title: Ventilation-perfusion relationships in the lung during head-out water immersion.
abstract: Water immersion can cause airways closure during tidal breathing, and his may result in areas of low ventilation-perfusion (VA/Q) ratios (VA/Q less than or equal to 0.1) and/or shunt and, ultimately, hypoxemia. We studied this in 12 normal males: 6 young (Y; aged 20-29 yr) with closing volume (CV) less than expiratory reserve volume (ERV), and six older (O; aged 40-54 yr) with CV greater than ERV during seated head-out immersion. Arterial and expired inert gas concentrations and dye-dilution cardiac output (Q) were measured before and at 2, 5, 10, 15, and 20 min in 35 degrees C water. During immersion, Y showed increases in expired minute ventilation (VE; 8.3-10.3 l/min), Q (6.1-8.2 l/min), and arterial PO2 (PaO2; 91-98 Torr; P less than or equal to 0.05). However, O2 uptake (VO2), shunt, amount of low-VA/Q areas (% of Q), and the log standard deviation of the perfusion distribution (log SDQ) were unchanged. During immersion, O showed increases in shunt (0.6-1.8% of Q), VE (8.5-11.4 l/min), and VO2 (0.31-0.40 l/min) but showed no change in low-VA/Q areas, log SDQ, Q, or PaO2. Throughout, O showed more VA/Q inequality (greater log SDQ) than Y (O, 0.69 vs. Y, 0.47).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, University of California San Diego, La Jolla 92093-0623.
authors.forename: T
authors.initials: T
authors.lastname: Derion
authors.forename: H J
authors.initials: HJ
authors.lastname: Guy
authors.forename: K
authors.initials: K
authors.lastname: Tsukimoto
authors.forename: W
authors.initials: W
authors.lastname: Schaffartzik
authors.forename: R
authors.initials: R
authors.lastname: Prediletto
authors.forename: D C
authors.initials: DC
authors.lastname: Poole
authors.forename: D R
authors.initials: DR
authors.lastname: Knight
authors.forename: P D
authors.initials: PD
authors.lastname: Wagner
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output; D006801:Humans; D007101:Immersion / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D005741:Noble Gases; D010100:Oxygen / Q000097:blood; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
chemical_list: D005741:Noble Gases; D002245:Carbon Dioxide; D010100:Oxygen