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Biomedical subjects

J C Hopman

Publications and source records attributed to J C Hopman.

At least 19 recordsLinked to original sources
PubMed1997

The effect of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in newborn infants investigated by near infrared spectrophotometry.

UNLABELLED: The objective of this study was to investigate the influence of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in relation to changes in cerebral blood flow velocity (CBFV) and other relevant physiological variables in newborn infants. Thirteen preterm infants with anaemia (haematocrit < 0.33) and ten infants with polycythaemia (haematocrit > 0.65) were studied during blood transfusion and haemodilution respectively using adult red blood cells and partial plasma exchange transfusion. Changes in cerebral concentrations of oxyhaemoglobin (cO2Hb), deoxyhaemoglobin (cHHb), total haemoglobin (ctHb), (oxidized-reduced) cytochrome aa3 (cCyt.-aa3) were continuously measured using near infrared spectrophotometry throughout the whole procedure. Simultaneously, changes of mean CBFV in the internal carotid artery were continuously measured using pulsed Doppler ultrasound. Heart rate, transcutaneous partial pressure of oxygen and carbon dioxide, and arterial O2 saturation were continuously and simultaneously measured. Blood transfusion resulted in increase of cO2Hb, cHHb, ctHb and red cell transport (product of CBFV and haematocrit), whereas CBFV decreased. The increase of cO2Hb exceeded that of cHHb, reflecting improvement of cerebral O2 supply. Haemodilution resulted in a decrease of cO2Hb, cHHb and ctHb, whereas CBFV increased. Red cell transport was unchanged. The decrease of cO2Hb exceeded that of cHHb, reflecting decreased cerebral O2 supply. cCyt.aa3 decreased after blood transfusion and remained unchanged after haemodilution, but the reliability of these results is uncertain. With the exception of a small, but significant increase in transcutaneous partial pressure of oxygen after blood transfusion, the other variables showed no changes. Each blood withdrawal during exchange transfusion resulted in only a significant increase in heart rate without changes in the other variables measured, suggesting unchanged cerebral perfusion. CONCLUSION: In newborn infants blood transfusion in anaemia results in improvement of cerebral oxygenation, but haemodilution in polycythaemia does not improve cerebral oxygenation despite possible improvement of cerebral perfusion.

Anemia↗
PubMed1997

Cerebral blood flow velocity and pulsation in neonatal respiratory distress syndrome and periventricular hemorrhage.

The present study addressed the hypotheses that cerebral ischemia and/or excessive cerebral blood pulsation contribute to periventricular hemorrhage in preterm newborns with respiratory distress and that the pulse width is a valuable tool to estimate the contribution of cerebral blood pulsation. These hypotheses were tested by following preterm newborns at risk for respiratory distress and periventricular hemorrhage. We monitored for cerebral blood flow velocity (CBFV), cerebral pulse width, and cerebral pulsatility index; for patent ductus arteriosus, capillary Pco2, heart rate (HR) and behavior; and for the occurrence of respiratory distress and periventricular hemorrhage (PVH). The data obtained were analyzed with linear regression with the mode of respiration (spontaneous or supported) and postnatal age as additional covariates. We observed that (a) respiratory distress, either uncomplicated or complicated by PVH, correlates with a low CBFV and a high cerebral pulsatility index; (b) PVH also correlates with a high cerebral pulse width; (c) the increased pulse width precedes the onset of the hemorrhage; and (d) these CBF alterations can be partly attributed to ductal shunting and are ameliorated by mechanical ventilation.

Analysis of Variance↗
PubMed1996

Is noninvasive determination of pulmonary artery pressure feasible using deceleration phase Doppler flow velocity characteristics in mechanically ventilated children with congenital heart disease?

