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Chapter 5

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Simon Fraser University
Biomedical Physio & Kines
BPK 143
Tony Leyland

Chapter 5 Cardiovascular system - Pulmonary circulation is where deoxygenated blood is pumped from the heart through the lungs and oxygenated blood is returned back to the heart - Systemic circulation is where oxygenated blood is pumped from the heart around the rest of the body and deoxygenated blood is returned back to the heart. Cardiovascular system The pathway of blood flow through the heart To summarize: - Blood from the head and upper extremities, and from the trunk and lower extremities, returns to the heart via the superior vena cava and inferior vena cava, respectively - It flows through  the right atrium  the tricuspid valve  the pulmonary valve and the pulmonary arteries  to the lungs - In the lungs, the blood gives up excess carbon-dioxide (CO2) and replenishes oxygen (O2) - It then flows through  the pulmonary veins  the left atrium  the bicuspid valve  the left ventricle  the aortic valve  and into the aorta - When our muscles are working, they like to produce energy while using oxygen, as this is more efficient than producing energy without oxygen - When exercising at a high enough level, you overload the system’s ability to deliver oxygen to the working muscles, and the body will improve this ability when subjected to overload - Cardiac output (Q): the amount of blood pumped in one minute by either the right or left ventricle of the heart - Stroke volume (SV): the amount of blood pumped by the left or right ventricle of the heart per beat - Heart rate (HR): the number of heart beats per minute - Heart isn’t entirely alone in the circulatory system - When you exercise, your muscles contract and squeeze your veins, pushing blood back to the heart - Veins have one-way valves to prevent blood flowing backwards - This rhythmic contraction and relaxation of your muscles helps with venous return and is refered to as the skeletal muscle pump - This is why aerobic exercise and other exercises that require alternating contraction-relaxation phases in muscle groups are preferable to isometric straining-type exercises, where muscles are held in contraction for long periods of time - Isometric and maximal-effort exercises close down blood vessels, making it harder for the heart to pump blood through them; hence, increases blood pressure (BP) to very high levels - Isometric contract’s drawback is that they primarily improve muscular strength ONLY at the angle at which the joint is exercised Respiratory (pulmonary) system - Respiration refers to the exchange of oxygen and carbon dioxide between the cells of an organism and the external environment - External respiration is the exchange of oxygen and carbon dioxide in the alveoli (lungs) - Internal respiration is the exchange of these gases at the cellular level - The conducing portion of the respiratory system consists of a series of highly branched, hollow rubes going from the mose and mouth to little sacs in the lungs called alveoli To summarize - Air enters through  the nose or mouth  and goes through the pharynx  the larynx  and the trachea - It then flows through  the two bronchi  and the bronchioles  into the alveoli - As air flows through the respiratory passages, it is warmed to 37o C and saturated with water - If you are breathing through the nose, hairs will help to trap particles and filter the air to some degree - During exercise, mouth breathing tends to replace nasal breathing because there is less resistance to the entry and exit of air - The alveoli are the tiny, thin-walled, hollow sacs where gas exchange takes place - Each lung contains millions of alveoli - The total area of alveolar membrane in contract with capillaries is approximately 70 square métiers in an average-size adult male Mechanism of breathing - Air molecules move from an area of higher pressure to an area of lower pressure - Inspiration—The diaphragm muscle plus external intercostal muscles contract to increase the volume within the thoracic cavity. Since the thoracic cavity is closed, this increases the volume within the lungs, and increased volume results in decreased pressure. So if your airway is open, air moves into the alveoli, as the air pressure in the alveoli is now less than air pressure in the atmosphere. - Expiration—The diaphragm plus external intercostal muscles relax to decrease the volume of the thoracic cavity. As lung elastic tissues recoil, alveoli air pressure becomes greater than atmospheric pressure and air is forced out of the alveoli. - At low ventilation volumes, expiration is a passive process, meaning that the diaphragm and external intercostals just relax and the ribs recoil - The amount of oxygen consumed by the ventilator muscles during rest is 1-2% of