Regulation of Arterial Pressure; Hypertension

J.L. Radcliffe
EMS 410/510 -- 18 Feb 2002

  • Peripheral vascular system
  • Regulation of arterial pressure
  • Hypertension
  • Medical management
Peripheral Vascular System

As we proceed from arteries, to arterioles, and capillaries, total vascular area increases, blood flow velocity (cm/sec, not Q in L/min) decreases, and pulse pressure is 'damped'.

Series vs. parallel resistance:

Note that the human vascular system is a 'parallel' system. If it existed in series, total peripheral resistance would be the sum of the individual resistances! We'd have sky high BP, even at rest, if this were the case!

Instead, the human vascular system exists in parallel. Thus, total resistance equals the SUM of the RECIPROCALS of the individual resistances! 1/R+ 1/R+1/R not.... R+R+R

Regulation of Arterial BP

Let’s begin with the basic flow equation:

Q = deltaP/r

In the human vascular system, we can say:

Q = MBP/TPR

Therefore:

MBP = Q x TPR.........................................MBP = [SBP + (2 x DBP)]/3

And:

TPR = MBP/Q

What is TPR?

Definition: Overall resistance to flow through entire systemic circulation.

MBP = Q x TPR

The figure below shows the determinants of blood pressure and many factors affecting TPR. Please review this figure carefully!

 

 

 
Regulation of BP

Regulation of BP is complicated...

Let's use angiotensin II as an example. The table below shows where Angiotensin II receptors are located and the effect we would observe if AngII bound to this receptor. Review the table below, and ask yourself..."Does this response result in a change cardiac output or TPR or both?

Arterial smooth muscle

(+) Vasoconstriction

Adrenal gland

(+) Aldosterone: (+) renal Na+ reabsorption

SNS

(+) Facilitates release of NE

Kidney

(+) Renal tubular Na+ reabsorption

Brain

(+) Thirst and vasopressin secretion

Heart

(+) Contractility and ventricular hypertrophy

Hypertension: The Silent Killer

Definition: Chronic elevation of BP > or = 140/90 mmHg (Joint Nat’l Committee Report, Arch Int Med 1997)

Review table 32.1 in your readings! Note the optimal BP is <120/80.

Public Health Stats: 50 million Americans; $22 billion annually

Incidence increases with age (TPR increases with age!)

Causes: 90-95% of all cases are idiopathic, AKA“Essential Hypertenion”

Other causes: 2-5% renal disease, primary aldosteronism, Cushing’s syndrome

 

Treatment

Meds

  • Diuretics
    • Thiazides, aldosterone antagonists
  • Sympatholytics
    • ß blockers, alpha 1 blockers
  • CCBs
  • Renin-angiotensin system antagonists
    • ACE inhibitors
    • Angiotensin II receptor blockers

Exercise as treatment for hypertension

Moderate aerobic exercise decreased resting BP in subjects w/ hypertension!
Kelley et al. Meta-analysis– 9 studies
  • Resting SBP decreased 7 +/- 5 mmHg
  • Resting DBP decreased 6 +/- 2 mmHg

Hagberg et al. – 47 studies

  • 70% of studies showed significant decrease in resting BP…
  • The avg. decrease… 10.5/8.6 mmHg

YET… only 48% of physicians recommend exercise to their hypertensive patients.

 

ACSM EXERCISE PRESCRIPTION FOR HYPERTENSION

  • MODE:
    • Moderate endurance – type exercise
  • INTENSITY:
    • Low-to-moderate intensity near lower end of ‘target HR range’ (40-70% maximum)
  • FREQUENCY:
    • 3-5 times per week
  • DURATION:
    • Gradually increase 30-to-60 min
    • Longer and more gradual warm-up and cool-down

What about RESISTANCE TRAINING?

Acute response… Both SBP and DBP increase. However, Rate-pressure product (MVO2) is often lower than with endurance exercise of equivalent intensity.

Chronic response? Meta-analysis showed: SBP decreased 2%, DBP decreased 4%.

Guidelines:

Use as a ‘supplement’ to endurance exercise, not a substitute.

Keep load at moderate % 1RM. Avoid Valsalva’s maneuver and isometric loading.

We'll finish next time discussing the BP dietary guidelines (DASH diet), then we'll begin a unit on diabetes. Please read the diabetes chapter in your packet, page 83-91.