Increased overall pressure is of therapeutic value when HBOT is used in treatment of decompression sickness & air embolus.
For many other conditions, the therapeutic principle of HBOT lies in a drastically increased partial pressure of oxygen in the tissues of the body. The oxygen partial pressures achievable under HBOT are much higher than those under breathing pure oxygen at normal atmospheric pressure.
A related effect is the increased oxygen transport capacity of blood. Normally, oxygen transport is limited by the oxygen binding capacity of hemoglobin in red blood cells and very little oxygen is transported by blood plasma. With HBOT, Oxygen transport by plasma, is significantly increased. In addition, plasma is approximately 60% of our total blood.