In 'yogash citta-vRtti-nirodhaH', 'citta-vRtti' seems like a tatpuruSa compound, being itself a part of the larger tatpuruSa, like this:
(citta-vRtti)-nirodhaH: nirodha *of* the vRtti_s *of* citta. http://en.wikipedia.org/wiki/Tatpurusa In the description of 'praaNaayaama', 'stambha-vRtti' feels to us like a bahuvriihi: baahyaabhyantara-*stambha-vRttir* desha-kaala-saMkhyaabhiH paridRSTo diirgha-suukSmaH. http://en.wikipedia.org/wiki/Bahuvrihi Taimni's translation: (It is in) external, internal or suppressed modification; is regulated by place, time and number, (and becomes progressively) prolonged and subtle. Vocabulary: (It is in) external (baahya), internal (aabhyantara) or suppressed (stambha) modification (vRttiH); is regulated (paridRSTaH) by place (desha), time (kaala) and number (saMkhyaabhiH; instrumental plural from 'saMkhyaa', implied[?] also for 'desha' and 'kaala'), (and becomes progressively) prolonged (diirgha) and subtle (suukSmaH). That seems to "prove" Bhojadeva's term 'stambha-ruupa', describing the fourth praaNaayaama, "must" refer to the unnoticeable breathing during "apneas" of Transcendental Meditation! Otherwise 'stambha- ruupa' would be synonymous with 'stambha-vRtti', which is, we believe, the third (tRtiiya) praaNaayaama!? :o