Enhanced open-loop but not closed-loop cardiac baroreflex sensitivity during orthostatic stress in humans

2011 ◽  
Vol 301 (5) ◽  
pp. R1591-R1598 ◽  
Author(s):  
Toshinari Akimoto ◽  
Jun Sugawara ◽  
Daisuke Ichikawa ◽  
Nobuyuki Terada ◽  
Paul J. Fadel ◽  
...  
Keyword(s):  
Heart Rate ◽  
Transfer Function ◽  
White Noise ◽  
Baroreflex Sensitivity ◽  
Closed Loop ◽  
Low Frequency ◽  
Open Loop ◽  
Orthostatic Stress ◽  
Arterial Baroreflex ◽  
Transfer Function Gain

The neural interaction between the cardiopulmonary and arterial baroreflex may be critical for the regulation of blood pressure during orthostatic stress. However, studies have reported conflicting results: some indicate increases and others decreases in cardiac baroreflex sensitivity (i.e., gain) with cardiopulmonary unloading. Thus the effect of orthostatic stress-induced central hypovolemia on regulation of heart rate via the arterial baroreflex remains unclear. We sought to comprehensively assess baroreflex function during orthostatic stress by identifying and comparing open- and closed-loop dynamic cardiac baroreflex gains at supine rest and during 60° head-up tilt (HUT) in 10 healthy men. Closed-loop dynamic “spontaneous” cardiac baroreflex sensitivities were calculated by the sequence technique and transfer function and compared with two open-loop carotid-cardiac baroreflex measures using the neck chamber system: 1) a binary white-noise method and 2) a rapid-pulse neck pressure-neck suction technique. The gain from the sequence technique was decreased from −1.19 ± 0.14 beats·min−1·mmHg−1 at rest to −0.78 ± 0.10 beats·min−1·mmHg−1 during HUT ( P = 0.005). Similarly, closed-loop low-frequency baroreflex transfer function gain was reduced during HUT ( P = 0.033). In contrast, open-loop low-frequency transfer function gain between estimated carotid sinus pressure and heart rate during white-noise stimulation was augmented during HUT ( P = 0.01). This result was consistent with the maximal gain of the carotid-cardiac baroreflex stimulus-response curve (from 0.47 ± 0.15 beats·min−1·mmHg−1 at rest to 0.60 ± 0.20 beats·min−1·mmHg−1 at HUT, P = 0.037). These findings suggest that open-loop cardiac baroreflex gain was enhanced during HUT. Moreover, under closed-loop conditions, spontaneous baroreflex analyses without external stimulation may not represent open-loop cardiac baroreflex characteristics during orthostatic stress.

Effect of heavy exercise on spectral baroreflex sensitivity, heart rate, and blood pressure variability in well-trained humans

2008 ◽  
Vol 295 (3) ◽  
pp. H1150-H1155 ◽  
Author(s):  
François Cottin ◽  
Claire Médigue ◽  
Yves Papelier
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Systolic Blood Pressure ◽  
Exercise Test ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Mechanical Effect ◽  
Heavy Exercise ◽  
Gas Exchange Parameters

The aim of the study was to assess the instantaneous spectral components of heart rate variability (HRV) and systolic blood pressure variability (SBPV) and determine the low-frequency (LF) and high-frequency baroreflex sensitivity (HF-BRS) during a graded maximal exercise test. The first hypothesis was that the hyperpnea elicited by heavy exercise could entail a significant increase in HF-SBPV by mechanical effect once the first and second ventilatory thresholds (VTs) were exceeded. It was secondly hypothesized that vagal tone progressively withdrawing with increasing load, HF-BRS could decrease during the exercise test. Fifteen well-trained subjects participated in this study. Electrocardiogram (ECG), blood pressure, and gas exchanges were recorded during a cycloergometer test. Ventilatory equivalents were computed from gas exchange parameters to assess VTs. Spectral analysis was applied on cardiovascular series to compute RR and systolic blood pressure power spectral densities, cross-spectral coherence, gain, and α index of BRS. Three exercise intensity stages were compared: below (A1), between (A2), and above (A3) VTs. From A1 to A3, both HF-SBPV (A1: 45 ± 6, A2: 65 ± 10, and A3: 120 ± 23 mm2Hg, P < 0.001) and HF-HRV increased (A1: 20 ± 5, A2: 23 ± 8, and A3:40 ± 11 ms2, P < 0.02), maintaining HF-BRS (gain, A1: 0.68 ± 0.12, A2: 0.63 ± 0.08, and A3: 0.57 ± 0.09; α index, A1: 0.58 ± 0.08, A2: 0.48 ± 0.06, and A3: 0.50 ± 0.09 ms/mmHg, not significant). However, LF-BRS decreased (gain, A1: 0.39 ± 0.06, A2: 0.17 ± 0.02, and A3: 0.11 ± 0.01, P < 0.001; α index, A1: 0.46 ± 0.07, A2: 0.20 ± 0.02, and A3: 0.14 ± 0.01 ms/mmHg, P < 0.001). As expected, once VTs were exceeded, hyperpnea induced a marked increase in both HF-HRV and HF-SBPV. However, this concomitant increase allowed the maintenance of HF-BRS, presumably by a mechanoelectric feedback mechanism.

