Blood Pressure Oscillations Research Articles

Synchronization of the Processes of Autonomic Control of Blood Circulation in Humans Is Different in the Awake State and in Sleep Stages.

The influence of higher nervous activity on the processes of autonomic control of the cardiovascular system and baroreflex regulation is of considerable interest, both for understanding the fundamental laws of the functioning of the human body and for developing methods for diagnostics and treatment of pathologies. The complexity of the analyzed systems limits the possibilities of research in this area and requires the development of new tools. Earlier we propose a method for studying the collective dynamics of the processes of autonomic control of blood circulation in the awake state and in different stages of sleep. The method is based on estimating a quantitative measure representing the total percentage of phase synchronization between the low-frequency oscillations in heart rate and blood pressure. Analysis of electrocardiogram and invasive blood pressure signals in apnea patients in the awake state and in different sleep stages showed a high sensitivity of the proposed measure. It is shown that in slow-wave sleep the degree of synchronization of the studied rhythms is higher than in the awake state and lower than in sleep with rapid eye movement. The results reflect the modulation of the processes of autonomic control of blood circulation by higher nervous activity and can be used for the quantitative assessment of this modulation.

Endothelial Nitric Oxide Synthase (eNOS) and the Cardiovascular System: in Physiology and in Disease States

Endothelial nitric oxide synthase (eNOS) plays a critical role in regulating and maintaining a healthy cardiovascular system. The importance of eNOS can be emphasized from the genetic polymorphisms of the eNOS gene, uncoupling of eNOS dimerization, and its numerous signaling regulations. The activity of eNOS on the cardiac myocytes, vasculature, and the central nervous system are discussed. The effects of eNOS on the sympathetic autonomic nervous system (SANS) and the parasympathetic autonomic nervous system (PANS), both of which profoundly influence the cardiovascular system, will be elaborated. The relationship between the eNOS protein with cardiovascular autonomic reflexes such as the baroreflex and the Exercise Pressor Reflex will be discussed. For example, the effects of endogenous nitric oxide (NO) are shown to be mediated by the eNOS protein and that eNOS-derived endothelial NO is most effective in regulating blood pressure oscillations via modulating the baroreflex mechanisms. The protective action of eNOS on the CVS is emphasized here because dysfunction of the eNOS enzyme is intricately correlated with the pathogenesis of several cardiovascular diseases such as hypertension, arteriosclerosis, myocardial infarction, and stroke. Overall, our current understanding of the eNOS protein with a focus on its role in the modulation, regulation, and control of the cardiovascular system in a normal physiological state and in cardiovascular diseases are discussed.

Characterization of Mayer-wave oscillations in functional near-infrared spectroscopy using a physiologically informed model of the neural power spectra.

.Significance: Mayer waves are spontaneous oscillations in arterial blood pressure that can mask cortical hemodynamic responses associated with neural activity of interest.Aim: We aim to characterize the properties of oscillations in the functional near-infrared spectroscopy (fNIRS) signal generated by Mayer waves in a large sample of fNIRS recordings. Further, we aim to determine the impact of short-channel correction for the attenuation of these unwanted signal components.Approach: Mayer-wave oscillation parameters were extracted from 310 fNIRS measurements using the fitting oscillations and one-over-f method to compute normative values. The effect of short-channel correction on Mayer-wave oscillation power was quantified on 222 measurements. The practical benefit of the short-channel correction approach for reducing Mayer waves and improving response detection was also evaluated on a subgroup of 17 fNIRS measurements collected during a passive auditory speech detection experiment.Results: Mayer-wave oscillations had a mean frequency of 0.108 Hz, bandwidth of 0.04 Hz, and power of . The distribution of oscillation signal power was positively skewed, with some measurements containing large Mayer waves. Short-channel correction significantly reduced the amplitude of these undesired signals; greater attenuation was observed for measurements containing larger Mayer-wave oscillations.Conclusions: A robust method for quantifying Mayer-wave oscillations in the fNIRS signal spectrum was presented and used to provide normative parameterization. Short-channel correction is recommended as an approach for attenuating Mayer waves, particularly in participants with large oscillations.

Blood pressure oscillations impact signal-averaged sympathetic transduction of blood pressure: implications for the association with resting sympathetic outflow.

