1. Cardiovascular System: The Integrated System for Blood Pressure Regulation
Prepared by iqra ayub

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
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 > 110 mmHg Results of pathology
With dialysis, what happens if patient’s 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

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

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)

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)