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

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-1 ) and 5 min (3.47 ± 1.48 aU s-1 ) compared with 1 min (2.42 ± 1.27 aU s-1 , 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.