The role of the left ventricle in the shape of the arterial pressure wave as affected by age

The role of the heart and its working conditions on the shape of aortic pressure curves was studied by analysis of pressure signals produced at the input of an artificial ejection circuit by 25 isolated working hearts of rats aged 4–22 months. The hearts were paced at five successive heart rates and three levels were imposed for the left auricular perfusion pressure (LAPP). With ageing of the myocardium, increased LAPP and low heart rates, there was an alteration of the pressure wave visual aspect towards a tele-systolic maximum. This modification was regularly associated with significant differences in the harmonic content of the pressure signal. More precisely, there was a bigger increase in the first harmonic amplitude than in the second and third harmonic amplitudes. Because of the physical linearity of the artificial ejection circuit and the controlled working conditions for the heart, it is possible to explain these changes in the pressure wave shape. Lowering of the heart rate is associated with an involvement of a more left part of the circuit impedance curve. Ageing of the myocardium and increased LAPP change the pressure wave shape because they were associated with an increase in left ventricular ejection time.