Cardiovascular Physiology: Cardiovascular (CV) adjustment during exercise:

Transcription

1 Cardiovascular Physiology: Cardiovascular (CV) adjustment during exercise: By Dr Dler Gallaly (Lecturer) PhD in Medical Physiology- Dept. of Physiology, College of Medicine, HMU- Erbil- Iraq / 2017 Mob.#: (+964) dlerqader74@yahoo.com Contents: Introduction 1. Depending upon the type of muscular contraction Dynamic exercise: Static exercise: 2. Based on the type of metabolism involved Aerobic exercise: Anaerobic exercise: Effects of exercise on Cardiovascular system: 1

2 Objectives: After studying this lecture you should be able to: Know the types of exercise: Dynamic exercise: Static exercise: Aerobic exercise: Anaerobic exercise: Explain the effects of exercise on: Blood, Blood volume, Heart rate, Cardiac output, Venous return, Blood flow to skeletal muscles, Blood pressure. Introduction: During exercise, there is an increase in metabolic needs of body tissues, particularly the muscles. Various adjustments in the body during exercise are aimed at: 1.Supply of various metabolic requisites like nutrients and O 2 to muscles and other tissues involved in exercise. 2.Prevention of increase in body temperature. 2

3 Exercise is generally classified into two types depending upon the type of muscular contraction: 1. Dynamic exercise 2. Static exercise. Cardiovascular changes are slightly different in these two types of exercise. Dynamic exercise It primarily involves the isotonic muscular contraction (It keeps the joints and muscles moving). eg; are swimming, bicycling, walking. It involves external work, which is the shortening of muscle fibers against load. 3

4 Dynamic exercise In this type of exercise: The heart rate (HR), force of contraction, cardiac output (CO) & systolic blood pressure (SBP) increase. The diastolic blood pressure (DBP) is unaltered or decreased. It is because, during dynamic exercise, peripheral resistance (PR) is unaltered or decreased depending upon the severity of exercise. Static exercise: It involves isometric muscular contraction without movement of joints. eg; pushing a heavy object. Static exercise does not involve external work. During this exercise, apart from increase in HR, force of contraction, CO and SBP, the DBP also increases. It is because of increase in PR during static exercise. 4

5 Aerobic and Anaerobic exercises: Based on the type of metabolism involved, exercise is classified into two types: 1. Aerobic exercise 2. Anaerobic exercise. Aerobic and Anaerobic exercises: The terms aerobic and anaerobic refer to the energy producing process during exercise. Aerobic means with air or with O 2. Anaerobic means without air or without O 2. Both types are required to maintain physical fitness. 5

6 Aerobic exercises: Aerobic exercise involves activities with lower intensity, which is performed for longer period. The energy is obtained by utilizing nutrients in the presence of O 2. Examples: Fast walking, Jogging, Running, Bicycling etc. Aerobic exercises: The body obtains energy by burning glycogen stored in liver. When stored glycogen is exhausted the body starts burning fat. (Body fat is converted into glucose, which is utilized for energy) Aerobic exercise requires large amount of O 2 to obtain the energy needed for prolonged exercise. 6

7 Anaerobic exercises: It involves exertion for short periods followed by periods of rest. It uses the muscles at high intensity and a high rate of work for a short period. Body obtains energy by burning glycogen stored in the muscles without O 2. Examples: Pull-ups, Push-ups, Weightlifting, Sprinting, Anaerobic exercises: Burning glycogen without O 2 liberates lactic acid. Accumulation of lactic acid leads to fatigue. Therefore: this type of exercise cannot be performed for longer period. a recovery period is essential before going for another burst of anaerobic exercise. Anaerobic exercise helps to increase the muscle strength. 7

8 Severity of exercise: Cardiovascular and other changes in the body depend upon the severity of exercise also. Based on severity, the exercise is classified into three types: 1. Mild exercise: 2. Moderate exercise: 3. Severe exercise: Severity of exercise: 1. Mild exercise: is the very simple form of exercise like slow walking. Little or no change occurs in cardiovascular system during mild exercise. 8

