Neuromechanical Features of the Cardiac Baroreflex After Exercise

Abstract

Abstract-A single bout of exercise is associated with postexercise hypotension, transient decreases in autonomic function, and changes in baroreflex sensitivity. The baroreflex is less sensitive to falling blood pressure than to rising blood pressure; we characterized the cardiac baroreflex in terms of hysteresis and its mechanical and neural components. We hypothesized that hysteresis would be exacerbated postexercise because of a greater relative decrease in falling blood pressure. In 10 healthy young humans (5 men), we used bolus injections of sodium nitroprusside and phenylephrine hydrochloride to drive transient decreases and increases in blood pressure, respectively, to quantify cardiac baroreflex sensitivity to falling and rising blood pressure. This was completed before and at 10, 30, and 60 minutes after 40 minutes of cycling at 60% estimated maximal oxygen consumption. Analyses of beat-to-beat blood pressure, R-R intervals and heart rate, and carotid artery diameter were used to determine the integrated cardiac baroreflex response; this was further quantified into a mechanical component (systolic blood pressure versus carotid diameter) and a neural component (carotid diameter versus R-R interval). There were 2 principle findings: after aerobic exercise baroreflex sensitivity is reduced and hysteresis manifests, and the reduction in sensitivity to falling blood pressure is mediated by decreased mechanical and neural gains, whereas the decreased baroreflex sensitivity to rising blood pressure is mediated by a reduced mechanical gain only. We suggest that impaired neural transduction of the cardiac baroreflex, and its influence on hysteresis, plays an important role in transient autonomic dysfunction after exercise. (Hypertension. 2011;57:927-933.)Key Words: baroreflex sensitivity Ⅲ cardiac Ⅲ exercise Ⅲ postexercise hypotension Ⅲ autonomic A single bout of moderate-to-high-intensity exercise is associated with postexercise alterations in cardiac baroreflex sensitivity (BRS) and often a period of postexercise hypotension. It has been reported that 10 to 30 minutes after exercise, in both hypertensive patients and young healthy subjects, BRS is initially reduced 1-3 or unchanged, 4 as assessed using nonpharmacological 1,4 or pharmacological techniques. 2,3 Some studies have demonstrated recovery or augmentation of BRS Ͼ20 minutes postexercise cessation, 2,4,5 whereas others indicated a maintained BRS attenuation. 3 On cessation of exercise, postexercise hypotension is common, with the magnitude of change dependant on resting blood pressure (BP) and the intensity and duration of exercise; hypertension and greater intensity exercise both elicit a larger postexercise BP drop. 6,7 During this postexercise period there is altered regulation of sympathetic vascular tone or increases in vasodilator substances, or both, such that systemic vascular resistance is not restored until hours later. 7,8 Likely because of these alterations to autonomic and vascular function, there is a high incidence of syncope after exerc...

Mechanisms of blood pressure control following acute exercise in adolescents: Effects of exercise intensity on haemodynamics and baroreflex sensitivity

“…However, because BRS is composed of a vascular (measured as changes in arterial diameter per changes in units of BP) and an autonomic (measured as changes in heart rate (HR) per units of vascular diameter) component (Bonyhay, Jokkel, & Kollai, 1996;Kornet, Hoeks, Janssen, Willigers, & Reneman, 2002;Taylor, Willie, Ainslie, & Tzeng, 2014), their different contribution to the total BRS gain following exercise is still controversial. For example, in adults decreases in BRS following exercise have been attributed to either both components (Willie et al, 2011), or the vascular component (Studinger, Lenard, Kovats, Kocsis, & Kollai, 2003), with both components returning to baseline values 60 min post-exercise (Studinger et al, 2003;Willie et al, 2011). The difference between exercise modalities, intensities and duration makes comparisons between the results challenging, as these exercise characteristics are likely to impact BRS regulation (Halliwill et al, 2013).…”

The Role of Ultrasonography in the Assessment of Arterial Baroreflex Function

“…45 We found that following aerobic exercise baroreflex gain is reduced and hysteresis manifests. The reduction in baroreflex gain to falling blood pressure is mediated by decreased mechanical and neural gains, whereas the decreased baroreflex gain to rising blood pressure is mediated by a reduced mechanical gain only.…”

Postural influences on the mechanical and neural components of the cardiovagal baroreflex

“…, Willie et al . ). Offline data processing was performed using custom written software in LabView 8.2 (National Instruments, Austin, TX, USA) on a Macintosh 3.1 GHz iMac computer (Apple, Cupertino, CA, USA).…”

“…Many activities in day‐to‐day living produce physiological challenges associated with changes in baroreflex function, such as exercise (Willie et al . ) and the assumption of an upright posture (O'Leary et al . ).…”