Noninvasive determination of pulmonary hemodynamics is important for the management of congenital heart disease complicated by pulmonary hypertension. Flow deceleration is less influenced by right ventricular function and would allow more accurate estimation of pulmonary hemodynamics than acceleration. Respiratory influences on pulmonary blood flow are exaggerated by mechanical ventilation. Doppler-derived pulmonary artery (PA) blood flow velocity characteristics were therefore compared with pulmonary hemodynamic parameters in 42 mechanically ventilated children, aged 0.2 to 14.8 years (mean +/- SD 6.7 +/- 4.9). Mean PA pressure ranged from 11 to 47 mm Hg (21 +/- 9 mm Hg). Pulmonary hypertension was present in 14 patients. Significant differences were found between patients with and without pulmonary hypertension in maximal velocity (1.03 +/- 0.22 vs 0.88 +/- 0.18 m/s), acceleration time (119 +/- 39 vs 136 +/- 29 ms), maximal acceleration (17.6 +/- 6.4 vs 13.1 +/- 4.0 m/s2), mean acceleration (9.3 +/- 2.6 vs 6.7 +/- 2.0 m/s2), and mean deceleration (4.5 +/- 1.0 vs 3.8 +/- 0.8 m/s2). In contrast to our hypothesis of the deceleration phase-derived parameters, only maximal deceleration correlated with PA pressure. Acceleration parameters showed closer relations with PA pressures, but correlations were generally low and did not permit accurate prediction of PA pressure (SEE 5 to 11 mm Hg), PA resistance (SEE 1.14 U. m2) or PA driving force (SEE 7 mm Hg). An analysis that took respiratory phase into account did not improve correlations. Measurement of mean acceleration, maximal deceleration, and rate-corrected preejection period permitted for accurate discrimination between the presence or absence of pulmonary hypertension, with positive and negative predictive values being 92% and 90%. In mechanically ventilated children with congenital heart disease, accurate noninvasive PA pressure assessment is not possible. Accurate predictions for the presence of pulmonary hypertension can be made by measurement of both acceleration and deceleration parameters.

Adolescent↗
PubMed1995

Influence of end expiratory pressure on cerebral blood flow in preterm infants.

The effect of interruption of positive and expiratory pressure (PEEP) on cerebral blood flow velocity (CBFV) and CBF fluctuation (CBFF) in the internal carotid arteries and on heart rate, restlessness and wakefulness has been studied in 17 mechanically ventilated neonates with RDS. A decrease in CBFV was found, but no significant change in CBFF. Multiple regression analysis showed that the decrease in CBFV is less pronounced if the PEEP interruption is accompanied by restlessness. It further appeared that the decrease in CBFV is more pronounced if CBFV is high, the ductus arteriosus is patent, or RDS follows a complicated course. These findings indicate that PEEP supports CBF, probably by a decrease in ductal stealing from the brain. Therewith PEEP protects against cerebral hypoperfusion which is one of the major risks in RDS and immaturity. Furthermore, our findings suggest that the decrease in CBF during PEEP interruption is moderated by restlessness and accentuated by brain damage.

Blood Flow Velocity↗
PubMed1995

Asymmetry of the cerebral blood flow: an ultrasound Doppler study in preterm newborns.

The purpose of this study was to investigate whether the preference of periventricular hemorrhage (PVH) for the left hemisphere is due to asymmetry of cerebral blood flow (CBF) and, if so, whether this asymmetry is due to patent ductus arteriosus (PDA). Thirty-three preterm newborns at risk for PVH were followed during their first 5 days after birth. Internal carotid CBF velocity (CBFV) and the flow direction in the common pulmonary artery, both determined by ultrasound Doppler, served as measures of CBF and PDA, respectively. The difference between right and left CBFV was analyzed statistically, with outcome, PDA, capillary PCO2, behavior, heart rate, and the average of right and left CBFV as covariates. Infants who developed PVH (n = 7) exhibited CBFV asymmetry to the disadvantage of the left side. This finding was partially attributable to PDA. Without PVH there was no significant CBFV asymmetry. Because all hemorrhages were bilateral, a relationship with the side of the hemorrhage could not be explored. In conclusion, asymmetry of CBFV is not normal, but is associated with PVH and PDA.

Case-Control Studies↗
PubMed1995

The influence of arterial carbon dioxide on cerebral oxygenation and haemodynamics during ECMO in normoxaemic and hypoxaemic piglets.

