A4 - Cardiovascular System

• The cardiovascular system consists of the heart and the blood vessels through which the heart pumps blood around the body
• During exercise, a number of changes take place to the cardiovascular system to ensure that the muscles receive the required amounts of oxygen and nutrients
• During exercise the heart rate needs to be increased in order to ensure that the working muscles receive adequate amounts of nutrients and oxygen, and that the waste products that are produced are removed
• Before you even start exercising there is an increase in your heart rate, called the anticipatory rise
• This increase in heart rate occurs because when you think about exercising it causes the sympathetic nervous system to release adrenaline
• One of the effects of adrenaline is to make the heart beat faster
• Once exercise has started, there is an increase in carbon dioxide and lactic acid in the body which is detected by chemoreceptors
• Chemoreceptors are a group of cells that detect changes in the chemical environment around them and transmit this message to the brain so that the body can respond accordingly
• The chemoreceptors trigger the sympathetic nervous system to increase the release of adrenaline, which further increases heart rate
• In a trained athlete, heart rate can increase by up to three times within one minute of starting exercises
• As exercise continues, the body becomes warmer, which also helps to increase the heart rate because it increases the speed of the conduction of nerve impulses across the heart
• Cardiac Output is the amount of blood pumped from the heart every minute and is the product of heart rate and stroke volume
• Cardiac Output = Heart Rate x Stroke Volume

  Q = HR x SV
• While exercising, the amount of blood that returns to the heart returns to the heart increases
• Blood returning to the heart is given the term venous return
• Venous return is the amount of blood returned to the heart after circulating around the body
• This increased volume of blood has the effect of stretching the cardiac muscle to a greater degree than normal. This stretching has the effect of making the heart contract much more forcibly and thereby pumping out more blood during each contraction, so stroke volume is increased during exercise. This effect is known as 'Starling's Law'
• Blood pressure is necessary in order for blood to flow around the body. The pressure is a result of the heart contracting and forcing blood into the blood vessels
• Systolic Value - when the heart is contracting

  Diastolic Value - when the heart is relaxing
• The value for a person's blood pressure is determined by the cardiac output (Q), which is a product of stroke volume and heart rate, and the resistance the blood encounters as it flows around the body
• Blood Pressure = Q X R

  R = Resistance to flow
• Resistance to blood flow is caused both by the size of the blood vessels through which it travels (the smaller the blood vessel, the greater the resistance) and by the thickness of the blood (the thicker the blood the greater the resistance)
• Changing the resistance to blood flow can alter blood pressure. This is done by involuntary smooth muscles in the arterioles relaxing or contracting in order to alter the diameter of the arterioles
• As the smooth muscles contracts, the diameter of the blood vessels gets smaller, so blood pressure increased; as the smooth muscle relaxes, the diameter of the blood vessel is increased, which decreases the pressure of the blood flowing through it
• A reduction in blood pressure is detected by baroreceptors in the aorta and the carotid artery
• Baroreceptors are a collection of cells that detect a change in blood pressure. They send signals to the brain so that the body can respond appropriately
• The detection of the decreased blood pressure is passed to the central nervous system, which then sends a nervous impulse signal to the arterioles to constrict. This increases the pressure of the blood and also has the effect of increasing the heart rate
• When blood pressure is increased, the baroreceptors detect this and signal the central nervous system, which makes the arterioles dilate, and reduces blood pressure
• Exercise has the effect if increasing heart rate, which will result in an increased cardiac output that will have the effect if increasing blood pressure
• BP = Q x R
• If the cardiac output is increased and the resistance to blood flow does not change, then blood pressure will also automatically increase
• Systolic blood pressure increases in line with exercise intensity - the higher the exercise intensity, the greater the increase in blood pressure. However, there is very little change in diastolic blood pressure as exercise intensity increases
• Immediately after exercise there is a fall in systolic pressure as the skeletal muscular pump is no longer pumping blood from the muscles to the heart. This can lead to blood pooling in the muscles and cause the athletes to faint as not enough blood is being pumped to the brain
• During aerobic exercise, systolic blood pressure can increase to around 180 mmHg. However, lower intensity exercise will not increase heart rate to the same degree, which in turn means blood pressure values will not reach higher values
• When taking part in strength training, blood pressure can increase to very high levels, which means it can be a dangerous activity for any person that already has high blood pressure
• The higher blood pressure that occurs in strength training is due to the fact that the muscles are contracting very forcibly. This force has the effect of constricting the blood vessels of the working muscles, which means that the heart has to work even harder to push blood through these blood vessels
• There is also an increase in blood flow to the thoracic activity when a person lifting a heavy weight performs the Valsalva Manoeurve
• Thoracic cavity is the part of the body that is enclosed by the ribcage and the diaphragm and contains the heart and lungs
• The Valsalva Manoeurve is the process whereby the person lifting the weight breathes out against a closed glottis or against a closed mouth and nose
• The process of performing the Valsalva Manoeurve while lifting heavy weights helps to stabilise the shoulder girdle and torso, which helps the lifter to move the weight more efficiently