Near-Infrared Spectroscopy During Reactive Hyperemia for the Assessment of Lower Limb Vascular Function

Our research is focused on understanding how impairments in vascular function and blood flow contribute to the decline in physical function with age and age related cardiovascular conditions. We also aim to develop novel therapies and exercise interventions that target vascular function and enhance physical capacity and quality of life in people living with cardiovascular disease. Differences in testing protocols, a mission of detailed, repeatable NIRS methods and a lack of uniformity in the description, presentation and analysis of NIRS response parameters makes comparisons across individual trials challenging.

This limits the collation of data for meta-analysis and the formulation of clinical assessment recommendations. Compared to plethysmography, NIRS has high temporal resolution and directly evaluates changes in microvasculature. Compared to ultrasound, NIRS does not require sophisticated image analysis or intravenous contrast agents.

The relative ease and affordability of NIRS means that users can be trained rapidly, enabling multicenter investigations with minimal inter operator variability. We're focused on improving skeletal muscle microvascular function through interventions like ischemic preconditioning and blood flow restriction exercise training. We're currently testing the effect of neuromuscular electrical stimulation as a therapy to promote vascular function and to enhance walking capacity in people with peripheral artery disease.

To begin, ask the participant to lie in a supine position on an examination plinth or bed. Place a cuff around the thigh proximal to the knee, ensuring that the tubes do not come into contact with the calf. Elevate the leg with the foot and ankle on foam support, leaving the lower leg stable and accessible for measurements.

Turn on the rapid cuff inflator module. Activate the cuff inflator air source, verify air passage through the hose, and connect the hose to the thigh cuff. Fix the near infrared spectroscopy or NIRS transmitter receiver probe on the skin overlying the measurement sites.

Cover the probe with black kinesiology tape to block ambient light preserving NIRS signal integrity. Instruct the participant to maintain a relaxed posture, avoid talking and keep their legs still throughout the data collection period. Using the computer interface, start the NIRS device and acquire the data for a minimum of two minutes before starting the measurement.

Monitor the computer screen to ensure data signal integrity and physiologically plausible values. If no fluctuations in the NIRS signal are noted, push the corresponding button on the software to set the NIRS data baseline. Collect at least one minute of baseline data ensuring no signal fluctuations or movement artifacts in recording.

Set the cuff pressure to 200 millimeters of mercury on the rapid cuff inflator before selecting the cuff mode. Inform the participant about potential sensations during the cuff's inflation to 200 millimeters of mercury for five minutes, and subsequent total cuff deflation. When ready to initiate cuff inflation, mark the end of the baseline period in the recording.

Inflate the thigh cuff to a suprasystolic pressure of 200 millimeters of mercury. Monitor the computer or screen to ensure data integrity during the occlusion period. Just before the end of the five minute occlusion, remind the participant to keep their legs still and refrain from talking for approximately three minutes after cuff deflation.

After five minutes, rapidly deflate the thigh cuff to zero millimeters of mercury, and simultaneously mark the end of the occlusive period in the recording. After a three minute post occlusion or after the NIRS data has returned to baseline, mark the end of the recovery period and stop the measurement. Finally, export the NIRS results and save the data treatment and analysis.

NIRS distinguishes microvascular responsiveness between healthy individuals and those with peripheral arterial disease during reactive hyperemia testing.