Biomedical subjects

M Mirmiran

Publications and source records attributed to M Mirmiran.

At least 19 recordsLinked to original sources

PubMed2000

Predictive value of neonatal neurological tests for developmental outcome of preterm infants.

BACKGROUND: There is a need to identify, as early as possible, infants who are at risk for long-term neurological morbidity. METHODS: To predict neurodevelopment outcome of preterm infants <30 weeks' gestation in a population of 100 infants, we used several neonatal and neurobehavioral tests, including cranial ultrasonography, the Prechtl neurological test, quality of spontaneous general movements, and quality of sleep-wake organization. RESULTS: The Prechtl test at corrected term age and findings on cranial sonograms both had high specificity, but the Prechtl test had better overall positive predictive power for normal neurological and developmental outcomes at 2 years' corrected age. Developmental changes in sleep and the amount of indeterminate sleep did not correlate with outcome. Scoring general movement quality did not predict outcome and did not augment the positive predictive power of the Prechtl test. CONCLUSIONS: The Prechtl test at corrected term age (independent of the other tests) is the best positive predictor of normal neurological outcome and Bayley test results at 2 years' corrected age.

Developmental Disabilities↗

PubMed1999

Dietary 18:3n-3 and 22:6n-3 as sources of 22:6n-3 accretion in neonatal baboon brain and associated organs.

The bioequivalence of dietary linolenic acid (LNA) and docosahexaenoic acid (DHA) for brain DHA accretion was measured in neonatal baboons at 4-6 wk of age using stable isotope tracers. Neonates consumed a conventional U.S. term-infant formula devoid of long chain polyunsaturates and with an n-6/n-3 ratio of about 10:1. At 4 wk of age, neonates were dosed with either 13C LNA or 13C DHA. At 6 wk of age, neonate brain, retina, and other organs were harvested for fatty acid and isotopic analyses. The relative accretion of labeled DHA was 7-fold greater as a percentage of dose for the DHA-dosed animals compared to the LNA-dosed animals. The baboon is an omnivore that regularly consumes meat and insects; its plasma lipid profile responds similarly to humans in response to changes in feeding and living habits. These observations suggest that the baboon is a suitable model for human unsaturated fatty acid studies.

Animals↗

PubMed1999

Effects of prone and supine position on sleep characteristics in preterm infants.

The purpose of this study was to address the influence of sleep position on sleep characteristics in preterm infants. We studied 16 infants at a mean post-conceptional age of 36.5 weeks. Infants were successfully recorded with videopolysomnograph in the supine and prone position. Between the two positions, there were no significant differences in percentage of active sleep and quiet sleep (QS), the occurrence of arousal, and the incidence of apnea. The first QS after the feeding was longer in the prone position. The sleep position could affect sleep characteristics but not respiratory characteristics in preterm infants.

Arousal↗

PubMed1999

Effects of skin-to-skin holding on general movements of preterm infants.

The study objective was to test the hypothesis that the effect of skin-to-skin (STS) holding increases the ratio of rest to activity in low birth weight preterm infants. Ten infants with birthweight < 2,000 grams were videotaped before and after STS holding. Video recordings were analyzed to determine the number of general movements. We found no statistically significant difference between the percentage of general movements over the two periods. We conclude that the ratio of rest-activity before and after STS holding does not change as measured by occurrence of general movements.

Female↗

PubMed1999

Bioequivalence of dietary alpha-linolenic and docosahexaenoic acids as sources of docosahexaenoate accretion in brain and associated organs of neonatal baboons.

