Sampling rate influences measures of blood pressure variability in ambulatory blood pressure monitoring

BACKGROUND: Ambulatory blood pressure monitoring (ABPM) is a valuable tool in the diagnosis and management of hypertension and it is a good predictor of future cardiovascular events. Lack of normal threshold values of ABPM parameters and inconsistency in the sampling rate of recording are hurdles in its wider usage. The aim of the present investigation was to study the influence of sampling rate on ABPM. METHODS: ABPM was performed in 47 healthy subjects and the effect of different sampling rates was studied on ABPM parameters. RESULTS: When data were down-sampled, there was a trend towards decreased concordance and increased dispersion with less frequent recordings. Percent dispersion of MESOR, 24-h average, 24 h standard deviation (SD), awake hours average and sleep hours average of systolic BP (SBP) were around 10% for a sampling interval of 1 h. While average real variability (ARV), morning surge and percent dip in SBP exhibited more than 30% dispersion at a sampling interval of 30 min. CONCLUSION: 24-h average blood pressure (BP) is less sensitive to sampling rate whereas BP variability parameters such as ARV, morning surge and percent dip in SBP are highly sensitive. We suggest that for improving the accuracy of BP variability parameters, a higher sampling rate is desirable around the time of awakening (~2 h before and after the expected time of awakening). At other times, a lower sampling rate may be used for maximizing patient comfort without compromising measurement accuracy.