PLASMA POTASSIUM CONCENTRATION AND DOPPLER BLOOD-FLOW DURING AND FOLLOWING SUBMAXIMAL HANDGRIP CONTRACTIONS

The aim of the present study was to investigate the time-course of blood velocity in the forearm during and following isometric handgrip contractions and to reveal a possible temporal relationship between the circulatory response and venous effluent potassium concentration ([K]) not only during contractions but also during the post-exercise recovery period. Contractions of 15% maximal voluntary contraction (MVC) and 30 % MVC with and without 3 min of arterial occlusion following the contractions were studied. All contractions induced a significant increase in venous plasma [K] from an average resting level of 4.0 to 5.0 mm during 15% MVC and 5.8 mm during 30% MVC. Blood velocity increased from a resting level of 0.07 to 0.22 m s-1 and 0.36 m s-1 during 15% and 30% MVC, respectively. MVC of 30% always elicited a larger blood velocity and [K] response than 15% MVC. Following the contractions hyperaemia was elicited. Recovery of the local blood velocity was markedly slower than the K recovery, since [K] remained significantly above resting level for only 25 s following 15% MVC and 45 s following 30% MVC, while blood velocity remained elevated for 2 min and more than 7 min following 15 and 30% MVC, respectively. Further, a larger hyperaemia following the occlusion was elicited as compared to the contraction without occlusion, in spite of [K] being lower immediately after the occlusion period than immediately after the contraction. Finally, [K] decreased below resting level in the recovery period while the blood velocity remained elevated. Therefore, the present study showed that the venous plasma [K] is not causally related to the prolonged post-exercise hyperaemia. The skin temperature remained unchanged during the contractions, while during the recovery period the skin temperature increased for several minutes. The major part of the temperature increase was likely to be due to conductance of heat from muscles to skin surface as a consequence of muscle hyperaemia.