Objective: To investigate the changes in the forearm magistral and precapillary vessel tone in two different situations – during spontaneous changes in sympathetic activity and after reduction of perfusion pressure (P_perf.).

Methods: Ten healthy volunteers were studied in supine position. Blood flow (I) and volume pulse amplitude (ΔV) in the forearm were recorded by venous occlusion plethysmographic method. Systemic arterial pressure was determined auscultatory on the upper arm. Distensibility (D) of magistral arteries was calculated as a ratio between ΔV and pulse pressure (ΔP). Hemodynamic resistance (R) was calculated as a ratio between mean arterial pressure and I in the forearm. All investigated parameters were studied during resting conditions and after passive raising the arm above heart level.

Results: In the resting conditions I in the forearm oscillated from 0.8–6.3 ml/100cm³ min. and corresponding changes was observed in D – when I increased D also increased and visa versa. After reduction of P_perf. forearm D always increased and after the increase of P_perf. - decreased. These changes in D occurred very rapidly (within 2–3 sec.) and remained permanent after the changing of P_perf. Whereas I in the forearm after reduction of P_perf. always decreased, but afterwards in 30% of the cases when initial value of I was below 2 ml/100cm³ min. isovolumic autoregulation occurred - I increased and within a minute stabilised on a new increased level.

Conclusion: Intramuscular vessel tone is submitted not only to sympathetic activity and Ptransm. changes as extramuscular arteries, but also to metabolic control.