Autonomic mediation of the interdependence between variability signals of heart rate and blood pressure in the lizard Gallotia galloti

2012 ◽  
Vol 90 (7) ◽  
pp. 839-848 ◽  
Author(s):  
Luis De Vera ◽  
Rubén V. Rial ◽  
Ernesto Pereda ◽  
Julián J. González
Keyword(s):  
Blood Pressure ◽  
Phase Synchronization ◽  
Low Frequency ◽  
Phase Lag ◽  
Frequency Range ◽  
Pharmacological Blockade ◽  
Systolic Blood Pressure Variability ◽  
Linear And Nonlinear ◽  
Magnitude Squared Coherence ◽  
Gallotia Galloti

Autonomic nervous system (ANS) involvement in the mediation of the synchronization between beat-to-beat RR interval variability (RRIV) and systolic blood pressure variability (SBPV) signals of the lizard Gallotia galloti (Oudart, 1839) was investigated through linear and nonlinear time series analysis methods in a pharmacological blockade context. The ANS blockers used were atropine, prazosin, and propranolol. The interdependence between the signals was quantified by means of the magnitude-squared coherence (MSC), which measures amplitude and phase linear synchronization; the phase lag index (PLI), which evaluates the phase synchronization; and the index L, which quantifies the generalized linear and nonlinear synchronization. Atropine decreased the PLI in the low-frequency (LF: 0.01–0.05 Hz) range; prazosin decreased the MSC in the medium-frequency (MF: 0.06–0.15 Hz) range; and propranolol did not alter any of the interdependence measures. It is suggested that (i) the cholinoceptor activity mediates the phase cardiovascular synchronization in the LF range; (ii) the α1-adrenoceptor activity mediates the amplitude and phase linear cardiovascular synchronization in the MF range; and (iii) the β-adrenoceptor activity plays no role in mediating any dynamics of cardiovascular synchronization in the studied frequency range. When comparing these results with those in mammals, a lesser overall autonomic involvement in the mediation of the studied cardiovascular interdependences is seen in reptiles.

scholarly journals Dynamic cerebral autoregulation during passive heat stress in humans

2009 ◽  
Vol 296 (5) ◽  
pp. R1598-R1605 ◽  
Author(s):  
David A. Low ◽  
Jonathan E. Wingo ◽  
David M. Keller ◽  
Scott L. Davis ◽  
Jian Cui ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heat Stress ◽  
Transfer Function ◽  
High Frequency ◽  
Cerebral Autoregulation ◽  
Low Frequency ◽  
Passive Heating ◽  
Frequency Range ◽  
Very Low Frequency ◽  
Dynamic Cerebral Autoregulation

This study tested the hypothesis that passive heating impairs cerebral autoregulation. Transfer function analyses of resting arterial blood pressure and middle cerebral artery blood velocity (MCA Vmean), as well as MCA Vmean and blood pressure responses to rapid deflation of previously inflated thigh cuffs, were examined in nine healthy subjects under normothermic and passive heat stress (increase core temperature 1.1 ± 0.2°C, P < 0.001) conditions. Passive heating reduced MCA Vmean [change (Δ) of 8 ± 8 cm/s, P = 0.01], while blood pressure was maintained (Δ −1 ± 4 mmHg, P = 0.36). Coherence was decreased in the very-low-frequency range during heat stress (0.57 ± 0.13 to 0.26 ± 0.10, P = 0.001), but was >0.5 and similar between normothermia and heat stress in the low- (0.07–0.20 Hz, P = 0.40) and high-frequency (0.20–0.35 Hz, P = 0.12) ranges. Transfer gain was reduced during heat stress in the very-low-frequency (0.88 ± 0.38 to 0.59 ± 0.19 cm·s−1·mmHg−1, P = 0.02) range, but was unaffected in the low- and high-frequency ranges. The magnitude of the decrease in blood pressure (normothermia: 20 ± 4 mmHg, heat stress: 19 ± 6 mmHg, P = 0.88) and MCA Vmean (13 ± 4 to 12 ± 6 cm/s, P = 0.59) in response to cuff deflation was not affected by the thermal condition. Similarly, the rate of regulation of cerebrovascular conductance (CBVC) after cuff release (0.44 ± 0.22 to 0.38 ± 0.13 ΔCBVC units/s, P = 0.16) and the time for MCA Vmean to recover to precuff deflation baseline (10.0 ± 7.9 to 8.7 ± 4.9 s, P = 0.77) were not affected by heat stress. Counter to the proposed hypothesis, similar rate of regulation responses suggests that heat stress does not impair the ability to control cerebral perfusion after a rapid reduction in perfusion pressure, while reduced transfer function gain and coherence in the very-low-frequency range during heat stress suggest that dynamic cerebral autoregulation is improved during spontaneous oscillations in blood pressure within this frequency range.

