Relationships of heart rate and heart rate variability with conventional and ambulatory blood pressure in the population

Background Most studies on relationships between blood pressure and autonomic nervous function, assessed by power spectral analysis of heart rate variability, have used conventional or clinic blood pressure measurements in selected subjects, which may have influenced the results, Objective We aimed to investigate, in a population-based approach, associations of heart rate and heart rate variability, assessed in basal resting conditions and in response to standing, with conventional blood pressure measured by an investigator, and with ambulatory blood pressure monitored outside the laboratory, Methods RR interval and respiration were registered in 614 men and women, ages 25-89 years. After exclusion of subjects with myocardial infarction or diabetes and elimination of unsatisfactory recordings, 549 subjects remained for analyses at supine rest and 515 of these to assess the orthostatic responses, Hypertension was present in 39% of the subjects, The low-frequency (LF) and high-frequency (HF) components of heart rate variability were quantified by use of autoregressive modelling and expressed in absolute and normalized units. Results At supine rest, indices of heart rate variability were not independently related to 24 h systolic blood pressure, whereas some indices showed weak associations with diastolic 24 h pressure; the relationships were in general stronger for conventional blood pressure. For example, partial correlation coefficients of the relationships of the LF:HF ratio with systolic pressure were 0.12 (P less than or equal to 0.01) for conventional pressure and 0.02 (NS) for 24 h pressure; these coefficients amounted to 0.20 (P less than or equal to 0.001) and 0,11 (P less than or equal to 0.01) for the diastolic pressures. The decrease of HF power and the increase of the LF:HF ratio on standing were significantly blunted at higher broad pressure, both when measured conventionally and by ambulatory monitoring (P less than or equal to 0.001 for the LF:HF ratio). Conclusions Relationships between autonomic nervous function at rest, assessed by use of power spectral analysis of heart rate variability, and conventional blood pressure, can at least partly be ascribed to the influence of the measurement conditions, whereas the orthostatic autonomic responses appear to be influenced by blood pressure per se. I Hypertens 19:389- 397 (C) 2001 Lippincott Williams & Wilkins.