 mu Eq/liter. Neither cooling nor ventilation affected fetal plasma GH concentrations which fell (P less than 0.001) from 160 +/- 17 ng/ml to 65 +/- 13 ng/ml upon cord occlusion. When the cord occluder was removed FFA levels fell (P less than 0.001) and GH concentrations rose (P less than 0.001) once more, and when the cord was again occluded FFA levels rose (P less than 0.001) and GH concentrations fell (P less than 0.001). In a second protocol nine fetuses were cooled, ventilated, and the umbilical cord occluded. Once more, plasma FFA levels rose (P less than 0.001) and GH concentrations fell (P less than 0.001); when thermogenesis was inhibited by the infusion of the adenosine agonist N6-(L-2-phenyl isopropyl)-adenosine, FFA levels fell from 725 +/- 88 mu Eq/liter to 265 +/- 56 mu Eq/liter and GH concentrations rose from 54 +/- 13 ng/ml to 323 +/- 73 ng/ml. In two further protocols the possibility that PIA was acting directly on GH secretion was excluded in six fetuses with low plasma FFA levels and in three fetuses with elevated plasma FFA levels secondary to a fatty acid emulsion infusion. These studies provide direct evidence that the pattern of change in plasma GH concentrations at birth in the sheep is determined in part by the rise in plasma FFAs of thermogenic origin.

Animals↗
PubMed1991

Breast feeding preterm infants.

Breast feeding is the optimal way to feed infants but may be difficult in preterm infants. In a study of 43 mothers with 49 preterm infants admitted to a neonatal unit during a 10 week period-84% (36 of 43) wished to breast feed and 92% (33 of 36) of these mothers left hospital breast feeding. Their infants were from 30 to 36.5 weeks gestation, weighing a mean 2590 (SD 530) g and were in hospital 16 (11) days. Only three mothers who wished to breast feed failed to do so. The 10 bottle fed infants were smaller, younger and remained longer in hospital. The majority of mothers (88%) who were discharged breast feeding were still successfully breast feeding their preterm infants three months later. This is in marked contrast to a previous study of mothers, of full term infants, where there was a marked decrease in breast feeding by three months. The mothercraft teaching described is an effective method of providing preterm infants and their mothers with the advantages of breast feeding.

Breast Feeding↗
PubMed1991

Factors influencing the initiation of nonshivering thermogenesis.

The aim of this study was to observe the sequential effects of oxygenation, umbilical cord occlusion, and finally cooling on circulating catecholamines and nonshivering thermogenesis in fetal sheep. We studied five fetal sheep at 132 +/- 3 days' gestation. The fetuses were first ventilated with oxygen; PaO2 levels were maintained above 150 mm Hg, and by 60 minutes there was a significant rise in both plasma glycerol and free fatty acid levels. After umbilical cord occlusion there was a peak in plasma catecholamine and triiodothyronine levels but no significant increase in lipolysis. Cooling, by circulating cold water through a coil around the fetus, induced maximum lipolysis and temperature difference between brown fat and body core, when plasma catecholamine levels were falling. During this study the changes in plasma catecholamine levels did not correlate with the onset of nonshivering thermogenesis. Cutaneous cooling, which causes neurally mediated sympathetic stimulation of brown adipose tissue, is the major signal for the initiation of nonshivering thermogenesis and thus neonatal adaptation.

Animals↗
PubMed1991

Reversible umbilical cord occlusion: effects on thermogenesis in utero.

The initiation of thermogenesis at birth is an important adaptation for survival. We examined the sequential effects of cooling, increased oxygenation, and repeated episodes of umbilical cord occlusion on nonshivering thermogenesis in six fetal sheep at 139 to 145 d of gestation. The fetal sheep were cooled by circulating cold water through a coil placed around the trunk for 4 h. The fetal core temperature fell 2.47 +/- 0.24 degrees C in the first 60 min of cooling with minimal changes in plasma FFA and glycerol levels. After fetal arterial O2 tension was increased above 6.65 kPa by ventilation, fetal temperature and thermogenic indices rose significantly in 60 min. After occlusion of the umbilical cord by a reversible occluder cuff, plasma FFA levels rapidly increased to 635 +/- 69 muEq/L (p less than 0.005) by 30 min, fetal temperature increased a further 0.96 +/- 0.20 degrees C (p less than 0.001) and fetal O2 consumption peaked at 25.3 +/- 4.9 mL.min-1.kg-1. Release of cord occlusion caused a rapid fall in FFA to 149 +/- 23 muEq/L (p less than 0.005) and a fall in fetal core temperature of 0.90 +/- 0.13 degrees C (p less than 0.001) in 30 min. After irreversibly snaring the umbilical cord, the plasma FFA rose to 611 +/- 83 muEq/L (p less than 0.005) and the fetal temperature rose 0.78 +/- 0.09 degrees C (p less than 0.02). The effects on thermogenesis of interrupting and reestablishing placental flow are rapid and reversible and suggest the presence of placental inhibitors of brown adipose tissue thermogenesis.

Adipose Tissue, Brown↗
PubMed1989

Prenatal cranial haemorrhages in 47 Pacific Islander infants: is traditional massage the cause?