the total oxygen consumed - In heavier exercise, the abdominal muscles aid in expiration and the amount of air ventilated per brea increases, and raise oxygen used by respiratory muscles to 8-10% of the total oxygen cost of heavy exercise - Minute ventilation (V )—Eolume of air inspired or expired in one minute. - Tidal volume (V )—Tolume of air ventilated per breath. - Respiratory frequency (F )—Number of breaths per minute. R Minute ventilation = Tidal volume x Respiratory frequency - During light to moderate exercise, minute ventilation linearly as workload increases - At moderate to heavy workloads, minute ventilation beings to increase out of proportion to workload called the hyperventilation - Minute ventilation begins to increase more rapidly when the workload requires 75-80% of the subject’s maximum oxygen uptake (VO2 max) - The process of delivering oxygen to your working muscles is not limited by the amount of air you can breathe and the amount of oxygen you can diffuse into your bloodstream Gas exchange and gas transport - Blood is composed of specialized cells (red blood cells, white blood cells, and platelets) suspended in a liquid (plasma) - Role of the red blood cells (erythrocytes) is to deliver oxygen to the cells and remove waste carbon dioxide - Red blood cells are an integral component in determining the aerobic power - The white blood cells (leukocytes) are part of the body’s immune system and platelets play a major role in blood clotting mechanisms - Hematocrit: the portion of blood composed of blood cells and formed elements - Hamatocrit levels are around 40-45% in males and 30-35% in females - Plasma makes up 50-60% of the blood by volume and is about 90% water - The total blood volume of an average man is approximately 8% of his body weight - Gas exchange between the alveolar-capillary membrance and the tissue-capillary membrane occurs via the process of diffusion - Diffusion : the random motion of molecules from areas of high concentration to areas of low concentration - As blood with a low concentration of oxygen and a high concentration of carbon dioxide enters the alveoli, oxygen is diffused into the blood and CO2 is diffused into the lungs - The opposite process occurs at cell throughout the body, where oxygen is “delivered” and the CoO2 is “picked up” - The arteries continually branch until they eventually lead to arterioles and then capillaries - Oxygen and CO2 exchange takes place ONLY in the capillaries due to the thickness of the walls of other blood vessels - 98% of the oxygen in blood is carried by red blood cells in chemical combination with hemoglobin (Hb), an iron-containing protein hat reversibly binds with oxygen molecules - Hemoglobin + Oxygen Oxyhemoglobin Hb + O 2 HbO 2 Normal values for hemoglobin:  Men—15.5 grams/100 mL blood.  Women—13.5 grams/100 mL blood. - Gender difference is likely due to the male hormone testosterone stimulating red blood cell production - Haemoglobin is 95-98.5% saturated with oxygen at sea level - Therefore, breathing pure oxygen at sea level adds only insignificant amounts of oxygen to the blood - Although breathing hyperoxic gas mixtures (containing higher than normal oxygen levels) will result in a very small increase in oxygen bound to haemoglobin and dissolved in the blood, any benefit will ONLY take palce is the subsequent exercise takes place without the individual breathing ambient air - Because the lower pressure of oxygen in the ambient air causes any additional oxygen in the blood to exit the body quickly Blood pressure and exercise - Blood pressure (BP): the pressure exerted on the walls of the arteries by the blood - It is the driving force (due to heart contractions) that moves the blood through the circulatory system - Systolic: the pressure in the arteries during ventricular contraction - Diastolic: the pressure when the ventricles are relaxed - Systolic blood pressure—The pressure on the artery walls when the left ventricle contracts and pushes a bolus of blood through the arteries. The normal range for systolic blood pressure is 100–140 mm Hg. Normal or average systolic blood pressure is usually reported as is 120 mm Hg. (Millimetres of mercury, abbreviated as mm Hg, is a common measure of pressure.) - Diastolic blood pressure—The pressure in the arteries between ventricular contractions after the bolus of blood has passed through. Normal diastolic blood pressure range is 60–90 mm Hg. Normal or average diastolic blood pressure is usually reported as 80 mm Hg. - Pulse pressure—Calculated as systolic pressure minus diastolic pressure. It refers to the additional pressure that is pushing blood through the system during systole (when the ventricles contract). - Hypertension—A medical term referring to high blood pressure. Hypertension is a leading cause of many forms of cardiovascular disease. It is usually listed as