668 
PHYSIOLOGY 
end tidal No reaches a stable, minimal level the 
spirometer valve is closed and the collected gas 
allovi^ed to equilibrate for 15 minutes. The vol- 
ume of N2 contained in the dog's lung at end- 
expiration and therefore the lung volume at 
that time, is calculated from the volume and No 
content of the expirate. The lung clearance 
index, a means of evaluating the intrapulmo- 
nary mixing of inspired gases, is calculated by 
dividing the liters of gas collected during the 
v^ashout by the functional residual capacity in 
liters. When another index of the distribution 
of ventilation is desired, sequential end tidal No 
concentrations recorded during the washout 
may be plotted on semilogarithmic graph paper 
and analyzed in the manner described by Fow- 
ler et al.^^ Respiratory frequency, tidal volume, 
and minute volume during 100% Oo breathing 
are calculated from the No traces and volume 
collected during the test. 
The steady state carbon monoxide method 
used for measuring diffusing capacity has been 
recently reported. The dog breathes a mix- 
ture of 500 ppm CO in air and a timed collection 
is made of the expirate. During the collection, 
end tidal gas samples are collected by a vol- 
ume-controlled sampling device actuated by 
changes in intraesophageal pressure. End tidal 
and expired gas tensions and expired volumes 
are used to calculate the fraction of CO ab- 
sorbed by the dog (fractional uptake of CO) 
and the rate of alveolarcapillary diffusion of CO 
(diffusing capacity) . 
Several parameters useful in characterizing 
gas exchange and ventilatory efficiency are ob- 
tained during an arterial blood sampling proce- 
dure. The dog is fitted with the face mask, re- 
strained in the supine position, and connected to 
the test apparatus. With the dog breathing 
dried room air, breath-by-breath Oo and COo 
tensions are recorded and the Douglas bag is 
flushed with expirate. The skin over a femoral 
artery is clipped and sprayed with a topical 
anesthetic-antiseptic solution (Cetacaine^, Ce- 
tylcide Industries, Inc., Long Island City, 
N. Y.), and a rectal thermometer is inserted. 
When the recorded gas tension traces stabilize, a 
timed collection of expirate is begun, during 
which a blood sample is collected by percuta- 
neous puncture of the femoral artery (Figure 
3) . Following the gas collection, rectal tempera- 
ture is recorded and the collected expirate is al- 
lowed to equilibrate for 5 minutes, after which 
the O2 and CO2 concentrations and volume are 
measured. Blood gas tensions and pH of the ar- 
terial samples are measured in a manner simi- 
lar to that previously reported^^ using a PHM 
71 analyzer, with a PHA 930 O2 module, E5046 
electrode, and D616 cuvette for P02, a PHA 931 
COo module, E5036 electrode, and D616 cuvette 
for Pco2, and a G297/G2 glass capillary elec- 
trode for pH (Radiometer Corp., Copenhagen, 
Denmark, and The London Company, Cleve- 
land, Ohio). A computer program developed in 
this laboratory^*' is used to correct the blood 
gas and pH values for differences between ana- 
lytical and rectal temperatures, and to calculate 
the saturation of hemoglobin with oxygen and 
acid-base parameters. Alveolar gas tensions are 
derived by multiplying the recorded end tidal 
fractions of O2 and CO2 by the barometric 
pressure minus the vapor pressure of water at 
the individual dog's body temperature, and the 
alveolar-arterial gas tension gradients are cal- 
culated. The gas tensions and volume of the ex- 
pirate are used to calculate O2 consumption, 
COo elimination, and the resulting respiratory 
exchange ratio. The volume of expired gas and 
Oo uptake allow calculation of specific ventila- 
tion (the milliliters of ventilation required per 
milliliter of Oo uptake). CO2 output, alveolar 
Pco2, and arterial Pco2 are used to calculate al- 
veolar ventilation, effective ventilation, and al- 
veolar dead space ventilation in the manner de- 
scribed' by Luft and Finkelstein.^^ Respiratory 
frequency, tidal volume, and minute volume 
during room air breathing are also calculated 
from data obtained during the bleeding proce- 
dure. 
Tests utilizing treadmill exercise have been 
performed on a limited number of dogs trained 
to run while wearing a latex mask (Figure 4). 
The mask, constructed by painting an appropri- 
ately-shaped mold with liquid latex, has large 
ports on both sides of the muzzle which are con- 
nected to large-bore flexible tubing. One-way 
valves positioned in the tubing just behind the 
dog's head allow the dog to inspire room air 
through a drying cannister, and expire into a 
100-liter Douglas bag. Small-bore tubing open- 
