A model-based study of the influence of vaso-active drugs on pulse delays measured from the electrocardiogram

The use of ECG-based pulse delays as a surrogate of the arterial blood pressure has long been questioned, especially when the subject is given vaso-active drugs altering the vascular resistance. When measured from the ECG, pulse delays include two components: the vascular pulse transit time and cardiac pre-ejection period (PEP). This paper analyses the relationships of both vascular and cardiac components with the blood pressure. As there is no known equation ruling PEP, a lumped model of arterial circulation is used to study the dependencies between blood pressure and PEP. When the peripheral resistance varies PEP shows a direct correlation with the blood pressure, opposite to the inverse pulse transit time dependency. Real-life signal examples from intensive care unit patients are presented and discussed.