When a healthy person has experiences hypoxia (a deficiency of oxygen in the blood) caused by reduced oxygen pressure in the air, their body compensates by increasing blood flow to vital organs and tissues such as the brain and muscles to maintain their oxygen supply and protect them. Hypoxia can be caused by scenarios ranging from high altitudes to airway obstruction such as what occurs in sleep apnea.

To understand how high blood pressure impacts these compensatory responses to hypoxia, a study conducted by researchers from the Fluminense Federal University, Brazil, and The University of Copenhagen, Denmark, involved measuring the blood flow to the brain and the leg muscles while middle-aged men with normal and high blood pressure inhaled air with a low oxygen concentration for 5 minutes. The results, published in The Journal of Physiology, shed light on the effects of high blood pressure by considering the way the body responds to a lack of oxygen.

The study found this increased blood supply response to hypoxia does not occur for middle-aged men with high blood pressure. So when they are deprived of oxygen, oxygen delivery to parts of the brain and the leg skeletal muscles is limited. This compromised response may be caused by the high blood pressure-induced impairment in the function of the blood vessels as well as increases in neural signals from the hypoxic brain to the circulation, increasing resistance to blood supply.

Importantly, this study only offers insights into the disturbances caused by high blood pressure during a short-term exposure (5 minutes) to low oxygen concentrations in a controlled environment (in the study, carbon dioxide concentration was kept constant and blood pressure to hypoxia did not change). Looking into these responses during a longer exposure to hypoxia in daily life situations such as high altitude exposure or sleep apnea is also necessary to confirm these findings, the authors say.

Lead investigator Igor A. Fernandes also highlights the importance to understand the mechanisms that maintain brain and skeletal muscle oxygen supply of healthy individuals in hypoxic conditions and how high blood pressure affects them. He says in a release, “We are interested in determining how high blood pressure impacts the mechanisms by which hypoxia increases brain and skeletal muscle blood supply and oxygen delivery. This will enable us to investigate how to prevent their deterioration or restore their adequate functioning.”