![]() ![]() ![]() In turn in obstructive diseases, the FRC is increased. In restrictive diseases, the decreased total lung capacity leads to a lower FRC. Clinical significance Ī lowered or elevated FRC is often an indication of some form of respiratory disease. However, beyond −30°, the drop in FRC is considerable. The greatest decrease in FRC occurs when going from 60° to totally supine at 0°. There is no significant change in FRC as position changes from 0° to Trendelenburg of up to −30°. Positioning plays a significant role in altering FRC. It is highest when in an upright position and decreases as one moves from upright to supine/prone or Trendelenburg position. In order to measure RV precisely, one would need to perform a test such as nitrogen washout, helium dilution or body plethysmography. It cannot be estimated through spirometry, since it includes the residual volume. Measurement įRC is the sum of expiratory reserve volume (ERV) and residual volume (RV) and measures approximately 3000 mL in a 70 kg, average-sized male. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles. ![]() Volume of air in the lungs at the end of passive expiration Lung volumesįunctional residual capacity ( FRC) is the volume of air present in the lungs at the end of passive expiration. ![]()
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