Journal of Applied Physiology, Vol 51, Issue 4 922-928, Copyright © 1981 by American Physiological Society
Postinspiratory mixing in the lung and cardiogenic oscillations
R. Arieli, A. J. Olszowka and H. D. Van Liew
Subjects inspired a 300-ml bolus of indicator gas cocktail (5% each of SF6,
Ar, Ne, and He) form residual volume (RV), then inspired air to functional
residual capacity (FRC). There was no evidence that a 10-s breath hold
changed the relative concentrations or amounts of indicator gases in phases
III and IV of expiration or allowed additional gas to mix into the RV, but
the breath hold caused cardiogenic oscillations (CO) in expired gas to
decrease in height. The units responsible for cardiogenic troughs and peaks
are different from the units responsible for phases III and IV,
respectively, in that the oscillation troughs had a lower He/SF6 ratio than
the peaks whereas phase III had a higher He/SF6 than phase IV. We explain
the CO as due to variation in mechanical properties, leading to variation
in response to the pressure wave caused by the heart, in units that are
relatively near to each other. We conclude that there is little or no
postinspiratory mixing between distant lung units, but the dampening of CO
suggests that units that are close to each other can mix if time is
allowed.
