Inspiratory muscle training device with variable loading

DETAILED DESCRIPTION What is claimed is: 1.
An inspiratory muscle training device comprising: a chamber having an opening for the passage of air to be inhaled and exhaled, an inlet permitting air to be inhaled to enter the chamber and to pass to the opening, a one-way exhaust valve permitting exhaled air entering through the opening to escape from the chamber, and means to resist the entry of air to be inhaled into the chamber, wherein the means to resist the entry of air includes means to vary the degree of resistance in dependence upon the volume of air that has passed through the inlet during a single inspiratory cycle.
2.
An inspiratory muscle training device according to claim 1, wherein the means to vary the degree of resistance is adapted to decrease the resistance to the entry of air as the volume of air that has passed through the inlet during a single inspiratory cycle increases.
3.
An inspiratory muscle training device according to claim 1, wherein the means to resist the entry of air into the chamber comprises a valve provided in the opening, the valve being urged by biasing means to a closed position in such a manner that the pressure differential across the valve required to open the same varies in dependence on the volume of air that has passed through the valve during a single inspiratory cycle.
4.
An inspiratory muscle training device according to claim 3, wherein means is provided to vary the initial pressure differential required to open the valve.
5.
An inspiratory muscle training device according to claim 3, wherein the means to vary the pressure differential in dependence upon the volume of air that has passed through the valve comprises a lever acting between the biasing means and the valve, the lever having a fulcrum which is movable in a lengthwise direction of the lever.
6.
An inspiratory muscle training device according to claim 5, wherein the fulcrum is movable in the lengthwise direction of the lever relative to the volume of air that has passed through the valve during a single inspiratory cycle