Intracranial haemorrhage is usually a very rare occurrence in the fetus before the onset of labour but we have identified major, mostly subdural, prenatal intracranial haemorrhages in 47 infants of immigrant Pacific Islander parentage. Forty-four infants have been stillborn and the numbers from 1983 to 1986 were sufficient to account for the stillbirth rate for Pacific Islanders in Auckland being approximately 60% higher than rates for Europeans or Maoris. Two of three liveborn infants survived with neurological sequelae. Similar haemorrhages may be the cause of a congenital hydrocephalus in Pacific Islanders. A bleeding disorder can be excluded in most cases, as can trauma from accidents or assaults. Trauma during attempts at cephalic version of breech presentations by traditional methods could explain why 53% of deliveries were breech and other pathological and clinical features. Advice at antenatal clinics about possible dangers of traditional massage has coincided with a reduction in the incidence of haemorrhages since 1986.

Adult↗
PubMed1989

Quality of outcome and cost in an obstetric and neonatal service.

A review has been made of the outcome and efficiency of the obstetric and neonatal service, St Helen's Hospital, Auckland. In the last seven years there has been a 33% fall in perinatal mortality rates to 5.88 per 1000 births in 1987. The average perinatal death rate for Maori infants was low, 4.81 per 1000 compared to 7.43 per 1000 for Europeans over this period. There has been a 38% increase in births to 3597 a year while the total hospital staffing has only risen 9%. Thus the ratio of births to staff has increased by 26.6% to 15.6. The cost per infant delivered in constant dollars has fallen 18.7% in the same period to $2432. The postnatal bed occupancy was 101% in 1987 and the average day stay fell to 5.7 days. An extra 61 full time staff would be needed to reduce the workload to that of 1981 and the staff is now unable to give the family focused holistic care that is needed.

Costs and Cost Analysis↗
PubMed1989

The safety and immunogenicity of a recombinant hepatitis B vaccine in neonates.

A study to evaluate the safety and immunogenicity of a yeast derived recombinant DNA hepatitis B vaccine (Engerix-B) was conducted in healthy newborn infants born to low risk European mothers negative for hepatitis B surface antigen (HBsAg). The vaccination schedule using 20 micrograms doses was administered intramuscularly at 0, 1 and 6 months. The seroconversion rate was 99% (90 of 91 infants). The geometric mean titer of antibody to hepatitis B was 1259 mIU/mL one month after the third dose of vaccine. Possible side effects reported by the mothers were minor and uncommon. This vaccine is highly immunogenic and safe for use in infants.

Drug Evaluation↗
PubMed1989

The endocrine control of the onset of thermogenesis at birth.

The experimental studies in the fetal sheep demonstrate that the central hypothalamic mechanisms for responding to a cold stress have differentiated well before birth. There are several major determinants of the initiation of maximal thermogenesis at birth. These are cutaneous cooling, oxygenation and separation from the placenta. Firstly the stimulation of cutaneous cold receptors regulates sympathetic nervous system activity, primarily local noradrenaline release from sympathetic nerve termini to the brown adipocyte adrenoreceptors. Circulating catecholamines, the euthyroid state and other hormones also play a role. Secondly an increase in oxygen delivery to brown adipose tissue through increased oxygen content and increased blood flow is required. Finally, our observations suggest that separation from the placenta is necessary for maximal nonshivering thermogenesis. The effects on thermogenesis of interrupting and reestablishing placental flow are rapid and reversible. Umbilical cord occlusion is the signal for a rapid increase in thermogenesis, while the release of cord occlusion is followed by an equally rapid fall in thermogenesis. This strongly suggests the presence of a placental inhibitor of brown adipose tissue thermogenesis. The problem of the regulation of growth and recruitment of brown adipose tissue in the fetus despite the lack of thermal stress in utero may be resolved by this evidence for an inhibitory factor of thermogenesis produced by the placenta. The withdrawal of the inhibitor at birth by separation from the placenta will allow the rapid initiation of thermogenesis in response to sympathetic nervous system stimulation of the brown adipose tissue.

Animals↗
PubMed1989

Upper airway measurements during inspiration and expiration in infants.

Accurate measurements of the upper airway of the infant are important but are difficult to obtain reliably because of the normal variation that occurs during respiration. X-ray films of the lateral upper airway were obtained during inspiration and expiration in healthy infants, by using as a timing device a respiration monitor which was wired to the x-ray machine and was attached to the abdominal wall of the infant. Cephalometric measurements were made of 44 "normal" full-term neonates and 29 infants at 6 weeks of age. Despite significant differences in head circumference between the sexes, only the nasion to sella length was significantly longer in the boys (P less than .01). The lateral upper airway measurements were independent of weight, head circumference, and sex in the neonates and infants at 6 weeks of age but were significantly smaller during inspiration than expiration (P less than .01). The measurements progressively increased from the middle to the posterior airway space at both ages. The middle airway space behind the caudal end of the hard palate was smaller during inspiration at 6 weeks of age compared to the neonate (P less than .01). During expiration, the posterior airway space was larger at 6 weeks compared to the neonate (P less than .01). The method described in this report enables reliable roentgenographic measurements to be made of the upper airway of the infant; normal values for the changes during inspiration and expiration are provided. This may assist in the evaluation of infants with suspected upper airway obstruction.

Cephalometry↗