Fig. 7

The phases of atrial function demonstrated using pressure volume loop—adapted from Negishi et al. The phases of the cardiac cycle have been highlighted on image A. Diastole has been divided into: E—early filling, D—diastasis and A—atrial contraction. The reservoir phase (red trace—1) occurs during ventricular systole: pulmonary venous blood enters the LA resulting in LA volume increasing from minimum to maximum. In normal circumstances, the associated increase in LA pressure is small, owing to atrial compliance and distensibility. Immediately after mitral valve opening, there is reduction in LA volume and pressure as blood enters the LV during the conduit phase (green trace—2). At a low enough HR there is a period between early and late diastolic filling where LA and LV pressures are close to equal with consequently minimal transmitral flow (dark blue trace—3). Finally, the atrium contracts, marking the onset of the pump phase (grey trace—4). This is accompanied by a rapid increase in LA pressure and blood is ejected from the LA into the LV with some retrograde flow into the PV’s (the A-reversal wave). Immediately after contraction, the LA recoils and relaxation commences (light blue trace—5), leading to the start of the reservoir phase [29]