Using Continuous And Interval Exercise To Manipulate Shear Rate Patterns In The Common Femoral Artery

Abstract

Vascular shear rate (SR) assessed via ultrasound represents frictional force of blood flowing over the endothelium. Low and oscillatory shear confers a pro-inflammatory phenotype, whereas greater shear has an anti-inflammatory phenotype decreasing CVD risk. Exercise increases SR, however the impact of continuous (CON) and interval (INT) exercise upon the balance of anterograde (ANT) and retrograde (RET) SR and thus the oscillatory shear index (OSI) is unknown. PURPOSE: To examine the impact of acute CON and INT (no active recovery) exercise on SR patterns and OSI in the common femoral artery (CFA) during exercise. METHODS: 10 healthy individuals (25±3 years, n=5 male) underwent two work-matched exercise sessions (CON and INT) on a supine cycle ergometer at 125% lactate threshold. In each protocol repetitive ultrasound scans were taken of the CFA during a brief cessation in exercise to determine in-exercise shears. Flow mediated dilatation (FMD) was measured before and after exercise to assess acute changes in endothelial function. RESULTS: FMD did not differ after exercise in either protocol (CON: 9.9±8.1% vs 8.4±6.2%; INT: 9.1±5.9% vs 6.6±3.4%: P>0.05). ANT and RET SR reached a plateau in each protocol. Total ANT SR was lower in CON than INT (CON: 861540±291534 vs INT: 1955615±674594 s-1: P<0.05), however total RET SR did not differ between protocols (CON: 76625±89390 vs INT: 78126±78697 s-1: P>0.05). Peak and mean SR were similar in CON and INT, respectively (peak ANT: 1258±403 vs 1480±510 s-1; RET: 107±123 vs 108±75 s-1: P>0.05; meanANT: 1171±372 vs 1358±469 s-1; RET: 61±81 vs 54±55 s-1: P>0.05). Mean and peak OSI were also similar in both types of exercise (peak CON: 0.07±0.08 vs INT: 0.08±0.0.06 AU; mean CON: 0.05±0.06 vs INT: 0.04±0.04 AU; P>0.05). No time was spent in pure oscillatory shear (>0.5 AU). CONCLUSION: During exercise matched for intensity and the duration of muscular work, using an INT approach ensured a similar OSI but a greater total ANT SR compared to CON. This would suggest that in the exercising limb INT exercise does not confer a negative oscillatory profile. GRANT FUNDING: Medical Research Council