{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,2]],"date-time":"2026-06-02T04:00:21Z","timestamp":1780372821441,"version":"3.54.1"},"reference-count":35,"publisher":"American Physiological Society","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Applied Physiology"],"published-print":{"date-parts":[[1998,8,1]]},"abstract":"<jats:p> This study examined the dynamics of the middle cerebral artery (MCA) blood flow response to hypocapnia in humans ( n = 6) by using transcranial Doppler ultrasound. In a control protocol, end-tidal[Formula: see text]([Formula: see text]) was held near eucapnia (1.5 Torr above resting) for 40 min. In a hypocapnic protocol, [Formula: see text]was held near eucapnia for 10 min, then at 15 Torr below eucapnia for 20 min, and then near eucapnia for 10 min. During both protocols, subjects hyperventilated throughout and[Formula: see text] and end-tidal[Formula: see text] were controlled by using the dynamic end-tidal forcing technique. Beat-by-beat values were calculated for the intensity-weighted mean velocity ([Formula: see text] <jats:sub>IWM<\/jats:sub>), signal power ([Formula: see text]), and their instantaneous product ([Formula: see text] <jats:sub>IWM<\/jats:sub>). A simple model consisting of a delay, gain terms, time constants (\u03c4<jats:sub>f,on<\/jats:sub>, \u03c4<jats:sub>f,off<\/jats:sub>) and baseline levels of flow for the on- and off-transients, and a gain term (g<jats:sub>s<\/jats:sub>) and time constant (\u03c4<jats:sub>s<\/jats:sub>) for a second slower component was fitted to the hypocapnic protocol. The cerebral blood flow response to hypocapnia was characterized by a significant ( P &lt; 0.001) slow progressive adaptation in[Formula: see text] <jats:sub>IWM<\/jats:sub>, with g<jats:sub>s<\/jats:sub> = 1.26 %\/Torr and \u03c4<jats:sub>s<\/jats:sub> = 427 s, that persisted throughout the hypocapnic period. Finally, the responses at the onset and relief of hypocapnia were asymmetric ( P &lt; 0.001), with \u03c4<jats:sub>f,on<\/jats:sub> (6.8 s) faster than \u03c4<jats:sub>f,off<\/jats:sub> (14.3 s). <\/jats:p>","DOI":"10.1152\/jappl.1998.85.2.388","type":"journal-article","created":{"date-parts":[[2017,12,22]],"date-time":"2017-12-22T20:55:50Z","timestamp":1513976150000},"page":"388-397","source":"Crossref","is-referenced-by-count":85,"title":["Fast and slow components of cerebral blood flow response  to step decreases in end-tidal   P  CO  2     in humans"],"prefix":"10.1152","volume":"85","author":[{"given":"Marc J.","family":"Poulin","sequence":"first","affiliation":[{"name":"University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, United Kingdom"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pei-Ji","family":"Liang","sequence":"additional","affiliation":[{"name":"University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, United Kingdom"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter A.","family":"Robbins","sequence":"additional","affiliation":[{"name":"University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, United Kingdom"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.3171\/jns.1982.57.6.0769"},{"key":"B2","doi-asserted-by":"publisher","DOI":"10.1161\/01.STR.18.3.649"},{"key":"B3","doi-asserted-by":"publisher","DOI":"10.1007\/BF02474565"},{"key":"B4","doi-asserted-by":"publisher","DOI":"10.1177\/106002809002400501"},{"key":"B5","doi-asserted-by":"publisher","DOI":"10.1093\/bja\/46.5.348"},{"key":"B6","doi-asserted-by":"publisher","DOI":"10.1097\/00004647-199611000-00021"},{"key":"B7","doi-asserted-by":"publisher","DOI":"10.1016\/0034-5687(95)00026-A"},{"key":"B8","doi-asserted-by":"publisher","DOI":"10.1176\/ajp.152.5.666"},{"key":"B9","first-page":"77","volume":"64","author":"Du Boulay G. 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