Hypertension Pathology and Management

• Hypertension:

  • Hypertension (HTN) is defined as a persistently elevated blood pressure (BP) associated with the potential to cause long term damage to organs including blood vessels – most notably arteries
  • In this module we will use the definition of hypertension as provided by the European Society of Cardiology (ESC) 2024 who define HTN as a systolic and diastolic BP equal to or greater than 140/90 mmHg
  • ESC 2024 also recommend a BP of < 120/70 mmHg
• Hypertension:

  • As a pathological entity HTN is heavily inter-twined with other disease processes such as obesity, type 2 diabetes mellitus (T2DM) atheroma formation, ACS, heart and renal failure just to highlight the main ones
• • The graph definitely seems to suggest that there is a close association between hypertension and increasing age
  • The number of people with high blood pressure/hypertension increases in each subsequent age group
  • This relationship appears really close when we consider those over 75 years of age of which between 50 - 60% have high BP
  • However a relationship does not necessarily mean causality – and should not be confused as such

  
• • From the table you can see that each life-style intervention reduces Systolic BP by approximately 5 mmHg, lets compare these reductions to those attained by drug therapy
  • We would expect any one drug to reduce BP by roughly 5 mmHg
  • Bearing in mind that all drugs have definite benefits but often unwanted side effects, it would seem crazy to rely on medication without making efforts to gain the benefits of life-style modification
  • The difficulty with gaining life-style benefits is that it’s hard to do; hard to get to target i.e. to get that 30 mins of exercise daily or to reduce salt intake to target
  • However, we need to recognise that some patient gains can be made just by moving in the right direction of targets
  • And patients should be encouraged to make changes even if they fall short of target.

  
• What causes BP?

  • BP = CO x TPR
• What causes BP? - cardiac output:

  • Cardiac Output = Heart rate x Stroke volume
  • CO = HR x SV
  • Where:
  • CO is the total volme of blood pumped from the heart each minute
  • HR is the number of contractions of the heart per minute
  • SV is the volume of blood ejected by the LV per contraction
  • A SV of 70 mls with a contraction frequency of 64 BPM (resting) → CO = 4.48 L/min
  • A SV of 140 mls with a contraction frequency of 190 BPM (exercise) → CO = 26.6 L/min
  • The cardiac output is a measure of how hard the heart is having to work to meet the metabolic demands of the tissues of the body
  • How hard the heart is working is reflected in systolic BP
  • The heart will worker harder when the SNS is switched on
• What causes BP? - total peripheral resistance:

  • TPR = total peripheral resistance – i.e the resistance that the blood vessels( notably the arterioles) offer to the blood that is being pushed through them
  • Why notably the arterioles? pt1
  • Because they are very numerous & most able to respond to the SNS, metabolites and as few other factors
  • Their response is for the smooth muscle which is wrapped around them to form the tunica media to contract more or less
  • Upregulating SNS activity causes the smooth muscle to contract more reducing the vessel calibre, causing vasoconstriction (VC) and increasing TPR which in turn will increase BP – specifically diastolic BP.
  • Note though that if the SNS is switched on to produce VC & increase TPR it will also simultaneously be having an effect on cardiac out-put increasing HR & SV (via inotropy and venoconstriction)
• What causes BP? - total peripheral resistance:

  • TPR = total peripheral resistance – i.e the resistance that the blood vessels( notably the arterioles) offer to the blood that is being pushed through them
  • Why notably the arterioles? pt2
  • Down-regulating SNS activity causes the smooth muscle fibres to contract less and hence a relative relaxation occurs resulting in an increase in vessel calibre i.e vasodilation VD - which lowers TPR
  • Metabolites as produced by normal metabolism but in much more significant amounts on exercise are potent arteriole VD.
  • The state of contraction or relaxation of the arterioles is reflected in the diastolic BP
• Why do we need a BP?

  • Your BP is the force that effectively pushes blood through your long network of arterial vessels in order to adequately perfuse the organs they supply
  • Put simply no BP = no perfusion = no life.
  • In instances of very low BP e.g in septiciaemia or severe haemorrhage unless prompt transfusion occurs severely underperfused organs will start to malfunction and fail – organ failure or in extreme cases multi-organ failure
• FINISH THIS WHEN REVISING