Measurement of Blood Pressure – Summary
Methods of blood pressure assessment have come a long way from the days when Hales (1773) developed the invasive glass tube gauges for measuring blood pressure directly. Most clinics in medical settings rely on the auscultatory method for measuring blood pressure because it is noninvasive, inexpensive, and accurate. Although sophisticated automated devices have been developed and validated using either auscultatory or oscillometric methods, they are typically more useful in research laboratories or in hospitals where frequent, regular measures of blood pressure are needed.
Likewise, continuous measures of blood pressure using the vascular unloading principle or measures of hemodynamic functioning using impedance cardiography are more likely to be used in research laboratories rather than clinic settings. In both cases, although the methods represent reliable ways for determining relative change in important cardiovascular parameters, their ability to derive accurate absolute measures of those parameters is lacking.
It is well known that clinic measures of blood pressure do not often correspond well with measures of blood pressure obtained outside the clinic. To obtain accurate measures of blood pressure during daily life, either home blood pressure recording or ambulatory methods of blood pressure assessment must be employed. Both home and ambulatory methods typically yield values lower than those observed in the clinic.
Furthermore, because they provide a more comprehensive evaluation of a person’s daily blood pressure profile, they are better predictors of hypertensive target organ pathology and risk for subsequent cardiovascular disease than clinic-derived measures.
Two clusters of patients exhibit considerable disagreement between blood pressure values obtained in the clinic and those obtained during daily life: isolated clinic hypertensives and isolated clinic normotensives. Isolated clinic hypertensives, who exhibit hypertensive blood pressure readings in the clinic but normal readings during daily life, typically have a lesser risk for target organ pathology and subsequent cardiovascular disease than essential hypertensive patients.
Conversely, isolated clinic normotensives, who exhibit elevated blood pressures in their daily life but normal values in the clinic, typically exhibit an elevated risk for target organ pathology. In other words, isolated clinic hypertensives tend to resemble normotensives, and isolated clinic normotensives tend to resemble untreated hypertensive patients. Because these two clusters of patients represent a substantial portion of patients seen in medical clinics, it could be argued that an accurate portrayal of blood pressure status necessarily involves obtaining multiple measures of blood pressure obtained both in the clinic and during daily life. With this type of assessment strategy, more reliable estimates of our constantly fluctuating blood pressures can be assuredly obtained.