title: 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.
authors.affiliation: Dipartimento di Scienze Biomediche Sperimentali e Cliniche, Università degli Studi dell'Insubria, Via J.H. Dunant 5, 21100 Varese, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Moriondo
authors.forename: Sylvain
authors.initials: S
authors.lastname: Mukenge
authors.forename: Daniela
authors.initials: D
authors.lastname: Negrini
mesh_terms: D000818:Animals; D006321:Heart / Q000502:physiology; D008208:Lymphatic System / Q000502:physiology*; D008297:Male; D009991:Oscillometry; D010994:Pleura; D051381:Rats; D012119:Respiration; D012121:Respiration, Artificial; D013314:Stress, Mechanical