Lung border sweep upon phrenic stimulation: dynamic fall in pleural liquid pressure

Pleural pressure was measured by a capsule in 9th or 10th intercostal space (ics) of dogs during tetanic stimulation of phrenic nerves (PS). When lung border passed under capsule (bor.I) a marked negative spike occurred, reflecting pleural liquid pressure (Pliq). In 9th ics spike was briefer than during spontaneous breathing (SB), speed of lung border being 4.6 times greater. During PS spike was greater and longer in 10th than in 9th ics, lung volume at bor.I being 228 ml greater. Lung volume at bor.I was smaller during PS than passive inflation because of chest wall deformation. Dynamic fall in Pliq at bor.I has been estimated about 4 cm H2O during SB, and at least 12 and 16 cm H2O (in 9th and 10th ics, respectively) during PS. Dynamic fall in Pliq seems essentially a viscous loss: it increased with thinning of pleural liquid (increase in lung volume), and with speed and displacement of lung border. Results suggest that at ordinary lung volume viscous loss of pleural liquid in this region is about 2 cm H2O per cm displacement at a speed of 1 cm/sec.