Perinatal supplemental oxygen alters the relationship between the hypoxic ventilatory and vasoconstrictor responses

Ascent to altitude presents a significant challenge to the human body. Specifically, it is associated with an increased ventilation and pulmonary vasoconstriction. In healthy subjects these are related such that a high ventilatory drive is associated with blunted pulmonary vasoconstriction. Adults born prematurely and given supplemental oxygen at birth have a blunted ventilatory response to hypoxia. We hypothesized that the hypoxic ventilatory and pulmonary vasoconstrictor responses would be unrelated following perinatal supplemental oxygen exposure. To test our hypothesis, we used a well-established rat model of 80% O2 (80%) exposure for 14 days post-natally, with 21% O2 exposure as a control (21%). We assessed the ventilatory response to graded hypoxia using barometric plethysmography 6-9 months post hyperoxia exposure. The left and right ventricles were catheterized to evaluate the hemodynamic response to 10 minutes of 12% O2 (hypoxia). To our surprise we found that 80% animals did not demonstrate a depressed ventilatory response to hypoxia. However, these animals experienced increased right ventricular systolic pressure in response to 12% O2. An increase in cardiac output was the primary driving force behind the increase in right ventricular end systolic pressure, not an increase in vascular resistance. We found no relationship between the hypoxic ventilatory drive and right ventricular pressure. In 21% animals exposed to hypoxia, the increase in right ventricular pressure was driven primarily by vasoconstriction and, as previous studies have shown, there was a relationship between the ventilatory and pressure responses. These data suggest that neonatal supplemental oxygen alters the hemodynamic response to hypoxia, possibly through enhanced sympathetic drive. The relationship between ventilation and pulmonary pressure may not translate to individuals born prematurely.