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Biomedical subjects

D Henderson-Smart

Publications and source records attributed to D Henderson-Smart.

33 records · Page 2Linked to original sources
PubMed1994

Carbon dioxide concentrations in the environment of sleeping infants.

In 22 infants continuous measurements were made of the concentration of carbon dioxide (CO2) in inspired air during sleep. Evidence was found of CO2 enrichment of inspired air in certain environmental conditions. The levels achieved were not sufficiently high to acutely endanger an infant. Carbon dioxide concentrations as high as 2-3% were observed in the prone position when the infant's head was under a blanket and when the lower face was obscured by bedding. Sleeping prone on a sheepskin also resulted in an increased concentration of CO2 but to a lesser extent than being under a blanket. In awake infants the presence of a pacifier also promoted an excess of CO2 in the inspired air, both in the prone and supine positions. The physiological and clinical implications of these findings, in relation to the Sudden Infant Death Syndrome (SIDS), are unknown and warrant investigation.

Air↗
PubMed1994

Subclinical persisting pulmonary hypertension in chronic neonatal lung disease.

The development of pulmonary hypertension is one of the adverse factors in the outcome of infants with chronic neonatal lung disese (CNLD). The purpose of this cross sectional study was to evaluate the prevalence and degree of pulmonary hypertension in a cohort of survivors of CNLD stable in air. Pulmonary artery pressure was assessed using its inverse correlation with the ratio of time to peak velocity and right ventricular ejection time (TPV:RVET) as measured from Doppler velocity time signals in the main pulmonary artery. A normal ratio is > or = 0.35, a possibly low ratio lies between 0.31 and 0.35, and a definitely low ratio is < 0.31. The subjects were divided into three groups. Group A comprised 58 infants with oxygen dependence and an abnormal chest radiograph at 28 days of age; group B comprised 18 infants with oxygen dependence and a normal chest radiograph at 28 days of age; and group C (controls) comprised 21 siblings without oxygen dependence by 10 days and a normal chest radiograph. There were significant differences in mean (SD) TPV:RVET ratio between group A 0.346 (0.045), group B 0.335 (0.057), and groups A + B 0.344 (0.048) when compared with group C controls 0.385 (0.034). The prevalence of a definitely low TPV:RVET ratio suggesting a raised pulmonary artery pressure was 19% in group A, 39% in group B, 24% in groups A + B, and none in group C. There were no clinical signs of pulmonary hypertension in any patient studied. Stepwise multiple linear regression failed to find significant associations with antenatal or neonatal putative risk factors. Additionally, there were no associations with childhood respiratory morbidity. These data suggest a high prevalence of subclinical pulmonary hypertension in CNLD patients. It is speculated that occult hypoxaemia may be occurring in this group of infants.

Age Factors↗
PubMed1993

Short-term outcome of mechanically ventilated infants weighing more than 2499 g at birth: a population based study.

Very little data exist describing the neonatal outcome of infants of birthweight 2500 g or more who require mechanical ventilation. Our aim was to collect population-based data on such infants in New South Wales (NSW), and to monitor their neonatal morbidity, mortality to 1 year of age and the associated risk factors. The study group (NICUS infants) comprised all 341 infants weighing > 2499 g who were admitted to the seven neonatal intensive care units in New South Wales and mechanically ventilated for 4 h or more between 1 January and 31 December, 1987. Two groups of infants emerged: those who were preterm and mostly had hyaline membrane disease, and term and post-term infants for whom the most common problem was 'perinatal asphyxia'. The most important factors associated with dying were a birthweight of over 3499 g (OR = 2.6; CI 1.03-6.6) and a 1 min Apgar score < 4 (OR = 4.8; CI 1.4-16.9). Study group mothers were significantly more likely than all NSW mothers to have had a spontaneous abortion in the previous pregnancy (P < 0.01), a pre-existing medical condition or an obstetric complication in this pregnancy, or a Caesarean section for this delivery (P < 0.001). This is the first population-based study of high-risk neonates without congenital anomalies to clearly document the worsening prognosis associated with a birthweight over 3499 g. Further research should be directed towards identifying prenatal and perinatal factors which might minimize the morbidity and mortality in this group of babies.

Apgar Score↗
PubMed1991

Early blood pressure control improves pregnancy outcome in primigravid women with mild hypertension.

OBJECTIVE AND DESIGN: The aim of this study was to evaluate treatment of mild to moderate hypertension (less than 170/110 mmHg) in pregnancy in a prospective, randomised, double-blind trial. SETTING AND PATIENTS: Pregnancy outcome was studied for 52 primigravid women, managed in hospital from early in the third trimester. INTERVENTIONS: Patients were randomly allocated either to placebo or to active treatment (clonidine plus hydralazine). MAIN OUTCOME MEASURES AND RESULTS: Maternal deterioration dictated withdrawal from trial therapy for eight patients receiving placebo, but for only one receiving active treatment. Maternal proteinuria occurred only in the placebo group. Intention-to-treat analysis showed a significant increase in premature delivery for complications in the placebo group (P less than 0.05), despite active blood pressure treatment for those withdrawn from the group because of severe hypertension (170/110 mmHg or higher). Neonatal respiratory distress requiring intensive care occurred only in babies born to women in the placebo group. There were no perinatal deaths and no adverse effects of treatment in the neonates. CONCLUSIONS: The study indicates that early control of mild hypertension in pregnancy can prevent progression to emergency premature delivery.

