Breath Sampling Device

A computer-implemented method of designing a breath sampling device comprising a housing through which a substantial portion of an exhaled breath passed and sorbent material which extends across a cross-section of the housing, the method comprising:

• identifying a plurality of parameters of the device, wherein the plurality of parameters comprises at least two of mass of the sorbent material, size of the sorbent material, thickness of the sorbent material, resistance of the sorbent material, breakthrough volume and flowrate within the device;
• selecting values of the plurality of parameters which maximise a global fitness value by;
• calculating fitness values for multiple parameter values of each of the identified plurality of parameters, wherein the fitness value for each parameter value is indicative of whether a design having the parameter value is suitable;
• combining the calculated fitness values for each of the plurality of parameters to obtain multiple global fitness values;
• and
• selecting a calculated fitness value for each of plurality of parameters which maximises the global fitness value;
• and
• outputting the parameter values of the plurality of parameters which have the selected calculated fitness value,
• wherein each fitness value is calculated by
• defining a fitness function for each of the identified plurality of parameters, wherein the fitness function describes the variation in the fitness value between 0 and 1 as a function of the parameter, where 0 indicates a completely unacceptable design and 1 indicates a completely acceptable design;
• and
• using the defined fitness function to calculate the fitness value for the multiple parameter values of each of identified plurality of parameters.