Figure 20-20 Correlation between left atrial pressure and plasma atrial natriuretic peptide (ANP) in a group of patients undergoing cardiac surgery. A, Significant correlation (r = 0.8, P < .001) between absolute preoperative left atrial pressure and plasma ANP. B, Significant correlation (r = 0.72, P < .002) between the postoperative decrease in left atrial pressure and the postoperative decrease in plasma ANP. ANF, atrial natriuretic factor (synonymous with ANP); Δ, change. (From Shannon RP, Libby E, Elahi D, et al: Impact of acute reduction in chronically elevated left atrial pressure on sodium and water excretion. Ann Thorac Surg 46:430–437, 1988.)