| roilers develop pulmonary hypertension when an elevated pulmonary arterial pressure (PAP) is required to propel the cardiac output (CO; volume of blood pumped by the heart per minute) through lungs having an inadequate pulmonary vascular capacity. Blood flowing at excessive velocity through the gas exchange area does not achieve full saturation of hemoglobin with oxygen (diffusion limitation) aggravating the increases in CO and PAP which are correlated with work hypertrophy, right ventricular dilation, and ineffective sealing of the right atrio-ventricular valve leading to pulmonary hypertension syndrome (PHS, ascites). Previous hemodynamic evaluations demonstrated that different lines of birds differ in their PAP and thus in their susceptibility to PHS, confirming an important genetic component influencing PHS susceptibility. The PHS has been intensively studied during the last two decades. However, the poultry industry still struggles with PHS associated mortality. Several questions in relation to the physiopathology and immunology of PHS remain to be answered. The experiments presented within this dissertation were aimed to consolidate the understanding of PHS within the following areas: (1) Differences in the pulmonary hemodynamics of PHS-resistant and -susceptible birds were addressed to establish clear base lines as a reference for future research. (2) The role of the pre-capillary vasculature as the specific anatomical segment responsible for the increase in PAP was confirmed. (3) A pulmonary diffusion limitation was confirmed as the main cause of low arterial blood oxygenation. (4) Gram negative toxins (lipopolysaccharide; LPS) exist in abundance within poultry houses and LPS injected intravenously was known to increase the PAP. It now has been confirmed that LPS also elicits pulmonary hypertension when administrated through the respiratory tract (intratracheal). Therefore, the environment (bacterial load) in which broilers are raised can influence their susceptibility to PHS. (5) Sentinel immune cells exist within the airways of broilers. It was confirmed that the number of immune cells within the airways increases after birds are exposed to priming doses of a mixture of aerosolized Red... |
