A simplified two-component model of blood pressure fluctuation

Contribution of the renin-angiotensin and kallikrein-kinin systems to short-term variability of blood pressure in two-kidney, one-clip hypertensive rats

Low-frequency oscillations in R–R interval and blood pressure across the continuum of cardiovascular risk

Many patients with severe obstructive sleep apnea (OSA) do not complain of excessive daytime sleepiness (EDS), possibly due to increased sympathetic nervous activity (SNA) and accompanying heightened alertness. We hypothesized that in patients with OSA, those without subjective EDS (Epworth Sleepiness Scale, ESS score < 11) would have higher very low frequency (VLF) heart rate variability (HRV) during sleep, reflecting greater sympathetic heart rate modulation than patients with an ESS score ≥ 11. Patients with severe OSA (AHI ≥ 30: 26 with and 65 without heart failure) were divided into those with and without EDS. Heart rate (HR) signals were acquired in stage 2 sleep during periods of recurrent apneas and hypopneas and submitted to coarse graining spectral analysis, which extracts harmonic, neurally mediated contributions to HRV from total spectral power. Because the apnea-hyperpnea cycle entrains muscle SNA at VLF (0 to 0.04 Hz), VLF power was our principal between-group comparison. Subjects without EDS had higher harmonic VLF power (944 ± 839 vs 447 ± 461 msec(2), p = 0.003) than those with EDS, irrespective of the presence or absence of heart failure (1218 ± 944 vs 426 ± 299 msec(2), p = 0.043, and 1029 ± 873 vs 503 ± 533 msec(2), p = 0.003, respectively). ESS scores correlated inversely with VLF power in all (r = -0.294, p = 0.005) and in heart failure subjects (r = -0.468, p = 0.016). Patients with severe OSA but without EDS have higher VLF-HRV than those with EDS. This finding suggests that patients with severe OSA but without EDS have greater sympathetic modulation of HRV than those with EDS that may reflect elevated adrenergically mediated alertness. Taranto Montemurro L; Floras JS; Picton P; Kasai T; Alshaer H; Gabriel JM; Bradley TD. Relationship of heart rate variability to sleepiness in patients with obstructive sleep apnea with and without heart failure.

Objective The aim of the study was to estimate the impact of whole-body cryotherapy (WBC) and subsequent kinesiotherapy on oxidative stress and lipid profile when performed in a closed cryochamber on healthy subjects. Material and Methods The effect of ten WBC procedures lasting 3 minutes a day followed by a 60-minute session kinesiotherapy on oxidative stress and lipid profile in healthy subjects (WBC group, n = 16) was investigated. The WBC group was compared to the kinesiotherapy only (KT; n = 16) group. The routine parameters of oxidative stress (antioxidant enzymatic and nonenzymatic antioxidant status, lipid peroxidation products, total oxidative status (TOS), and oxidative stress index (OSI)) and lipid profile were estimated one day before the beginning and one day after the completion of the research program. Results After treatment, in the WBC group, a significant decrease of oxidative stress markers (TOS and OSI) and a significant increase of total antioxidant capacity were observed. The activity of plasma SOD-Mn and erythrocyte total SOD increased significantly in the WBC group. In the KT group, the erythrocyte activity of total SOD, CAT, and GR decreased significantly after the treatment. The levels of T-Chol and LDL-Chol decreased significantly after treatment in both groups, but the observed decrease of these lipid parameters in the WBC group was higher in comparison to the KT group. The level of TG decreased significantly after treatment in the WBC group only. Conclusion WBC performed in a closed cryochamber followed by kinesiotherapy improves lipid profile and decreases oxidative stress in healthy subjects.

‘Respiratory’ oscillations of cardiovascular parameters during voluntary apnea

Interactions between mechanisms governing ventilation and blood pressure (BP) are not well understood. We studied in 11 resting normal subjects the effects of sustained isocapnic hyperventilation on arterial baroreceptor sensitivity, determined as the alpha index between oscillations in systolic BP (SBP) generated by respiration and oscillations present in R-R intervals (RR) and in peripheral sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA)]. Tidal volume increased from 478 +/- 24 to 1,499 +/- 84 ml and raised SBP from 118 +/- 2 to 125 +/- 3 mmHg, whereas RR decreased from 947 +/- 18 to 855 +/- 11 ms (all P < 0.0001); MSNA did not change. Hyperventilation reduced arterial baroreflex sensitivity to oscillations in SBP at both cardiac (from 13 +/- 1 to 9 +/- 1 ms/mmHg, P < 0.001) and MSNA levels (by -37 +/- 5%, P < 0.0001). Thus increased BP during hyperventilation does not elicit any reduction in either heart rate or MSNA. Baroreflex modulation of RR and MSNA in response to hyperventilation-induced BP oscillations is attenuated. Blunted baroreflex gain during hyperventilation may be a mechanism that facilitates simultaneous increases in BP, heart rate, and sympathetic activity during dynamic exercise and chemoreceptor activation.

