Ventilatory Responses to Hypercapnic and Hypoxic Conditions in Hyperventilants

"The hypercapnic ventilatory response (HCVR) described by Read in 1967 (Read's rebreathing method) is a clinical way to assess the central and peripheric sensitivity to CO2, using a small bag (4-6 l) to achieve prompt equilibrium between the apparatus compartments and the lungs.~By rebreathing a hyperoxic mixture with an initial composition of 70% O2, 7% CO2 and 23% N2, this equilibrium is assumed to be achieved after 15 seconds of rebreathing, when the relationship between VE and PetCO2 has become linear."

The hypoxic eucapnic ventilatory response (HOVR) is a clinical way to assess the peripheric chemosensitivity to O2, using a small bag (4-6 l) to rebreathe a gas mixture initially composed of 20% O2, 0% CO2 and Δ% N2. Eucapnia is achieved by the activation of a CO2 reabsorption cell during the course of the test.