Force – Length Relationship in Heart

Guyton 2011

Chapter 9

Heart as a pump

Cardiac valves

Heart as a pump

Cardiac valves

Semilunar Valves

Av ValvesMitral

Tricuspid Aorta

Pulmonary

Heart as a pump

Cardiac Sounds

• Low frequency

• Loudest and longest

• High frequency

• Shorter duration

• Low intensity

• In children with thin chest wall

and heart failure

• In early diastole

•Atrial contraction

•Occasionally in healthy

individual

S1

S4

S2

S3

Heart as a pump

The Force-length Relationship of Myocardial Fibers

Heart as a pump

The Force-length Relationship of Myocardial Fibers

Heart as a pump

Muscle Length and Force of Contraction

Passive Tension

Total Tension

Active Tension

Heart as a pump

The Volume – Pressure Relationship of Myocardial Fibers

10

Heart as a pump

Ventricular Pressure-Volume Relationship

End -Diastolic Ventricular

Volume(EDV)

End -Systolic Ventricular

Volume(ESV)

Stroke Volume(SV)

Ejection Fraction(EF)

= SV/EDV

11

Heart as a pump

Points

Efficiency of Cardiac Contraction• In normal condition is about 20-25 percent• In heart failure is as low as 5-10 percent

Preload and Afterload

Chemical Energy Required for Cardiac Contraction• 70 to 90 percent derived from oxidative catabolism of fatty

acids• 10 to 30 percent from other nutrients especially lactate

and glucose

12

Heart as a pump

Regulation of Heart Pumping

Intrinsic Regulation

Frank-Starling

Extrinsic Regulation

Nervous Control

13

Heart as a pump

Intrinsic Regulation of Heart Pumping The Frank-Starling

Mechanism

14

Heart as a pump

Intrinsic Regulation of Heart Pumping The Frank-Starling

Mechanism

15

Heart as a pump

Extrinsic Regulation - Nervous

Control

16

Heart as a pump

17

Heart as a pump

Effect of Potassium and Calcium ions on Heart Function

CaK

Arrest in Diastole

Bradycardia

Arrest in Systole

Bradycardia

18

Heart as a pump

Effect of Temperature Heart Function

Tachycardia

Bradycardia

The End