Actually, you have the pressure exactly opposite and off. 1.3 would be 7440 below sea level. 1.3 ATA is 14.7 psi times 1.3 That equals 19.11 PSI. The differential of 4.41 PSI is like descending from 7440 feet to sea level then climbing to 7440 feet. Even more air pressure change to tolerate than the first calculation. I used a chart that was hard to read. As a previous pilot, 7440 feet down and up can be uncomfortable if done too fast. I've had passengers who were uncomfortable with 1000 feet of quick altitude change. 500 fpm is consider the max comfort range.

$6,000 gets the tiny tube and cheapest O2 concentrator. A bit tough for somebody with claustrophobia. The 33 inch system with a good concentrator is close to $10,000.

A couple of local chiros tried to promote HBOT to their clients but discontinued their programs or stopped advertising. They charge $80 to $120 per dive.

From what I've read, the best results were at 1.25 ATA with 1.5 showing less value. Wound healing does better at the higher pressures. I've followed the research for more than 10 years hoping they would find good value to it.