Noninvasive measurement of temperature and fractional dissociation of imidazole in human lower leg muscles using 1H-nuclear magnetic resonance spectroscopy.

The temperature change of the fractional dissociation of imidazole (alpha-imidazole) in resting human lower leg muscles was measured noninvasively using (1)H-nuclear magnetic resonance spectroscopy at 3.0 and 1.5 T on five normal male volunteers aged 30.6 +/- 10.4 yr (mean +/- SD). Using (1)H-nuclear magnetic resonance spectroscopy, water, carnosine, and creatine in the muscles could be simultaneously analyzed. Carnosine contains imidazole protons. The chemical shifts of water and carnosine imidazole protons relative to creatine could be used for estimating temperatures and alpha-imidazole, respectively. Using the chemical shift, the values of temperature in gastrocnemius (Gast) and soleus muscles at ambient temperature (21-25 degrees C) were estimated to be 35.5 +/- 0.5 and 37.4 +/- 0.6 degrees C (means +/- SE), respectively (significantly different; P < 0.01). The estimated values of alpha-imidazole in these muscles were 0.620 +/- 0.007 and 0.630 +/- 0.013 (means +/- SE), respectively (not significant). Alternation of the surface temperature of the lower leg from 40 to 10 degrees C significantly changed the temperature in Gast (P < 0.0001) from 38.1 +/- 0.5 to 28.0 +/- 1.2 degrees C, and the alpha-imidazole in Gast decreased from 0.631 +/- 0.003 to 0.580 +/- 0.011 (P < 0.05). However, the values of alpha-imidazole and the temperature in soleus muscles were not significantly affected by this maneuver. These results indicate that the alpha-imidazole in Gast changed significantly with alternation in muscle temperature (r = 0.877, P < 0.00001), and its change was estimated to be 0.0058/ degrees C.