Age dependency of cardiovascular autonomic responses to head-up tilt in healthy subjects

2004 ◽  
Vol 96 (6) ◽  
pp. 2333-2340 ◽  
Author(s):  
Tomi Laitinen ◽  
Leo Niskanen ◽  
Ghislaine Geelen ◽  
Esko Länsimies ◽  
Juha Hartikainen
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
High Frequency ◽  
Healthy Subjects ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Upright Position ◽  
Vascular Responses ◽  
Autonomic Responses ◽  
Head Up Tilt

In elderly subjects, heart rate responses to postural change are attenuated, whereas their vascular responses are augmented. Altered strategy in maintaining blood pressure homeostasis during upright position may result from various cardiovascular changes, including age-related cardiovascular autonomic dysfunction. This exploratory study was conducted to evaluate impact of age on cardiovascular autonomic responses to head-up tilt (HUT) in healthy subjects covering a wide age range. The study population consisted of 63 healthy, normal-weight, nonsmoking subjects aged 23–77 yr. Five-minute electrocardiogram and finger blood pressure recordings were performed in the supine position and in the upright position 5 min after 70° HUT. Stroke volume was assessed from noninvasive blood pressure signals by the arterial pulse contour method. Heart rate variability (HRV) and systolic blood pressure variability (SBPV) were analyzed by using spectral analysis, and baroreflex sensitivity (BRS) was assessed by using sequence and cross-spectral methods. Cardiovascular autonomic activation during HUT consisted of decreases in HRV and BRS and an increase in SBPV. These changes became attenuated with aging. Age correlated significantly with amplitude of HUT-stimulated response of the high-frequency component ( r = -0.61, P < 0.001) and the ratio of low-frequency to high-frequency power of HRV ( r = -0.31, P < 0.05) and indexes of BRS (local BRS: r = -0.62, P < 0.001; cross-spectral baroreflex sensitivity in the low-frequency range: r = -0.38, P < 0.01). Blood pressure in the upright position was maintained well irrespective of age. However, the HUT-induced increase in heart rate was more pronounced in the younger subjects, whereas the increase in peripheral resistance was predominantly observed in the older subjects. Thus it is likely that whereas the dynamic capacity of cardiac autonomic regulation decreases, vascular responses related to vasoactive mechanisms and vascular sympathetic regulation become augmented with increasing age.

Abstract P206: Improvement Of Autonomic Function, Sleep, Depression, Anxiety, And Stress In Military Personnel With Traumatic Stress After Use Of A Closed Loop Neurotechnology

Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Catherine Tegeler ◽  
Lindsay Howard ◽  
Kenzie L Brown ◽  
Faiza Asif-Fraz ◽  
Dawn C Kellar ◽  
...  
Keyword(s):  
Heart Rate ◽  
Traumatic Stress ◽  
Baroreflex Sensitivity ◽  
Primary Outcome ◽  
Closed Loop ◽  
Autonomic Function ◽  
Brain Activity ◽  
Acoustic Stimulation ◽  
Beneficial Effects ◽  
Symptom Scores

