Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow

Michael C. Hogan, Bruno Grassi, Michele Samaja, Creed M. Stary, L. B. Gladden
2003 Journal of applied physiology  
Hogan, Michael C., Bruno Grassi, Michele Samaja, Creed M. Stary, and L. B. Gladden. Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow. .-The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine
more » ... muscle (n ϭ 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O 2 uptake, tension-time integral, and mean venous blood flow increased significantly (P Ͻ 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 Ϯ 6, 139 Ϯ 8, and 145 Ϯ 8 ml⅐100 g Ϫ1 ⅐min Ϫ1 ) and noncontractile phases (64 Ϯ 3, 78 Ϯ 4, and 91 Ϯ 5 ml⅐ 100 g Ϫ1 ⅐ min Ϫ1 ) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 Ϯ 0.03, 0.32 Ϯ 0.02, and 0.36 Ϯ 0.03 ml ⅐ N Ϫ1 ⅐ min Ϫ1 , respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 Ϯ 4, 30 Ϯ 4, and 38 Ϯ 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction. oxygen uptake; exercise; muscle pump IT HAS BEEN DEMONSTRATED THAT muscle blood flow during rhythmic contractions is pulsatile (4, 7, 10, 11, 16, 20) . During the contractile phase of the muscle duty cycle, there is significant resistance to arterial flow into the muscle because of the intramuscular pressure generated. Simultaneously, there is rapid ejection of blood from the muscle into the venous circulation. In the noncontractile phase (i.e., when force is not being produced) of the muscle duty cycle, arterial flow is restored as compression on the vessels within the muscle is removed, and venous flow is reduced compared with that seen during the contractile phase. During the contractile phase, the amount of blood expelled from the muscle depends on the force of the contraction and the volume of blood within the muscle at the start of the contraction. In contrast, blood flow through the muscle during the noncontractile phase is determined by the vascular pressure difference across the muscle and the resistance within the muscle to blood flow. When the arterial and venous pressures remain relatively stable during muscle contractile work, the overall mean muscle blood flow will be determined in large part by the degree of vasodilation within the muscle (10), which in turn is regulated by numerous factors (see Ref. 18). In addition, if the time spent in the contractile phase during rhythmic contractions is high, mean blood flow may be impeded by the long periods of vascular compression (25). Therefore, the mean muscle blood flow is determined by a complex interaction of factors that are strongly influenced by the metabolic rate and the time the muscle is in the contractile and noncontractile phases (5, 11). Although the pulsatile nature of muscle blood flow has been known to significantly influence mean blood flow, there have been few studies in which the percent contribution of the two muscle phases to total muscle blood flow have been carefully examined when duty cycle and metabolic rate are varied. In the present study, we tested the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. METHODS Five adult mongrel dogs of either sex with a weight range of 12-19 kg were anesthetized with 30 mg/kg pentobarbital
doi:10.1152/japplphysiol.00226.2003 pmid:12794032 fatcat:qcvvfhd4ojbcnahncxmge3orvy