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Biomedical subjects

J H Kok

Publications and source records attributed to J H Kok.

At least 19 recordsLinked to original sources
PubMed2001

Postnatal thyroid hormone replacement in very preterm infants.

Transient hypothyroxinemia occurs frequently in very preterm infants and is caused by a combination of factors as immaturity of the hypothalamo-pituitary-thyroid system, loss of the maternal thyroxine (T4) contribution, immaturity of thyroid hormone metabolism, and neonatal illness. Thyroid hormone is important in maturation of the brain, but also of heart and lungs. Low neonatal T4 concentrations in plasma are related to worse clinical and neurodevelopmental outcome. Despite these relationships, only few randomized clinical trials have been performed to find out whether T4 supplementation can improve clinical and/or neurodevelomental outcome of preterm infants. The currently available evidence does not support use of supplemental T4 in all preterm infants. There are, however, indications that T4 might improve neurodevelopmental outcome in infants born before 27 to 29 weeks of gestation. Therefore, it is necessary that new trials are set up to further study the benefits of thyroid hormones given in the neonatal period of very preterm infants.

Hormone Replacement Therapy↗
PubMed2001

Efficacy of automated auditory brainstem response hearing screening in very preterm newborns.

OBJECTIVE: To investigate the efficacy of an automated auditory brainstem response (AABR) hearing screening method in very preterm newborns in the neonatal intensive care setting. STUDY DESIGN: In this prospective cohort study, 90 consecutive preterm newborns (<32 weeks' gestational age) had AABR hearing screening weekly from birth until a bilateral pass result was obtained. If the newborn had a unilateral pass result, AABR screening was repeated in the same week. Data were analyzed by using the Kaplan-Meier survival function technique, resulting in a cumulative pass rate curve for postmenstrual age. Cox's regression method was used to analyze the effect of co-variables, such as sex and growth restriction, on pass rates. RESULTS: Median gestational age was 29.5 weeks (range, 25.3-31.9 weeks), and median birth weight was 1115 g (range, 600-1960 g). Mean age was 6.2 days (SD 4.3) at first test, 15.7 (SD 8.1) at second test, and 21.4 (SD 8.6) at third test. Eighty percent (CI: 70.2%-89.8%) of the newborns passed at 30.3 weeks' postmenstrual age, 90% (CI: 83.6%-96.4%) passed at 31.2 weeks, and 100% passed at 34 weeks' postmenstrual age. The attainment of these pass rates correlated to postmenstrual age was not significantly influenced by sex, growth restriction, or gestational age at birth. Postnatal pass rates (in days) were strongly influenced by gestational age. CONCLUSION: AABR pass rates of >80% can be obtained from 30 weeks' postmenstrual age. Therefore AABR neonatal hearing screening can be used before discharge from a neonatal intensive care unit.

Brain Stem↗
PubMed2001

Neonatal thyroxine supplementation in very preterm children: developmental outcome evaluated at early school age.

OBJECTIVE: Transient hypothyroxinemia in very premature infants is associated with developmental problems. A randomized, placebo-controlled trial of thyroxine (T(4)) supplementation was conducted in a group of 200 infants <30 weeks' gestation. T(4) supplementation improved mental outcome at 2 years old in children of 25/26 weeks' gestation only. The effect of T(4) supplementation beyond 2 years of age is unknown. We present the effects of neonatal T(4) supplementation on outcome at early school age. METHODS: Standardized measurements were used to assess cognitive, behavioral, and motor outcome, as well as a qualitative assessment of neurologic functioning. Survivors of the T(4) trial were assessed at the age of 5.7 years. RESULTS: Ninety-nine percent of the 157 survivors participated. Outcome on all domains was comparable between the T(4) group and placebo group. In children <27 weeks' gestation, a 10 IQ point difference was found in favor of the T(4) group, whereas in children of 29 weeks' gestation, a difference of 15 IQ points was found in favor of the placebo group. Teachers' reports showed less behavioral problems in the T(4)-treated children of 25/26 weeks' gestation, but more behavioral problems in the T(4)-treated children of 27 weeks' gestation. Differences in motor outcome and neurologic outcome were in favor of the T(4)-treated children <29 weeks' gestation, but not of the T(4)-treated children of 29 weeks' gestation. CONCLUSIONS: We found benefits of T(4) supplementation for children <29 weeks' gestation, and especially in children of 25/26 weeks' gestation. However, in children of 29 weeks' gestation T(4) supplementation is associated with more developmental problems.

