Development and evaluation of a MRI compatible non- rebreathing sequential gas delivery circuit to maintain constant end tidal Carbon dioxide (ETCO2), to be used for Cerebro Vascular Reactivity (CVR) assessment using fMRI and allied techniques.

The circuit will be tested first outside the MR environment and later in the MRI suite.

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Healthy volunteers will be connected to peripheral oxygen saturation monitor and ETCO2 monitor. The ETCO2 will be continuously monitored from a sample at the nose. The baseline blood pressure will be obtained and then at 5 minute intervals.

 The volunteers will breathe a fresh gas flow (FGF) consisting of oxygen and air with this SGD through a mouth piece and a well fitting face mask.

 The FGF of oxygen in air through the unidirectional valve will be adjusted in such a way that the reservoir bag collapses at the end of each inspiration. This will be noted as the minute ventilation. The fresh gas flow will be further reduced and ETCO2 will be noted. The FGF at which the ETCO2 rises will be noted as the alveolar ventilation.

 The inspired CO2 will be altered and ETCO2 will be observed. The optimum FGF required to maintain a constantETCO2 will be assessed. Further to find out if this ETCO2 correlates with the PaCO2, arterial blood gas will be analysed in the first five volunteers.

 Once standardisation of the circuit is completed, fMRI study to test CVR will be performed using the device in the next ten volunteers. Standard EPI fMRI sequences will be adapted for the CVR study and the data analysis methods for CVR will also be developed.

 For the Cerebro- Vascular Reactivity (CVR) study, we need to vary the Pa CO2 level from approximately 35 to 50 mm of Hg in short cycles of 1-2 minutes for a total of 6 cycles. Planning to study such 2 runs, for each volunteer. The total time for MRI study would be approximately 30-40 minutes including anatomic scans.

                There is no risk to the volunteer from breathing 10% carbondioxide (CO2). Carbondioxide has been used safely in many studies previously without any adverse effects from its use in concentrations as high as 40% (1).

 Carbondioxide is a physiological gas.The maximum level of inspired carbondioxide during the study period will be kept well within physiological levels of CO2 (2). We will make sure the inspiratory carbon dioxide level will not exceed 7 %. Therefore the maximum carbon dioxide level that will be obtained in the body will be 50 mm Hg. The inspiratory carbondioxide level will be continuously monitored and adjusted. In the rare event that the subject should breathe 10% carbon dioxide, which is the maximum level of inspiratory carbon dioxide possible from this circuit, it would still result in 68 mm Hg carbon dioxide in the blood, which is the level of permissive hypercapnia (3), i.e. the maximum allowable level of carbon dioxide in the body during disease states such as acute respiratory distress syndrome.

 For the Cerebro- Vascular Reactivity (CVR) study, we need to vary the Pa CO2 level from approximately 35 to 50 mm of Hg in short cycles of 1-2 minutes for a total of 6 cycles. Planning to study such 2 runs, for each volunteer. The total time for MRI study would be approximately 30-40 minutes including anatomic scans.

The carbon dioxide level in the cylinder will be tested before being used on the first volunteer.

 The oxygen levels could go down during the study if there is any malfunction of the parts of the circuit for eg. Sticky valves which can lead to hypoxemia.

 fMRI is a safe study in normal healthy volunteers with no contraindications for MR imaging.