Spectral analysis of the heart rate variability in sleep

Spectral analysis of heart rate variability (HRV) during overnight polygraphic recording was performed in 11 healthy subjects. The total spectrum power, power of the VLF, LF and HF spectral bands and the mean R-R were evaluated. Compared to Stage 2 and Stage 4 non-REM sleep, the total spectrum power was significantly higher in REM sleep and its value gradually increased in the course of each REM cycle. The value of the VLF component (reflects slow regulatory mechanisms, e.g. the renin-angiotensin system, thermoregulation) was significantly higher in REM sleep than in Stage 2 and Stage 4 of non-REM sleep. The LF spectral component (linked to the sympathetic modulation) was significantly higher in REM sleep than in Stage 2 and Stage 4 non-REM sleep. On the contrary, a power of the HF spectral band (related to parasympathetic activity) was significantly higher in Stage 2 and Stage 4 non-REM than in REM sleep. The LF/HF ratio, which reflects the sympathovagal balance, had its maximal value during REM sleep and a minimal value in synchronous sleep. The LF/HF ratio significantly increased during 5-min segments of Stage 2 non-REM sleep immediately preceding REM sleep compared to 5-min segments of Stage 2 non-REM sleep preceding the slow-wave sleep. This expresses the sympathovagal shift to sympathetic predominance occurring before the onset of REM sleep. A significant lengthening of the R-R interval during subsequent cycles of Stage 2 non-REM sleep was documented, which is probably related to the shift of sympathovagal balance to a prevailing parasympathetic influence in the course of sleep. This finding corresponds to a trend of a gradual decrease of the LF/HF ratio in subsequent cycles of Stage 2 non-REM sleep.     

Periodicities in respiration and heart rate in newborns

Periodic breathing is common in normal infants, but may be associated with prolonged apnea leading to crib death. The mechanisms of periodic breathing and its relation to normal breathing patterns are unclear. We recorded respiratory and heart rate (HR) patterns of 11 healthy newborn infants during quiet sleep, in both normal and periodic breathing. Spectral analysis of the respiratory pattern revealed a low-frequency (LF) periodicity in normal breathing approximately equal to the frequency of periodic breathing when this occurs. Periodic breathing thus appears to be an exaggeration of an underlying slow amplitude variation which is present in regular breathing. LF periodicity also appeared in the HR pattern in both normal and periodic breathing, suggesting an LF modulation of cardiovascular control as well. The lack of a definite phase relation between HR and ventilation at LF may indicate dominant peripheral, rather than central, interactions between HR and respiration at these frequencies.     

Spectral analysis and interpretation of spectral components of heart rate variability

Requirements for a fragment of a random process taken for spectral analysis are formulated. It has been demonstrated that both the random process and its periodic components should be stationary within the fragment selected. Only in this case will the results of spectral analysis reflect the actual characteristics of the process studied. Variations in the depth of breathing and other factors have been shown to cause modulatory fluctuations of the HF and LF waves of the cardiac rhythm. The modulatory fluctuations are expressed as the VLF peak in the heart rate variability spectrum, the position of the peak on the frequency axis and its amplitude being determined by the frequency and depth of modulation, respectively. Depending on the modulation depth and the ratio between the modulation period and the length of the sample studied, spectral analysis of the same process may yield considerably different results. The ambiguity of the results of spectral analysis is the cause of discrepancy about the nature of individual spectral components of heart rate variability.     

Spectral analysis of heart rate variability during constant and pseudorandom exercise

The purpose of this study was to investigate the limitation for applying a linear model to the cardiorespiratory control system. Four subjects performed the two types of exercise bouts, constant (CONST) and pseudorandom (PRBS) exercise, on an electrically braked cycle ergometer at three different work rates. The target work rate of CONST were set to 80, 100, 120% of the individual anaerobic threshold (AT). In PRBS, the work rates were varied between +/- 10% of the individual AT around the respective target work rates of CONST. Although the spectral density of beat-to-beat heart rate fluctuations showed the conventional patterns for most cases, there was no obvious difference between CONST and PRBS. These results indicated that the variation of +/- 10% of AT did not affect the heart rate variation as the output response, suggesting a dilemma inevitable to apply a linear model based on the transfer function.     

