Why Is Pulmonary Hypertension Test Prescribed?

Yes, my specialist has given me breathing tests pulmonary eg, mist of radioactive material in tube,then scan of lungs and lung xray and vp something? Now am due another test whuich is just breathing into tube for lung capacity. Its called a pulmonary hypertension test. What am I to expect? Blood pressure is fine am active everyday, watch healthy food intake and keep weight down.