Signal-averaged sympathetic transduction of blood pressure (BP) is inversely related to resting muscle sympathetic nerve activity (MSNA) burst frequency in healthy cohorts. Whether this represents a physiological compensatory adaptation or a methodological limitation, remains unclear. The current analysis aimed to determine the contribution of methodological limitations by evaluating the dependency of MSNA transduction at different levels of absolute BP. Thirty-six healthy participants (27 ± 7 yr, 9 females) underwent resting measures of beat-to-beat heart rate, BP, and muscle sympathetic nerve activity (MSNA). Tertiles of mean arterial pressure (MAP) were computed for each participant to identify cardiac cycles occurring below, around, and above the MAP operating pressure (OP). Changes in hemodynamic variables were computed across 15 cardiac cycles within each MAP tertile to quantify sympathetic transduction. MAP increased irrespective of sympathetic activity when initiated below the OP, but with MSNA bursts provoking larger rises (3.0 ± 0.9 vs. 2.1 ± 0.7 mmHg; P < 0.01). MAP decreased irrespective of sympathetic activity when initiated above the OP, but with MSNA bursts attenuating the drop (-1.3 ± 1.1 vs. -3.1 ± 1.2 mmHg; P < 0.01). In participants with low versus high resting MSNA (12 ± 4 vs. 32 ± 10 bursts/min), sympathetic transduction of MAP was not different when initiated by bursts below (3.2 ± 1.0 vs. 2.8 ± 0.9 mmHg; P = 0.26) and above the OP (-1.0 ± 1.3 vs. -1.6 ± 0.8 mmHg; P = 0.08); however, low resting MSNA was associated with a smaller proportion of MSNA bursts firing above the OP (15 ± 5 vs. 22 ± 5%; P < 0.01). The present analyses demonstrate that the signal-averaging technique for calculating sympathetic transduction of BP is influenced by the timing of an MSNA burst relative to cyclic oscillations in BP.NEW & NOTEWORTHY The current signal-averaging technique for calculating sympathetic transduction of blood pressure does not consider the arterial pressure at which each muscle sympathetic burst occurs. A burst firing when mean arterial pressure is above the operating pressure was associated with a decrease in blood pressure. Thus, individuals with higher muscle sympathetic nerve activity demonstrate a reduced sympathetic transduction owing to the weighted contribution of more sympathetic bursts at higher levels of arterial pressure.

Use of Mayer wave activity to demonstrate aberrant cardiovascular autonomic control following sports concussion injury.

Dysregulation of cardiovascular autonomic control is gaining recognition as a prevailing consequence of concussion injury. Characterizing the presence of autonomic dysfunction in concussed persons is inconsistent and conventional metrics of autonomic function cannot differentiate the presence/absence of injury. Mayer wave (MW) activity originates through baroreflex adjustments to blood pressure (BP) oscillations that appear in the low‐frequency (LF: 0.04–0.15 Hz) band of the BP and heart rate (HR) power spectrum after a fast Fourier transform. We prospectively explored MW activity (∼0.1 Hz) in 19 concussed and 19 noninjured athletes for 5 min while seated at rest within 48 h and 1 week of injury. MW activity was derived from the LF band of continuous digital electrocardiogram and beat‐to‐beat BP signals (LFHR, LF‐SBP, MWHR, and MW‐SBP, respectively); a proportion between MWBP and MWHR was computed (cMW). At 48 h, the concussion group had a significantly lower MWBP and cMW than controls; these differences were gone by 1 week. MWHR, LFHR, and LF‐SBP were not different between groups at either visit. Attenuated sympathetic vasomotor tone was present and the central autonomic mechanisms regulating MW activity to the heart and peripheral vasculature became transiently discordant early after concussion with apparent resolution by 1 week.

The Influence of Carbon Dioxide on Cerebral Autoregulation During Sevoflurane-based Anesthesia in Patients With Type 2 Diabetes.

Cerebral autoregulation (CA) continuously adjusts cerebrovascular resistance to maintain cerebral blood flow (CBF) constant despite changes in blood pressure. Also, CBF is proportional to changes in arterial carbon dioxide (CO 2 ) (cerebrovascular CO 2 reactivity). Hypercapnia elicits cerebral vasodilation that attenuates CA efficacy, while hypocapnia produces cerebral vasoconstriction that enhances CA efficacy. In this study, we quantified the influence of sevoflurane anesthesia on CO 2 reactivity and the CA-CO 2 relationship. We studied patients with type 2 diabetes mellitus (DM), prone to cerebrovascular disease, and compared them to control subjects. In 33 patients (19 DM, 14 control), end-tidal CO 2 , blood pressure, and CBF velocity were monitored awake and during sevoflurane-based anesthesia. CA, calculated with transfer function analysis assessing phase lead (degrees) between low-frequency oscillations in CBF velocity and mean arterial blood pressure, was quantified during hypocapnia, normocapnia, and hypercapnia. In both control and DM patients, awake CO 2 reactivity was smaller (2.8%/mm Hg CO 2 ) than during sevoflurane anesthesia (3.9%/mm Hg; P <0.005). Hyperventilation increased CA efficacy more (3 deg./mm Hg CO 2 ) in controls than in DM patients (1.8 deg./mm Hg CO 2 ; P <0.001) in both awake and sevoflurane-anesthetized states. The CA-CO 2 relationship is impaired in awake patients with type 2 DM. Sevoflurane-based anesthesia does not further impair this relationship. In patients with DM, hypocapnia induces cerebral vasoconstriction, but CA efficacy does not improve as observed in healthy subjects.

