Fractal and nonlinear changes in the long-term baseline fluctuations of fetal heart rate

The interpretation of heart rate patterns obtained by fetal monitoring relies on the definition of a baseline, which is considered as the running average heart rate in the absence of external stimuli during periods of fetal rest. We present a study along gestation of the baseline's fluctuations, in relation to fractal and nonlinear properties, to assess these fluctuations according with time-varying attracting levels introduced by maturing regulatory mechanisms. A low-risk pregnancy was studied weekly from the 17th to 38th week of gestation during long-term recording sessions at night (>6 h). Fetal averaged pulse rate samples and corresponding baseline series were obtained from raw abdominal ECG ambulatory data. The fractal properties of these series were evaluated by applying detrended fluctuation analysis. The baseline series were also explored to evaluate nonlinear properties and time ordering by applying the scaling magnitude and sign analyses. Our main findings are that the baseline shows fractal and even nonlinear anticorrelated fluctuations. This condition was specially the case before mid-gestation, as revealed by α values near to unit, yet becoming significantly more complex after 30 weeks of gestation as indicated by α(mag) values >0.5. The structured (i.e. not random) fluctuations and particular nonlinear changes that we found thus suggest that the baseline provides on itself information concerning the functional integration of cardiac regulatory mechanisms.

Reproducibility of heart rate variability from short-term recordings during five manoeuvres in normal subjects

PRIMARY OBJECTIVE

Due to limited and contradictory information available, the reproducibility of temporal and spectral measurements of heart rate variability from short-term recordings was evaluated in normal subjects during supine, controlled breathing, standing, exercise and recovery conditions.

METHODS AND PROCEDURES

Five-minute tachograms from 11 individuals were obtained during the specified manoeuvres, and repeated three times in a five day period. Besides temporal and spectral indexes, the central frequencies were also computed.

MAIN OUTCOMES AND RESULTS

The ANOVA presented non-significant differences among the repetitions for any of the parameters studied. Most intra-class correlation coefficients were over 0.68. The central frequency of the low component diminished during the manoeuvres.

CONCLUSIONS

In healthy individuals, the temporal and spectral measurements of the heart rate variability from short-term records are stable in a five day period for the manoeuvres studied. Central frequencies of the spectral components might be used as indexes of the autonomic activity.

Genotypes of the C677T and A1298C polymorphisms of the MTHFR gene as a cause of human spontaneous embryo loss

BACKGROUND Polymorphisms C677T and A1298C of the MTHFR gene have been implicated in fetal viability. In this study, we determined the allele and genotype frequencies of these polymorphisms in different populations, including spontaneous abortion (SA) fetal tissues, with the objective of evaluating their impact on fetal viability. METHODS 342 samples of fetal tissues, selected from SA occurring during the 1980s, 230 samples from subjects born in the 1980s and a third set of samples from 204 subjects born in the 1950s, were genotyped by using TaqMan probes. RESULTS The wild CC genotype of the C677T polymorphism showed a strong protective effect against abortion (0.03 in SA versus 0.47 in 1950s and 0.43 in 1980s) (P < 0.0001). Genotypes of three mutations in the combinations of polymorphisms for C677T and A1298C showed a very low frequency in the living population; however, the three mutations genotypes were over expressed in the SA group (0.02 in 1950s; 0.03 in 1980s and 0.17 in SA) (P < 0.0001). Samples with four mutations (n = 2) were found only in the SA group. CONCLUSIONS There is no linkage disequilibrium between C667T and A1298C polymorphisms. Fetal viability is directly related to the CC genotype as a protector while the three and four mutation MTHFR genotypes appear to be a determinant on fetal non-viability and SA.

