INTRAMUSCULAR LASER-DOPPLER FLOWMETRY IN THE SUPRASPINATUS MUSCLE DURING ISOMETRIC CONTRACTIONS

To study the regulation of microvascular blood flow in a compartment m uscle, laser-Doppler measurements of muscle microcirculation were reco rded in the supraspinatus muscle in eight volunteers during and follow ing submaximal isometric muscle contractions. The subjects performed i sometric shoulder abductions at five contraction levels from 5% to 50% maximal voluntary contraction for 1 min each and a sustained 30 degre es shoulder abduction for 20 min. The subjects' perceived exertion inc reased from ''no perceived exertion'' to ''near maximal exertion'' dur ing the 20-min period with 30 degrees shoulder abduction. Microcircula tion increased during all 1-min contractions. Following the contractio ns at 20%,30% and 50% MVC post-exercise reactive hyperaemia was seen f or a period of at least 1 min. The reactive hyperaemia increased in ma gnitude in response to increasing contraction level. The results showe d the same time-history of the blood flow at microvascular level as pr eviously seen in larger peripheral vessels in response to muscle contr actions. During the 20-min contraction microcirculation increased in l ine with the findings during the brief contractions. However, in contr ast to the brief contractions no postexercise reactive hyperaemia occu rred following the prolonged contraction, Lack of postexercise reactiv e hyperaemia following the prolonged shoulder abduction would suggest insufficient regulation of the vascular resistance. Alternatively, lac k of hyperaemia could be taken as an indication of sufficient microcir culation during the preceding contraction. From previous studies on in tramuscular pressure and metabolism the latter alternative would seem unlikely.