“BASIC SUMMARY” of CARDIOVASCULAR PHYSIOLOGY
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Transcript of “BASIC SUMMARY” of CARDIOVASCULAR PHYSIOLOGY
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“BASIC SUMMARY” of
CARDIOVASCULAR PHYSIOLOGY The purpose/goal of C.V.S. is : adequate PERFUSION
of the Tissues
PERFUSION = BLOOD FLOW,
THUS, DELIVERY of vital O2 nutrients, etc, REMOVAL of wastes.
“HEMODYNAMICS” refers to ALL the mechanisms
(blood moving/changing) involved in keeping blood flow ‘normal’
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DETERMINANTS OF PERFUSION: 1) CARDIAC OUTPUT Proper Electrical and Mechanical Function of the HEART as a PUMP
2) BLOOD VOLUME the vascular ‘tank’ must be adequately filled with fluid to supply the need
3) BLOOD PRESSURE : “ FLOW” of a fluid is dependent upon PRESSURE - and is always
from “high” pressure area to lower pressure area.
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At rest, typically, Cardiac Output is 5 liters per minute
(recall that an average man’s total Blood Volume is ~ 5 liters)
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CARDIAC OUTPUT depends on 2 ‘functions’ of the heart: A) ELECTRICAL function (Conduction system) Generation and Propagation of a coordinated
Impulse to contract, from atrium to ventricle Conduction system: SA node, AV node, AV Bundle,
R and L Bundle Branches, Purkinje system(graphic measure of conduction: electrocardiogram) ECG = “EKG” p wave, QRS complex, t
wave B) MECHANICAL FUNCTION 1. CONTRACTILITY of the Myocardium ( strength / force of the
contractions) 2. VALVULAR function
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AV Bundle, (Bundle of His)
Cardiac conduction system: SA node AV node Bundle of His Right Bundle Branch Left Bundle Branch Purkinje Fibers
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ELECTRICAL FUNCTION
REGULATED RATE AND RHYTHM:
Rate -- optimal rate depends on demand.
normal at rest 60-100 bpm (Lance Armstrong’s is
in the 30’s ) abnormal rates: bradycardia
too slow
tachycardia too fast RHYTHM -- SHOULD BE
REGULAR not skippy or chaotic
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Nor
Normal sinus, rate ~64 bpmOnset, supraventricular tachycardia, rate ~120
Normal sinus rhythm, rate ~72 bpm
Atrial fibrillation, V.rate varies, ~130-150
Ventricular fibrillation, a terminal rhythm
Rhyth
m strip
s
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MECHANICAL FUNCTION CONTRACTILITY of the MYOCARDIUM: the strength / force &
completeness of the Contractions
(effects of ischemia / necrosis; CAD, HTN drugs, etc)
The essence of “Congestive Heart Failure”
is usually that of INADEQUATE
squeeze capacity of the heart muscle
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Cardiac Cycle DIASTOLE - atria contract, Vent. relax;
blood flows thru the AV valves, fills Ventricles.
(P wave on the EKG)
SYSTOLE –Ventricles contract, Blood EJECTED into Aorta and Pulm.
Trunk, Art. (QRS complex on the EKG)
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VALVULAR FUNCTION NARROWED VALVE: STENOSIS diminished outflow INCOMPETENT VALVE: REGURGITATION or INSUFFICIENCY: abnormal “Backflow
“
the “ Heart Sounds “ are made by the valves closing – ‘ Lub Dupp lub dupp lub duppMurmur : swishing sound , made by TURBULENCE of flow can be either from Stenosis or Regurgitation *** abnormal valvular function affects Cardiac Output
directly, and indirectly by eventually affecting Contractility of the muscle
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CARDIAC OUTPUT CARDIAC OUTPUT - HOW MUCH BLOOD
CAN BE PUMPED each minute? normal, resting ~ 5 liters / min
(roughly the entire blood volume makes one cycle in one minute)
CO = HR x SV
CARDIAC HEART RATE X STROKE VOLUME
OUTPUT pulse amt blood ejected
beats per minute each beat
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BLOOD VOLUME Euvolemia hypovolemia volume overload Multiple variants:
“Hydration” status (intake -- outgo) diuresis, diarrhea, vomiting, sweating, hyperthermia/ fever,
Proper blood production by bone marrow
Lack of ‘hemorrhage’, or blood loss
complex regulatory mechanisms involving kidney function, endocrine regulatory centers, plasma protein conc., & others
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BLOOD PRESSURE 1. It takes adequate BLOOD Volume for
normal BP 2. It takes adequate ‘FORCE’ on the FLUID to make it FLOW:
A. Contractions of the Heart generate initial PRESSURE SURGE, but, the chief
determinant of Blood pressure is: B. VASCULAR RESISTANCE- affects
the BLOOD VOLUME IN THE ARTERIES:
Increased resistance VASOCONSTRICTION ^’s BP
(but less flow)
Decreased resistance decr’s BP: VASODILATION
(more flow)
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REGULATION of Arterial Resistance The regulation / changes made in Arterial
resistance in the various ‘REGIONs’ of the body Account for the Alterations
/adjustments in BLOOD FLOW to those areas(increased flow to MUSCLES during exercise,
Incr. Flow to Digestive tract after meals,
^ flowed to skin to dissipate heat,
Whereas Blood Flow to BRAIN and KIDNEYS must remain rel. CONSTANT
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Measuring blood pressure:
SPHYGMOMANOMETER AND STETHOSCOPE
SYSTOLIC BLOOD PRESSURE / DIASTOLIC BLOOD
PRESSURE (Korotkoff
sounds)
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other important effects (on CO, and PERFUSION)
VENOUS RETURN: THE FLOW OF BLOOD BACK TO THE HEART AFTER DELIVERY TO THE CAPILLARIES VEINS: larger diameter, with elastic walls, increased CAPACITANCE compared to corresp. Artery
IMPORTANT - GRAVITY generally impedes VENOUS return ----- so,
VEINS have series of one way VALVES - which keep
the blood from flowing backwards
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Also: There are 2 FUNCTIONAL
VENOUS ‘PUMPS’:
1. SKELETAL MUSCLE CONTRACTIONS, and
2. RESPIRATORY MOTIONS create negative inspiratory pressure, which ‘’SUCKS’ VENOUS BLOOD INTO THE THORAX, TOWARD THE HEART
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Modifications that promote venous return: Large lumens Valves
Muscular pump – skeletal muscle activity “milks” blood toward heart
Respiratory pump – pressure changes during breathing move blood toward heart
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And FINALLY: CAPILLARIES must mention : CAPILLARIES –
Where the ‘ACTION IS’ regarding EXCHANGE of
substances between the Vascular &
INTERSTITIAL spaces , at the
Cells / Tissues level. (fluid, o2, co2 WBC’s,
molecules, etc ) can diffuse back and forth
( importance of hydrostatic and osmotic pressure )
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Structure of Capillaries: ONLY 1 layer of endothelium and A basement membrane, with “SPACES” for DIFFUSION - no muscle or connective tissue covering. A large number of capillaries in a specific
region is called a CAPILLARY BED
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5. Circulatory Shock (or circulatory failure, a state
of hypoperfusion)Inadequate blood flow to meet cellular needs.
Hypovolemic shock – due to decreased blood volume.
Septic shock (or vascular shock) – due to inappropriate vasodilation, brought about by response to overwhelming infection.
Cardiogenic shock – due to poor heart function.