Cardiorespiratory Responses to Acute Exercise PDF

Dianne Salvaleon 5.2.24 Cardiorespiratory Responses to Acute Exercise After reviewing the basic anatomy and physiology of the cardiovascular and respiratory systems, this time we’ll look speci cally at how these systems respond to the increased demands place on the body during acute exercise. fi fi...

Dianne Salvaleon 5.2.24 Cardiorespiratory Responses to Acute Exercise After reviewing the basic anatomy and physiology of the cardiovascular and respiratory systems, this time we’ll look speci cally at how these systems respond to the increased demands place on the body during acute exercise. fi fi Recall that acute exercise is de ned as a single bout of exercise. Physiological responses are temporary/short-term and in response to the demands of exercise. These changes in the cardiorespiratory systems will return to normal values once exercise ends. In this chapter we will: Describe the cardiovascular responses to acute exercise Examine the respiratory responses to acute exercise With exercise, oxygen demand by the active muscles increases signi cantly, and more nutrients are used. Metabolic process speed up, so more waste products are created. During prolonged exercise or exercise in a hot environment, body temperature increase. fi These are just some examples on what happened to our body when we exercise, so in this chapter we’ll break down the responses of our cardiorespiratory system to acute exercise. Cardiovascular Responses to Acute Exercise Primary goal of adjustments is to increase blood ow to working muscles. Examine responses of the : Heart Rate Stroke Volume Blood Flow The blood Numerous interrelated cardiovascular changes occur during dynamic exercise. ff fl To better understand the changes that occur, we’ll examine the following and see how these changes are integrated to maintain adequate blood pressure and provide for the exercising body’s needs. Heart Rate Good indicator of relative exercise intensity Resting Heart Rate (RHR) average: 60-80 bpm; endurance trained athletes: 28-40 bpm a ected by extreme temp and altitude Pre-exercise HR is normally above Heart Rate during Exercise HR increases directly in proportion to the increase in exercise intensity Maximal Heart Rate (HRmax) (MHR) Highest HR value achieved in an all-out e ort to the point of volitional fatigue. resting values due to the body’s anticipatory response So what happens to our heart rate when we exercise? We mentioned previously that our heart rate is an indicator of how many times our heart contracts to pump blood out of its chambers and throughout the body. Along with this line, heart rate is also a good indicator of relative exercise intensity. Or how hard our body exerts e ort. To know the responses our heart through its heart rate, we need to look at what the normal resting heart rate is. ff ff ff Extreme temperature: for every degree centigrade, bpm increases ~10 bpm Altitude: at 14,000 feet, there is a 10-30 percent increase in heart rate Intensity 60% = 150 bpm = 160 bpm Altitude: 165% HRmax is often estimated based on age because HRmax shows a slight but steady decrease about one beat per year beginning at 10-15 years old There are two ways to measure maximal heart rate: HRmax= 220 - (age in years) HRmax= 208 - (0.7 x age in years) More accurate measure for maximal heart rate So, if one is 24 years old, what is their maximal heart rate? 40 years old 220-40 (180, but in reality 68% will have a HRmax higher or lower than than 168-192 bpm, while 95% will fall between 156-204 bpm) More accurate equation: the volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction Changes during acute exercise to allow the heart to meet the demands of exercise intensities Determined by four factors: Volume of venous blood returned to the heart. Note: Heart can only pump what returns Ventricular distensibility: Capacity to enlarge the ventricle, to allow maximal lling Ventricular contractility: Inherent capacity of the ventricle to contract forcefully Aortic or pulmonary artery pressure: The pressure against which the ventricles must contract First two factors in uence the lling capacity of the ventricle. Last two characteristics in uence the ventricles ability to empty during systole, determining the force of which blood is ejected and the pressure against which it must be expelled into the arteries. 