Acute changes in extracellular volume fraction in skeletal muscle monitored by 23Na NMR spectroscopy.

Teresa Gerhalter,Benjamin Marty,Pierre G Carlier

doi:10.14814/phy2.13380

Abstract

In this article, we induced acute changes in extracellular volume fraction in skeletal muscle tissue and compared the sensitivity of a standard 1H T2 imaging method with different 23Na‐NMR spectroscopy parameters within acquisition times compatible with clinical investigations. First, we analyzed the effect of a short ischemia on the sodium distribution in the skeletal muscle. Then, the lower leg of 21 healthy volunteers was scanned under different vascular filling conditions (vascular draining, filling, and normal condition) expected to modify exclusively the extracellular volume. The first experiment showed no change in the total sodium content during a 15 min ischemia, but the intracellular weighted 23Na signal slowly decreased. For the second part, significant variations of total sodium content, sodium distribution, and T1 and T2∗ of 23Na signal were observed between different vascular filling conditions. The measured sodium distribution correlates significantly with sodium T1 and with the short and long T2∗ fractions. In contrast, significant changes in the proton T2w signal were observed only in three muscles. Altogether, the mean T2w signal intensity of all muscles as well as their mean T2 did not vary significantly with the extracellular volume changes. In conclusion, at the expense of giving up spatial resolution, the proposed 23Na spectroscopic method proved to be more sensitive than standard 1H T2 approach to monitor acute extracellular compartment changes within muscle tissue.

Highlights

Cellular life depends on the ability to tightly control the solute/water balance
We propose a multiparametric approach using nonlocalized 23Na-NMR spectroscopy to produce quantitative indices reflecting the sodium distribution in the skeletal muscle, in particular the intracellular sodium content and the extracellular volume fraction
Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society

Summary

Introduction

Water passively distributes bidirectionally into the extra- and intracellular compartments, water channel proteins, so-called aquaporin, accelerate the water movement possessing a 10–100-fold higher capacity for water permeation (Agre et al 2002). This water flux directed by osmotic and hydraulic gradients is determined by the effective osmotic equilibrium and establishes cell volume. While intracellular Na+ concentrations remain at a low level of about 10–15 mmol/L, extracellular concentrations range between 140 and 150 mmol/L (Skou 1998) This ion transport performed against the electrochemical gradient is essential to protect the cell from bursting as a result of osmotic swelling.

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