Question Time Questions Why are ventricle walls thicker than atrium walls? Which ventricle wall is the thickest? WHY? What are the 2 functions of heart valves? What are the names of the blood vessels that supply blood to the heart? What do you know about Cardiac Output, Stroke Volume and Heart Rate? Answers Because ventricles pump blood against gravity and around the whole body Left – pumps to whole body whilst the right only pumps to the lungs Controls the forward directions of the blood flow through the heart and prevents backflow of blood within the heart chambers Coronary (pulmonary) artery supplies the heart with blood, coronary (vena cavae) veins drain deoxygenated blood back into right atrium. Q = amount of blood pumped out of LV in 1min SV = LV 1 beat HR=beats per minute

Cardiac Dynamics Learning Objectives Know what is meant by heart rate (HR), stroke volume (SV) and cardiac output (Q) Understand how activity impacts upon these Be able to explain the changes HR, SV and Q during exercise

Heart Rate ‘The number of cardiac cycles (times the heart beats) per minute (bpm)’ Resting HR on average is: 72 This figure depends on: Genetics Gender Fitness What is Bradycardia? Elite athletes having a resting HR less that 60bpm. Can be a result of Hypertrophy of the cardiac muscle HRmax = 220 - age Learning Objectives Know what is meant by heart rate (HR), stroke volume (SV) and cardiac output (Q) Understand how activity impacts upon these Be able to explain the changes HR, SV and Q during exercise

Resting Heart Rates 30bpm 33bpm 43bpm 35bpm

Heart Rate Response To Exercise Increases linearly with intensity To maximum at 100% intensity (theoretical maximum of 220 – Age) HR Intensity

Heart Rate Response To Exercise Maximal Sub-Maximal Around 100 – 130 bpm HR HR Rest Exercise Recovery Rest Exercise Recovery Anticipatory Rise Oxygen Debt

Stroke Volume (SV) ‘The amount of blood your heart pumps out of the left ventricle each beat’ SV is determined by 3 factors: Venous return – the volume of the returning blood Elasticity of cardiac fibres – greater force of contraction (Starling’s Law) Contractility of cardiac tissue – increases amount of blood actually pumped out of left ventricle.

Homework Task – stick it down

SV changes during exercise Approx. 40 -60% of max Intensity SV Increases linearly with intensity This only occurs to a point, plateau at approximately 40 – 60% of maximum exercise intensity Maximal SV values are reached during sub-maximal exercise

Can increase due to the following: Increased venous return-volume of blood returning from the body. During exercise this obviously increases meaning more blood is returning to the heart and filling the ventricles The Frank Starling Mechanism (Starling’s Law)- SV is dependent on venous return. More blood filling the ventricles (end-diastolic volume) the greater the stretch of the ventricle walls. The greater the stretch the greater the force of ventricular contraction, ejecting a larger volume of blood. The lower the HR the more time available to maximise the effect, hence greater exercising SV in trained athletes It will plateau as maximal intensity doesn’t allow time for the ventricles to fill. This limits the Starling mechanism SV is maintained during the early stages of recovery as heart rate decreases to help with the removal of waste products and gradually reduce the stress on the cardiac muscle

Cardiac Output (Q) CO=SVxHR ‘Volume of blood ejected from the heart ventricles in one minute’ Cardiac Output (Q) = Stroke Volume (SV) x Heart Rate (HR)

Cardiac Output (Q) = Stroke Volume (SV) x Heart Rate (HR) Q (L/min) = SV (ml per beat) X HR (bpm) Cardiac output increase in line with exercise intensity and plateaus during maximal exercise intensity In recovery there is a rapid decrease followed by a slower decrease to resting levels

What about when you exercise past 40-60% maximal intensity? As we have seen, SV only increases up to 40-60% maximal exercise intensity. What happens if you exercise above this level, towards maximal exertion? Q still needs to increase. HEART RATE MUST INCREASE! Q = SV x HR, so any further increase in Q must be due to an increase in HR.

HR responses to physical activity Question: (not exam based) A fit 18 year old student performs a 400m time trial in one minute. Sketch and label a graph to show a typical response from a point 5 minutes before the run, during the time trial and over a 20min recovery period. (5) Explain why heart rate takes some time to return to it’s resting value (3)

Answer Anticipatory rise Initial rapid increase HR max reached near end of exercise Recovery initially rapid Tapers off gradually towards resting values Raised O2 demand of active muscles and raised levels of CO2 and lactic acid Organs such as the heart need additional O2 above resting consumption This reflects the size of the oxygen debt Hence HR values stay elevated until the oxygen debt is recovered

Exam Practice Describe how the heart’s conduction system controls the contraction and relaxation phases of the cardiac cycle (5) SA node receives a signal Atria contract Blood pushed into ventricles Signal reaches AV node Signal travels down Bundle of HiS to Purkinje fibres causing ventricles to contract