Influence of the cold pressor test upon aortic pulse wave reflection in individuals with increased arterial stiffness

Abstract

Aortic pulse wave reflection is an indicator of LV after load, myocardial O2 demand and a predictor of cardiovascular events and is partly determined by muscular and elastic artery stiffness and pulse wave velocity. Acute stimulation of the sympathetic nervous system increases the vascular resistance of the muscular arteries thereby influencing arterial stiffness. The aim of this study was to examine the influence of acute sympathetic stimulation via the cold pressor test upon aortic pulse wave reflection in individuals with and without increased arterial stiffness. Eleven participants (4 males, 31±12yrs; 172±10cm; 75±15kg) completed a cold pressor test (CPT) wherein the left hand was immersed up to the wrist in 2–4°C water for 3 minutes. Blood pressure (mean arterial pressure; MAP) and pulse wave reflection (radial tonometry) were measured throughout. Stroke volume was calculated (photoplethysmography; NexFin) and heart rate measured (ECG; HR) throughout to provide cardiac output (Q). Aortic pulse wave velocity was measured before the CPT (Mobil‐O‐Graph®; aPWV). Pulse wave reflection was referenced to a heart rate of 75 bpm (augmentation index; Aix75). At baseline heart rate was 66±8 bpm and the change during CPT was variable between participants (Range: −11 to +14 bpm). Prior to CPT, Aix75 was 0±19% (Range −31 to 31%) and MAP was 87±10 mmHg. During the CPT Aix75 increased to 17±13% while MAP increased to 102±7 mmHg (both P ≤ 0.05). The change in Aix75 during CPT correlated poorly with age (R2 = 0.13), baseline MAP (R2 = 0.03), the change in MAP during CPT (R2 = 0.05) and baseline aPWV (R2 = 0.08) (all P > 0.05). However, the increase in Aix75 during the CPT correlated moderately with baseline Aix75 (R2 = 0.75; P = 0.0006) and the change in Q during CPT (R2 = 0.40; P = 0.049). Increases in aortic pulse wave reflection during the cold pressor test were inversely related to baseline aortic pulse wave reflection. This may be indicative of a ceiling effect where individuals with evidence of existing arterial stiffening demonstrate a reduced increase in pulse wave reflection during sympathetic stimulation via cold pressor test. Nevertheless individuals with evidence of increased arterial stiffness still experience acute increases in pulse wave reflection during sympathetic stimulation via the cold pressor test.