270 
PULMONARY MODELS 
Figure 4. — Changes in blood gases and mean pulmo- 
nary artery pressure (Pp:0 after removal of carotid 
bodies (S) in calves. Control values are indicated by 
(C). FFa, PaOj, and PaCOa are in mmHg. The 
solid lines represent the results from a sham operated 
calf. 
body excision at sea level hypoventilated to the 
same extent, this did not lower Pa02 enough 
and they did not develop the pulmonary hyper- 
tension (Figure 4). This study showed that the 
carotid chemoreceptors are very important in 
maintaining ventilation of calves at sea level 
and at moderate altitudes. Thus the calf with 
carotid bodies removed is also useful as a model 
of chronic respiratory acidosis and pulmonary 
hypertension in the absence of airway disease. 
DISCUSSION 
Why does the bovine calf develop more severe 
pulmonary hypertension than other animals or 
man at high altitude? A comparison of blood 
gas data between man and the bovine calf at 
3,400 m altitude (Table I) indicates that the ar- 
terial PCO2 of the calf is not decreased at alti- 
Table I. — Comparison of Blood Gas Data in Man and 
the Calf 
Sea Level 3,400 meters 
Man* 
Calf 
Man** 
Calf 
PaOz, mmHg. 
95 
87 
58 
50 
Pv02, mmHg. 
41 
35 
39 
33 
PaCOz, mmHg. 
40 
40 
30 
40 
Sa02% 
97 
92 
90 
79 
Sv02% 
75 
57 
73 
46 
• Data obtained from Comroe et al.i" 
Data obtained from Grover"^ 
tude. Grover, et al.^ noted a transient hyperven- i 
tilation and decreased PaCOa in calves at 3,800 
m, but the PaC02 returned to pre-altitude val- 
ues in less than 2 weeks. Hence, these steers j 
failed to sustain hyperventilation at a Pa02 of i 
45 mmHg. Later studies by Bisgard^ demon- i 
strated the absence of hyperventilation even I 
during the first 24-48 hours at 3,400 m (Table j 
II and Figure 5). Pa02 had already reached a i 
mean of about 50 mmHg and the mean pulmo- i 
Table II. — Blood Gas and pH Values of Hereford Calves 
at Sea Level and 3^00 Meters 
Sea Level 
3,400 meters 
24-48 Hours 
6 weeks 
PaOj, mmHg. 
87 ±2* 
53 ±2 
50 ±3 
PvOa, mmHg. 
35 ±0.5 
33 ±1 
31 ±1 
PaCOa, mmHg. 
39 ±1 
41 ±2 
40 ±1 
pHa 
7.39 ±0.01 
7.41 ±0.02 
7.41 ±0.01 
* All values are mean ± SEM in the same 6 calves. 
C 1-2 D 2W 6W 4W 
SL A A A SL 
Figure 5. — Resting minute ventilation of Hereford 
calves taken to 3400 m altitude. One star indicates a 
statistical significance of P < 0.05, two stars, P < 
0.01. f = frequency; C/SL = control, sea level; 
D/A and W/A indicate days and weeks at altitude or 
sea level. 
