Control of cardiac output and blood pressure Flashcards
What must cardiac output (CO) be adjusted to meet?
The metabolic needs of the body’s tissues.
How are the systemic and pulmonary circulations arranged?
They are in series, and the cardiovascular system is closed.
What must be equal between the left and right ventricles over time?
The outputs of the left and right ventricles must be the same over time (COlv = COrv).
What must venous return equal?
Venous return must be the same as cardiac output, although transient differences can occur (e.g., when you stand up).
What two factors determine cardiac output (CO)?
Heart Rate (bpm) and Stroke Volume (ml).
How is cardiac output (CO) calculated?
CO = Heart Rate (bpm) × Stroke Volume (ml).
In what units is cardiac output measured?
Milliliters per minute (ml/min).
What are the four factors that can directly affect cardiac output (CO)?
Preload, Afterload, Contractility, and Heart Rate.
What is preload, and how does it affect stroke volume?
Preload is the filling pressure of the right ventricle and affects stroke volume by influencing ventricular filling during diastole.
What is afterload, and how does it affect stroke volume?
Afterload is the resistance to outflow from the left ventricle and affects stroke volume by increasing the workload on the heart to pump blood.
What is contractility, and how does it affect cardiac output?
Contractility refers to the heart’s pumping function or strength of contraction, directly impacting stroke volume and cardiac output.
What is preload?
The degree of stretch of a ventricle immediately before it contracts.
What determines preload?
Preload is a function of the end-diastolic volume (EDV).
How is preload related to filling pressure?
It is related to the filling pressure of the ventricle.
What is the filling pressure for the left ventricle (LV)?
LVEDP (Left Ventricular End-Diastolic Pressure) = Left atrial pressure = Pulmonary venous pressure.
What is the filling pressure for the right ventricle (RV)?
RVEDP (Right Ventricular End-Diastolic Pressure) = Right atrial pressure (RAP) = Central venous pressure (CVP).
What is the normal pressure range associated with preload?
3-8 mmHg.
What does the venous system do?
It collects blood from the microcirculation and brings it back to the heart.
What pressure gradient allows blood flow to the right heart?
A small pressure gradient of 5-10 mmHg between the microcirculation and the right heart.
What 3 things allow the venous system to accomplish blood return with a small pressure gradient?
What is CVP a function of?
The amount of blood in the veins and the vein capacitance.
What happens when veins are constricted (e.g., by the SNS)?
Venous capacitance decreases, and CVP increases.
Example: Venoconstriction during exercise increases CVP, allowing the right and left ventricles to output more blood to meet muscle demands.
How do changes in blood volume affect CVP?
Decrease in blood volume:
- Example: Hemorrhage decreases CVP (as ~65% of blood is in systemic veins), reducing cardiac output (CO).
- Example: Sustained exercise causes fluid loss (sweating), reducing CVP and exercise capacity.
Increase in blood pooling (orthostasis):
- Example: Pooling in the lower extremities decreases CVP, CO, and blood pressure.
What is afterload?
The force against which a ventricle pumps to eject blood.