New indices from microneurography to investigate the arterial baroreflex

Abstract

Baroreflex‐mediated changes in heart rate and vascular resistance in response to variations in blood pressure are critical to maintain homeostasis. We aimed to develop time domain analysis methods to complement existing cross‐spectral techniques in the investigation of the vascular resistance baroreflex response to orthostatic stress. A secondary goal was to apply these methods to distinguish between levels of orthostatic tolerance using baseline data. Eleven healthy, normotensive males participated in a graded lower body negative pressure protocol. Within individual neurogenic baroreflex cycles, the amount of muscle sympathetic nerve activity (MSNA), the diastolic pressure stimulus and response amplitudes, diastolic pressure to MSNA burst stimulus and response times, as well as the stimulus and response slopes between diastolic pressure and MSNA were computed. Coherence, gain, and frequency of highest coherence between systolic/diastolic arterial pressure (SAP/DAP) and RR‐interval time series were also computed. The number of MSNA bursts per low‐frequency cycle increased from 2.55 ± 0.68 at baseline to 5.44 ± 1.56 at −40 mmHg of LBNP. Stimulus time decreased (3.21 ± 1.48–1.46 ± 0.43 sec), as did response time (3.47 ± 0.86–2.37 ± 0.27 sec). At baseline, DAP‐RR coherence, DAP‐RR gain, and the time delay between decreases in DAP and MSNA bursts were higher in participants who experienced symptoms of presyncope. Results clarified the role of different branches of the baroreflex loop, and suggested functional adaptation of neuronal pathways to orthostatic stress.

Lower Body Negative Pressure: Physiological Effects, Applications, and Implementation

“…Furthermore, the sensitivity of this intricate feedback mechanism increases during progressive LBNP-induced central hypovolemia as reflected by an elevated coherence between arterial pressure and sympathetic nerve activity (67,77). Laurin et al (217) quantified these interaction bursts at 0.1 Hz (Mayer waves) between MSNA and blood pressure changes during progressive steps of LBNP up to Ϫ60 mmHg in young, healthy subjects. Two new parameters for assessing the sympathetic nervous interaction with diastolic blood pressure at the level of the neuromuscular interface were quantified: stimulus time, defined as the time from the steepest drop in DBP to the first increase in MSNA; and response time, defined as time from the last bust of MSNA to the end of the DBP pulse response.…”

Increased respiratory modulation of cardiovascular control reflects improved blood pressure regulation in pregnancy

“…Figure 2C shows the neurogram from the MSNA signal. Depolarizations of the sympathetic fibers that result in bursts can be observed ( Schreiber and Schmitz, 2000 ; Park et al, 2018 ; Dell’Oro et al, 2019 ; Laurin et al, 2017 ). Supplementary Figure S1 shows similar results for the NNP group in terms of BP.…”

“…The study of the pathophysiological mechanisms behind arterial hypertension in pregnant women and the physiological changes that pregnancy entails have been widely discussed over the years. While most of these studies focus on analyzing cardiovascular and nervous variables in terms of the magnitude of the effect of some stressors ( Park et al, 2018 ; Dell’Oro et al, 2019 ; Laurin et al, 2017 ; Wehrwein and Joyner, 2013 ; Marchi et al, 2015 ; Béchir et al, 2003 ), the present study focused on studying the dynamics of the interactions between the cardiovascular, respiratory, and nervous systems through wavelet phase coherence analysis. The results showed that in the HF band: i) normotensive pregnant women have a higher coupling between MSNA and respiration at rest than normotensive non-pregnant women; ii) normotensive pregnant women have a higher coupling of MSNA-RR and MSNA-BP than normotensive non-pregnant women at rest; iii) hypertensive pregnant women have a lower coupling of MSNA-RR and MSNA-BP than normotensive pregnant women during CPT.…”