9 Severity of exercise: 2. Moderate exercise: It does not involve strenuous muscular activity. So, this type of exercise can be performed for a longer period. Exhaustion does not occur at the end of moderate exercise. The examples of this type of exercise are fast walking and slow running. Severity of exercise: 3. Severe exercise: It involves strenuous muscular activity. The severity can be maintained only for short duration. Fast running for a distance of 100 or 400 meters is the best example of this type of exercise. Complete exhaustion occurs at the end of severe exercise. 9

10 Effects of exercise on: Blood, Blood volume, Heart rate, Cardiac output, Venous return, Blood flow to skeletal muscles, Blood pressure. 1. ON BLOOD Mild hypoxia developed during exercise stimulates the juxtaglomerular apparatus to secrete erythropoietin. Erythropoietin stimulates the bone marrow and causes release of RBCs. Increased CO 2 content in blood decreases the ph of blood 10

11 2. ON BLOOD VOLUME: More heat is produced during exercise and the thermoregulatory system is activated. This in turn, causes secretion of large amount of sweat leading to: Fluid loss Reduced blood volume Hemoconcentration Sometimes, severe exercise leads to even dehydration 3. ON HEART RATE: Heart rate increases during exercise. Even the thought of exercise or preparation for exercise increases the heart rate. It is because of impulses from cerebral cortex to medullary centers, which reduces vagal tone. In moderate exercise, HR increases to 180 bpm In severe muscular exercise, it reaches bpm. Increased HR during exercise is mainly because of vagal withdrawal (Increase in sympathetic tone also plays some role) 11

12 3. ON HEART RATE: Increased HR during exercise is due to four factors: Impulses from proprioceptors that act through higher centers and increase the heart rate. Increased CO 2 tension, which acts through medullary centers. Rise in body temperature: acts on cardiac centers via hypothalamus stimulates SA node directly. Circulating catecholamines, which are secreted in large quantities during exercise. 4. ON CARDIAC OUTPUT: In moderate exercise CO increases up to 20 L/minute In severe exercise it increases up to 35 L/minute. Increase in CO is directly proportional to the increase in the amount of O 2 consumed during exercise. 12

13 4. ON CARDIAC OUTPUT: During exercise, the CO increases because of increase in heart rate and stroke volume. Stroke volume increases due to increased force of contraction. Because of vagal withdrawal, sympathetic activity increases leading to increase in rate and force of contraction. 5. ON VENOUS RETURN: Venous return increases remarkably during exercise because of: muscle pump, respiratory pump and splanchnic vasoconstriction. 13

14 6. ON BLOOD FLOW TO SKELETAL MUSCLES: There is a great increase in the amount of blood flowing to skeletal muscles during exercise. The blood supply to the skeletal muscles: in resting condition, 3-4 ml/100g of the muscle/minute. in moderate exercise It increases up to ml. in severe exercise up to ml. 6. ON BLOOD FLOW TO SKELETAL MUSCLES: Several factors are responsible for the increase in blood flow to muscles during exercise. All such factors increase the amount of blood flow to muscles (dilatation of blood vessels of the muscles) Such factors are: Hypercapnea. Hypoxia. Potassium ions. Metabolites like lactic acid. Rise in temperature. Adrenaline secreted from adrenal medulla. Increased sympathetic cholinergic activity (ACh). 14

15 7. ON BLOOD PRESSURE: During moderate isotonic exercise, the SBP is increased. It is due to increase in HR and SV. DBP is not altered because PR is not affected during moderate isotonic exercise. 7. ON BLOOD PRESSURE: In severe exercise involving isotonic muscular contraction, the SBP enormously increases but the DBP decreases. Decrease in DBP is because of the decrease in PR. Decrease in PR is due to vasodilatation caused by metabolites. During exercise involving isometric contraction, the PR increases. So, the DBP also increases along with SBP. 15