Artery Function Responses to Changes in Blood Flow
Condition: Endothelial Dysfunction
Study type: Interventional

Summary: 
      The purpose of this study is to determine if different blood flow patterns change artery
      function. We hypothesize that the temporary induction of an oscillatory blood flow pattern
      will result in an immediate improvement in artery function. Participants will be asked to
      come to the Vascular Dynamics Lab (IWC E102) at McMaster University for a total of 3 visits.
      The first visit will allow the participant to get comfortable with the lab and the upcoming
      tests; and the next 2 visits will be scheduled at the same time of day to collect data. For
      visits 2 and 3, participants will be asked to arrive after a 4 hour fast. At these visits,
      ultrasound imaging will be used to examine the arteries and how they may change when blood
      flow patterns through an artery in the arm are changed. To change blood flow in the arm,
      heat, rhythmic squeezing of the forearm with a cuff, or handgrip exercise will be used. These
      interventions will be applied to the left forearm, from the elbow to the fingertips. A
      trained technician will also draw a blood sample during both data collection visits. A total
      of 10 participants will be recruited for the entire study.
    

Detailed description: 
      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.
    

Intervention name(s): Suprasystolic (300 mmHg) cuff compressions; Handgrip exercise; Passive heat stress
Intervention type(s): Other; Other; Other
Intervention description(s): 10 minutes of ECG-gated repeated suprasystolic (300 mmHg) cuff compressions, with inflation occurring every other heart cycle. These cuff compressions may be triggered 0 seconds, 0.2 seconds, or 0.4 seconds from the R spike (systole) on the ECG signal.; 10 minutes of ECG-gated rhythmic handgrip exercise at 30% maximal voluntary contraction, with contraction occurring every other heart cycle; 10 minutes of passive heat stress at 42 degrees Celsius with a commercially available heating blanket
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: blood flow; endothelial function; shear stress