Major Adjustments to Circulatory System During Exercise. Flashcards
Increase Cardiac Output (Q) Formula
(Q = HR * SV); Typical values at rest and during exercise depend on training state and gender
Heart Rate (HR)
Number of beats per minute
Stroke Volume (SV)
Amount of blood ejected in each beat
Parasympathetic Nervous System
Via vagus nerve; Slows HR by inhibiting SA and AV Node
Sympathetic Nervous System
Via cardiac accelerator nerves; Increases HR by stimulating SA and AV node
Low resting HR due to…
Parasympathetic Tone
Increase in HR at onset of exercise
1st parasympathetic withdrawal (up to ~100 bpm), 2nd increased SNS stimulation
Expected Values for Untrained Male at Rest
72 b/min x 70 ml/beat = 5.00
Expected Values for Untrained Female at Rest
75 b/min x 60 ml/beat = 4.50
Expected Values for Trained Male at Rest
50 b/min x 100 ml/beat = 5.00
Expected Values for Trained Female at Rest
55 b/min x 80 ml/beat = 4.40
Expected Values for Untrained Male at Max Exercise
200 b/min x 110 ml/beat = 22.0
Expected Values for Untrained Female at Max Exercise
200 b/min x 90 ml/beat = 18.0
Expected Values for Trained Male at Max Exercise
190 b/min x 180 ml/beat = 34.2
Expected Values for Trained Female at Max Exercise
190 b/min x 125 ml/min = 23.8
End-Diastolic Volume (EDV)
Volume of blood in the ventricles at the end of diastolic (“Preload”)
Average Aortic Blood Pressure
Pressure the heart must overcome to eject blood (“Afterload”)
Strength of Ventricular contraction (contractility) is enhanced by
Circulating epinephrine and norepinephrine, Direct sympathetic stimulation of heart
SV is influenced by:
Frank Starling Mechanism, Catecholamines
Frank Starling Mechanism
(Only beneficial to 60% Max exercise) Greater EDV results in more forceful contraction due to stretch of ventricles (Length/Tension Relationship) and is dependent on venous return
Venous return is influenced by:
1) Venoconstriction (via SNS), (2) Skeletal Muscle Pump (Skeletal muscle cx force blood back toward the heart, One-way valves in veins prevent backflow of blood), (3) Respiratory Pump (Changes in thoracic pressure pull blood toward heart)
Catecholamines
influence stroke volume by increasing cardiac contractility by increasing the amount of calcium available to the myocardial cell; specifically increase the entry of extracellular calcium into the cardiac muscle fiber which increases cross bridge activation and force production
Where does majority of blood goes at rest?
15-20% of cardiac output to muscle
Where does majority of blood goes during exercise?
Increases to 80-85% during maximal exercise; Decreased blood flow to less active organs (Liver, Kidneys, GI Tract), Redistribution depends on metabolic rate (Exercise Intensity)
Metabolic need:
Autoregulation refers to intrinsic control of blood flow by increases in local metabolites (e.g., nitric oxide, prostaglandins, ATP, adenosine, and endothelium-derived hyperpolarization factors). These factors work together to promote vasodilation to increase blood flow to the working muscles.
The exercise-induced increase in local factors result in…
Increased vasodilation of arterioles/small arteries and promote increased blood flow to the contracting muscle in order to match the metabolic demand.
Autoregulation
Blood flow increased to meet metabolic demands of tissue due to changes in O2 tension, CO2 tension, Nitric Oxide, Potassium, Adenosine, and pH
Cardiovascular Control Center
Regulates vascular resistance in skeletal muscle decreases during exercise, vascular resistance to flow in the visceral organs and other inactivity tissue increases.
As a result of the increase in visceral vasoconstriction during exercise (resistance increases):
blood flow to the viscera can decrease to only 20% to 30% of resting values
