Functional residual capacity and body position in the dog.

Resting lung volumes in the supine position (FRCs) were determined by N2 washout method in 67 dogs under pentobarbital anesthesia and computed in ml/kg body weight (BW). In 21 other dogs, FRCs and the change in FRC from the supine to upright positions (deltaFRC) were determined; these lung volumes were expressed in ml/kg BW and in percentage of TLC40 (lung volume at 40 cmH2O positive-pressure inflation). It was found that a) FRCs averaged 38.6 plus or minus 8.2 and 42 plus or minus 5.9 ml/kg BW in the two groups of dogs; b) deltaFRC averaged 23 plus or minus 4 ml/kg BW resulted in large data dispersion, a large coefficient of variation (CV) and a poor correlation (r) of lung volume to BW; D) on the contrary, marked uniformity of FRCs and FRCu (upright FRC) was obtained by expressing the resting lung volumes in %TLC40, allowing an accurate prediction of FRC from the inspiratory capacity (IC). Relationship of FRCu to TLC was comparable to human data reported in the literature. FRCs (%TLC40) was smaller than values previously reported for awake human subjects, probably due to the FRCs reduction in our dogs by anesthesia.