The dietary bioequivalence of alpha-linolenic (LNA) and docosahexaenoic acids (DHA) as substrates for brain and retinal n-3 fatty acid accretion during the brain growth spurt is reported for neonatal baboons who consumed a long-chain-polyunsaturate free commercial human infant formula with a n-6/n-3 ratio of 10:1. Neonates received oral doses of 13C-labeled fatty acids (LNA*) or (DHA*) at 4 wk of age, and at 6 wk brain (occipital cortex), retina, retinal pigment epithelium, liver, erythrocytes, and plasma were analyzed. In the brain, 1.71% of the preformed DHA* dose was detected, whereas 0.23% of the LNA* dose was detected as DHA*, indicating that preformed DHA is 7-fold more effective than LNA-derived DHA as a source for DHA accretion. In LNA*-dosed animals, DHA* was greater than 60% of labeled fatty acids in all tissues except erythrocytes, where docosapentaenoic acid was 55%. Estimates using dietary LNA levels as tracees indicate that brain turnover of DHA is less than 5% per week between weeks 4 and 6 of life. For retina and retinal pigment epithelium, preformed DHA was at levels 12-fold and 15-fold greater than LNA-derived DHA. Liver, plasma, and erythrocytes ratios were 27, 29, and 51, respectively, showing that these pools do not parallel tissue metabolism of a single dose of omega-3 fatty acids. The distributions of labeled fatty acids for LNA*-dosed animals were similar, in the order DHA > DPA > EPA > LNA, except for erythrocytes where docosapentaenoic acid predominated. These are the first direct measurements of the bioequivalence of DHA and LNA in neonatal primate brain and associated tissues.

Administration, Oral↗

PubMed1999

More awakenings and heart rate variability during supine sleep in preterm infants.

OBJECTIVE: The Task Force of The American Academy of Pediatrics (1996) recommends the nonprone sleeping position for asymptomatic preterm infants to prevent sudden infant death syndrome. The mechanism by which the nonprone sleeping position reduces the rate of sudden infant death syndrome is unclear for full-term infants and the precise effect of sleeping position on sleep and cardiorespiratory characteristics has never been addressed in preterm infants. The purpose of the present study was to clarify the effect of sleeping position on sleep and cardiorespiratory characteristics in preterm infants at an age when they are ready for discharge. STUDY DESIGN: Sixteen asymptomatic preterm infants were studied in both supine and prone sleeping positions at 36.5 +/- 0.6 weeks' postconceptional age using videosomnography. Sleep, respiratory, and heart rate characteristics were compared between the two positions using each infant as his/her own control. RESULTS: More awakenings (ie, arousals >/=60 seconds) were seen during all sleep states in the supine sleeping position but overall the total sleep and percent sleep state were not affected by sleeping position. After each feeding, the first quiet sleep was significantly shorter, with more heart rate variability and awakenings in the supine position. There were no significant differences in the occurrence of arousals (<60 seconds) or the incidence or severity of apnea and periodic breathing. No clinically significant apnea (>/=15 seconds), bradycardia, or oxygen desaturations were seen. CONCLUSION: In 36-week-postconceptional age preterm infants, the supine sleeping position had less quiet sleep and was associated with greater heart rate variability during the first sleep cycle after the feeding. More awakenings were seen during all sleep states in the supine position. These data support the American Academy of Pediatrics recommendation for "Back to Sleep" for asymptomatic preterm infants because more awakenings and lower threshold for arousal may provide some benefit for the infant responding to a life-threatening event. However, further studies are needed to address positional effect on the physiologic measures in preterm infants at older ages (later stages of development). Precisely what constitutes the most healthy or advantageous sleep for newborn infants remains an important question.

Arousal↗

PubMed1998

Fetal and maternal diurnal rhythms during the third trimester of normal pregnancy: outcomes of computerized analysis of continuous twenty-four-hour fetal heart rate recordings.

