BMS 2.6 quiz
Describe the effects of prolonged exercise at a constant work rate on cardiac output, stroke volume, and heart rate
1) Cardiac output is maintained.2) Gradual decrease in stroke volume- due to dehydration and reduced plasma volume- a drop in plasma volume reduces venous return to the heart and therefore reduces stroke volume3) Gradual increase in heart rate (particularly in heat)- if heart rate did not increase to compensate for the drop in stroke volume, cardiac output would decrease
Does prolonged exercise at high heart rates pose a risk for cardiac injury?
Almost always no for healthy individuals. However, sudden cardiac deaths have occurred in individuals of all ages during exercise
Describe a-v O2 difference and the changes in a-v O2 difference during exercise
Arterial mixed venous O2 difference (a-v O2 difference). a-v O2 difference represents the amount of O2 that is taken up from 100 ml of blood by the tissues during one trip around the systemic circuit. a-v O2 difference increases during exercise. Due to an increase in the amount of O2 taken up and used for the oxidative production of ATP by skeletal muscle
Describe how the body redistributes blood flow at rest and during exercise to the heart
As compared to other organs of the body, the volume and percentage of blood allocated to the heart during maximal exercise is unique. The percentage of total cardiac output that reaches the myocardium is the same at rest and during maximal exercise (4%-5%). The percentage of cardiac blood flow is virtually identical between rested and maximal exercise. The metabolic rate of the heart must be precisely controlled at all times to ensure that the shifting energy demands of the body can be met rapidly. The total coronary blood flow is increased to match the elevated cardiac output during intense exercise.
Describe the changes in HR, SV, and CO from transition to rest
At the onset of exercise (from rest to exercise), there is a rapid increase in HR, SV, and CO. Heart rate and cardiac output begin to increase within the first second after muscular contraction begins. If the work rate is constant and below the lactate threshold, a steady-state plateau in HR, SV, and CO is usually reached within 2-3 minutes
Describe arm vs leg exercise effects on mean arterial pressure and heart rate
At the same oxygen uptake, arm work results in:1) Higher heart rate- due to higher sympathetic stimulation2) Higher blood pressure- due to vasoconstriction of large inactive muscle mass in the lower body
Describe the two factors that primarily determine blood flow to muscles during exercise bases on the exercise and motor units
Autoregulation is the most important means by which blood flow to muscle is controlled during exercise. The magnitude of vasodilation that occurs in arterioles and small arteries leading to skeletal muscle is influenced by metabolic (oxygen and nutrients) need of the muscleBlood flow to the muscles is determined by the:1) intensity of exercise2) number of motor units recruited determines the overall need for blood flow to the muscle
Describe blood flow, HR, and cardiac output during incremental exercise and the two primary factors that increases cardiac output during incremental exercise
Blood flow to muscle increases as a function of oxygen uptake. HR and CO increase linearly with work rate. The increase in cardiac output during incremental exercise is achieved due to: 1) A decrease in vascular resistance to blood flow2) An increase in mean arterial blood pressure- MAP increases linearly with increasing work rate (systolic BP increases and diastolic BP remains fairly constant)Both CO and HR reach a plateau at approximately 100% max of VO2. This physiologic plateau represents a maximal ceiling for oxygen transport to exercising skeletal muscles. Occurs simultaneously with the attainment of maximal oxygen uptake
Describe the impact of body position on stroke volume changes during exercise and during upright and supine exercise
Body position has a major influence on stroke volume at rest and during exercise because of the effect of gravity on venous return.At rest and in the upright position, gravity promotes blood pooling in the leg. It results in a reduced venous return to the heart and a reduced end-diastolic volume which results in a smaller stroke volume. Decreased venous return ---> decreased end diastolic volume ---> decreased preload --> decreased stroke volumeExercise in the upright position (running or cycling) results in increased venous return, a larger end-diastolic volume, and improved SVExercise in a supine position (swimming) results in smaller increases (20%-40%) in stroke volume above resting conditions. If you transition from rest to exercise in the supine position, resting blood does not pool in legs, and therefore, venous return to the heart is not impeded and starts higher than if you transition from rest to exercise in the upright position.Compared to the upright position, rest to exercise end-diastolic volumes and stroke volumes are higher in the supine position. Since stroke volume is already high in the supine position, the increase in stroke volume that occurs during swimming exercise is not as great as the increase in stroke volume that occurs during upright exercise
