Predictive value of very low frequency at spectral analysis among patients with unexplained syncope assessed by head-up tilt testing

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.

Download Full-text

Unexplained Syncope Evaluated by Electrophysiologic Studies and Head-up Tilt Testing

Annals of Internal Medicine ◽

10.7326/0003-4819-114-12-1013 ◽

1991 ◽

Vol 114 (12) ◽

pp. 1013 ◽

Cited By ~ 164

Author(s):

Jasbir S. Sra

Keyword(s):

Tilt Testing ◽

Head Up Tilt ◽

Unexplained Syncope ◽

Electrophysiologic Studies

Download Full-text

Sympathetic-Parasympathetic Activation During Spontaneous Attacks of Cluster Headache: Evaluation by Spectral Analysis of Heart-Rate Fluctuations

Cephalalgia ◽

10.1046/j.1468-2982.1995.1506504.x ◽

1995 ◽

Vol 15 (6) ◽

pp. 504-510 ◽

Cited By ~ 11

Author(s):

M De Marinis ◽

S Strano ◽

M Granata ◽

C Urani ◽

S Lino ◽

...

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Spectral Analysis ◽

Cluster Headache ◽

Low Frequency ◽

Sympathetic Activation ◽

Autonomic Balance ◽

Spectral Parameters ◽

Rate Fluctuation ◽

Head Up Tilt

Twenty-four hour ECG Holter and blood-pressure monitorings were performed in eight patients suffering from cluster headache. Spectral analysis of heart-rate fluctuation was used to assess the autonomic balance under basal conditions, after head-up tilt, and during a spontaneous attack. Normal autonomic balance was found at rest and during sympathetic activation obtained with head-up tilt in the interparoxysmal period. Before the onset of headache, an increase in the low-frequency (LF) component of the power spectrum was apparent in all patients. This sign of sympathetic activation was followed by an increase in the high-frequency (HF) component that developed about 2000 beats after the onset of headache and rapidly overcame the LF component until the end of pain. Significant differences were found when comparing the spectral parameters [total spectral values (TP), power of the LF and HF components and LF/HF ratio] obtained before, during and after headache. During the attack, blood pressure increased and heart rate decreased in all subjects. There appears to be a primary activation of both sympathetic and parasympathetic functions in cluster headache attacks. The sympathetic component seems to be involved mostly in the development of the attack, whereas the parasympathetic activation seems to occur, following the onset of the attack, independently of the pain.

Download Full-text

Continuous, on-line, real-time spectral analysis of SAP signals during cardiopulmonary bypass

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1995.268.6.h2329 ◽

1995 ◽

Vol 268 (6) ◽

pp. H2329-H2335

Author(s):

M. W. Yang ◽

T. B. Kuo ◽

S. M. Lin ◽

K. H. Chan ◽

S. H. Chan

Keyword(s):

Spectral Analysis ◽

Cardiopulmonary Bypass ◽

Blood Vessels ◽

Real Time ◽

Low Frequency ◽

Frequency Component ◽

Very Low Frequency ◽

Frequency Components ◽

On Line ◽

Very High

We communicated the application of continuous, on-line, real-time power spectral analysis of systemic arterial pressure (SAP) signals during cardiopulmonary bypass when the heart was functionally but reversibly disconnected from the blood vessels. Based on observations from 15 cases of successfully completed coronary artery bypass grafting procedures, we found that the very low (0.00-0.08 Hz), low (0.08-0.15 Hz)-, high (0.15-0.25 Hz)-, and very high (0.80-1.60 Hz) frequency components of SAP signals exhibited differential changes before, during, and after cardiopulmonary bypass. In particular, the very low-frequency component, which purportedly represents the contribution of vasomotor activity to SAP, presented only a mild decrease in power during hypothermic cardioplegia. Interestingly, the total peripheral resistance also manifested only a slight reduction during the same period. On the other hand, the low-, high-, and very high frequency components were essentially eliminated. These results unveiled an active role for the blood vessels in the maintenance of SAP during cardiopulmonary bypass, possibly as a result of a maintained vasomotor tone as reflected by the sustained very low frequency component of the SAP signals.

Download Full-text

Methodology of head-up tilt testing potentiated with sublingual nitroglycerin in unexplained syncope

The American Journal of Cardiology ◽

10.1016/s0002-9149(99)00919-4 ◽

2000 ◽

Vol 85 (8) ◽

pp. 1007-1011 ◽

Cited By ~ 29

Author(s):

Attilio Del Rosso ◽

Angelo Bartoletti ◽

Paolo Bartoli ◽

Andrea Ungar ◽

Francesco Bonechi ◽

...

Keyword(s):

Sublingual Nitroglycerin ◽

Tilt Testing ◽

Head Up Tilt ◽

Unexplained Syncope

Download Full-text

Path length variations due to changes in tropospheric refraction

Symposium - International Astronomical Union ◽

10.1017/s0074180900065955 ◽

1979 ◽

Vol 89 ◽

pp. 157-162 ◽

Cited By ~ 1

Author(s):

Allen Joel Anderson

Keyword(s):

Spectral Analysis ◽

Gravitational Radiation ◽

Path Length ◽

Low Frequency ◽

Length Variation ◽

Deep Space ◽

Very Low Frequency ◽

Tropospheric Refraction ◽

Detection Capabilities

An experiment is described in which microwave Doppler is used to determine very small changes in path length to spacecraft tracked by the Deep Space Tracking Network (DSN). The experiment was carried out to test the detection capabilities of the DSN system to gravitational radiation of very low frequency (10−2–10−4 Hz). In this work spectral analysis of Doppler variations were performed for periods over 4 hours and more.These results indicated that one of major sources of noise was due to rapid variations in tropospheric refraction. The results obtained a differential path length variation, ΔL/L, of 1 part in 1014 for periods between 100 and 1 000 seconds.Doppler spectra are shown and a general discussion of the experiment is given.

Download Full-text