OBJECTIVE: We quantified the presence of diurnal rhythms in various computerized fetal heart rate parameters in normal pregnancies to assess their clinical relevance. STUDY DESIGN: Modified cosine analysis was applied to the outcomes of computerized analysis of continuous 24-hour fetal heart rate recordings in 26 normal pregnancies. Diurnal rhythms in maternal heart rate and plasma hormones were assessed in 15 and 17 pregnancies, respectively. Correlations between maternal and fetal rhythms were calculated. RESULTS: A significant diurnal rhythm in basal heart rate was present in 73% of the fetuses and was closely related to the maternal heart rate rhythm. Diurnal rhythms in heart rate variability, accelerations, and activity were present in only 30% to 50% of the fetuses. CONCLUSIONS: The mother entrains fetal diurnal rhythms. The normal variability in neural development may account for the absence of diurnal rhythms in some fetuses.

Circadian Rhythm↗

PubMed1998

Development of macronutrient composition of very preterm human milk.

The effects of gestational age at delivery (GA), postnatal age (PNA) and post-menstrual age (PMA = PNA + GA, an indicator of autonomous developmental processes not affected by the moment of birth) on macronutrient composition of very preterm milk were studied. Total N, fat, lactose and carbohydrate concentrations, energy density and 24 h volume were determined in 282 24 h milk samples collected at weekly intervals (days 7-55 of lactation) from seventy-nine women delivering their babies between 25 and 29 weeks of gestation. GA related differences were found for carbohydrate concentration only: carbohydrate concentration was lower with increasing GA. PNA was related to a decrease in total N and an increase in lactose concentration. PMA was not related to milk composition. Our data indicate that PNA strongly influences the development of the composition of very preterm human milk, while GA affects carbohydrate content with a negligible effect on the nutritional value of the milk. We conclude that in accordance with current opinion in paediatrics, human milk is the best source of nutrients even for very preterm (< 30 weeks GA) infants.

Analysis of Variance↗

PubMed1998

A new actigraph for long-term registration of the duration and intensity of tremor and movement.

Actigraphy, the long-term measurement of human movement with a small solid state recorder, is gaining acceptance as a useful method in many research fields. Currently available actigraphs assess or estimate the movement duration per time interval. However, the output gives no information on movement type or intensity, and cannot be used in subjects suffering from tremor. The present paper describes a new type of actigraph, that has been developed primarily for the long-term evaluation of motor symptoms in Parkinson patients. The device is the first to discriminate tremor from other movements and to assess both duration and intensity of the two types of movement. It is based on a Motorola 68HC805B6 microcontroller and contains: an accelerometer, programmable gain stages, programmable low- and highpass filters, a programmable level comparator, a peak detector, interface circuits, a real time clock, data storage, and control circuitry. The micro-controller performs a period amplitude sequence analysis (PASA) on the conditioned accelerometer signal, and stores four output variables (tremor duration, tremor amplitude, movement duration, and movement amplitude) at the end of programmable time intervals. The analysis of fluctuations in the motor symptoms of, e.g., Parkinson patients using this actigraph can be of great help in the pharmacological management of symptoms.

Aged↗

PubMed1998

Membrane properties and morphology of vasopressin neurons in slices of rat suprachiasmatic nucleus.

Vasopressin (VP) neurons in the suprachiasmatic nucleus (SCN) are thought to be closely linked to neural mechanisms for circadian timekeeping. To gain insight into the cellular-physiological principles that govern spike-driven VP release and to examine whether VP cells can be electrophysiologically and morphologically identified by a unique combination of features, we recorded membrane properties by whole cell patch-clamp methods and stained the cells with biocytin. In current-clamp mode, VP neurons recorded during subjective daytime expressed a clear time-dependent inward rectification but no pronounced low-threshold Ca2+ potential after hyperpolarizing current pulses. Their spontaneous firing rate varied between 0.6 and 13.4 Hz and was generally tonic and irregular. Spike afterhyperpolarizations (AHPs) were steeply rising and monophasic. Spikes were preceded by depolarizing ramps mediated by a slow component of Na+ current. Spike trains evoked by depolarizing current pulses displayed frequency adaptation and were usually followed by an AHP lasting 0.5-2.0 s. Spontaneous postsynaptic potentials were present in a majority of cells. Voltage-clamp recordings revealed a Ba2+-sensitive K+ current that exerts a tonic, hyperpolarizing influence on the membrane potential. This set of membrane properties was not significantly different from other cells in the dorsomedial region and is characteristic for cluster I cells, which were described previously and are widely encountered throughout the SCN. None of the cells could be classified as belonging to cluster II or III, which were indeed found mainly outside the dorsomedial region. Morphologically, single VP neurons were characterized by compact, mono- or bipolar dendritic branching patterns and numerous varicosities throughout the dendrites. They generally possessed few axon collaterals, most of which remained inside the boundaries of the SCN but were occasionally seen to project to SCN target areas. In conclusion, VP neurons in the SCN express several active membrane poperties, including time-dependent inward rectification, frequency adaptation in spike trains, monophasic spike AHPs, and Ba2+-sensitive K+ current. VP release is proposed to be governed by tonic and irregular patterns of spontaneous firing. The electrophysiological and cytological properties of VP neurons are representative for a majority of SCN cells and define them as a subset of previously defined cluster I cells.

