Causal relationships between heart period and systolic arterial pressure during graded head-up tilt

In physiological conditions, heart period (HP) affects systolic arterial pressure (SAP) through diastolic runoff and Starling's law, but, the reverse relation also holds as a result of the continuous action of baroreflex control. The prevailing mechanism sets the dominant temporal direction in the HP-SAP interactions (i.e., causality). We exploited cross-conditional entropy to assess HP-SAP causality. A traditional approach based on phases was applied for comparison. The ability of the approach to detect the lack of causal link from SAP to HP was assessed on 8 short-term (STHT) and 11 long-term heart transplant (LTHT) recipients (i.e., less than and more than 2 yr after transplantation, respectively). In addition, spontaneous HP and SAP variabilities were extracted from 17 healthy humans (ages 21–36 yr, median age 29 yr; 9 females) at rest and during graded head-up tilt. The tilt table inclinations ranged from 15 to 75° and were changed in steps of 15°. All subjects underwent recordings at every step in random order. The approach detected the lack of causal relation from SAP to HP in STHT recipients and the gradual restoration of the causal link from SAP to HP with time after transplantation in the LTHT recipients. The head-up tilt protocol induced the progressive shift from the prevalent causal direction from HP to SAP to the reverse causality (i.e., from SAP to HP) with tilt table inclination in healthy subjects. Transformation of phases into time shifts and comparison with baroreflex latency supported this conclusion. The proposed approach is highly efficient because it does not require the knowledge of baroreflex latency. The dependence of causality on tilt table inclination suggests that “spontaneous” baroreflex sensitivity estimated using noncausal methods (e.g., spectral and cross-spectral approaches) is more reliable at the highest tilt table inclinations.

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Influences of neural mechanisms on heart period and arterial pressure variabilities in quadriplegic patients

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1994.266.3.h1112 ◽

1994 ◽

Vol 266 (3) ◽

pp. H1112-H1120 ◽

Cited By ~ 10

Author(s):

S. Guzzetti ◽

C. Cogliati ◽

C. Broggi ◽

C. Carozzi ◽

D. Caldiroli ◽

...

Keyword(s):

Arterial Pressure ◽

Spectral Component ◽

Systolic Arterial Pressure ◽

Neural Mechanisms ◽

Heart Period ◽

Recording Session ◽

Sympathetic Modulation ◽

Arterial Pressure Variability ◽

Head Up Tilt ◽

Vasomotor Activity

The heart period (R-R) variability power spectrum presents two components, at low (LF; approximately 0.10 Hz) and high (approximately 0.25 Hz) frequencies, whose reciprocal powers appear to furnish an index of sympathovagal interaction modulating heart rate. In addition, the LF component of the systolic arterial pressure variability spectrum furnishes a marker of sympathetic modulation of vasomotor activity. The contribution of spinal and supraspinal neural circuits to the genesis of these rhythmic oscillatory components remains largely unsettled. Therefore we performed spectral analysis of R-R and systolic arterial pressure variabilities in 15 chronic neurologically complete quadriplegic patients (QP) and in 15 control subjects during resting conditions, controlled respiration, and head-up tilt. At rest, in seven QP the LF component was undetectable in both cardiovascular variability spectra; in two QP this component was present only in R-R variability spectrum, whereas the remaining six showed a significantly reduced LF in both signals. In QP, the LF component, when present, underwent paradoxical changes with respect to controls, decreasing during tilt and increasing during controlled respiration. In five QP in whom the recording session was repeated after 6 mo, a significant increase in LF was observed in both variability spectra. These data confirm the finding that a disconnection of sympathetic outflow from supraspinal centers can cause the disappearance of the LF spectral component. However, LF presence in some QP supports the hypothesis of a spinal rhythmicity likely to be modulated by the afferent sympathetic activity.

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Information Transfer through the Spontaneous Baroreflex in Healthy Humans

Methods of Information in Medicine ◽

10.3414/me09-02-0036 ◽

2010 ◽

Vol 49 (05) ◽

pp. 506-510 ◽

Cited By ~ 7

Author(s):

A. M. Catai ◽

A. C. M. Takahashi ◽

V. Magagnin ◽

T. Bassani ◽

E. Tobaldini ◽

...

