Marco Di Rienzo

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.

24-Hour blood pressure monitoring: Evaluation of Spacelabs 5300 monitor by comparison with intra-arterial blood pressure recording in ambulant subjects

The accuracy of 24-h blood pressure values obtained by ambulatory monitoring via the Spacelabs 5300 device was evaluated by comparison with simultaneous 24-h intra-arterial blood pressure recording from the contralateral arm. The comparison was made in eight essential hypertensive subjects in whom non-invasive blood pressure was measured every 15 (day) or 30 min (night). The measurements were automatically and visually edited to eliminate artefactual readings and hourly and 24-h means were calculated separately for systolic and diastolic blood pressure. The corresponding intra-arterial blood pressure means were also calculated. In the group as a whole, hourly means obtained by the non-invasive device were similar or only slightly different from those recorded intra-arterially. The 24-h systolic blood pressure mean obtained non-invasively was not significantly different from that obtained intra-arterially (138.4 +/- 9.1 and 142.9 +/- 9.2 mmHg, respectively), nor were the corresponding 24-h diastolic blood pressure means significantly different (83.5 +/- 4.5 and 80.6 +/- 3.5 mmHg, respectively). However, in spite of these similarities, there were contrasting and often large discrepancies between non-invasive and intra-arterial values in individual subjects. For the 24-h systolic blood pressure mean the discrepancies ranged from 7.6 +/- 1.1 to 16.1 +/- 2.2 mmHg and for the 24-h diastolic blood pressure mean, from 3.5 to 13.2 mmHg. Thus, the Spacelabs 5300 device has a limited ability to correctly estimate ambulatory blood pressure in individual subjects. It may be better suited for the estimation of group blood pressures, but only because errors are smoothed by the summation of individual errors of opposing signs.

Estimation of Blood Pressure Variability From 24-Hour Ambulatory Finger Blood Pressure

Portapres is a noninvasive, beat-to-beat finger blood pressure (BP) monitor that has been shown to accurately estimate 24-hour intra-arterial BP at normal and high BPs. However, no information is available on the ability of this device to accurately track ambulatory BP variability. In 20 ambulatory normotensive and hypertensive subjects, we measured 24-hour BP by Portapres and through a brachial artery catheter. BP and pulse interval variabilities were quantified by (1) the SDs of the mean values (overall variability) and (2) spectral power, computed either by fast Fourier transform and autoregressive modeling of segments of 120-second duration for spectral components from 0.025 to 0.50 Hz or in a very low frequency range (between 0.00003 and 0.01 Hz) by broadband spectral analysis. The 24-hour SD of systolic BP obtained from Portapres (24+/-2 mm Hg) was greater than that obtained intra-arterially (17+/-1 mm Hg, P<0.01), but the overestimation was less evident for diastolic (3+/-1 mm Hg, P<0.01) and mean (3+/-1 mm Hg, P<0.01) BP. The BP spectral power <0.15 Hz was also overestimated by Portapres more for systolic than for diastolic and mean BPs; similar findings were obtained by the fast Fourier transform, the autoregressive approach, and focusing on the broadband spectral analysis. BP spectral power >0.15 Hz obtained by the Portapres was similar during the day but lower during the night when compared with those obtained by intra-arterial recordings (P<0.01). No differences were observed between Portapres and intra-arterial recordings for any estimation of pulse interval variabilities. The overestimation of BP variability by Portapres remained constant over virtually the entire 24-hour recording period. Thus, although clinical studies are still needed to demonstrate the clinical relevance of finger BP variability, our study shows that Portapres can be used with little error to estimate 24-hour BP variabilities if diastolic and mean BPs are used. For systolic BP, the greater error can be minimized by using correction factors.

