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Biomedical subjects

J G Aarnoudse

Publications and source records attributed to J G Aarnoudse.

At least 37 records · Page 2Linked to original sources
PubMed1996

Reflectance pulse oximetry at the forehead of newborns: the influence of varying pressure on the probe.

OBJECTIVE: Transmission pulse oximetry (TPO) is not a practical method of intrapartum fetal monitoring of arterial oxygen saturation. Reflectance pulse oximetry (RPO) requires a sensor applied to the skin of the fetal head and may be a useful technique. During labor, various degrees of pressure will be exerted on the RPO sensor. Previous studies have shown that moderate pressure on the sensor can improve the RPO signal. At increasing pressure, however, blood flow underneath the sensor will be occluded. This study examines the influence of pressure applied to the RPO sensor on the signal from the forehead of healthy newborns as a model for the fetal situation. METHODS: After institutional approval, 12 healthy newborns were studied. The RPO probe was placed at the forehead. Pressure on the probe was increased stepwise from 0 to 80 mmHg, and the effect on the ratio between the relative changes of the red and infrared light intensities (R/IR, inversely related to oxygen saturation) and pulse sizes was evaluated. Additionally, the effect of firm pressure (> 150 mmHg) on the probe was evaluated. RESULTS: R/IR values remained virtually unchanged when pressure onto the probe was increased from 0 to 80 mmHg, although the standard deviation slightly decreased. The pulse size increased as pressure on the probe increased. During firm pressure on the probe (> 150 mmHg), plethysmographic signals remained detectable, but R/IR values markedly increased. CONCLUSIONS: In newborns, mild to moderate pressure on the probe has little influence on the RPO signal at the forehead. Even during firm pressure, RPO can be used to obtain pulsatile signals, that presumably derive from tissue underneath the skull, such as the cerebral circulation.

Fetal Monitoring↗
PubMed1995

N-methyladrenaline: age-dependent urinary excretion, perinatal organ content and relation with 'classical' catecholamines.

Using high performance liquid chromatography with electrochemical detection we determined free dopamine, noradrenaline, adrenaline and N-methyladrenaline in: (1) urines from newborns (n = 32), children (n = 45) and adults (n = 19) and (2) adrenals, organ of Zuckerkandl, dorsal roots and perirenal brown adipose tissue from deceased fetuses (n = 2), very premature (n = 6) and term (n = 2) newborns and infants (n = 2). Data from children and adults showed that contributions of adrenaline and N-methyladrenaline to the sum of urinary free catecholamines increase with age. Relative amounts of adrenaline and N-methyladrenaline increased in both adrenal and extra adrenal chromaffin tissues from late gestation up to several months of postnatal life. Increase of adrenal N-methyladrenaline content follows endocrine maturation of the medulla, phenylethanolamine-N-methyltransferase induction and subsequent adrenaline synthesis. Relative amounts of N-methyladrenaline in extra adrenal chromaffin tissue increase in a period that is associated with its regression. Further investigations are necessary to elucidate the function and possible clinical chemical usefulness of N-methyladrenaline.

Adrenal Glands↗
PubMed1995

Reflectance pulse oximetry at the forehead improves by pressure on the probe.

In this study, we investigated the possibility of improving reflectance (back-scatter) pulse oximetry measurements by pressure applied to the probe. Optimal signal detection, with the probe applied to an easily accessible location, is important to prevent erroneous oxygen saturation readouts. At the foreheads of 10 healthy adult volunteers, the effects of pressure applied onto the reflectance pulse oximeter probe were studied. Distances between the LEDs (660 nm and 940 nm) and the three photodiodes in the sensor were 4 mm, 7 mm, and 10 mm. For each detector, recordings were evaluated regarding red-to-infrared (R/IR) ratios and pulse sizes in relation to the stepwise increased pressure applied to the probe. R/IR variability decreased with applied pressures between 60 and 120 mm Hg. These findings are partly attributed to a corresponding increase in red and infrared pulse sizes at the detectors, which results in an improved signal-to-noise ratio. It is thought that pressure onto the oximeter sensor forces venous blood out of the tissues underneath the sensor. Consequently, the disturbing influence of pulsating and non-pulsating venous blood is reduced. Moreover, the increased difference in vessel diameter between diastole and systole and the corresponding difference in light absorption and an increase in flow velocities, causes an increase in pulse size with increasing pressure on the probe. Pressure applied to the probe may be useful in increasing the accuracy of reflectance pulse oximetry.