Blood pressure behavior during mechanical thrombectomy and drugs used for conscious sedation or general anesthesia.

The optimal blood pressure (BP) during mechanical thrombectomy for acute ischemic stroke is currently unclear. To investigate BP behavior during mechanical thrombectomy in patients with acute ischemic stroke and its relationship with drugs used for sedation or general anesthesia. Additionally, we investigated the association between BP oscillation during mechanical thrombectomy and recanalization status, and with functional outcome at discharge. Consecutive patients treated with mechanical thrombectomy for acute ischemic stroke were evaluated in a tertiary hospital from December/2009 to December/2015. Maximum, minimum, and mean systolic and diastolic BP, and mean arterial pressures were collected during the procedure. Sedative drugs were also reviewed. Fifty-three patients with a mean age of 71.9 years (60.4% men) were treated with mechanical thrombectomy. The mean reduction in systolic BP and mean arterial pressure from hospital admission to mechanical thrombectomy were respectively 42 and 36 mmHg. During the procedure, oscillations were 50.4 mmHg for systolic, and 33.2 mmHg for diastolic BP. Patients treated with neuromuscular blocking drugs had more oscillation in systolic BP from hospital admission to procedure (51.1 versus 26.2 mmHg, P=0.06). The use of cisatracurium (43.9 versus 29.6 mmHg, P=0.02) and succinylcholine (44.7 versus 29.3 mmHg, P=0.01) were associated with a significant drop in BP during the procedure. Significant BP oscillation occurs during mechanical thrombectomy. Drugs used for conscious sedation or general anesthesia, specifically neuromuscular blocking agents, might have an influence upon BP levels.

Rapid Assessment of Blood Pressure Variability and Outcome After Successful Thrombectomy.

High blood pressure (BP) variability after endovascular stroke therapy is associated with poor outcome. Conventional BP variability measures require long recordings, limiting their utility as a risk assessment tool to guide clinical decision-making. Here, we performed rapid assessment of BP variability by spectral analysis and evaluated its association with early clinical improvement and long-term functional outcomes. We conducted a prospective study of 146 patients with anterior circulation ischemic stroke who underwent successful endovascular stroke therapy. Spectral analysis of 5-minute recordings of beat-to-beat BP was used to quantify BP variability. Outcomes included initial clinical response and modified Rankin Scale at 90 days. Increased BP variability at high frequencies was independently associated with poor functional outcome at 90 days (adjusted odds ratio [aOR], 1.85 [95% CI, 1.07-3.25], P=0.03; low-/high-frequency ratio aOR, 0.67 [95% CI, 0.46-0.92], P=0.02) and reduced likelihood of an early neurological recovery (aOR, 0.62 [95% CI, 0.44-0.91], P=0.01 and aOR, 1.37 [95% CI, 1.03-1.87], P=0.04, respectively). High-frequency BP oscillations after successful reperfusion may be harmful and associate with a decreased likelihood of neurological recovery and favorable functional outcomes. Rapid assessment of BP variability throughout the postreperfusion period is feasible and may allow for a more personalized BP management.

Blood Pressure Variability and Baroreflex Sensitivity in Premature Newborns-An Effect of Postconceptional and Gestational Age.

