Aim: To study the determinants (or mechanisms) of isolated systolic hypertension in the elderly.
Methods: Pulsatile blood pressure and flow (multisensor catheter) were measured in the ascending aorta and impedance spectra were calculated in 18 subjects undergoing cardiac catheterization. Nine subjects (mean +/- SEM age 58 +/- 1.4 years) had increased aortic systolic (166 +/- 2.3 mmHg, P < 0.001), mean (116 +/- 2.1 mmHg, P < 0.02) and pulse blood pressure (83 +/- 2.1 mmHg, P < 0.001) and normal diastolic blood pressure (84 +/- 2.0 mmHg, NS) and constituted the isolated systolic hypertension group. The other nine age-matched (58 +/- 1.1 years) subjects had normal aortic systolic and diastolic blood pressure and constituted the normotensive control group.
Results: Both static (peripheral vascular resistance) and dynamic (characteristic impedance and wave reflection) components of left ventricular external load (aortic input impedance) were elevated in the isolated systolic hypertensives compared to the normotensive subjects; peripheral vascular resistance was 44% higher (P < 0.001), characteristic impedance (index of aortic stiffness) was 107% higher (P < 0.001), the first harmonic of impedance moduli (index of wave reflection) was 57% higher (P < 0.004) and the first impedance moduli minimum was shifted to a higher frequency (from 3.4 +/- 0.2 Hz to 4.2 +/- 0.13 Hz, P < 0.008) in the group with isolated systolic hypertension.
Conclusions: The changes in impedance spectra in the isolated systolic hypertensives indicate that the cross-sectional area of the peripheral vascular bed was reduced and that the aorta and large arteries were stiffer, producing an increased pulse wave velocity and an early return of pulse wave reflection in systole. The marked increase in arterial stiffness in isolated systolic hypertension offset the increase in diastolic blood pressure that would have been expected from an increase in peripheral vascular resistance alone, and early return of the reflected pressure wave augmented aortic pressure throughout systole and accounted for the large increase observed in systolic and pulse pressure in the aorta.