“…However, despite the importance of this factor, we found only one study in 16 male ischemic patients measuring the accuracy of a smart phone derived pulse rate versus ECG, where an excellent correlation was found at rest, which was slightly deteriorated during exercise. 42 2. Respiration: Since respiration alters the intrathoracic pressure and causes blood fl ow variations in both the veins the DC component of the PPG waveform shows minor changes with respiration.…”