title: Interrelationships between regional blood flow, blood volume, and ventilation in supine humans.
abstract: Positron emission tomography was used to measure alveolar gas volume, pulmonary blood volume (VB), regional alveolar ventilation (VA), and the regional ventilation-to-perfusion ratio (VA/Q) in a transaxial slice at midheart level in eight supine subjects and one prone normal subject during quiet breathing. These relationships allow regional blood flow (Q) to be calculated as VA/(VA/Q). No significant differences between right and left lung were found. Within the volume studied, which excluded the peripheral 2 cm of the lung, there was an exponential increase in Q by 11%/cm from 1.2 ml.min-1.cm-3 in the upper (ventral) to 3.5 ml.min-1.cm-3 in the lower (dorsal) lung regions, explaining 61% of the total variation within groups, whereas the horizontal gradient only explained 7% (right lung; supine subjects). Similar gravitational gradients were found in the single prone subject. VA and Q were well matched except at the dorsal lung thoracic border where low values of VA/Q due to a reduction in ventilation were occasionally found even in these normal subjects. VB and Q were reasonably well matched, implying that variations in vascular transit time due to gravity are kept to a minimum. The coefficient of local variation of peripheral vascular transit times (VB/Q) (33%) was, therefore, less than would have been expected if VB and Q were uncorrelated (57%).
authors.affiliation: Medical Research Centre Cyclotron Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
authors.forename: L H
authors.initials: LH
authors.lastname: Brudin
authors.forename: C G
authors.initials: CG
authors.lastname: Rhodes
authors.forename: S O
authors.initials: SO
authors.lastname: Valind
authors.forename: T
authors.initials: T
authors.lastname: Jones
authors.forename: J M
authors.initials: JM
authors.lastname: Hughes
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology*; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D009356:Neon; D016684:Prone Position / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*; D016683:Supine Position / Q000502:physiology*; D014055:Tomography, Emission-Computed; D014692:Ventilation-Perfusion Ratio / Q000502:physiology
chemical_list: D009356:Neon