Spectral analysis of heart rate fluctuations: physiological basis and complicating factors

The main stages of investigation into the changes of the heart rate in human (HRH), are presented. A satisfactory coincidence of results of the HRH oscillation power estimation within two frequency ranges obtained with the aid of two techniques: by the Yamamoto algorithm and by search for sources of non-harmonic oscillations, was shown.     

Relationship between respiratory pauses and heart rate during sleep in normal premature and full-term newborns

To investigate the relationship between central respiratory pauses and heart rate, we performed polygraphic recordings in 23 normal newborns (35 to 41 weeks conceptional age). We monitored the electroencephalogram, rapid eye movements, movements of the upper and lower limbs, chin and diaphragmatic electromyogram, electrocardiogram, thoracic and abdominal respiratory movements, air flow and transcutaneous PO2. Heart rate changes were analysed by computer measurement of R-R intervals and by cardiotachography. Respiratory pauses occurring after body movements and those not preceded by movements were studied separately. We analysed 1128 respiratory pauses greater than 3 s duration. No respiratory pause lasted more than 12 s. Independently of age, sleep state and respiratory pause duration, heart rate was significantly lower at the onset of respiratory pause, compared to control periods (selected away from the pause: 10 s before its onset and 20 s after its end). Heart rate slowed still further through the respiratory pause and reverted toward the baseline level after its end. When no movements preceded the respiratory pause, heart rate just before the pause was lower compared to control periods. These findings suggest the existence of simultaneous central commands responsible for both respiratory pause and heart rate deceleration.     

Objective characterization and differentiation of sleep states in healthy newborns and newborns-at-risk by spectral analysis of heart rate and respiration rhythms

Best parameters of power and coherence spectra of heart rate fluctuations (HR) and respiration rhythms (RR) were established to differentiate sleep states in healthy newborns and newborns-at-risk by means of multivariate variance and discriminant analysis. Nine healthy newborns and 20 newborns with low risk features were examined polygraphically. Long-term-variability of both HR and RR and coherence between HR and RR in the frequency range of 0.26-0.97 Hz, corresponding to Respiratory Sinus Arrhythmia, allow the best differentiation of neonatal sleep states S 1 and S2. Differentiation of healthy newborns and newborns-at-risk by these parameters was not possible. Thus, in studies dealing with low risk features in newborns sleep states must be previously classified. State 1 and 2 represent different autonomic organisations. State 1 is a neuro-vegetative, relatively stable state. State 2 shows cyclic increases of coherence between HR and RR within the frequency range of Respiratory Sinus Arrhythmia. These properties are related to autonomic brain stem functions and were absent in 6 out of the 20 newborns-at-risk.     

Spectral analysis of the heart rate,blood pressure,and respiratory rate variability in 8- to 11-year-old children at rest

Spectral analysis was performed to assess the periodic variations in the heart rate (HR), blood pressure (BP), and respiratory volume (RV) in 8- to 11- year-old children at rest. Age- and gender-related differences were revealed in the total power and spectral components of the HR, BP, and RV spectra.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 33–39.Original Russian Text Copyright © 2005 by Kuznetsova, Sonkin.     

Dimensional analysis of heart rate variability in heart transplant recipients

Periodicities in the heart rate have been known for some time. We discuss these periodicities in normal and transplanted hearts. We then consider the possibility of dimensional analysis of these periodicities in transplanted hearts and problems associated with the record.     

Factor analysis of the heart rate spectrum

The methodical problems of factor analysis of the heart rate spectrum have been considered: the multivariate normal assumption, factorability of the intercorrelation matrix, criteria for determining the number of factors, and the validity of the factor analysis model. Unnormalized and normalized variables, the matrices of Pearson’s and Spearman’s correlation coefficients were used. In the process of factor analysis (principal components method, Varimax Rotation), the restrictions and the possibility of different statistical criteria and procedures were explored. The meaning of the selected factors and the possibility of using the intercorrelation matrix of Spearman coefficients for unnormalized variables were considered.     

Autonomic control of heart rate during exercise studied by heart rate variability spectral analysis.

