Paolo Castiglioni

Spectral and sequence analysis of finger blood pressure variability. Comparison with analysis of intra-arterial recordings.

The aim of our study was to assess whether the Finapres device is able to accurately monitor not only average blood pressure values but also blood pressure variability. To examine this issue, we analyzed 30-minute recordings of finger and intra-arterial pressure simultaneously obtained at rest in 14 patients. We compared systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse interval (the reciprocal of heart rate), overall variability (standard deviation), and specific time-domain and frequency-domain components. Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse interval spectral powers were computed by fast Fourier transform over three frequency bands: low frequency (0.025 to 0.07 Hz), midfrequency (0.07 to 0.14 Hz), and high frequency (0.14 to 0.35 Hz). The coherence, ie, the degree of association between blood pressure and pulse interval powers obtained by the two techniques, was also assessed. Standard deviations of diastolic blood pressure, mean arterial pressure, and pulse interval were similar when assessed from the two recordings, whereas standard deviation of systolic blood pressure was overestimated by analysis of finger pressure recordings. All powers of diastolic blood pressure and mean arterial pressure and high-frequency powers of systolic blood pressure estimated from analysis of finger blood pressure tracings were superimposable to those obtained by analyzing invasive recordings. Low-frequency and midfrequency powers of intra-arterial systolic blood pressure were significantly overestimated by the analysis of finger blood pressure tracings (+13.7 +/- 4.4 mm Hg2, P < .01, and +2.3 +/- 0.9 mm Hg2, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic cardiac regulation in obstructive sleep apnea syndrome : evidence from spontaneous baroreflex analysis during sleep

Objective To assess spontaneous baroreceptor-heart rate reflex sensitivity during sleep in patients with obstructive sleep apnea syndrome, a condition associated with increased cardiovascular morbidity and mortality and characterized by marked sympathetic activation, which is believed to originate from hypoxic chemoreceptor stimulation, although little is known of other possible mechanisms such as baroreflex impairment. Design and methods In 11 patients with severe obstructive sleep apnea syndrome (mean ± SD age 46.8 ± 8.1 years, apnea/hypopnea index 67.9 ± 19.1 h), who were normotensive or borderline hypertensive during wakefulness by clinic blood pressure measurements, finger blood pressure was monitored beat-by-beat non-invasively (Finapres) at night during polysomnography. Periods of wakefulness and sleep were identified based on electroencephalographic recordings. Baroreflex sensitivity was assessed by the sequence technique, as the slope of the regression line between spontaneous increases or reductions in systolic blood pressure (SBP) and the related lengthening or shortening in the RR interval, occurring over spontaneous sequences of four or more consecutive beats. The number of these sequences was also computed, as an additional index of baroreflex engagement by the spontaneous blood pressure fluctuations. The controls were age-related normotensive or borderline hypertensive subjects without sleep apnea who had been investigated in previous studies; in these subjects blood pressure was recorded intra-arterially over 24 h in ambulatory conditions and spontaneous baroreflex sensitivity was assessed by the sequence technique. Results In our patients the lowest nocturnal arterial oxygen saturation was 78.6 ± 12.1% (mean ± SD). During sleep, the number of pooled +RR/+SBP and −RR/−SBP sequences per hour was 20.3 ± 2.7 per h in patients with sleep apnea and 27.1 ± 2.1/h in controls (means ± SEM). The average baroreflex sensitivity during sleep periods was 7.04 ± 0.8 ms/mmHg in sleep apnea patients and 10.05 ± 2.1 ms/mmHg in controls. Both the pooled number of sequences and baroreflex sensitivity values of the sleep apnea patients were significantly (P <0.01) less than the corresponding night values of control subjects. In the sleep apnea patients, at variance from controls, baroreflex sensitivity did not show any increase during sleep compared with its values during wakefulness (6.9 ± 1.0 ms/mmHg). Conclusions Our data provide evidence that spontaneous baroceptor reflex sensitivity is depressed in severe obstructive sleep apnea syndrome. This suggests that in such patients baroreflex dysfunction and not only chemoreceptor stimulation by hypoxia may be involved in the sympathetic activation which occurs during sleep. Such dysfunction may contribute to the higher rate of cardiovascular morbidity and mortality reported in these patients.

