24-27. Cardiovascular Flashcards
Describe VO2 using the Fick Principle. Identify each element in this equation for CV oxygen delivery.
VO2 = Q(c) x (a-V)O2
- “Oxygen consumption = total blood flow x uptake of O2 from blood by tissue”
- Q = cardiac output
- a = arterial
- V = venous
What are the general purposes of the CV system?
- To support cellular metabolism by delivering metabolic substrates & removing wastes
- Provide an optimized cell bath for every cell in body
What are the coronary arteries?
Arteries running along surface of heart
Describe the sequence of depolarization in the heart starting at the sino-atrial node.
LOOKUP
Give a brief description of the cardiac cycle, noting the timing of isometric contraction and relaxation, the closing and opening of the atrio-ventricular vs. aortic/pulmonic valves, and when ejection of blood occurs.
LOOKUP
In a cardiac pressure-volume loop , what would be the effects of increased preload? Afterload? Contractility?
- Preload = increased EDV (ESV same), increased SV, increased EF
- Afterload = decreased SV, increased ESV, decreased EF
- Contractility = increased SV, decreased ESV, increased EF
Define stroke volume.
EDV - ESV
Define ejection fraction.
SV / EDV
Define cardiac output.
HR x SV
If EDV = 90 ml, ESV = 30 ml, and HR = 70 b/min, what is the SV? EF? Q?
- SV = 60 ml
- EF = 60/90
- Q = 70 x 0.06 = 4.2 L/min
What are the factors affecting cardiac output during exercise?
- Preload
- Afterload
- Contractibility
- HR
What ultimately causes cardiac output?
Venous return
Describe the Frank-Starling curve. How do changes in preload or contractility alter this curve?
- Muscle length-tension in heart
- Preload increases tension –> increases strength of contracility
What are the 2 factors that control MAP? What happens to these factors during exercise?
MAP = CO x TPR
- CO increases during exercise
- TPR decreases during exercise
What are the trends in vessel diameter and blood velocity, from the aorta to the capillaries to the vena cava?
- Aorta = large diameter, fastest velocity
- Capillaries = smallest diameter, slow velocity
- Vena cava = largest diameter, medium velocity
Describe the pressure and volume distribution of the blood throughout the systemic circulation.
LOOKUP
Describe Poiseuille’s Law and the effects of pressure, radius, and length on flow through a vessel.
- Flow through a tube is directly proportional to the driving pressure along the tube and r^4 (major factor)
- Flow is inversely proportional to the length of the segment (constant) and the viscosity of the liquid (constant, minor factor)
What is the effect of hematocrit on the relative viscosity of blood?
Hematocrit predicts blood viscosity
-Viscosity increases exponentially as hematocrit increases above 50%
How does hematocrit change with training?
Decreases
Define preload.
EDV (ventricular stretch) due to venous return
Define afterload.
Pressure in the aorta that must be overcome in order to begin ejection phase
Define contractility.
Velocity and force produced by heart muscle contraction
What are the factors affecting preload? How does each affect cardiac function?
- Cardiac output
- Muscle pump
- *increase in factors increases cardiac function
What are the factors affecting afterload? How does each affect cardiac function?
Sympathetic and parasympathetic impulses
**increase in factors decreases cardiac function
What are the factors affecting contractility? How does each affect cardiac function?
- Sympathetic and parasympathetic impulses
- Circulating catecholamines
- *increase in factors increases cardiac function
What is the equation for venous return?
VR = (pressure in systemic veins - pressure in right atria) / resistance in great veins
How would an increase in driving pressure (pressure in systemic veins) affect venous return?
Increases VR
How would an increase in right atrial pressure affect venous return?
Decreases VR
What are the mechanisms that increase P(sv) during exercise?
- Venous muscle pump
- Vasoconstriction of high compliance vessels
- Venoconstriction
How does vasoconstriction increase P(sv) during exercise?
- Vasoconstriction of high compliance vascular beds automatically recruits blood back into the central circulation
- Limits delivery of blood to high compliance vascular beds
How does the CV system adapt to chronic dynamic exercise? (structural & regulatory changes)
- Bigger hearts = increase in LV cavity and wall thickness
- More blood = increase in plasma, decrease in hematocrit
- Less stress = reduced catecholamine response to any submaximal workload, increase capacity for catecholamine secretion to support new maximal abilities
- Vessels bud = more blood vessels for diffusion of O2 to the cells
How does the Bainbridge reflex help match cardiac output to venous return?
HR accelerates during inhalation to accommodate the transient increase in VR created by negative intrathoracic pressure
What are the 3 types of sympathetic receptors? Functions? Distribution?
- alpha 1 = vasoconstriction of all vessels
- beta 1 = increase in spontaneous depolarization and contractility in cardiac muscles and pacemakers
- beta 2 = vasodilation in pulmonary bronchi and coronary arteries
How does the venous muscle pump increase P(sv) during exercise?
Increase amount of muscle recruited & contractility of muscle
From where are epinephrine and norepinephrine released?
Adrenal gland
What are some factors that affect vessel diameter?
- Venous muscle pump
- Vasoconstriction of high compliance vessels
- Venoconstriction
Is there a general vasoconstriction or vasodilation at the onset of exercise? As exercise progresses?
- Onset = vasoconstriction
- Progresses = vasodilation
What are the factors involved in neuroendocrine control of circulation?
Norepinephrine and epinephrine
What is the specificity of sympathetic nervous action dependent on?
- Type of adrenergic receptors
- Local overrides
To and from where is blood flow redistributed during exercise? How?
- To organs in need
- From heart and major arteries
