title: Effects of hypercapnia with and without acidosis on hypoxic pulmonary vasoconstriction.
abstract: Acute respiratory disorders and permissive hypercapnic strategy may lead to alveolar hypoxia and hypercapnic acidosis. However, the effects of hypercapnia with or without acidosis on hypoxic pulmonary vasoconstriction (HPV) and oxygen diffusion capacity of the lung are controversial. We investigated the effects of hypercapnic acidosis and hypercapnia with normal pH (pH corrected with sodium bicarbonate) on HPV, capillary permeability, gas exchange, and ventilation-perfusion matching in the isolated ventilated-perfused rabbit lung. No alteration in vascular tone was noted during normoxic hypercapnia with or without acidosis compared with normoxic normocapnia. Hypercapnia with normal pH resulted in a transient increase in HPV during the course of consecutive ventilation maneuvers, whereas hypercapnic acidosis increased HPV over time. Hypercapnic acidosis decreased exhaled NO during hypoxia more than hypercapnia with normal pH and normocapnia, whereas intravascular NO release was unchanged. However, inhibition of NO synthesis by nitro-L-arginine (L-NNA) resulted in a loss of the increased HPV caused by hypercapnic acidosis but not that caused by hypercapnia with normal pH. Furthermore, capillary permeability increased during hypoxic hypercapnia with normal pH but not hypoxic hypercapnic acidosis. This effect was NO-dependent because it disappeared during L-NNA administration. Ventilation-perfusion matching and arterial PO2 were improved according to the strength of HPV in hypercapnia compared with normocapnia during Tween nebulization-induced lung injury. In conclusion, the increased HPV during hypercapnic acidosis is beneficial to lung gas exchange by improving ventilation-perfusion matching and preserving the capillary barrier function. These effects seem to be linked to NO-mediated pathways.
authors.affiliation: School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Ketabchi
authors.forename: Bakytbek
authors.initials: B
authors.lastname: Egemnazarov
authors.forename: Ralph T
authors.initials: RT
authors.lastname: Schermuly
authors.forename: Hossein A
authors.initials: HA
authors.lastname: Ghofrani
authors.forename: Werner
authors.initials: W
authors.lastname: Seeger
authors.forename: Friedrich
authors.initials: F
authors.lastname: Grimminger
authors.forename: Mostafa
authors.initials: M
authors.lastname: Shid-Moosavi
authors.forename: Gholam A
authors.initials: GA
authors.lastname: Dehghani
authors.forename: Norbert
authors.initials: N
authors.lastname: Weissmann
authors.forename: Natascha
authors.initials: N
authors.lastname: Sommer
mesh_terms: D000142:Acidosis, Respiratory / Q000150:complications* / Q000503:physiopathology; D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D006935:Hypercapnia / Q000150:complications* / Q000503:physiopathology*; D000860:Hypoxia / Q000150:complications* / Q000503:physiopathology*; D066298:In Vitro Techniques; D008168:Lung / Q000098:blood supply* / Q000187:drug effects / Q000503:physiopathology; D008297:Male; D008665:Metalloporphyrins / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D019335:Nitroarginine / Q000494:pharmacology; D010313:Partial Pressure; D012123:Pulmonary Ventilation / Q000187:drug effects; D011817:Rabbits; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
chemical_list: D008665:Metalloporphyrins; C097284:manganese(III)-tetrakis(4-benzoic acid)porphyrin; D019335:Nitroarginine; D009569:Nitric Oxide