No abstract

We assessed the effects of cold face test (eFT) and active orthostatic test (AOT) on the RR intervals (RR), systolic pressure (SP) and maximal amplitude of arterial pressure first derivative (dmAP) time series of 25 healthy volunteers, and the instantaneous dynamics of their low frequency powers (LF RR, LFsp and LFdmAP), to characterize their time course, and compare their performance as sympathetic markers as well as the magnitude of the sympathetic response evoked by each maneuver. All the variables studied displayed distinct instantaneous response patterns to each maneuver: while in eFT they increased to a plateau, in AOT they presented overshoots at the beginning and end of the test.In both tests, LFdmAP and LFsp dynamics were similar and strongly correlated, and presented a weak correlation with LFRR. Means of LFdmAP and LFsp in eFT were 7 times smaller than in AOT. Our findings support that LFsp and LFdmAP powers exhibit similar performance as noninvasive sympathetic markers and that all variables studied show distinctive beat-to-beat response patterns to each maneuver. Using the sympathetic response produced by AOT as reference, the one evoked by eFT is smaller.

To test the sympathetic activity estimating capability of central frequencies of low frequency ( CF LF) components of systolic pressure ( CF LF SP ), diastolic pressure ( CF LF DP ) and R-R intervals ( CF LF RR ), in 31 healthy subjects performing continuously increasing legs muscle force until fatigue, we assessed: the instantaneous time courses of CF LF SP , CF LF DP , CF LF RR , their respective low frequency powers ( P LF), estimated by a time-frequency distribution, CF LF-P LF correlations and the comparisons between CF LF. Based on the threshold effect they showed, the time courses of all measures were divided into before (BTP) and after (ATP) threshold periods. Time courses of CF LF SP , CF LF DP and CF LF RR showed: 1. similar patterned responses of gradual increment in BTP, abrupt decrease in ATP and fast increment in the initial recovery period (IRP), inverse to the pattern presented by P LF dynamics; 2. 20-s epoch means (EM) differences (p<0.04) between them in control and BTP according to the inequality CF LF RR > CF LF SP > CF LF DP , that disappeared in ATP and IRP. CF LF-P LF correlations (p<0.01) of the three variables were negative and greater (p<0.01) in ATP than BTP and IRP. Our findings support that CF LF can be used as sympathetic activity measures with some specificity: CF LF RR for the cardiac sympathetic outflow and CF LF DP for the vasomotor one.

In 25 healthy volunteers, we examined if active orthostatic test (AOT) and cold face test (CFT) cause opposite effects on the instantaneous dynamics of baroreflex sensitivity (BRS), high-frequency power of RR intervals (HFRR), low-frequency power of systolic pressure (LFSP), LFRR/HFRR IntroductionCold face test (CFT) and active orthostatic test (AOT) are part of the battery of noninvasive tests commonly used for assessing autonomic-cardiovascular function [1] in physiological and clinical settings. While AOT provokes baroreflex sensitivity (BRS) reduction and shifts the autonomic balance towards sympathetic predominance [2], CFT elicits increases of vagal activity, BRS and respiratory sinus arrhythmia sensitivity (RSAS) [3]. It has been reported that great fluctuations of arterial pressure (AP) and heart rate (HR) occur in the first minute of AOT [4,5] and CFT [6]. However, the instantaneous time course of BRS has not been studied, the involvement of RSAS is unclear, and a quantitative comparison between their autonomic-cardiovascular effects for normalizing purposes has not been performed yet. For instance, it is unknown how many times larger are the vagal activity, RSAS and BRS changes induced by CFT in relation to those of AOT. We hypothesize that the pooled values of BRS during CFT and AOT will present strong correlations with autonomic indexes, positive with vagal activity measures and negative with the sympathetic outflow ones. Our aims were to examine if AOT and CFT cause opposite effects on the instantaneous dynamics of BRS, RSAS, and sympathovagal balance, and to assess the correlations between the BRS values of the two tests and the spectral measures of autonomic activity, high-frequency power of RR intervals (HFRR), low-frequency power of systolic pressure (LFSP), LFRR/HFRR ratio and the RSAS. Methods SubjectsTwenty-five healthy, normotensive and sedentary subjects, 14 men and 11 women, were studied. Mean age, height and weight were 22.2±2.2 years, 167±8 cm and 69.1±10.4 kg respectively. Their written informed consent was requested to participate. ProtocolVolunteers visited the laboratory twice. The first time, their health status and anthropometric variables were evaluated, and in the second visit the experimental stage was carried out. Volunteers underwent 1-min control, 1-min maneuver and 2-min recovery stages for both CFT

To assess the linearity of the relation between muscular force (%MF) and baroreflex sensitivity (BRS), respiratory sinus arrhythmia sensitivity (RSAS) and their respective coherences (cBRS and cRSAS), 35 healthy subjects performed static handgrip (HG) or leg extension (LE) linearly increased until fatigue (LIF). From the time-frequency spectra of R-R intervals (RR), respiration (Res), systolic (SP) and diastolic pressures (DP) series, their instantaneous low-frequency (LF RR , LF SP , LF DP) and high-frequency (HF RR , HF Res) powers were estimated to compute, by alpha index, BRS and RSAS, as well as their time-frequency coherences. Relations of %MF with BRS, cBRS, RSAS and cRSAS were inverse, and those with heart rate (HR), DP and HF Res , were direct, all but RSAS with greater slopes and correlations in LE than HG. RSAS can be computed analogously to BRS by alpha index, and their coherences can be used as complementary measures of the degree of their inputoutput coupling. Performing HG and LE in a LIF format provokes moderately to strongly correlated effects, greater for LE than HG, consisting in progressive vagal withdrawal with loss of respiratory-cardiac modulation and release of sympathetic activity that cause the parallel increases of DP and HR with increasing regularity, greater for LE than HG.