Previous studies have shown that normal arterial PCO2 can be maintained during apnea in anesthetized dogs by delivering a continuous stream of inspired ventilation through cannulas aimed down the main stem bronchi, although this constant-flow ventilation (CFV) was also associated with a significant increase in ventilation-perfusion (V̇A/Q̇) inequality, compared with conventional mechanical ventilation (IPPV). Conceivably, this V̇A/Q̇ inequality might result from differences in V̇A/Q̇ ratios among lobes caused by nonuniform distribution of ventilation, even though individual lobes are relatively homogeneous. Alternatively, the V̇A/Q̇ inequality may occur at a lobar level if those factors causing the V̇A/Q̇ mismatch also existed within lobes. We compared the efficiency of gas exchange simultaneously in whole lung and left lower lobe by use of the multiple inert gas elimination technique in nine anesthetized open-chest dogs. Measurements of whole lung and left lower lobe gas exchange allowed comparison of the degree of V̇A/Q̇ inequality within vs. among lobes. During IPPV with positive end-expiratory pressure, arterial PO2 and PCO2 (183 ± 41 and 34.3 ± 3.1 Torr, respectively) were similar to lobar venous PO2 and PCO2 (172 ± 64 and 35.7 ± 4.1 Torr, respectively; inspired O2 fraction = 0.44 ± 0.02). Switching to CFV (3 l·kg-1·min-1) decreased arterial PO2 (112 ± 26 Torr, P < 0.001) and lobar venous PO2 (120 ± 27 Torr, P < 0.01) but did not change the shunt measured with inert gases (P > 0.5). Transition to CFV also caused an index of V̇A/Q̇ inequality independent of shunt (log SD of blood flow) to increase in whole lung (0.68 ± 0.13 to 1.36 ± 0.22 P < 0.001) and in the lobe 0.22, P < 0.001) and in the lobe (0.78 ± 0.29 to 1.10 ± 0.42, P < 0.05). Since the increased V̇A/Q̇ dispersion found within the lobe during CFV was only about one-half that seen for the lung, we conclude that the increased V̇A/Q̇ inequality found during CFV must reflect contributions between, as well as within, lobes.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of applied physiology|
|State||Published - 1988|
ASJC Scopus subject areas
- Physiology (medical)