Cardiovascular System: The Integrated System for Blood Pressure Regulation

1

• Cardiovascular System The Integrated System for
  Blood Pressure Regulation
• Mary Christenson, PT, PhD
• DPT 732 Management Applications
• of Physiology II
• Spring 2009

2
Kidney Facts

• 50 gallons of blood pass through the 2 kidneys
  every day
• 1.3 quarts of urine produced from the 50 gallons
• Kidneys about the size of a computer mouse
• Several important functions including role in
  maintaining BP

3
Objectives

• Compare and contrast the integrated system of
  both short-term and long-term (including kidney
  involvement) regulation of arterial blood
  pressure
• Compare and contrast the effects of various
  physiologic stressors on the integrated
  regulation of the cardiovascular system

4
Objectives (cont.)

• Describe components in measuring cardiac output
• Describe factors that contribute to the
  homeostatic disruption of normal circulatory
  function

5
What We Already Know

• Rapidly Acting Arterial Pressure Control
  Mechanisms
• SNS effect on total peripheral vascular
  resistance and capacitance and cardiac pump
• Shift of fluid through the capillary walls

6
What We Are Missing

• Long-term control mechanisms for arterial blood
  pressure

7
Long-term mechanisms for BP Regulation

• Related to maintaining homeostasis of body fluid
  volume
• Based on maintaining a balance between intake and
  output of body fluid
• Overall regulation of kidney excretion of H2O and
  Na
• Variables account for variation in blood volume

8
Simple Concept

• Increase in extracellular fluid results in
  increased blood volume and arterial pressure
• Normal body response kidneys excrete excess
  extracellular fluid and returns the pressure to
  normal
• Mechanism reverses if reduced blood volume

9
Terminology/General Concepts

• Pressure diuresis
• Pressure natriuresis
• blood volume blood pressure
• blood volume blood pressure
• Excess salt intake increase H2O retention
  increase MAP

10
Volume X Pressure Guyton Hall, 2006
8
Urinary Volume Output (x normal)
1
20
200
Arterial Pressure mmHg
11
Renal Output Curve and Net Water/Salt Intake

• Over long-term, water and salt intake must equal
  output
• Demonstrated at equilibrium point of curve
• Two determinants of long-term arterial pressure
• Location of renal output curve (shift?)
• Level of intake line

12
TPR, Arterial Pressure and Kidney Function

• Arterial Pressure CO X TPR
• If increase TPR
• Get acute rise in arterial pressure
• However, normal kidney function will respond by
  returning arterial pressure to the pressure level
  of the equilibrium point Why?

13
Effect of Fluid Volume on Arterial Pressure

• Increased extracellular fluid volume
• Increases blood volume
• Increased mean circulatory filling pressure
• Increased venous return
• Increased CO
• Increased arterial pressure

14
CO Two Mechanisms to Increase Arterial Pressure

• Direct effect
• Increased CO increases pressure
• Indirect effect
• Autoregulation

15
Salt Intake

• Effect of Na greater than effect of H2O
• Why?
• Amount of salt accumulation in body is main
  determinant of extracellular fluid volume

16
Chronic Hypertension

• MAP gt 110 mmHg
• Results of pathology
• With dialysis, what happens if patients body
  fluid level is not kept at a normal level?

17
Renal Mechanisms for Control of BP

• Review 1st mechanism of kidney control of
  arterial pressure
• 2nd system Renin-Angiotensin

18
Renin-Angiotensin System

• Renin hormone that acts as an enzyme released
  when arterial pressure drops i.e., when renal
  perfusion is inadequate
• Helps raise arterial pressure
• Can be life-saving system in circulatory shock

19
(No Transcript)
20
Renin-Angiotensin Pathway
Renin (kidney)
Decreased Arterial Pressure
Angiotensin I
Renin substrate (angiotensinogen)
Angiotensin II
Vasoconstriction
Inactivation
Retention (salt/H2O)
Increased Arterial Pressure
21
Angiotensin and Salt/Water Retention

• Direct effect on kidneys to retain salt and
  water
• Indirect effect causes adrenal glands to secrete
  aldosterone which increases salt/water
  reabsorption by kidneys

22
Renin-Angiotensin and Salt Regulation

• Allows body to deal with widely varying Na
  intake and maintain normal BP

salt intake
extracellular volume
arterial pressure
renin and angiotensin
renal retention of Na and H2O
Return of extracellular volume almost to normal
Return of arterial pressure almost to normal
23
(No Transcript)
24
Primary Hypertension Silent Killer

• Unknown Cause i.e., not secondary to a known
  cause
• Influence of weight gain and sedentary lifestyle
• PT role?

25
Weight Gain and Obesity Role in HTN

• Cardiac output increased
• SNS activity increased
• Angiotensin II/Aldosterone levels increased

26
Treatment Options in HTN

• Lifestyle modifications
• Pharmacological
• Vasodilator drugs
• Natriuretic or diuretic drugs

27
Summary of Mechanisms to Control Arterial Pressure

• Rapid (seconds)
• Semi-rapid (minutes/hours)
• Long-term (hours/days/months/years)

28
(No Transcript)
29
Additional Circulatory Factors

• Cardiac Output
• Venous Return

30
Cardiac Output and Venous Return

• Cardiac output controlled by venous return under
  most normal unstressful conditions
• Factors in the peripheral circulation affecting
  venous return to the heart (not heart itself)
• Sum of local blood flows contribute to venous
  return
• CO inversely related to TPR

31
Heart Influence on CO

• Frank-Starling Law
• Receptors
• Heart is limiting factor if receives more venous
  return than it can handle

32
Cardiac Output

• Normal 5L/min
• Normal CO plateaus at 13 L/min without any
  special stimulation
• Hypereffective heart
• Hypoeffective heart

33
How Can We Measure CO?

• Fick Principle
• CO (L/min) O2 absorbed per minute by the lungs
  (ml/min)/A-VO2 difference (ml/L of blood)