Introduction: Cardiovascular system is the vitally important system in the dynamical adaptation process of the newborns to the extrauterine environment. To reliably detect immaturity in the given organ system, it is crucial to study the development of the organ functions in relation to maturation process.Objectives: The objective was to determine the changes in the spontaneous short-term blood pressure variability (BPV) and baroreflex sensitivity (BRS) reflecting various aspects of cardiovascular control during the process of maturation in preterm babies and to separate effects of gestational age and postnatal age.Methods: Thirty-three prematurely born infants without any signs of cardio-respiratory disorders (gestational age: 31.8, range: 27–36 weeks; birth weight: 1,704, range: 820–2,730 grams) were enrolled. Continuous peripheral blood pressure signal was obtained by non-invasive volume-clamp photoplethysmography method during supine rest. The recordings of 250 continuous beat-to-beat blood pressure values were processed by spectral analysis of BPV (assessed measures: total power, low frequency and high frequency powers of systolic BPV) and BRS calculation. For each infant we also assessed systolic, diastolic and mean blood pressures, heart rate and respiratory rate.Results: With the postconceptional age, BPV measures decreased (for total power: Spearman correlation coefficient rs = −0.345, P = 0.049; for low frequency power: rs = −0.365, P = 0.037; for high frequency power rs = −0.349; P = 0.046); and BRS increased significantly (rs = 0.448, P = 0.009). The further analysis demonstrated that these effects were more attributable to gestational age than to postnatal age. BRS correlated negatively with BPV magnitude (rs = −0.479 to −0.592, P = 0.001–0.005). Mean blood pressure and diastolic blood pressure increased during maturation (rs = 0.517 and 0.537, P = 0.002 and 0.001, respectively) while heart rate and respiratory rate decreased (rs = −0.366 and −0.516, P = 0.036 and 0.002, respectively).Conclusion: We conclude that maturation process is accompanied by an increased involvement of baroreflex buffering of spontaneous short-term blood pressure oscillations. Gestational age plays a dominant role not only in BPV changes but also in BRS, mean blood pressure, diastolic blood pressure and heart rate changes.

Similar Effects of an Orexin Receptor Antagonistand Benzodiazepine Receptor Agonist on Cerebral Blood Flow Regulation

Orexin receptor antagonists have a different sleep-inducing mechanism from common hypnotic benzodiazepinereceptor agonists. Thus, orexin receptor antagonists may affect cerebral circulation differently, although theireffects have rarely been investigated. In this study, the effects of an orexin receptor antagonist on cerebral bloodflow regulation were compared with those of a benzodiazepine, including dynamic cerebral autoregulation. Fifteenhealthy males received suvorexant (1 tablet, 20 mg), an orexin receptor antagonist, and brotizolam (1 tablet, 0.25mg), a benzodiazepine receptor agonist, in a randomized order at least 7 days apart. Before and 1.5 h after drugadministration, arterial blood pressure and cerebral blood flow velocity were measured by transcranial Doppler ina supine position. Dynamic cerebral autoregulation was evaluated by transfer function analysis between mean arterial blood pressure variability and mean cerebral blood flow velocity variability. The steady-state mean cerebralblood flow velocity decreased significantly with both suvorexant and brotizolam (significant main effect of time,P = 0.003) and was associated with unchanged steady-state mean arterial blood pressure. Moreover, transfer function gain in the low- and high-frequency ranges were decreased significantly by both suvorexant and brotizolam(significant main effect of time, P < 0.001), suggesting a decrease in the magnitude of transfer from arterial bloodpressure oscillations to cerebral blood flow fluctuations. These changes were not significantly different betweensuvorexant and brotizolam (no significant interaction effect). The present results indicate that suvorexant andbrotizolam, two different types of hypnotic drug, have similar effects on cerebral blood flow regulation, includingpossible improvements in dynamic cerebral autoregulation with decreased steady-state cerebral blood flow.

Overexpression of endothelial SIRT1 prevents the development of hypertension in PER2 mutant mice

