Table 1. Arterial Blood Gases in Open-Chest Mice
Group A
Group B
Group C
(n=6)
(n=6)
(n=11)
Ventilation rate
95±1
105±2
121±1
(breaths/min)
Tidal volume
2.2±0.1
2.2±0.1
2.2±0.1
(ml)
PaO2
176.6±63.9
327.2±45.2
321.0±36.1
(mmHg)
pH
7.30±0.02
7.39±0.01
. 7.51±0.02
PaCO2
43.3±2.4
31.0±2.3
17.8±2.3
(mmHg)
HCO3-
21.6±1.5
18.6±1.6
14.1±1.5
(mM/L)


 
Open-chest mice (n=23) were ventilated using a tidal volume of 2.2±0.1 ml at different rates in order to identify the optimal ventilation rate. The mice were allowed to stabilize for 40 min after the chest was opened and then arterial blood gases were measured in each animal.  In mice ventilated at a rate of 95±1 breaths/min (n=6), arterial pH was 7.30±0.02. Increasing  the ventilatory rate to 105±2 breaths/min (n=6) resulted in a normal arterial pH (7.39±0.01) as well as in a higher arterial pO2 (327±45 mmHg). A further increase in the ventilatory rate to 121±1 breaths/min (n=11) caused the arterial pH to be abnormally high (7.51±0.02) without any further increase in arterial pO2 (321±36 mmHg). Accordingly, a ventilatory rate of 105 breaths/min was used in the present study.

Data are means ± SEM. 

Reproduced from Ref. 2 with permission.