Doppler Ultrasound-Based Leg Blood Flow Assessment During Single-Leg Knee-Extensor Exercise in an Uncontrolled Setting

This method is widely recognized and applied in numerous clinical and research settings. The primary objective of this study was to assist the reproducibility of the method, thereby providing valuable insights into the measurement error. By doing so, we can see what is genuine physiological change and what is due to measurement error.

Ultimately, this will enhance our understanding of this method. The primary obstacle lies in exploring physiological changes during various activities in everyday life, as conducting such investigation is feasible only under specific experimental setups. It has been over two decades since the last reliability study was conducted during single-leg knee-extensor exercise.

Over this period technology has significantly evolved, making it imperative to revisit this research area to gain valuable insight into the measurement error associated with the current method. Doppler ultrasound is non-invasive compared to other blood flow determination methods like thermodilution, and it can be combined with arterial and venous catheterization if necessary. It also enables beat-to-beat blood flow velocity measurements so we can detect rapid changes.

In the future our main goal is to investigate the regulation of blood flow to contracting skeletal muscle in patients with chronic obstructive pulmonary disease. To begin position the participant in the single-leg knee-extensor chair with their back resting against the chair. Place a chair or bench to stabilize the inactive leg.

To ensure the electrodes are equidistant from the heart fix one ECG electrode on the right side of the chest wall in the third intercostal space. Place the second one on the left side in the third intercostal space. Then place the third one on the left side in the 11th intercostal space.

After electrode placement position the participant at an angle greater than 90 degrees between the abdomen and thigh. Adjust the arm connecting the single-knee extensor chair to the flywheel. This enables the participant to extend the knee fully.

Tie the leg tightly to the pedal of the chair to avoid the usage of muscles in the lower part of the limb. Next, press the Turn-On button on the ultrasound apparatus. Press Patient to create a new file for the examination.

Move the cursor to New Patient and press Enter. Then fill out the Patient ID.Move the cursor to Create and press Enter. Connect the lead to the electrodes.

Press Probe and choose the linear probe. Apply ultrasound gel to the probe. To begin, place the probe on the inguinal region of the participant.

Then find the optimal arterial section for leg blood flow, or LBF, measurements. Make a cross-sectional image of the common femoral artery. Turn the Gain button clockwise to increase gain and counterclockwise to decrease gain.

Turn the Depth button clockwise to increase the depth and counterclockwise to decrease it. After adjustment, ensure that the artery is in the middle of the screen and the blood is black. In 2D mode press Freeze once, then scroll using the trackball to find an end-systolic image.

Press Measure once and move the cursor to the superficial intimal layer of the artery, then press Enter. Next, move the cursor to the deep intimal layer of the artery and press Enter to obtain the diameter at end systole. Press Freeze, then turn the probe 90 degrees clockwise while keeping the artery centered on the screen and probe parallel to the artery to create a longitudinal view.

Press the PW button followed by the Measure button. Move the cursor to Auto and press Enter. Then click Flow Volume and press Enter.

Move the cursor to Live and press Enter to obtain the trace and finish by pressing Measure once. To obtain the velocity at an insonation angle of less than 60 degrees turn the Steer Angle button clockwise to decrease it and counterclockwise to increase it. Turn the Angle Correction button to validate the trace captured with the cursor horizontal to the artery.

Press Sample Volume to adjust the volume according to the width of the artery while avoiding contact with the artery wall. To decrease the sample size press the left arrow and increase by pressing the right arrow. Next, turn the Sound button clockwise.

Then obtain the blood flow velocity trace with simultaneous 2D visualization of the artery and audio-visual blood velocity feedback. Obtain the first trace during seated rest for 30 seconds and press Image Store twice to save the trace. Then instruct the participant to maintain a pace of 60 RPM during the test.

Using the same conditions record the trace data at a pace of 60 RPM and zero watts. Add resistance to the single-leg knee-extensor chair. Then ask the participant to complete a minimum of 150 seconds of exercise.

Before obtaining 30 seconds of trace press Image Store twice to save the trace. Once all the images are obtained press Review, press trackball, and move the cursor to the desired image, then double-click on Enter. Once the desired trace appears press Measure.

Then from the dropdown menu select Flow Volume and press Enter. Next, select 2D Ultrasound Image and press Enter, then drag the cursor until it reaches the diameter measured during rest and press Enter again. Turn the Cursor Select button clockwise twice.

Then by scrolling the trackball and pressing Enter choose a 30-second trace between two vertical lines. There were no statistically significant differences in the absolute LBF values between the within-day or between-day measurements. LBF increased progressively across the incremental workloads.

The value ranges from 0.36 liter per minute at rest to 2.44 liter per minute during exercise at 18 watts. Bland-Altman plots of LBF measurements for within-day reliability showed no outliers. In contrast, a few outliers were observed in the between-day measurements, and several outliers were observed during the inter-rater measurements.

In test-retest reliability the smallest real difference values were lower for within-day measurements compared to the between-day and inter-rater measurements. Similarly, the coefficient of variation values were higher in the between-day and inter-rater measurements compared to the within-day measurements. The intraclass correlation coefficient values showed that the reliability at all workloads during within-day and between-day were higher than 0.90.

Conversely, the inter-rater measurements yielded ICC values as low as 0.41.