Child↗
PubMed2000

Neonatal effects of nifedipine and ritodrine for preterm labor.

OBJECTIVE: We compared nifedipine and ritodrine for treatment of preterm labor with respect to neonatal outcome. METHODS: We conducted an open randomized multicenter study of neonatal outcome in 185 women who received either oral nifedipine (n = 95) or intravenous (IV) ritodrine (n = 90) for treatment of preterm labor. Secondary outcome measures included neonatal mortality and morbidity, especially neonatal intensive care unit (NICU) admission, respiratory distress syndrome (RDS), and intracranial bleeding. RESULTS: There were no significant differences in umbilical artery pH values and Apgar scores between groups. Nifedipine was associated with lower admission rates to the NICU (49% versus 66%; odds ratio 0. 51, confidence interval 0.28, 0.93) compared with ritodrine, and lower incidences of RDS (21% versus 37%; 0.46, 0.24, 0.89), intracranial bleeding (18% versus 31%; 0.48, 0.24, 0.96), and neonatal jaundice (52% versus 67%; 0.53, 0.29, 0.97). Logistic regression analysis showed that even after correction for gestational age at birth, newborn risk of RDS, intracranial bleeding, or neonatal jaundice was significantly lower in the nifedipine group than the ritodrine group. CONCLUSION: Nifedipine for treatment of preterm labor was associated with a lower incidence of neonatal morbidity than ritodrine. That difference appeared to be partly because of the higher tocolytic efficacy of nifedipine and partly because of an intrinsic beneficial effect of nifedipine, or the lack of harmful effects when compared with ritodrine.

Adult↗
PubMed2000

Somatosensory evoked potentials in very preterm infants.

OBJECTIVE: Cross-sectional and longitudinal reference values of cortical N(1) peak latency of the median nerve SEP in very preterm infants. METHODS: In infants in a placebo control group within an L-thyroxine supplementation trial, born at less than 30 weeks' gestation, cortical N(1) peak latency was measured at 2 weeks, at term and at 6 months corrected age. Cross-sectional N(1) latency values obtained in 50 infants and complete series of longitudinal values obtained in 15 infants were analyzed in relation to postmenstrual age (PMA). RESULTS: Mean N(1) latency decreased from 66 ms at 2 weeks to 38 ms at term and 20 ms at 6 months corrected age. Possible confounding factors did not have any significant effect on N(1) latency at 2 weeks or at term age except cranial ultrasound abnormalities at 2 weeks of age. CONCLUSIONS: Longitudinal N(1) latency values were consistent with cross-sectional N(1) latency values. The observed N(1) latency at term and at 6 months corrected age suggest that extrauterine maturation of the somatosensory pathway in infants born at less than 30 weeks' gestation is delayed by extrauterine life.

Cross-Sectional Studies↗
PubMed2000

Changes in plasma thyroid hormone levels after a single dose of triiodothyronine in premature infants of less than 30 weeks gestational age.

