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.

Optimizing the operation of the Qingshitan Reservoir in the Lijiang River for multiple human interests and quasi-natural flow maintenance

For reservoir operation, maintaining a quasi-natural flow regime can benefit river ecosystems, but may sacrifice human interests. This study took the Qingshitan Reservoir in the Lijiang River as a case, and developed an optimization model to explore a trade-off solution between social-economic interests and nature flow maintenance on a monthly base. The objective function considered irrigation, cruise navigation and water supply aspects. An index of flow alteration degree was proposed to measure the difference between the regulated discharge and the natural flow. The index was then used as an additional constraint in the model besides the conventional constraints on reservoir safety. During model solving, different criteria were applied to the index, representing various degrees of alteration of the natural flow regime in the river. Through the model, a relationship between social-economic interests and flow alteration degree was established. Finally, a trade-off solution of the reservoir operation was defined that led to a favorable social-economic benefit at an acceptable alteration of the natural flow.