Influence of vascular filling and perfusion on BOLD contrast during reactive hyperemia in human skeletal muscle

Abstract

Mechanisms generating BOLD contrast are complex and depend on parameters that are prone to large variations, in particular in skeletal muscle. Here, we simultaneously measured perfusion by ASL, and BOLD response in the calf muscle of 6 healthy volunteers during post-ischemic reactive hyperemia. We tested whether the relation between the two was altered for varying degrees of leg vascular replenishment induced by prior positioning of the leg at different heights relative to the heart. We found that the BOLD response depended on perfusion, but also on the degree of repletion of leg blood vessels. We conclude that simultaneous determination of perfusion by ASL is important to identify the mechanisms underlying BOLD contrast in the skeletal muscle.

Muscle blood flow and oxygenation measured by NMR imaging and spectroscopy

“…Cuff release after an ischaemic period results in a strong positive BOLD contrast (27,51,61) and there is a striking parallel between the time-course of the BOLD signal and NIRS oxygenation curves during this reactive hyperemia (62). The slope of the ascending phase of the BOLD response and the early reperfusion peak has also been noted to be proportional (60) (Fig. 2).…”

“…The BOLD information can also be extracted from pulsed arterial spin labelling (PASL) acquisitions. For instance, with SATIR, one of many PASL sequences, the image calculated by averaging a pair of positively and negatively tagged acquisitions (see below, ASL description), contains the SE-BOLD information (60) (Fig. 2).…”

“…2). However, after a short ischaemic period, typically of a few minutes, muscle perfusion quickly resumes baseline resting values, while BOLD signal decays at a much slower rate (60,61). Several groups have suggested the possible use of BOLD contrast as a marker of muscle activation during contraction (54)(55)(56)63).…”

“…Although it primarily reflects blood oxygenation changes, BOLD is in reality, multifactorial (55). Blood volume changes, vascular network architecture, and tissue blood flow can, directly or indirectly, all modulate the BOLD response (51,55,59,60). In addition, particularly in skeletal muscle, the preferential alignment of capillaries along muscle fibres might render the BOLD effect dependent on the fibre angulation with respect to the main magnetic field.…”

Imagerie et spectroscopie par résonance magnétique nucléaire du muscle strié squelettique

“…où l'extraction en oxygène décroît dans les tissus (Donahue et al 1998 ;Lebon et al 1998 ;Meyer et al 2004 ;Damon et al 2007 ;Baligand et al 2011). Le volume sanguin au niveau des veines et des capillaires influence le signal BOLD et rend son interprétation relativement complexe (Duteil et al 2006). La consommation du muscle en oxygène peut être calculée, selon la loi de Fick, comme le produit de la perfusion tissulaire par la différence d'oxygénation entre artère et veine.…”