Ra. Klocke et al., DISTRIBUTION OF PULMONARY CAPILLARY TRANSIT TIMES, American journal of respiratory and critical care medicine, 152(6), 1995, pp. 2014-2020
Citations number
36
Categorie Soggetti
Emergency Medicine & Critical Care","Respiratory System
The length of time that blood remains in the pulmonary capillary is an
important variable in gas exchange. We have investigated the distribu
tion of capillary transit times in isolated rabbit lungs perfused with
a bicarbonate-free buffer. The time course of gas exchange was monito
red by enclosing the lungs in a plethysmograph. A bolus of buffer cont
aining dissolved acetylene was injected into the perfusion system, Exc
hange of this inert gas occurred as soon as the bolus reached the capi
llary bed, thereby describing the input function into the bed. A separ
ate bolus injection of bicarbonate solution resulted in production and
excretion of CO2 as long as the bolus remained in the capillary bed.
The rate of CO2 production was adjusted by partial inhibition of endot
helial carbonic anhydrase. The distribution of capillary transit times
was computed from a model of CO2 production in the capillary bed and
the observed rates and volumes of acetylene and carbon dioxide excreti
on. The recovered distributions indicate that there is a fairly wide d
istribution of capillary transit times (relative dispersion, 0.45) aro
und the mean value of 1.71 s (+/- 0.53 [SD]). Only 10% of capillary tr
ansit times are less than one half of mean transit time, It is likely
that gas exchange reaches equilibrium in the capillary bed except poss
ibly during strenuous exercise or exposure to high altitude or in dise
ase.