Keyword(s):

Arterial Pressure ◽

Information Transfer ◽

Function Analysis ◽

Systolic Arterial Pressure ◽

Heart Period ◽

Uniform Quantization ◽

Transfer Function Analysis ◽

Head Up Tilt ◽

Spontaneous Baroreflex

Summary Objectives: This study assesses the information transfer through the spontaneous baroreflex (i.e. through the pathway linking systolic arterial pressure to heart period) during an experimental condition soliciting baroreflex (i.e. head-up tilt). Methods: The information transfer was calculated as the conditional entropy of heart period given systolic arterial pressure using a mutual neighbor approach and uniform quantization. The information transfer was monitored as a function of the forecasting time k. Results: We found that during head-up tilt the information transfer at k = 0 decreased but the rate of rise of information transfer as a function of k was faster. Conclusions: We suggest that the characterization of the information transfer from systolic arterial pressure to heart period might complement the traditional characterization of the spontaneous baroreflex based on transfer function analysis.

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Short-term complexity indexes of heart period and systolic arterial pressure variabilities provide complementary information

Journal of Applied Physiology ◽

10.1152/japplphysiol.00755.2012 ◽

2012 ◽

Vol 113 (12) ◽

pp. 1810-1820 ◽

Cited By ~ 52

Author(s):

A. Porta ◽

P. Castiglioni ◽

M. Di Rienzo ◽

V. Bari ◽

T. Bassani ◽

...

Keyword(s):

Arterial Pressure ◽

Systolic Arterial Pressure ◽

Adrenergic Blockade ◽

Sympathetic Blockade ◽

Heart Period ◽

Complementary Information ◽

Beta Adrenergic ◽

Orthostatic Challenge ◽

Vagal Blockade ◽

Head Up Tilt

It is unclear whether the complexity of the variability of the systolic arterial pressure (SAP) provides complementary information to that of the heart period (HP). The complexity of HP and SAP variabilities was assessed from short beat-to-beat recordings (i.e., 256 cardiac beats). The evaluation was made during a pharmacological protocol that induced vagal blockade with atropine or a sympathetic blockade (beta-adrenergic blockade with propranolol or central sympathetic blockade with clonidine) alone or in combination, during a graded head-up tilt, and in patients with Parkinson's disease (PD) without orthostatic hypotension undergoing orthostatic challenge. Complexity was quantified according to the mean square prediction error (MSPE) derived from univariate autoregressive (AR) and multivariate AR (MAR) models. We found that: 1) MSPEMAR did not provide additional information to that of MSPEAR; 2) SAP variability was less complex than that of HP; 3) because HP complexity was reduced by either vagal blockade or vagal withdrawal induced by head-up tilt and was unaffected by beta-adrenergic blockade, HP was under vagal control; 4) because SAP complexity was increased by central sympathetic blockade and was unmodified by either vagal blockade or vagal withdrawal induced by head-up tilt, SAP was under sympathetic control; 5) SAP complexity was increased in patients with PD; and 6) during orthostatic challenge, the complexity of both HP and SAP variabilities in patients with PD remained high, thus indicating both vagal and sympathetic impairments. Complexity indexes derived from short HP and SAP beat-to-beat series provide complementary information and are helpful in detecting early autonomic dysfunction in patients with PD well before circulatory symptoms become noticeable.

