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Biomedical subjects

G H Visser

Publications and source records attributed to G H Visser.

At least 19 recordsLinked to original sources
PubMed2001

Flow redistribution in the major cerebral arteries after carotid endarterectomy: a study with transcranial Doppler scan.

PURPOSE: This open single-center prospective study aimed to determine the redistribution of blood flow within the circle of Willis and through collateral pathways after carotid endarterectomy. Blood flow velocity and flow direction in the major cerebral arteries were determined, both at rest and during CO(2) inhalation. METHODS: Carotid endarterectomy was performed in 148 patients with a 70% or greater diameter stenosis of the internal carotid artery while patients were under general anesthesia. Arteriotomy closure was done with a venous patch. Selective shunting was performed with an electroencephalogram. Baseline blood flow velocity of the basal cerebral arteries was measured by means of transcranial Doppler sonography preoperatively (within 1 week before surgery) and 3 months postoperatively. At the same times, cerebrovascular reactivity was calculated during CO(2) inhalation insonating both middle cerebral arteries. RESULTS: Baseline blood flow velocity in the ipsilateral middle cerebral artery hardly changed 3 months postoperatively, but there was a considerable redistribution of flow in the circle of Willis. This was characterized by a decrease in contribution from the contralateral hemisphere through the anterior communicating artery, reduced cerebropetal flow rates in the ophthalmic artery, and smaller contribution of the posterior collateral sources. The CO(2) reactivity on the side of surgery increased in all patients. In patients with a contralateral occlusion, CO(2) reactivity increased on both sides. The redistribution of flow was most pronounced in patients who needed intraoperative shunting and in patients with a contralateral internal carotid artery occlusion. CONCLUSION: After carotid endarterectomy, flow redistribution, as expressed by changes in blood flow velocity values, occurs in the circle of Willis. The contribution of collateral sources is diminished, and the CO(2) reactivity increases, both of which reflect improvement of the hemodynamic condition. The most improvement occurs in patients with contralateral occlusion.

Aged↗
PubMed2000

Recurrent ischemia in symptomatic carotid occlusion: prognostic value of hemodynamic factors.

OBJECTIVE: To identify hemodynamic factors that predict recurrence of ipsilateral cerebral ischemic events in patients with symptomatic carotid artery occlusion (CAO). PATIENTS AND METHODS: The authors studied 117 consecutive patients with CAO and corresponding recent (</=6 months) ischemic symptoms of the brain or eye that were transient or at most mildly disabling. They determined, using Cox proportional hazards analysis, the prognostic value for recurrence of ipsilateral cerebral ischemic events of 1) clinical features believed to indicate hemodynamic compromise, 2) collateral blood flow pattern, and 3) transcranial Doppler CO(2)-reactivity. RESULTS: None of the 24 patients with symptoms of retinal ischemia alone had a recurrent cerebral ischemic event. In the 93 patients with cerebral ischemic symptoms on entry, recurrence of these symptoms was independently predicted by 1) the nature of the initial symptoms being of purported hemodynamic origin (limb-shaking, precipitation of symptoms by rising, exercise or low blood pressure, retinal claudication) (hazard ratio [HR] 3.8, 95% CI 1.5 to 9.5), 2) continuing symptoms after the CAO had been documented, but before inclusion in the study (HR 5.9, 95% CI 2.2 to 16.1), and 3) the presence of collateral blood flow via leptomeningeal vessels (HR 4.1, 95% CI 1.3 to 13.1). CO(2)-reactivity did not predict recurrence of cerebral ischemic events. CONCLUSIONS: Having cerebral in contrast to retinal ischemia, clinical features suggestive of hemodynamic compromise, continuing symptoms after demonstration of the CAO, and presence of leptomeningeal collaterals may help to identify patients with symptomatic CAO at high risk of future cerebral ischemia.

Aged↗
PubMed2000

Perinatal changes in myocardial metabolism in lambs.

