Search PubMed⌕ Search

Biomedical subjects

J C Hopman

Publications and source records attributed to J C Hopman.

29 records · Page 2Linked to original sources
PubMed1990

The influence of physiological parameters on long term heart rate variability in healthy preterm infants.

The instantaneous heart rate shows a variation around the mean heart rate caused by cardioregulatory mechanisms which are mediated through the sympathetic and vagal autonomic nervous system. To gain more insight into the influence of physiological parameters on neonatal heart rate variability a study was performed in four healthy preterm newborns during the first five days of life. Instantaneous heart rate, respiration rate, transcutaneous pO2, blood pressure and behaviour were recorded during 40 minutes four times a day. Long term heart rate variability was calculated as the difference between p95 and p5 of instantaneous heart rate values sampled during three minutes. A clear relationship between long term variability and age (maturity of the autonomic nervous system), respiration rate (respiratory sinus arrhythmia or a tidal volume mediated effect) and behaviour (increase of sympathetic tone during REM sleep) was found. No influence of blood pressure, heart rate, and transcutaneous pO2 within physiological ranges could be detected. The relative influence of the different physiological parameters on heart rate variability has to be established before the value of heart rate variability as a monitoring tool in neonatal intensive care can be investigated.

Age Factors↗
PubMed1989

Repeatability of Doppler ultrasound measurement of blood flow velocity and its variability in the supraclinoid segment of the internal carotid artery in preterm newborns.

Accuracy of transfontanellar Doppler ultrasound measurement of blood flow velocity and its variability in the supraclinoid segment of the internal carotid artery was studied in preterm newborns. Measurements were performed in duplicate, on a well defined site, under negligible angle of insonation, and during stable physical condition. The measurements included the base value and variability over 20 seconds, for: diastolic velocity; mean velocity; systolic velocity; resistance index; diastolic time interval; systolic time interval; heart beat duration. As a measure of accuracy the coefficient of repeatability was calculated for each parameter. Coefficients several times smaller than the range of measured values, were found for most parameters. These parameters and their coefficients include: diastolic velocity (base value 3.1 cm s-1, variability 1.6 cm s-1); mean velocity base value 3.1 cm s-1; systolic velocity base value 4.5 cm s-1; resistance index (base value 0.13, variability 0.08); diastolic time interval base value 25 ms; systolic time interval base value 27 ms; heart beat duration base value 27 ms. Thus, Doppler ultrasound enables differentiation within the biological variation of certain properties of cerebral blood flow.

Blood Flow Velocity↗
PubMed1989

Influence of behavioural state on blood pressure in preterm infants during the first 5 days of life.

The influence of behavioural state on neonatal blood pressure was studied in 19 healthy preterm infants. During the first five days of life every three hours a series of oscillometric blood pressure measurements was made. During the measurements the behavioural state was scored. The predominant states were quiet and active sleep. We confirmed the age-dependency of blood pressure with a steep increase during the first day of life. After the first day blood pressure and heart rate were slightly higher when the infant was awake than when asleep. Paired comparison (t-test) before and after spontaneous state transitions showed significant differences in median heart rate and ranges of heart rate and blood pressure, but not in median blood pressure. We conclude that especially movements influence oscillometric determination of blood pressure and heart rate.

Blood Pressure↗
PubMed1989

Assessment of the orifice diameter by a multigated pulsed Doppler system in children with congenital semilunar valve stenosis.

This study investigated whether the jet diameter measured by a multigated pulsed Doppler system could be used to assess the severity of valve disease in children with pulmonary (n = 11) or aortic (n = 4) valve stenosis. The results obtained were compared with those obtained at cineangiography and at operation. Multigated pulsed Doppler examination of a stenosed valve showed a region of relatively high velocities in the velocity profile (jet flow). There was good agreement between the diameter of the disturbed region on the Doppler echocardiogram and the diameter of the jet on the lateral angiocardiogram. In severe valve stenosis the agreement between the valve diameters measured by multigated pulsed Doppler and at operation was also good. In less severe valve stenosis Doppler measurements systematically underestimated the valve diameter at operation. It is likely that the functional opening of a semilunar valve is a more relevant estimate of the degree of stenosis than the anatomical measurement of the orifice. The findings of this study indicate that multigated pulsed Doppler systems are useful in the noninvasive diagnosis of stenotic valve disease.

Aortic Valve↗
PubMed1989

[Cerebrovascular Doppler studies in infants and neonates. Marginal observations on the method].

By means of Doppler ultrasound the blood velocity can be measured in the cerebral arteries in neonates and infants. In this article various modifications of the method are discussed. We conclude that for the time being the method of choice should be: measurement of absolute velocity in the internal carotid artery by use of transfontanellar duplex examination. The reliability of the method, the pathophysiological meaning of velocity curve parameters and the normal variation of the parameter values, are still a matter of debate.

Blood Flow Velocity↗
PubMed1988

Automated calculation of stenosis diameters from the width of the velocity jet with the use of a multi-gate pulsed Doppler system.

The aim of this study was to evaluate an algorithm for automated estimation of the width of a jet stream originating from a stenosis. The evaluation was performed in a pulsatile flow model. The width of the jetstream was assessed by measuring the diameter of the region with relatively high velocities (the jet) in the velocity profiles, as recorded with a multi-gate pulsed Doppler system. Measurements were performed at 3, 6, and 9 mm downstream of three different stenoses (stenosis diameter: 3, 5, or 8 mm) at different Reynolds numbers (200-1600) based on time averaged flow velocity for a tube of diameter 15 mm. The developed algorithm was used successfully for automated detection and quantification of jet flow diameters downstream to a stenosis. The algorithm can be used for calculating the stenosis diameter notwithstanding a theoretically predictable overestimation of about 1 mm, depending on the Reynolds number and the distance from the stenosis.

Algorithms↗
PubMed1987

The usefulness of cross-sectional Doppler flow imaging in the detection of small ventricular septal defects with left-to-right shunt.

Small ventricular septal defects (VSDs) with left to right (L-R) shunt have been difficult to diagnose with conventional ultrasound techniques. Using the cross-sectional Doppler flow imaging system, additional information can be obtained. In a group of 60 patients with a clinical diagnosis of VSD with L-R shunt, the new technique proved valuable, especially in detecting muscular and apical VSDs.

Adolescent↗
PubMed1982

Ultrasound detection of congenital arteriovenous aneurysm of the great cerebral vein of Galen.

Using combined echoencephalography and Doppler flow determination the diagnosis Arteriovenous aneurysm of the great cerebral vein of Galen could be made in two infants. Without vascular surgery one patient died, the other recovered completely. CT scanning confirmed the diagnosis. Invasive methods such as cerebral angiography were avoided. Case histories, neuropathological findings, ultrasound method and results are presented. Pathogenesis, clinical signs, treatment and prognosis are discussed. With the ultrasound method presented, the nature and location of the vascular anomaly were demonstrable, thus additional higher risk diagnostic methods could be avoided or planned more purposefully.

Autopsy↗
PubMed1982

Doppler flow characteristics in the main pulmonary artery and the LA/Ao ratio before and after ductal closure in healthy newborns.

Echo-Doppler (ED) techniques were used to estimate the time of closure of the ductus arteriosus in 30 normal neonates. We found that after birth there was a left-to-right (L-R) shunt through the ductus, which disappeared within 14 hours in 50% of the neonates investigated. Furthermore, patency of the ductus was not associated with a murmur. After closure of the ductus there was a significant diminution of the echocardiographically determined left atrium/aortic (LA/Ao) ratio, which was used as a measure of the L-R shunt.

Blood Circulation↗