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Regulation of local blood flow during exercise: What regulates blood flow to organs during exercise? • Autoregulation: skeletal muscle and other organs ? their own blood flow in proportion to their ? needs. • Skeletal muscle arterioles have ? vascular resistance during rest due to ?? stimulation causing ?. • Vasodilation of skeletal muscle arterioles leads to ? in vascular resistance and ? in blood flow due to changes in local metabolites: -?O2 -?CO2 -?nitric oxide -?potassium -?adenosine -?pH • Skeletal muscle ? "?" also increases blood flow to muscle. -At rest, only # to #% of capillaries in skeletal muscle are open at any one time but during intense exercise almost ? may be open.

What regulates blood flow to organs during exercise? • Autoregulation: skeletal muscle and other organs regulate their own blood flow in proportion to their metabolic needs. • Skeletal muscle arterioles have high vascular resistance during rest due to adrenergic sympathetic stimulation causing vasoconstriction. • Vasodilation of skeletal muscle arterioles leads to ↓ in vascular resistance and ↑ in blood flow due to changes in local metabolites: -↓O2 -↑CO2 -↑nitric oxide -↑potassium -↑adenosine -↓pH • Skeletal muscle capillary "recruitment" also increases blood flow to muscle. -At rest, only 50 to 80% of capillaries in skeletal muscle are open at any one time but during intense exercise almost all may be open.

do slide 23 on powerpoint

do slide 23 on powerpoint

Changes in arterial-mixed venous O2 content during exercise: • Arterial-mixed venous O2 difference (=arteriovenous or a-vO2 difference): amount of ? taken up from # ml blood • ↑ a-vO2 difference during exercise due to ? amount of O2 taken up and used for ? ATP production • Relationship between cardiac output (Q), a-vO2 difference, and VO2 is given by the ? equation: VO2 = ? x ?-??? difference

• Arterial-mixed venous O2 difference (=arteriovenous or a-vO2 difference): amount of O2 taken up from 100 ml blood • ↑ a-vO2 difference during exercise due to ↑ amount of O2 taken up and used for aerobic ATP production • Relationship between cardiac output (Q), a-vO2 difference, and VO2 is given by the Fick equation: VO2 = Q x a-vO2 difference

Transition from rest to exercise and exercise to recovery: • At the onset of exercise: -Rapid ↑ in ??, ??, ?? within the # second after muscular contraction begins -Steady state is reached within #-# min when exercise is ? • During recovery • ? in HR, SV, and cardiac output toward ? levels • Depends on: -? & ? of exercise (following ? exercise recovery is ?) -Training ? of subject (well conditioned athletes recover ?)

• At the onset of exercise: -Rapid ↑ in HR, SV, cardiac output within the first second after muscular contraction begins -Steady state is reached within 2-3 min when exercise is submaximal • During recovery • ↓ in HR, SV, and cardiac output toward resting levels • Depends on: -Duration and intensity of exercise (following prolonged exercise recovery is slower) -Training state of subject (well conditioned athletes recover faster)

Redistribution of blood flow during exercise: • During exercise it is necessary to ? blood flow to working skeletal muscle -At rest, #-#% of cardiac output to muscle -During maximal exercise, ↑ to #-#% to muscle • ? blood flow to less active organs -?,?,? tract • Redistribution depends on ?? (exercise intensity)

• During exercise it is necessary to ↑ blood flow to working skeletal muscle -At rest, 15-20% of cardiac output to muscle -During maximal exercise, ↑ to 80- 85% to muscle • Decreased blood flow to less active organs -Liver, kidneys, GI tract • Redistribution depends on metabolic rate (exercise intensity)

Sources of vascular resistance: • Greatest vascular resistance in blood flow occurs in ? • Large drop (# to #% decline) in ??? across the ?

• Greatest vascular resistance in blood flow occurs in arterioles • Large drop (70 to 80% decline) in MAP across the arterioles

Changes in maximal cardiac output with aging: • Maximal cardiac output ? in a linear fashion after age # in both men and women • This is primarily due to a ? in maximal HR Max HR = # - ? (?) • For a 20 year-old: Max HR=?-?=200 • For a 60 year-old Max HR=?-?=160

• Maximal cardiac output ↓ in a linear fashion after age 30 in both men and women • This is primarily due to a ↓ in maximal HR Max HR = 220 - age (years) • For a 20 year-old: Max HR=220-20=200 • For a 60 year-old Max HR=220-60=160

Changes in oxygen delivery during exercise: • Oxygen demand by muscles during exercise ↑ ? to ?x greater than at rest • Increased O2 delivery accomplished by: -Increased ?? -? of blood flow ----from ?? to ?? muscle

• Oxygen demand by muscles during exercise ↑ 15 to 25x greater than at rest • Increased O2 delivery accomplished by: -Increased cardiac output -Redistribution of blood flow ----from inactive organs to working skeletal muscle

Relationships among pressure, resistance, and flow: • Pressure -If pressure is higher in one end of a vessel then blood will flow from region of ? pressure to ? pressure, but if ?difference then ? flow • Blood flow -Proportional to the difference between ??? and ?? pressure (change in Pressure) -? proportional to resistance blood flow= change in ?/?