BACKGROUND: Lactate accounts for a third of myocardial oxygen consumption before and in the first 2 weeks after birth. It is unknown how the remainder of myocardial oxygen is consumed. Glucose is thought to be important before birth, whereas long-chain fatty acids (LC-FA) are the prime substrate for the adult. However, the ability of the myocardium of the newborn to use LC-FA has been doubted. METHODS AND RESULTS: We measured the myocardial metabolism of glucose and LC-FA with [U-(13)C]glucose and [1-(13)C]palmitate in chronically instrumented fetal and newborn lambs. In fetal lambs, myocardial oxidation of glucose was high and that of LC-FA was low. Glucose and LC-FA accounted for 48+/-4% and 2+/-2% of myocardial oxygen consumption, respectively. In newborn lambs, oxidation of glucose decreased, whereas oxidation of LC-FA increased. Glucose and LC-FA accounted for 12+/-3% and 83+/-19% of myocardial oxygen consumption. To test whether near-term fetal lambs could use LC-FA, we increased the supply of LC-FA with a fat infusion. In fetal lambs during fat infusion, the oxidation of LC-FA increased 15-fold. Although the oxidation of LC-FA was still lower than in newborn lambs, the contribution to myocardial oxygen consumption (70+/-13%) was the same as in newborn lambs. CONCLUSIONS: These data show that glucose and lactate account for the majority of myocardial oxygen consumption in fetal lambs, whereas in newborn lambs, LC-FA and lactate account for the majority of myocardial oxygen consumption. Moreover, we showed that the fetal myocardium can use LC-FA as an energy substrate.

Animals↗
PubMed2000

Sotalol in the treatment of fetal dysrhythmias.

BACKGROUND: Fetal tachycardia may cause hydrops fetalis and lead to fetal death. No unanimity of opinion exists regarding the optimum treatment. This study evaluates our experience with transplacental sotalol therapy to treat fetal tachycardias in terms of safety and efficacy. METHODS AND RESULTS: The charts of 21 patients who were treated with sotalol for fetal tachycardia were reviewed. Ten fetuses had atrial flutter (AF), 10 had supraventricular tachycardia (SVT), and 1 had VT. Hydrops fetalis was present in 9 fetuses. Drug treatment was successful in establishing sinus rhythm in 8 of 10 fetuses with AF and in 6 of 10 fetuses with SVT. The mortality rate in this study was 19% (4 of 21 fetuses; 3 had SVT and 1 had AF); 3 deaths occurred just days after the initiation of sotalol therapy, and 1 occurred after a dosage increase. At birth, tachycardia was present in 6 infants. Two patients who converted to sinus rhythm in utero suffered from neurologic pathology postnatally. CONCLUSIONS: Fetal tachycardia is a serious condition in which treatment should be initiated, especially in the presence of hydrops fetalis. The high success rate in fetuses with AF suggests that sotalol should be considered a drug of first choice to treat fetal AF. The low conversion rate and the fact that 3 of the 4 deaths in this study occurred in fetuses with SVT indicate that the risks of sotalol therapy outweigh the benefits in this group and that sotalol should, therefore, be limited in the treatment of fetal SVT.

Anti-Arrhythmia Agents↗
PubMed2000

[Pregnancy in women with diabetes mellitus type I: maternal and perinatal complications, in spite of good blood glucose control].

OBJECTIVE: To examine the maternal and neonatal outcome of pregnancies of women with type I diabetes mellitus. DESIGN: Retrospective. METHODS: The medical records of pregnancies (> or = 16 weeks) in women with type I diabetes mellitus between 1986/'97 were studied in University Medical Center Utrecht, Academic Hospital Groningen and Isala Clinics, location 'De Weezenlanden', Zwolle, the Netherlands. RESULTS: During the study period, 172 women had 220 pregnancies: 212 single and 8 twin pregnancies. The mean age was 29.1 years (SD: 4.1), the mean duration of standing of the diabetes was 12 years (range: 1-32) and the mean concentration of glycosylated haemoglobin (HbA1c) was 6.3% at 10 weeks of pregnancy. The incidence of children with congenital malformations was 4 times higher (n = 19; 9.0%) than that in the Dutch population (2%). Macrosomia occurred in 92 children (43.4%) and perinatal mortality in 7 (3.3%). Maternal hypertensive complications occurred in 39 single pregnancies (18.4%), which is 2-3 times more often than in the Dutch population. CONCLUSION: In type I diabetic women maternal complications, perinatal morbidity and mortality are increased, despite near optimal glycaemic control.

