FIGURE 1.

Schematic of the previously utilized inspiratory resistance circuit (Faull et al., 2016, 2017; Faull and Pattinson, 2017) (presented in A) and the new circuit design (B) that allows remote administrations of inspiratory resistance. In both systems, medical air is supplied to the subject, with a reservoir of 2 L. Excess flow and expiration escapes through a one-way valve (labeled H), close to the mouth to minimize rebreathing. A diving mouthpiece (labeled A) is connected to a bacterial and viral filter (labeled C), and sampling lines connect to a pressure transducer (labeled U) and amplifier (Pressure transducer indicator, PK Morgan Ltd., Kent, United Kingdom) for inspiratory pressure readings, and to a gas analyzer (via sampling line labeled V) (Gas Analyzer; ADInstruments Ltd., Oxford, United Kingdom) for respiratory gases. In (A), resistive inspiratory loading is induced by discontinuing the delivery of medical air (via the flowmeter and emptying of the reservoir bag), forcing the subject to draw air through the resistor (porous glass disc labeled I). In (B), resistive inspiratory loading is automatically achieved via the stimulus computer, whereby signals are sent through the parallel port to control valve 1 (labeled W) to redirect the supply of medical air to vent to the environment, forcing the subject to draw air through the POWERbreathe device (labeled Y). Periodically throughout scanning, small boluses of additional carbon dioxide (CO₂) can be administered through manual control of the CO₂ flowmeter (labeled S) in (A), or automatic control via valve 2 (labeled X) in (B), to raise the partial pressure of end-tidal CO₂ (P_ETCO₂) to match the P_ETCO₂ rise induced by inspiratory loading periods. A final flowmeter (labeled T) is available for manual input of additional oxygen (O₂) to the system. A full list of the labeled component parts can be found in the Supplementary Material.