Sequential spectral analysis of 24-hour blood pressure and pulse interval in humans.

Blood pressure and pulse interval are characterized not only by erratic variations but also by rhythmic fluctuations at low-, mid-, and high-frequency (0.025-0.07, 0.07-0.14, and 0.14-0.35 Hz, respectively). However, information on these phenomena has largely been derived from analysis of short-term recordings taken in standardized laboratory conditions. In seven normotensive and 10 untreated mild essential hypertensive subjects, power spectrum analysis was performed on the intra-arterial blood pressure and pulse interval signal collected over a 24-hour period using the fast Fourier transform algorithm and splitting the recording into contiguous segments of 256 beats. About 70% of the segments were suitable for the analysis; the segments excluded for a nonstationary signal amounted to only 30%. All powers were characterized by a high segment-to-segment variability, but in each subject the mid- and high-frequency powers of diastolic blood pressure and the mid-frequency power of systolic blood pressure were markedly reduced during the night as compared with the daytime period, whereas the opposite occurred for the low- and high-frequency powers of the pulse interval. Over the 24-hour period, mid- and high-frequency powers of blood pressure were positively correlated to each other, but both accounted for less than 25% of the 24-hour blood pressure variance. No difference between mean normalized power values of normotensive and hypertensive subjects was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Time versus frequency domain techniques for assessing baroreflex sensitivity.

Background Newer techniques to evaluate baroreflex sensitivity (BRS) are based on the analysis of blood pressure (BP) and heart rate (HR) time series in the time or frequency domain. These novel approaches are steadily gaining popularity, since they do not require injection of vasoactive substances, nor do they rely on a complex experimental set-up. Aim This review outlines and compares some basic features of the latest methods to assess spontaneous baroreflex function. Results Modern techniques for the estimation of spontaneous BRS are based on a variety of signal processing schemes and derive information on the baroreflex function from different perspectives. Thus factors such as respiration and other non-stationary agents may have different influences on the estimates provided by each of these approaches. Notwithstanding such individual specificity, however, it has been observed that in several physiological and pathophysiological conditions these techniques often provide comparable information on BRS changes over time, particularly when the estimates are averaged over time windows of a few minutes. Conclusions Due to the general agreement in the pattern of BRS among most modern methods, it seems reasonable to employ the most validated of these techniques, for which data obtained in several studies are already available.

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 is discussed. It includes: (1) sampling of a 24-h intra-arterial BP recording and extraction of the systolic and diastolic 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; and (3) estimation of power spectral density via fast Fourier transform (FFT) in each stationary record and computation of the power of each target oscillation. Using this procedure data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique was analyzed. The results revealed different patterns for 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. A second spectral estimate based on autoregressive modeling was performed. The results validate the FFT approach.<<ETX>>

Non-invasive beat-to-beat blood pressure monitoring: new developments

Continuous blood pressure monitoring is an essential prerequisite for any study on blood pressure variability. Invasive procedures are no longer acceptable for research projects in a clinical setting, and recently developed devices able to record blood pressure on a beat-by-beat basis in a non-invasive fashion may represent valuable alternative tools. This article will briefly review the available information on the most recent advances in this field. It will focus on further developments of the original technology for finger blood pressure monitoring introduced by Penáz et al., as well as on newer devices that have been proposed over the last few years for non-invasive cardiovascular monitoring both in research and in clinical studies.

Scale exponents of blood pressure and heart rate during autonomic blockade as assessed by detrended fluctuation analysis

It is still unknown how the autonomic nervous system influences the fractal dynamics of cardiovascular signals. We show that in supine volunteers vagal and sympathetic outflows contribute differently to the fractal structures of heart rate and blood pressure. The vagal outflow contributes with a ‘white‐noise’ component to the heart rate dynamics, indirectly influencing also the fractal dynamics of blood pressure. The sympathetic outflow contributes with a Brownian motion component to the heart rate dynamics, increasing long‐term fractal coefficients, without affecting long‐term coefficients of blood pressure. Results are explained by the different distribution and dynamics of acetylcholine receptors and of α‐ and β‐adrenergic receptors. Our findings may allow better delineating alterations of cardiovascular fractal dynamics in physiological and pathophysiological settings.

