A blunted nocturnal blood pressure (BP) fall is a marker of worse cardiovascular outcomes, and autonomic imbalance may be involved. The objective was to evaluate the associations between the nocturnal BP fall and heart rate variability (HRV) parameters in resistant hypertension.
In a cross-sectional analysis, 424 resistant hypertensive patients performed 24-h ambulatory BP and Holter monitoring, and 221 patients also performed polysomnography. Time-domain HRV parameters evaluated were the standard deviation of all normal RR intervals (SDNN), the standard deviation of the averaged normal RR intervals for all 5-min segments (SDANN), the root mean square of differences between adjacent R-R intervals (rMSSD) and the percentage of adjacent R-R intervals that varied by more than 50 ms (pNN50). Multivariate linear and logistic regressions assessed associations between the nocturnal BP fall and HRV parameters.
Two hundred and sixty-six patients (63%) presented a nondipping pattern. These patients had lower SDNN and SDANN than normal dipping patients, but equal rMSSD and pNN50. On multivariate analysis, after adjustments for several confounders, a reduced SDNN (<70 ms) implied a 2.9 to 3.4-fold [95% confidence interval (CI) 1.2–8.5] and a reduced SDANN (<50 ms) a 3.7 to 4.2-fold (95% CI 1.5–11.4) higher odds of having a nondipping pattern. Further adjustment for the presence and severity of obstructive sleep apnoea did not change the results.
Reduced SDNN and SDANN, two HRV parameters that mainly reflect sympathetic overactivity, were independently associated with a blunted nocturnal BP fall in resistant hypertension. These relationships offer insight into physiopathological mechanisms linking the circadian BP variability to cardiovascular outcomes.
Internal Medicine Department, University Hospital Clementino Fraga Filho, School of Medicine, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Correspondence to Gil Fernando Salles, Rua Croton, 72, Jacarepagua, Rio de Janeiro 22750-240, Brazil. Tel: +55 21 2447 3577; fax: +55 21 2562 2514; e-mail: firstname.lastname@example.org
Abbreviations: ABPM, ambulatory blood pressure monitoring; AHI, apnea–hypopnea index; BP, blood pressure; CHD, coronary heart disease; CI, confidence interval; HRV, heart rate variability; LVMI, left ventricular mass index; OSA, obstructive sleep apnea; pNN50, the percentage of adjacent R-R intervals that varied by >50 ms; PWV, pulse wave velocity; rMSSD, the root mean square of differences between adjacent R-R intervals; SDANN, the standard deviation of the averaged normal RR intervals for all 5-min segments; SDNN, the standard deviation of all normal RR intervals; SNS, sympathetic nervous system
Received 25 July, 2013
Accepted 6 November, 2013