OBJECTIVE: Evaluation of thyroid hormone response to a single administration of triiodothyronine (T3) early postnatally to premature infants of <30 weeks gestational age. DESIGN: A prospective clinical trial with historical control. METHODS: Ten infants born <28 weeks gestational age and ten infants born between 28 and 30 weeks gestational age were given 0.5 microg/kg T3 intravenously at 12 h after birth. The infants <28 weeks gestational age were also treated with thyroxine (T4; 8 microg/kg, once daily) during the first 6 weeks of life. Premature infants from a previous trial served as a matched historical control group. Analysis of variance for repeated measurements was performed. RESULTS: For the infants <28-30 weeks gestational age mean plasma T3 concentrations were significantly higher in the T3-treated group (P=0.027) for at least 2 weeks, whereas mean plasma levels of T4, free T4 and TSH were comparable. For the infants <28 weeks gestational age plasma T3 levels were also significantly different after correction for gestational age (P=0.0002), with either comparable or higher values in the T3-treated infants up to 56 days after injection of T3. Mean plasma free T4 levels were lower during the first 3 days and higher or comparable thereafter (P=0.0014), and TSH suppression was more evident in the T3-treated infants (P=0.003). CONCLUSION: A single administration of T3 to premature infants <30 weeks gestational age early postnatally results in a sustained increase of plasma T3 levels during the first weeks of life. In infants of 28-30 weeks gestational age this occurs without change in plasma free T4 levels, whereas in infants <28 weeks gestational age a transient decrease of plasma free T4 was present. The increase in plasma T3 is possibly caused by a T3-induced increase of type I deiodinase activity.

Blood Pressure↗
PubMed2000

Neurologic development of the newborn and young child in relation to maternal thyroid function.

A prospective observational study was performed in pregnant women with known thyroid disease. We studied the effect of maternal thyroid function in the first half of pregnancy on the neurologic development of the infant in the first 2 y of life. Clinical and thyroid function data were collected from 20 pregnant women with known thyroid disease and their newborn children. Infants were divided into three groups according to their maternal thyroid function within the first half of pregnancy: Group A (n = 7): maternal subclinical hypothyroidism, Group B (n = 6): maternal euthyroidism, and Group C (n = 7): maternal hyperthyroidism or subclinical hyperthyroidism. Neurophysiologic, i.e. motor nerve conduction velocity and somatosensory evoked potentials and neurologic and developmental (Bayley scales) assessments were done. One infant, born to a mother with Graves' disease, developed transient hyperthyroidism. At the age of 6 and 12 mo, the mean mental developmental index (MDI) score was 16 points lower for infants in Group A than for those in Group B (p = 0.03 and 0.02, respectively). At the age of 24 mo, the mean MDI score was 6 points lower, which was not statistically significant. Neurophysiologic and neurologic assessments and the mean Psychomotor Developmental scores did not differ among the three groups. In conclusion, maternal subclinical hypothyroidism in the first half of pregnancy was associated with a lower mean MDI score in their infants during the first year of life.

Developmental Disabilities↗
PubMed2000

Evaluation of a new system of lens parameter selection and comparison of traditional vs one-step lens care systems for aspheric high-Dk RGP contact lenses.

PURPOSE: We investigated the value of newly developed systems for parameter selection on the performance of high Dk rigid gas permeable (RGP) contact lenses with a spheric-aspheric design made of Boston Equa material in normal daily wear conditions. A comparison was also made between the safety and efficacy of a traditional care system vs a one-step chemical care system during the follow-up period of 1 year. METHODS: A total of 66 patients were randomly assigned to traditional and newly developed systems for computing the back optical zone radius (BOZR) and the total diameter (TD) of the lenses. Evaluation parameters incorporated assessment of fit, visual acuity, wearing time, comfort, and lens condition. RESULTS: The traditional method of computing the BOZR, using a method based on flat-K, predicted the BOZR successfully in 83% of the cases. Corneal topometry reached a lower, but not significantly different (P > 0.01) value of 75% correct prediction of BOZR. Analysis of the differences in eccentricity (E) values between quadrants per eye was a significant (P < 0.001) factor in fault predictions in the topometric system. A newly developed guide forTD selection performed, with 90% correct predictions, significantly (P < 0.01) better than a traditional method (72%) based on corneal diameter on supraversion. No significant differences (P > 0.05) were found in the capabilities of care systems (a traditional care system using a surfactant cleaner vs a one-step solution) to keep the lenses in proper condition and without deformation, over the 1 year follow-up period. The final success rate was 85%. CONCLUSIONS: Although high Dk RGP contact lenses can be fit and used with a 85% success rate using advanced systems for determining the BOZR and TD, it remains necessary to evaluate the fit before dispensing high Dk RGP lenses in 15% of the cases. The one-step solution used in this study was a good starting point for lens care. If needed, surfactant cleaning in the traditional care system can be done without the risk of lens deformation.