Action Potentials↗

PubMed1997

Indirect bright light improves circadian rest-activity rhythm disturbances in demented patients.

Light is known to be an important modulator of circadian rhythms. We tested the hypothesis than an enduring increase in the daytime environmental illumination level improves rest-activity rhythm disturbances in demented patients. Actigraphy was performed before, during, and after 4 weeks of increased illumination in the living rooms of 22 patients with dementia clinically diagnosed as probable Alzheimer's disease, multi-infarct dementia, dementia associated with alcoholism, or normal pressure hydrocephalus. The results indicated that during increased illumination, the stability of the rest-activity rhythm increased in patients with intact vision, but not in visually impaired patients.

Aged↗

PubMed1997

The diurnal rhythm in fetal heart rate in a twin pregnancy with discordant anencephaly: comparison with three normal twin pregnancies.

In a discordant anencephalic twin the hypothesis was tested that the fetal brain is necessary for the expression of a diurnal rhythm in fetal heart rate. Fetal heart rate recordings were made over a 24 h period in a discordant anencephalic twin pregnancy and in three normal twin pregnancies. Cosinor analysis was used to assess rhythmicity in fetal heart rate and maternal heart rate or activity. Correlations between maternal and fetal rhythms were calculated. A significant diurnal rhythm was found for the fetuses of the control twins, but in neither of the fetuses of the discordant anencephalic twin pregnancy. The maternal rhythm was 1-2 h in advance of the heart rate rhythms in all fetuses except the anencephalic one, whose heart rate did not show any correlation with the maternal diurnal rhythm. We conclude that the fetal brain contributes to the generation of the diurnal rhythm in fetal heart rate and synchronization of maternal-fetal rhythms.

Adult↗

PubMed1997

Long-term fitness training improves the circadian rest-activity rhythm in healthy elderly males.

In old age, the circadian timing system loses optimal functioning. This process is even accelerated in Alzheimer's disease. Because pharmacological treatment of day-night rhythm disturbances usually is not very effective and may have considerable side effects, nonpharmacological treatments deserve attention. Bright light therapy has been shown to be effective. It is known from animal studies that increased activity, or an associated process, also strongly affects the circadian timing system, and the present study addresses the question of whether an increased level of physical activity may improve circadian rhythms in elderly. In the study, 10 healthy elderly males were admitted to a fitness training program for 3 months. The circadian rest-activity rhythm was assessed by means of actigraphy before and after the training period and again 1 year after discontinuation. As a control for possible seasonal effects, repeated actigraphic recordings were performed during the same times of the year as were the pre and post measurements in a control group of 8 healthy elderly males. Fitness training induced a significant reduction in the fragmentation of the rest-activity rhythm. Moreover, the fragmentation of the rhythm was negatively correlated with the level of fitness achieved after the training. No seasonal effect was found. Previous findings in human and animal studies are reviewed, and several possible mechanisms involved in the effect of fitness training on circadian rhythms are discussed. The results suggest that fitness training may be helpful in elderly people suffering from sleep problems related to circadian rhythm disturbances.

