Effects of respiratory frequency on distribution of inspired gas in normal subjects and in patients with chronic obstructive lung disease.

Abstract

The relationship between distribution of inspired gas and respiratory frequency was studied in normal subjects and in patients with mild to advanced obstructive lung disease. The influence of tidal volume on this relationship was also explored, because marked variations of respiratory rate occurring during spontaneous breathing may be associated with changes of the tidal volume. Each subject was studied at two respiratory rates. The gas distribution was evaluated by analysis of nitrogen washout. In 7 patients instructed to breathe with the same tidal volume at both frequencies, the distribution of inspired gas became more uneven, and the efficiency of ventilation decreased with increasing frequency. A group of 4 normal subjects studied under the same experimental conditions showed no definite changes. The tidal volume was found to influence the relationship between gas distribution and respiratory rate. In 5 patients instructed to reduce their tidal volume during rapid breathing, the distribution of inspi...