Interhemispheric connectivity estimated from EEG time-correlation analysis in preterm infants with normal follow-up at age of five.

Brain connectivity is associated with axonal connections between brain structures. Our goal was to quantify the interhemispheric neuronal connectivity in healthy preterm infants by automated quantitative EEG time-correlation analysis. As with advancing postmenstrual age (PMA, gestational age + postnatal age) the neuronal connectivity between left and right hemisphere increases, we expect to observe changes in EEG time-correlation with age. Thirty-six appropriate-for-gestational age preterm infants (PMA between 27-37 weeks) and normal neurodevelopmental follow-up at 5 years of age were included. Of these, 22 infants underwent 3-8 repeated EEG recordings at weekly intervals. The reduced 10-20 EEG electrode system for newborns was used with five sets of bipolar channels: central-temporal, frontal polar-temporal, frontal polar-central, temporal-occipital and central-occipital. We performed EEG time-correlation analysis between homologous channels of the brain hemispheres to identify interhemispheric similarity in EEG signal shape. For each 8 s epoch of the EEG the time-correlation values and the corresponding lag times were calculated for homologous channels on both hemispheres. In all channels, the median correlation value decreased significantly (between -40% and -60% decrease) from 27 to 37 weeks PMA, for gestational maturation. For the postnatal maturation only the central-temporal channel showed a significantly decreasing trend. In contrast, the median lag time showed no uniform change with PMA. The decreasing median correlation values in all homologous channels indicate a decrease in similarity in signal shape with advancing PMA. This finding may reflect greater functional differentiation of cortical areas in the developing preterm brain and may be explained by the increase of complex neural networks with excitatory and inhibitory circuitries.

Functional connectivity in preterm infants derived from EEG coherence analysis.

OBJECTIVE: To quantify the neuronal connectivity in preterm infants between homologous channels of both hemispheres. METHODS: EEG coherence analysis was performed on serial EEG recordings collected from preterm infants with normal neurological follow-up. The coherence spectrum was divided in frequency bands: δnewborn(0-2 Hz), θnewborn(2-6 Hz), αnewborn(6-13 Hz), ßnewborn(13-30 Hz). Coherence values were evaluated as a function of gestational age (GA) and postnatal maturation. RESULTS: All spectra show two clear peaks in the δnewborn and θnewborn-band, corresponding to the delta and theta EEG waves observed in preterm infants. In the δnewborn-band the peak magnitude coherence decreases with GA and postnatal maturation for all channels. In the θnewborn-band, the peak magnitude coherence decreases with GA for all channels, but increases with postnatal maturation for the frontal polar channels. In the ßnewborn-band a modest magnitude coherence peak was observed in the occipital channels, which decreases with GA. CONCLUSIONS: Interhemispherical connectivity develops analogously with electrocortical maturation: signal intensities at low frequencies decrease with GA and postnatal maturation, but increase at high frequencies with postnatal maturation. In addition, peak magnitude coherence is a clear trend indicator for brain maturation. SIGNIFICANCE: Coherence analysis can aid in the clinical assessment of the functional connectivity of the infant brain with maturation.

Treatment options for active removal of renal stones.

This study provides an update on the technological aspects of the methods for active removal of renal stones. Currently, extracorporeal shock wave lithotripsy (ESWL), ureteroscopy (URS) and percutaneous nephrolithotomy (PCNL) are the available options. Findings are based upon recent literature from the PubMed database and the European Association of Urology (EAU) guidelines. ESWL remains the option of choice for stones with diameter ≤ 20 mm due to its low invasive character, whereas PCNL is the standard for stones with diameter > 20 mm because of its high stone-free rates. Although ESWL treatment has become more patient friendly, its efficacy has not improved. On the other hand, URS has gained renewed interest due to new technological developments and improved treatment methods.

Beat-to-beat heart rate detection in multi-lead abdominal fetal ECG recordings.

Reliable monitoring of fetal condition often requires more information than is provided by cardiotocography, the standard technique for fetal monitoring. Abdominal recording of the fetal electrocardiogram may offer valuable additional information, but unfortunately is troubled by poor signal-to-noise ratios during certain parts of pregnancy. To increase the usability of abdominal fetal ECG recordings, an algorithm was developed that enhances fetal QRS complexes in these recordings and thereby provides a promising method for detecting the beat-to-beat fetal heart rate in recordings with poor signal-to-noise ratios. The method was evaluated on generated recordings with controlled signal-to-noise ratios and on actual recordings that were performed in clinical practice and were annotated by two independent experts. The evaluation on the generated signals demonstrated excellent results (sensitivity of 0.98 for SNR≥1.5). Only for SNR<2, the inaccuracy of the fetal heart rate detection exceeded 2 ms, which may still suffice for cardiotocography but is unacceptable for analysis of the beat-to-beat fetal heart rate variability. The sensitivity and positive predictive value of the method in actual recordings were reduced to approximately 90% for SNR≤2.4, but were excellent for higher signal-to-noise ratios.

