The vascular origin of slow wave flowmotion in skeletal muscle during local hypotension

Intravital microscopy (IVM) and laser-Doppler-flowmetry- or fluxmetry (LDF) were used to simultaneously assess periodic hemodynamics (vaso/flowmotion) in the tenuissimus muscle of eleven New Zealand White (NZW)-rabbits during local reduction of arterial pressure. Diameter changes of transverse arterioles (TR) were monitored with the microscope, and in six animals also blood cell velocity measurements were performed with a cross-correlation technique. One LDF was positioned at the tenuissimus muscle as close to the objective as possible without causing optical interference. A second LDF was positioned at the underlying gastrocnemius muscle. Slow wave vaso/flowmotion was not present at control arterial pressure (x = 73 mmHg, range-r: 60-87) but was induced as local femoral pressure was reduced, being minimal at 35 mmHg (r: 20-50). The vaso/flowmotion frequencies of the IVM, tenuissimus-LDF, and the gastrocnemius-LDF signals were in the order of 1.5 cpm. LDF-flowmotion frequencies in the two muscles showed no correlation (R = +0.06, P = 0.4). The IVM flow-frequencies in the TR, however, correlated well with the oscillations recorded with the tenuissimus-LDF placed nearby (R = +0.89, p +0.01). Regular diameter variations were recorded only in the eleven cases where the microscope focused on the proximal portion of the TR; these oscillation frequencies were correlated with corresponding LDF-tenuissimus recordings (R = +0.97, p < 0.01). We conclude that slow wave vasomotion in rabbit skeletal muscle is not present during control conditions, but is induced on a regular basis by local blood pressure reduction and that it originates in the proximal part of the TR as reflected by slow wave flowmotion in LDF.