Simultaneous Characterization of Sympathetic and Cardiac Arms of the Baroreflex through Sequence Techniques during Incremental Head-Up Tilt

Abstract

We propose a sympathetic baroreflex (sBR) sequence method for characterizing sBR from spontaneous beat-to-beat fluctuations of muscle sympathetic nerve activity (MSNA) and diastolic arterial pressure (DAP). The method exploits a previously defined MSNA variability quantifying the fluctuations of MSNA burst rate. The method is based on the detection of MSNA and DAP sequences characterized by the contemporaneous DAP increase and MSNA decrease or vice versa. The percentage of sBR sequences (SEQ%sBR) was taken as an indication of the degree of sBR solicitation and the average slope of the regression lines in the (DAP, MSNA) plane was taken as sBR sensitivity (sBRSSEQ) and expressed in bursts.s−1.mmHg−1. sBRSSEQ was compared to a more traditional estimate based on the baroreflex threshold analysis (sBRSBTA). An incremental head-up tilt protocol, carried out in 12 young healthy subjects (age: 20–36 yr, median = 22.5 yr, 9 females) sequentially tilted at 0, 20, 30, 40, 60° table inclinations, was utilized to set the sBR sequence method parameters. Traditional sequence analysis was exploited to estimate cardiac baroreflex (cBR) sensitivity (cBRSSEQ) and percentage of cBR sequences (SEQ%cBR). The head-up tilt induced the progressive increase of SEQ%sBR and SEQ%cBR and gradual decrease of both sBRSSEQ and cBRSSEQ, thus suggesting the gradual rise of the sBR and cBR solicitations and the progressive reduction of their effectiveness with the stimulus. sBRSSEQ was significantly associated with sBRSBTA. sBRSSEQ and cBRSSEQ were significantly correlated as well as SEQ%sBR and SEQ%cBR, even though the correlation was not strong, thus suggesting a certain degree of independence between the baroreflex arms. The proposed sBR sequence approach provides a dynamical characterization of the sBR alternative to more traditional static pharmacological and nonpharmacological methods and fully homogenous with the cBR sequence technique.

Time domain measurement of the vascular and myocardial branches of the baroreflex: A study in physically active versus sedentary individuals

“…This problem can be resolved using invasive techniques. For example, recently Marchi et al (), using direct invasive recordings of sympathetic nerve bursts, have applied the sequence technique for the analysis of baroreflex modulation of MSNA. However, invasive techniques are typically not used in psychophysiological research, and the availability of an easy‐to‐implement and noninvasive method for the assessment of vascular and myocardial baroreflex branches can be useful in basic and clinical research.…”

“…This slow response can be explained by the conduction velocities, release of norepinephrine from the nerve ending, its diffusion to the vascular smooth muscle, and its subsequent effect. However, results of studies measuring the baroreflex modulation of muscle sympathetic nerve activity (MSNA; Kienbaum et al, ; Marchi et al, ; Sundlof & Wallin, ) showed delays between BP and the onset of MSNA bursts of 0.9 to 1.7 s (compatible with lags of 1–2 beats between SBP and measured sympathetic variables).…”

Assessing the strength of cardiac and sympathetic baroreflex controls via transfer entropy during orthostatic challenge

“…three variations) that met the following prerequisites [9]: (i) the absolute value of the total MSNA burst rate variation was larger than 0 bursts · s −1 ; (ii) the absolute value of the total DAP variation was larger than 1 mm Hg; (iii) the linear correlation coefficient, r MSNA-DAP , computed in the [DAP(i), MSNA(i + τ MSNA-DAP )] plane over the correspondent MSNA burst rate and DAP sequences, was larger than 0.85, where τ MSNA-DAP represents the lag between MSNA burst rate and DAP. τ MSNA-DAP was set to 0 [9] fully in agreement with the typical latency of sBR [36,37] given the definition of MSNA burst rate variability [23]. The slope of the regression line was calculated for each sBR sequence and subsequently averaged over all sequences.…”

“…Out of all recordings obtained from the 12 subjects, signals were of insufficient quality or the tilt protocol was not completed, respectively, for one subject during T30 and T40. At difference with [9] recordings during T60 were not used in this study given the inability of finding stationary RM traces in this specific experimental condition. The same situation was found in four, two, one and one subjects during T0, T20, T30 and T40.…”

“…In the computation of CJTE SAP,RM→HP|RM the delay from SAP and RM to HP was set to 0 to account for a fast vagal action of cBR and cardiopulmonary reflexes [13,35]. In the computation of CJTE DAP,RM→MSNA|RM the delay from DAP and RM to MSNA burst rate was set to 0 [9] because the duration of the running window used for the calculation of the MSNA burst rate (i.e. 5 s) makes this value fully compatible with the latency of sBR and disturbing action of respiratory activity [36,37].…”