Quantitative analysis of the postcontractile blood-oxygenation-level-dependent (BOLD) effect in skeletal muscle

Abstract

Previous studies show that transient increases in both blood flow and magnetic resonance image signal intensity (SI) occur in human muscle after brief, single contractions, and that the SI increases are threefold larger in physically active compared with sedentary subjects. This study examined the relationship between these transient changes by measuring anterior tibial artery flow (Doppler ultrasound), anterior muscle SI (3T, one-shot echo-planar images, TR/TE = 1,000/35), and muscle blood volume and hemoglobin saturation [near-infrared spectroscopy (NIRS)] in the same subjects after 1-s-duration maximum isometric ankle dorsiflexion contractions. Arterial flow increased to a peak 5.9 ± 0.7-fold above rest (SE, n = 11, range 2.6-10.2) within 7 s and muscle SI increased to a peak 2.7 ± 0.6% (range 0.0-6.0%) above rest within 12 s after the contractions. The peak postcontractile SI change was significantly correlated with both peak postcontractile flow (r = 0.61, n = 11) and with subject activity level (r = 0.63, n = 10) estimated from 7-day accelerometer recordings. In a subset of 7 subjects in which NIRS data acquisition was successful, the peak magnitude of the postcontractile SI change agreed well with SI calculated from the NIRS blood volume and saturation changes (r = 0.80, slope = 1.02, intercept = 0.16), confirming the blood-oxygenation-level-dependent (BOLD) mechanism underlying the SI change. The magnitudes of postcontractile changes in blood saturation and SI were reproduced by a simple one-compartment muscle vascular model that incorporated the observed pattern of postcontractile flow, and which assumed muscle O(2) consumption peaks within 2 s after a brief contraction. The results show that muscle postcontractile BOLD SI changes depend critically on the balance between O(2) delivery and O(2) consumption, both of which can be altered by chronic physical activity.

Blood oxygenation level‐dependent (BOLD) MRI of human skeletal muscle at 1.5 and 3 T

“…also a difference in the biochemical properties of the muscle fibers which may also influence the muscle BOLD signal (14). A recent study has demonstrated that the detected muscle BOLD signal is the result of both blood oxygenation as well as blood volume within the muscle microcirculation (20).…”

Dynamic Blood Oxygen Level-dependent MR Imaging of Muscle: Comparison of Postocclusive Reactive Hyperemia in Young Smokers and Nonsmokers

“…In the post-hyperemia normalized phase, mB changes reflect a combination of functional changes in muscle oxygen metabolism and venous washout. 18,20 Prolonged normalization may be an additional indication of impaired muscle reperfusion; T 1/2nor was relatively prolonged in smokers, but this did not reach statistical significance.…”

“…[18][19][20] We postulate that prolongation of T 1/2peak and TTP in early stage vascular dysfunction leads to decreases in mB peak after compensatory responses have become impaired. In the post-hyperemia normalized phase, mB changes reflect a combination of functional changes in muscle oxygen metabolism and venous washout.…”

“…[7][8][9] Blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging, an established functional imaging technique, 10,11 is widely used in neuroradiology to assess the function of organs such as the heart 12 and skeletal muscle. [13][14][15][16][17][18][19] According to Ogawa's group, 10 the signal intensity (SI) of BOLD primarily reflects the concentrations of deoxyhemoglobin and oxyhemoglobin in the local microcir-culation. Inhomogeneity of the local magnetic field caused by paramagnetic deoxyhemoglobin in the microvasculature results in decreased apparent transverse relaxation time (T 2 *).…”

“…Many other factors besides concentrations of oxyhemoglobin and deoxyhemoglobin, including perfusion and capillary bed volume, affect BOLD SI. 18,21 Changes in dynamic skeletal muscle BOLD SI during ischemiareperfusion has been investigated in healthy volunteers 16,17 and disease states. 14,20 Noninvasive techniques are needed for assessing early stage vascular dysfunction, and BOLD MR is potentially such a technique.…”