OBJECTIVE: To investigate the cerebrovascular response to changes in arterial CO2 tension during extracorporeal membrane oxygenation (ECMO) in normoxaemic and hypoxaemic piglets. METHODS: Four groups of six anaesthetized, paralysed and mechanically ventilated piglets: group 1-normoxaemia without ECMO, group 2-ECMO after normoxaemia, group 3-hypoxaemia without ECMO, and group 4-ECMO after hypoxaemia, were exposed successively to hypercapnia and hypocapnia. Changes in cerebral concentrations of oxyhaemoglobin (cO2Hb), deoxyhaemoglobin (cHHb), (oxidized-reduced) cytochrome aa3 (cCyt.aa3) and blood volume (CBV) were continuously measured using near infrared spectrophotometry. Heart rate, arterial O2 saturation, arterial blood pressure, central venous pressure, intracranial pressure (ICP) and left common carotid artery blood flow (LCaBF) were measured simultaneously. RESULTS: Hypercapnia resulted in increased CBV, cO2Hb and ICP in all groups, while cHHb was decreased. No changes in LCaBF were found. Hypocapnia resulted in decreased cO2Hb and increased cHHb except in group 3. LCaBF decreased in all groups except group 2. CBV decreased only in groups 2 and 4. No effect on ICP was observed in any of the groups. The other variables showed no important changes either during hypercapnia or hypocapnia. ECMO after hypoxaemia resulted in a greater response of cO2Hb and cO2Hb and cHHb during hypocapnia. The effect of hypercapnia on CBV while on ECMO was greater than without ECMO. CONCLUSION: Since cerebrovascular reactivity to CO2 remains intact during ECMO in piglets, it is important to keep arterial CO2 tension stable and in normal range during clinical ECMO.

Anesthesia, General↗
PubMed1995

The influence of artificial ventilation on heart rate variability in very preterm infants.

To study the influence of artificial ventilation rate on neonatal heart rate variability (HRV), ECG and respiratory impedance curves were recorded four times a day in 20 preterm infants (< 33 wk) during the first 3 d after birth while the infants were ventilated at a wide range of ventilator rates. The contents of selected frequency bands within the R-R interval power spectrum were calculated for 3-min periods. Respiratory distress syndrome severity was assessed at each measurement. Respiratory sinus arrhythmia (RSA) induced by the ventilator appeared to mimic spontaneous RSA. As in spontaneous respiration, the amount of RSA (power in a frequency band around the respiratory rate) increases as the ventilation rate decreases. This phenomenon is most probably due to entrainment with baroreflex-related fluctuations in the heart rate. Although the artificial ventilation rate influences RSA and thus high-frequency HRV, an increase in respiratory distress syndrome severity results in a decrease in low-frequency HRV. Thus, the attenuation of low-frequency HRV by respiratory distress syndrome is not likely to be due to artificial ventilation.

Analysis of Variance↗
PubMed1995

Cerebral oxygenation and hemodynamics during induction of extracorporeal membrane oxygenation as investigated by near infrared spectrophotometry.

OBJECTIVE: To investigate cerebral oxygenation and hemodynamics in relation to changes in some relevant physiologic variables during induction of extracorporeal membrane oxygenation (ECMO) in newborn infants. METHODS: Twenty-four newborn infants requiring ECMO were studied from cannulation until 60 minutes after starting ECMO. Concentration changes of oxyhemoglobin (cO2Hb), deoxyhemoglobin (cHHb), total hemoglobin (ctHb), and (oxidized-reduced) cytochrome aa3 (cCyt.aa3) in cerebral tissue were measured continuously by near infrared spectrophotometry. Heart rate (HR), transcutaneous partial pressures of oxygen and carbon dioxide (tcPO2 and tcPCO2), arterial O2 saturation (saO2), and mean arterial blood pressure (MABP) were measured simultaneously. Intravascular hemoglobin concentration (cHb) was measured before and after starting ECMO. In 18 of the 24 infants, mean blood flow velocity (MBFV) and pulsatility index (PI) in the internal carotid and middle cerebral arteries were also measured before and after starting ECMO using pulsed Doppler ultrasound. RESULTS: After carotid ligation, cO2Hb decreased whereas cHHb increased. After jugular ligation, no changes in cerebral oxygenation were found. At 60 minutes after starting ECMO, the values of cO2Hb, saO2, tcPO2, and MABP were significantly higher than the precannulation values, whereas the value of cHHb was lower. There were no changes in cCyt.aa3, tcPCO2, and HR, whereas cHb decreased. The MBFV was significantly increased in the major cerebral arteries except the right middle cerebral artery, whereas PI was decreased in all measured arteries. Cerebral blood volume, calculated from changes in ctHb and cHb, was increased in 20 of 24 infants after starting ECMO. Using multivariate regression models, a positive correlation of delta ctHb (representative of changes in cerebral blood volume) with delta MABP and a negative correlation with delta tcPO2 were found. CONCLUSIONS: The alterations in cerebral oxygenation after carotid artery ligation might reflect increased O2 extraction. Despite increase of the cerebral O2 supply after starting ECMO, no changes in intracellular O2 availability were found, probably because of sufficient preservation of intracellular cerebral oxygenation in the pre-ECMO period despite prolonged hypoxemia. The increase in cerebral blood volume and cerebral MBFV may result from the following: (1) reactive hyperperfusion, (2) loss of autoregulation because of prolonged hypoxemia before ECMO and/or decreased arterial pulsatility, or (3) compensation for hemodilution related to the ECMO procedure.

