Influence of Cuff-occlusion Duration on Contrast-enhanced Ultrasound Assessments of Calf Muscle Microvascular Blood Flow Responsiveness in Older Adults

New Findings: 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 5 min 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 5 min cuff-occlusion compared with 1 min. The reliability of post-occlusion CEUS measurements was also improved following 5 min occlusion. The use of a standardized 5 min occlusion period should therefore be considered in future studies and clinical practice.

Abstract: 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 ± 11 years) following 1, 3 and 5 min 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 (200 mmHg) periods of 1, 3 and 5 min in a random order. Microvascular blood flow was higher following 3 min (3.71 ± 1.46 aU s ) and 5 min (3.47 ± 1.48 aU s ) compared with 1 min (2.42 ± 1.27 aU s , P = 0.002), which corresponded with higher microvascular volumes after 3 and 5 min compared with 1 min. Reliability was good following 5 min (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 5 min cuff-occlusion protocol compared with 1 min in older adults.