Influence of cuff-occlusion duration on contrast-enhanced ultrasound assessments of calf muscle microvascular blood flow responsiveness in older adults.

Abstract

What is the central question of the study? Cuff-occlusion duration may influence contrast-enhanced ultrasound (CEUS) assessments of skeletal muscle microvascular blood flow responsiveness: what are the effects of 1, 3 and 5min cuff-occlusion on the magnitude and reliability of calf muscle microvascular blood flow responsiveness in older adults? What is the main finding and its importance? Calf muscle microvascular blood flow responsiveness was enhanced following 5min cuff-occlusion compared with 1min. The reliability of post-occlusion CEUS measurements was also improved following 5min occlusion. The use of a standardized 5min occlusion period should therefore be considered in future studies and clinical practice. Contrast-enhanced ultrasound (CEUS) is increasingly used in assessments of skeletal muscle microvascular blood flow responsiveness. In response to limb cuff-occlusion, some studies have reported significant impairments in CEUS measurements of microvascular blood flow in older adults with cardiovascular or metabolic disease, whereas others have failed to detect significant between-group differences, which has brought the reliability of the technique into question. In the absence of a standardized CEUS protocol, there is variance in the duration of cuff-occlusion used, which is likely to influence post-occlusion measurements of muscle microvascular blood flow. We aimed to determine the effect of cuff-occlusion duration by comparing the magnitude and reliability of CEUS measurements of calf muscle microvascular blood flow responsiveness in older adults (n=15, 67±11years) following 1, 3 and 5min occlusion periods. Microvascular blood flow (=microvascular volume × microvascular velocity) within the calf muscle was measured using real-time destruction-replenishment CEUS. Measurements were made following thigh cuff-occlusion (200mmHg) periods of 1, 3 and 5min in a random order. Microvascular blood flow was higher following 3min (3.71±1.46aUs-1 ) and 5min (3.47±1.48aUs-1 ) compared with 1min (2.42±1.27aUs-1 , P=0.002), which corresponded with higher microvascular volumes after 3 and 5min compared with 1min. Reliability was good following 5min (intraclass correlation coefficient (ICC) 0.49) compared with poor following 1 min (ICC 0.34) and 3 min (ICC 0.35). This study demonstrates that the magnitude and reliability of calf muscle microvascular responsiveness is enhanced using a 5min cuff-occlusion protocol compared with 1 min in older adults.