Figure 1b:

Effect of changing arterial carbon dioxide on myocardial BOLD MR signal intensities in healthy humans. (a) Representative short-axis myocardial BOLD MR images collected from a volunteer at baseline (PetCO₂ = 37 mm Hg) and hypercapnia (PetCO₂ = 47 mm Hg). BOLD signal intensity increased during hypercapnia. For ease of visualization, color overlays of the left ventricle (with color bar showing BOLD signal intensity in arbitrary units [a.u.]) that correspond to the gray-scale images are shown directly below. (b) Box and whisker plot shows the dependence of percentage of hyperemic BOLD response on PetCO_2, and standard dose of adenosine. Percentage of hyperemic response increased at higher PetCO₂ values; response at +10 mm Hg (Plus10) did not differ from that of standard adenosine infusion. Percentage of hyperemic BOLD response for adenosine is from reported values in the literature (14). * = significant difference relative to resting (Rest) (P < .05). Top and bottom of boxes indicate upper limit, +1 standard deviation, and lower limit, −1 standard deviation, respectively; error bars (whiskers) are maximum and minimum of data. The mean and median are represented as a point and a band within the box, respectively. For adenosine, the whiskers represent the boundaries of first and 99th percentile of the data.