The circadian clock and rhythmicity regulate cardiovascular function and energy homeostasis. Mice with selective mutation of the Per2 protein (a circadian regulator) in the hypothalamus (PER2Brdm1) were established to investigate blood pressure regulation through the circadian clock. We hypothesize that disruption of the circadian rhythm adversely affects blood pressure regulation which can be restored by overexpression of SIRT1 in the vascular endothelium. To investigate this, radio transmitter telemetry was implanted in PER2Brdm1, Per2 mutant mice with selective overexpression of SIRT1 in the endothelium (PER2Brdm1/eSIRT1), as well as in wild type (WT) littermates. At 12-weeks old, a telemetry catheter was surgically inserted into the left carotid artery and extended into the aorta and a transmitter device was placed under the skin along the animal's flank. Mice were allowed free access to water and diet, as well as normal housing conditions post recovery. Twenty-four (24)-hour blood pressure recording was taken at 16-, 20- and 24-weeks for four consecutive days. Quantitative PCR (qPCR) and western blotting were performed to evaluate mRNA levels of SIRT1 and expressions of key enzymes involved in leucine metabolism respectively. The mean systolic and diastolic pressures (147 ± 9.3 mmHg; 123 ± 7.3 mmHg) were found to be higher in PER2Brdm1 when compared to PER2Brdm1/eSIRT1(118 ± 3.4 mmHg; 90 ± 2.6 mmHg) and WT (121 ± 2.2 mmHg; 90.7 ± 2.1 mmHg) respectively. Day and night blood pressure oscillation in PER2Brdm1 at the age of 16, 20 & 24-weeks showed a loss of in circadian rhythmicity as day and night blood pressures were not significantly different. The circadian rhythm was however restored in PER2Brdm1/eSIRT1 mice as blood pressure was significantly higher during the night when compared to during the day. The mean differences in day and night systolic pressure in WT, PER2Brdm1 and PER2Brdm1/eSIRT1 were found to be: 9.7 ± 0.7 mmHg vs 1.74 ± 0.5 mmHg vs 5.62 ± 1.5 mmHg, respectively. Similarly, the diastolic differences in day and night were 9.2 ± 0.5 mmHg vs 0.06 ± 1.3 mmHg vs 4.45 ± 2.0 mmHg, respectively. The non-dipping pattern of day/night blood pressure changes in PER2Brdm1 was restored to normal dipping in PER2Brdm1/eSIRT1 mice. SIRT1 mRNA levels in skeletal muscles were found to be significantly lower in PER2Brdm1 mice when compared to WT and PER2Brdm1/eSIRT1. Also, protein levels of enzymes involved in leucine metabolism were significantly lower in PER2Brdm1 when compared with the controls. In summary, mutation of Per2 in the hypothalamus induces dysregulation of leucine metabolism, resulting in increased blood pressure and loss of diurnal blood pressure oscillation. However, increased endothelial SIRT1 expression attenuates the hypertensive phenotype of Per2 mutation and restores day and night blood pressure rhythmicity.

Dynamic Cerebral Autoregulation following the Acute Consumption of Soft‐drinks in Healthy Adults

Chronic consumption of high-fructose corn syrup (HFCS) and artificially sweetened beverages (ASB) are associated with an increased risk of stroke. An attenuation in dynamic cerebral autoregulation (dCA), a measure cerebral vascular function during changes in arterial blood pressure, may indicate cerebral vascular dysfunction. Thus, understanding the acute effects that HFCS and ASB consumption has on dCA may help understand the increased risk of stroke associated with the chronic consumption of these beverages. Purpose We tested the hypothesis that dynamic cerebral autoregulation (dCA) is attenuated following the acute consumption of HFCS and ASB soft-drinks compared to Water. Methods Twelve healthy adults (age: 23±2 y, 4 females) completed three randomized, double-blind trials. Participants drank 500 mL of Water, HFCS (Mountain Dew) or ASB (Diet Mountain Dew). We continuously measured blood pressure (MAP), mean middle cerebral artery blood velocity (MCAv), and end-tidal CO2 tension (PETCO2). Cerebral vascular conductance (CVC) was calculated as mean MCAv/MAP. Twenty minutes after experimental beverage consumption participants completed a 5 minute seated baseline, followed by an oscillatory blood pressure challenge. The oscillatory blood pressure challenge consisted of squat-to-stand intervals at two different frequencies (0.10 Hz and 0.05 Hz) for 5 minutes each separated by 5 minutes of seated rest. dCA was assessed in the MCA using transfer function analysis. Coherence, gain and phase are reported in in predefined frequency domains: low frequency (LF; 0.07-0.2 Hz) and very low frequency (VLF; 0.01-0.07 Hz) for the 0.10 Hz and 0.05 Hz, respectively. Values are reported as mean±SD. Results At baseline, MCAv (HFCS: 53.7±11.5 and ASB: 52.2±10.3 vs. Water: 61.4±10.8 cm/s; p<0.01) and MCA CVC (HFCS: 0.6±0.2 and ASB: 0.5±0.1 vs. Water: 0.7±1 cm/s/mmHg; p<0.02) were lower following HFCS and ASB vs. Water. During the 0.10 Hz squat-to-stand, there were no differences between beverages for coherenceLF (p=0.30) or phaseLF (p=0.68). GainLF was lower following ASB (0.81±0.21 cm/s/mmHg) compared to Water (0.95±0.27 cm/s/mmHg; p=0.01) but there was no difference in gainLF between HFCS (0.92±0.23 cm/s/mmHg) and Water (p=0.53). During the 0.05 Hz squat-to-stand, there were no differences between beverages for coherenceVLF (p=0.83) or gainVLF (p=0.28). PhaseVLF was higher following ASB (45.4±8.5 degrees) compared to Water (39.8±8 degrees; p=0.06) but there was no difference in phaseVLF between HFCS (43.8±10.3 degrees) and Water (p=0.31). Conclusions Our data indicate that acute consumption of an ASB did not consistently alter dCA in both frequency bands. Additionally, dCA was not altered following a HFCS soft-drink. However, future research is warranted to determine the effects of chronic consumption of HFCS and ASB soft-drinks on cerebral vascular function and the increased the risk of stroke.