A continuous wavelet transform-based method for time-frequency analysis of artefact-corrected heart rate variability data.

Time-frequency analysis of heart rate variability (HRV) provides relevant clinical information. However, time-frequency analysis is very sensitive to artefacts. Artefacts that are present in heart rate recordings may be corrected, but this reduces the variability in the signal and therefore adversely affects the accuracy of calculated spectral estimates. To overcome this limitation of traditional techniques for time-frequency analysis, a new continuous wavelet transform (CWT)-based method was developed in which parts of the scalogram that have been affected by artefact correction are excluded from power calculations. The method was evaluated by simulating artefact correction on HRV data that were originally free of artefacts. Commonly used spectral HRV parameters were calculated by the developed method and by the short-time Fourier transform (STFT), which was used as a reference. Except for the powers in the very low-frequency and low-frequency (LF) bands, powers calculated by the STFT proved to be extremely sensitive to artefact correction. The CWT-based calculations in the high-frequency and very high-frequency bands corresponded well with their theoretical values. The standard deviations of these powers, however, increase with the number of corrected artefacts which is the result of the non-stationarity of the R-R interval series that were analysed. The powers calculated in the LF band turned out to be slightly sensitive to artefact correction, but the results were acceptable up to 20% artefact correction. Therefore, the CWT-based method provides a valuable alternative for the analysis of HRV data that cannot be guaranteed to be free of artefacts.

Normalized spectral power of fetal heart rate variability is associated with fetal scalp blood pH.

BACKGROUND: Spectral power of fetal heart rate variability is related to fetal condition. Previous studies found an increased normalized low frequency power in case of severe fetal acidosis. AIMS: To analyze whether absolute or normalized low or high frequency power of fetal heart rate variability is associated with fetal scalp blood pH. STUDY DESIGN: Prospective cohort study, performed in an obstetric unit of a tertiary care teaching hospital. SUBJECTS: Consecutive singleton term fetuses in cephalic presentation that underwent one or more scalp blood samples, monitored during labour using ST-analysis of the fetal electrocardiogram. Ten-minute continuous beat-to-beat fetal heart rate segments, preceding the scalp blood measurement were used. OUTCOME MEASURES: Absolute and normalized spectral power in the low frequency band (0.04-0.15 Hz) and in the high frequency band (0.4-1.5 Hz). RESULTS: In total 39 fetal blood samples from 30 patients were studied. We found that normalized low frequency and normalized high frequency power of fetal heart rate variability is associated with fetal scalp blood pH. The estimated ß of normalized low frequency power was -0.37 (95% confidence interval -0.68 to -0.06) and the relative risk was 0.69 (95% confidence interval 0.51-0.94). The estimated ß of normalized high frequency power was 0.33 (95% confidence interval 0.01-0.65) and the relative risk was 1.39 (95% confidence interval 1.01-1.92). CONCLUSIONS: Normalized low and normalized high frequency power of fetal heart rate variability is associated with fetal scalp blood pH.

A robust physiology-based source separation method for QRS detection in low amplitude fetal ECG recordings.

The use of the non-invasively obtained fetal electrocardiogram (ECG) in fetal monitoring is complicated by the low signal-to-noise ratio (SNR) of ECG signals. Even after removal of the predominant interference (i.e. the maternal ECG), the SNR is generally too low for medical diagnostics, and hence additional signal processing is still required. To this end, several methods for exploiting the spatial correlation of multi-channel fetal ECG recordings from the maternal abdomen have been proposed in the literature, of which principal component analysis (PCA) and independent component analysis (ICA) are the most prominent. Both PCA and ICA, however, suffer from the drawback that they are blind source separation (BSS) techniques and as such suboptimum in that they do not consider a priori knowledge on the abdominal electrode configuration and fetal heart activity. In this paper we propose a source separation technique that is based on the physiology of the fetal heart and on the knowledge of the electrode configuration. This technique operates by calculating the spatial fetal vectorcardiogram (VCG) and approximating the VCG for several overlayed heartbeats by an ellipse. By subsequently projecting the VCG onto the long axis of this ellipse, a source signal of the fetal ECG can be obtained. To evaluate the developed technique, its performance is compared to that of both PCA and ICA and to that of augmented versions of these techniques (aPCA and aICA; PCA and ICA applied on preprocessed signals) in generating a fetal ECG source signal with enhanced SNR that can be used to detect fetal QRS complexes. The evaluation shows that the developed source separation technique performs slightly better than aPCA and aICA and outperforms PCA and ICA and has the main advantage that, with respect to aPCA/PCA and aICA/ICA, it performs more robustly. This advantage renders it favorable for employment in automated, real-time fetal monitoring applications.

