Is hyperbaric oxygen therapy dangerous to those with copd?

Sometimes: Since you are under increased atmoshpheric pressure in a hyperbaric chamber, there is increased pressure in the lungs. If one has COPD with blebs, (fragile air-filled sacks of air) the pressure could cause the lung to leak into the chest cavity and to collapse.

Possibly: If you are a co2 retainer and have COPD you could have an fatal event in a hyperbaric dive situation.

Not certain.: While there is anecdotal evidence that patients with COPD (more precisely, emphysema) have problems with (1) high oxygen concentrations and (2) are more prone to blebs and spontaneous pneumothorax, this has not been borne out in my practice. Moreover, there is some new studies which challenge the first conjecture (positive pressure ventilation helps copd). I would treat on a case-by-case basis.