Can Oxygen Therapy Improve Brain Blood Vessel Function in COPD?

Breathing in additional oxygen improves the function of blood vessels in the brains of people with chronic obstructive pulmonary disease (COPD), according to research published in Experimental Physiology.

The study said that patients with COPD are at higher risk of dementia, possibly because of lower brain oxygen levels as a result of problems with blood supply from brain blood vessels. According to other research cited by the study, giving patients with COPD additional oxygen reduced their risk of developing dementia, but the mechanisms underlying this effect had not been explored.

The latest research aimed to establish the effect of supplying additional oxygen on both blood flow to the brain and blood vessel function in patients with COPD. Fourteen hypoxemia patients were included in the study, which tracked cerebral blood flow (CBF), oxygen delivery (CDO₂), and neurovascular coupling (NVC), which is the relationship between local neuron activity and changes in CBF.

The researchers used ultrasound to view and measure blood flow in the brain in these patients at rest, before and during delivery of this additional oxygen. Ultrasound measured the extent to which brain blood flow increased.

Participants began this test with their eyes shut, having to open them and then read a piece of text. This test was designed to increase activity in the brain, and brain blood flow was expected to increase to provide adequate oxygen supply.

Pairing these ultrasound measures with a measurement of blood oxygen levels allowed authors to estimate how much oxygen delivery to the brain increased during the eyes-open reading test.

Measurements were assessed and the authors found that blood flow and oxygen delivery to the brain was significantly increased during reading. This was due to blood vessels in the brain becoming dilated in response to the greater oxygen demand when the brain was active.

Specifically, peripheral oxyhemoglobin saturation increased from 91 ± 3.3 to 97.4 ± 3% (P <.01). CBF was unaltered (593.0 ± 162.8 vs 590.1 ± 138.5 mL min−1; P = .91) with supplemental O₂.

However, both CDO₂ (98.1 ± 25.7 versus 108.7 ± 28.4 ml dl−1; P = 0.02) and NVC improved.

The posterior cerebral artery cerebrovascular conductance increased to a greater extent after O₂ normalization (+40%, from 20.4 ± 9.9 to 28 ± 10.4% increase in conductance; P = .04). The posterior cerebral artery cerebrovascular resistance decreased to a greater extent during O₂ normalization (+22%, from −16.7 ± 7.3 to −21.4 ± 6.6% decrease in resistance; P = .04).

The cerebral vasculature of patients with COPD appears insensitive to oxygen, because CBF was unaltered in response to O₂ supplementation, leading to improved CDO₂.

Providing extra oxygen to patients with COPD improved the function of blood vessels in the brain by matching blood supply to the demands of the brain activity during this short test.

Other research is needed to see how long-term oxygen use would impact the function of brain blood vessels.

These improvements might provide a physiological link between oxygen therapy and a reduced risk of cerebrovascular diseases such as stroke, mild cognitive impairment, and dementia.

Reference

Hoiland RL, Mladinov S, Barak, OF, et al. Oxygen therapy improves cerebral oxygen delivery and neurovascular function in hypoxaemic chronic obstructive pulmonary disease patients [published online July 5, 2018]. Exp Physiol. doi: 10.1113/EP086994.