Brain↗
PubMed1994

Effects of repeated indomethacin administration on cerebral oxygenation and haemodynamics in preterm infants: combined near infrared spectrophotometry and Doppler ultrasound study.

The objectives of this study were to evaluate the effect of repeated indomethacin administration on cerebral oxygenation in relation to changes in cerebral blood flow velocity (CBFV) and other relevant physiological variables. Fourteen preterm infants with patent ductus arteriosus were studied during three subsequent indomethacin bolus administrations with intervals of 12 and 24 h. Changes in concentration of oxyhaemoglobin (cO2Hb), deoxyhaemoglobin (cHHb) and oxidized cytochrome aa3 (cCyt.aa3) in cerebral tissue and changes in cerebral blood volume (CBV) were measured by near infrared spectrophotometry; changes in mean CBFV in the internal carotid artery were measured by pulsed Doppler ultrasound. Simultaneously heart rate, transcutaneous pO2 and pCO2, arterial O2 saturation and blood pressure were measured. All variables were continuously recorded until 60 min after indomethacin administration. Within 5 min after each indomethacin administration, significant decreases in CBFV, CBV and cO2Hb and cCyt.aa3 were observed which persisted for at least 60 min, while cHHb increased or did not change at all. There were no changes in the other variables recorded. These data demonstrate that indomethacin administration is accompanied by a reduction in cerebral tissue oxygenation due to decreased cerebral blood flow. Therefore, low arterial oxygen content, either caused by low arterial O2 saturation or by low haemoglobin concentration, may be a contraindication for indomethacin treatment in preterm infants.

Blood Flow Velocity↗
PubMed1994

Cerebral blood flow fluctuation in neonatal respiratory distress and periventricular haemorrhage.

The relationship of cerebral blood flow fluctuation (CBFF) with periventricular haemorrhage (PVH) and respiratory distress syndrome (RDS) was studied in 35 preterm newborns. CBFF was defined as the interquartile range in the ensemble of pulses of a 20-s Doppler recording of CBF velocity (CBFV) in the internal carotid artery. We found a statistically significant increase in end diastolic CBFF in PVH and RDS. This increase was related to the mode of respiration (spontaneous or mechanically supported), the state of the ductus arteriosus, and the level of end diastolic CBFV. Differences before and after the onset of PVH were not found. In view of this, we conclude that RDS increases CBFF, that this increase is related to pleural pressure fluctuations, that these can be damped by mechanical ventilation, and that their propagation to the CBF is promoted by patency of the ductus arteriosus and foramen ovale. Whether the CBFF increase causes PVH, or is merely an expression of coincident RDS, remains a question that needs further investigation.

Blood Flow Velocity↗
PubMed1993

Heart rate variability.

PURPOSE: To present an overview of the applicability of heart rate variability measurements in medicine. DATA SOURCES: During a 4-year period all new papers concerning heart rate variability were collected. A selection of the most recent publications in the presented research area was used for this review. DATA SYNTHESIS: The amount of short- and long-term variability in heart rate reflects the vagal and sympathetic function of the autonomic nervous system, respectively. Therefore heart rate variability can be used as a monitoring tool in clinical conditions with altered autonomic nervous system function. In postinfarction and diabetic patients, low heart rate variability is associated with an increased risk for sudden cardiac death. A sympathovagal imbalance is also detectable with heart rate variability analysis in coronary artery disease and essential hypertension. Besides diabetic neuropathy, in many other neurologic disorders, such as brain damage, the Guillain-Barré syndrome, and uremic neuropathy, heart rate variability analysis can provide insight into which division of the autonomic nervous system is most affected. Heart rate variability can be influenced by various groups of drugs, but it can also shed light on the mode of action of drugs. The protective effect of cardiovascular drugs in postinfarction patients has been investigated. CONCLUSIONS: Heart rate variability analysis is easily applicable in adult medicine, but physiologic influences such as age must be considered. The most important application is the surveillance of postinfarction and diabetic patients to prevent sudden cardiac death. With heart rate variability analysis, individual therapy adjustments to achieve the most favorable sympathetic-parasympathetic balance might be possible in the future.