Adult↗
PubMed2000

Validation of the doubly labeled water method in Japanese Quail Coturnix c. japonica chicks: is there an effect of growth rate?

The Doubly Labeled Water (DLW) method was validated against respiration gas analysis in growing Japanese Quail chicks (between 1 week and 3 weeks of age) as well as in birds after having achieved sexual maturity (7 weeks of age). A comparison was made between a strain selected for high growth rates (P-strain, n = 18), and a non-selected strain (C-strain, n = 18). Relative growth rates of individual chicks during the measurement ranged from -13.8% day(-1) to 23.1% day(-1). When employing a single-pool model (eq. 34, Lifson and McClintock 1966), it was found that the relative error of the DLW method was sensitive to assumptions concerning fractional evaporative water loss. The best fit was obtained after taking a fractional evaporative water loss value of 0.33. When applying this value for all chicks, it was found that neither strain, relative growth rate of the chick during measurement, nor age significantly contributed to the explained variance. When employing two-pool models, it was found that the DLW method significantly underestimated the true rates of CO2 production at all assumed levels of fractional evaporative water loss. Based on an evaluation of DLW validation studies in growing shorebirds, terns, and quail we recommend Speakman's Eq. 7.17 (Speakman 1997) for general use in young birds.

Age Factors↗
PubMed2000

Fetal heart rate in relation to its variation in normal and growth retarded fetuses.

OBJECTIVES: (1) to assess the relationship of basal fetal heart rate (FHR) with both long term (LTV) and short term (STV) FHR variation in low-risk pregnancies, longitudinally from 24 weeks gestation onwards and (2) to investigate the relationship of FHR with LTV and STV in intrauterine growth retarded (IUGR) fetuses. STUDY DESIGN: Computerised FHR recordings were made in twenty-nine uncomplicated pregnancies (n=224) and in twenty-seven IUGR fetuses who were selected retrospectively from three databases (n=135). Nomograms of FHR variation with FHR and GA were constructed using multilevel analysis. RESULTS AND CONCLUSIONS: There was a strong negative relationship of FHR with both LTV and STV in the control group (R2=53% and 52%, respectively). In the IUGR fetuses, FHR was generally higher than in normal fetuses whereas LTV and STV were lower. The relationship of FHR with LTV and STV in the IUGR group was less strong (for both: R2=18%). Correction of FHR variation for basal FHR in the IUGR fetuses only resulted in a slight reduction in the number of recordings with a variation below the normal range. As it does not improve the recognition of fetuses being considered at the highest risk, such a correction of FHR variation for basal FHR is therefore not necessary. Intrafetal consistency, known to be present in healthy fetuses, was also present in the IUGR fetuses with a low FHR variation.

Female↗
PubMed2000

Increase in alpha rhythm frequency after carotid endarterectomy.

OBJECTIVES: Besides preventing stroke, carotid endarterectomy (CEA) is reported to improve cerebral circulation and brain function. We tested whether this improvement is reflected by changes in the qEEG. METHODS: qEEG changes in 166 patients with a >70% stenosis of the internal carotid artery (ICA) were assessed after subtraction of the preoperative and postoperative spectra (eyes closed condition) before and 3 months after CEA. The mean frequency of the alpha band (MFA), the peak frequency of the alpha band (F alpha), and bands with limits relative to each patient's F alpha were studied in relation to neurological symptoms, patency or occlusion of the contralateral ICA, shunt requirement, and side of surgery. RESULTS: MFA and F alpha significantly increased over both hemispheres. After alignment on F alpha, a decrease of spectral band power was seen below F alpha, and a band power increase above F alpha. The group of patients with a contralateral ICA occlusion showed significantly more improvement than the group without. The group of patients with neurological deficits showed a tendency for improvement. No differences were found concerning shunt requirement or the side of surgery. CONCLUSIONS: After CEA the alpha rhythm frequency increases. In general, patients with a contralateral ICA occlusion improve more than other patients, in agreement with data from the literature on cerebral circulation and brain function.