Describe the changes in cardiac output during exercise
Cardiac output increases during exercise in direct proportion to the metabolic rate required to perform the exercise.Cardiac Output = Heart rate x Stroke volumeThe relationship between cardiac output and intensity is essentially linear. Percent maximal oxygen uptake is a measure of intensity. The increase in cardiac output during exercise is achieved by an increase in both stroke volume and heart rate
Describe the factors that changes in heart rate, stroke volume and blood pressure depend on
Changes in HR, SV, and BP depends on type of exercise (arm vs leg), intensity of exercise, duration of exercise, environmental conditions (hot/humid vs cool), and training state of the individual
Describe the changes in metabolic need for oxygen during exercise and the two mechanisms used to meet those changes
During exercise, the metabolic need for oxygen in skeletal muscle increases many times over the resting value. During intense exercise it may increase 15 times to 25 times greater than at rest.To meet this rise in oxygen demand, blood flow to the contracting muscle must increase. Increased oxygen delivery to exercising skeletal muscle is accomplished via two mechanisms1) Increased cardiac output2) Redistribution of blood flow from less active organs to the more active skeletal muscles
Describe vasodilation and vasoconstriction during exercise
During exercise, vascular resistance to flow in skeletal muscle decreases. Vascular resistance to flow in the visceral organs and other less active tissue and organs increases. Increased vascular resistance to flow in the visceral organs and other less active tissue and organs occurs due to an increased sympathetic output to organs and tissues. This response is regulated by the cardiovascular control center. As such, it represents the "default" for less metabolically active organs and tissues
Describe the increase in blood flow to skeletal muscles during exercise, how muscles regulate, and what factors determine the amount of increased muscle blood flow
During maximum exercise, the CO increases 5 fold.Muscle have the unique ability to regulate their own blood flow in direct proportion to their metabolic needs. During exercise, skeletal muscle blood flow increases in direct proportion to the metabolic demand. Alterations in blood flow are proportional to the recruited muscle mass. Blood delivery to contracting skeletal muscle during intense exercise may rise 100 time blood flow at rest.Increased muscle blood flow occurs because of:1) A decrease in vascular resistance- vasodilation of blood vessels going to skeletal muscle2) Combined with "recruitment" of the capillaries in skeletal muscle- at rest, only 50% to 80% of the capillaries in skeletal muscle are open at any one time- however, during intense exercise, almost all of the capillaries in contracting muscle are open, resulting in increased oxygen delivery to the contracting muscle fibers
Describe the factors that influence recovery of HR, SV, and CO from exercise
During recovery, the decrease in HR, SV, and CO toward resting levels depend on duration and intensity of exercise and training state of subject. Age-matched trained subjects recover faster following exercise because they don't achieve as high a heart rate as untrained subjects during a particular bout of sub-maximal exercise. Recovery from short-term, low-intensity exercise is generally rapid. Recovery from long-term exercise than shorter exercise is much slower. Particularly when the exercise is performed in hot/humid conditions because an elevated body temperature delays the fall in heart rate during recovery from exercise
Describe how the body redistributes blood flow at rest and during exercise to the brain
Even though the percentage of total cardiac output received by the brain is reduced during heavy exercise as compared to rest (from 15% to 3-4%), the absolute volume of blood that reaches the brain is actually slightly increased above resting values. The slight increase in blood supply to the brain is due to the elevated cardiac output during physical activity. It emphasizes the physiologic importance of continued brain function even during exercise
Describe the intrinsic and extrinsic control of blood flow during exercise
Extrinsic controls: control is from outside of the tissue or organ. Nervous system (SNS) and endocrine system control blood flow through the whole body. They act on smooth muscle of arterioles.Intrinsic control (autoregulation or local control): control is entirely from within the tissue or organ. Autoregulation control of blood flow is adjusted locally to meet specific tissue's requirement. Organs regulate their own blood flow by varying resistance of their own arterioles. Local arterioles that feed capillaries can undergo modification of their diameters. Uses paracrine signaling or properties of muscle tissue.