• Pressure -If pressure is higher in one end of a vessel then blood will flow from region of higher pressure to lower pressure, but if no difference then no flow • Blood flow -Proportional to the difference between MAP and right atrial pressure (change in Pressure) -Inversely proportional to resistance blood flow=change in pressure/resistance

Nitric oxide is an important vaso?: • Produced in the ?? • Promotes smooth muscle ? -Results in vaso? and ? blood flow • Important in ? of blood flow in conjunction with other local factors • Possibly one of several factors involved in blood flow ? during exercise • Muscular contraction may ? nitric oxide production -? of arterioles feeding working muscle -? muscle blood flow

• Produced in the vascular endothelium • Promotes smooth muscle relaxation -Results in vasodilation and increased blood flow • Important in autoregulation of blood flow in conjunction with other local factors • Possibly one of several factors involved in blood flow regulation during exercise • Muscular contraction may ↑ nitric oxide production -vasodilation of arterioles feeding working muscle -↑muscle blood flow

Stroke Volume ? Plateau in Endurance Athletes: • Stroke volume reaches a plateau at #-#% VO2 max in untrained subjects because -At high HR, filling time is ? leading to decreased ??? and ?? • Stroke volume ? plateau in trained subjects because of -? ventricular filling during heavy exercise due to increased ?? leading to increased force of ?? and increased ??

• Stroke volume reaches a plateau at 40-60% VO2 max in untrained subjects because -At high HR, filling time is decreased leading to decreased EDV and stroke volume • Stroke volume does not plateau in trained subjects because of -Improved ventricular filling during heavy exercise due to increased venous return leading to increased force of ventricular contraction and increased stroke volume

In summary: Oxygen delivery to exercising skeletal muscle increases due to: (1) an increased ?? and (2) a redistribution of ?? from inactive organs to the contracting skeletal muscle. Cardiac output ? as a linear function of ? uptake during exercise. During exercise in the upright position, stroke volume reaches a plateau at approximately #% of VO2 max; therefore, at work rates above #% VO2 max, the rise in cardiac output is due to increases in ?? alone. During exercise, blood flow to contracting muscle is ?, and blood flow to less active tissues is ?. Regulation of muscle blood flow during exercise is primarily regulated by local factors (called ?). Autoregulation refers to ? control of blood flow by changes in local metabolites (e.g., oxygen tension, pH, potassium, adenosine, and nitric oxide) around ?.

Oxygen delivery to exercising skeletal muscle increases due to: (1) an increased cardiac output and (2) a redistribution of blood flow from inactive organs to the contracting skeletal muscle. Cardiac output increases as a linear function of oxygen uptake during exercise. During exercise in the upright position, stroke volume reaches a plateau at approximately 40% of VO2 max; therefore, at work rates above 40% VO2 max, the rise in cardiac output is due to increases in heart rate alone. During exercise, blood flow to contracting muscle is increased, and blood flow to less active tissues is reduced. Regulation of muscle blood flow during exercise is primarily regulated by local factors (called autoregulation). Autoregulation refers to intrinsic control of blood flow by changes in local metabolites (e.g., oxygen tension, pH, potassium, adenosine, and nitric oxide) around arterioles.

Arm versus leg exercise • At the same oxygen uptake, arm work results in: ----? HR due to higher ? stimulation ---- ? BP due to ? of large inactive muscle mass (i.e., legs) • The larger the muscle group involved the more ? are dilated, the lower the ? resistance, the lower the ??

Arm versus leg exercise • At the same oxygen uptake, arm work results in: ----↑ HR due to higher sympathetic stimulation ---- ↑ BP due to vasoconstriction of large inactive muscle mass (i.e., legs) • The larger the muscle group involved the more arterioles are dilated, the lower the peripheral resistance, the lower the BP

Relationships among pressure, resistance, and flow cont: Blood flow=change in ?/? • Blood flow can be increased by ? blood pressure or ? resistance. -but a large ? in blood pressure can be hazardous -↑ in blood flow during exercise are primarily achieved through ? resistance and small ? in blood pressure. • Resistance is: -? proportional to the length of the vessel -? proportional to the viscosity of the blood -? proportional to the radius of the vessel resistance=? times ?/? to the # power • ? and ? do not change in normal physiology • The primary factor that regulates blood flow is the ?(i.e., ? and ?) • The effect of changes in ? on changes on blood flow are magnified by a power of #

Blood flow=change in pressure/resistance • Blood flow can be increased by ↑ blood pressure or ↓ resistance. -but a large ↑ in blood pressure can be hazardous -↑during exercise are primarily achieved through↓ resistance and small ↑ in blood pressure. • Resistance is: -Directly proportional to the length of the vessel -Directly proportional to the viscosity of the blood -Inversely proportional to the radius of the vessel resistance=length times viscosity/radius to the fourth power • Viscosity and length do not change in normal physiology • The primary factor that regulates blood flow is the radius (i.e., vasoconstriction and vasodilation) • The effect of changes in radius on changes on blood flow are magnified by a power of four

Central Command Theory • Initial signal to "drive"cardiovascular system comes from ?? centers ---- Due to centrally generated ?? • Fine-tuned by feedback from: -- ?? -- ?? ----Sensitive to muscle ? (?+,? acid) • Muscle mechanoreceptors -- Sensitive to ? and ? of muscular movement • Baroreceptors -- Sensitive to changes in ???

