The effect of vagal stimulation on the distribution of inspired gas in the lungs.

We investigated the direct effects of efferent vagal activity on the distribution of inspired gas by stimulating the vagus nerve of one lung and measuring the topographic distribution of a radioactive tracer (133Xe) to both lungs. The distribution of inspired (133Xe) boli was measured with NaI scintillation detectors placed apex-base over each posterior lung of intubated, paralyzed, anesthetized dogs. In 7 supine dogs vagal stimulation reduced the distribution of rapidly insufflated 133Xe boli (flow greater than 2.5 L/s) to the test lung (P less than 0.02), but not when boli were insufflated slowly (flow less than 0.5 L/s), suggesting that vagal stimulation affects pulmonary gas distribution primarily by increasing airway resistance and not through changes in lung compliance. The effect of vagal stimulation on the regional apex-base distribution of inspired gas (greater than 2.5 L/s) was measured in 7 supine and 5 upright dogs. In the supine position, vagal stimulation did not change the uniform apex-base bolus distribution, whereas in the upright position less of the bolus was distributed to the middle and lower lung regions (P less than 0.043), compared to control measurements. This indicates that the regional effects of vagal stimulation on the distribution of inspired gas are uniform in the supine position, but that vagal stimulation alters the distribution of inspired gas when the apex-base pleural pressure gradient is increased.