In one previous study, the authors looked at 3 groups of 7 pigs, ventilated at 12 (100% O2), 30 (100%), and 30 (5% CO2, 95% 02) breaths per minute during cardiac arrest, and showed increased mortality with increasing respiratory rate. Survival rates were 6/7, 1/7, and 1/7 respectively. The results of this study led to changing the CPR guidelines in 2005 to include fewer ventilations.