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Using the clamping method (closing and opening the flap feeding artery) and continuous laser Doppler flowmetry, the effects of blood withdrawals on flap blood flow and on active and passive mechanisms regulating it were investigated in 12 Sprague-Dawley rats. Measurements were made during stable normovolemic conditions, during hypovolemia (after 3 ml/kg and after 6 ml/kg blood withdrawal), and after retransfusion of the shed blood. The continuous blood flow responses during and after the clamping procedure were analyzed. After clamp release, the increase in blood flow, duration of overshoot, and peak flow of overshoot were significantly greater (the level of significance was set equal to 0.05) in the registrations performed after blood withdrawals than before them. The post-ischemic response curves indicating significantly increased flap hyperemia during reperfusion in the registrations after blood withdrawals may be associated with decreased vascular resistance in the flap. Thus, the authors conclude that a short-term decrease in blood pressure caused by blood loss may prepare the flap microcirculation for tolerating more ischemia.

Research in the field of microvascular surgery has shown that ischemic preconditioning (repeated brief episodes of feeding artery occlusions followed by reperfusion) improves flap survival. The authors used a custom-designed clamping method and laser Doppler flowmetry to investigate changes in blood flow (BF) responses, either with acute ischemic preconditioning or without it. The animal model used was the partially elevated epigastric flap of adult Sprague-Dawley rats. In the preconditioned group (n=12), the flaps underwent preconditioning with three cycles of 10-min of feeding artery clamping, followed by 10 min of reperfusion, for a total preconditioning period of 1 hr. In the control group (n=12), the flaps were perfused without clamping for 1 hr. All the flaps underwent occlusion of the feeding artery for 15, 30, 60, 120 and 180 sec to observe the changes in the BF responses, 60 min and 150 min after flap elevation. To compare the responses between preconditoned and control groups the BF responses were analyzed during the overshoot period (i.e., BF being above the baseline after different feeding artery occlusion periods). Statistical analysis of the responses showed that the magnitude of increase in BF after clamp release (p<0.001), the duration of overshoot (p=0.014), and the amplitude of overshoot after clamp release (p=0.002) were statistically significantly greater in the preconditioned group than in the control group. The results suggest that vessels and their responses to change in perfusion pressure are involved in the multifactorial process of the ischemia-protective effect caused by acute ischemic preconditioning. As far as is known, this is the first report showing changes in flap vascular responses after acute ischemic preconditioning.

A number of clinical disorders of free vascularized flap are presumed to reflect insufficient blood flow (BF) or an inadequate range of vascular responsiveness. We compared the changes in BF in a pedicled and free epigastric flap, directly after and 90 min after performing microsurgical artery anastomoses. We used the clamping method and laser Doppler flowmetry in six Sprague-Dawley rats. The BF response curves shortly after re-anastomosing of the artery differ markedly from those in a pedicled flap model and curves registered 90 min after performing the anastomosis. We conclude that the clamping method is reliable and reproducible when studying the short-term autoregulatory BF patterns of epigastric pedicled and free flaps. [ABSTRACT FROM AUTHOR]