Empirical and theoretical analysis of the extremely low frequency arterial blood pressure power spectrum in unanesthetized rat

2006 ◽  
Vol 291 (6) ◽  
pp. H2816-H2824 ◽  
Author(s):  
David R. Brown ◽  
Lisa A. Cassis ◽  
Dennis L. Silcox ◽  
Laura V. Brown ◽  
David C. Randall
Keyword(s):  
Blood Pressure ◽  
Time Series ◽  
Power Spectrum ◽  
Arterial Blood Pressure ◽  
Low Frequency ◽  
Absolute Difference ◽  
Frequency Range ◽  
Low Frequencies ◽  
Extremely Low Frequency ◽  
Arterial Blood

The slope of the log of power versus the log of frequency in the arterial blood pressure (BP) power spectrum is classically considered constant over the low-frequency range (i.e., “fractal” behavior), and is quantified by β in the relationship “1/ fβ.” In practice, the fractal range cannot extend to indefinitely low frequencies, but factor(s) that terminate this behavior, and determine β, are unclear. We present 1) data in rats ( n = 8) that reveal an extremely low frequency spectral region (0.083–1 cycle/h), where β approaches 0 (i.e., the “shoulder”); and 2) a model that 1) predicts realistic values of β within that range of the spectrum that conforms to fractal dynamics (∼1–60 cycles/h), 2) offers an explanation for the shoulder, and 3) predicts that the “successive difference” in mean BP (mBP) is an important parameter of circulatory function. We recorded BP for up to 16 days. The absolute difference between successive mBP samples at 0.1 Hz (the successive difference, or Δ) was 1.87 ± 0.21 mmHg (means ± SD). We calculated β for three frequency ranges: 1) 0.083–1; 2) 1–6; and 3) 6–60 cycles/h. The β for all three regions differed ( P < 0.01). For the two higher frequency ranges, β indicated a fractal relationship (β6–60/h = 1.27 ± 0.01; β1–6/h = 1.80 ± 0.16). Conversely, the slope of the lowest frequency region (i.e., the shoulder) was nearly flat (β0.083–1 /h = 0.32 ± 0.28). We simulated the BP time series as a random walk about 100 mmHg with ranges above and below of 10, 30, and 50 mmHg and with Δ from 0.5 to 2.5. The spectrum for the conditions mimicking actual BP time series (i.e., range, 85–115 mmHg; Δ, 2.00) resembled the observed spectra, with β in the lowest frequency range = 0.207 and fractal-like behavior in the two higher frequency ranges (β = 1.707 and 2.057). We suggest that the combined actions of mechanisms limiting the excursion of arterial BP produce the shoulder in the spectrum and that Δ contributes to determining β.

Two ranges in blood pressure power spectrum with different 1/f characteristics

1994 ◽  
Vol 267 (2) ◽  
pp. H449-H454 ◽  
Author(s):  
C. D. Wagner ◽  
P. B. Persson
Keyword(s):  
Blood Pressure ◽  
Time Series ◽  
Power Spectrum ◽  
Low Frequency ◽  
Frequency Range ◽  
F Region ◽  
Autonomic Blockade ◽  
Beta Receptor Blockade ◽  
The Difference ◽  
Fast Fourier Analysis

