Nasa did worse than that. To simulate space they pressurized Apollo 1 to one atmosphere above external pressure. So they were at two atmospheres of pressure,

Nasa did worse than that. To simulate space they pressurized Apollo 1 to one atmosphere above external pressure. So they were at two atmospheres of pressure, which is ironically about the same pressure as the hyperbaric oxygen therapy used in the OP. The patients in the OP were using masks.