Describe heart rate variability and why a wider variation is considered healthy compared to a narrower variation
Heart rate variability (HRV) is the variation between beats. Standard deviation of the R-R interval.Represents a balance between SNS and PNS (sympathovagal balance)A wide variation in resting heart rate is considered "healthy", so a higher resting HRV is healthy. A low variation in resting HRV is a predictor of cardiovascular morbidity and mortality. It indicates an imbalance exists in autonomic regulation. Patients with existing cardiovascular disease often have low resting HRV
Describe how the body redistributes blood flow at rest and during exercise to the skin
In the transition from rest, skin blood flow increases during both light and moderate exercise in order to dissipate heat.During maximal exercise, skin blood flow decreases in order to support muscular work. Given that maximal-intensity exercise is not sustainable for an extended time period, the reduction in skin blood flow is not problematic in terms of thermal regulation
Describe the stroke volume changes during exercise
In untrained or moderately endurance trained individuals: stroke volume seems to plateau around 40% to 60% max of workload. At work rates greater than 40% to 60% max, the rise in cardiac output in these individuals is achieved by increases in heart rate alone. At high HR, filling time is decreased --> decrease in EDV ---> decrease in SVIn highly endurance trained individuals: stroke volume does not seem to plateau. Highly trained endurance athletes have improved ventricular filling due to increased venous return. Increased venous return increases EDV, which increases preload and increases SV, even at high HR. Therefore, at all work rates, the rise in cardiac output in these individuals is achieved by increases in heart rate and stroke volume
Describe the HR changes during exercise
Increased heart rate: there is a linear increase in HR as intensity increases. It will increase in a linear fashion as intensity increases but only up to an individual's maximum HR.For adults: Max HR = 220 - age in yearsFor children: Max HR = 208 - 0.7 x age in years
Describe the central command theory
Initial signal to "drive" cardiovascular system comes from higher brain centers due to centrally generated motor signals. Fine-tuned by feedback from:1) Heart mechanoreceptors2) Muscle chemoreceptors- sensitive to muscle metabolites (K+, lactic acid)- exercise pressor reflex3) Muscle mechanoreceptors- sensitive to force and speed of muscular movement4) Barorecpetors- sensitive to changes in arterial blood pressure
Describe the effects of age on cardiac output
Maximal cardiac output tends to decrease in a linear fashion in both men and women after 30 years of age. In healthy individuals, the age-dependent drop in maximal cardiac output is primarily due to a decrease in maximal heart rate with age. The formula is only an estimate and actual maximal heart rates can be 20 beats x min higher or lower in a given individual
Describe what effects recovery of heart rate and blood pressure during incremental exercise
Recovery of heart rate and blood pressure between bouts depend on fitness level, temperature and humidity, and duration and intensity of exercise.With a relatively light effort in a cool environment, there is often complete recovery when exercise intervals are separated by several minutes. However, if the exercise is intense or the work is performed in hot/humid environment, there is a cumulative increase in heart rate between efforts, and thus recovery is not complete.During high-intensity intermittent exercise, heart rate and blood pressure can approach maximal values
Describe the emotional influence on submaximal and maximal exercise
Submaximal exercise is an emotionally charged atmosphere when compared to the same work in a psychologically "neutral" environment results. Elevated HR and BP in emotionally charged environments due to increase in SNS activity.If the exercise intensity is maximal, high emotion elevates the pre-exercise heart rate and blood pressure, but does not generally alter the peak heart rate or blood pressure observed during the exercise itself
Describe sudden cardiac death
Sudden cardiac death during exercise is not common.
