Historical Vignettes in Heart Failure

“It is astonishing that no one has arrived at the following obvious method by which the amount of blood ejected by the ventricle of the heart with each systole may be determined directly, at least in animals. One measures how much oxygen an animal absorbs from the air in a given time, and how much carbon dioxide it gives off. During the experiment one obtains a sample of arterial and venous blood; in both the oxygen and carbon dioxide content are measured. The difference in oxygen content tells how much oxygen each cubic centimeter of blood takes up in its passage through the lungs. As one knows the total quantity of oxygen absorbed in a given time one can calculate how many cubic centimeters of blood passed to the lungs in this time. Or if one divides by the number of heart beats during this time one can calculate how many cubic centimeters of blood are ejected with each beat of the heart. The corresponding calculation with the quantities of carbon dioxide gives a determination of the same value which controls the first.”1 This passage by Aldolf Fick in 1870 describes the measurement of cardiac output by a formula that includes the oxygen consumption of breathing divided by the difference in oxygen content between the left and right chambers of the heart. The following cardiac output equation—(L/min) = oxygen consumption (mL/min)/arteriovenous oxygen difference in mixed blood (mL/L)—is known to many cardiologists today. This equation is known as the indirect Fick principle, because at the time of its description there were no techniques for measurement of the components. The verification of the Fick principle in humans had to wait until 1930. Arterial puncture allowed the measurement of the oxygen content of the arterial blood. Moreover, the calculation of cardiac output was performed by obtaining mixed venous blood by puncturing the right ventricle and by placing a rubber tube in the right heart through the median basilic vein.2,3 Aldolf Fick was born in Kassel, Germany, in 1829. He attended medical school in Marburg where he met and established a lifelong relationship with Carl Ludwig, a very influential mentor in physiology. After spending 16 years in Zurich with Ludwig, Fick returned to Wurzburg where he created a famous institute of physiology. He retired at age 70 and died in August 1901. In addition to his many scientific papers and his classic textbook, Medical Physics (1856), Fick wrote on other subjects, such as A Compendium of Physiology (written in 1860–1890); Handbook of Anatomy and Physiology of the Sense Organs; and Circulation of Blood (1872). He will be remembered in the field of cardiovascular physiology for the enunciation of the principle that allowed the measurement of cardiac output.