Aged↗
PubMed2000

The use of preoperative transcranial Doppler variables to predict which patients do not need a shunt during carotid endarterectomy.

OBJECTIVES: to analyse whether preoperative transcranial Doppler (TCD) variables can predict intraoperative shunt requirement. DESIGN AND METHODS: the blood-flow velocity (BFV) in the major basal cerebral arteries was measured preoperatively with TCD, in 178 patients scheduled for CEA. Carotid artery compression and CO2 reactivity tests were also performed. Intraoperative electroencephalography was used to decide whether a shunt was needed. Differences in the probability of shunt requirement between the categories of variables were assessed with crosstabs statistics. RESULTS: preoperative TCD criteria clearly identified a subgroup of 59 patients (33%) who did not require a shunt. In general, these patients appeared to have adequate collateral flow through the anterior communicating artery. In contrast, prediction of the need for a shunt was less reliable. TCD variables could predict the need for a shunt with a probability of only 60%. CONCLUSIONS: preoperative TCD can be used to identify patients who do not require a shunt during carotid endarterectomy.

Aged↗
PubMed2000

Obstetric outcome of twin pregnancies after in-vitro fertilization: a matched control study in four Dutch university hospitals.

In singleton pregnancies after in-vitro fertilization (IVF), increased rates of obstetric and perinatal complications have been reported. Studies that compared IVF twin pregnancies with spontaneously conceived twins have yielded conflicting results. We compared 96 IVF twin pregnancies to 96 controls after elaborate matching. The design of our study precluded matching by zygosity. The monozygosity rate was higher in the control group and this implies that beforehand the risk for a less favourable outcome in the control group was higher than in the IVF group. However, the average birthweight of the IVF children was less than that of children in the control group (P = 0.04). This was not due to more intrauterine growth retardation in the IVF group. The mean gestational age at birth was 5 days shorter in IVF than control pregnancies, and although this difference was not significant it might explain the lower birthweight in the IVF group. The discordance rate in the IVF group was significantly increased. We found no difference in perinatal mortality and morbidity. We conclude that this study provides further evidence for a different outcome of IVF twin pregnancies in comparison with spontaneously conceived twin pregnancies.

Adult↗
PubMed2000

Obstetric outcome of singleton pregnancies after IVF: a matched control study in four Dutch university hospitals.

In singleton pregnancies after IVF a high rate of preterm deliveries and an increased rate of small-for-gestational age (SGA) children in comparison to the general parturient population have been reported. However, due to differences between IVF mothers and their peers who conceived naturally, careful selection of the control group is necessary to assess whether IVF pregnancies really carry increased risks of adverse outcome. In our study 307 IVF pregnancies were compared with 307 control pregnancies after elaborate matching for an extensive number of maternal characteristics, as well as for the hospital that provided the obstetric care. Four Dutch university hospitals contributed to the study. In cases with spontaneous onset of labour, gestational age at delivery was 3 days shorter in the IVF group (275 versus 278 days, P = 0.05). The proportion of SGA was higher in the IVF group (16.2 versus 7.9%, P < 0.001). The combination of these two results denotes a distinct difference between IVF and control pregnancies. Placental weight was comparable in both groups.

Abnormalities, Multiple↗
PubMed2000

The effect of immersion on haemodynamic and fetal measures in uncomplicated pregnancies of nulliparous women.