Differences in foetal heart rate variability from phonocardiography and abdominal electrocardiography

The agreement of the phonocardiographic method to provide foetal heart rate variability (FHRV) indices equivalent to those derived from abdominal electrocardiography was tested. 15 pregnant women were recruited in order to obtain antepartum foetal phonocardiograms and abdominal electrocardiograms three minutes long. From the respective sound (SS) and electric (RR) time series, typical temporal and spectral indices of FHRV were computed and compared. Means of the SS and RR intervals were not significant (P> 0.05) and these showed a correlation r=0.98. However, the temporal indices, P(TOT), HF and LF/HF presented differences (P< 0.05), since SS values were higher. Spectral coherence decreased below 0.5 for frequencies above 0.28+ 0.07 Hz, where bands resembling maternal and foetal breathing movements were noted. Particularly above 0.28Hz, temporal and spectral FHRV indices derived from phonocardiography and electrocardiography show differences. Quality of the signal, processing techniques, and maternal and foetal respiratory factors could account to explain these.

Correlation among Poincaré plot indexes and time and frequency domain measures of heart rate variability

PRIMARY OBJECTIVE

In order to corroborate the rported performance advantage of Poincaré plot indexes as autonomic activity markers, the correlation among these indexes and those computed from the time and frequency domains were obtained.

METHODS AND PROCEDURES

Starting from the RR series derived from the ECG of 21 healthy volunteers during five manoeuvres, longitudinal (L), transverse (T) axis, and autocorrelation (r) from Poincaré plots, rMSSD and standard deviation (SD) in the temporal domain, and frequency domain indexes were computed.

MAIN OUTCOMES AND RESULTS

Poincaré plot indexes were correlated in a better way with the time indexes, rather than the spectral measures. A strong correlation (0.997) between L and SD was observed, while an underlying mathematical relationship was established for T vs rMSSD.

CONCLUSIONS

Poincaré plot indexes may be considered as equivalent or surrogates of the temporal ones, and they do not have a better performance as autonomic markers.

Reliability of reference models for vital capacity in young Mexican females

OBJECTIVE

To assess the reliability of 29 prediction models for vital capacity when these are applied as reference for young females, natives and residents in Mexico City (altitude = 2,240 m).

DESIGN

Transversal, prospective and comparative study.

SETTING

Metropolitan Autonomous University, Mexico.

SUBJECTS

Sixty females clinically healthy, 17 to 29 years old, non-smokers.

PROCEDURE

Vital capacity was predicted from 29 models and measured with a bell spirometer (Collins 9 L) according to the American Thoracic Society guidelines. Statistical comparison was done between measured and predicted values by linear regression, analysis of variance and analysis of residuals.

RESULTS

Mean of measured vital capacity was 3,625 mL while mean values of predicted vital capacities varied from 2,644 mL to 3,962 mL. Actual and reference values showed a small but significative correlation (r = 0.40 to 0.49). By Dunnett's test, means from six of the 29 models showed non-significant differences (p > 0.05) with the mean of the measured vital capacity; however, all 29 models presented significative bias in the regression line between actual values and the residuals of predicted values (correlation coefficient, slope and intercept statistically different from zero, p < 0.05).

CONCLUSION

Due to the large bias found, models tested in the present study have limitations to predict accurate reference values for young mexican females.

Reliability of reference models for vital capacity in young Mexican males

The reliability of 33 prediction models for vital capacity was assessed in university students living in Mexico City (altitude = 2,240 m). Forced vital capacity (FVC) was predicted and measured in 83 healthy male students, 18 to 30 years old and non-smokers. Spirometric tests were performed with a 9 liter bell spirometer, according to ATS guidelines. Mean measured FVC was 5,094 +/- 555 mL (BTPS) while mean predicted FVC by the models ranged from 3,700 mL to 5,350 mL (BTPS) with a small but significative correlation between actual and reference values (r = 0.398 to 0.474, p < 0.05). The residual standard deviation showed values from 503 to 577 mL which were similar to those seen in the original population. Although 11 of the 33 models were able to predict mean observed FVC by Dunnett's test (p < 0.05), all of them showed significant bias on the regression between measured values and residuals of predicted values, i.e. intercepts (2,435 to 4,127 mL), slopes (-0.61 to -0.87) and correlations (-0.59 to -0.95) were statistically different from zero (p < 0.01). Our data remark the need to obtain appropriate reference FVC values in young Mexican males due to the questionable predictability of the models tested.