AMBULATORY BLOOD PRESSURE MONITORING BY A NOVEL CUFFLESS DEVICE: POTENTIAL ROLE IN OVERWEIGHT PATIENTS

Objective: Inappropriate cuff size can lead to erroneous blood pressure (BP) measurements and, therefore, to misclassification and potential unnecessary treatment; this problem has a particular relevance in overweight patients. We assessed whether a new cuffless BP device was equally effective for BP measurements over the 24 hours compared to a standard oscillatory BP device in overweight patients (BMI &gt;25). Design and method: BP was measured simultaneously by the cuffless (CL-BP, Rooti RX TM) and by a standard device (C-BP, SpacelabsTM,90207) over the 24 hours in 100 consecutive patients. Calculations included 24 hour mean systolic (S) and diastolic (D) BP and heart rate (HR). Correlations between the CL-BP and C-BP measurements were sought using Pearson's correlation coefficients and Bland-Altman plots. Results: Using the C-BP device, the 24 hour SBP value was 125.4 ± 10.9 mmHg (mean ± SD); the corresponding DBP value being 75 ± 8.3 mmHg. Mean SBP/DBP with the CL-BP device were 131.1 ± 15.9/80.2 ± 9.7 mmHg. The correlation coefficients between the two sets of values was significant (SBP: r = 0.58, p = 0.006 - DBP: r = 0.65, p = 0.0002). Mean absolute SBP and DBP disagreements between CL-BP and C-BP were 5.7 ± 13.1 mmHg and 5.2 ± 7.7 mm Hg, respectively. In the 54 patients classified as overweight, C-BP mean SBP value was 126.4 ± 10.6 and mean DBP value was 76,2 ± 8,5; in the CL-BP device arm SBP was 130 ± 14,1 and DBP was 80,9 ± 9,9. Better SBP and DBP correlations for SBP and DBP was found in patients with BMI &gt; 25 (SBP: r = 0.65, p = 0.13 - DBP: r = 0.70, p = 0.009) compared to those with BMI &lt;25 (SBP: r = 0.52, p = 0.02 - DBP: r = 0.51, p = 0.06). Conclusions: Our results show that a CL-BP device was accurate in estimating 24 hours BP in overweight patients, compared to a classical oscillometric device. Therefore, if confirmed on a larger population scale, CL-BP device could be used to provide accurate standardized BP measurements, independently by the arm size of the patients, and avoid a significant number of BP quantification mistakes.

Predicting Vasovagal Responses: A Model-Based and Machine Learning Approach.

Vasovagal syncope (VVS) or neurogenically induced fainting has resulted in falls, fractures, and death. Methods to deal with VVS are to use implanted pacemakers or beta blockers. These are often ineffective because the underlying changes in the cardiovascular system that lead to the syncope are incompletely understood and diagnosis of frequent occurrences of VVS is still based on history and a tilt test, in which subjects are passively tilted from a supine position to 20° from the spatial vertical (to a 70° position) on the tilt table and maintained in that orientation for 10–15 min. Recently, is has been shown that vasovagal responses (VVRs), which are characterized by transient drops in blood pressure (BP), heart rate (HR), and increased amplitude of low frequency oscillations in BP can be induced by sinusoidal galvanic vestibular stimulation (sGVS) and were similar to the low frequency oscillations that presaged VVS in humans. This transient drop in BP and HR of 25 mmHg and 25 beats per minute (bpm), respectively, were considered to be a VVR. Similar thresholds have been used to identify VVR's in human studies as well. However, this arbitrary threshold of identifying a VVR does not give a clear understanding of the identifying features of a VVR nor what triggers a VVR. In this study, we utilized our model of VVR generation together with a machine learning approach to learn a separating hyperplane between normal and VVR patterns. This methodology is proposed as a technique for more broadly identifying the features that trigger a VVR. If a similar feature identification could be associated with VVRs in humans, it potentially could be utilized to identify onset of a VVS, i.e, fainting, in real time.

