Pressure Dominated PTT Calculation and Its Relation with BP

Pulse transit time (PTT) which can be obtained from the peaks of r-wave of Electrocardiogram (ECG) and pulse wave, is promising for non-invasive continuous blood pressure measurement. However, there are different kinds of waves can be employed in this method, namely pressure pulse wave (PPW), photoplethysmography (PPG) and modulated magnetic signature of blood (MMSB). It is critical to clarify the relationship between those three kinds of pulse waves for practical applications. In this paper, the relationship between blood pressure (BP) and three different types of pulse wave is investigated experimentally. It is found that the MMSB and the PPW measured at the same position have a fixed phase difference. This means that we have to established different models for MMSB and PPW to obtain accurate blood pressure. We calculate blood pressure based on PPG and PPW, respectively. We find that both PPG and PPW shows high dependency on systolic blood pressure, while PPW appears to be more reasonably correlated with diastolic blood pressure (DBP). This implies that PPG may be not a good signature for blood pressure measurement. A model on the relationship between those three pulse waves is proposed. The different relationships between three pulse waves and BP are explained based on that model.