Bio-Med 350 Normal Heart Function and Congestive Heart Failure
Basic Concepts: • The Cardiac Cycle • Myocardial Filling -- “Diastole”ComplianceLeft ventricular filling curves • Myocardial Emptying -- “Systole” Cardiac OutputFrank-Starling Performance Curves • The relationship of filling and emptying:Pressure - Volume Loops
Cardiac Output is defined as: Stroke Volume X Heart Rate Blood Pressure is defined as: Cardiac Output X Systemic Vascular Resistance Basic Definitions What happens to each of these during: Exercise? When LV filling is impaired?? When systolic function is impaired???
What happens to the runner during exercise? OR “Why the jogger didn’t blow his top!”
Basic Definitions • Cardiac Output is defined as: Stroke Volume X Heart Rate • Blood Pressure is defined as: Cardiac Output X Systemic Vascular Resistance
Basic Concepts: #1 • The Cardiac Cycle
The Normal Cardiac Cycle • Components of Diastole: Isovolumic relaxationRapid Ventricular filling Atrial contraction (“kick”) • Components of Systole Isovolumic contraction L.V. Ejection
The Normal Cardiac Cycle • Let’s take a look at the cycle in some depth............
Basic Concepts: #2 • The Cardiac Cycle • Myocardial Filling -- “Diastole”ComplianceLeft ventricular filling curves • Myocardial Contractility -- Systole Frank-Starling Performance Curves • The relationship of filling and emptying:Pressure - Volume Loops
Left ventricular filling curves • Relationship of pressure to volume defines L.V. “stiffness” or “non-compliance” • At low pressures, almost linear
“Compliance” is proportional to change in volume over change in pressure “Stiffness” is the inverse. Stiffness is proportional to change in pressure over change in volume Relationships to Remember
Basic Concepts: #3 • The Cardiac Cycle • Myocardial Filling -- “Diastole”ComplianceLeft ventricular filling curves • Myocardial Emptying -- “Systole” Cardiac OutputFrank-Starling Performance Curves • The relationship of filling and emptying:Pressure - Volume Loops
Relationships to Remember • “Preload” and “afterload” are defined as the wall tension during diastole and systole, respectively • Wall tension is defined as: P x r 2h (where h = wall thickness)
Preload • Is the wall tension during ventricular filling • Is defined as P x r 2h during diastole!!!
Why is volume the most important determinant of ventricular preload?? (Hint: look at the cardiac cycle)
Afterload • Is the wall tension during ventricular ejection • Is defined as: P x r 2h during systole!!!
Why is systolic pressure the most important determinant of ventricular afterload??? (Hint: look again at the cardiac cycle)
How do we relate myocardial performance to: • Loading conditions: i.e. preload and afterloadAnd how does “myocardial contractility” relate to all of the above??
Frank - Starling Curves • L.V. “performance” curves relating: • L.V.E.D.P. (i.e." preload”) • L.V. “performance” (i.e. cardiac output)
Heart rate Blood pressure Cardiac output Vascular resistance When: LV filling falls LV systolic function is impaired The LV is non-compliant Afterload increases What happens to:
How do we measure..... ? • Blood pressure • Cardiac output • Stroke volume • LVEDP • Systemic vascular resistance
Fick Method -- O2 consumptionA-V O2 difference Thermodilution method --“The Black Box” Measuring Cardiac Output
The Fick Principle Lungs O2 Body
Measuring O2 consumption The Waters Hood
The Thermodilution Method • Similar in principle to the Fick method • Uses change in temperature per unit time, rather than change in O2 saturation • Requires a thermal probe in the right side of the heart
Pressure - Volume Loops • Relate L.V. pressure to L.V. volume in a single cardiac cycle • Can be used to explore the effects of various therapies on stroke volume and L.V.E.D.P. Pressure (mm Hg)
Pressure - Volume Loops • Holding afterload and contractility constant • Varying “preload”, measured as end-diastolic volume
Heart Failure Forward Failure: Inability to pump blood forward to meet the body’s demands Backward Failure: Ability to meet the body’s demands, at the cost of abnormally high filling pressures
Systolic vs. Diastolic Dysfunction • Systolic dysfunction • Decreased stroke volume • Decreased forward cardiac output • Almost always associated with diastolic dysfunction as well • Diastolic Dysfunction • One third of patients with clinical heart failure have normal systolic function – i.e. “pure” diastolic dysfunction
Diastolic Dysfunction • Impaired early diastolic relaxation (this is an active, energy dependent process) • Increased stiffness of the left ventricle (this is a passive phenomenon) • LVH • LV fibrosis • Restrictive or infiltrative cardiomyopathy
Compensatory Mechanisms for Heart Failure • Frank – Starling Mechanism • Neuro-humoral alterations • Left ventricular enlargement • LV Hypertrophy ↑ contractility • LV “remodeling” ↑ stroke volume