Adult↗
PubMed1991

Absent or reversed end diastolic flow velocity in the umbilical artery and necrotising enterocolitis.

Absent or reversed end diastolic flow (AREDF) velocities in the umbilical artery were identified in 25 high risk pregnancies. In six pregnancies the fetus was abnormal and all but one of these ended in perinatal death. Of the 19 morphologically normal fetuses, three died in utero and there were four neonatal or infant deaths. The mortality rate was 48% for all pregnancies and 37% for those with morphologically normal fetuses. There was a highly significant increased risk for the development of necrotising enterocolitis in these morphologically normal fetuses with AREDF (53%) compared with controls (6%) who did have umbilical artery end diastolic flow velocities in fetal life. There were no significant differences between the matched pairs for parameters of neonatal outcome chosen to reflect neonatal morbidity. These findings demonstrate the close association between AREDF and necrotising enterocolitis that appears to be independent of other variables such as degree of growth retardation, prematurity, and perinatal asphyxia.

Blood Flow Velocity↗
PubMed1991

Ventilatory response of the sleeping newborn to CO2 during normoxic rebreathing.

The ventilatory response of the newborn to CO2 was studied using a rebreathing method that minimized changes in arterial PO2 during the test. The aim was to study the variability of the ventilatory response to CO2 and take this into account to assess the relative magnitude of the response to CO2 during rapid-eye-movement (REM) sleep and quiet sleep (QS). Five full-term babies aged 4-6 days were given 5% CO2 in air to rebreathe for 1.5-3 min. O2 was added to the rebreathing circuit to maintain arterial O2 saturation and transcutaneous PO2 (Ptco2) at prerebreathing levels. Tests were repeated four to five times in REM sleep and QS. Mean Ptco2 levels varied between individuals but were similar during REM sleep and QS tests for each subject. The mean coefficient of variability of the ventilatory response was 35% (range 15-77%) during QS and 120% (range 32-220%) during REM sleep. PtcO2 fluctuations during tests [6.0 +/- 3.0 (SD) Torr, range 1-13 Torr] were not correlated with ventilatory response. Overall the ventilatory response was significantly lower in REM sleep than in QS (12.2 +/- 3.0 vs. 38.7 +/- 3.0 ml.min-1.Torr-1.kg-1, P less than 0.001; 2-way analysis of variance) due to a small (nonsignificant) fall in the tidal volume response and a significant fall in breathing rate. In 12 REM sleep tests there was no significant ventilatory response; mean inspiratory flow increased significantly during 8 of these 12 tests. We conclude that there is a significant decrease in the ventilatory response of the newborn to CO2 rebreathing during REM sleep compared with QS.

Carbon Dioxide↗
PubMed1985

Hypertension in pregnancy. A study of 142 women presenting before 32 weeks' gestation.

This study evaluates the outcome of 142 consecutive pregnancies in women in whom hypertension was diagnosed before 32 weeks' gestation and who were managed by a team comprising obstetricians, physicians and perinatologists. Arterial pressure was lowered to 140/90 mmHg or lower with clonidine hydrochloride or methyldopa therapy to which, in most cases, a vasodilator, hydralazine or diazoxide was added. The outcome of patients who were managed by the multidisciplinary team from the clinical onset of their disease was compared to the outcome of those who were transferred after the onset of hypertension from other centres. A greater perinatal mortality rate was found among the infants of patients with pre-eclampsia and patients with essential hypertension in pregnancy when the mothers were referred late for management. Reasons for the difference in pregnancy outcome are not clear. Possible explanations are discussed which emphasize the need for further study to establish optimal management of this common complication of pregnancy.

Antihypertensive Agents↗
PubMed1980

Fetal breathing.

Explore the source record for details and available documents.

Animals↗
PubMedDate not supplied

Autonomic reflexes in preterm infants.

Some autonomic nervous reflexes often tested in adult medicine have been studied in 21 preterm infants (25-37 gestational weeks). The aim was to develop such tests for preterm infants and see if there were any differences in babies with recurrent apnea and bradycardia and babies who had been exposed to sympathicolytic drugs before birth. To test sympathetic nervous activity the peripheral vascular resistance was measured before and during 45 degrees of head-up tilting. To test parasympathetic nervous activity the degree of bradycardia was measured in response to cold face test (application of an ice-cube on the fore-head) and laryngeal stimulation with saline. Finally the heart rate changes after a sudden noise (85 dB) were studied as an indicator of both sympathetic and vagal activity. The peripheral resistance was found to be relatively low in these preterm infants, particularly in some infants tested at the postnatal age of about two months. Heart rate and mean blood pressure did not change during tilting, while the peripheral resistance increased significantly mainly due to lowered limb blood flow. The median decrease of the heart rate during the cold face test was 20.0% and during laryngeal receptor stimulation 23.7%. The sudden noise usually caused a biphasic heart rate response. An autonomic nervous reflex score was calculated and found to be negative (parasympathetic) in infants with recurrent prolonged apnea and bradycardia and positive in infants with clinical signs of increased sympathetic nervous activity.

Apnea↗