Sherwin T. Nugent

Heart rate variability in infants, children and young adults

Heart rate variability was studied in normal subjects age 1 month-24 years while awake and in active and quiet sleep using 24 h continuous recordings of the ECG. Variability was quantified by spectral analysis for the two frequency bands: low frequency (LF) 0.03-0.15 Hz, high frequency (HF) 0.15-0.6 Hz. Heart rate variability showed an age dependence, being in general an increase in LF, HF and total power from 0-6 years, followed by a decrease to 24 years. The infant group showed some exceptions to this trend. Developmental changes of parasympathetic and sympathetic mediation of heart rate are postulated as important determinants of age dependence of heart rate variability.

Spectral Analysis of Periodic and Nonnal Breathing in Infants

Spectral analysis techniques are used to study periodic and normal breathing in infants. Power density spectra of respiration and heart rate are obtained using the fast Fourier transform technique. For the periodic breathing case, these spectra are used to determine the coherency function. From these results, information is obtained about: 1) the modulation of heart rate by respiration, 2) the strength of the modulation as indicated by the coherency, and 3) for cases where the coherency is high, an estimate of the time delay between respiration and heart rate interaction.

Periodic Breathing in Infants: A Model Study

A model has been adapted to explain periodic breathing in infants during sleep. Using parameter values determined in various studies by others, it is shown that the respiratory control system of certain infants is marginally stable so that a small change in one or more of the parameters can cause periodic breathing with a period of about 14 s.

Self and forced oscillations in multivariable relay control systems

This paper generalizes the well known Tsypkin method for use in prediction of self or forced oscillations in multivariable relay control systems. The method is valid for all systems having linear plants whose transfer matrix elements have at least two more poles than zeros. The relays may have hysteresis and dead band and need not be identical. It is shown that certain multivariable relay control systems can be represented by a related set of single variable control systems for stability analysis purposes. This result permits Tsypkins stability criteria for single variable systems to be used to determine the stability of these systems. The methods developed are illustrated by an example and the theoretically predicted behaviour is confirmed by analogue simulation.

Spectral analysis of heart rate variability in children and young adults during sleep and awake states

Maturation of heart rate variability was studied by comparing the heart rate variation of 26 children and young adults between 5 and 24 years of age when awake and during quiet and active sleep. Spectral analysis was used to determine the intensity of the variation in each of two main frequency bands in which variation occurs: LF 0.03–0.15 Hz and HF, 0.15–0.6 Hz. The results of the study show that many children have reached a mature pattern by 5 years of age.

Baroreflex sensitivity in children: a spectral analysis evaluation

Spectral analysls technlques are used to determine the baroreflex sensltlvlty In children. Results were obtalned for SIX chlldren aged 2 to 12 years. Tho baroreflex sensitivity was found to range from 2.9 to 34.4 mdmm Hg. The technlque uses normal resplratory variations In systolic blood pressure as the stlmulus for creatlng varlatlons In cardlac lengths and when used with nonlnvaslve moasurement of Instantaneous blood pressure should enable the evaiuatlon of baroreflex sensltivlty In a wlde range of ages and wnditlona

Baroreflex Evaluation In Children At Respiratory Frequencies

An analytical technique for determining the baroreflex sensitivity in children is presented. Scatter plots and spectral analysis techniques are used to determine the relationship between RR intervals and peak systolic blood pressure. Results were obtained for five children aged two months to 15 years. The baroreflex sensitivity was found to range from 3.15 to 36.3 mslmmHg. This technique which uses normal respiratory variations in systolic blood pressure as the stimulus for creating variations in cardiac cycle lengths is potentially very useful in the study of baroreflex sensitivity in children since no artificial or pharmacologic stimuli are necessary.

Maturation Of Heart Rate Variability In Children During The Awake State

The effects of maturation on heart rate were studied by comparing the heart rate variation of 29 children and young adults in three groups between 5 and 24 years of age. Spectral analysis was used to determine the intensity of the variation in each of the two main frequency bands in which variation occur: HF, 0.15 - 0.45 Hz, and LF, 0.03 - 0.15 Hz. The results of the study suggest that many children have a significant decrease in sympathetic activity between 5 and 10 years of age, and possibly a slight decrease in parasympathetic activity.

Spectral analysis of heart rate variability: effects of unilateral stellate blockade

Spectral analysis has been used as a means of quantifying frequency-specific contributions from heart rate variability signals under the effects of unilateral stellate blockade. Eight adults who were undergoing left and right blocks were used in the preliminary study where areas under the frequency bands LF (0.05-0.15 Hz) and HF (0.15-0.45 Hz) were computed for preblockade and postblockade conditions in the supine and standing positions. Results suggest that stellate blockade decreased LF areas by 43% when standing. The reduction was not significant compared to that obtained in previous work, where the reduction was 79%. These results underline the importance of efferents from the contralateral and higher cervical ganglia in the control of heart rate.<<ETX>>