Cerebral, Muscle and Blood Oxygenation in Patients with Pulmonary Vascular Disease Whilst Breathing Normobaric Hypoxia vs. Normoxia Before and After Sildenafil: Data from a Randomised Controlled Trial.

Background

In patients with pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension (summarized as pulmonary vascular disease; PVD), it is unclear whether the brain is protected against acute hypoxia and whether acute pulmonary vascular dilatation by sildenafil would influence cerebral and muscle tissue oxygenation whilst breathing normoxia or hypoxia.

Methods

Adult patients with PVD underwent right heart catheterization, while cerebral and muscular tissue oxygenation and tissue hemoglobin index were measured using near-infrared spectroscopy along with arterial and mixed-venous blood gases. Participants underwent a four-stage protocol in which they were blinded to breathing either normoxia (FiO2 0.21) or normobaric hypoxia (FiO2 0.15), both before and after a single oral dose of sildenafil (50 mg) according to a randomized, cross-over design.

Results

In 22 PVD patients (9 women, age 54 ± 14 y) under hypoxia, mean cerebral tissue oxygenation decreased by -2% (95% CI -4 to 0%, p = 0.046), muscular tissue oxygenation by -1% (95% CI -3 to 0%, p = 0.011) and mean arterial partial pressure of oxygen by -2.3 kPa (95% CI -2.7 to -1.8 kPa, p < 0.0001). Sildenafil improved the cerebral tissue hemoglobin index under hypoxia compared to hypoxia without sildenafil by 0.12 (95% CI 0.00 to 0.23, p = 0.049), but not the muscular tissue hemoglobin index.

Conclusions

In PVD patients, acute exposure to normobaric hypoxia leads to a reduction in arterial oxygenation as well as cerebral and muscular tissue oxygenation. Sildenafil improves cerebral blood flow but has no effect on arterial, cerebral or muscular oxygenation.