1. Heart can only pump what returns 2. Capacity to enlarge the ventricle, to allow maximal lling 3. The pressure against which the ventricles must contract First two factors in uence the lling capacity of the ventricle. Last two characteristics in uence the ventricles ability to empty during systole, determining the force of which blind is ejected and the pressure against which it must be expelled into the arteries. fi fl fi fl fi fl fl Di erence in SV accdg to body position In supine position, blood returns more easily to the heart because blood does not pool in the lower extermities. ff fi Stroke Volume Stroke Volume Stroke Volume increase with Exercise plateaus as exercise intensity increases There is a di erence in SV according to body position: When body is in upright position Untrained Individuals: SV 60-70ml/beat to 110-130ml/beat Elite endurance athlete: SV 80-110ml/beat to 160-200ml/beat Supine position SV increases to 20-40% Di erence exists because in supine position, ff ff blood returns more easily to the heart because blood does not pool in the lower extremities. https://www.medicine.mcgill.ca/physio/vlab/exercise/muscle.htm Cardiac Output (Q) Maximum Q varies Sedentary: less than 20 L/min Elite endurance athlete: 40 L/min Q predictably increases with increasing exercise intensity To match the need for Product of HR and SV = Q Resting Q: ~5.0L / min Varies in proportion to the size of the person increased blood ow to exercising muscle As Q approaches maximal exercise intensity it may reach plateau Cardiac Output is the amount of blood the heart pumps out. Resting cardiac output is approximately 5.0 L/min but varies in proportion to the size of the person. Qmax varies between less than 20 L in sedentary individuals to 40 or more L/min in elite endurance athletes/ Qmax is a function of both body size and endurance training. The linear relationship between cardiac output and exercise intensity is expected because the major purpose of Q is to meet the muscle’s increased demand for oxygen. Like VO2 max, when Q approaches maximal exercise intensity it may reach a plateau. In fact it is likely that VO2 max is ultimately limited by the inability of Q to increase further fl VO2 max is the maximum amount of oxygen that individual can utilize during intense or maximal exercise Integrated Cardiac Response to Exercise As exercise intensity increases, HR increase proportionately, approaching HR max near the maximal exercise intensity Stroke volume also increase proportionately with increasing exercise intensity but plateaus when it reaches its maximal value Increases in HR and SV combine to increase cardiac output. As exercise intensity increases, HR increase proportionately, approaching HR max near the maximal exercise intensity Stroke volume also increase proportionately with increasing exercise intensity but achieves its maximal value at about 40-60% VO2max in untrained individuals. Highly trained individuals can continue to increase SV, sometimes up to maximal exercise intensity. Increases in HR and SV combine to increase cardiac output. Thus, more blood is pumped during exercise, ensuring that an adequate supply of oxygen and metabolic substrates reach the exercising muscles and that the waste products of muscle metabolism are cleared away. Upper body exercise causes greater BP that leg exercise BP increases with resistance training. With high intensity resistance training BP can brie y reach 480/350 mmHg. Commonly seen when individual Normal Blood pressure: 120/80 mmHg performs a valsalva maneuver to overcome heavy lifts. In endurance exercise, systolic BP increases in direct proportion to the increase in exercise intensities Arterial BP also increases Increases from 120 mmHg to 200 mmHg for normal, healthy, untrained indv.) at maximal exercise This facilitates the increase in blood ow through the vasculature Diastolic pressure does not change signi cantly At max intensities can slightly Up to 240-250mmHg (normal, healthy, elite indv) increase at max intensities of aerobic exercise Looking at the Vascular System: Blood pressure: force exerted by the blood on the walls of the arteries Mmhm: Millieters of mercury Systolic: stronger contraction of the heart, contracting more forcefully as it send more blood throughout the body- - fl fl The greater the pressure (created by the strong contraction of the heart(, the faster the blood will ow throughout the body fi fl Blood Pressure (BP) Blood Flow Redistribution of blood during Acute increases in Q and BP exercise during exercise allows for increased total blood ow to the body Through vasoconstriction action of the sympathetic nervous system on local arterioles In turn facilitate increased blood to areas with the greatest metabolic need During high intensity exercise, skeletal muscle may receive 80-85% Q Exercising in hot environment, increase in blood ow to the skin to dissipate internal heat Blood Flow: created by the more volume of blood to deliver, the stronger contraction of the heart, more force used to eject blood from the heart, the faster the blood will ow throughout the body Through vasoconstriction action of the sympathetic nervous system on local arterioles blood ow is redirected from areas where elevated ow is not essential to those that are active during exercise fl fl fl fl fl fl fl This shift in blood ow to the muscles is accomplished primarily by reducing the blood ow to the kidneys, splanchnic circulation (liver, intestine, stomach, pancreas). fl Cardiovascular Drift Generally associated increasing body temperature and dehydration Happens during prolonged aerobic exercise in a hot environment at a steady state SV decreases, HR increases, Q is the same but Arterial BP decreases Competition for Blood Supply Skeletal muscle v. Gastrointestinal System Athletes should be cautious in timing their meals