explanation of the major hemodynamic diagrams

1. Physiology of
HEMODYNAMICS-1
DR. GHALEB ALMEKHLAFI

2. OBJECTIVES
TO DESCRIBE THE BASIC HEMIDYNAMIC DIAGRAMS
•vascular function diagram
•cardiac function diagram
•Ventricular pressure-volume loops

3. Introduction-why physiology?
• The biologic system is complex
• the organs cross-talk
• disease disrupt function and interaction of organs
• The organ interaction try to compensate-physiologic reserve
• Derangement of function indicate failure of compensation
• critically illness indicate organ failure
• Knowing Physiology and pathophysiology Can help directing the
management of complex situations

4. Anatomy of the circulation

6. arterial vs venous circulations
Arterial circulation
• function is to distribute blood
• 10%of blood volume
• maintaining high pressure is a
guarantee of perfusion-MAP
• governed by laws of pressure
difference
Venous circulation
• function is to collect blood-reservoir
• contain ∼70% of blood volume
Capacitance = volume / transmural pressure mmHg
• low pressure 0-10 mmhg
• The volume is primarily regulated ,not
tone
• BF is governed laws of pressure
difference
MAP-RAP = CO x SVR

7. The circulation dynamics

8. The cardiac output

9. Vascular function
diagram

10. “Obviously, except under momentary
conditions the venous return and the
cardiac output must be equal.” — Arthur
Guyton
Arthur Clifton Guyton
(September 8, 1919 – April 3, 2003)

11. The experiment
• The invention of extracorporeal pumps allowed Guyton to
control the heart function via the speed of a mechanical pump
and separate pump effects from the vascular tree as the circuit.
• He achieved maximum venous return with zero RAP.
• Further increases in flow via increases in pump function were
limited by collapse of the intrathoracic vessels.
• When he increased RAP above zero (i.e., above atmospheric
pressure), pump flow and therefore venous return would decline
until flow ceased completely.
• He termed the pressure at zero flow mean circulatory filling
pressure (MCFP).
• By influencing MCFP via volume expansion or epinephrine, he
could increase venous return without changes in pump function
(7,8,10).
• From this, Guyton reasoned that in the steady state circulation,
venous return (and therefore cardiac output in conclusion) was
driven by the venous return driving pressure
• (VRdP = MCFP minus RAP) divided by the resistance to venous
return (RVR):

13. Venous Return
• rate at which blood is
returned to the heart (in
L.min-1).
• driven by the pressure
difference between MSFP
and RAP
• At steady state, venous
return is equal to cardiac
output
VR=MSFP−RAP/RVR

14. MSFP
• In a circulatory standstill,
pressure and volume
equilibrate in the whole
system at MCFP
• Volume is distributed
according to each segments
compliances
• The equilibrating pressure is
related to blood volume and
is independent of the hearts’
function.

15. mean systemic filling pressure [Pmsf]
•The Pmsf is determined
by
1. venous blood volume
• Filling volume
• Stretching volume
2-venous compliance

16. 2 volumes-Stressed and unstressed

17. Stressed and unstressed vascular volume
unstressed volume :
fills the system without
exerting tension in the
vessel wall. P=0
stressed volume:
blood volume that creates
positive transmural
pressure via the elastic
recoil of the vessel wall

18. below –4 mm Hg,the veins collapse preventing any further
increase in flow. Vascular waterfall= maximal flow
independent of downstream pressure

20. Venous return-normal
Vascular
waterfall

21. VR=MSFP−RAP/RVR
•MSFP
• Volume
e.g. Haemorrhage, resuscitation.
• Compliance
•RAP
• Respiratory pump
(Negative intrathoracic pressure reduces RAP, improving
venous return.)
• Positive pressure ventilation
• Pericardial compliance
• Constriction
• Tamponade
•Resistance to Venous Return
• Posture
• Vascular compression
• Obesity
• Pregnancy
• Laparoscopy
• Ascites, edema,ACS
•Other factors affecting venous return
• Skeletal muscle pump
Contraction of leg muscles in combination with an intact
venous system propels blood back towards the heart.
• Venous valves
Factors Affecting Venous Return

22. MSFP-relevance to critical care practitioners

24. VR=MSFP−RAP/RVR
•MSFP
• Volume
e.g. Haemorrhage,
resuscitation.
• Compliance
Factors Affecting Venous
Return
Change in msfp
Change in resistance to VR
VR can only be zero if Pms – PRA is
zero
resistance becomes infinite below –4 mm Hg, preventing any
increase in flow above that present at –4 mm Hg.

26. SELECTIVITY OF VASO ACTIVE DRUGS
Predominant venous vasodilators like
nitroglycerin reduce preload .
Arterial vasodilators like hydralazine reduce
afterload
norepinephrine
augment Pmsf,
increase cardiac function,
increasing the resistance to venous
return and afterload
leading to decreased VR and rt and
down-shifting the cardiac function
curve

27. vasopressor

30. CARDIAC FUNCTION DIAGRAM

31. STARLING’S LAW
By raising or lowering an artificial venous reservoir
Starling showed that increased RAP resulted in increased SV

33. STARLING’S LAW
The curve status is defined by the existing
conditions of
• afterload
• inotropy and
• diastolic compliance

34. Vascular function curve

35. Dependant or independent-RAP,CO,VR
Do the cardiac output and venous return
depend on RAP?
Does RAP depend on the cardiac output and
venous return?
The answer to both is yes!
They all depend on each other.
Both curves can be equal only at the single
point where the two curves intersect.
Only transient and small deviations in these two
curves are possible unless either or both of the
function curves change in shape.

36. Momentary changes
• CO and VR are equal (at 5 L/min) only
when the CVP is 2 mm Hg.
• If CVP decrease to 0 for any reason, CO
would fall (to 2 L/min) but VR would
increase (to 7 L/min).
• Increase VR will return CVP back to the
original level (2 mm Hg) in a very short
time.
• Conversely, in the same logic the similar
thing would happen when CVP were to
increase.
• conclusion: CVS automatically adjusts to
operate at the point where the cardiac
and venous function curve intersect.

38. Dynamics of the curves-matching

39. Dynamics of the curves-matching
Eh is the slope of the
Frank-Starling curve
Eh=pmsf-pra
Both curves increase
or decrease by the
msfp and RAP
difference
high cardiac performance [Eh] low cardiac performance
Starling did not consider the MSFP

40. Function curves-clinical relevance

42. Cardiac Cycle

43. SAGAWA

44. Ventricular pressure-
volume loops

47. clinical implications of
vascular and cardiac
function curves=part2

48. Thank you