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Joint symbolic dynamics for the assessment of cardiovascular and cardiorespiratory interactions

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2014.0097 ◽

2015 ◽

Vol 373 (2034) ◽

pp. 20140097 ◽

Cited By ~ 10

Author(s):

Mathias Baumert ◽

Michal Javorka ◽

Muammar Kabir

Keyword(s):

Arterial Pressure ◽

Symbolic Dynamics ◽

Systolic Arterial Pressure ◽

Symbolic Analysis ◽

Heart Period ◽

Short Term ◽

Cardiorespiratory Control ◽

Baroreflex Control ◽

Simple Description ◽

Cardiorespiratory Coupling

Beat-to-beat variations in heart period provide information on cardiovascular control and are closely linked to variations in arterial pressure and respiration. Joint symbolic analysis of heart period, systolic arterial pressure and respiration allows for a simple description of their shared short-term dynamics that are governed by cardiac baroreflex control and cardiorespiratory coupling. In this review, we discuss methodology and research applications. Studies suggest that analysis of joint symbolic dynamics provides a powerful tool for identifying physiological and pathophysiological changes in cardiovascular and cardiorespiratory control.

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Influence of age and gender on the phase and strength of the relation between heart period and systolic blood pressure spontaneous fluctuations

Journal of Applied Physiology ◽

10.1152/japplphysiol.00903.2017 ◽

2018 ◽

Vol 124 (3) ◽

pp. 791-804 ◽

Cited By ~ 10

Author(s):

Juliana C. Milan-Mattos ◽

Alberto Porta ◽

Natália M. Perseguini ◽

Vinicius Minatel ◽

Patricia Rehder-Santos ◽

...

Keyword(s):

Arterial Pressure ◽

Coherence Function ◽

Low Frequency ◽

Systolic Arterial Pressure ◽

Progressive Increase ◽

Heart Period ◽

Baroreflex Control ◽

And Gender ◽

Spontaneous Fluctuations ◽

Cardiovascular Variables

Aging affects baroreflex regulation. The effect of senescence on baroreflex control was assessed from spontaneous fluctuations of heart period (HP) and systolic arterial pressure (SAP) through the HP-SAP gain, while the HP-SAP phase and strength are usually disregarded. This study checks whether the HP-SAP phase and strength, as estimated, respectively, via the phase of the HP-SAP cross spectrum (PhHP-SAP) and squared coherence function (K2HP-SAP), vary with age in healthy individuals and trends are gender-dependent. We evaluated 110 healthy volunteers (55 males) divided into five age subgroups (21–30, 31–40, 41–50, 51–60, and 61–70 yr). Each subgroup was formed by 22 subjects (11 males). HP series was extracted from electrocardiogram and SAP from finger arterial pressure at supine resting (REST) and during active standing (STAND). PhHP-SAP and K2HP-SAP functions were sampled in low-frequency (LF, from 0.04 to 0.15 Hz) and in high-frequency (HF, above 0.15 Hz) bands. Both at REST and during STAND PhHP-SAP(LF) showed a negative correlation with age regardless of gender even though values were more negative in women. This trend was shown to be compatible with a progressive increase of the baroreflex latency with age. At REST K2HP-SAP(LF) decreased with age regardless of gender, but during STAND the high values of K2HP-SAP(LF) were more preserved in men than women. At REST and during STAND the association of PhHP-SAP(HF) and K2HP-SAP(HF) with age was absent. The findings points to a greater instability of baroreflex control with age that seems to affect to a greater extent women than men. NEW & NOTEWORTHY Aging increases cardiac baroreflex latency and decreases the degree of cardiac baroreflex involvement in regulating cardiovascular variables. These trends are gender independent but lead to longer delays and asmaller degree of cardiac baroreflex involvement in women than in men, especially during active standing, with important implications on the tolerance to an orthostatic stressor.

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RT variability unrelated to heart period and respiration progressively increases during graded head-up tilt

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01206.2009 ◽

2010 ◽

Vol 298 (5) ◽

pp. H1406-H1414 ◽

Cited By ~ 45

Author(s):

Alberto Porta ◽

Eleonora Tobaldini ◽

Tomaso Gnecchi-Ruscone ◽

Nicola Montano

Keyword(s):

