Hemodynamic Changes and Atrial Function
Normal hemodynamics begin with a pressure gradient. When the pressure in the atria predictably rises, blood rushes into the ventricles, filling their cavities. This process is crucial for preparing the heart for the subsequent powerful ejection.
By the end of atrial systole, baseline pressure values are established in the chambers. In the right ventricle, it reaches up to 5 mm Hg, while in the left ventricle, this figure is slightly higher, reaching up to 10 mm Hg. At the same moment, the blood volume in the ventricles increases to its maximum value. This metric is called the end-diastolic volume (EDV) and is normally equal to 125 mL.
Blood Pressure in the Left Ventricle
On the cardiac cycle graph, left ventricular pressure is typically displayed as a dotted line (Curve III). This curve demonstrates the most significant and sharp pressure fluctuations in the entire cardiovascular system.
Depending on the specific phase of the cycle (systole or diastole), pressure values within the left ventricular cavity can range from minimal values close to 0 mm Hg to a maximum of 120 mm Hg. It is this colossal differential that provides sufficient force to eject blood into the systemic circulation.
Aortic Pressure Dynamics
Aortic blood pressure (Curve I) reflects arterial pressure changes directly at the left ventricular outflow tract. The graph highlights several key elements, each corresponding to a specific mechanical event:
- Anacrotic wave (Anacrota) — the initial phase of steep pressure rise. It forms during the active ejection of the stroke volume from the ventricle.
- Catacrotic wave (Catacrota) — the subsequent phase of pressure drop when ejection ends and blood distributes across the vascular bed.
- Incisura — a characteristic sharp notch on the descending limb of the curve. It strictly corresponds to the moment the aortic valve cusps close.
- Dicrotic wave (Dicrota) — the so-called dicrotic pressure rise. This small secondary pressure peak is caused by the elastic recoil of the blood mass against the freshly closed aortic valve.
Left Atrial Pressure
Unlike the ventricles and aorta, blood pressure in the left atrium (Curve II, often designated by a dashed line) lacks sharp spikes. The graph reflects only low-amplitude pressure oscillations. This is because the atria primarily function as blood reservoirs and conduits, without generating strong resistance or high pressure.