Most time series of biological systems contain a considerable amount of 1/f noise. This form of noise is characterized by fluctuations in which power steadily increases at lower frequencies. To determine the origin of 1/f noise, blood pressure (BP) was measured over 4 h in conscious foxhounds. The power spectrum of BP was obtained by fast Fourier analysis. After log-log transformation, the power spectrum (log power vs. log frequency) characteristically revealed a linear regression. Surprisingly, there were two 1/f ranges. The first 1/f region was located within a low-frequency range (< 10(-1.7) Hz; slope -0.9; r = -0.9). The second 1/f range was identified at 10(-1.4) to 10(-1) Hz (slope -1.2; r = -0.7). After baroreceptor denervation (n = 7), the steepness of both slopes increased significantly (P < 0.05 for lower 1/f range, P < 0.001 for higher 1/f range), and the difference in slopes was clearly greater (slope in lower range -1.2; r = 0.96 vs. -3.1, r = -0.92 in the higher range; P < 0.001). Neither alpha-receptor (n = 6) nor beta-receptor blockade (n = 4) considerably changed the slopes after denervation. However, autonomic blockade (n = 5) restored the slope in the low-frequency range (-0.9; r = -0.9). In conclusion, there are two independently modulated 1/f frequency ranges in BP time series. Baroreceptors especially attenuate 1/f noise in the higher frequency range.

Incoherent oscillations of respiratory sinus arrhythmia during acute mental stress in humans

2012 ◽  
Vol 302 (1) ◽  
pp. H359-H367 ◽  
Author(s):  
Kyuichi Niizeki ◽  
Tadashi Saitoh
Keyword(s):  
Heart Rate ◽  
Respiratory Sinus Arrhythmia ◽  
Mental Stress ◽  
Phase Synchronization ◽  
Mental Arithmetic ◽  
Recovery Period ◽  
Low Frequency ◽  
Phase Lag ◽  
Arithmetic Task ◽  
Sinus Arrhythmia

Respiratory sinus arrhythmia (RSA) has been widely used as a measure of the cardiac vagal control in response to stress. However, RSA seems not to be a generalized indicator because of its dependency on respiratory parameter and individual variations of RSA amplitude (ARSA). We hypothesized that phase-lag variations between RSA and respiration may serve as a normalized index of the degree of mental stress. Twenty healthy volunteers performed mental arithmetic task (ART) after 5 min of resting control followed by 5 min of recovery. Breathing pattern, beat-to-beat R-R intervals, and blood pressure (BP) were determined using inductance plethysmography, electrocardiography, and a Finapres device, respectively. The analytic signals of breathing and RSA were obtained by Hilbert transform and the degree of phase synchronization (λ) was quantified. With the use of spectral analysis, heart rate variability (HRV) was estimated for the low-frequency (LF) and high-frequency (HF) bands. A steady-state 3-min resting period (REST), the first 3 min (ART1), and the last 3 min (ART2) of the ART period (ranged from 6- to 19 min) and the last 3 min of the recovery period (RCV) were analyzed separately. Heart rate, systolic BP, and breathing frequency (fR) increased and λ, ARSA, and HF power decreased from REST to ART ( P < 0.01). The λ was correlated with normalized ARSA and the HF power. The decrease in λ could not be explained solely by the increase in fR. We conclude that mental stress exerts an influence on RSA oscillations, inducing incoherent phase lag with respect to breathing, in addition to a decrease in RSA.

Effects of whole body heating on dynamic baroreflex regulation of heart rate in humans

2000 ◽  
Vol 279 (5) ◽  
pp. H2486-H2492 ◽  
Author(s):  
C. G. Crandall ◽  
R. Zhang ◽  
B. D. Levine
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heat Stress ◽  
Transfer Function ◽  
High Frequency ◽  
Low Frequency ◽  
Whole Body ◽  
High Frequency Range ◽  
Frequency Range ◽  
Transfer Function Analysis

The purpose of this project was to identify whether dynamic baroreflex regulation of heart rate (HR) is altered during whole body heating. In 14 subjects, dynamic baroreflex regulation of HR was assessed using transfer function analysis. In normothermic and heat-stressed conditions, each subject breathed at a fixed rate (0.25 Hz) while beat-by-beat HR and systolic blood pressure (SBP) were obtained. Whole body heating significantly increased sublingual temperature, HR, and forearm skin blood flow. Spectral analysis of HR and SBP revealed that the heat stress significantly reduced HR and SBP variability within the high-frequency range (0.2–0.3 Hz), reduced SBP variability within the low-frequency range (0.03–0.15 Hz), and increased the ratio of low- to high-frequency HR variability (all P < 0.01). Transfer function gain analysis showed that the heat stress reduced dynamic baroreflex regulation of HR within the high-frequency range (from 1.04 ± 0.06 to 0.54 ± 0.6 beats · min−1 · mmHg−1; P < 0.001) without significantly affecting the gain in the low-frequency range ( P = 0.63). These data suggest that whole body heating reduced high-frequency dynamic baroreflex regulation of HR associated with spontaneous changes in blood pressure. Reduced vagal baroreflex regulation of HR may contribute to reduced orthostatic tolerance known to occur in humans during heat stress.