Random Order ◽

Open Loop ◽

Parametric Models ◽

Heart Period ◽

Tilt Table ◽

Indirect Measure ◽

T Wave ◽

Healthy Humans ◽

Surface Ecg ◽

Head Up Tilt

Open-loop linear parametric models were exploited to describe ventricular repolarization duration (VRD) variability during graded head-up tilt. Surface ECG and thoracic movements were recorded in 15 healthy humans (age: 24–54 yr, median: 28 yr; 6 women and 9 men). Tilt table inclinations ranged from 15 to 90° and were varied in steps of 15°. All subjects underwent recordings at every step in random order. Heart period was assessed as the time difference between two consecutive R-wave peaks (RR) and the respiratory signal (R) as the sampling of the thoracic movement signal at the R-wave peaks. VRD was measured automatically as the temporal difference between the R-wave peak and T-wave apex (RTa) or T-wave end (RTe). The best model decomposed RT variability as due to RR changes (RR-related RT variability) to direct respiratory-related inputs (R-related RT variability) and to unknown rhythmical sources unrelated to RR changes and R (RR-R-unrelated RT variability). Using this model, RTe variability was found to be less predictable than RTa variability and composed of a smaller fraction of RR-related RT variability and a larger fraction of RR-R-unrelated RT variability. Predictability progressively decreased with tilt table angles, suggesting increased complexity of RT regulation. RT variance progressively increased with tilt table inclination. This increase was characterized by a gradual rise of the amount of RR-R-unrelated RT variability, whereas the amount of RR-related RT variability remained unchanged. These results suggest that the amount of RT variability, complexity of RT dynamics, and amount of RR-R-unrelated RT variability increase with the magnitude of the sympathetic drive directly related to tilt table inclination. We propose the utilization of the amount of RR-R-unrelated RT variability instead of overall RT variability as an indirect measure of autonomic regulation directed to ventricles.

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Exploring directionality in spontaneous heart period and systolic pressure variability interactions in humans: implications in the evaluation of baroreflex gain

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00594.2004 ◽

2005 ◽

Vol 288 (4) ◽

pp. H1777-H1785 ◽

Cited By ~ 78

Author(s):

Giandomenico Nollo ◽

Luca Faes ◽

Alberto Porta ◽

Renzo Antolini ◽

Flavia Ravelli

Keyword(s):

Spectral Analysis ◽

Spectral Component ◽

Systolic Pressure ◽

Low Frequency ◽

Systolic Arterial Pressure ◽

Phase Lag ◽

Healthy Humans ◽

Head Up Tilt ◽

Causal Approach ◽

Young Subjects

Although in physiological conditions RR interval and systolic arterial pressure (SAP) are likely to interact in a closed loop, the traditional cross-spectral analysis cannot distinguish feedback (FB) from feedforward (FF) influences. In this study, a causal approach was applied for calculating the coherence from SAP to RR ( Ks-r) and from RR to SAP ( Kr-s) and the gain and phase of the baroreflex transfer function. The method was applied, compared with the noncausal one, to RR and SAP series taken from 15 healthy young subjects in the supine position and after passive head-up tilt. For the low frequency (0.04–0.15 Hz) spectral component, the enhanced FF coupling ( Kr-s = 0.59 ± 0.21, significant in 14 subjects) and the blunted FB coupling ( Ks-r = 0.17 ± 0.17, significant in 4 subjects) found at rest indicated the prevalence of nonbaroreflex mechanisms. The tilt maneuver recovered FB influences ( Ks-r = 0.47 ± 0.16, significant in 14 subjects), which were stronger than FF interactions ( Ks-r = 0.34 ± 0.19, significant in 9 subjects). At the respiratory frequency, the RR-SAP regulation was balanced at rest ( Ks-r = 0.30 ± 0.18 and Kr-s = 0.29 ± 0.20, significant in 11 and 8 subjects) and shifted toward FB mechanisms after tilt ( Ks-r = 0.35 ± 0.19 and Kr-s = 0.19 ± 0.11, significant in 14 and 8 subjects). The causal baroreflex gain estimates were always lower than the corresponding noncausal values and decreased significantly from rest to tilt in both frequency bands. The tilt-induced increase of the phase lag from SAP to RR suggested a shift from vagal to sympathetic modulation. Thus the importance of nonbaroreflex interactions pointed out the necessity of accounting for causality in the cross-spectral analysis of the interactions between cardiovascular variables in healthy humans.

