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Abstract

Introduction: Hypertension is a complex spectrum of diseases with differing morbidities. Defining risk profiles in individuals and selecting and monitoring treatment response relies heavily on epidemiologic studies with uncertain application to the individual. Hypertension continues to be defined without reference to a hemodynamic basis for changes in pressure. If pressure is always the product of cardiac performance and vascular resistance, then it cannot be understood apart from a hemodynamic cause. Methods: Over 52 months, hemodynamic data was collected and graphically analysed in 501(253M,248F) elderly male and female subjects presenting for elective and urgent major surgery. Guyton’s equation relating systemic pressure to cardiac performance was simplified by removal of HR, and the alternative equation used to define cardiac and vascular components of systemic pressure. Using this “Pressure Field method”, hemodynamic data at 20–60 second intervals was collected and graphed for periods from 2 hours to 28 days. All systemic pressure measurements were referenced to a database of subjects of similar age, gender and body surface area. Results: The systemic pressure gradient (MAP-CVP) in older male and female subjects presenting for elective and urgent major surgery was at least 80 mm Hg, and increased after 55 yrs to 110 mm Hg in females and 100 mm Hg in male subjects. Hypertension was present when the age and gender specific gradient exceeded values for age-matched normal subjects. The pathophysiology of hypertension using the Pressure Field method could be subdivided into 5 hemodynamic subgroups, consisting of an increased age and gender specific Systemic Pressure gradient and one of the following: (1) decreased R, increased SV (2) increased SV, constant R (3) increased SV, increased R (4) increased R, constant SV and (5) decreased SV, increased R. The resistance value (R) was defined by the equation “(MAP-CVP)=SV x R”. Conclusions: Diagnosis and therapy of hypertension depends on defining the physiology in each individual and using normal controls as the reference point for pharmacological management of the circulation. The pressure field model differentiates cardiogenic and vasogenic hypertension and mixed patterns and permits individualization of therapy. This contrasts with the current approach which is based on noninvasive measurement of pressure without any hemodynamic measurements.