before competition to maximize blood ow to active muscles during exercise. Exercise in a hot environment Redirection of blood to skin for cooling lessens the blood returning to heart Redirection of blood to skin for cooling lessens the blood returning to heart thus explaining SV decrease. To compensate, HR increases to maintain Q. Oxygen Content With increasing exercise intensity, (a- ) O2 di erence increases progressively Di erence re ects decreasing venous oxygen content At rest: (a- ) O2 di erence: 4-5 mL/100mL of blood; during exercise: up to 16 mL/100mL of blood More oxygen is extracted from the blood by the working muscles Plasma Volume Upon standing or onset of exercise, there is an immediate loss of plasma from the blood to the interstitial uid space With prolonged exercise, 10-15% reduction in plasma occurs During resistance training, plasma volume loss in proportional to the intensity of the e ort. If exercise produces sweat, more plasma volume is lost. (Prolonged; hot temperatures) Reduction of plasma volume impairs performance (60%) (a- ) O2 di erence: (arteriovenous oxygen di erence) di erence between the oxygen content of arterial blood and mixed venous blood At rest, the average arterial-venous oxygen di erence is about 4–5 mL per 100 mL of blood, but it increases progressively during exercise reaching up to 16 mL per 100 mL of blood, indicating that more oxygen is extracted from the blood by active muscles. Plasma: composed of salt, water, proteins: liquid part of the blood fl ff ff ff ff ff fl ff Decrease in plasma volume of more than 60% will impair performance because it increases blood viscosity, which impeded blood ow thus limiting oxygen transport. ff fl Blood Blood Hemoconcentration Occurs when plasma volume decreases When plasma is reduced, the cellular and protein portion become more concentrated in the blood In turn increase the RBC concentration in the blood Note: increase in RBC concentration/unit of blood, substantially increases blood’s oxygen carrying capacity. This is advantageous during exercise esp. at altitude. Hemoconcentration: Blood becomes more concentrated with hemoglobin, hematocrit and plasma proteins. Respiratory Responses to Acute Exercise Pulmonary Ventilation During Dynamic Exercise Anticipatory response to exercise is accompanied with increase in breathing/ ventilation Initial respiratory responses is controlled by the brain. Second phase of respiratory response is controlled by changes in the chemical status of arterial blood Increase in CO2 and H+ sensed by chemoreceptors in the brain, carotid bodies, lungs, muscles, and right ventricle to increase the rate and depth of inspiration. Second phase of respiratory response is controlled by changes in the chemical status of arterial blood (during heavy exercise) As exercise progresses, increased metabolism in the muscles generates more CO2 and H+. This is sensed in the muscles, and when the CO2 and H+ venous blood unloaded by the muscle. Respiratory Responses to Acute Exercise Pulmonary Ventilation During Dynamic Exercise At the end of exercise, pulmonary ventilation returns to normal at a slower rate Respiratory recovery takes several minutes after exercise, which suggest that post exercise breathing is regulated primarily by acid-base balance, the partial pressure of dissolved carbon dioxide, and blood temperature At the end of exercise, muscle’ energy demands decrease almost to resting levels. But pulmonary ventilation returns to normal at a slower rate Respiratory Responses to Acute Exercise Respiratory Limitations to Performance As rate and depth of ventilation increase, energy cost of respiration increase Diaphragm, intercostal muscles and abdominal muscle account for 11% of the total oxygen consumption; 15% Q During recovery from dynamic exercise, sustained elevations in ventilation account for 9% to 12% of the total oxygen consumed post exercise Pulmonary ventilation is not a limiting factor for performance even during maximal e ort However, respiratory system can limit performance of people with restricted or obstructed airways ff Respiration requires energy. This energy is used by the respiratory muscles during pulmonary ventilation; Respiratory Responses to Acute Exercise Respiratory Regulation of Acid-Base Balance Excess H+ (decrease pH) impairs muscle contractility and ATP generation To maintain acid-base balance, respiratory system increases rate and depth of inspiration Inspiration removes CO2 (which reduces H+ concentration) CO2 is transported via blood attached to bicarbonate, then when in the lungs, become CO2 again and exhaled. By product of muscle contraction is lactic acid, if the lactic acid remains in the muscle, the muscle’s pH level decreases and become more acidic Another by product of metabolism is carbon dioxide. In closing In this chapter we highlighted the cardiovascular system’s responses to acute exercise. We described the mechanisms they employ to address the demands of exercise on our body. We also considered the limitations that these systems can impose on abilities to perform sustained aerobic exercise. Thank You