Category: Theory

Pulse wave velocity, or PWV, describes how fast the pressure and flow pulse from each heartbeat travels along the arteries. A common way to estimate PWV is to measure the pulse at two locations and compute distance divided by transit time. PWV is widely used because it correlates with arterial stiffness. When arteries are stiffer,…

Impedance matching is an engineering concept that describes how well an energy source is adapted to its load. In electrical systems, a source such as an amplifier has an internal opposition to current flow, its internal impedance, and the load, such as an antenna, a cable, or another circuit, has its own impedance. When these…

When the ventricle ejects, it generates a pressure and flow wave that propagates along the pulmonary or arterial tree. Pressure and flow do not transmit instantaneously through the circulation but travel at finite speed in the form of waves. Spatial variations in vessel diameter, wall stiffness, branching patterns, and distal terminations create a distributed, time-dependent…

In the analysis of cardiovascular waveforms, certain derived variables maintain their value under transformations of the signal. These invariants are of particular interest because they offer robustness to variations in signal acquisition, calibration, and sampling. Invariant features are especially valuable in clinical research and automated signal processing, where measurement conditions often differ across devices, sites,…

Invasive measurement of physiological pressure, particularly arterial or intracardiac pressure, is a central component of critical care and anesthetic monitoring. These measurements provide real-time information about cardiovascular function and are essential for guiding treatment in unstable patients. The accuracy of such measurements depends not only on the placement of the catheter but also on the…

A pressure-volume loop is a graphical representation that illustrates the relationship between pressure and volume in the heart throughout a single cardiac cycle, providing valuable insights into the heart’s mechanical function and assisting in the diagnosis of various cardiac conditions. In a pressure-volume loop, the y-axis represents pressure (in mmHg), while the x-axis represents volume…

Afterload can be effectively understood through the concept of impedance, which provides a comprehensive view of the forces the heart must overcome during ventricular ejection. Impedance encompasses both the resistance to blood flow and the elastic properties of the vascular system, giving a more dynamic understanding of cardiovascular mechanics. Impedance, represented mathematically as Z=R+jX, refers…

Atrial, ventricular, and arterial blood pressure waveforms each provide a unique view into the cardiovascular system’s functioning. The atrial blood pressure waveform reflects the changes in pressure within the atria of the heart. It consists of three key components: the A-wave, which represents atrial contraction; the C-wave, which occurs when the ventricle contracts and pushes…

The relationship between flow and volume is closely tied to the concept of time. Flow refers to how much volume of a fluid moves through a system over a specific period, while volume represents the total quantity of fluid being transported. Essentially, flow rate is the speed at which the volume is moving. Flow rate…

The relationship between pressure and volume in a fluid can be better understood through the concept of compliance, which measures how easily the volume of a fluid changes in response to changes in pressure. Simply put, compliance is a way of describing how flexible or stiff a system is: the higher the compliance, the easier…