J. L. MAUDERLY AND J. A. PICKRELL 
667 
ance are measured by relating transpulmonary 
pressure fluctuations to simultaneous respira- 
tory volume and flow rate changes, respectively. 
Airflow rate is monitored by a pneumotacho- 
graph (Vol-0-Flow 10-R-lOO, National Instru- 
ment Laboratories, Rockville, Md.) and differ- 
ential pressure transducer (PM97, Statham 
Instruments, Inc., Oxnard, Calif.). Transpulmo- 
nary pressure changes are estimated by varia- 
tions of pressure in the intraesophageal catheter 
as monitored by another differential pres- 
sure transducer (PM5TC, Statham). The refer- 
ence port of the esophageal pressure transducer 
is vented to the face mask to eliminate any arti- 
facts caused by the slight pressure drop across 
the pneumotachograph. These signals are trans- 
lated into compliance and resistance by an ana- 
log computer (794444 R/C Computer, Honey- 
well) . The computer utilizes two subtract circuits 
which allow the subtraction of either the 
compliance or resistance component from hys- 
teresis loops produced from the input signals. 
Subtracted voltages required to flatten the loops 
displayed on an oscilloscope are used to calcu- 
late compliance and resistance by a method sim- 
ilar to that reported by Mead and Whittenber- 
gQJ-S 
The general technique for performing the 
open circuit nitrogen washout measurement of 
the functional residual capacity of Beagle dogs 
has been reported.^ The dog is switched at end- 
expiration from breathing room air to breath- 
ing 100% O2, and the expirate is collected in 
the spirometer which had previously been 
flushed with O2. The washout of nitrogen from 
the lungs is continuously recorded and when the 