Textile Technology for the Vital Signs Monitoring in Telemedicine and Extreme Environments

This paper illustrates two extensive applications of a smart garment we previously developed for the monitoring of ECG, respiration, and movement. In the first application, the device, named Maglietta Interattiva Computerizzata (MagIC), was used for the home monitoring of cardiac patients. The used platform included MagIC for signals collection, a touchscreen computer with a dedicated software for data handling, and a universal mobile telecommunications system (UMTS) dongle for data transmission, via email, to three cardiologists. Three patients daily-performed 3-min telemonitoring sessions for 30 days by using the platform. The whole system behaved correctly in 85 out of 90 sessions. In five instances, a second session was required due to UMTS traffic congestion. Only in three sessions, cardiologists asked the patient to repeat the acquisition because of poor signal quality. In the second application, MagIC was used to evaluate the effects of high-altitude hypoxia on sleep and 24 h daily life in 30 healthy subjects at 3500 and 5400 m above sea level on Mount Everest slopes. The use of MagIC garment was reported to be simple and requiring short instrumentation time even in the demanding expedition environment. The signal quality was adequate in 111 out of 115 recordings and 90% of the subjects found the vest comfortable.

Sympathectomy and Cardiovascular Spectral Components in Conscious Normotensive Rats

We examined the extent to which sympathetic influences are reflected by spectral powers of blood pressure and pulse interval in specific frequency bands in spontaneously behaving Wistar-Kyoto rats subjected to continuous intraarterial blood pressure recording. The rats were pretreated with 6-hydroxydopamine (150 mg/kg twice in 1 week, n = 19) to produce chemical sympathectomy or received vehicle (n = 15). In the sympathectomized group, additional monitoring sessions were performed with rats under alpha-adrenergic receptor blockade with phenoxybenzamine (n = 8), beta-receptor blockade with propranolol (n = 7), or cholinergic receptor blockade with atropine (n = 8). Blood pressure signals were analyzed by a computer to calculate spectral powers (fast Fourier transform) in the low-frequency (0.025 to 0.1 Hz), mid-frequency (0.1 to 0.6 Hz), and high-frequency (0.8 to 3.0 Hz) bands. In sympathectomized rats, low-frequency power of blood pressure was 70% greater than in intact rats, whereas mid-frequency power was 60% smaller (P < .05 for both) and high-frequency power was unchanged. High-frequency power of pulse interval was also unchanged in sympathectomized rats, whereas low- and mid-frequency powers were reduced by approximately 50% (P < .05). No further alterations in spectral powers were observed by adding alpha- or beta-adrenergic blockade to sympathectomy, whereas adding cholinergic blockade caused a striking reduction in all pulse interval powers. Thus, mid-frequency blood pressure power depends on sympathetic but also to a substantial extent on nonsympathetic influences. Sympathetic influences do not contribute to low-frequency blood pressure power, having instead a restraining effect. The low- and mid-frequency pulse interval powers depend on both sympathetic and vagal influences. Thus, no blood pressure or pulse interval power in the mid- and low-frequency ranges can be regarded as a specific marker of sympathetic activity.

Reflex control of blood pressure and heart rate by arterial baroreceptors and by cardiopulmonary receptors in the unanaesthetized cat.

Studies in unanaesthetized animals have reported that section of the carotid sinus and aortic nerves is accompanied by an increased blood pressure variability but not by a sustained blood pressure rise, thus questioning the role of arterial baroreceptors in the long term control of mean blood pressure values. However, sino-aortic denervation (SAD) does not produce denervation of all baroreceptor areas, and it has been suggested that aortic baroreceptor fibres in the vagus and cardiopulmonary vagal afferents that restrain sympathetic vasoconstrictor tone prevent blood pressure from permanently rising. In unanaesthetized cats we recorded blood pressure intra-arterially for 8-12 h when baroreflexes were intact, 7 days after SAD and 1-2 days additional bilateral cervical vagotomy. Blood pressure signals were analysed by computer to provide means and coefficients of variation (CV, variabilities) for each recording period. In intact cats, mean blood pressure was 99 +/- 7 mmHg (average +/- s.e.) and CV 6 +/- 1%. SAD did not alter mean blood pressure but markedly increased CV (12 +/- 2%; P less than 0.01). Additional vagotomy did not alter mean blood pressure (104 +/- 6 mmHg), nor did it alter the increased CV observed after SAD alone. Vagotomy failed to affect mean blood pressure and CV even when performed in cats with intact carotid and aortic nerves. The lack of effect of vagotomy did not depend on simultaneous section of afferent and efferent fibres, because selective blockade of the latter by atropine also failed to affect mean blood pressure and CV.(ABSTRACT TRUNCATED AT 250 WORDS)