scholarly journals Effects of Chronic Cholinergic Stimulation Associated With Aerobic Physical Training on Cardiac Morphofunctional and Autonomic Parameters in Spontaneously Hypertensive Rats

2021 ◽  
Author(s):  
Camila B. Gardim ◽  
Ana Catarine V. Oliveira ◽  
Bruno Augusto Aguilar ◽  
Stella V. Philbois ◽  
Hugo C. D. Souza
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Physical Training ◽  
Spontaneously Hypertensive Rats ◽  
Low Frequency ◽  
Pyridostigmine Bromide ◽  
Cholinergic Stimulation ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Pharmacological Blockade

Abstract We investigated in spontaneously hypertensive rats (SHR) the hemodynamic, cardiac morphofunctional, and cardiovascular autonomic adaptations after a protocol of aerobic physical training associated with chronic cholinergic stimulation. Fifty-four SRH were divided into two groups: trained and untrained. Afterward, each group was subdivided into three smaller groups: vehicle, treated with pyridostigmine bromide at 5mg/kg/day, and at 15mg/kg/day. The following protocols were assessed: echocardiography, autonomic double pharmacological blockade, analysis of heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS). Physical training and pyridostigmine bromide reduced blood pressure and heart rate and increased vagal participation in cardiac tonic autonomic balance. Associated the responses were potentialized. Pyridostigmine bromide increased the oscillation of low frequency (LF:0.2-0.75Hz) and high frequency (HF:0.75-3Hz) of HRV. However, the association with physical training attenuated HF oscillations. Pyridostigmine bromide also increased LF oscillations of BPV. Both treatments promoted morphofunctional adaptations and associated increased the ejection volume, ejection fraction, cardiac output, and cardiac index. In conclusion, the association of pyridostigmine bromide and physical training promoted greater benefits in hemodynamic parameters and increase vagal influence on cardiac autonomic tonic balance. Nonetheless, pyridostigmine bromide alone seems to negatively affect BPV, while the association of treatment negatively influences HRV.

scholarly journals PHASE DIFFERENCE BETWEEN LOW-FREQUENCY OSCILLATIONS OF CEREBRAL DEOXY- AND OXY-HEMOGLOBIN CONCENTRATIONS DURING A MENTAL TASK

2011 ◽  
Vol 04 (02) ◽  
pp. 151-158 ◽  
Author(s):  
ANGELO SASSAROLI ◽  
FENG ZHENG ◽  
MICHELE PIERRO ◽  
PETER R. BERGETHON ◽  
SERGIO FANTINI
Keyword(s):  
Near Infrared ◽  
Phase Synchronization ◽  
Mental Workload ◽  
Low Frequency ◽  
Phase Lag ◽  
Low Frequency Oscillations ◽  
Potential Applications ◽  
Rest Condition ◽  
The Brain ◽  
Initial Results

Hemodynamic low-frequency (~0.1 Hz) spontaneous oscillations as detected in the brain by near-infrared spectroscopy have potential applications in the study of brain activation, cerebral autoregulation, and functional connectivity. In this work, we have investigated the phase lag between oscillations of cerebral deoxy- and oxy-hemoglobin concentrations in the frequency range 0.05–0.10 Hz in a human subject during a mental workload task. We have obtained a measure of such phase lag using two different methods: (1) phase synchronization analysis as used in the theory of chaotic oscillators and (2) a novel cross-correlation phasor approach. The two methods yielded comparable initial results of a larger phase lag between low-frequency oscillations of deoxy- and oxy-hemoglobin concentrations during mental workload with respect to a control, rest condition.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
Author(s):  
G. Jianmin ◽  
R. Gall ◽  
W. Zuomin
Keyword(s):  
Dynamic Behavior ◽  
Variable Parameter ◽  
Low Frequency ◽  
Vertical Load ◽  
Frequency Range ◽  
Inflation Pressure ◽  
Vehicle Simulation ◽  
Dynamic Damping ◽  
Speed Range ◽  
Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

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