Could pranayam cure anxiety disorders like ocd ?

Difficult question: Yoga will not hurt you and there is growing evidence of the benefits and brain changes with yoga/meditation. Ocd and anxiety can affect people in such broad ways i would imagine some people would find their solution in yoga while others may have little or no or not enough benefit. I could see that this is one part of a several part solution or program for general wellbeing/recovery.

No, but can help.: Pranayama, or breathing exercises, do not cure anxiety disorders like OCD. This is something that should be addressed by a professional such as a psychologist and/or a psychiatrist. Although yoga does support treatment, it is not a cure. The best treatments for this type of disorder are the behaviorally based treatments such as CBT, cognitive behavioral therapy.

You mean from yoga?: If this is what you mean, the breathing in yoga of various types can do many things. Some are relaxing, others activating. These techniques have been used by yogis to quiet the mind. I know,that breath work can reduce anxiety. I have not seen anything suggesting it as a cure,for OCD. Keep breathing but speak with your doctor as well.