{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,29]],"date-time":"2026-08-29T07:03:45Z","timestamp":1787987025960,"version":"build-2784847793"},"reference-count":57,"publisher":"Wiley","issue":"12","license":[{"start":{"date-parts":[[2024,10,24]],"date-time":"2024-10-24T00:00:00Z","timestamp":1729728000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["physoc.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Experimental Physiology"],"published-print":{"date-parts":[[2024,12]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>Postural fluid shifts may directly affect respiratory control via a complex interaction of baro\u2010 and chemo\u2010reflexes, and cerebral blood flow. Few data exist concerning the steady state ventilatory responses during head\u2010down tilt. We examined the cardiorespiratory responses during acute 50\u00b0 head\u2010down tilt (HDT) in 18 healthy subjects (mean [SD] age 27 [10] years). Protocol 1 (<jats:italic>n<\/jats:italic>\u00a0=\u00a08, two female) was 50\u00b0 HDT from 60\u00b0 head\u2010up posture sustained for 10\u00a0min, while exposed to normoxia, normoxic hypercapnia (5% CO<jats:sub>2<\/jats:sub>), hypoxia (12% inspired O<jats:sub>2<\/jats:sub>) or hyperoxic hypercapnia (95% O<jats:sub>2<\/jats:sub>, 5% CO<jats:sub>2<\/jats:sub>). Protocol 2 (<jats:italic>n<\/jats:italic>\u00a0=\u00a010, four female) was 50\u00b0 HDT from supine, sustained for 10\u00a0min, while breathing either medical air or normoxic hypercapnic (5% CO<jats:sub>2<\/jats:sub>) gas. Ventilation (, pneumotachograph), end\u2010tidal O<jats:sub>2<\/jats:sub> and CO<jats:sub>2<\/jats:sub> concentration and blood pressure (Finapres) were measured continuously throughout each protocol. Middle cerebral artery blood flow velocity (MCAv; transcranial Doppler) was also measured during protocol 2. Ventilation increased significantly (<jats:italic>P\u00a0<\/jats:italic>&lt;\u00a00.05) compared to baseline during HDT in both hyperoxic hypercapnia (protocol 1 by mean [SD] 139 [26]%) and normoxic hypercapnia (protocol 1 by mean [SD] 131 [21]% and protocol 2 by 129 [23]%), despite no change in  or  from baseline. No change in  was observed during HDT with medical air or hypoxia, and there was no significant change in MCAv during HDT compared to baseline. The absence of change in cerebral blood flow leads us to postulate that the augmented ventilatory response during steep HDT may involve mechanisms related to cerebral venous pressure and venous outflow.<\/jats:p>","DOI":"10.1113\/ep092014","type":"journal-article","created":{"date-parts":[[2024,10,24]],"date-time":"2024-10-24T21:34:03Z","timestamp":1729805643000},"page":"2134-2146","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Ventilatory response to head\u2010down\u2010tilt in healthy human subjects"],"prefix":"10.1113","volume":"109","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7535-3378","authenticated-orcid":false,"given":"Abdulaziz","family":"Alsharifi","sequence":"first","affiliation":[{"name":"Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine King's College London London UK"},{"name":"Department of Respiratory Therapy, College of Applied Medical Sciences Jazan University Jazan Saudi Arabia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Niamh","family":"Carter","sequence":"additional","affiliation":[{"name":"Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine King's College London London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akbar","family":"Irampaye","sequence":"additional","affiliation":[{"name":"Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine King's College London London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Charlotte","family":"Stevens","sequence":"additional","affiliation":[{"name":"Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine King's College London London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elisa","family":"Mejia","sequence":"additional","affiliation":[{"name":"Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine King's College London London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joerg","family":"Steier","sequence":"additional","affiliation":[{"name":"Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine King's College London London UK"},{"name":"Lane Fox Unit\/Sleep Disorders Centre Guy's &amp; 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