Adolescent↗
PubMed1999

Motor nerve conduction velocity in very preterm infants.

Sufficient reference values for motor nerve conduction velocity (MNCV) in very preterm infants are not yet available. In the placebo infants within an L-thyroxine supplementation trial, born at less than 30 weeks' gestation, ulnar and posterior tibial MNCV measurements were performed shortly after birth. Repeated measurements were done at 2 weeks, at term, and at 6 months corrected age. Cross-sectional MNCV values obtained in 50 infants and longitudinal MNCV values obtained in 15 infants were analyzed in relation to postmenstrual age (PMA). Mean ulnar MNCV increased from 13 to 44 m/s and mean tibial MNCV from 11 to 37 m/s. Motor nerve conduction velocity was clearly related to PMA. Longitudinal MNCV values were consistent with cross-sectional MNCV values. Possible confounding factors did not have any significant effect on MNCV. In the ulnar nerve, extrauterine maturation during the first 2 weeks of life was delayed compared with intrauterine maturation.

Aging↗
PubMed1999

Evaluation of the effect of thyroxine supplementation on behavioural outcome in very preterm infants.

Two-hundred infants of <30 weeks gestational age were included in a randomized double-blind controlled trial to study the effect of thyroxine administration on neurodevelopmental outcome in very preterm children. The infants were given either a fixed dose of thyroxine (8 microg/kg birthweight/day) or placebo for the first 6 weeks of life. This paper evaluates the effect of thyroxine administration on behavioural outcome at the age of 2 years. More externalizing, especially destructive, behaviours were found in the group given thyroxine than in the placebo group. This difference was more pronounced in boys and in children born after 27 weeks' gestation. The thyroxine-treated children with behavioural problems had lower plasma-free thyroxine levels than the thyroxine-treated children without behavioural problems. This finding suggests that the presence of more behavioural problems in the group given thyroxine was not an immediate consequence of the treatment.

Aggression↗
PubMed1999

Thyroid function in very preterm newborns: possible implications.

Thyroid hormones are essential for brain maturation. Very preterm infants, who are at risk of neurodevelopmental disabilities also have low thyroxine (T4) and free thyroxine (FT4) values in the first weeks after birth. This transient hypothyroxinemia may in part be causal to the neurodevelopmental problems. We have carried out a randomized, double-blind, placebo-controlled trial with T4 in 200 infants less than 30 weeks gestation. T4 (or placebo) was given in fixed dose of 8 microg/kg birth weight per day during the first 6 weeks after birth. It resulted in a significant increase of T4, FT4, and reverse triiodothyronine (rT3). Thyrotropin (TSH) secretion was suppressed, and, probably as a result of TSH suppression, triodothyronine (T3) levels were decreased in the T4 group. Mortality was 14% in the T4 group and 21% in the placebo group (NS). No effect was found on morbidity. Heart rate was significantly higher in T4-treated infants less than 28 weeks gestation, but not in T4-treated infants 28 weeks or more, who had the highest FT4 levels. In the study groups as a whole, no clear effect of T4 administration was found on neurodevelopmental outcome. However, there was a strong trend toward improvement of adverse outcome, defined as death or abnormal developmental outcome at 2 years of age. In addition, mental outcome in a subgroup of T4-treated infants less than 27 weeks' gestation was significantly better than in placebo infants of the same age group. In conclusion, this trial does not clearly have conclusive results. New trials of thyroid hormone treatment should be carried out in preterm infants, in order to investigate whether indeed T4 supplementation is required in preterm infants less than 27 or 28 weeks gestation. Addition of T3 to the treatment schedule needs to be considered.

Blood Proteins↗
PubMed1999

In vivo human corneal hydration control dynamics: a new model.

