Nuclear magnetic resonance transverse relaxation in muscle water

Fung, B. M.; Puon, P.S.

doi:10.1016/s0006-3495(81)84870-9

Cited by 81 publications

(51 citation statements)

References 32 publications

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“…Fung and Puon (12) found that R 2 varies directly with pH i in chemically skinned rabbit psoas muscle fibers. Moser et al (13) also observed a direct linear relationship between R 2 and pH i in isolated rat liver throughout the range of ϳ6.2 to ϳ6.8 pH units.…”

Section: The R 2i Decrease Is Partly Due To Increased Intracellular Vmentioning

confidence: 98%

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Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Damon

Gregory

Hall

et al. 2001

Magnetic Resonance in Med

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Exercise-induced decreases in the 1 H transverse relaxation rate (R 2 ) of muscle have been well documented, but the mechanism remains unclear. In this study, the hypothesis was tested that R 2 decreases could be explained by pH decreases and apparent intracellular volume (V i ) increases. 31 P and 1 H spectroscopy, biexponential R 2 analysis, and imaging were performed prior to and following fatiguing exercise in iodoacetate-treated (IAA, to inhibit glycolysis), NaCN-treated (to inhibit oxidative phosphorylation), and untreated frog gastrocnemii. In all exercised muscles, the apparent intracellular R 2 (R 2i ) and pH decreased, while intracellular osmolytes and V i increased. These effects were larger in NaCN-treated and untreated muscles than in IAAtreated muscles. Multiple regression analysis showed that pH and V i changes explain 70% of the R 2i variance. Separate experiments in unexercised muscles demonstrated causal relationships between pH and R 2i and between V i and R 2i . These data indicate that the R 2 change of exercise is primarily an intracellular phenomenon caused by the accumulation of the end-products of anaerobic metabolism. In the NaCN-treated and untreated muscles, the R 2i change increased as field strength increased, suggesting a role for pH-modulated chemical exchange. Key words: skeletal muscle; exercise; hydrogen-ion concentration; osmolarity; nuclear magnetic resonance Exercise-induced increases in the apparent 1 H transverse relaxation time (T 2 ) of muscle water have been well documented. The amount of T 2 change increases as exercise intensity increases; T 2 plateaus 3-4 min after the onset of exercise (1). Following isometric leg extension to fatigue, T 2 recovery follows an approximately exponential time course and is complete after ϳ35 min. (2). The increase in signal intensity from active muscles in T 2 -weighted images allows muscle activity to be detected reliably and noninvasively, which may aid in the placement of regions of interest or surface coils in spectroscopic studies (2,3). With a full understanding of the mechanism(s) of the T 2 change, this phenomenon may also be useful in functional studies of muscle activation during exercise (e.g., Refs. 4 -6), noninvasive studies of pathologic conditions in which the T 2 response to exercise is altered (e.g., Refs. 7 and 8), and as a means of studying noninvasively those physiological changes that increase T 2 .The most universally offered and best-studied explanation for the T 2 increase during exercise is the concomitant increase in muscle volume. However, the mechanism of the T 2 increase is more complex than total water accumulation. For example, recovery of the muscle's anatomical cross-sectional area is faster than T 2 recovery (2), and enhancement of the extracellular fluid volume increase during exercise is not proportional to the T 2 increase (9). A further complication is that both ex vivo amphibian (10) and in vivo mammalian (11) studies suggest that exchange between the intra-and extracellular spaces in muscle is sl...

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Section: The R 2i Decrease Is Partly Due To Increased Intracellular Vmentioning

confidence: 98%

“…T 2 is inversely related to intracellular pH (pH i ) in chemically-skinned rabbit psoas muscle (12) and in isolated rat liver (13). End-exercise pH i and T 2 are also correlated (2,14); however, during incremental arm ergometer exercise, pH i changes lag T 2 changes, and during recovery from this exercise, pH i recovers more quickly than T 2 (15).…”

mentioning

confidence: 99%

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Damon

Gregory

Hall

et al. 2001

Magnetic Resonance in Med

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“…In addition to alterations in the size, shape, and charge of surfaces in muscle cells, contraction involves the production and/or translocation of ions and metabolites. These processes would have osmotic effects that alter the concentration of water as well as direct effects on the MR relaxation of water; e.g., T 2 was shown to increase as pH was lowered (12).…”

