Physiological response of rats to delivery of helium and xenon: implications for hyperpolarized noble gas imaging

The physiological effects of various hyperpolarized helium and xenon MRT-co mpatible breathing protocols were investigated in 17 Sprague-Dawley rats, b y continuous monitoring of blood oxygen saturation, heart rate, EKG, temper ature and endotracheal pressure. The protocols included alternating breaths of pure noble gas and oxygen, continuous breaths of pure noble gas, breath -holds of pure noble gas for varying durations, and helium breath-holds pre ceded by two helium rinses. Alternate-breath protocols up to 128 breaths ca used a decrease in oxygen saturation level of less than 5% for either heliu m or xenon, whereas 16 continuous-breaths caused a 31.5% +/- 2.3% decrease in oxygen saturation for helium and a 30.7% +/- 1.3% decrease for xenon. Br eath-hold protocols up to 25 s did not cause the oxygen saturation to fall below 90% for either of the noble gases. Oxygen saturation values below 90% are considered pathological. At 30 s of breath-hold, the blood oxygen satu ration dropped precipitously to 82% +/- 0.6% for helium, and to 76.5% +/- 7 .4% for xenon. Breath-holds longer than 10 s preceded by pre-rinses caused oxygen saturation to drop below 90%. These findings demonstrate the need fo r standardized noble gas inhalation procedures that have been carefully tes ted, and for continuous physiological monitoring to ensure the safety of th e subject. We find short breath-hold and alternate-breath protocols to be s afe procedures for use in hyperpolarized noble gas MRI experiments. Copyrig ht (C) 2000 John Wiley & Sons, Ltd.