Effects of clonidine on power spectral analysis of heart rate variability in mild essential hypertension

This study was addressed to investigate the contribution of vagal and sympathetic mechanisms to the genesis of low-frequency (LF) oscillations of RR-interval. To this aim, we utilized the pathophysiological model of tetraplegics, who have intact vagal afferent and efferent pathways of the baroreceptor reflex arc but interrupted medullary-spinal sympathetic pathways. We studied nine complete, traumatic, tetraplegics (C4-C7, TET) and 10 normally healthy subjects (NR) at rest and during physiological baroreceptors unloading induced by 70 degrees head-up tilt. Autoregressive power spectral analysis was used to investigate RR-interval and systolic arterial pressure (SAP) variabilities. Baroreflex modulation of sinus node was assessed by the spontaneous baroreflex sequences method. Both at-rest and during-tilt LF and high frequency (HF) components were detected in RR-interval of NR, whereas in TET only the HF component was observed in both conditions (with one exception). Baroreflex sensitivity (BRS) did not significantly differ between TET and NR at rest, and underwent a significant and similar decrease during tilt in both groups, being accompanied in NR by a significant increase in LF relative power. Spectral analysis of SAP provided results similar to RR-interval. Tilt also slowed the centre frequency of the LF components of RR-interval and SAP. During unperturbed physiological conditions, a change in efferent vagal activity to the heart from baroreflex stimulation by spontaneous arterial pressure changes, is unlikely to contribute on its own to the genesis of LF heart period oscillations in humans who lack the ability to modulate sympathetic nerve traffic to the heart. However, the possibility that a baroreflex modulation of LF oscillations require an intact sympathetic control should be carefully considered.

The aim of the study was to compare changes in blood pressure (BP) and heart rate (HR) variability, catecholamine and neuropeptide Y (NPY) plasma levels induced by passive head-up tilt in normal and sino-aortic denervated (SAD) chloralose-anaesthetized dogs. In controls, 80 degrees head-up tilt test failed to change BP and increased HR. Plasma noradrenaline and NPY levels (but not adrenaline) significantly rose. In SAD dogs, head-up tilt test induced a marked and reproducible decrease in BP without any change in HR or noradrenaline and NPY plasma levels. In SAD dogs, spectral analysis in supine position was characterized by reduced variability in the high frequency (HF) band of the HR spectrum without changes in low frequency (LF) bands of both HR and systolic blood pressure (SBP). Head-up tilt test increased the LF component of SBP variability and decreased the HF component of HR variability in controls but failed to modify HR and BP variabilities in SAD dogs. In conclusion, sino-aortic denervation in dogs elicits a reproducible postural fall in BP with impaired adaptation of sympathetic nervous system activity. This model may be of value in evaluating the pharmacological effects of drugs for the management of orthostatic hypotension.

It takes two to tango: the coherence of cardiac output and sympathetic nerve activity

The effects of electrical vestibular stimulation upon movement and perception suggest two evoked sensations: head roll and inter-aural linear acceleration. The head roll vector causes walking subjects to turn in a direction dependent on head pitch, requiring generation of torque around a vertical axis. Here the effect of vestibular stimulation upon vertical torque (T(z)) was investigated during quiet stance. With the head tilted forward, square-wave stimuli applied to the mastoid processes evoked a polarity-specific T(z) response accompanied by trunk yaw. Stochastic vestibular stimulation (SVS) was used to investigate the effect of head pitch with greater precision; the SVS–T(z) cross-correlation displayed a modulation pattern consistent with the head roll vector and this was also reflected by changes in coherence at 2–3 Hz. However, a separate response at 7–8 Hz was unaffected by head pitch. Head translation (rather than rotation) had no effect upon this high frequency response either, suggesting it is not caused by a sense of body rotation induced by an inter-aural acceleration vector offset from the body. Instead, high coherence between medio-lateral shear force and T(z) at the same frequency range suggests it is caused by mechanical coupling to evoked medio-lateral sway. Consistent with this explanation, the 7–8 Hz response was attenuated by 90 deg head roll or yaw, both of which uncouple the inter-aural axis from the medio-lateral sway axis. These results demonstrate two vertical torque responses to electrical vestibular stimulation in standing subjects. The high frequency response can be attributed to mechanical coupling to evoked medio-lateral sway. The low frequency response is consistent with a reaction to a sensation of head roll, and provides a novel method for investigating proprioceptive-vestibular interactions during stance.

