Correlation of 24-Hour Blood Pressure and Heart Rate Variability to Renal Function Parameters in Hypertensive Patients. The Effect of Smoking

Intrarenal hemodynamics depend on blood pressure (BP), heart rate (HR), and smoking. Although BP levels have been associated with kidney function, the effect of HR levels, BP, and HR variability on renal function are less well clarified. This cross-sectional study sought to determine the association of 24-hour BP and HR variability with kidney function in hypertensive patients, stratified by smoking. The study comprised 9600 nondiabetic, never-treated hypertensive individuals without evident renal impairment examined from 1985 to 2014 (aged 53.3±13.4 years, 55.3% males). The 24-hour systolic BP (SBP) and HR variability were estimated via their coefficient of variation (CV=standard deviation×100/mean value) derived from ambulatory recording. The CVSBP-to-CVHR ratio (CVR) was used as a marker of the interplay between 24-hour SBP and HR variability. Renal function was estimated via 24-hour urine creatinine clearance (CrCl), estimated glomerular filtration rate (eGFR), albumin-to-creatinine ratio (ACR), and 24-hour urine α1-microglobulin. After adjustment for age, sex, and smoking, CVSBP was found to be weakly correlated to eGFR (r=−0.017, P=.1) and somewhat more strongly to CrCl, ACR, and α1-microglobulin (r=−0.032, 0.072, and 0.065; P=.002, <.001 and <.001, respectively). CVHR was much better related to renal function, with stronger adjusted correlations to CrCl, eGFR, ACR, and α1-microglobulin (r=0.185, 0.134, −0.306, −0.247; all P<.001, respectively). CVR also showed equally good adjusted correlations (r=−0.175, −0.125, 0.336, 0.262; all P<.001, respectively). Most adjusted correlations for CVHR and CVR were even better in smokers (r=0.213, 0.158, −0.332, −0.272 and −0.183, −0.118, 0.351, 0.275, respectively; all P<.001). CVHR and CVR emerge as better related to kidney function than CVSBP, especially in smokers. The correlation of CVHR and CVSBP to renal function is inverse to each other. ACR and α1-microglobulin are better related to variability indices than CrCl and eGFR. However, causal relations cannot be proved.