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Through both backward (Pb) and forward (Pf) wave effects, a lower heart rate (HR) associates with increased central (PPc), beyond brachial pulse pressure (PP). However, the relative contribution to Pf of aortic flow (Q) versus re-reflection of Pb, has not been determined. Using central pressure, aortic velocity and diameter measurements in the outflow tract (echocardiography), we constructed central pressure waveforms that account for the relative contribution of Q versus re-reflection to Pf. We thus evaluated the mechanisms of HR-PPc relations in a community sample (n=824) and the impact of age thereon. Inverse HR-PPc ( P <0.0001), but not HR-brachial PP ( P =0.064) relations were noted. The slope of HR-PPc relation was increased in older adults ( P <0.005). HR was inversely associated with ventricular filling time, ejection duration, stroke volume, and peak Pf ( P <0.001 to P <0.0001). However, an increased Q and hence pressures generated by the product of aortic characteristic impedance and Q did not account for Pf effects. Age-dependent HR-PPc and Pf relations were both accounted for by enhanced Pb ( P <0.0001) with an increased Pf mediated by increments in wave re-reflection ( P <0.0001). The lack of impact of ejection duration on PPc was explained by an increased time to peak Pb ( P <0.0001). In conclusion, increases in PPc and Pf at a decreased HR are accounted for by an enhanced Pb rather than by a prolonged ejection or filling duration and hence flow (Q). These effects at a young-to-middle age are of little clinical significance, but at an older age, are of clinical importance.

The relative contribution of loading conditions at different ages across the full adult lifespan to decreases in left ventricular (LV) diastolic function is unclear. Using central arterial pressure and aortic velocity and diameter measurements in the outflow tract, we determined the contribution of systemic vascular resistance, compression wave pressures (characteristic impedance [Zc]×aortic flow [Q], [PQ×Zc]) and backward wave pressures (Pb) to LV diastolic function (echocardiography) in a community sample across the full adult lifespan (n=605). Starting from early adulthood, stepwise age-related increases in LV filling pressures (E/e') and decreases in myocardial relaxation (e') were noted (P<0.0001). Before 50 years of age, before when PQ×Zc positively correlates with age, Pb, but not systemic vascular resistance was independently associated with LV mass index (P<0.002), E/e' (P<0.002), and e' (P<0.05). Moreover, in those over 50 years of age, when PQ×Zc positively correlates with age, again Pb, but neither PQxZc nor systemic vascular resistance was independently associated with LV mass index (P<0.01), E/e' (P<0.001), and e' (P<0.001). The contribution of Pb to age-related decreases in LV diastolic function was as strong in those younger as compared with older than 50 years of age and poorly indexed by brachial BP. In conclusion, a striking age-related deterioration in LV diastolic function begins at an early adult age and Pb is the dominant hemodynamic factor that accounts for this relationship. Age-related increases in Pb in young adults contribute as much to functional abnormalities ultimately responsible for LV diastolic dysfunction in hypertension as at an older age, effects poorly indexed by brachial BP. [ABSTRACT FROM AUTHOR]