Comparison Between the Time Available and the Time Required for Co2 Equilibration in the Lung*

Abstract

We have previously shown that the injection of sodium bicarbonate into the pulmonary artery of a dog enclosed in a body plethysmograph results in the evolution of gas in the alveoli which is measurable as an increase in the pressure in the plethysmograph (1). By comparing the time elapsed between injection and gas evolution following injection of a bicarbonate solution with the analogous time interval following injection of an inert gas, ether (2), a value for the over-all rate of the reactions leading to CO2 liberation in the lung can be obtained. Relatively small doses (5 mg per kg) of a carbonic anhydrase inhibitor, acetazolamide, given intravenously, markedly suppressed the evolution of CO2 after bicarbonate injection. This observation suggested to us a method for carrying out experiments to investigate the relationship between the time available and the time required for CO2 equilibration in the lungs. These experiments form the basis of the present report. METHODSFour dogs weighing 16 to 20 kg were used in these experiments. They were anesthetized with pentobarbital sodium in an initial dose of 25 mg per kg; this was usually supplemented by 100 mg about one hour later. A tracheal tube was inserted. A shortened no. 9 cardiac catheter (capacity 0.9 ml) was introduced via the external jugular vein into the pulmonary artery. The dog was then enclosed in a body plethysmograph, and just before the start of the actual experimental period, spontaneous breathing was arrested with appropriate doses of succinylcholine chloride and ventilation was maintained by a Starling pump. The pulmonary artery pres-* Supported by Contract DA-CML-18-108-G-46 with the Army Chemical Corps.tResearch Fellow of the American College of Physicians, 1961-1964. t This work was done during the tenure of an Established Investigatorship of the American Heart Association. sure 1 and the plethysmograph pressure 2 were recorded by using strain gauges and a direct-writing oscillograph.3 The electrocardiogram was monitored continuously. The details of the calibrating and the recording procedure are reported elsewhere (2).After checking the plethysmograph for air tightness and calibrating it, an injection of 0.5 ml of 1: 4 ether in alcohol was made into the pulmonary artery to determine the circulation time from the pulmonary artery to the site of gas exchange (2). This was followed by the injection, in the same manner, of 3 ml of a saturated solution of sodium bicarbonate (approximately 1.2 M at room temperature 200 C). At least duplicate control injections of both ether and bicarbonate were made. An injection of 10 or 20 mg of sodium acetazolamide (Diamox sodium) was then made into the pulmonary artery, and 10 to 12 minutes later duplicate ether and bicarbonate injection records were obtained. The process was then repeated using 10-to 20-mg increments of sodium acetazolamide until a total dose had been reached which markedly suppressed gas evolution.Analysis of records. All the records obtained were analyzed by determining the time taken for ha...

Rate of disappearance of labeled carbon dioxide from the lungs of humans during breath holding: a method for studying the dynamics of pulmonary CO2 exchange

“…Dimensions and dynamics of CO2 stores in the lungs of man. The data presented above support the findings of a number of investigators (3)(4)(5), that the various forms of carbon dioxide present in the lungs exchange so rapidly, that the alveolar Pco2 can be considered to come from one common CO2 pool. Representative figures for an adult human with a resting lung volume of 3000-ml STPD at an alveolar Pco2 of 40 mm Hg are: 150 ml of CO2 in the alveolar gas, 200 ml of CO2 in the pulmonary tissue (Vti.…”

“…They concluded that the interconversion of the various forms of The Journal of Clinical Investigation Volume 47 1968CO2 is so rapid that the expired CO2 may be considered to come from one large common CO2 pool. Similar conclusions were reached by Feisal, Sackner, and DuBois who injected bicarbonate into the pulmonary artery of the dog and measured the evolution of CO2 in the alveoli with a sensitive body plethysmograph (5). These investigators as well as others have found that inhibition of the enzyme carbonic anhydrase modified the exchange of CO2 between blood, pulmonary tissues, and alveolar gas sufficiently to produce a significant alveolar to end-capillary CO2 gradient (A-C CO2 gradient) (6)(7)(8).…”

“…Because only the conversion of *CO2 to bicarbonate inhibited by acetazolamide was taken into account by this calculation, these percentages are minimal values. The above findings support the view that the carbonic anhydrase in lung tissues and blood is necessary in order to have equilibration of the CO2 stores in Vti., Vc, and alveolar gas during the time it takes blood to traverse the pulmonary capillaries (3,5 (Fig. 2) there was little change in the zero intercepts but subsequent disappearance was twice as fast.…”

“…This equilibration takes place in less than 1-2 sec and the amount of CO2 entering the alveoli will be a function of the CO2 dissociation curves of Vti. and Vc (5,19). The CO2 contained in the residual volume (RV), Vti., and Vc before inspiration plus any C02 contained in the inspired gas will equal the CO2 contained in the alveolar volume, Vti.…”

Management of the acid-base balance by the red blood cell carbonic anhydrase (RCA). I. Correlation of the RCA activity and acid-base balance in the in vitro and in vivo experiments.

“…Therefore, Ooshima et al (1977) could not find out the linear correlation between RCA activity and acid-base balance. As Feisal et al (1963), Klocke (1978) and Nagal et al (1974) reported that RCA activity affects the Pco2 level, it is thought that the RCA activity also has a correlation with Pco2 which changes in parallel with pH and HC03-/Pco2 ratio through the Henderson-Hasselbalch formula.…”