Recent Insights into Carotid Baroreflex Function in Humans Using the Variable Pressure Neck Chamber

Abstract

The variable pressure neck chamber has provided an invaluable research tool for the non‐invasive assessment of carotid baroreflex (CBR) function in human investigations. The ability to construct complete stimulus‐response curves and define specific parameters of the reflex function curve permits statistical comparisons of baroreflex function between different experimental conditions, such as rest and exercise. Results have convincingly indicated that the CBR stimulus‐response curve is reset during exercise in an intensity‐dependent manner to functionally operate around the prevailing pressure elicited by the exercise workload. Furthermore, both at rest and during exercise, alterations in stroke volume do not contribute importantly to the maintenance of arterial blood pressure by the carotid baroreceptors, and therefore, any reflex‐induced changes in cardiac output (Q) are the result of CBR‐mediated changes in heart rate. However, more importantly, the CBR‐induced changes in mean arterial pressure (MAP) are primarily mediated by alterations in vascular conductance with only minimal contributions from Q to the initial reflex MAP response. Thus, the capacity of the CBR to regulate blood pressure depends critically on its ability to alter vascular tone both at rest and during exercise. This review will emphasize the utility of the variable pressure neck chamber to assess CBR function in human experimental investigations and the mechanisms by which the CBR responds to alterations in arterial blood pressure both at rest and during exercise.

Enhanced open-loop but not closed-loop cardiac baroreflex sensitivity during orthostatic stress in humans

“…Importantly, this technique can isolate carotid baroreflex-mediated responses without counteraction from aortic and cardiopulmonary baroreceptors under closed-loop conditions. Indeed, the brief period of stimulation typically used obviates any counterresponses emanating from extracarotid baroreceptors (7,(31)(32)(33). In addition, the peak reflex responses of HR and ABP to NP-NS are unaffected by baseline hemodynamic changes (33).…”

“…The neck chamber technique has been used extensively to estimate arterial baroreflex control in human investigations. Importantly, with the use of the variable-pressure neck chamber to selectively describe carotid baroreflex control, the assumption is made that the aortic baroreflex operates in parallel with the carotid baroreflex and, therefore, will respond similarly (7,32,33). Physiologically, aortic baroreceptors are integrated within the central nervous system in a manner similar to the carotid sinus baroreceptors, making this supposition very reasonable.…”

Carotid baroreflex control of arterial blood pressure at rest and during dynamic exercise in aging humans

“…Full carotid baroreflex stimulusresponse curves for the control of BP were derived at rest and during moderate intensity cycling (16,35) at least 48 h following the incremental maximal exercise test. Following instrumentation, subjects were fitted with a malleable lead collar that encircled the anterior two-thirds of the neck for the application of NP and NS.…”

Sex differences in carotid baroreflex control of arterial blood pressure in humans: relative contribution of cardiac output and total vascular conductance

“…During familiarization sessions, subjects were screened to identify the location of the carotid sinus bifurcation using Doppler ultrasound to ensure that the neck collar fully enclosed the carotid sinuses. Indeed, although transmission to the carotid sinus has been shown to be near complete, there is variability in the location of the carotid sinuses that requires consideration (20,46). Appropriate neck chamber placement was determined by fitting the subjects based on carotid sinus location and observed neck size and then performing resting trials of NP and NS to determine directionally appropriate and consistent cardiovascular responses.…”