Tolerance and ventilatory response to inhaled CO2 during exercise and with inspiratory resistive loading

In British coalmines underground workers carry a self-rescuer, a small respirator designed for emergency protection against carbon monoxide. However, the inhaled air is likely to be contaminated by carbon dioxide. The effects of this have been examined.

Gas exchange and ventilation were determined in 80 miners, part-time rescue workers, breathing 2, 3, 4 and 5% CO 2 through an inspiratory resistance simulating a self-rescuer (10 cm H 2 O at a flow rate of 100 1. min −1 ) while walking on a treadmill at 1.25 m s −1 on a 9% grade.

The average minute volume increased linearly with CO 2 concentration, from 31% above the fresh air value at 2% CO 2 to a 73% increase at 5% CO 2 . There were considerable differences in response between individuals, for which there appeared to be no simple explanation. There was some evidence that older men tended to have a lesser increase in ventilation.

A majority of subjects experienced breathlessness and headache during inhalation of 4% and 5% CO 2 . The breathlessness could partly have been caused by the external resistance. It is concluded that under the exercise conditions of this experiment CO 2 is not well tolerated at concentrations above 3%.

It is clear that the design of respirators for use under conditions in which increased CO 2 might be inhaled should allow for the consequential increased ventilation.