Continuous Positive Airway Pressure Modulates Effect of Inhaled Nitric Oxide on the Ventilation-Perfusion Distributions in Canine Lung Injury: Results

Dead space ventilation was lowered by CPAP (p<0.05). Blood flow distribution curves shifted to the left and their dispersions were above the upper normal limit (logSDQ >0.6). Ventilation distributions were shifted to the right, while dispersions of the curves were increased (logSDv >0.6). Application of CPAP decreased V. No effect was observed on Q, logSDQ, and log SDv. The index DISPr-e decreased during CPAP and was lowest with simultaneous NO inhalation. Predicted РаОг was close to measured Pa02 for all conditions (Table 4).
This study was designed to evaluate if CPAP modulates the effects of NO inhalation on pulmonary gas exchange in a canine oleic acid lung injury model. We found that NO inhalation in the absence of CPAP did not influence Va/Q matching in this setting, but significantly augmented the improvement effected by the application of CPAP. A decrease in mean Ppatm and PVR was consistently seen during NO inhalation. in detail

Our observations were made in dogs with severe oleic acid-induced lung injury indicated by a uni-modal Va/Q distribution with 48 ±2 percent of the pulmonary blood flow perfusing shunt units. Distributions of Va/Q observed in dogs with oleic acid-induced lung injury are comparable to those in humans with acute lung injury, where blood flow is distributed to either shunt or normal Va/Q units.2 High PaC02 in conjunction with low pH in our spontaneously breathing dogs may have contributed to the Va/Q inequality. However, hypercapnia and respiratory acidosis remained unchanged and therefore are not responsible for the observed changes in the Va/Q distributions. The small differences between predicted and measured Pa02 values throughout the investigation indicate complete alveolar-end-capillary oxygen equilibration. Therefore, observed changes in pulmonary gas exchange can be almost entirely explained by the measured Va/Q mismatch. A small amount in the variation in РаОг may be explained by factors other than Va/Q mismatch that directly or through their effects on Pv02 govern Pa02.

Table 4—Predicted vs Measured РаС>2

Ambient Pressure CPAP
N0=0 ppm N0=40 ppm N0=0 ppm N0=40 ppm
Predicted PaC>2, mm Hg 60 ±5 62 ±10 90± 11 106±11
Measured РаОг, mm Hg 62 ±8 64 ±9 92 ±8 111 ±13
r2 0.93 0.90 0.91 0.92
This entry was posted in Lung injury and tagged acute lung injury, continuous positive airway pressure, Nitric oxide, pulmonary gas exchange, ventilation-perfusion distribution.