Noninvasive estimation of temperature and pH in human lower leg muscles using 1H nuclear magnetic resonance spectroscopy

Abstract

The temperature and pH of human lower leg muscles were estimated noninvasively using 1H-NMR spectroscopy at 3.0 and 1.5 T on five normal volunteers (21M, 24M, 27M, 34M, 47M). The chemical shifts of water and imidazole protons relative to cholines (-N+CH3) or creatines (-CH3) could be used as the temperature and pH probes, respectively [1-4]. Using the chemical shift, estimated values of the temperature in gastrocnemius (GAS; shell region) and soleus muscles (SOL; core region) under ambient temperature (21-25°C) were 33.6 ± 0.4 and 35.3 ± 0.4°C (mean ± SE), respectively (significantly different; P < 0.01). The values of pH in these muscles were estimated to be 6.97 ± 0.01 and 6.96 ± 0.02, respectively. Alternation of the surface temperature of the lower leg from 40 to 10°C significantly changed the temperature in GAS (P < 0.0001) from 35.8 ± 0.4 to 26.2 ± 1.2°C and the pH in GAS rose from 6.95 ± 0.01 to 7.01 ± 0.01 (P < 0.01). However, the values of pH and temperature in SOL were not significantly affected by this maneuver. These results indicate that the pH in GAS was moderately changed by muscle temperature (r = -0.59, P < 0.01), and its change was estimated to be -0.005 pH units/°C.