Cardiac and haemodynamic influence on carotid artery longitudinal wall motion
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NEW FINDINGS: What is the central question of this study? Carotid artery longitudinal wall motion (CALM) is a bidirectional forward and backward motion of the arterial wall; however, there is no evidence in humans for what controls CALM despite proposals for pulse pressure, left ventricular motion and shear rate. What is the main finding and its importance? Carotid artery longitudinal wall motion responses were heterogeneous when manipulating sympathetic activation and endothelium-independent vasodilatation, leading to non-significant group responses. However, individual CALM responses were associated with left ventricular rotation and shear rate. These findings are important when interpreting changes in CALM in humans with acute or chronic experimental designs. Carotid artery longitudinal wall motion (CALM) has recently attracted interest as an indicator of arterial health; however, the regulation of CALM is poorly understood. We conducted a series of studies aimed at manipulating pulse pressure (PP), left ventricular (LV) motion and carotid shear rate, which have been previously suggested to regulate various components of CALM pattern and magnitude. To determine the regulatory influences on CALM, 15 healthy men (22 ± 2 years old) were exposed to three acute interventions: the serial subtraction test (SST); the cold pressor test (CPT); and exposure to sublingual nitroglycerine (NTG). The SST elicited increases in PP (P < 0.01), apical LV rotation (P < 0.01) and carotid shear rate (P < 0.01), with no changes in CALM (P > 0.05). Likewise, the CPT elicited increases in PP (P = 0.01), basal LV rotation (P = 0.04) and carotid shear rate (P = 0.01), with no changes in CALM (P > 0.05). Conversely, exposure to NTG elicited no change in PP (P = 0.22), basal (P = 0.65) or apical LV rotation (P = 0.45), but did decrease carotid shear rate (P < 0.01), without altering CALM (P > 0.05). Considerable individual variability in CALM responses prompted further analyses where all three interventions were pooled for change scores. Changes in LV basal rotation were related to changes in systolic retrograde CALM (B = -0.025, P = 0.03), whereas changes in carotid shear rate were related to changes in diastolic CALM displacement (B = 0.0009, P = 0.01). The interventions were underpinned by relationships between CALM and both LV basal rotation and local shear rate at the individual level, indicating that cardiac and haemodynamic factors may influence CALM in humans.
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