Introduction: Symptoms associated with military-related traumatic stress (MTS) include insomnia, depression, anxiety, and impaired autonomic control. High-resolution, relational, resonance-based, electroencephalic mirroring (HIRREM®) is a noninvasive, closed-loop acoustic stimulation technology that identifies dominant brain frequencies and translates them in real time into audible tones of variable pitch and timing, to support self-optimization of brain activity. Objective: Evaluate changes in autonomic and symptoms scores after use of HIRREM in subjects enrolled in a pilot study for MTS. Methods: Thirty-two service members or Veterans (1 female), mean (SD) age 40.8 (6.4), with MTS symptoms for 7.3 years (3.9), received 19.2 (1.0) HIRREM sessions over 12 days. Continuous recordings of blood pressure and heart rate, for analysis of baroreflex sensitivity (BRS) and heart rate variability (HRV), were done at V1 and V2. Symptom inventories collected before (Visit 1, V1), immediately after (primary outcome, V2, n = 32), and at 1, 3, and 6 months after completion of HIRREM included traumatic stress (PCL-M), insomnia (ISI), depression (CES-D), and anxiety (GAD-7). Paired t-tests were performed. Results: HIRREM improved BRS measured as HF alpha (10.8 ms/mmHg, 2.5, p<0.001), Sequence Down (7.3 ms/mmHg, 2.1, p<0.001), Sequence Up (7.6 ms/mmHg, 2.4, p=0.001), and Sequence All (7.3 ms/mmHg, 1.8, p<0.001), as well as HRV; SDNN (14.1 ms, 3.6, p=0.005), rMSSD (12.8 ms, 2.6, p<0.05). MAP dropped 2.7 mmHg, 1.2, p<0.05 and SAP dropped 5.9 mmHg, 1.8, p=0.007. Mean symptom scores were reduced at V2; PCL-M [-12.9 (± 9.1), p<0.001], ISI [-6.3 (± 5.0), p<0.001], CES-D [-13.7 (±9.2), p<0.001], and GAD-7 [-6.7. (± 4.7), p<0.001]. Symptom scores improved 1-month post-HIRREM for all measures, and clinically relevant and significant benefits persist at 3 and 6 months. Conclusions: These results suggest improved autonomic cardiovascular regulation and statistically significant reduction in scales associated with the use of HIRREM for symptoms of MTS. Controlled trials could provide important insights regarding both the mechanisms associated with the beneficial effects of HIRREM, and the functional disturbances underlying MTS.

scholarly journals Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain

2017 ◽  
Vol 312 (5) ◽  
pp. H1076-H1084 ◽  
Author(s):  
Jun Sugawara ◽  
Tsubasa Tomoto ◽  
Tomoko Imai ◽  
Seiji Maeda ◽  
Shigehiko Ogoh
Keyword(s):  
Transfer Function ◽  
Frequency Domain ◽  
Systemic Vascular Resistance ◽  
Vascular Resistance ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Slow Oscillations ◽  
Transfer Function Gain ◽  
The Brain

High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (−10, −20, and −30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02–0.30 Hz) and the intra-beat rapid change (0.78–9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07–0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during −20 and −30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance ( r = 0.41, P = 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation ( P = 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07–0.20 Hz). NEW & NOTEWORTHY We characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.

EXPERIMENTAL RESULTS FOR THE SMALL-SIGNAL STUDY OF THE PWM BOOST DC–DC CONVERTER WITH AN INTEGRAL-LEAD CONTROLLER

1995 ◽  
Vol 05 (04) ◽  
pp. 747-755 ◽  
Author(s):  
MARIAN K. KAZIMIERCZUK ◽  
ROBERT C. CRAVENS, II
Keyword(s):  
Closed Loop ◽  
Transfer Functions ◽  
Low Frequency ◽  
Input Voltage ◽  
Open Loop ◽  
Small Signal ◽  
Loop Control ◽  
Pulse Width Modulated ◽  
Bode Plots ◽  
Step Responses

An experimental verification of previously derived small-signal low-frequency open- and closed-loop characteristics and step responses of a voltage-mode-controlled pulse-width-modulated (PWM) boost DC–DC converter is presented. The Bode plots of the voltage transfer function of the control circuit, the converter and the PWM modulator, the open-loop control-to-output and input-to-output transfer functions, the loop gain, and the closed-loop control-to-output and input-to-output transfer functions are measured. The step responses to the changes in the input voltage, the duty cycle, and the reference voltage are measured. The theoretical results were in good agreement with the measured results. The small-signal model of the converter is experimentally verified.

Differential effects of acute hypoxia and high altitude on cerebral blood flow velocity and dynamic cerebral autoregulation: alterations with hyperoxia

2008 ◽  
Vol 104 (2) ◽  
pp. 490-498 ◽  
Author(s):  
Philip N. Ainslie ◽  
Shigehiko Ogoh ◽  
Katie Burgess ◽  
Leo Celi ◽  
Ken McGrattan ◽  
...  
Keyword(s):  
Blood Flow ◽  
Transfer Function ◽  
High Altitude ◽  
Blood Flow Velocity ◽  
Cerebral Autoregulation ◽  
Acute Hypoxia ◽  
Low Frequency ◽  
Frequency Range ◽  
Transfer Function Gain ◽  
Dynamic Cerebral Autoregulation

