Exchange of CO2 and bicarbonate between the circulation and cerebrospinal fluid in piglets.

The dynamic exchange of CO2 and HCO-3 between the central circulation and peripheral sites such as the cerebrospinal fluid (CSF) is not completely understood. To examine this we administered a tracer dose of NaHCO3 labeled with the stable isotope 13C into the central circulation of nine 3- to 4-wk-old anesthetized, instrumented piglets. Serial samples of arterial and venous blood, breath, and CSF were obtained to determine the 13C/12C ratio by isotope-ratio mass spectrometry. Gas-exchange and hemodynamic parameters were obtained through standard techniques. The patterns of tracer washout in venous blood, arterial blood, and breath were nearly indistinguishable from each other, and the mean residence time was 113 +/- 24 min (average +/- SD). In contrast, the CSF 13C/12C ratio was not equivalent to that in venous blood, arterial blood, or breath until 20 min after tracer administration. Tracer washout data were used to determine the best-fit three-exponential-term equation and to calculate compartmental parameters of a three-compartment mammillary system in which CO2 and HCO3- residing in the central compartment (compartment 1) exchanges relatively rapidly with one peripheral compartment (compartment 2) and slowly with the other (compartment 3). The turnover time for the CSF was 6.8 +/- 2.5 min and the estimate for compartment 2 was 7.1 +/- 3.7 min. Accordingly, CSF appears to be one of the rapidly interchanging peripheral compartments.

Improved echocardiographic evaluation of the closed-chest canine: methods and anatomic observations.

This report describes an improved and convenient method of obtaining echocardiograms from the precordial surface of the closed-chest conscious dog. All major cardiac structures were identified using contrast echocardiography. Anatomic relations and the orientation of cardiac structures to the ultrasound transducer in the position of study were established by postmortem examinations. Good quality echocardiograms were obtained from nine of 11 conscious dogs. Highly significant correlations were found when comparing left ventricular systolic time intervals measured from simultaneous echo and pressure recordings. This method has advantages over other echo techniques; namely, elimination of surgical intervention, displacement of interfering lung tissue, and wider field available for study with a minimum of reverberation artifact. The ability to obtain echocardiograms from the chronic experimental dog under physiologic conditioins might provide new and improved applications of echocardiography for the evaluation of human cardiac disorders.