Ischemia-induced ADC changes are larger than osmotically-induced ADC changes in a neonatal rat hippocampus model.

Diffusion-weighted imaging (DWI) is frequently used to diagnose stroke. However, the origin of the observed reduction in the apparent diffusion coefficient (ADC) in the acute phase following ischemia is not well understood. Although cell swelling is considered to play an important role, it is unclear whether this can completely explain the large ADC decrease. We developed a method to induce in neonatal rat hippocampal slices both osmotic perturbations, which lead to cell swelling, and oxygen/glucose deprivation (OGD), which simulates ischemia. A perfusion system was used to provide the hippocampal slices with nutrients and oxygen to maintain slice viability, which was verified with the use of fluorescent dyes (live/dead staining). Upon induction of OGD, the ADC decreased to approximately 57% of the initial value within 2 hr. The ADC reduction cannot fully be explained by changes due to cell swelling, since these led only to a maximum decrease of approximately 83%. Therefore, in addition to cell swelling, other changes must contribute significantly to the ADC reduction.

MRI for diagnosing aortic valve stenosis: a comparison study of MRI and ultrasound.

BACKGROUND: In cases when Doppler ultrasound examinations are not reliable for determining the severity of aortic valve stenosis, patients undergo a catheterisation. Cardiac magnetic resonance imaging (MRI) is a promising tool for the determination of this disease. AIM: We investigated the value of MRI as a substitute for catheterisation in such circumstances, by comparing MRI measurements with Doppler ultrasound measurements. METHODS: Five volunteers and ten patients entered this study, which was approved by the Institutional Ethics Committee. A 1.0T MRI scanner was used for cardiac MRI. On the same day, a Doppler ultrasound examination was performed. The maximum velocity and the orifice area of the aortic valve (called orifice) were compared. RESULTS: A good correlation was observed between the maximum velocity measured with MRI and that measured with ultrasound (r2=0.95) and between the orifice determined by MRI and by ultrasound (r2=0.94); however, the orifice determined by MRI is consistently larger than the orifice determined by ultrasound. CONCLUSION: MRI measurements of velocity and orifice of the aortic valve correlate well with Doppler ultrasound measurement. MRI is a useful diagnostic tool and can be a good substitute for catheterisation, in particular because it allows simultaneous acquisition of anatomical and functional information.

Myocardial adaptation in different endurance sports: an echocardiographic study.

OBJECTIVE: Of this study was to investigate three groups of highly trained competitive endurance athletes consisting of marathon runners, triathletes and cyclists for differences in left ventricular adaptation. METHODS: 25 marathon athletes, 21 triathlon athletes and 38 cyclists underwent a standard echocardiographic and Doppler study. RESULTS: The left ventricular internal diameter in diastole divided by body surface area was significantly larger in cyclists than in marathon runners (31.6+/-3.0 vs. 30.0+/-2.0 mm/ m2, p < 0.05) but did not differ of that of triathletes. Left ventricular mass was significantly different between marathon runners and triathletes (253.6+/-63.7 vs. 322.0+/-62.1 g, p < 0.005) and between marathon runners and cyclists (253.6+/-63.7 vs. 314.2+/-79.2 g, p < 0.005). Systolic wall stress was significantly different between the marathon runners and the triathletes (88.4+/-11.7 vs. 78.9+/-11.0 g/cm2 p < 0.05). Only a minority of the endurance athletes showed concentric remodeling (7%), whereas a majority showed eccentric remodeling (65%) of the left ventricle. The prevalence of eccentric remodeling was more apparent in cyclists. There were some specific differences in left ventricular diastolic function between the three different endurance sports, but no left ventricular diastolic dysfunction could be detected. CONCLUSION: There is a sport-specific left ventricular adaptation in endurance athletes. The triathlon heart and the heart of a cyclist differ significantly from a marathon heart.

Customized spectral band analysis compared with conventional Fourier analysis of heart rate variability in neonates.

