The analysis of pulse oximetry as a method of rapid diagnosis of the state of the body in real time was performed. Data are presented that the high rate of pulse wave propagation through the arteries in patients with COVID-19 may indicate a high risk of death. It is noted that modern device designs and pulse wave signal processing methods have a number of disadvantages. This leads to an unreliable interpretation of the data. Using a charge-coupled device increases the accuracy of measuring the position of maxima and minima on the time scale. This makes it possible to determine the moment of closure of the aortic valves of the left ventricle more accurately. The registered pulse waves of various people are presented, as well as the results of the study of the time intervals of the rising and falling fronts.