PubMed · 7171521
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S L Duncan. 1982. Menopausal flushing: where now?. https://doi.org/10.1111/j.1471-0528.1982.tb04648.x
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To examine the baroreceptor reflex function, a beat-to-beat analysis between systolic blood pressure (SBP) and R-R interval fluctuations was studied in 10 stable appropriate-for-gestational age preterm infants (range, 27.2-33.7 wk) in the first postnatal week during quiet sleep. Spectral power analysis, using fast Fourier transform, and transfer functions (gain and phase difference) between SBP and R-R fluctuations were estimated in a low-frequency band (LF, 0.03-0.2 Hz) and high-frequency band (HF defined as the frequency band between the 10th and 90th centiles of the individual respiratory frequency). The LF/HF ratio reflects the sympathovagal balance. The mean frequency (+/-SD) of LF peaks was centered at 0.07 +/- 0.02 Hz. The mean frequency (+/-SD) of the individual HF band was 0.82 +/- 0.21 Hz. The LF/HF ratio in the R-R interval series [median, 29; interquartile range (IQR), 16-40] was higher than in the SBP series (median, 8; IQR, 4-14). The gain between R-R interval and SBP fluctuations (median, 4.2 ms/mm Hg; IQR, 2.4-5.0) in the LF band was higher than in the HF band (median, 1.7 ms/mm Hg; IQR, 1.4-3.0). SBP fluctuations lead R-R interval fluctuations in the LF band with a median phase difference of +96 degrees (IQR, 67-132). At LF the fluctuations in SBP precede changes in R-R interval with a time delay of 3.8 s. These observations indicate a dominant role of the sympathetic system in stable preterm infants in comparison with published adult values. Cross-spectral analysis allows a test for tracking the development of the sympathetic system in neonates.
A mathematical model of short-term cardiovascular regulation is used to investigate how heart period variability reflects the action of the autonomic regulatory mechanisms (vagal and sympathetic). The model includes the pulsating heart, the systemic (splanchnic and extrasplanchnic) and pulmonary circulation, the mechanical effect of respiration on venous return, two groups of receptors (arterial baroreceptors and lung stretch receptors), the sympathetic and vagal efferent branches, and a very low-frequency (LF) vasomotor noise. All model parameters were given on the basis of physiological data from the literature. We used data from humans whenever possible, whereas parameters for the regulation loops are derived from dog experiments. The model, with basal parameter values, produces a heart period power spectrum with two distinct peaks [a high frequency (HF) peak at the respiratory rate and a LF peak at approximately 0.1 Hz]. Sensitivity analysis on the mechanism gains suggests that the HF peak is mainly affected by the vagal mechanism, whereas the LF peak is increased by a high sympathetic gain and reduced by a high vagal gain. Moreover, the LF peak depends significantly on the reactivity of resistance vessels and is affected by noise, amplified by the sympathetic control loop at its resonance frequency. The model may represent a new tool to study alterations in the heart period spectrum on the basis of quantitative physiological hypotheses.
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