Describe the causes of sudden cardiac death and measures we can take to prevent it from occurring
The causes of sudden cardiac death are diverse and vary as a function of age. In children and adolescents, often due to genetic anomalies of coronary arteries, cardiomyopathy, or myocarditis. Occurs in 1/200,000 youth athletes. Often caused by abnormal, lethal heart rhythms. In adults, it is often due to coronary heart disease, cardiomyopathy, and lethal cardiac arrhythmias.A medical exam can identify people at risk for sudden cardiac death during exercise:1) Medical history2) A complete medical exam can often identify individuals with underlying heart disease or genetic defects would place them at risk for sudden cardiac death during exercise.A complete medical exam often includes (but is not limited to) a graded exercise test with 12-lead ECG and metabolic data, an echocardiographic, a coronary artery calcium scan by a qualified physician.
Describe the double rate product
The increase in HR and SBP that occurs during exercise results in an increased afterload on the heart. The increased metabolic demand placed on the heart during exercise can be estimated using the double product.Double product = HR x Systolic BPThe double product indicates the work of the heart and increases linearly with exercise intensity
Describe cardiovascular drift
The increase in heart rate and decrease in stroke volume observed during prolonged exercise is often referred to as cardiovascular drift.Cardiovascular drift is the progressive drift in heart rate is due to the influence of rising body temperature on dehydration and a reduction in plasma volume
Describe the intrinsic factors that promote vasodilation of blood vessels to skeletal muscle during exercise
The increased rate of skeletal muscle during exercise causes several factors to promote vasodilation by increasing smooth muscle relaxation in arterioles thereby dilating them.Decreased O2, increased CO2, increased [H+] (decreased pH)Increased [K+]Increased production of nitric oxide, prostaglandins, ATP, adenosine, endothelium-derived hyperpolarization factorsThe interplay between these factors causes vasodilation of arterioles of blood vessels going to contracting skeletal muscles. The vasodilation reduces the vascular resistance and, therefore, increases blood flow
Describe the Fick equation and the relationship of the variables in the Fick equation
The relationship between cardiac output, a-vO2 difference, and oxygen uptake is given by the Fick equation.VO2 = CO x a-VO2 differenceAn increase in cardiac output and/or a-vO2 difference would increase VO2. During exercise, oxygen consumption increases due to both an increase in CO and an increase in the difference
Describe how the body redistributes blood flow at rest and during exercise to skeletal muscles
To meet the increased oxygen demand of the skeletal muscles during exercise, it is necessary:1) To increase blood flow to active muscles blood flow2) While reducing blood flow to less active organs such as the liver, kidneys, or GI tractThe amount of redistribution depends on the exercise intensity (metabolic rate increases). Muscle and splanchnic (pertaining to the viscera) blood flow change as a function of exercise intensity.At rest, approximately 15% to 20% of total cardiac output is directed toward skeletal muscle. During intense exercise, upwards of 80% to 85% of total cardiac output goes to contracting skeletal muscle. The increase in blood flow to skeletal muscle is necessary to meet the large increase in oxygen requirements during intense exercise. In the transition from rest to maximal intensity exercise, there is an increase in both the volume and percentage of total cardiac output that skeletal muscle receives.During exercise the body will vasodilate the blood vessels going to skeletal muscles in order to increase blood flow to active muscles and vasoconstrict blood vessels to less active organs which decrease blood flow to less organs such as the liver, kidneys, and digestive organs.
Describe the velocity of blood flow
Velocity of flow changes as blood travels through systemic circulation. It is the fastest in aorta, slowest in capillaries, and then increases in veins againVelocity is inversely related to total cross-sectional area. Capillaries have largest area so slowest flow. Slow capillary flow allows adequate time for exchange between blood and tissues
