TITLE:
Assessment of voluntary rhythmic muscle contraction-induced exercising blood flow variability measured by Doppler ultrasound
AUTHORS:
Takuya Osada, Bengt Saltin, Göran Rådegran
KEYWORDS:
Exercising Blood Flow; Doppler Ultrasound; Muscle Contraction; Blood Flow Alterations
JOURNAL NAME:
Open Journal of Molecular and Integrative Physiology,
Vol.3 No.4,
November
13,
2013
ABSTRACT: 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.