CO2 elimination by high frequency ventilation (4 to 10 Hz) in normal subjects.

We measured the rate of CO2 elimination (VCO2) by oscillatory high frequency ventilation (HFV) in 8 normal subjects and studied the effects of varying frequency, stroke volume, lung volume, and bronchodilation on VCO2. Subjects breath-held while a loudspeaker at the mouth sinusoidally forced low volumes (15 to 150 ml) of air at a high frequency (4 to 10 Hz) into the respiratory system. The CO2 eliminated from the lungs was washed out by a bias flow at the mouth. In each of 6 subjects studied, VCO2 was greater at 8 Hz than at 4 Hz (130 versus 74 ml/min; p less than 0.05) with oscillation volumes (VT) of 100 ml. At a fixed frequency of 10 Hz there was a positive linear correlation (p less than 0.01) between oscillation volume and VCO2. At a lung volume 500 ml below total lung capacity VCO2 ranged from 130 to 215 ml/min at a mean VT of 130 ml and 5 to 60 ml/min at a VT of only 10% of the estimated anatomic dead space. In 3 subjects, after inhalation of isoproterenol, there was a greater VCO2 over the entire vital capacity (p less than 0.01). We concluded that HFV can achieve values of CO2 elimination close to the estimated metabolic CO2 production in normal unintubated subjects over short periods of time.