Spectral analysis of heart rate variability (HRV) might provide an index of relative sympathetic (SNS) and parasympathetic nervous system (PNS) activity during exercise. Eight subjects completed six 17-min submaximal exercise tests and one resting measurement in the upright sitting position. During submaximal tests, work rate (WR) was increased for the initial 3 min in a ramp fashion until it reached constant WRs of 20 W, or 30, 60, 90, 100, and 110% of the predetermined ventilatory threshold (Tvent). Ventilatory profile and alveolar gas exchange were monitored breath by breath, and beat-to-beat HRV was measured as R-R intervals of an electrocardiogram. Spectral analysis was applied to the HRV from 7 to 17 min. Low-frequency (0-0.15 Hz) and high-frequency (0.15-1.0 Hz) areas under power spectra (LO and HI, respectively) were calculated. The indicator of PNS activity (HI) decreased dramatically (P less than 0.05) when the subjects exercised compared with rest and continued to decrease until the intensity reached 60% Tvent. The indicator of SNS activity (LO/HI) remained unchanged up to 100% Tvent, whereas it increased abruptly (P less than 0.05) at 110% Tvent. The results suggested that (cardiac) PNS activity decreased progressively from rest to a WR equivalent to 60% Tvent, and SNS activity increased only when exercise intensity exceeded Tvent.     

Spectral analysis of fetal heart rhythm in relation to fetal regular mouthing

Fetal heart rate variation during fetal regular mouthing in behavioural state 1F was investigated applying spectral analysis. Periods with and without fetal regular mouthing movements were compared. The power spectrum of the periods with regular mouthing movements showed a peak at the frequency of the clusters of mouthing movements which was absent in the power spectrum of the corresponding periods without movements. The oscillations in the fetal heart rate associated with this peak in the power spectrum were detectable both in the heart rate tracings obtained from the abdominal electrocardiogram and those recorded by means of wide range Doppler ultrasound.     

Sample entropy analysis of neonatal heart rate variability

Abnormal heart rate characteristics of reduced variability and transient decelerations are present early in the course of neonatal sepsis. To investigate the dynamics, we calculated sample entropy, a similar but less biased measure than the popular approximate entropy. Both calculate the probability that epochs of window length m that are similar within a tolerance r remain similar at the next point. We studied 89 consecutive admissions to a tertiary care neonatal intensive care unit, among whom there were 21 episodes of sepsis, and we performed numerical simulations. We addressed the fundamental issues of optimal selection of m and r and the impact of missing data. The major findings are that entropy falls before clinical signs of neonatal sepsis and that missing points are well tolerated. The major mechanism, surprisingly, is unrelated to the regularity of the data: entropy estimates inevitably fall in any record with spikes. We propose more informed selection of parameters and reexamination of studies where approximate entropy was interpreted solely as a regularity measure.     

The genetic contribution to heart rate and heart rate variability in quiescent mice

Recent studies have suggested a genetic component to heart rate (HR) and HR variability (HRV). However, a systematic examination of the genetic contribution to the variation in HR and HRV has not been performed. This study investigated the genetic contribution to HR and HRV using a wide range of inbred and recombinant inbred (RI) mouse strains. Electrocardiogram data were recorded from 30 strains of inbred mice and 29 RI strains. Significant differences in mean HR and total power (TP) HRV were identified between inbred strains and RI strains. Multiple significant differences within the strain sets in mean low-frequency (LF) and high-frequency (HF) power were also found. No statistically significant concordance was found between strain distribution patterns for HR and HRV phenotypes. Genomewide interval mapping identified a significant quantitative trait locus (QTL) for HR [LOD (likelihood of the odds) score = 3.763] on chromosome 6 [peak at 53.69 megabases (Mb); designated HR 1 (Hr1)]. Suggestive QTLs for TP were found on chromosomes 2, 4, 5, 6, and 14. A suggestive QTL for LF was found on chromosome 16; for HF, we found one significant QTL on chromosome 5 (LOD score = 3.107) [peak at 53.56 Mb; designated HRV-high-frequency 1 (Hrvhf1)] and three suggestive QTLs on chromosomes 2, 11 and 15. In conclusion, the results demonstrate a strong genetic component in the regulation of resting HR and HRV evidenced by the significant differences between strains. A lack of correlation between HR and HRV phenotypes in some inbred strains suggests that different sets of genes control the phenotypes. Furthermore, QTLs were found that will provide important insight to the genetic regulation of HR and HRV at rest.