A customized filtering technique is introduced and compared with fast Fourier transformation (FFT) for analyzing heart rate variability (HRV) in neonates from short-term recordings. FFT is classically the most commonly used spectral technique to investigate cardiovascular fluctuations. FFT requires stability of the physiological signal within a 300 s time window that is usually analyzed in adults. Preterm infants, however, show characteristics of rapidly fluctuating heart rate and blood pressure due to an immature autonomic regulation, resulting in non-stationarity of these signals. Therefore neonatal studies use (half-overlapping or moving) windows of 64 s length within a recording time of 2-5 min. The proposed filtering technique performs a filtering operation in the frequency range of interest before calculating the spectrum, which allows it to perform an analysis of shorter periods of only 42 s. The frequency bands of interest are 0.04-0.15 Hz (low frequency, LF) and 0.4-1.5 Hz (high frequency, HF). Although conventional FFT analysis as well as the proposed alternative technique result in errors in the estimation of LF power, due to spectral leakage from the very low frequencies, FFT analysis is more sensitive to this effect. The response times show comparable behavior for both the techniques. Applying both the methods to heart rate data obtained from a neonate before and after atropine administration (inducing a wide range of HRV), shows a very significant correlation between the two methods in estimating LF and HF power. We conclude that a customized filtering technique might be beneficial for analyzing HRV in neonates because it reduces the necessary time window for signal stability.

Left atrial and ventricular dimensions in highly trained cyclists.

OBJECTIVES: This study sought to investigate the development of left ventricular remodeling during active cycling. METHODS: A group of 17-year-old (+/- 0.2 years) highly trained competitive cyclists (group I, n = 66) and a group of 29-year old (+/- 2.6 years) professional cyclists (group II, n = 35) underwent two-dimensional (2D) echocardiography. Data from groups I and II were compared with values of normal untrained subjects based on the literature. RESULTS: Left atrial dimensions were significantly increased in group II as compared to group I (44 +/- 5 vs. 36 +/- 4 mm, p < 0.005). Left ventricular end diastolic diameter was significantly increased in group II as compared to group I (61 +/- 5 vs. 54 +/- 6 mm, p < 0.005). Left ventricular mass was also significantly increased in group II as compared to group I (321 +/- 77 vs. 246 +/- 59 g, p < 0.005). Wall stress showed a significant inverse relation: 104 +/- 42 mmHg in group I vs. 83 +/- 14 mmHg in group II (p < 0.005). The early filling phase of the left ventricular inflow was significantly larger in both athlete groups in relation to the normal value. The E-wave in the athletes compared to the E-wave in normal subjects was 0.87 +/- 0.17 vs. 0.71 +/- 0.14 m/s in group I, p < 0.005, 0.82 +/- 0.17 vs. 0.71 +/- 0.14 m/s in group II, p < 0.05. Late filling phase and the ratio of the diastolic filling pattern did not show significant differences between the two groups. CONCLUSIONS: Left atrial and left ventricular remodeling starts early in the athlete's career. Athletes of 17 years of age already show significant left atrial and left ventricular dilatation compared to data of untrained subjects described in literature. The process of dilatation continues during the athlete's career. Also left ventricular mass is increased at a young age which continues for several years. More than 60% of the athletes in both groups demonstrated an intermediate form of left ventricular hypertrophy. Diastolic function of the left ventricle remains normal during a long period of athletic career performance.

Detection and treatment of claudication due to functional iliac obstruction in top endurance athletes: a prospective study.

BACKGROUND: Endurance athletes often have restrictions in flow in their iliac arteries during exercise. Such restrictions have previously been ascribed solely to intravascular lesions. We postulate that flow could also be restricted by functional kinking in the arteries, and that surgical release of these kinks might be an effective treatment. METHODS: We prospectively studied 80 endurance athletes who had complaints suggestive of flow restriction in the iliac arteries of one (n=74) or both (6) legs (total 92 legs). Using vascular diagnostic tools, we examined athletes while they were doing activities that often provoke flow restrictions. Restrictions were determined by measurement of systolic pressure in the ankle after exercise; peak systolic velocities were measured with echo-doppler. Kinks were detected with echo-doppler and magnetic-resonance angiography. When functional kinking was diagnosed as the cause of the restriction, the athlete was offered surgery to release the iliac arteries, as part of our prospective study. FINDINGS: We recorded flow restrictions in the iliac arteries of 58 of 92 (63%) legs. In 40 of these legs (69%), kinks were the most important cause of the restriction, making these legs suitable for surgical release. We operated on 23 of 58 (40%) legs. All athletes who had an operation subjectively improved. Maximum workload in a cycling test and ankle pressure significantly improved after the operation. 20 (87%) athletes were able to successfully return to their desired high level of competition. INTERPRETATION: Our sports-specific protocol is effective in detecting kinking of the iliac arteries as a cause for flow restriction in athletes who have few intravascular abnormalities when investigated with conventional vascular diagnostic tools. Surgical treatment directed at the kinking was less invasive and therefore a better alternative to vascular reconstruction in these athletes.