MRI measures of perfusion-related changes in human skeletal muscle during progressive contractions

Abstract

Although skeletal muscle perfusion is fundamental to proper muscle function, in vivo measurements are typically limited to those of limb or arterial blood flow, rather than flow within the muscle bed itself. We present a noninvasive functional MRI (fMRI) technique for measuring perfusion-related signal intensity (SI) changes in human skeletal muscle during and after contractions and demonstrate its application to the question of occlusion during a range of contraction intensities. Eight healthy men (aged 20-31 yr) performed a series of isometric ankle dorsiflexor contractions from 10 to 100% maximal voluntary contraction. Axial gradient-echo echo-planar images (repetition time = 500 ms, echo time = 18.6 ms) were acquired continuously before, during, and following each 10-s contraction, with 4.5-min rest between contractions. Average SI in the dorsiflexor muscles was calculated for all 240 images in each contraction series. Postcontraction hyperemia for each force level was determined as peak change in SI after contraction, which was then scaled to that obtained following a 5-min cuff occlusion of the thigh (i.e., maximal hyperemia). A subset of subjects (n = 4) performed parallel studies using venous occlusion plethysmography to measure limb blood flow. Hyperemia measured by fMRI and plethysmography demonstrated good agreement. Postcontraction hyperemia measured by fMRI scaled with contraction intensity up to approximately 60% maximal voluntary contraction. fMRI provides a noninvasive means of quantifying perfusion-related changes during and following skeletal muscle contractions in humans. Temporal changes in perfusion can be observed, as can the heterogeneity of perfusion across the muscle bed.

Blood flow and muscle oxygenation during low, moderate, and maximal sustained isometric contractions

“…Nevertheless, the similarity of NIRS-derived oxygen saturation at 60 and 100% MVC during exercise (Fig. 5) and the comparable postexercise hyperemic response of MBF and TOI may (see below for a conflicting perspective) support the suggestion (31) that IMP at 60% MVC is sufficient to occlude blood flow to the contracting muscle, most likely at the lower-order arterioles or the capillary bed (15,28).…”

“…In a variety of muscle groups (e.g., elbow flexors, knee extensors, plantar flexors, and dorsiflexors), data collected indirectly using isotope clearance (22), VOP (25), or fMRI (31) suggest that the IMP generated during isometric exercise will occlude MBF at a relative contraction strength of 50 -65% MVC (60% MVC in the dorsiflexors of young males; Ref. 31).…”

“…IMP is positively related to contraction intensity (22,24); thus, it is held that there is a critical force threshold beyond which mechanical pressure will occlude MBF (24,25,29,30) and below which flow will be affected to varying degrees depending on the contraction intensity and anatomical location (compartmental pressure). Results obtained using a variety of techniques suggest that complete occlusion of MBF and perfusion occur at 50 -60% of maximal voluntary contraction (MVC) force (13,22,25,31). However, relatively few studies have recorded MBF directly during a sustained isometric effort, and the degree to which perfusion is compromised by high-intensity contraction remains uncertain.…”

“…The dorsiflexor muscle group was selected for this experiment because the restrictive fascial sheath of the anterior compartment induces high levels of IMP during voluntary isometric contractions (26), and a proposed contraction intensity for complete occlusion has been identified in young males (60% MVC; Ref. 31). …”

Muscle study in experimental scoliosis in rabbits with costotransversectomy: evidence of ischemic process

“…The alterations noticed in this experimental model seemed to be due to muscular ischemia [15], either due to the progressive arteries stretching inside the convex side muscle or due to trauma during the costotransversectomy procedure. Further works are needed in human idiopathic scoliosis to see if the same pathological process happens in the paraspinal muscles using muscle blood flow measurement ''in site'' with magnetic resonance techniques [25,46]. …”