Effect of sinoaortic denervation on frequency-domain estimates of baroreflex sensitivity in conscious cats

In animals and humans, baroreceptor modulation of the sinus node in daily life can be studied by identification of the number of sequences in which systolic blood pressure (SBP) and pulse interval (PI) linearly decrease or increase for several beats. It is also studied by power spectral analysis of SEP and PI in regions where their powers are coherent, although, in contrast to the sequence method, whether this frequency-domain method specifically reflects the baroreceptor-heart rate reflex has not been adequately tested. We recorded intra-arterial BP for similar to 3.5 h in eight conscious cats, first intact and then 7-10 days after sinoaortic denervation (SAD). Sensitivity of baroreceptor-heart rate reflex was assessed in 120-s segments by the square: root of the ratio of PI and SEP spectral powers (alpha) in the regions around 0.1 (MF) and 0.3 (RF) Hz, and coherence between PI and SEP spectral powers in MF and HF regions was computed. SAD increased overall SEP variability and reduced PI variability throughout the frequency range examined. SAD markedly reduced (P 0.5] and average coherence values in the MF region. In the HF region, however SAD did not alter the number of coherent segments, and although average coherence value throughout the HF band was reduced, in restricted portions of the band (different between animals), a high coherence value survived denervation. No significant changes were seen in any measured variables in five sham-operated cats. Thus the frequency-domain method specifically reflects baroreflex modulation of heart rate in the MF region only. In the HF region, in contrast, baroreflex and nonbaroreflex influences on the sinus node both contribute to a variable degree to determination of heart rate responses to BP oscillations. If used to study baroreflex function in daily life, this method should use the coefficient derived from MF data

24 h sequential spectral analysis of arterial blood pressure and pulse interval in free-moving subjects.

A procedure for the 24 h tracking of the 0.25, 0.1, and 0.05 Hz oscillations in blood pressure (BP) and pulse interval (PI) in ambulant subjects has been developed. It includes: 1) sampling of a 24 h intra-arterial BP recording, extraction of the systolic (S) and diastolic (D) BP and PI from each heart beat followed by storage into separate series; 2) high-pass filtering and a splitting of each series into consecutive records of 256 values; 3) estimation of power spectral density (PSD) via FFT in each stationary record, and finally, computation of the power of each target oscillation. Using this procedure we analyzed data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique. The results revealed different patterns of the 0.25, 0.1, and 0.05 oscillations over the day-night cycle, showing a differentiated involvement during the 24 h of the mechanisms responsible for such rhythmic phenomena. Moreover, in order to reinforce the meaning of the obtained results and to exclude the possible negative effects due to the drawbacks typical of the FFT algorithm, we also performed a second spectral estimate based on the AR modeling. The obtained results validates the FFT approach

Smoking impairs baroreflex sensitivity in humans

In 10 healthy smokers, finger blood pressure was recorded continuously for 1 h in a supine control condition and for 1 h while smoking four cigarettes, one every 15 min. Smoking increased average systolic blood pressure (+19%, P < 0.01) and its variability and reduced pulse interval (reciprocal of heart rate, -22%, P < 0.01) and its variability. Baroreflex sensitivity, as assessed by the slope of spontaneous hypertension/bradycardia or hypotension/tachycardia sequences and by the alpha-coefficient (squared ratio between pulse interval and systolic blood pressure spectral powers at 0.1 Hz) was significantly decreased (P < 0.01) during smoking, whereas there were no effects of smoking on the reflex changes in pulse interval induced by carotid baroreceptor stimulation through a neck suction device. Sham smoking by a drinking straw had no effects on any of the above parameters. Thus, when assessed in the absence of laboratory maneuvers in daily life conditions, baroreflex sensitivity is markedly impaired by smoking. This impairment may contribute to the smoking-induced increase in blood pressure and heart rate as well as to the concomitant alterations in their variability

Baroreflex modulation of the cardiovascular system: new insights from the joint analysis of blood pressure and heart rate signals.

This paper focuses on a number of methods for the analysis of the relationship between the arterial baroreflex and different components of blood pressure and heart rate variability. Broad-band spectral analysis techniques have allowed us to obtain experimental evidence that the arterial baroreflex exerts its influence not only on fast but also on slow components of blood pressure and heart rate, i.e., on components with periods longer than 60 sec. Focusing on faster changes in blood pressure and heart rate, both time domain and frequency domain techniques have been developed to track the sensitivity of baroreflex heart rate modulation over time, either in laboratory or in daily life conditions. These approaches have considerably broadened our understanding of the role of baroreflex modulation of the heart and peripheral circulation in a number of pathological and physiological conditions