Subatmospheric pressure in the rabbit pleural lymphatic network

1. Hydraulic pressure in intercostal and diaphragmatic lymphatic vessels wa s measured through the micropuncture technique in 23 anaesthetised paralyse d rabbits. Pleural lymphatic vessels with diameters ranging from 55 to 950 mu m were observed under stereomicroscope view about 3-4 h after intrapleur al injection of 20 % fluorescent dextrans. 2. Lymphatic pressure oscillated from a minimum (P-min) to a maximum (P-max ) value, reflecting oscillations in phase with cardiac activity (cardiogeni c oscillations) and lymphatic myogenic activity. With intact pleural space, P-min in submesothelial diaphragmatic lymphatic vessels of the lateral app osition zone was -9.1 +/- 4.2 mmHg, more subatmospheric than the simultaneo usly recorded pleural liquid pressure amounting to -3.9 +/- 1.2 mmHg. In ex trapleural intercostal lymphatic vessels P-min averaged -1.3 +/- 2.7 mmHg. 3. Cardiogenic pressure oscillations (P-max - P-min), were observed in all recordings; their mean amplitude was about 5 mmHg and was not dependent upo n frequency of cardiac contraction, nor lymphatic vessel diameter, nor the P-min value. 4. Intrinsic contractions of lymphatic vessel walls caused spontaneous pres sure waves of about 7 mmHg in amplitude at a rate of 8 cycles min(-1). 5. These results demonstrated the ability of pleural lymphatic vessels to g enerate pressure oscillations driving fluid from the subatmospheric pleural space into the lymphatic network.