Activity Cycles↗

PubMed1997

Developmental care does not alter sleep and development of premature infants.

OBJECTIVE: The Neonatal Individualized Developmental Care Program (NIDCAP) for very low birth weight (VLBW) preterm infants has been suggested by Als et al to improve several medical outcome variables such as time on ventilator, time to nipple feed, the duration of hospital stay, better behavioral performance on Assessment of Preterm Infants' Behavior (APIB), and improved neurodevelopmental outcomes. We have tested the hypothesis of whether the infants who had received NIDCAP would show advanced sleep-wake pattern, behavioral, and neurodevelopmental outcome. METHODS: Thirty-five VLBW infants were randomly assigned to receive NIDCAP or routine infant care. The goals for NIDCAP intervention were to enhance comfort and stability and to reduce stress and agitation for the preterm infants by: a) altering the environment by decreasing excess light and noise in the neonatal intensive care unit (NICU) and by using covers over the incubators and cribs; b) use of positioning aids such as boundary supports, nests, and buntings to promote a balance of flexion and extension postures; c) modification of direct hands-on caregiving to maximize preparation of infants for, tolerance of, and facilitation of recovery from interventions; d) promotion of self-regulatory behaviors such as holding on, grasping, and sucking; e) attention to the readiness for and the ability to take oral feedings; and f) involving parents in the care of their infants as much as possible. The infants' sleep was recorded at 36 weeks postconceptional age (PCA) and at 3 months corrected age (CA) using the Motility Monitoring System (MMS), an automated, nonintrusive procedure for determining sleep state from movement and respiration patterns. Behavioral and developmental outcome was assessed by the Neurobehavioral Assessment of the Preterm Infant (NAPI) at 36 weeks PCA, the APIB at 42 weeks PCA, and by the Bayley Scales of Infant Development (BSID) at 4, 12, and 24 months CA. RESULTS: Sleep developmental measures at 3 months CA showed a clear developmental change compared with 36 weeks PCA. These include: increased amount of quiet sleep, reduced active sleep and indeterminate sleep, decreased arousal, and transitions during sleep. Longest sleep period at night showed a clear developmental effect (increased) when comparing nighttime sleep pattern of infants at 3 months with those at 36 weeks of age. Day-night rhythm of sleep-wake increased significantly from 36 weeks PCA to 3 months CA. However, neither of these sleep developmental changes showed any significant effects of NIDCAP intervention. Although all APIB measures showed better organized behavior in NIDCAP patients, neither NAPI nor Bayley showed any developmental advantages for the intervention group. The neurodevelopmental outcome measured by the Bayley at 4, 12, and 24 months CA showed 64% of the NIDCAP intervention group at the lowest possible score compared with 33% of the control group. These findings could not be explained by the occurrence of intraventricular hemorrhage or the socioeconomic status of the parents, which showed no significant group effect. CONCLUSION: The results of this study, including measures of sleep maturation and neurodevelopmental outcome up to 2 years of age did not demonstrate that the NIDCAP intervention results in increased maturity or development. Buehler et al (Pediatrics. 1995;96:923-932) have reported that premature infants (N = 12; mean gestational age 32 weeks, mean birth weight 1700 g) who received developmental care compared with a similar group of infants who received routine care showed better organized behavioral performance on an APIB assessment at 42 weeks PCA. None of the medical outcome measures were significantly different in this study. Although our APIB results are in agreement, the results of the NAPI, the Bayley and sleep measures do not show an increase in neurodevelopmental maturation. In the earlier report by Als et al (Journal of the American Medical Associatio

Adult↗

PubMed1996

Circadian rest-activity rhythm disturbances in Alzheimer's disease.

