We have measured with positron emission tomography (PET) the regional distribution of extravascular lung water (EVLW) and hematocrit (Hct(L)) in normal supine dogs. H215O and C15O were used as total lung water (TLW) and intravascular water (IVW) compartment labels, respectively. An additional plasma volume label (68Ga-transferrin) was used to determine regional Hct(L). EVLW was calculated as the difference between TLW and IVW. In 13 dogs, EVLW was relatively constant along a gravity-dependent vertical gradient, although values in the most anterior regions were statistically less (P < 0.05) than those in more posterior ones. The average value for EVLW (13 dogs) was 14.4 ± 2.5 ml H2O/100 ml lung. When EVLW was compared with IVW on a regional basis, the EVLW/IVW ratio decreased significantly in a gravity-dependent direction from 1.95 ± 0.28 to 0.88 ± 0.18. In 7 dogs, no significant difference between Hct(L) and systemic hematocrit (average ratio 1.01 ± 0.08) was found nor was any significant variation of Hct(L) within the lung detected. Thus, in contrast to gravimetric techniques, a hematocrit correction does not appear to be necessary when regional EVLW is studied by PET.
ASJC Scopus subject areas
- Physiology (medical)