title: Internal carotid artery blood flow in healthy awake subjects is reduced by simulated hypovolemia and noninvasive mechanical ventilation.
abstract: Intact cerebral blood flow (CBF) is essential for cerebral metabolism and function, whereas hypoperfusion in relation to hypovolemia and hypocapnia can lead to severe cerebral damage. This study was designed to assess internal carotid artery blood flow (ICA-BF) during simulated hypovolemia and noninvasive positive pressure ventilation (PPV) in young healthy humans. Beat-by-beat blood velocity (ICA and aorta) were measured by Doppler ultrasound during normovolemia and simulated hypovolemia (lower body negative pressure), with or without PPV in 15 awake subjects. Heart rate, plethysmographic finger arterial pressure, respiratory frequency, and end-tidal CO2(ETCO2) were also recorded. Cardiac index (CI) and ICA-BF were calculated beat-by-beat. Medians and 95% confidence intervals and Wilcoxon signed rank test for paired samples were used to test the difference between conditions. Effects on ICA-BF were modeled by linear mixed-effects regression analysis. During spontaneous breathing, ICA-BF was reduced from normovolemia (247, 202-284 mL/min) to hypovolemia (218, 194-271 mL/min). During combined PPV and hypovolemia, ICA-BF decreased by 15% (200, 152-231 mL/min, P = 0.001). Regression analysis attributed this fall to concurrent reductions in CI (β: 43.2, SE: 17.1, P = 0.013) and ETCO2(β: 32.8, SE: 9.3, P = 0.001). Mean arterial pressure was maintained and did not contribute to ICA-BF variance. In healthy awake subjects, ICA-BF was significantly reduced during simulated hypovolemia combined with noninvasive PPV Reductions in CI and ETCO2had additive effects on ICA-BF reduction. In hypovolemic patients, even low-pressure noninvasive ventilation may cause clinically relevant reductions in CBF, despite maintained arterial blood pressure.
authors.affiliation: Division of Physiology, Institute of Basic Medical Sciences University of Oslo, Oslo, Norway maria.skytioti@medisin.uio.no.
authors.forename: Maria
authors.initials: M
authors.lastname: Skytioti
authors.affiliation: Deptartment of Anaesthesia and Intensive Care, Akershus University Hospital, Lørenskog, Norway.
authors.forename: Signe
authors.initials: S
authors.lastname: Søvik
authors.affiliation: Division of Physiology, Institute of Basic Medical Sciences University of Oslo, Oslo, Norway.
authors.forename: Maja
authors.initials: M
authors.lastname: Elstad
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000502:physiology; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D005260:Female; D064368:Healthy Volunteers; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics; D006801:Humans; D016857:Hypocapnia / Q000150:complications* / Q000503:physiopathology; D020896:Hypovolemia / Q000150:complications* / Q000503:physiopathology; D002534:Hypoxia, Brain / Q000150:complications / Q000503:physiopathology; D008150:Lower Body Negative Pressure / Q000009:adverse effects; D008297:Male; D063087:Noninvasive Ventilation / Q000009:adverse effects*; D012039:Regional Blood Flow; D012121:Respiration, Artificial / Q000009:adverse effects*; D018608:Ultrasonography, Doppler / Q000379:methods
keywords: Cerebral blood flow; cerebrovascular circulation; hypovolemia; internal carotid artery blood flow; noninvasive ventilation