This study was designed to establish the neurally-mediated effects of baroceptor and cardiopulmonary reflexes on heart rate in normal subjects. We therefore studied the effects of various interventions, able to modify the activity of arterial baroreceptors and cardiopulmonary receptors, on the power spectrum of the R-R interval in nine healthy men. To confirm the efficacy of these interventions left ventricular volume was monitored using a portable radionuclide probe. Isosorbide dinitrate (5 mgm sublingually) while sitting unloads both baroreceptors and the cardiopulmonary receptors; it decreased left ventricular end-diastolic volume (p < 0.01) and the mean R-R interval (p < 0.005), increased the power of the low-frequency (LF) component of the R-R interval (p < 0.01), decreased the power of the high-frequency (HF) component (p < 0.005) and increased the LF/HF ratio (p < 0.05). The application of cuffs around the thighs in the supine position, which unloads only cardiopulmonary receptors, decreased left ventricular end-diastolic volume (p < 0.05) but did not affect mean R-R interval, LF component, HF component and LF/HF ratio (p > or = 0.10). Leg raising, which loads only cardiopulmonary receptors, increased left ventricular end-diastolic volume (p < 0.05) and did not affect the mean R-R interval, LF component, HF component and LF/HF ratio (p > or = 0.10). In conclusion, our data suggest that, in normal man, baroreceptor unloading increased sympathetic and decreased parasympathetic neural control of heart rate; cardiopulmonary reflexes do not appear to have a direct neurally mediated effect on heart rate.

The purpose of this study was to assess Analgesia/Nociception Index (ANI) and bispectral index (BIS) variations in supine and prone position during closed-tracheal suction in intensive care unit (ICU) patients with severe COVID-19 pneumonia requiring myorelaxation and prone positioning. We retrospectively reviewed the data of 15 patients hospitalized in ICU for severe COVID-19 pneumonia requiring sedation, myorelaxation and prone positioning. The BIS, instant ANI (ANIi), mean ANI (ANIm), heart rate (HR), systolic blood pressure (SBP) and SpO2 were retrieved in supine and prone position 1 min before tracheal suction then every minute from the beginning of tracheal suction during 4 min and compared using ANOVA for repeated measures (p < 0.05 considered as statistically significant). Both ANIm and ANIi decreased significantly during tracheal suction with no difference between positions, whereas BIS showed no significant variation within time and between groups. The median [Q1–Q3] ANIm value decreased from 87 [68–98] to 79 [63–09] in supine position and from 79 [63–95] to 78 [66–98] in prone position 2 min after the beginning of tracheal suction. The median [Q1–Q3] ANIi value decreased earlier 1 min after the beginning of tracheal suction from 84 [69–98] to 73 [60–90] in supine position and from 84 [60–99] to 71 [51–88] in prone position. Both HR, SBP and SpO2 varied modestly but significantly during tracheal suction with no difference between positions. Monitoring ANI, but not BIS, may be of interest to detect noxious stimuli such as tracheal suction in ICU myorelaxed patients with severe COVID-19 pneumonia requiring prone positioning.Electronic supplementary materialThe online version of this article (10.1007/s10877-020-00612-w) contains supplementary material, which is available to authorized users.

Heart rate variability in patients presenting with neurally mediated syncope in an emergency department

The function of the autonomic nervous system in patients with vertigo was examined, and several parameters of the RR interval were analyzed quantitatively in the supine and upright positions. Fifty-five patients with vertigo associated with autonomic nerve dysfunction were examined, and were analyzed by computer. Patients with normal autonomic function (Group 1: n=26) and those with autonomic dysfunction (Group 2: n=25) were compared statistically. Group 2 contained four subgroups: Group 2a: 15 patients with sympathetic hyperfunction; Group 2b: 9 patients with sympathetic hypofunction; Group 2c: 2 patients with parasympathetic hyperfunction; and Group 2d: 6 patients with parasympathetic hypofunction). Six patients had double dysfunctions.The parameters examined were:1. Heart Rate (HR).2. Coefficient of variation of RR interval (RRcv).3. Relation between RRcv and age.4. Power spectrum of RR interval.HR and RRcv were recorded in the supine and upright positions. RR intervals of 20 seconds were computed with FFT, and 2 major components (low frequency; 0.1Hz (P1): high frequency; 0.3Hz (P2)) of the power spectrum were analyzed. HR of Group 2a was significantly higher than that of Group 1 in both the supine and upright positions. RRcv of Group 2b was lower than that of Group 1. RRcv of Group 2c was reduced in the upright position. RRcv of Group 2d was lower than that of Group 1 and tended to rise in the upright position. RRcv of Group 1 in the upright position was related to age (r=-0.62), but that of Group 2 showed no significant relation. The power spectrum of Group 1 showed a dominant P2 in the supine position and a dominant P1 in the upright position, but the power spectrum of Group 2a revealed a dominant P1 in both the supine and upright positions and that of Group 2b showed no marked P1 and P2 components.