Endothelial Function Responses to Manipulations in Blood Flow Pattern

Interested individuals will be invited to the lab for a screening and familiarization visit, in which the brachial artery (BA) will be scanned to vet for image quality and a BA flow-mediated dilation test will be performed to ensure participant tolerance during collection visits. All qualified participants will be instructed to refrain from vigorous physical activity > 24 hours, alcohol and caffeine > 6 hours, and food > 4 hours prior to each of the two collection visits. Upon arrival, basic anthropometric measures will be collected and hematocrit will be measured in duplicate with a finger prick blood sample equivalent to two 70 µl capillary tubes. Each of the two data collection visits will begin 10 minutes of supine rest, while the participant is instrumented with skin temperature probes on the forearms and hands for measurement of skin temperature, single-lead ECG (Powerlab model ML795, ADInstruments, Colorado Springs, CO, USA) and non-invasive finger cuff (Finometer MIDI, Finapres, The Netherlands) for continuous heart rate and blood pressure monitoring. On the first data collection visit, following rest, the participant will then undergo three 10-minute interventions applied to the left forearm in the following sequence: (1) ECG-gated suprasystolic (300 mmHg) cuff compressions with inflation occurring every other heart cycle, (2) 42 °C heating with a heating blanket, and (3) ECG-gated rhythmic handgrip exercise at 30% MVC with contraction occurring every other heart cycle. 10-minute rest periods will separate each of the interventions to allow for return to baseline conditions. On the second data collection visit, following rest, the participant will undergo three variations of the 10-minute cuff compression intervention, the order of which will be randomized. The three variations differ in the trigger delay from the R spike of the ECG to cause inflation of the cuff for compressions. The original intervention involves the data acquisition unit triggering inflation of the cuff at systole (R spike) (0s delay). This condition will be compared to two other trigger delays, specifically triggering inflation of the cuff at 0.2s and 0.4s after the R spike. For both data collection visits, BA blood velocities, blood flow turbulence, endothelial shear stress, and oscillatory shear index will be assessed before and during each of the interventions; and relative flow-mediated dilation will be assessed before and immediately after each of the interventions. Participants will provide written informed consent prior to beginning any portion of the study.