We hypothesized that 1) acute severe hypoxia, but not hyperoxia, at sea level would impair dynamic cerebral autoregulation (CA); 2) impairment in CA at high altitude (HA) would be partly restored with hyperoxia; and 3) hyperoxia at HA and would have more influence on blood pressure (BP) and less influence on middle cerebral artery blood flow velocity (MCAv). In healthy volunteers, BP and MCAv were measured continuously during normoxia and in acute hypoxia (inspired O2 fraction = 0.12 and 0.10, respectively; n = 10) or hyperoxia (inspired O2 fraction, 1.0; n = 12). Dynamic CA was assessed using transfer-function gain, phase, and coherence between mean BP and MCAv. Arterial blood gases were also obtained. In matched volunteers, the same variables were measured during air breathing and hyperoxia at low altitude (LA; 1,400 m) and after 1–2 days after arrival at HA (∼5,400 m, n = 10). In acute hypoxia and hyperoxia, BP was unchanged whereas it was decreased during hyperoxia at HA (−11 ± 4%; P < 0.05 vs. LA). MCAv was unchanged during acute hypoxia and at HA; however, acute hyperoxia caused MCAv to fall to a greater extent than at HA (−12 ± 3 vs. −5 ± 4%, respectively; P < 0.05). Whereas CA was unchanged in hyperoxia, gain in the low-frequency range was reduced during acute hypoxia, indicating improvement in CA. In contrast, HA was associated with elevations in transfer-function gain in the very low- and low-frequency range, indicating CA impairment; hyperoxia lowered these elevations by ∼50% ( P < 0.05). Findings indicate that hyperoxia at HA can partially improve CA and lower BP, with little effect on MCAv.

scholarly journals Simulation of Performance Response of State Variables of a Chemical Boiler Process

2018 ◽  
pp. 1-5
Author(s):  
Donatus O. Njoku ◽  
Asagba P. O ◽  
Chilaka U. Longinus ◽  
Amaefule I. A. ◽  
Igwe S. Onyema
Keyword(s):  
Transfer Function ◽  
Closed Loop ◽  
Control Process ◽  
Open Loop ◽  
The State ◽  
Feedback Gain ◽  
State Variables ◽  
Simulink Model ◽  
Performance Response ◽  
Optimal Regulator

This paper has presented simulation of performance response of state variables of a chemical boiler process. The transfer function of a boiler flow control process of a chemical plant was obtained. The transfer function was transformed into state space form to study the state variables of the system. An optimal regulator was designed using MATLAB programme. The developed optimal regulator was added to the loop of the system to form a closed loop system. A Simulink model was developed and used to study performance response of the system. Simulation was carried out for two conditions, open loop and closed loop. The simulation results indicated that the performance responses of the state variables were improved and better stability achieved with the inclusion of the designed feedback gain matrix of the optimal regulator.

scholarly journals 0461 Blunted Baroreflex Sensitivity and Reduced Morning Parasympathetic Activity in Sleep-Onset Insomnia

SLEEP ◽  
2020 ◽  
Vol 43 (Supplement_1) ◽  
pp. A177-A177
Author(s):  
H Tsai ◽  
T Kuo ◽  
C Yang
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Cardiovascular Events ◽  
Blood Pressure Variability ◽  
Baroreflex Sensitivity ◽  
Sleep Onset ◽  
Low Frequency ◽  
Sleep Structure ◽  
Frequency Power

Abstract Introduction Insomnia is a risk factor for hypertension and cardiovascular events, and this association is strongest for sleep-onset insomnia. However, little is known about insomnia on cardiovascular modulation, especially soon after morning awakening, the peak period of time for cardiovascular incidents. This study explored morning cardiovascular function in individuals with sleep-onset insomnia by analysing heart rate variability, blood pressure variability, and baroreflex sensitivity. Methods Sleep structure of the participants (15 good sleepers and 13 individuals with sleep-onset insomnia) was measured by laboratory polysomnography, followed by continuous recordings of the participant’s blood pressure and heart rate for 10 min in the morning. Results When compared to the good sleepers, the insomnia group showed significant reductions in total sleep time, a longer sleep-onset latency, and reduced sleep efficiency. The sleep structure, including durations of sleep stages, numbers of awakenings and arousal index did not differ between the groups. After morning awakening (averaged time: 12.33 ± 10.48 min), the shorter R-R intervals, lower total power, and lower high-frequency power of heart rate variability were observed among individuals with sleep-onset insomnia, compared with good sleepers. Elevated slopes of systolic and diastolic blood pressure, as well as lower baroreflex sensitivity, were also shown in the insomnia group. Indices of sympathetic activity, including low-frequency percentage of heart rate variability or low-frequency power of blood pressure variability, did not differ between the groups. Conclusion Weak vagal activity and blunted baroreflex sensitivity were evident among sleep-onset insomnia. These findings indicate difficulty in initiating sleep, without significant sleep fragmentation, can independently affect morning cardiovascular function. This study provides a possible link between sleep-onset insomnia and risk of cardiovascular events. Support N/A

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