Aging↗
PubMed1992

Cerebral blood flow fluctuation in low-risk preterm newborns.

Cerebral blood flow (CBF) fluctuation was studied by analyzing Doppler internal carotid blood velocity recordings of 13 healthy preterm newborns obtained in the course of their first 5 days of life. As measures of fluctuation we used the interquartile range (IQR) and the coefficient of variation (CV) of the ensemble of heart beats of a 20-s recording. In this way we determined fluctuation of the following velocity curve parameters (VCPs): end diastolic velocity; mean velocity; peak systolic velocity and pulsatility index (PI). The pooled data 5-95% intervals for fluctuation thus measured, were: 93-281% for CV; 0.6-3.7 cm/s for the IQR of the velocities; and 4-19% for the PI-IQR. Multiple regression analysis of IQR revealed significant relationships with: the VCP level; with restlessness; and with patency of the ductus arteriosus. Our findings imply that: (1) CBF has various qualities with different stability, mean velocity being the most stable; (2) for all the VCPs investigated, fluctuation is physiological in the early days after preterm birth; (3) most likely, there exists no age trend; (4) restlessness rather than wakefulness, enhances fluctuation; (5) patent ductus arteriosus destabilizes CBF; and (6) for a proper insight into fluctuation, the level of the VCP in question must be taken into account. We suggest that, the enhancing effect that patent ductus arteriosus has on fluctuation pays a contribution to the pathogenesis of brain damage. Finally, we conclude that the IQR represents fluctuation better than does the more commonly used CV.

Blood Flow Velocity↗
PubMed1991

Influences on heart rate variability in spontaneously breathing preterm infants.

To investigate the influence of maturational and physiological factors on heart rate variability in spontaneously breathing very preterm infants (n = 29) a multiparametric study was performed during the first 3 days of life in infants born at a gestational age below 33 weeks. Four times a day, RR-intervals, respiration curve and rate, transcutaneously measured blood gases and observed body movements were recorded while the infants were asleep. All data were stored simultaneously in a micro-computer. Non-invasively measured blood pressure and patency of the ductus arteriosus were documented as well. Four sets of short- (STV) and long term variability (LTV) indices were calculated. Both STV and LTV appeared to be significantly influenced by conceptional and postnatal age in the appropriate for gestational age infants. LTV was influenced by the behavioural state and body movements. During state coincidence 2 ('active sleep') LTV was influenced by respiratory rate and the variations in transcutaneous PO2. An effect of blood pressure or ductus patency could not be demonstrated.

Age Factors↗
PubMed1991

The influence of respiratory distress syndrome on heart rate variability in very preterm infants.

In a multi-parametric study the influence of pathological neonatal conditions on heart rate variability was investigated in 60 preterm infants born at a gestational age below 33 weeks. Measurements were performed during the first 3 days of life. Four times a day, RR-intervals, respiration curve and rate, transcutaneously measured blood gases and observed body movements were recorded while the infants were asleep. All data were stored simultaneously in a micro-computer. Severity of respiratory distress syndrome (RDS), patency of ductus arteriosus and periventricular haemorrhage were documented as well. Four sets of short- (STV) and long-term variability (LTV) indices were calculated. Severe RDS was associated with a significant decrease in LTV. The influence of RDS on LTV persisted after correction for conceptional age, postnatal age, behavioural state and variations in respiratory rate and in transcutaneous PO2. Infants with a symptomatic patent ductus arteriosus had lower LTV than controls with the same severity of RDS. STV was predominantly influenced by postnatal and conceptional age, and tended to be lower in infants with periventricular haemorrhage.

Age Factors↗
PubMed1991

The agreement between pulmonary and systemic blood flow measurements in babies by dual beam Doppler echocardiography.

Measurement of cardiac output within the great arteries of infants by non-invasive Doppler echocardiographic techniques is limited. This paper describes a simple method, based on dual beam Doppler, that is capable of measuring the pulmonary and systemic blood flows independently of the vessel diameter and beam-blood flow angle. In 27 babies (12 of them were premature born) without intracardial shunts the accuracy of this method in measuring cardiac output was evaluated. The mean difference between pulmonary and systemic blood flow measurements was 0.02 (SD 0.06) 1 min-1. This study demonstrates a good agreement between the pulmonary and systemic blood flow measurements using dual beam Doppler ultrasound in babies.

Aorta↗