Adult↗
PubMed1995

Variability of continuously measured arterial pH and blood gas values in the near term fetal lamb.

In fetal sheep, arterial blood gas values show considerable spontaneous fluctuations. The aim of the present study was to obtain quantitative data on fetal blood gas variability. Accurate assessment of the intraindividual variations can hardly be obtained from intermittent blood samples, but requires continuous measurement. For this purpose we developed a small extracorporeal flow-through cuvette, containing pH and blood gas electrodes and the fiber optic probe of an oximeter. The cuvette is connected through two catheters to the fetal circulation. Blood from the carotid artery flows through the cuvette at a constant rate of 2 mL/min and is drained into the jugular vein. Continuous recordings for 6 h were obtained from five chronically instrumented sheep fetuses at 134-137-d gestational age. Intraindividual variability of fetal arterial blood pH (pHa), partial pressure of arterial blood CO2 (Paco2) and O2 (Pao2), and saturation of arterial blood (Sao2) is quantitatively described. The individual variation coefficients ranged from 0.1 to 0.4% (pHa), from 1.4 to 7.6% (Paco2), from 2.5 to 5.5% (Pao2), and from 3.6 to 7.0% (Sao2). The 5th to 95 percentile intervals (delta) of the individual blood gas values ranged from 0.03 to 0.09 (pHa), from 0.3 to 1.6 kPa (Paco2), from 0.22 to 0.5 kPa (Pao2), and from 10.5 to 26.0% (Sao2). These findings indicate that considerable fluctuations in fetal arterial blood gases occur during a 6-h period. These fluctuations are associated with uterine contractures and changes in maternal and fetal activity.

Analysis of Variance↗
PubMed1994

Enhancement of hepatic artery resistance to blood flow in preeclampsia in presence or absence of HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets)

OBJECTIVE: Our purpose was to test the hypothesis that the HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome is the result of excessive vasoconstriction of the hepatic arterial circulation. STUDY DESIGN: Doppler ultrasonography was used to measure the pulsatility index of the common hepatic artery in 14 women with preeclampsia, 15 with preeclampsia complicated by HELLP syndrome, and 8 with HELLP syndrome but without proteinuria. Gestational age ranged from 24 to 38 weeks. The study group was compared with a reference group (n = 42). RESULTS: Both in preeclampsia and in the HELLP syndrome the hepatic artery pulsatility index values were significantly increased compared with the reference group. However, no significant differences were found between the preeclamptic group, the HELLP group with proteinuria, and those with HELLP without proteinuria. CONCLUSIONS: These findings indicate that hepatic artery resistance to blood flow is increased in preeclampsia in the presence or absence of the HELLP syndrome. The results also demonstrate that vasoconstriction of the hepatic arteries is not more pronounced in the HELLP syndrome than in other manifestations of preeclampsia. Therefore factors other than vasoconstriction are likely to be responsible for the development of the HELLP syndrome.

Adult↗
PubMed1993

Maternal haemolysis, elevated liver enzymes and low platelets syndrome: specific problems in the newborn.

To evaluate the effects of maternal haemolysis, elevated liver enzymes and low platelets (HELLP) syndrome on the fetus and neonate we retrospectively investigated the outcome of 87 pregnancies. All women showed thrombocytopenia, elevated liver enzymes and haemolysis. None of them died. Nine infants were stillborn (9.9%). Of the 82 liveborn infants, 66 were delivered by caesarean section. Median gestational age of the liveborn infants was 32.6 weeks, mean birth weight was 1576 g +/- 699 g (mean +/- SD). Of these infants, 44% were small for gestational age. Perinatal asphyxia rate was 21.6%. Nine infants died in the 1st week after birth. Complications during admission included neonatal respiratory disease (43.2%), hyperbilirubinaemia (44.7%), persistent ductus arteriosus (16.2%), thrombocytopenia (34%) and hypoglycaemia (16.2%). Artificial ventilation was necessary in 37 infants. Mean duration of admission was 51 days. HELLP syndrome is associated with poor perinatal outcome; the incidence of caesarean section is high and there is an increased risk for preterm birth and growth retardation. No specific neonatal pathology due to maternal HELLP syndrome was found.

Female↗
PubMed1993

Behavioural states and Doppler velocimetry of the renal artery in the near term human fetus.