OBJECTIVE: To evaluate the effect of immersion in water on maternal haemodynamic measures and fetal heart rate patterns in healthy nulliparous women. DESIGN: A randomised cross-over study. PARTICIPANTS: Twenty pregnant women were studied between 26-29 weeks and between 34-37 weeks of gestation. METHODS: The women were either immersed in water for 35 minutes or rested on a bed for a similar period of time. Maternal blood pressure, thoracic electrical bioimpedance, urine and blood samples, and fetal heart rate patterns were obtained before and after immersion or bedrest. RESULTS: Compared with bedrest and pre-immersion values, immersion resulted in a significant decrease in blood pressure, which returned to baseline values within 1.5 hour. Urine production increased for a short period after immersion, but 24 hour samples showed no difference compared with bedrest. Sodium, potassium and creatinine levels in urine remained constant. No significant changes were found for the other haemodynamic measures. There were no effects on fetal heart rate nor on its variation. CONCLUSION: In healthy pregnant women immersion for 35 minutes has a clear effect on blood pressure and urine production. However, these effects are short lasting.

Adult↗
PubMed2000

Ingested water equilibrates isotopically with the body water pool of a shorebird with unrivaled water fluxes.

We investigated the applicability of (2)H to measure the amount of body water (TBW) and water fluxes in relation to diet type and level of food intake in a mollusk-eating shorebird, the Red Knot (Calidris canutus). Six birds were exposed to eight experimental indoor conditions. Average fractional (2)H turnover rates ranged between 0. 182 day(-1) (SD = 0.0219) for fasting birds and 7.759 day(-1) (SD = 0.4535) for birds feeding on cockles (Cerastoderma edule). Average TBW estimates obtained with the plateau method were within the narrow range of 75.9-85.4 g (or between 64.6 and 70.1% of the body mass). Those obtained with the extrapolation method showed strong day-to-day variations (range 55.7-83.7 g, or between 49.7 and 65.5%). Average difference between the two calculation methods ranged between 0.6% and 36.3%, and this difference was strongly negatively correlated with water flux rate. Average water influx rates ranged between 15.5 g/day (fasting) and 624.5 g/day (feeding on cockles). The latter value is at 26.6 times the allometrically predicted value and is the highest reported to date. Differences in (2)H concentrations between the blood and feces (i.e., biological fractionation) were small but significant (-3.4% when fed a pellet diet, and -1.1% for all the other diets), and did not relate to the rate of water flux (chi(2)(1) = 0.058, P < 0.81). We conclude that the ingested water equilibrated rapidly with the body water pool even in an avian species that shows record water flux rates when living on ingested marine bivalves.

Animals↗
PubMed1999

[Pregnancy course and outcome in 2956 pregnancies after in-vitro fertilization in Netherlands].

OBJECTIVE: Description of the outcome of pregnancies after in vitro fertilisation (IVF) in Dutch IVF centers. DESIGN: Descriptive, retrospective. METHOD: Data were collected on IVF pregnancies in the period 1984-1992 from seven Dutch IVF centers. RESULTS: The study comprised 2956 pregnancies. Five centres provided data on 2133 ongoing and non-ongoing pregnancies. More than 25% ended in a spontaneous abortion (22.3%) or ectopic pregnancy (3.6%). From the seven centres there were data available on 2311 ongoing pregnancies. Of these, 30.8% were multiple; preterm delivery occurred in 29.2%. The birth weight of 40.6% of 3173 neonates was lower than 2500 g and that of 10.1% lower than 1500 g. A birth weight under the 10th percentile of the national reference curve was found in 16.7% and under the 2.3rd percentile in 4.3% of cases. Perinatal mortality was 31.3 pro mille. In 1588 singleton pregnancies preterm birth occurred in 15.6%; 41.3% of the singletons weighed less than 2500 g, of which 3.6% less than 1500 g while 12.3% had a birth weight below the 10th percentile. The results of our study are similar to those of other major studies in the literature and are unfavourable compared with to Dutch reference values. This is mainly due to the high proportion of multiple pregnancies. However, we found indications of a slight disturbance of pregnancy in IVF singleton and twin pregnancies.

