Acid-base changes of the thoracic duct lymph during hypercapnia and an estimation of cellular contribution to ECF...

During 90 min of spontaneous or controlled CO2 breathing in splenectomized dogs, the acid-base parameter changes of the thoracic duct lymph were compared with those of the arterial and postcaval venous blood. (1) The lymph reached an apparent steady state in the acid-base parameters at least 10 min after the blood. (2) The lymph bicarbonate concentration gradually increased almost in parallel with the lymph PCO2 elevation, while the raised plasma bicarbonate concentration remained nearly unchanged until the end of CO2 inhalation. (3) The in vivo buffer slope of the lymph increased strikingly within 10 min, reaching three times the in vitro slope at 90 min after inception of CO2 breathing. After 10 min, the lymph value became higher than the venous value, suggesting early cellular contribution to ECF buffering. (4) Considering the lymph values as representative of the interstitial fluid values, cellular contribution to ECF buffering was computed; they were 7.8, 15.6, and 10.7% in the spontaneously breathing group, and 8.9, 10.6, and 12.0% in the controlled ventilation group at 30, 60, and 90 min of CO2 breathing, respectively.