Fig. 1

a CO levels in W1 cotinine negative subjects. Exhaled carbon monoxide levels (parts per millions; ppm) given on the x-axis. The box plot with bars indicating mean or standard deviation with individual data distribution outside of the 2nd SD indicated by filled circles is given above the histogram. The count of subjects with a particular CO level is given on y-axis. Each of these subjects in W1 had a negative cotinine level (defined as < 2 ng/mL), suggesting no nicotine use within the past 48 h (n = 329). b CO levels in W3 cotinine negative subjects. Exhaled carbon monoxide levels (parts per million; ppm) given on the x-axis. The box plot with bars indicating mean or standard deviation with individual data distribution outside of the 2nd SD indicated by filled circles is given above the histogram. The count of subjects with a particular CO level is given on y-axis. Each of these subjects in W3 had a negative cotinine level (defined as < 2 ng/mL), suggesting no nicotine use within the past 48 h (n = 257). c CO levels in W1 cotinine positive subjects. Exhaled carbon monoxide levels (parts per million; ppm) given on the x-axis. The box plot with bars indicating mean or standard deviation with individual data distribution outside of the 2nd SD indicated by filled circles is given above the histogram. The count of subjects with a particular CO level is given on y-axis. Each of these subjects in W1 had a positive cotinine level (defined as > 2 ng/mL), suggesting nicotine use within the past 48 h (n = 38). d CO levels in W3 cotinine positive subjects. Exhaled carbon monoxide levels (parts per million; ppm) given on the x-axis. The box plot with bars indicating mean or standard deviation with individual data distribution outside of the 2nd SD indicated by filled circles is given above the histogram. The count of subjects with a particular CO level is given on y-axis. Each of these subjects in W3 had a positive cotinine level (defined as > 2 ng/mL), suggesting nicotine use within the past 48 h (n = 75)