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Comparison of phenylephrine bolus and infusion methods in baroreflex measurements

Journal of Applied Physiology ◽

10.1152/jappl.1990.69.3.962 ◽

1990 ◽

Vol 69 (3) ◽

pp. 962-967 ◽

Cited By ~ 27

Author(s):

J. T. Sullebarger ◽

C. S. Liang ◽

P. D. Woolf ◽

A. E. Willick ◽

J. F. Richeson

Keyword(s):

Heart Rate ◽

Arterial Pressure ◽

Baroreflex Sensitivity ◽

Heart Rate Response ◽

Pressor Response ◽

Plasma Catecholamines ◽

Systolic Arterial Pressure ◽

Normal Subjects ◽

Vagus Nerves ◽

Baroreflex Control

Phenylephrine (PE) bolus and infusion methods have both been used to measure baroreflex sensitivity in humans. To determine whether the two methods produce the same values of baroreceptor sensitivity, we administered intravenous PE by both bolus injection and graded infusion methods to 17 normal subjects. Baroreflex sensitivity was determined from the slope of the linear relationship between the cardiac cycle length (R-R interval) and systolic arterial pressure. Both methods produced similar peak increases in arterial pressure and reproducible results of baroreflex sensitivity in the same subjects, but baroreflex slopes measured by the infusion method (9.9 +/- 0.7 ms/mmHg) were significantly lower than those measured by the bolus method (22.5 +/- 1.8 ms/mmHg, P less than 0.0001). Pretreatment with atropine abolished the heart rate response to PE given by both methods, whereas plasma catecholamines were affected by neither method of PE administration. Naloxone pretreatment exaggerated the pressor response to PE and increased plasma beta-endorphin response to PE infusion but had no effect on baroreflex sensitivity. Thus our results indicate that 1) activation of the baroreflex by the PE bolus and infusion methods, although reproducible, is not equivalent, 2) baroreflex-induced heart rate response to a gradual increase in pressure is less than that seen with a rapid rise, 3) in both methods, heart rate response is mediated by the vagus nerves, and 4) neither the sympathetic nervous system nor the endogenous opiate system has a significant role in mediating the baroreflex control of heart rate to a hypertensive stimulus in normal subjects.

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Temporal asymmetries of short-term heart period variability are linked to autonomic regulation

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00129.2008 ◽

2008 ◽

Vol 295 (2) ◽

pp. R550-R557 ◽

Cited By ~ 120

Author(s):

A. Porta ◽

K. R. Casali ◽

A. G. Casali ◽

T. Gnecchi-Ruscone ◽

E. Tobaldini ◽

...

Keyword(s):

Autonomic Regulation ◽

Heart Period ◽

Short Term ◽

Time Reversibility ◽

Heart Period Variability ◽

Period Variability ◽

Healthy Humans ◽

Inclination Angles ◽

Head Up Tilt ◽

Important Shift

We exploit time reversibility analysis, checking the invariance of statistical features of a series after time reversal, to detect temporal asymmetries of short-term heart period variability series. Reversibility indexes were extracted from 22 healthy fetuses between 16th to 40th wk of gestation and from 17 healthy humans (aged 21 to 54, median = 28) during graded head-up tilt with table inclination angles randomly selected inside the set {15, 30, 45, 60, 75, 90}. Irreversibility analysis showed that nonlinear dynamics observed in short-term heart period variability are mostly due to asymmetric patterns characterized by bradycardic runs shorter than tachycardic ones. These temporal asymmetries were 1) more likely over short temporal scales than over longer, dominant ones; 2) more frequent during the late period of pregnancy (from 25th to 40th week of gestation); 3) significantly present in healthy humans at rest in supine position; 4) more numerous during 75 and 90° head-up tilt. Results suggest that asymmetric patterns observable in short-term heart period variability might be the result of a fully developed autonomic regulation and that an important shift of the sympathovagal balance toward sympathetic predominance (and vagal withdrawal) can increase their presence.

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