Counterlung for a rebreathing apparatus

A method of using a breathing hose configured to duct inhaled and exhaled gas between a user and a rebreather apparatus, the breathing hose including a non-collapsible flexible outer tube and a collapsible inner tube located within the non-collapsible flexible outer tube, the method comprising:

• connecting the breathing hose to a rebreather apparatus, wherein the collapsible inner tube of the breathing hose is configured for fluid communication with a mouthpiece of the rebreather apparatus and the collapsible inner tube is configured to inflate between a first end of the collapsible inner tube affixed about an interior of the non-collapsible flexible outer tube at a first location and a second end of the collapsible inner tube affixed about the interior of the non-collapsible flexible outer tube at a second location and expand to the interior of the non-collapsible flexible outer tube between the first location and the second location to accommodate the exhaled gas of the user passing through the mouthpiece, and to deflate to accommodate the inhaled gas of the user passing through the mouthpiece;
• further connecting the breathing hose to an external air tank to thereby form a closed circuit rebreather apparatus or a semi closed circuit rebreather apparatus;
• recycling unused oxygen and nitrogen in a user's breath as the user breathes air supplied by the closed circuit rebreather apparatus or semi closed circuit rebreather apparatus;
• injecting oxygen from the external air tank into the breathing hose to thereby compensate for metabolic usage of oxygen by the user from the inhaled gas;
• and
• removing carbon dioxide from the exhaled gas.