Adult↗
PubMed1999

Temporal organization of fetal behavior from 24-weeks gestation onwards in normal and complicated pregnancies.

Developmental aspects of behavioral organization were investigated in 29 healthy fetuses from 24-weeks gestation onwards: (a) short-term association between body (GM) and eye (EM) movements; (b) linkage of pairs of the three state variables [fetal heart rate pattern (FHRP), GM, and EM]; and (c) sequence of change of state variables during transitions. Linkage and sequence were also studied in complicated pregnancies. Short-term association between GM and EM was well established after 28 weeks. Linkage of state variables improved considerably after 32-34 weeks. FHRP was the first variable to change during synchronized transitions from 1F to 2F between 28-39 weeks, and the last variable during 2F to 1F transitions between 32-39 weeks. Although clear developmental patterns could be recognized, the interfetal variability was such that identification of the abnormal fetus is still difficult. Only transitions were significantly different in growth-restricted fetuses, as they showed no specific sequence of change. Assessing the temporal organization of fetal behavior seems, therefore, until now, not of great clinical value.

Adult↗
PubMed1999

Adverse obstetric outcome in low- and high- risk pregnancies: predictive value of maternal serum screening.

OBJECTIVE: To determine whether the relationship between adverse pregnancy outcome and elevated maternal serum alpha-fetoprotein (MSAFP) and/or maternal serum hCG levels in women whose fetuses have no chromosomal abnormalities or neural tube defects is restricted to pregnancies with a priori elevated risk for pathology or also present in low-risk pregnancies. METHODS: The outcomes of pregnancy in two groups of patients with elevated MSAFP and/or maternal serum hCG values were compared with the outcomes of a reference group with normal serum values. The first study group consisted of 83 women without pre-existing risk for poor outcome as defined by the guidelines of the Dutch Society of Obstetrics and Gynecology. The second study group consisted of 62 women with a priori elevated risk according to these guidelines. RESULTS: Fetal or neonatal death, pregnancy-induced hypertension, placental abruption, placenta previa, preterm delivery, delivery of infants with birth weights in the 2.3rd percentile, and complications during the third stage of labor occurred significantly more often in patients with elevated values and low a priori risk than in women with normal values and without pre-existing risk factors. There was no significant increase in adverse pregnancy outcome in women with elevated values and high a priori risk compared with women with normal values and elevated a priori risk. CONCLUSION: In women at low risk, elevated MSAFP and/or maternal serum hCG values are predictive of adverse pregnancy outcome. In women with a priori elevated risk, abnormal serum values do not increase this risk.

Adult↗
PubMed1999

Quantitative analysis of fetal general movements: methodological considerations.

OBJECTIVES: We studied the effects of gestational age and various smoothing procedures on four incidence parameters of fetal general movement, to evaluate reported variation in previous studies and to establish the optimal way of smoothing. SUBJECTS AND METHODS: General movements were studied longitudinally between 24 and 40 weeks of gestation in 29 healthy fetuses. The number of movement bursts per hour, burst duration, onset-onset interval between successive bursts (OOI) and the percentage incidence were analysed in detail. RESULTS: Advancing gestation was characterised by a proportional increase in OOI's lasting > 60 s and a decreased number of bursts, whereas burst duration remained relatively stable (unsmoothed data). Smoothing resulted in an exaggerated decrease in the number of bursts and in increases in burst duration, OOI and percentage incidence. These changes occurred in a gestational age specific manner and could largely explain the variation in results between previous studies. CONCLUSIONS: The temporal patterning of fetal general movements undergoes developmental change, as shown by differential effects of smoothing between mid and late pregnancy. A smoothing procedure is to be preferred which includes short intervals (1-3 s) between the elements composing a burst, since small changes in movement generation can still be recognised this way.

Adult↗