Some tissues of our body have redundancy of blood supply, by which I mean that if an artery that supplies blood to this area becomes obstructed, overlapping blood supply is enough to limit tissue death. I first saw this phenomenon demonstrated very clearly to me years ago when I saw a 50-year-old male patient in previously good health who complained of numbness in his great toe for several weeks. I noticed that the toe looked a bit pale, but not strikingly so. On the top of his good foot, I could feel a bounding pulse, but I felt nothing in the corresponding spot on the bad foot. It turned out that he had a blood clot in the dorsalis pedis artery, the main—but not the only—artery that supplies the great toe. A vascular surgeon friend of mine took this man to the operating room and easily removed the clot. The patient had an uneventful recovery with absolutely no damage to his foot, at least none that anyone ever could see or measure. And, the patient, my surgeon friend and I were very pleased because this patient had just dodged a bullet.
If that very same clot had traveled “north” to the patient’s brain instead of “south” to his foot, the outcome would not have been so happy—the poor fellow would have had a stroke. Brain has precious little in redundant blood supply so that if an artery that supplies the brain becomes obstructed, the tissue supplied by the obstructed artery quickly dies. Between the dead zone and normal brain lies a relatively thin zone, the so-called ischemic penumbra, which remains alive, at least for a period of time, because of slight overlapping blood flow from nearby arteries. Clot busting and other wonder drugs help to resupply blood to the penumbra and salvage as much of the penumbra as possible. But, all the interventions, including hyperbaric oxygen, can only bring improvement, not the kind of cure I saw in the gentleman with the blood clot to his foot.
Although the mechanism is not fully understood, it has been known for decades that repeated treatments with hyperbaric oxygen stimulates the growth of new blood vessels into hypoxic tissue. (Hypoxic tissue is the medical term for tissue with a reduced amount of oxygen in it, the most common cause of which is a reduced blood supply.) Another thing long known about hyperbaric oxygen is that the new blood vessels are permanent; they do not die off when the hyperbaric oxygen is treatments are over.
I just wanted to introduce the topic today. In ensuing articles, I plan to develop this theme.