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Blood pressure definition acc to harrison

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I now have comprehensive content from Harrison's 22nd edition. Here is the full answer:

Blood Pressure - Definition According to Harrison's Principles of Internal Medicine (22nd Ed., 2025)

Physiological Definition

According to Harrison's, at the most basic level:
"Arterial blood pressure (BP) is controlled by cardiac output and peripheral resistance."
More specifically, arterial pressure is largely thought to be controlled by a renal-volume-endocrine pressure control system, in which blood volume and total peripheral resistance are manipulated to adjust arterial BP.
The two fundamental determinants are:
  • Cardiac output - influenced by stroke volume (related to myocardial contraction and intravascular compartment size) and heart rate
  • Peripheral vascular resistance - determined by functional and anatomic changes in small arteries and arterioles
(Harrison's Principles of Internal Medicine 22E, Chapter 288 - Blood Pressure Physiology and Pathophysiology)

BP Regulation Mechanisms (Harrison's)

Harrison's explains that multiple systems interplay to keep these two parameters in balance:
  • Sodium handling by the kidney (primary long-term regulator)
  • Vasoconstrictor systems: sympathetic nervous system, renin-angiotensin-aldosterone system (RAAS)
  • Vasodilator systems: bradykinin, nitric oxide, natriuretic peptides
  • Endothelial factors: nitric oxide, endothelin, arachidonic acid metabolites, reactive oxygen species
The Guyton hypothesis - that the kidney's capacity to excrete sodium ultimately dictates long-term BP levels - has been profoundly influential, though it has been challenged and alternatives proposed.

ACC/AHA Blood Pressure Classification (per Harrison's Table 288-1)

BP CategorySystolic BP (mmHg)Diastolic BP (mmHg)
Normal BP<120and<80
Elevated BP120-129and<80
Stage 1 Hypertension130-139or80-89
Stage 2 Hypertension≥140or≥90

Measurement Definition

Harrison's states that BP is measured using an average of two or more readings obtained at two or more visits for proper classification of an individual's usual BP level. The key clinical goal is to estimate:
  1. An individual's average level of BP
  2. Their risk of cardiovascular disease (CVD)
  3. The need for hypertension prevention or treatment
(Harrison's Principles of Internal Medicine 22E, Chapter 288 - Blood Pressure Measurement)
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