Hyperbaric Oxygen Therapy and its Effects on Left Ventricular function

Hyperbaric oxygen therapy, provides enhanced oxygen delivery, increasing partial pressure of oxygen (pO2) in the bloodstream, allowing for greater oxygen diffusion into tissues, while also helping to restore oxygenation to tissues with compromised blood flow or oxygen delivery. However these known hyperbaric and hyperoxic effects on cardiac and especially left ventricular (LV) function, may pose a risk on patients with cardiovascular co-morbidities, especially at depth. Daily hyperbaric oxygen therapy at the chamber consist of elective hyperbaric treatment 'tables' consisting of periods where patients breathe 100% oxygen at pressure for 20-25 mins in a hyperbaric chamber at 2.4 ATA, followed by 'air breaks' of 5-10 mins where breathing gas is switched to medical air with composition equivalent to terrestrial air composition. Attendant staff during these treatment tables do not normally breathe 100% oxygen except for 15-20 mins at the end of the treatment 'table', where chamber pressure is returned to atmospheric sea level (1.0 ATA) as a means of 'off-gassing' the acquired nitrogen load from breathing medical air in a hyperbaric setting and preventing decompression illness. Patient participants will be required to transit temporarily from their treatment chamber to a smaller chamber to allow us to perform an echocardiogram (done by a qualified echocardiographer) during the already-scheduled 'air break' that forms part of their standard elective hyperbaric treatment. This will take no longer than the expected 5-10 mins of a normal 'air break' and they will return immediately to their treatment chamber and resume their planned treatment 'table', ensuring no appreciable difference in their planned hyperbaric oxygen therapy. Staff participants will be required to breathe additional 100% oxygen for the initial 20-25 mins of the treatment table, after which they will follow the same procedure as patient participants to transit to the smaller chamber for an echocardiogram. The additional exposure to oxygen is the only deviation from their typical attendant oxygen exposure, and is meant to provide an equivalent exposure as comparison and control to patient participants. Both sets of participants will already have had a pre-treatment echocardiogram done. Participants will be required to provide consent to collection and storage of anonymised data generated by the echocardiogram, as well as the echocardiogram itself. Staff participants will have to consent to the additional oxygen exposure while performing their work as chamber attendants. This makes a total of two echocardiograms (one just before the start of the hyperbaric oxygen therapy and the second during scheduled 'air break'). Both echocardiograms and an initial consent process is not expected to take more than a cumulative total of 20 mins for both patients and staff. The echocardiogram will be performed for one treatment session only.