Influence of arterial pressure on reactive hyperemia in skeletal muscle capillaries

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Abstract
The influence of arterial pressure on reactive hyperemia was studied in cat sartorius muscle capillaries over a pressure range from 60-140 mmHg. Red cell velocity was measured in the capillaries following a 30 s arterial occlusion by means of the dual-slit photometric method. Reactive hypermia was absent or quite weak and prolonged at the lower perfusion pressures (60 and 80 mmHg); at the higher pressures (120 and 140 mmHg) the flow peak was high, duration was short, and all capillaries showed hyperemia. Mean capillary peak flow velocity rose from 0.68 to 1.25 mm/s and peak-to-control flow ratio increased from 2.1 to 3.5 as pressure was increased from 60 to 140 mmHg. Mean time required to reach peak flow fell from 24 to 12 s and hyperemia duration decreased from 52 to 22 s as pressure was increased. Excess flow increased modestly (from 2.2 to 2.8 mm) as pressure was elevated, since hyperemia duration decreased while peak flow increased. Strongly autoregulated capillaries had a significantly higher peak-to-control flow ratio in reactive hyperemia, but a lower excess flow than weakly regulated vessels. The strongly autoregulated group also had markedly shorter time to peak flow and hyperemia duration. Perfusion pressure may have an important influence on the characteristics of reactive hyperemia patterns at the capillary level. The findings can be explained in terms of metabolic and/or myogenic mechanisms but are not explicable in terms of the unidirectional vasodilator response to pressure pulses.

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