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Biomedical subjects

R Mrowka

Publications and source records attributed to R Mrowka.

24 records · Page 2Linked to original sources
PubMed1996

[Sleep structure in relation to respiration and heart rate in children in puberty].

The different expression of respiratory sinus arrhythmia in REM- versus nonREM-sleep indicates a dependence of cardiorespiratory interaction on patterns of sleep. Investigations of the intensity of respiratory entrainment on heart rhythmicity during various stages of sleep will provide an insight into the coupling of cardiorespiratory interaction and sleep patterns. 42 healthy children (12 to 15 years old) were polygraphically investigated over 24 h. An ECG, EOG, and actogram were performed, respiratory movements were observed, and the skin temperature was taken. The power spectra of the instantaneous heart rate and the respirograms were calculated. The analysis of coherence was carried out to determine how pronounced the cardiorespiratory interaction is. REM-sleep, nonREM-phases, and wakefulness were compared. The spectral parameters of instantaneous heart rate show differences between both stages of sleep and the waking state. Due to a dependence of spectral power on breathing patterns, drawing quantitative conclusions is not possible. The analysis of coherence provides more information about sleep patterns within the cardiorespiratory interaction. It is very pronounced during non-REM-sleep (0.80 +/- 0.07; mean +/- standard deviation). Heart rhythmicity proceeds independent of breathing during REM-sleep (0.52 +/- 0.11). The coupling is weaker than during wakefulness (0.64 +/- 0.09).

Adolescent↗
PubMed1995

Does low frequency power of arterial blood pressure reflect sympathetic tone?

We tested whether power spectral analysis of arterial blood pressure (ABP) is a feasible tool to detect differences in peripheral sympathetic nerve activity in normotensive and hypertensive rats with differing basal sympathetic tones. Nine Wistar Kyoto rats (WKY), 10 Sprague-Dawley rats (SD), 10 spontaneously hypertensive rats (SHR) and 9 hypertensive transgenic rats harbouring the mouse Ren-2 gene (TGR) were chronically instrumented with femoral artery catheters and nerve electrodes around the sympathetic major splanchnic nerve. Two days after surgery ABP and splanchnic nerve activity (SpNA) were recorded in the conscious state during basal conditions as well as during alpha 1-adrenergic receptor blockade. Power spectra and squared coherence in the low (LF, 0.02-0.20 Hz), mid (MF, 0.20-0.80 Hz) and high (HF, respiration peak +/- 0.3 Hz) frequency bands were calculated for ABP and SpNA. Mean blood pressure in SHR (133 +/- 8 mmHg) and TGR (142 +/- 8 mmHg) was significantly higher (P < 0.05) than in WKY (115 +/- 3 mmHg) and SD (95 +/- 4 mmHg). SpNA in SHR was higher than in WKY (23.4 +/- 6.4 microV vs. 11.6 +/- 0.8 microV, P < 0.05) while SpNA in TGR was lower than in SD (20.1 +/- 3.9 microV vs. 28.8 +/- 4.2 microV, P < 0.05). LF and MF components of ABP variability were not significantly higher in those rats with high sympathetic tones. However, alpha 1-adrenergic receptor blockade reduced LF and MF components of ABP and SpNA in all strains except SHR. LF and MF coherence was not greater in rats with high sympathetic tones than in those with low sympathetic tones. The reduction of LF and MF components of ABP variability by alpha 1-adrenergic receptor blockade indicates an important contribution of peripheral sympathetic nerve activity to LF and MF blood pressure variability on an acute basis. However, the lack of higher LF and MF power in the ABP spectra of those rats with high SpNA together with the finding that LF and MF coherence was not higher in those rats with high SpNA led to the conclusion that LF and MF spectral components of ABP do not appear to be suitable markers for the prevailing sympathetic nerve activity.

Adrenergic alpha-1 Receptor Antagonists↗
PubMed1995

Complexity and "chaos" in blood pressure after baroreceptor denervation of conscious dogs.

To investigate how arterial baroreceptors affect the dynamic properties of short-term blood pressure control, we determined Lyapunov exponents and correlation dimensions of blood pressure. Two groups of conscious dogs were studied: a control group (n = 7) and a group subjected to total sinoaortic and cardiopulmonary baroreceptor denervation (n = 7). As a measure of variability, standard deviation was determined and power spectra were calculated. In the lower frequency range (f < 0.1 Hz) power density was inversely related to frequency in both groups, indicating "1/f noise." Estimating the correlation dimension via the Grassberger-Procaccia algorithm as a quantification of complexity revealed a decrease after baroreceptor denervation (1.74 +/- 0.2 vs. 3.05 +/- 0.23 control; P < 0.05). Determination of the largest Lyapunov exponents lambda 1, which indicates the sensitive dependence on initial conditions, a hallmark of chaos, also yielded a diminution after denervation (lambda 1 = 0.74 +/- 0.08 vs. 1.85 +/- 0.18, P < 0.01). The results were cross-checked with surrogate data statistics. The null hypothesis, that there is no nonlinear structure in arterial blood pressure time series, was rejected. This shows that after baroreceptor denervation, blood pressure control is less complex and less sensitive to initial conditions ("chaos"). In contrast, variability (standard deviation) is increased (22.2 +/- 3.1 denervation vs. 8.3 +/- 1.4 control; P < 0.05). It is concluded that under physiological conditions, arterial and cardiopulmonary baroreceptors reduce variability of blood pressure, however, at the cost of blood pressure being less predictable. Thus the regulation is more sensitive depending on initial conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1995

[Correlation between respiration and heart rate in 12- to 14-year-old children during sleep and wakefulness].

The coupling of respiratory and cardiac rhythm is determined by interactions of oscillating brain stem centers and external physical and psychical influences. Not well known are effects of sleep and wakefulness which will be investigated over the day. From the ECG and respirogram of 42 healthy children (11 female, 31 male, 12 to 14 years) during 24 h the time series of instantaneous heart rate (HR) and respiratory rhythm and from this by FFT the density spectra of power, the maximal power and related frequency in the respiratory range were ascertained. Differences between nonREM sleep and wakefulness and the strength of coupling were determined by coherence analysis. In all probands the maximal power of HR and of the coherence were higher during nonREM sleep than in wakefulness. Both values were stable during each state. The maximum related frequencies of HR and respiration shifted parallel between sleep and wakefulness. The results mean augmentation in nonREM sleep following to improved transfer of respiratory activity to the control of HR. The increased coherence hints at a stronger linear coupling which is stable during each state. The changes of cardiorespiratory coupling may be effected by stronger non-linear parts in the interactions during wakefulness.

Adolescent↗
PubMed1995

[Development of heart rate in newborn infants during quiet sleep].

The small number of investigations of the development of heart rhythm during the first half year of life provide only rough ideas regarding the maturation of heart rate control. In the present study, in 10 newborns, ECG and respiratory effort were recorded in 13 sessions from birth up to the sixth month. The total power (TP), power in the low (LF) and high frequency range (HF), and the ratio LF/HF were used from the heart rate power spectra. All parameters reveal no linear developmental patterns: TP, LF, and HF increase during the first days to a maximum, then decrease subsequently and remain low until the second month. TP and HF increase between the second and sixth month. LF/HF increases up to the second month followed by a decrease down to the sixth month. The developmental courses of TP, HF and LF/HF correlate with the course of breathing rate (BR), whereby high BR is associated with low HF and TP. The results hint at a maturated cardiorespiratory system.

Child Development↗