To focus on the impact of heart rate on systemic hemodynamics.Design and method:
Blood pressure (BP), heart rate (HR), cardiac output (CO), stroke volume index (SVI), systemic vascular resistance (SVR) and SVR index (SVRI) were analyzed in 3 sub studies. Sub study A: 24-hour PWA (MobilOGraph, IEM, Stolberg, DE) was performed in a convenience sample (n = 65) stratified into 3 groups by systolic BP levels (<120, 120–139, > 139 mmHg) and separately stratified by age (<55, > 55 years). Sub study B: Each individual PWA was analyzed for within-individual trends in stroke volume index (SVI); these were compared to the trends obtained from comparing inter-individual means. Sub study C: Laboratory supine hemodynamics and echocardiographic parameters measured in a reference population developed in our laboratory (n = 76) stratified by age and blood pressure.Results:
BP was independent of HR in all 3 sub studies, overall and for each BP or age subgroup. There were very strong inverse correlations between SVI- HR and SVRI- HR in sub studies A and C (p < 0.001 each), and within each BP subgroup in sub study A (see Figure 1). In sub studies A and C, the regression lines for SVRI- HR exhibited a parallel upward-rightward shift in proportion to the increase in mean BP for the group. Inverse SVR-HR curves were similar to the corresponding SVR-cardiac output relationships. In older individuals, strong inverse relationships of (SV-HR or SVI-HR and SVR-HR or SVRI- HR) were also present but when their individual 24-hour hemodynamic studies were analyzed (Sub study B), there was a trend toward flattening of the slope of the SVI- HR relationship with age (p = .052).Conclusions:
Heart rate is a major determinant of systemic hemodynamic counter-regulation between and within individuals. The strong inverse relationships between heart rate and both stroke volume and systemic vascular resistance must be considered in hemodynamic analyses of hypertension and cardiovascular diseases. Rate-volume counter-regulation deserves further study.