Section: Rmmentioning

confidence: 99%

Magnetic resonance imaging and electromyography as indexes of muscle function

Adams

Duvoisin

Dudley

1992

Journal of Applied Physiology

219

213

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1992.-Electromyography (EMG) is commonly used to determine the electrical activity of skeletal muscle during contraction. To date, independent verification of the relationship between muscle use and EMG has not been provided. It has recently been shown that relaxation-(e.g., T 2 ) weighted magnetic resonance images (MRI) of skeletal muscle demonstrate exercise-induced contrast enhancement that is graded with exercise intensity. This study was conducted to test the hypothesis that exercise-induced magnetic resonance (MR) contrast shifts would relate to EMG amplitude if both measures reflect muscle use during exercise. Both MRI and EMG data were collected for separate eccentric (ECC) and concentric (CON) exercise of increasing intensity to take advantage of the fact that the rate of increase and amplitude of EMG activity are markedly greater for CON muscle actions. Seven subjects 30 ± 2 (SE) yr old performed five sets of 10 CON or ECC arm curls with each of four resistances representing 40, 60, 80, and 100% of their 10 repetition maximum for CON curls. There was 1.5 min between sets and 30 min between bouts (5 sets of 10 actions at each relative resistance) . Multiple echo, transaxial T 2 -weighted MR images (1.5 T, TR/TE 2,000/30) were collected from a 7-cm region in the middle of the arm before exercise and immediately after each bout. Surface EMG signals were collected from both heads of the biceps brachii and the long head of the triceps brachii muscles. CON and ECC actions resulted in increased integrated EMG (IEMG) and T 2 values that were strongly related (r = 0.99, P < 0.05) with relative resistance. The rate of increase and absolute value of both T 2 and IEMG were greater for CON than for ECC actions. IEMG and T 2 for both CON and ECC actions were correlated (r = 0.99, P < 0.05). The results suggest that J) surface IEMG accurately reflects the contractile behavior of muscle and 2) exercise-induced increases in MRI T 2 values reflect some processes that scale with muscle use. muscle function MAGNETIC RESONANCE SPECTROSCOPY (MRS) has become an accepted tool for in vivo biochemical studies of muscle tissue. Magnetic r esonance (MR) imaging (MRI) is a variant of this methodology that is rapidly becoming the standard for many clinical diagnostic applications because it provides unparalleled visualization of anatomic detail of soft tissues such as muscle, tendon, cartilage, and various organs. MRI has also begun to be used in basic muscle research. For example, MR images of skeletal muscle show exercise-induced contrast enhance-1578 ment, which appears to be graded with exercise intensity (7). This has been used to infer which muscles were used during the activity and the extent of their contribution.Electromyography (EMG) has long been the noninvasive method of choice for analyses of muscle activation during exercise (2). It entails sampling electrical activity from a muscle region of interest with needle or surface electrodes. There is good relation between EMG amplitude and force development for a variety of...

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“…Proposed explanations for intracellular T2 increases include the accumulation of end products of cellular energy metabolism, which cause water to move into the cell (4,21), decreased intracellular pH (4,8), and water shifts from an intracellular compartment possessing a short T2 (ϳ20 ms) to a second intracellular compartment having a longer T2 (ϳ40 ms) (22,23). Any of these possible explanations, acting alone or in concert with the others, suggests that the intracellular T2 increase results from changes in the chemical behavior of water resulting from increased flux through energy metabolism pathways.…”

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confidence: 99%

Cluster analysis of muscle functional MRI data

Damon¹,

Wigmore²,

Ding³

et al. 2003

Journal of Applied Physiology

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magnetic resonance imaging (mfMRI) is frequently used to determine spatial patterns of muscle involvement in exercising humans. A frequent finding in mfMRI is that, even within synergistic muscle groups, signal intensity (SI) data from individual voxels can be quite heterogeneous. The purpose of this study was to develop a novel method for organizing heterogeneous mfMRI data into clusters whose members behave similarly to each other but distinctly from members of other clusters and apply it in studies of functional compartmentalization in the anterior compartment of the leg. An algorithm was developed that compared the SI time courses of adjacent voxels and grouped together voxels that were sufficiently similar. The algorithm's performance was verified by using simulated data sets with known regional differences in SI time courses that were then applied to experimental mfMRI data acquired from six male subjects (age 22.6 Ϯ 0.9 yr, mean Ϯ SE) who sustained isometric contractions of the dorsiflexors at 40% of maximum voluntary contraction. The experimental data were also characterized by using a traditional analysis (userspecified regions of interest from a single image), in which the relative change in SI and the contrast-to-noise ratio [CNR; 100%ϫ(SI RESTING Ϫ SIACTIVE)/(noise standard deviation)] were measured. In general, clusters were found in areas in which the CNR exceeded 5. Cluster analysis made functional distinctions between regions of muscle that were not seen with traditional analysis. In conclusion, cluster analysis's use of the full SI time course provides more sensitivity to muscle functional compartmentation than traditional analysis.transverse relaxation time constant; image processing; time series; exercise; dorsiflexors DURING THE PAST 15 YEARS, muscle functional magnetic resonance imaging (mfMRI) has emerged as a promising tool for studying muscle involvement during exercise because it is sensitive to the spatial pattern and extent of muscle utilization. For example, mfMRI has been used to identify different muscle utilization patterns in novice and elite rowers (9) and in uphill and horizontal running (25). It has also been used to detect changes in muscle function consequent to clinical conditions such as peripheral vascular disease (31). The interpretation of these data, however, is limited by the absence of a full theoretical understanding of which physiological variables produce the mfMRI response and how their contributions may differ during and after exercise.Multiexponential relaxation analysis has shown that the major contribution to signal intensity (SI) changes in mfMRI is made by the increase in the transverse relaxation time constant (T2) of intracellular water protons (4,22,23). Proposed explanations for intracellular T2 increases include the accumulation of end products of cellular energy metabolism, which cause water to move into the cell (4, 21), decreased intracellular pH (4, 8), and water shifts from an intracellular compartment possessing a short T2 (ϳ20 ms) to a second int...

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Nuclear magnetic resonance transverse relaxation in muscle water

Cited by 81 publications

References 32 publications

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Magnetic resonance imaging and electromyography as indexes of muscle function

Cluster analysis of muscle functional MRI data

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Nuclear magnetic resonance transverse relaxation in muscle water

Cited by 81 publications

References 32 publications

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

Magnetic resonance imaging and electromyography as indexes of muscle function

Cluster analysis of muscle functional MRI data

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Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle