Assessment of voluntary rhythmic muscle contraction-induced exercising blood flow variability measured by Doppler ultrasound

Given recent technological developments, ultrasound Doppler can provide valuable measurements of blood velocity/flow in the conduit artery with high temporal resolution. In human-applied science such as exercise physiology, hemodynamic measurements in the conduit artery is commonly performed by blood flow feeding the exercising muscle, as the increase in oxygen uptake (calculated as a product of arterial blood flow to the exercising limb and the arterio-venous oxygen difference) is directly proportional to the work performed. The increased oxygen demand with physical activity is met through a central mechanism, an increase in cardiac output and blood pressure, as well as a peripheral mechanism, an increase in vascular conductance and oxygen extraction (a major part of the whole exercising muscles) from the blood. The increase in exercising muscle blood flow in relation to the target workload (quantitative response) may be one indicator in circulatory adjustment for the ac- tivity of muscle metabolism. Therefore, the determination of local blood flow dynamics (potential oxygen supply) feeding repeated (rhythmic) muscle contractions can contribute to the understanding of the factors limiting work capacity including, for instance, muscle metabolism, substance utilization and magnitude of vasodilatation in the exercising muscle. Using non-invasive measures of pulsed Doppler ultrasound, the validity of blood velocity/flow in the forearm or lower limb conduit artery feeding to the muscle has been previously demonstrated during rhythmic muscle exercise. For the evaluation of exercising blood flow, not only muscle contraction induced internal physiological variability, or fluctuations in the magnitude of blood velocity due to spontaneous muscle contraction and relaxation induced changes in force curve intensity, superimposed in cardiac beat-by-beat, but also the alterations in the blood velocity (external variability) due to a temporary sudden change in the achieved workload, compared to the target workload, should be considered. Furthermore, a small amount of inconsistency in the voluntary muscle contraction force at each kick seems to be unavoidable, and may influence exercising muscle blood flow, although subjects attempt to perform precisely similar repeated voluntary muscle contractions at target workload (muscle contraction force). This review presents the methodological considerations for the variability of exercising blood velocity/flow in the limb conduit artery during dynamic leg exercise assessed by pulsed Doppler ultrasound in relation to data previously reported in original research.

Measurement of the exercising blood flow during rhythmical muscle contractions assessed by Doppler ultrasound:Methodological considerations

Given the recent technological developments, ultra-sound Doppler can provide valuable measurements of arterial blood flow with high temporal resolution. In a clinical setting, measurements of hemodynamics is used to monitor, diagnose and manage changes in blood velocity profile for cardiac valve disease, relatively large vessel stenosis and other cardiovascular diseases. In health science and preventive medicine for cardiovascular disease with exercise therapy, evaluation of cardiac and vascular function is a useful indicator not only at rest but also during exercise, leading to improved exercise tolerance as well as physical activity. During exercise, the increase in oxygen uptake (calculated as product of arterial blood flow to the exercising limb and the arteriovenous oxygen difference) is directly proportional to the work performed. The increased oxygen demand is met through a central mechanism, an increase in cardiac output and blood pressure, as well as a peripheral mechanism, an increase in vascular conductance and oxygen extraction (major part in the whole exercising muscles) from the blood. Therefore, the determination of the local blood flow dynamics (potential oxygen supply) feeding to rhythmic muscle contractions can contribute to the understanding of the factors limiting the work capacity including, for instance the muscle metabolism, substance utilization and vasodilatation in the exercising muscle. Using non-invasive measures of pulsed Doppler ultrasound the validity of evaluating blood velocity/flow in the fore- arm or lower limb conduit artery feeding to the mus- cle is demonstrated during rhythmic muscle exercise;however the exercising blood velocity profile (fast Fourier transformation) due to muscle contractions is always seen as a physiological variability or fluctuations in the magnitude in blood velocity due to the spontaneous muscle contraction and relaxation induced changes in force curve intensity. Considering the above mentioned variation in blood velocity in relation to muscle contractions may provide valuable information for evaluating the blood flow dynamics during exercise. This review presents the methodological concept that underlines the methodological considerations for determining the exercising blood velocity/flow in the limb conduit artery in relation the exercise model of dynamic leg exercise assessed by pulsed Doppler ultrasonography.