Transmural pressure in rat initial subpleural lymphatics during spontaneous or mechanical ventilation

Abstract

The role played by the mechanical tissue stress in supporting lymph formation and propulsion in thoracic tissues was studied in deeply anesthetized rats (n = 13) during spontaneous breathing or mechanical ventilation. After arterial and venous catheterization and insertion of an intratracheal cannula, fluorescent dextrans were injected intrapleurally to serve as lymphatic markers. After 2 h, the fluorescent intercostal lymphatics were identified, and the hydraulic pressure in lymphatic vessels (P lymph) and adjacent interstitial space (P int) was measured using micropuncture. During spontaneous breathing, end-expiratory P lymph and corresponding P int were -2.5 +/- 1.1 (SE) and 3.1 +/- 0.7 mmHg (P < 0.01), which dropped to -21.1 +/- 1.3 and -12.2 +/- 1.3 mmHg, respectively, at end inspiration. During mechanical ventilation with air at zero end-expiratory alveolar pressure, P lymph and P int were essentially unchanged at end expiration, but, at variance with spontaneous breathing, they increased at end inspiration to 28.1 +/- 7.9 and 28.2 +/- 6.3 mmHg, respectively. The hydraulic transmural pressure gradient (DeltaP tm = P lymph - P int) was in favor of lymph formation throughout the whole respiratory cycle (DeltaP tm = -6.8 +/- 1.2 mmHg) during spontaneous breathing but not during mechanical ventilation (DeltaP tm = -1.1 +/- 1.8 mmHg). Therefore, data suggest that local tissue stress associated with the active contraction of respiratory muscles is required to support an efficient lymphatic drainage from the thoracic tissues.

Quantitative measurement of lymphatic function in mice by noninvasive near-infrared imaging of a peripheral vein

“…Lymphatic outflow from the peritoneal cavity has been described as mostly passing through the diaphragmatic stomata and corresponding lymphatic vessels and, therefore, may be dependent on muscular movement of this organ associated with breathing (19,38). Our results indicated that, unlike after subcutaneous injection, some outflow from the peritoneal cavity continued under anesthetized conditions.…”

“…However, similar to the periphery, there was a large increase in the lymphatic transport of tracer to blood when the mice were awake compared with when they were anesthetized. It has previously been reported that respiratory movement is reduced in anesthetized animals lying on their back (38,39). Other investigators have also previously found decreased lymphatic outflow from the peritoneum under anesthesia (40)(41)(42) and have speculated that abdominal muscle tone plays a large role in driving flow out of the peritoneum.…”

Anatomy and roles of lymphatics in inflammatory diseases

“…Both spontaneous active (intrinsic) lymphangion contractions and passive (extrinsic) tissue compressive forces cooperate to generate sufficient pressure gradients to propel lymph centrally. [73][74][75][76] To maintain a unidirectional lymph flow, lymphatics can propel lymph by spontaneous phasic contractions as a result of coordinated contractility of the LMC in the wall of collecting lymphatics. 77 Rat and guinea pig studies have shown that the spontaneous phasic contractions of lymphatics are initiated by a pacemaker electrical activity located in each segment near the valves, with the contraction cycles of lymphatics divided into a contraction phase (systolic) and a relaxation phase (diastolic).…”

Lymph flow pattern in pleural diaphragmatic lymphatics during intrinsic and extrinsic isotonic contraction

“…Subsequent lymph propulsion relies on the presence of hydraulic pressure gradients developing between two consecutive tracts of the lymphatic vessel, separated by unidirectional intraluminal valves. It has been shown that the pressure gradients necessary for both formation and propulsion of diaphragmatic lymph may result from forces arising in the tissue and transmitted to the vessel lumen during the cardiac (30) and/or respiratory cycle (22). In addition, unlike what was observed in linear vessels of the central tendineous diaphragm, several loops and short linear tracts located at the outer diaphragm muscular periphery display an intrinsic pumping activity.…”

“…Being that this is true also for the lung and with the consideration that passive mechanical ventilation without active inspiratory muscle contraction inhibits lymph flow from thoracic tissues (22), maintenance of spontaneous ventilation would be crucial in preventing and/or limiting the occurrence of pulmonary edema.…”