PURPOSE: To introduce a new model describing human in vivo corneal deswelling after hypoxic contact lens wear, based on a damped harmonic oscillator, which can describe an overshoot in corneal deswelling, to compare this new model with the currently used exponential model, and also to test whether a diurnal variation in baseline corneal thickness exists that would have to be taken into consideration when calculating corneal deswelling curves. METHODS: In nine healthy young adults, corneal thickness was measured every 30 minutes for 11.5 hours on average using modified optical pachometry (natural test). On another day, corneal deswelling was monitored for 11.1 hours on average after 2 hours of hypoxic contact lens wear (stress test). The damped harmonic oscillator model and the exponential model were used to calculate best-fitting deswelling curves. Natural test data were analyzed for the presence of a trend. Goodness of fit of the curves to the experimental data was analyzed using the F test. RESULTS: In 82% of the deswelling curves the new damped harmonic oscillator model provided a better fit to the data than the exponential model (P < 0.05). An average overshoot in corneal thickness recovery of 5 microm (range, 0-11 microm) was found. In 50% of the natural tests significant trends were found, without any consistent similarities. The overshoot could not be explained by these trends. CONCLUSIONS: The new damped harmonic oscillator model describes corneal deswelling after hypoxic contact lens wear more accurately than the exponential model. No consistent diurnal variation could be demonstrated.

Adult↗
PubMed1998

Neurodevelopmental outcome at three years of age after fetal 'brain-sparing'.

Intrauterine growth restriction (IUGR), occurring preterm, may be related to impaired neurodevelopmental outcome. We measured neurodevelopmental outcome (Hempel examination) at the age of three years in a cohort of infants born between 26 and 33 weeks in 1989. Fetuses were studied haemodynamically, using Doppler ultrasound. The ratio between the umbilical and the cerebral artery Pulsatility Index (U/C ratio) was calculated. This is a measure of redistribution of fetal blood preferentially to the brain and this may be a marker of fetal adaptation to placental insufficiency. Impaired fetal growth was also measured by the fetal growth ratio. Neonatal cranial ultrasound was performed to document intracranial haemorrhages and/or ischaemia. From the original cohort of 106 infants, 96 (91%) infants were examined at three years. After adjustment for obstetric variables, adverse Hempel outcome was related to neonatal cranial ultrasound abnormality and low head circumference at three years. Neither the U/C ratio nor fetal growth were independently associated with Hempel outcome. Fetal 'brain-sparing' in IUGR appears to be a benign adaptive mechanism preventing severe brain damage.

Brain↗
PubMed1998

Motor nerve conduction velocity in very preterm infants in relation to L-thyroxine supplementation.

BACKGROUND: Transient hypothyroxinemia is common in preterm infants and has been associated with neurodevelopmental dysfunction and slow nerve conduction velocity. It is still unknown whether L-thyroxine supplementation is required. During an L-thyroxine supplementation trial, motor nerve conduction velocity was measured to answer the question whether L-thyroxine supplementation improves motor nerve conduction velocity. METHODS: Two hundred infants < 30 weeks' gestational age were enrolled in a randomized, double-blind, placebo-controlled L-thyroxine supplementation trial. L-Thyroxine (8 micrograms/kg birthweight per day) or a placebo was administered during the first 6 weeks of life. Motor nerve conduction velocity was measured in the ulnar and posterior tibial nerve shortly after birth, at 2 weeks, at 40 weeks, and at 66 weeks postmenstrual age. RESULTS: At 2 weeks, the ulnar motor nerve conduction velocity had improved in the L-thyroxine group compared with the placebo group, although the difference was not statistically significant (difference between means: 0.8 msec; 95% CI: -0.13 to 1.80; p = 0.06). Later on, no effect of L-thyroxine supplementation on motor nerve conduction velocity was found. CONCLUSION: This study shows that in infants < 30 weeks' gestational age L-thyroxine supplementation during the first 6 weeks of life does not clearly improve motor nerve conduction velocity.

Double-Blind Method↗
PubMed1998

Outcome of very preterm small for gestational age infants: the first nine years of life.

