The relationship between rapid growth and pulmonary hemodynamics in the fast-growing broiler chicken

Very fast-growing (VFG) broiler chickens tend to have marked right ventricular hypertrophy when compared with slower growing chickens. We hypothesized that, in the setting of rapid growth, a hypoxic stimulus would cause greater pulmonary hypertension and right ventricular hypertrophy (RVH). We have studied the relationship between artial oxygenation (SaO2), RVH, and pulmonary artery pressure (Ppa) in 28 awake VFG chickens. We found that the hypoxemic chickens had pulmonary hypertension and that the Ppa was linearly related to the SaO2. The relationship between Ppa and RVH, however, was best described by a broken line (p less than 0.05). Thus, at higher pressures, the RVH seemed excessive for a given Ppa. We have also studied the effects of reducing FIO2 on Ppa, systemic pressure, cardiac output, and calculated total pulmonary resistance (TPR) in lightly anesthetized fast-growing and normal chickens. We found that normal chickens and fast growers had similar TPR in room air, but that the fast growers had a greater increase in TPR than did the normal chickens in response to hypoxia (p less than 0.05). Finally, we placed 2-wk-old normal and VFG chicks in a hypobaric chamber set at "10,000 feet" for 2 wk and found that the VFG but not the normal chickens developed marked RVH in response to the hypoxia. However, the RVH in the fast-growing chickens could be prevented by restricting their diet, and hence their growth. We conclude that hypoxemia probably caused the pulmonary hypertension and RVH in the fast-growing chickens, but that the rapid growth appeared to act as an important amplifier of this response.