Short-Term and Long-Term Blood Pressure Variability
Blood pressure (BP) is highly variable within a 24-h period, as well as between days, months, years, and seasons. Available evidence shows that within 24-h (or short-term) BP, variabilities have prognostic significance, i.e., their size is related to card
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Short-Term and Long-Term Blood Pressure Variability Giuseppe Mancia
8.1
Introduction
It has long been known that over the short- and long-term, blood pressure (BP) is characterized by large spontaneous variations [1]. That is, its values vary markedly within the 24-h period due to BP changes between the day and night, but also between hours, minutes, and even adjacent beats. BP also shows large variations over more prolonged time periods because of differences between days, months, and seasons [2] with, in addition, a trend to an age-related, yearly increase [3]. Whether some or all of the features of BP variability mentioned above have clinical significance has been, and still is, the object of intensive research. This chapter will review the most important evidence so far available that short- and long-term BP variability represents a risk for cardiovascular morbidity and mortality and thus merits clinicians’ attention.
8.2
Twenty-Four-Hour or Short-Term Blood Pressure Variability
8.2.1
Overall Twenty-Four-Hour Blood Pressure Variability and Organ Damage
Because BP values within a 24-h period have a normal or near normal distribution [1], the overall magnitude of BP variability during this period can be quantified by the standard deviation or the coefficient of variation (standard deviation normalized for mean BP) of the 24-h mean value [1]. Using this approach, Parati et al. [4]
G. Mancia (&) Centro Interuniversitario di Fisiologia Clinica e Ipertensione, Fondazione Ipertensione e Prevenzione Cardiovascolare, Università Milano-Bicocca, Milan, Italy e-mail: [email protected] A. E. Berbari and G. Mancia (eds.), Special Issues in Hypertension, DOI: 10.1007/978-88-470-2601-8_8, Ó Springer-Verlag Italia 2012
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showed that for each quintile of 24-h mean intra-arterial BP, hypertensive patients in whom systolic and diastolic BP variability was above the median value had a greater score for organ damage [calculated from electrocardiogram, chest X-ray, ocular fundus, and patient history] than hypertensive patients with a variability below the median value (Fig. 8.1, upper panels). Similarly, in a much larger study in which 24-h BP was monitored noninvasively, Mancia et al. [5] found that for each quintile of 24-h mean BP, hypertensive patients with a greater than median BP variability had a greater carotid artery wall thickness than that of patients with a lower than median BP variability (Fig. 8.1, lower panels). Although their crosssectional nature did not allow for a cause and effect relationship, these observations raised the possibility that 24-h BP variability could be a factor that adversely affects the appearance and progression of organ damage with recognized prognostic significance [6–8]. This finding has received support from longitudinal studies. In a 7.5 year follow-up of hypertensive patients, Frattola et al. [9] observed a relationship between initial 24-h BP variability (intra-arterial monitoring) and the subsequent progression, measured by means of echocardiography, of
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