OBJECTIVE: To determine the influence of intrauterine growth retardation of preterm infants on mortality and cognitive development. DESIGN: A nationwide study cohort of very preterm and/or small for gestational age infants (< 32 weeks and/or < 1500 g) born alive in 1983 in the Netherlands. Assessment on neuromotor and cognitive development at five years, and a parental questionnaire on school performance at nine years. Cognitive outcome is defined as handicap for mental and speech-language development, and need for special education. SAMPLE: 134 small for gestational age infants (< 10th centile) and 410 appropriate for gestational age infants (between 25th and 75th centile) of all infants between 25 and 32 weeks of gestational age were identified; infants with congenital malformations and not of caucasian race were excluded. MAIN OUTCOME MEASURES: Neonatal mortality, in-hospital and five years mortality; Cognitive outcome at five years; School performance at nine years. RESULTS: The mortality risk for small for gestational age compared with appropriate for gestational age infants was significantly higher, after adjustment for gestational age, sex, multiple pregnancy and mode of delivery (OR 2.56, 95% CI 1.26-5.26). Small for gestational age infants showed more often gross motor and minor neurological dysfunction, but less cerebral palsy than appropriate for gestational age infants. Cognitive outcome at five years in small for gestational age infants was significantly worse than appropriate for gestational age infants stratified for mode of delivery OR 2.44 (95% CI 1.05-5.55). At nine years of age significantly more small for gestational age infants (16.4%) needed special education than appropriate for gestational age infants (11.9%). CONCLUSION: Intrauterine growth retardation increases the risk of mortality and of cognitive disorders.

Child↗
PubMed1998

Thyroxine administration to infants of less than 30 weeks gestational age decreases plasma tri-iodothyronine concentrations.

OBJECTIVE: To investigate the effect on thyroid hormone metabolism of the administration of thyroxine to very preterm infants. DESIGN AND METHODS: Two hundred infants of less than 30 weeks gestation were enrolled into a randomized, double-blind, placebo-controlled trial. Thyroxine (T4) (at a fixed daily dose of 8 microg/kg birthweight) or placebo was started 12-24h after birth and discontinued 6 weeks later. Plasma concentrations of T4, tri-iodothyronine (T3), reverse T3 (rT3), TSH, and thyroxine-binding globulin were measured weekly during trial medication and 2 weeks thereafter. RESULTS: The T4 and the placebo group each comprised 100 infants. Antenatal, perinatal, and postnatal clinical characteristics were comparable in both groups. T4 and rT3 were significantly increased in the T4 group. TSH concentrations were depressed in the T4 group and T3 was significantly decreased, probably as a result of TSH depression. The T4/T3 and T4/rT3 ratios differed significantly between the two study groups. CONCLUSIONS: Daily T4 administration during the first 6 weeks after birth to infants of less than 30 weeks gestation prevents hypothyroxinemia, but decreases plasma T3 concentrations. Our finding possibly implies that very preterm infants should receive supplements of both T4 and T3.

Depression, Chemical↗
PubMed1998

Somatosensory evoked potentials in very preterm infants in relation to L-thyroxine supplementation.

OBJECTIVE: To study the effect of L-thyroxine supplementation on neurologic maturation in very preterm infants with transient hypothyroxinemia. DESIGN: Randomized, double-blind, placebo-controlled, L-thyroxine supplementation trial. SETTING: Level III neonatal intensive care unit. SUBJECTS: A total of 200 infants <30 weeks' gestational age. INTERVENTION: Subjects were randomly assigned to receive L-thyroxine (8 microg/kg birth weight per day) or a placebo during the first 6 weeks of life. METHODS: Median nerve somatosensory evoked potentials were recorded, measuring cortical N1 peak latency at 2 weeks of age, at term, and at 6 months (corrected) age. RESULTS: Cortical N1 peak latency was not decreased significantly in the L-thyroxine group compared with the placebo group throughout the study period. CONCLUSION: L-Thyroxine supplementation during the first 6 weeks of life did not decrease cortical N1 peak latency in infants of <30 weeks' gestational age.

Double-Blind Method↗