Functional residual capacity(FRC)-helium(He) rebreathing
A disinfected mouthpiece was attached to the disinfected pneumotach,
O2 gas cylinder was opened and rebreathing bag (RB)
was connected. With starting the measurement program, the
rebreathing bag was emptied, flushed with O2 and a zero
adjustment of the He gas analyzer was performed. Then the
RB bag was filled with helium and oxygen according to the
preset filling volume and its contents were analyzed. The
patient was asked to approach the mouthpiece and close his
nose with the noseclip. He should breathe quite normally.
From normal breathing, the patient was asked to slowly
breathe out as deeply as possible and then continue to breathe
normally. The patient breathed the gas mixture consisting of
about 9% helium and 32% oxygen contained in the RB bag.
In order to keep the oxygen content in the RB constant, about
250–300 ml oxygen per minute was added. The inhaled He gas
mixture was spread out evenly into the lung. The trend of the
He wash-in curve should be observed and the He value was
displayed in the status line. The following were measured: total
lung capacity (TLC), residual volume (RV) and FRC.