Differences in exercising limb blood flow variability between cardiac and muscle contraction cycle related analysis during dynamic knee extensor

• Aim. Blood flow in peripheral conduit arteries during steady-state, dynamic exercise, can be estimated noninvasively with Doppler ultrasound, by measuring the conduit arterial diameter and the mean blood velocity averaged over consecutive cardiac beat-by-beat cycles (BBcycle) or muscle contraction-relaxation cycles (CRcycle). The precise impact fluctuations in the 1-BBcycle- or 1-CRcycle-rate may impose on the average blood flow measurements has previously not been clearly defined. The hypothesis investigated in the present study was that the blood flow measurements obtained, and its variability, during exercise, may differ between the 1-BBcycle and 1-CRcycle at incremental exercise intensities; as the BBcycle-measurements may be influenced by transient alterations in heart rate; whereas the CRcycle-measurements are dependent on the muscle contraction-relaxation frequencies independent of the exercise intensities per se. The main purpose was therefore to determine if fluctuations in blood flow for 1-BBcycle and 1-CRcycle varies at incremental exercise intensities (work rates) using the one-legged dynamic knee-extensor exercise (DKE) model. Methods. Limb femoral artery blood flow (LBF) was determined, for 1-BBcycle and 1-CRcycle, in 8 healthy male subjects during 4-min of steady-state DKE at 60 contractions per minute at 10, 20,30 and 40 W. The variability of LBF was determined from the coefficients of variation (CVLBF). Results. The CVLBF for the CRcycle-measurements at each work rate were similar (P=NS). The CVLBF for the BBcycle-measurements were higher (P<0.05) at 40 W compared to at 10 W. Furthermore, the CVLBF for the 1-BBcycle was higher (P<0.05) than for the 1-CRcycle at 30 and 40 W, despite almost identical mean LBF values for the BBcycle- and the CRcycle-measurements at each exercise intensity. Conclusions. The present data suggests that estimates of LBF at slightly higher exercise intensities such as above 30 W, for a few number of consecutive BBcycle renders a higher variability than for CRcycle-measurements. This may consequently result in slight over- and under-estimations of LBF compared to the CRcycle-measurement.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Hälsovetenskap -- Idrottsvetenskap (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Health Sciences -- Sport and Fitness Sciences (hsv//eng)

Nyckelord

Doppler ultrasonography

cardiac beat

muscle contraction-relaxation cycle

flow variability

dynamic knee-extensor exercise

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