Arterial baroreflex regulation of muscle sympathetic nerve activity at rest and during stress

Abstract

Key points The arterial baroreflex controls vasoconstrictor muscle sympathetic nerve activity (MSNA) in a negative feedback manner by increasing or decreasing activity during spontaneous blood pressure falls or elevations, respectively. Spontaneous sympathetic baroreflex sensitivity is commonly quantified as the slope of the relationship between MSNA burst incidence or strength and beat‐to‐beat variations in absolute diastolic blood pressure. We assessed the relationships between blood pressure inputs related to beat‐to‐beat blood pressure change or blood pressure rate‐of‐change (variables largely independent of absolute pressure) and MSNA at rest and during exercise and mental stress. The number of participants with strong linear relationships between MSNA and beat‐to‐beat diastolic blood pressure change variables or absolute diastolic blood pressure were similar at rest, although during stress the beat‐to‐beat diastolic blood pressure change variables were superior. Current methods may not fully characterize the capacity of the arterial baroreflex to regulate MSNA. Abstract Spontaneous sympathetic baroreflex sensitivity (sBRS) is commonly quantified as the slope of the relationship between variations in absolute diastolic blood pressure (DBP) and muscle sympathetic nerve activity (MSNA) burst incidence or strength. This relationship is well maintained at rest but not during stress. We assessed whether sBRS could be calculated at rest and during stress (static handgrip, rhythmic handgrip, mental stress) using blood pressure variables that quantify relative change: beat‐to‐beat DBP change (ΔDBP), ΔDBP rate‐of‐change (ΔDBP rate), pulse pressure (PP) and PP rate‐of‐change (PP rate). Sixty‐six healthy participants underwent continuous measures of blood pressure (finger photoplethysmography) and multi‐unit MSNA (microneurography). At rest, absolute DBP (91%), ΔDBP (97%) and ΔDBP rate (97%) each yielded higher proportions of participants with strong linear relationships (r ≥ 0.6) with MSNA burst incidence compared to PP (57%) and PP rate (56%) and produced similar sBRS slopes (DBP: −4.5 ± 2.0 bursts 100 heartbeats–1/mmHg; ΔDBP: −5.0 ± 2.1 bursts 100 heartbeats–1/ΔmmHg; ΔDBP rate: −4.9 ± 2.2 bursts 100 heartbeats–1/ΔmmHg s–1; P > 0.05). During stress, ΔDBP (74%) and ΔDBP rate (74%) yielded higher proportions of strong linear relationships with MSNA burst incidence than absolute DBP (43%), PP (46%) and PP rate (49%) (all P < 0.05). The absolute DBP associated with a 50% chance of a MSNA burst (T50) was shifted rightward during static handgrip (Δ+15 ± 11 mmHg, P < 0.001) and mental stress (Δ+11 ± 7 mmHg, P < 0.001); however, the ΔDBP T50 was shifted rightward during static handgrip (Δ+2.5 ± 3.7 mmHg, P = 0.009) but not mental stress (Δ0.0 ± 4.4 mmHg, P = 0.99). These findings suggest that calculating sBRS using absolute DBP alone may not adequately characterize arterial baroreflex regulation of MSNA, particularly during stress.

Within-breath sympathetic baroreflex sensitivity is modulated by lung volume but unaffected by acute intermittent hypercapnic hypoxia in men

“…Arterial baroreflex control of MSNA was quantified with the baroreflex threshold analysis method and determined by the slope of the weighted linear regression between diastolic BP and MSNA burst occurrence (bursts•100 heartbeats Ϫ1 •mmHg Ϫ1 ), as previously described (13,16). Briefly, MSNA bursts were time shifted to align with the appropriate ECG R wave and diastolic BP (~1.3 s).…”

The Assessment of Autonomic Nervous System Activity Based on Photoplethysmography in Healthy Young Men

“…For the CPT, the intense cold stimulation activated the baroreflex modulation (Cui et al, 2002;Incognito et al, 2019) and high-threshold nociceptive fibers (Kregel et al, 1992), which might cause a more marked increase in muscle sympathetic nerve activity (MSNA) if compared with SDB and MAT. As a result, the most obvious changes caused by CPT were concentrated on the amplitude-related features [mean(H1), mean(Rs), Rmssd(Rs), mean(He), Std(Hz), Std(He), Std(Ha/Ha), Rmssd(Hw), Rmssd(Ha), Rmssd(Hb), Rmssd(He), and Rmssd(Hb/Ha)].…”

Cardiovagal Baroreflex Hysteresis Using Ellipses in Response to Postural Changes

“…The barosensory vessels become less inflated, whereas the afferent (vagal) activity of baroreceptors declines ( Steinback et al, 2005 ; Taylor et al, 2013 ) and reduces the BRS of the spontaneous CBC in standing ( Figure 3A ) with damped respiratory sinus arrythmia ( Faes et al, 2011 ). In addition, the autonomic nervous system increases the total periphery resistance in standing while accelerating the sympathetic outflow ( Incognito et al, 2019 ); e.g., higher angles of the tilt table elevate the muscle sympathetic nerve activity ( Cooke et al, 1999 ). This outflow seems to add more nonlinearity through the efferent sympathetic pathway ( Wang et al, 1993 ; Ursino, 1998 ) to the hysteresis of the spontaneous CBC than for supine, resulting in a wider hysteresis for standing.…”

“…In addition, the autonomic nervous system increases the total periphery resistance in standing while accelerating the sympathetic outflow (Incognito et al, 2019); e.g., higher angles of the tilt table elevate the muscle sympathetic nerve activity (Cooke et al, 1999). This outflow seems to add more nonlinearity through the efferent sympathetic pathway (Wang et al, 1993;Ursino, 1998) to the hysteresis of the spontaneous CBC than for supine, resulting in a wider hysteresis for standing.…”

“…Small changes of pressure would mainly disclose only the linear parts of the hysteresis near the working point. To investigate the baroreflex, common autonomic provocations include orthostatic tests, head up tilt tests, neck chamber testing, handgrip tests, and the Valsalva maneuver ( Hainsworth, 1998 ; Convertino, 2001 ; La Rovere et al, 2008 ; Hart et al, 2011 ; Ichinose and Nishiyasu, 2012 ; De Maria et al, 2019 ; Incognito et al, 2019 ) as well as pharmacologic interventions ( La Rovere et al, 1998 ; Ler et al, 2010 ; Hart et al, 2011 ; Taylor et al, 2013 ; Incognito et al, 2020 ). Here, the provoked pressure changes provide a possibility to extract the sympathetic outflow of the autonomic nervous system (e.g., by recording sympathetic nerve activity to the blood vessels) and the corresponding parasympathetic vagal outflow (e.g., by recording heart periods) in terms of baroreflex regulation ( Saul et al, 1991 ; Hart et al, 2011 ; Taylor et al, 2013 ).…”