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: -- Heart mechanoreceptors -- Muscle chemoreceptors ----Sensitive to muscle metabolites (K+, lactic acid) • Muscle mechanoreceptors -- Sensitive to force and speed of muscular movement • Baroreceptors -- Sensitive to changes in arterial blood pressure

Circulatory responses to exercise: Changes in HR and BP depend on: -?, ?, & ? of exercise Environmental conditions: -• ? & ? conditions result in higher exercise HR • Emotional influence -Emotionally charged atmosphere can raise pre-exercise ?? and ?? compared to a neutral environment -Due to increased ??? activity -does not generally increase peak ?? and ?? during maximal exercise (e.g., 400-meter dash)

Changes in HR and BP depend on: -Type, intensity, and duration of exercise Environmental conditions: -• Hot and humid conditions result in higher exercise HR • Emotional influence -Emotionally charged atmosphere can raise pre-exercise HR and BP compared to a neutral environment -Due to increased SNS activity -does not generally increase peak HR and BP during maximal exercise (e.g., 400-meter dash)

Incremental exercise: • Heart rate and cardiac output ---- ? in direct proportion to ? uptake ---- Reach maximum and plateau at #% VO2 max • ↑ in cardiac output during incremental exercise is achieved via ? in vascular resistance and ? in MAP • Blood pressure ---- MAP ? linearly due to ? in ? BP ---- ? BP remains fairly ? • The ↑ in heart rate and ? BP during exercise results in ? workload on the heart

Incremental exercise • Heart rate and cardiac output ---- ↑ in direct proportion to O2 uptake ---- Reach maximum and plateau at 100% VO2 max • ↑ in cardiac output during incremental exercise is achieved via ↓ in vascular resistance and ↑ in MAP • Blood pressure ---- MAP ↑ linearly due to ↑ in systolic BP ---- Diastolic BP remains fairly constant • The ↑ in heart rate and systolic BP during exercise results in ↑ workload on the heart

Intermittent exercise (i.e. interval training) • Recovery of heart rate and blood pressure between bouts depend on: • ? level • ? & ? • ? & ? of exercise

Intermittent exercise (i.e. interval training) • Recovery of heart rate and blood pressure between bouts depend on: • Fitness level • Temperature and humidity • Duration and intensity of exercise

Prolonged exercise: • Cardiac output is maintained at ? level • Gradual ? in SV and ? HR called cardiovascular ?. ---- due to influence of ? body temperature on ? ---- ? in plasma volume → ? venous return to the heart → ? SV • If prolonged exercise in hot/humid environment the ? in HR and ? in SV is more ?. • During 2.5-hour marathon race in the heat at 70 to 75% of VO2max, maximal HR may be maintained during the last ? of the race

Prolonged exercise • Cardiac output is maintained at constant level • Gradual ↓ in SV and ↑ HR called cardiovascular drift. ---- due to influence of rising body temperature on dehydration ---- ↓ in plasma volume → ↓ venous return to the heart → ↓ SV • If prolonged exercise in hot/humid environment the ↑ in HR and ↓ in SV is more dramatic. • During 2.5-hour marathon race in the heat at 70 to 75% of VO2max, maximal HR may be maintained during the last hour of the race

Changes in cardiac output during exercise: formula for cardiac output=?? times ?? • Cardiac output ? in proportion to metabolic need. • During ? exercise cardiac output ? due to: -?HR ----Linear ? to max • ↑ in SV -?, then plateau at ~# to #% VO2 max in untrained or ? trained -No ? in highly trained subjects

Q=HRxSV • Cardiac output ↑ in proportion to metabolic need. • During upright exercise cardiac output ↑ due to: -↑HR ----Linear ↑ to max • ↑SV -↑, then plateau at ~40 to60% VO2 max in untrained or moderately trained -No plateau in highly trained subjects

Regulation of cardiovascular adjustments to exercise • CV adjustments at the beginning of exercise are ?. • Within 1 sec after muscular contraction begins, there is: -- Cardiovagal ? followed by ? stimulation of the heart. -- Vasodilation of ? in active skeletal muscle -- Reflex ? in resistance in ?-active areas. • End result is ? cardiac output to ensure blood flow to muscle matches the ? needs.

Regulation of cardiovascular adjustments to exercise • CV adjustments at the beginning of exercise are rapid. • Within 1 sec after muscular contraction begins, there is: -- Cardiovagal withdrawal followed by sympathetic stimulation of the heart. -- Vasodilation of arterioles in active skeletal muscle -- Reflex ↑ in resistance in less-active areas. • End result is ↑ cardiac output to ensure blood flow to muscle matches the metabolic needs.