Daily Life Blood Pressure Changes Are Steeper in Hypertensive Than in Normotensive Subjects

Abstract—Target organ damage in hypertensive patients is related to their increased average blood pressure and greater 24-hour blood pressure variability. Whether the rate of blood pressure changes is also greater in hypertension, producing a greater stress on arterial walls, is not known, however. Our study aimed at addressing this issue by computer analysis of 24-hour ambulatory intra-arterial blood pressure recordings in 34 subjects (29 males), 13 normotensive subjects and 21 uncomplicated hypertensive subjects (mean age±SD, 40.4±11.8 years). The number, slope (mm Hg/s), and length (beats) of systolic blood pressure ramps of 3 or more consecutive beats characterized by a progressive increase (+) or reduction (−) in systolic blood pressure of at least 1 mm Hg per beat were computed for each hour and for the whole 24-hour period. Twenty-four-hour average systolic blood pressure was 112.9±2.1 and 159.4±5.7 mm Hg in normotensive and hypertensive subjects, respectively. Over the 24 hours, the number and length of systolic blood pressure ramps were similar in both groups, whereas the slope was markedly different (24-hour mean±SE slope, 4.80±0.30 in normotensives and 6.50±0.40 mm Hg/s in hypertensives, P <0.05). Ramp slope was not influenced by age or reflex pulse interval changes, but it was greater for higher ramp initial systolic blood pressure values. Thus, in daily life, hypertensive subjects are characterized by steeper blood pressure changes than normotensives, and this, regardless of the mechanisms, may have clinical implications, because it may be associated with greater traumatic effect on the vessel walls of hypertensive patients.

Daytime sleepiness and neural cardiac modulation in sleep-related breathing disorders.

Sleep‐related breathing disorders are common causes of excessive daytime sleepiness, a socially and clinically relevant problem. Mechanisms responsible for daytime sleepiness are still largely unknown. We investigated whether specific alterations in autonomic cardiac modulation during sleep, commonly associated with sleep‐related breathing disorders, are related to excessive daytime sleepiness. Fifty‐three patients with sleep‐related breathing disorders underwent nocturnal polysomnography. Excessive daytime sleepiness was diagnosed as a Multiple Sleep Latency Test response less than or equal to 600 s. We explored the relation of excessive daytime sleepiness, objectively determined, with indices of autonomic cardiac regulation, such as baroreflex sensitivity and heart rate variability, with polysomnographic indices of the severity of sleep‐related breathing disorders and with quality of sleep. Patients with excessive daytime sleepiness, when compared with patients without, had significantly lower baroreflex sensitivity and significantly higher low‐to‐high frequency power ratio of heart rate variability during the different stages of nocturnal sleep. By contrast, no differences were found in indices quantifying the severity of sleep‐related breathing disorders or sleep quality. We demonstrated that excessive daytime sleepiness is accompanied by a deranged cardiac autonomic control at night, the latter probably reflecting autonomic arousals not detectable in the EEG. As abnormal autonomic regulation is also known to be associated with increased cardiovascular risk, a possible relation between excessive daytime sleepiness and cardiovascular events in patients with sleep‐related breathing disorders deserves to be investigated in future studies.

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 SBP 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 ∼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 SBP spectral powers (α) in the regions around 0.1 (MF) and 0.3 (HF) Hz, and coherence between PI and SBP spectral powers in MF and HF regions was computed. SAD increased overall SBP variability and reduced PI variability throughout the frequency range examined. SAD markedly reduced ( P < 0.01) both α-MF (-65.6%) and α-HF (-79.9%) and consistently reduced the number of coherent segments [i.e., where coherence ( K 2) > 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.