Previous studies showed circadian rhythm disturbances in patients with Alzheimer's disease. Rest-activity rhythm disturbances manifest themselves through a fragmentation of the rhythm, a weak coupling with Zeitgebers, and high levels of activity during the night. The aim of the present study was to investigate which factors contribute to the presence of these disturbances. Therefore, several rest-activity rhythm, constitutional, and environmental variables were assessed in a heterogeneous group of 34 patients with Alzheimer's disease, including presenile and senile patients living at home or in a nursing home, as well as in 11 healthy controls. Circadian rest-activity rhythm disturbances were most prominent in institutionalized patients. Regression analyses showed the involvement of the following variables. First stability of the rest-activity rhythm is associated with high levels of daytime activity and high levels of environmental light resulting from seasonal effects as well as from indoor illumination. Presenile onset contributed to instability of the rhythm. Second, fragmentation of periods of activity and rest is associated with low levels of daytime activity, and is most prominent in moderately severe dementia. Third, night-time activity level is higher during the times of the year when the days are getting shorter and lower when the days are growing longer. These findings indicate that rest-activity rhythm disturbances may improve by increasing environmental light and daytime activity, an assumption for which empirical evidence has recently been published.

Aged↗

PubMed1996

Gravitational artefact in frequency spectra of movement acceleration: implications for actigraphy in young and elderly subjects.

Actigraphy, the long-term assessment of wrist movements by means of a small solid-state recorder, is widely used in a variety of human research fields, among which sheep, circadian rhythms and aging. Actigraphs assess movement with the use of accelerometers, which sense accelerations resulting from muscle force as well as accelerations due to changes in the position of the sensor in the gravitational field. In the present paper a method is described to minimise gravitational artefact in movement assessment by calculating the instantaneous acceleration vector from 3 perpendicular acceleration signals. It is shown that the power spectra of single axis acceleration signals are dominated by low-frequency components (+/- 0.25 Hz) due to gravitational artefact. Spectra of the instantaneous acceleration vector indicate that 'true' movement accelerations resulting from muscle force are present in a much wider range: from 0.25 to 11 Hz. Wrist accelerations in elderly subjects were found to be of lower amplitude and frequency as compared to young subjects. It is furthermore shown that a bandpass filter of 0.25 to 2 or 3 Hz, as has been used in commercially available actigraphs, is far from optional, and may even result in a positive bias for movement detection in the elderly. This bias may underly contradictory findings in actigraphic studies on human aging. When a bandpass filter of 0.5-11 Hz is applied to a single-axis acceleration signal, the influence of gravitational artefact and bias are minimized, and the age-related decline in activity is properly detected.

Acceleration↗

PubMed1996

An on-line automated sleep-wake classification system for laboratory animals.

A computerized sleep-wake classification program is presented that is capable of classifying sleep-wake states on-line in four animals simultaneously. Every 10 s the classification algorithm assigns sleep-wake states on the basis of the power spectrum of an EEG signal and the standard deviation of an EMG signal. The system was developed specifically for long-term circadian rhythm experiments and can run uninterrupted for an unlimited period of time. To validate the system a total of 5760 sleep-wake epochs from 4 rats was classified both visually and by computer. The results show a good agreement between visual and computer automated (kappa = 0.770) sleep-wake scoring. Therefore, the presented sleep-wake classification system can be regarded as a reliable time saving alternative for visual scoring in sleep research.

Animals↗

PubMed1996

Is brain plasticity preserved during aging and in Alzheimer's disease?

Alzheimer's disease is a progressive neurodegenerative disorder believed to involve selective neuronal cell atrophy/loss in certain brain regions. The progress of the disease is accompanied by selective cognitive impairments and behavioral disturbances. The hypothesis has been put forward that by activation of selective brain areas throughout life one might protect or delay the degenerative process. This hypothesis, paraphrased as "a differential level of brain cell activity may account for cell selective loss" or "use it or lose it", further suggests that a certain level of neuronal plasticity persists during aging and even in Alzheimer's disease.

Aging↗