second only to tobacco smoking as a primary cause of heart disease. If your blood pressure is higher than 140/90 (normal BP is 120/80 and ideal BP is 110/70), you are considered to have high blood pressure. Blood pressure during dynamic exercise - Mean arterial blood pressure = cardiac output x peripheral resistance - Ohm’s law of heart: states that the pressure difference between two ends of a blood vessel (the force that pushes blood through the vessel) is determined by cardiac output and the impediment to flow (vascular resistance) - The pressure is affected by the amount of blood you are trying to push through a vessel (Q), and te resistance put up by the vessel, which is affected by the diameter and elasticity of the vessel - Systolic blood pressure increases progressively as exercise intensity increases, and diastolic blood pressure remains constant or increase only slightly - Blood pressure drops as the arteries branch so that the pressure in the capillaries is very low - The drop in pressure is caused by a dramatic increase in the total area of the blood vessel - The increase in area also causes the blood velocity to slow so that gas exchange can take place - The pressure in the veins is also low and this explains the presence of one-way valves in the veins which prevent blood flowing backwards Blood pressure during static (isometric) exercise - Sustained straining exercises compress the peripheral arterial system, which brings about a significant increase in resistance to blood flow - Causes a large and rapid rise in both systolic and diastolic blood pressure with a corresponding increase in the workload of the heart - When exercising dynamically with the arms as compared to legs, there is a greater than normal increase in blood pressure Changes in blood flow during exercise - At rest, 15-20% of systemic blood flow goes to the skeletal muscles - During maximal exercise, 85% of total blood flow (cardiac output) can be diverted to the working skeletal muscles - Increased blood flow to the working muscles is caused by 1) Increased blood pressure 2) Dilation of arterioles in working muscles due to relaxation of smooth muscle in the walls of the arterioles 3) Decrease in blood flow to other tissues such as the viscera (liver, stomach, intestines, and kidneys), and non-working muscles due to constrictions of arterioles in these regions  Blood flow to these areas can be decreased by up to 80% during severe exercise  Blood flow to the heart increases due to the extra work required  Skin blood floor also increases during exercise in order to dissipate heat Oxygen uptake and VO2 max - A muscle needs a high level of capillarization for a large volume of blood to be delivered to it - Aerobic training increases capillarization of muscles used in that exercise and not the muscles that are not being used - Arterial-mixed venous oxygen difference : measure how much oxygen is in the arteries and how much is in the blood returned to the heart - The Fick Equation (oxygen transport equation): oxygen uptake = cardiac output x (arterial – mixed venous oxygen difference)  The dote above the V means it is a rate of floor – litres per minute - Cardiorespiratory fitness = oxygen transport x oxygen utilization (extraction) - The oxygen content of arterial blood is the same in all arteries of the body, as the blood pumped out by the left ventricle cannot deliver oxygen until it is flowing through capillaries - HOWEVER, the oxygen content of venous blood that has just left a working muscle would be must less than the oxygen content of blood in a vein from a non-working muscle - Because of the difference in oxygen content, the preceding equation uses the term mixed venous oxygen, represent by the dash above the V - Endurance athletes have a much higher maximum oxygen uptake which enables them to do much more work - The main difference between endurance athletes and other subjects is that endurance athletes can produce a very high stroke volume, which enables them to attain a very high cardiac output (able to transport large quantities of oxygen to the working muscles) - Trained and elite subjects have a lower resting heart rate than untrained subjects. This is because the resting stroke volume of trained subjects is higher, so they can attain the same resting cardiac output as the untrained subjects, with a lower heart rate Exercise heart rate - Heart rate usually increases linearly with increasing workload until the subject’s maximum heart rate is reached Stroke Volume during exercise - For most individuals, stroke volume increases to its highest values during sub-maximal exercise at approximately 40% VO2 max and does not increase further during steady-state aerobic work for most individuals High intensity interval training (HIIT): an advanced technique to be used only after a minimum of six weeks of general conditioning - Example would be several maximal 400-metre sprints, each sprint followed by one-to three=minute recovery period - During internal training, stroke volume reaches higher levels more often because of the numerous relief intervals - Stroke volume has been shown to be higher during the recovery period from intense exercise The paradox of aerobic training - The best way to improve an oxygen delivery system is to work so hard that you surpass your VO2 max and work anaerobically - Anaerobic exercise: when you work at an intensity that exceeds the body’s ability to deliver enough oxygen for the muscles to sustain that that exercise by burning oxygen - By really challenging the ability to deliver oxygen to working muscles, the body adapts to improve that ability - Traditional weight training activities can be used to improve aerobic conditioning, and they can do it by improving aerobic conditioning of all muscle groups - The heart is working hard no matter which muscles are demanding a high blood supply - The benefit of varying your training this way is that you are better able to handle what life throws at you - Those who only train for power lifting will not be able to sustain even moderate power outputs for an extended period - They simply cant get enough blood into their strong muscles to perform extended periods of muscular endurance work - Capillary dilution : occurs when you only perform high-weight low-rep work with losts of rests between sets - As all the work is anaerobic (does not require oxygen), there is no overload for the odoy to build more capillaries - If muscle is getting bigger, but no new capillaries are being developed, the number capillaries per amount of muscle is going down Aerobic training routines - While HIIT is a very useful tool, on its own, it will not get you to that best time on a long-distance endurance event Maximal aerobic Power - Maximum oxygen uptake is the highest oxygen utilization that an individual can attain during physical work while breathing air at sea level ( use doesn’t = to how much breathe in) - The best way to report is in millititres per kilogram of lean body tissue per minute - The most important physiological factors that determine in a given person are as follows 1) The ability of the heart to pump blood (Q) 2) The oxygen-carrying capacity of the blood (hemoglobin content) 3) The ability of the working muscles to accept a large blood supply ( amount of capillarization within a muscle) 4) The ability of the muscle cells (fibres) to extract oxygen from the capillary blood and use it to produce energy ( the number of mitochondria and aerobic enzymes in the muscle will determine this) - is measured by determining the amount of oxygen in the air inspired by the test subject, and then measuring the amount of oxygen in the expired air. The difference is the amount of oxygen used by the body - As the oxygen is being used to burn fuels and produce energy, the energy is used to perform the work , and hence more work equates to a higher oxygen need - Once the subject is close to or at the , the relationship breaks down and the subject starts to burn fuel in the absence of oxygen ( called working anaerobically) Age and gender differences in maximal aerobic power - Maximum oxygen uptake increases with age, and on average, reaches its peak between 18 and 25 years of age - After age 25, declines steadily - By age 55, is about 27% below values reported for a 20 year old - Decrease in maximum heart rate, and become less physically active - Even if a subject is aerobically fit enough, he/she still needs to take knowledge about training, recovery, nutrition and racing tactics - Before age 12, there is no significant difference in between boys and girls - After 12, the average male has a per unit body weight that is 20-25% higher than the average female - Reason for difference is the body composition, as males have more muscles and less fat - Difference of is around 9%, because the average male has a higher hemoglobin concentration and hence a greater oxygen-carrying capacity per unit of blood - Cross country skiers show the highest values in average because they use more muscle groups Maximal aerobic power and endurance performance - A person with a high isn’t necessarily an outstanding endurance performer - Other factors include 1) Anaerobic or lactate threshold—the percentage of that can be utilized in significant amounts before the muscle environment becomes acidic, causing local muscle fatigue and discomfort. This will be discussed in more detail in Chapter 6. 2) Individual variation in mechanical efficiency—As we have all seen in runners who are inefficient in their running style. The oxygen requirement for a given workload or running speed varies, so an efficient individual may run faster with a lower . 3) Motivation—Alw
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