Transition of fetal behavioural state 1F to 2F coincides with cardiovascular changes measured by Doppler velocimetry e.g. a decrease in pulsatility index (PI) in the internal carotid arteries and in the descending aorta, indicating redistribution of blood flow. Recently, we reported a considerable reduction in fetal urine production rate of 47% during fetal behavioural state 2F as compared to 1F. It was suggested that this reduction is caused by an increase in renal vascular resistance during 2F. Using Doppler ultrasound, flow velocity waveforms (FVW) of fetal renal arteries were recorded during behavioural states 1F and 2F. Fetal behavioural states 1F and 2F were assessed by recording fetal heart rate pattern, eye movements and body movements. The PI of the renal artery FVWs were calculated as an index of renal vascular resistance to blood flow. Fifteen healthy pregnant women between 36 and 40 weeks gestational age were studied and the relationship between fetal renal vascular resistance to blood flow and behavioural states was determined. We found that PI values in the renal arteries did not change relative to behavioural state 1F and 2F. These findings suggest that renal vascular resistance to blood flow is not appreciably different in 1F and 2F. This is in contrast with urine production rate which is almost reduced by half during 2F in the near term fetus.

Behavior↗
PubMed1993

Urine production rate is related to behavioural states in the near term human fetus.

OBJECTIVE: To investigate the relation between hourly fetal urine production rate (HFUPR) and behavioural states 1F and 2F (corresponding to quiet and active sleep, respectively) in normal near term fetuses. DESIGN: An observational study. SETTING: A clinic for antenatal care at a university hospital. SUBJECTS: Nineteen healthy pregnant women examined at 37 to 40 weeks of gestation. MAIN OUTCOME MEASURES: Fetal behavioural states (1F and 2F) were assessed by means of fetal heart rate patterns (FHR A and FHR B). Using real time ultrasonography, HFUPR (ml/h) was estimated during behavioural states 1F and 2F. RESULTS: During behavioural state 1F, HFUPR was significantly higher than during state 2F (P < 0.01). HFUPR falls by 47% from 50.8 +/- 24.4 ml/h in state 1F to 25.7 +/- 15.0 ml/h in state 2F. CONCLUSIONS: During active sleep (state 2F) hourly fetal urine production rate is considerably reduced as compared to quiet sleep (state 1F).

Behavior↗
PubMed1993

Death of one twin followed by extremely variable flow velocity waveforms in the surviving fetus.

Intrauterine death of one fetus after the second trimester in a twin pregnancy, with continuation of the pregnancy is a rare complication. The risks of morbidity and mortality for the surviving fetus are high. A 32-year-old woman was admitted to the antenatal ward at 27 weeks gestation because of intrauterine death of one twin. During the first 24 h after the death of one twin, Doppler ultrasound assessment showed a remarkable variability in flow velocity waveforms in the umbilical artery of the surviving fetus. Changes from reversed to normal end-diastolic flow velocities were recorded within 6 min. These findings are explained by twin-to-twin transfusion due to intravascular blood pressure changes, or by release of vasoactive substances by the dead fetus.

Adult↗
PubMed1992

Fetal Doppler velocimetry in the internal carotid and umbilical artery during Braxton Hicks' contractions.

Using Doppler ultrasound, previous studies revealed a considerable increase in vascular resistance in the uteroplacental circulation during Braxton Hicks' contractions. Consequently, uteroplacental blood flow is reduced and this affects placental oxygen transfer to the fetus, causing a fall in fetal arterial PO2. In view of the important role of arterial PO2 in the regulation of cerebral blood flow in the fetus, we hypothesised that Braxton Hicks' contractions cause a decrease in cerebral vascular resistance. A study was undertaken in 16 healthy near term pregnancies, using pulsed-wave Doppler ultrasound to evaluate the influence of Braxton Hicks' contractions on cerebral vascular resistance of the fetus. Flow velocity waveforms (FVWs) were recorded of the fetal internal carotid and umbilical artery and the Pulsatility Index (PI) was calculated. During Braxton Hicks' contractions the PI in the recorded vessels did not change. Fetal heart rate showed also no changes during Braxton Hicks' contractions. These findings indicate that resistance to blood flow downstream of these arteries, is not significantly altered, suggesting that Braxton Hicks' contractions have little or no effect on fetal haemodynamics and on fetal oxygenation in the healthy near term fetus.

Carotid Artery, Internal↗