Cardiac Cycle Pressure and Volume Timing Map

Cardiac Cycle Pressure and Volume Timing Map is the integrated framework that aligns the continuously changing intraventricular pressure and volume values with each named phase of the cardiac cycle, providing a unified temporal reference in which the pressure trajectory, the volume trajectory, and the valvular and auscultatory events of a single heartbeat can be located relative to one another along a common timeline.

Purpose of the Integrated Map

Combining Two Parallel Trajectories

Pressure and volume within the ventricle each follow their own characteristic trajectory across a single cardiac cycle, rising and falling at different rates during different phases. The timing map exists to align these two trajectories against a shared timeline, allowing the precise moment at which pressure and volume interact to produce a given phase transition, such as a valve opening or closing, to be identified.

Anchoring Valvular Events to the Combined Timeline

Because each valve opens or closes at the specific instant when pressure on one side of it exceeds or falls below pressure on the other side, the timing map uses the intersection points of the pressure trajectories, considered alongside the corresponding volume trajectory, to precisely locate each valvular event within the overall sequence of the cycle.

Sequential Mapping of Phases

Diastolic Filling Phases

Rapid filling begins at atrioventricular valve opening, when ventricular pressure falls below atrial pressure while ventricular volume is at its minimum, and is characterized by a steep rise in volume accompanying a modest rise in pressure. Diastasis follows, marked by near-plateau behavior in both variables as the pressure gradient diminishes. Atrial systole concludes the diastolic sequence, contributing a final small rise in both pressure and volume.

Isovolumetric Contraction

Isovolumetric contraction begins at atrioventricular valve closure, the instant ventricular pressure first exceeds atrial pressure, and is mapped on the timing framework as an interval of steeply rising pressure occurring at a fixed, unchanging volume, continuing until ventricular pressure reaches the level of arterial pressure.

Ejection Phases

Ejection begins at semilunar valve opening, the instant ventricular pressure exceeds arterial pressure, and is mapped as an interval during which volume falls, first steeply during rapid ejection and then more gradually during reduced ejection, while pressure rises briefly to a peak before beginning to decline.

Isovolumetric Relaxation

Isovolumetric relaxation begins at semilunar valve closure, the instant ventricular pressure falls below arterial pressure, and is mapped as an interval of steeply falling pressure occurring at a fixed, unchanging volume corresponding to the end systolic value, continuing until ventricular pressure falls below atrial pressure.

Quantitative Relationships Embedded in the Map

Stroke Volume and Ejection Timing

The interval between semilunar valve opening and closure, as located on the timing map, corresponds precisely to the period during which the volume difference constituting stroke volume is delivered into the arterial circulation.

Isovolumetric Interval Durations

The timing map allows the combined duration of both isovolumetric intervals, during which pressure changes without any corresponding volume change, to be identified and distinguished from the volume-changing intervals of filling and ejection.

Integration with Auscultatory and Electrical Landmarks

Heart Sound Placement

The timing map situates the first heart sound at the pressure crossover marking atrioventricular valve closure and the second heart sound at the pressure crossover marking semilunar valve closure, anchoring both audible events to specific, identifiable points along the combined pressure and volume trajectories.

Electrocardiographic Alignment

Because the electrical events of the QRS complex and T wave precede, respectively, the onset of isovolumetric contraction and isovolumetric relaxation by a brief coupling delay, the timing map can be further aligned with the electrocardiogram, situating each pressure and volume transition relative to its corresponding electrical trigger.

Functional Significance of the Representation

Unified Reference for Cardiac Cycle Analysis

The cardiac cycle pressure and volume timing map functions as a unified reference framework that consolidates the pressure trajectory, the volume trajectory, and the associated valvular and auscultatory events into a single coherent timeline, eliminating the need to consider each variable in isolation.

Foundation for Deriving Comprehensive Hemodynamic Indices

Because this map explicitly locates every phase transition relative to both pressure and volume, it provides the necessary foundation for deriving comprehensive hemodynamic indices, such as stroke volume, ejection fraction, and the durations of isovolumetric and volume-changing intervals, from a single integrated representation of the cardiac cycle.