Jan 19 - Heart Failure Flashcards
What is vascular resistance?
The “squeeze” of the blood vessels outside the heart resisting blood flow
What is cardiac output?
A measure of how much blood is pumped out of the left ventricle of the heart in 1 minute (reminder: humans have about 5L of blood circulating at one time)
What is stroke volume?
The volume of blood ejected with each beat of the heart
What is inotropy?
The force at which the heart beats (squeeziness)
What is chronotropy?
The speed at which the heart beats
What are the 3 factors that can affect stroke volume?
Contractility (inotropy) - direct relationship
Afterload (squeeze/resistance) - inverse relationship
Preload (stretch/filling) - direct relationship
What is the LVEDV?
The left ventricular end diastolic volume; it’s volume of blood in the left ventricle at the end of diastole (preload)
How is the stroke volume affected by heart damage?
Even if their preload increases, their stroke volume still sucks
Explain what happens to the heart following an event such as an MI, stress, cardiac arrest, etc.
The heart becomes damaged, so that portion of the heart can’t work properly. The high blood pressure causes back up within the veins. The damage and the pressure causes a decrease in stroke volume so the heart tries to compensate
How does the heart compensate in heart failure?
- It increases chronotropy (heart rate) via sympathetics (norepinephrine)
- It increases preload via the RAAS
- Redirects blood flow to the heart via vasoconstriction of blood vessels, endothelin, RAAS, SNS
- Ventricular hypertrophy and remodeling
What are the pros to increasing heart rate (sympathetic activation) to compensate for heart failure?
It helps maintain cardiac output (CO=SVxHR)
What are the cons to increasing heart rate (sympathetic activation) to compensate for heart failure?
Short filling time, increased oxygen demand, risk of arrhythmias
What are the pros to increased preload using RAAS (sodium and water retention) to compensate for heart failure?
Increase stroke volume (more stretch, more preload)
What are the cons to increased preload using RAAS (sodium and water retention) to compensate for heart failure?
Pulmonary and/or peripheral oedema, increased oxygen demand
What are the pros to peripheral vasoconstriction (endothelin, RAAS, SNS) to compensate for heart failure?
Maintains blood pressure, recruits blood to the heart and brain
What are the cons to peripheral vasoconstriction (endothelin, RAAS, SNS) to compensate for heart failure?
Increased afterload (resistance) which decreases stroke volume
What are the pros to ventricular hypertrophy and remodelling to compensate for heart failure?
Helps to maintain cardiac output, decreases oxygen deman
What are the cons to ventricular hypertrophy and remodelling to compensate for heart failure?
Increased risk of ischemia, dysfunction, fibrosis and arrhythmias
Explain how the compensatory mechanisms are a vicious cycle
When the heart is damaged, the cardiac output sucks. So heart rate and preload are increased, blood pressure increases (good to a point), but then so does afterload (which is bad). Even though all of these things are happening, the heart still can’t push out what it wants (the cardiac output still sucks)
Name neurohormonal factors
Angiotensin II, norepinephrine, aldosterone, natriuretic peptides, arginine vasopressin
What is the mechanism of angiotensin II as a neurohormonal factor?
It causes vasoconstriction, activates SNS, causes sodium retention by the kidneys and aldosterone release (RAAS)
What is the mechanism of the norepinephrine as a neurohormonal factor?
It causes tachycardia, vasoconstriction, increased contractility
What is the mechanism of aldosterone as a neurohormonal factor?
It causes sodium and water retention in the kidney (RAAS), and contributes to ventricular remodelling