Data Acquired to Demonstrate a Low-Cost, Microcontroller-Based Gas Delivery System for Respiratory Stimuli in MRI Studies

Two respiratory stimuli were implemented: a hypercapnic stimulus and a hyperoxic stimulus. The hypercapnic stimulus consisted of three 60 s blocks of hypercapnia (5% CO2, 21% O2, 74% N2) interleaved with four 60 s blocks of normocapnia (medical air: 21% O2, 79% N2) to give a total duration of 7 minutes. The hyperoxia stimulus had two repeats of the following block: 120 s normocapnia, 30 s hyperoxia (100% O2) and 90 s with both normoxic and hyperoxic gases flowing simultaneously (equivalent to 60.5% O2, 39.5% N2). This block was repeated twice and followed by a further 120 s normocapnic period to give a total duration of 10 minutes. The initial 30 s 100% oxygen block was implemented to produce a large oxygen gradient between the alveolar gas and the blood and results in a rapid increase in end tidal partial pressure of oxygen (PetO2). The switch to 60.5% oxygen then rapidly reaches a plateau for the remainder of the block. Each of the medical flow meters were set to 15 lpm which resulted in a total flow of 30 lpm during the plateau of the hyperoxia stimulus. Expired gases were measured (O2 and CO2) using a respiratory gas analyser (ML206, AD Instruments, Dunedin, New Zealand).本实验采用两种呼吸刺激范式：高碳酸刺激（hypercapnic stimulus）与高氧刺激（hyperoxic stimulus）。高碳酸刺激范式包含三段时长60秒的高碳酸血症环境（hypercapnia，气体成分为5%二氧化碳、21%氧气、74%氮气），并穿插四段时长60秒的正常碳酸血症环境（normocapnia，医用空气：21%氧气、79%氮气），总时长为7分钟。高氧刺激范式则重复两次下述流程：120秒正常碳酸血症环境、30秒高氧环境（hyperoxia，100%氧气），以及90秒同时通入常氧与高氧气体的环境（气体成分为60.5%氧气、39.5%氮气）。该流程重复两次后，再追加一段120秒的正常碳酸血症环境，总时长为10分钟。初始的30秒100%氧气阶段旨在构建肺泡气与血液间的较大氧梯度，从而使呼气末氧分压（end tidal partial pressure of oxygen，简称PetO2）快速升高。随后切换至60.5%氧气浓度，该混合气体阶段的剩余时长内将快速趋于平台期。每台医用流量计均设置为15升/分钟，因此高氧刺激范式平台期的总气流量为30升/分钟。 呼出气中的氧气与二氧化碳浓度采用呼吸气体分析仪（ML206，AD Instruments，新西兰达尼丁）进行检测。