Received March 28, 2007
Revised April 17, 2007
Accepted after revision April 26, 2007
Autonomic Neuroscience [200]
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Wavelet analysis of autonomic outflow of normal subjects
on head-up tilt, cold pressor test, Valsalva manoeuvre
and deep breathing
Jose-Luis Ducla-Soares 1,
Mariana Santos-Bento 2,
Sergio Laranjo 2,
Alexandre Andrade 3,
Eduardo Ducla-Soares 2,
Joao-Pedro Boto 4,
Luis Silva-Carvalho 2,
Isabel Rocha 2*
1 Instituto de Medicina Molecular
2 Lisbon
3 Lisbon,
4 CMAF, Lisbon
* To whom correspondence should be addressed. E-mail: isabelrocha{at}fm.ul.pt.
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Abstract |
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Abstract
Non-invasive autonomic evaluation has used Fourier Transform to assign a range of low (LF) and high frequencies (HF) as markers of sympathetic and parasympathetic influences, respectively. However, FFT cannot be applied to brief transient phenomena as those observed on performing autonomic tests where the acute changes of cardiovascular signals (blood pressure and heart rate) that represent the first and most important stage of the autonomic performance towards a new state of equilibrium occur. In this study, we evaluate with wavelets the acute changes in RR intervals (RRI) and systolic blood pressure (SBP) that are observed in normal subjects during four classical autonomic tests: head-up tilt (HUT), cold pressor test (CPT), deep breathing (DB) and Valsalva manoeuvre (VM). Continuous monitoring of ECG and BP was performed. Also LF, HF and LF/HF were calculated. Subjects were tilted at 60°; for 7min and data analysed during four periods: 1) resting period; 2) 15s on HUT (TT); 3)1stmin of tilt adaptation (TA1); 4) 1stmin after tilt adaptation (TA2). In CPT, the subjects hand was immersed in ice-cold water for 1min and data are analysed during that period. In VM, subjects breath for 15s against a pressure of 40 mmHg and data are analysed during three periods: 1) resting period; 2) 15s of VM; 3) 35s after VM. In DB test, subjects breath deeply at a rate of 6 cycles/minute; data are analysed during two periods: 1)resting period; 2) 1min on DB. Student t-test was used to compare data during CPT and DB and values were considered significant by differences for p<0.05. ANOVA test was performed for HUT and VM data. All data were expressed as meanSEM. Head-up tilt: LFSBP increased during TT and TA1. LFRRI increased during TA1 and HFRRI decreased during TA1 and TA2. LF/HF index increased for both signals during TA1 and TA2 and during TT for SBP signal. Cold pressure test: An increase of LFSBP was observed without changes in HFSBP. Valsalva manoeuvre: LF increased in both SBP and RRI. HFRRI increased significantly after VM but not during VM. Deep breathing: A shift of parasympathetic frequencies to LF range with increased values of band amplitude was observed on RRI. Data show an increase of sympathetic activity in HUT, CPT and VM. On DB, results reflected an increase in parasympathetic activity and frequencies. In conclusion, when compared with FFT, wavelet analysis allows the evaluation of autonomic variability during short and non-stationary periods of time and may constitute a useful advance in the assessment of autonomic function both in physiological and pathological conditions.
Key Words:
Autonomic nervous system, Sympathetic activity