Study of heart rate recovery and cardiovascular autonomic modulation in healthy participants after submaximal exercise

Heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) provide important information on cardiovascular autonomic control. However, little is known about the reorganization of HRV, BPV, and BRS after aerobic exercise. While there is a positive relationship between heart rate (HR) recovery rate and cardiorespiratory fitness, it is unclear whether there is a relationship between cardiorespiratory fitness and reorganization of cardiovascular autonomic modulation during recovery. Thus, this study aimed to investigate whether cardiorespiratory fitness influences the cardiovascular autonomic modulation recovery, after a cardiopulmonary exercise test. Sixty men were assigned into groups according to their cardiorespiratory fitness: low cardiorespiratory fitness (LCF = VO2: 22–38 mL kg−1 min−1), moderate (MCF = VO2: 38–48 mL kg−1 min−1), and high (HCF = VO2 > 48 mL kg−1 min−1). HRV (linear and non-linear analysis) and BPV (spectral analysis), and BRS (sequence method) were performed before and after a cardiopulmonary exercise test. The groups with higher cardiorespiratory fitness had lower baseline HR values and HR recovery time after the cardiopulmonary exercise test. On comparing rest and recovery periods, the spectral analysis of HRV showed a decrease in low-frequency (LF) oscillations in absolute units and high frequency (HF) in absolute and normalized units. It also showed increases in LF oscillations of blood pressure. Nonlinear analysis showed a reduction in approximate entropy (ApEn) and in Poincare Plot parameters (SD1 and SD2), accompanied by increases in detrended fluctuation analysis (DFA) parameters α1 and α2. However, we did not find differences in cardiovascular autonomic modulation parameters and BRS in relation to cardiorespiratory fitness neither before nor after the cardiopulmonary test. We concluded that cardiorespiratory fitness does not affect cardiovascular autonomic modulations after cardiopulmonary exercise test, unlike HR recovery.

Coupling between Blood Pressure and Subarachnoid Space Width Oscillations during Slow Breathing.

The precise mechanisms connecting the cardiovascular system and the cerebrospinal fluid (CSF) are not well understood in detail. This paper investigates the couplings between the cardiac and respiratory components, as extracted from blood pressure (BP) signals and oscillations of the subarachnoid space width (SAS), collected during slow ventilation and ventilation against inspiration resistance. The experiment was performed on a group of 20 healthy volunteers (12 females and 8 males; BMI kg/m; age years). We analysed the recorded signals with a wavelet transform. For the first time, a method based on dynamical Bayesian inference was used to detect the effective phase connectivity and the underlying coupling functions between the SAS and BP signals. There are several new findings. Slow breathing with or without resistance increases the strength of the coupling between the respiratory and cardiac components of both measured signals. We also observed increases in the strength of the coupling between the respiratory component of the BP and the cardiac component of the and vice versa. Slow breathing synchronises the SAS oscillations, between the brain hemispheres. It also diminishes the similarity of the coupling between all analysed pairs of oscillators, while inspiratory resistance partially reverses this phenomenon. BP–SAS and SAS–BP interactions may reflect changes in the overall biomechanical characteristics of the brain.

Simulating Dynamics of Circulation in the Awake State and Different Stages of Sleep Using Non-autonomous Mathematical Model With Time Delay.

We propose a mathematical model of the human cardiovascular system. The model allows one to simulate the main heart rate, its variability under the influence of the autonomic nervous system, breathing process, and oscillations of blood pressure. For the first time, the model takes into account the activity of the cerebral cortex structures that modulate the autonomic control loops of blood circulation in the awake state and in various stages of sleep. The adequacy of the model is demonstrated by comparing its time series with experimental records of healthy subjects in the SIESTA database. The proposed model can become a useful tool for studying the characteristics of the cardiovascular system dynamics during sleep.

