03 Jul The heart as a pump

1. Recall the heart is a pump, and we can relate the chambers’ activity to specific phases of the cardiac cycle. Those phases are systole and diastole. When the chambers are NOT contracting/pumping, they are relaxed and filling with blood (diastole). When the chambers are contracting/pumping they are ejecting blood into another chamber or artery (systole). Remember that cardiac output is calculated by heart rate (HR) x stroke volume (SV). Heart rate gives us a unit of time, beats per minute (BPM), and stroke volume gives us the amount of blood in ml/beat; therefore, cardiac output is measured as ml/min or L/min (there are 1000ml in 1 L). Any increase or decrease in either stroke volume or heart rate affects the cardiac output.
   1. Predict what would happen to stroke volume and blood flow if there was an increase in resistance?

Blood flow directly affects the stroke volume. Anything that affects blood flow, like resistance, affects stroke volume. 

 

1. Recall from activity 1 we used the equation for flow, F= (PA – PV)/R. Where F = Flow; PA = Arteriole Pressure, PV = Venous Pressure and R = Resistance. We can simplify the (PA – PV) to change in pressure (
   

   P). Therefore, we can solve for

   

   P = F x R (Change in Pressure = Flow x Resistance).  

We can develop a mathematical equation substituting cardiac output for flow to get 

P = HR x SV x R which means heart rate, stroke volume and resistance all have an impact on the blood pressure in the body. To maintain a normal blood pressure, heart rate, stroke volume and resistance can be altered

 

1. Predict what would happen to blood pressure if resistance was increased due to vasoconstriction of the arterioles.

 

 

 

1. Afterload is the amount of resistance the left ventricle must overcome to force open the aortic semilunar valve, ejecting the blood into the ascending aorta. The greater the afterload, the harder it is to open the aortic semilunar valve, and less blood is ejected into the ascending aorta. Stroke volume is the amount of blood ejected into the ascending aorta during left ventricular systole. Stroke volume can be calculated by subtracting the End Systolic Volume (ESV)from the End Diastolic Volume (EDV). SV = EDV – ESV. EDV is the amount of blood in the ventricle when the ventricle is 100% filled. ESV is the amount of blood left in the ventricle after systole (contraction) ends. The greater the afterload, the larger the ESV. 

Resistance is generated from the body’s arterioles pushing blood back towards the heart and is called peripheral vascular resistance. When there is an increase in peripheral vascular resistance afterload is increased.

1. Predict what would happen to the ESV if peripheral vascular resistance was increased.

 

 

1. Predict what would happen to cardiac output if the ESV amount was increased.

 

 

 

 

1. Coronary artery disease is a form of atherosclerosis, where plaques form in the coronary arteries of the heart.  This causes a decrease in the radius of the arteries due to the accumulation of plaque within the lumen of the arteries. Recall the right and left coronary arteries come off the ascending aorta, just above the aortic semilunar valve.
2. Predict what will happen to the resistance in the coronary vessels that contain plaques.

 

 

 

 

1. What will happen to the resistance on the aortic semilunar valve? How will this impact afterload? Explain.

 

 

 

 

1. How will this impact the ability of the heart to contract (with greater or less force)?

 

 

 

1. Calcium channel blockers like verapamil are used to help the smooth muscle of the arteries relax and is often a treatment for coronary artery disease. 
2. Explain how verapamil will affect resistance in the coronary arteries. How will this affect blood pressure in the body as a whole? How will this impact the ability of the heart to contract (with greater or less force)?

 

 

 

 

 

 

Terms to Understand for the Practical:

Blood flow	Poiseuille’s law	Diastole
Friction	Vasoconstriction	Systole
Afterload	Vasodilation	End diastolic volume
Resistance	Laminar flow	Stroke volume
Viscosity	Velocity
Stenosis	Albumin
Blood pressure	End systolic volume
Pressure Gradient	Peripheral vascular resistance

 

Formulas to Understand and Calculate for Practical

 

                    F= (PA – PV)/R   or 

P = F x R                F = V ⋅ A