Guyton Curves

Question 1

4 Factors that Influence CO

Answer 1

• Intrinsic factors - contractility and HR

* Extrinsic factors - preload/venous return and after load/TPR

Question 2

Psf

Answer 2

Systemic filling pressure

• P if flow were to go to 0 (no heart) and arterial and venous pressure equilibrated
• Psf = 7 mmHg in humans (much closer to venous pressure of 0 b/c veins so much more compliant than arteries; change in volume is same for both but veins have less change in pressure for given change in volume)

Question 3

What is the vascular function curve?

What is the main takeaway?

Answer 3

• Determine how vasculature affects pressure in the system
• Manipulate CO and see how it affects systemic venous pressure by REMOVING heart
• THERE IS AN INVERSE RELATIONSHIP BETWEEN CO (flow through the system) AND R ATRIAL PRESS in this model

Question 4

RVR

Answer 4

RVR= R*Ca/Ca+Cv (resistance to venous return)

*Can be thought of as TPR that takes compliance into consideration)

• Slope of venous return curve = 1/RVR
  (Shows that as RVR inc CO dec)

Question 5

What is the cardiac function curve?

What is the main takeaway?

Answer 5

• Determine how changing preload affects CO and BP
• Manipulate systemic venous pressure and see how it affects CO when INCLUDING heart
• When R atrial pressure is low… CO=0 b/c too little blood to generate pressure in systole
• As R atrial pressure inc the CO inc until reaches plateau where ventricle cannot fill anymore (this is limiting factor of filling - normally limited by time instead)

Question 6

Chronotropic and Ionotropic Effects on Cardiac Function Curve

Answer 6

• HR
• Inc HR…initially inc CO (Bowditch effect) but then once too fast no time for filling so dec HR
• Hyper effective heart (sympathetic NS or ventricle hypertrophy) - inc CO
• Hypo-effective heart (ventricle damage, no sympathetic NS, inc after load) - dec CO

Question 7

Equilibrium Point

Answer 7

• When superimpose 2 curves; this is point when curves cross paths
• tells you the CO and R atrial pressure

Question 8

What happens w/ sympathetic NS stim?

Answer 8

• Inc contractility (inc CO)
• Inc HR (complex - inc CO unless filling time too short)
• Dec venous compliance by vasoconstriction (inc CO)
• Inc TPR (dec CO - inc RVR makes slope less steep)

Shifts both curves up; shifts vascular function curve right as well

Question 9

What happens in exercise?

Answer 9

• Inc Psf and dec RVR
• Vasodilation, inc venous return (skeletal muscle pumping)
• MUCH GREATER INC IN CO than sympathetic NS alone

Shifts both curves up (to greater extent) and vascular function curve shifts right too

Question 10

Unstressed Volume

Stressed Volume

How does change in volume affect vascular function curve?

Answer 10

• Unstressed volume - 4L; Psf=0 b/c no stretch on vessel walls
• Stressed volume- anything above unstressed
• Inc volume (transfusion) …inc Psf which shifts curve to right and upward; higher CO as long as slope (RVR) the same
• Dec volume (hemorrhage) …dec Psf which shifts curve left and thus down; lower CO as long as slope (RVR is same)