Cerebral Autoregulation and Blood Flow Redistribution in the Precerebral Arteries in Patients with Carotid Artery Occlusion

Abstract Background: State of cerebral autoregulation and changed blood flow in the precerebral arteries can serve as selection criteria in favor of extra-intracranial bypass surgery and as a prediction factor in patients with carotid artery occlusion. However, information capacity of quantitative values of this functional state of the brain circulation has not been studied well enough. Objective: The objective is to assess the state of cerebral autoregulation and blood flow redistribution in the precerebral arteries in patients with carotid artery occlusion. Material and Methods: The study involved 24 patients aged 41 to 80 with carotid artery occlusion. Eight of them were asymptomatic. We measured blood flow velocity in intracranial arteries by using transcranial Doppler (MultiDop X) and flow velocity index in precerebral arteries - by using duplex scanning (Vivid e). Cerebral autoregulation was evaluated with cross-spectral analysis of spontaneous oscillations of blood pressure (CNAP, Austria) and blood flow velocity within the range of Mayer’s waves (80-120 mHz). Results: In most symptomatic patients the cerebral autoregulation decreased on both sides (0.3±0.3 rad ipsilaterally and 0.6±0.4 rad contralaterally). There was no cerebral autoregulation impairment in all asymptomatic patients (1.1±0.5 rad ipsilateral and 1.3±0.5 rad contralateral). We noticed an increased blood flow index in the contralateral internal carotid artery (312±113 ml/min) and ipsilateral vertebral and external carotid arteries (126±64 ml/min and 158±72 ml/min, respectively). Conclusion: A comprehensive analysis of cerebral autoregulation and blood flow in the precerebral arteries helps to identify the extent of cerebral hemodynamics compensation in carotid artery occlusion, which can classify patients in need of revascularization surgery. Keywords Blood flow index; Carotid artery occlusion; Cerebral autoregulation; Cerebrovascular reserve; Extra-intracranial bypass surgery

Myths and methodologies: Reliability of non-invasive estimates of cardiac autonomic modulation during whole-body passive heating.

Observed individual variability in cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV) is extensive, especially during exposure to stressors such as heat. A large part of the observed variation may be related to the reliability (consistency) of the measurement. We therefore examined the test-retest reliability of cBRS and HRV measurements on three separate occasions in 14 young men (age: 24 (SD 5) years), at rest and during whole-body heating (water-perfused suit) to raise and clamp oesophageal temperature 0.6°C, 1.2°C and 1.8°C above baseline. Beat-to-beat measurements of RR interval and systolic blood pressure (BP) were obtained for deriving HRV (from RR), and cBRS calculated via (i) the spontaneous method, α coefficients and transfer function analysis at each level of heat strain, and (ii) during forced oscillations via squat-stand manoeuvres (0.1Hz) before and after heating. Absolute values and changes in all cBRS estimates were variable but generally consistent with reductions in parasympathetic activity. cBRS estimates demonstrated poor absolute reliability (coefficient of variation ≥25%), but relative reliability (intraclass correlation coefficient; ICC) of some frequency estimates was acceptable (ICC ≥0.70) during low-heat strain (ICC: 0.56-0.74). After heating, forced oscillations in BP demonstrated more favourable responses than spontaneous oscillations (better reliability, lower minimum detectable change). Absolute reliability of HRV estimates were poor, but relative reliability estimates were often acceptable (≥0.70). Our findings illustrate how measurement consistency of cardiac autonomic modulation estimates are altered during heat stress, and we demonstrate the possible implications on research design and data interpretation.

The frequency spectrum of sympathetic nerve activity and arrhythmogenicity in ambulatory dogs

Sympathetic nerve activity, heart rate (HR), and blood pressure (BP) all have very low frequency (VLF), low frequency (LF), and high frequency (HF) oscillations. The purpose of this study was to test the hypothesis that the frequency spectra of subcutaneous nerve activity (ScNA), stellate ganglion nerve activity (SGNA), HR, and BP are important to cardiac arrhythmogenesis. We used radiotransmitters to record SGNA, ScNA, HR, and BP in 6 ambulatory dogs and determined the dominant frequency and paroxysmal atrial tachyarrhythmias (PATs) episodes in 3-minute windows over a 24-hour period. The frequency spectra determined in ScNA reflected that in SGNA. HF oscillations were present in both ScNA and SGNA at all time but could be overshadowed by the much larger LF and VLF burst activities. The dominant frequency could occur in any of the 3 frequency bands. There were circadian variations with more frequent occurrences of HF oscillations at night. HF oscillations in HR and BP matched HF oscillations in SGNA and ScNA. PATs occurred only when dominant frequencies of SGNA and ScNA were in the LF and VLF bands. HF oscillations in BP and HR correlate with HF oscillations in sympathetic nerve activity and are present at all time. HF oscillations can be overshadowed by the much larger LF and VLF burst activities. PATs occur only when LF or VLF, but not when HF, is the dominant frequency. The frequency spectra determined in ScNA reflect that in SGNA.