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heart pressures
- atrial systole - pressure in 2 atria exceeds resistance of ventricles and tricuspid and mitral valves open
- ventricular systole - pressure in 2 ventricles exceeds resistance of outflow vessels, tricuspid and mitral close, pulmonic and aortic valves open
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preload
- volume of blood filling the ventricles at end of diastole
- measured by:
- 1. RV - central venous pressure (CVP)
- 2. LV - pulmonary artery end diastole pressure (PCWP) or Wedge
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assessment of right heart preload
- increased right heart preload (fluid overload):
- 1. jugular vein distention
- 2. ascites
- 3. hepatic engorgement
- 4. peripheral edema
- decreased right heart preload (dehydration):
- 1. poor skin turgor (immediate sign)
- 2. dry mucous membranes
- 3. orthostatic hypotension
- 4. flat jugular veins
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assessment of left heart preload
- increased left heart preload (mostly pulmonary symptoms):
- 1. dyspnea
- 2. cough
- 3. third and fourth heart sounds
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starling's law
- force of contraction of cardiac muscles is dependent on stretch of cardiac muscle fibers
- increased preload=increased contractility
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factors affecting preload
- blood volume
- 1. hypo/hypervolemia
- atrial contractions
- 1. atrial kick - 25-30% of cardiac output
- 2. loss of atrial kick in atrial fibrillation
- venous return to heart
- 1. physical, physiological, and medication factors
- cardiac muscle fibers
- 1. heart failure
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afterload
- resistance to ejection of blood from the ventricle or the pressure the ventricle must generate to overcome resistance created by arteries
- measured by systemic vascular resistance (SVR) normal=800 to 1200
- increased afterload=increased workload on heart
- increased workload=increased O2 demand
- dilated vessels=low SVR
- constricted vessels=high SVR
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factors affecting afterload
- outflow obstructions
- 1. aortic stenosis
- vascular tone
- 1. vasodilation (septic shock)
- 2. vasoconstriction (HTN)
- medications
- 1. vasodilators
- 2. vasoconstrictors
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contractility
- ability of cardiac muscle fibers to shorten in length
- increased muscle fiber shortening=increased contractility=increased cardiac squeeze
- inotropy - meds that affect contractility
- 1. positive inotrope - increase contractility (digoxin, epi, milronone)
- 2. negative inotrope - decrease contractility (beta blocker & CCB)
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factors affecting contractility
- autonomic nervous system stimulation
- 1. increased stimulation=fight or flight= catecholamines=increased contractility
- medication - positive and negative inotropes
- electrolytes - imbalances=decreased contractility
- oxygenation - hypoxia=decreased contractility
- acid base balance (7.35-7.45) - acidosis= decreased contractility
- preload (fluid balance) - increased preload
- =increased contractility (starling's law)
- muscle fiber condition - CHF/cardiomegaly= decreased contractility
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diagnostic testing
- creatinine phosphokinase (CPK) - onset 4 to 12 hrs post damage
- troponin - found in cardiac muscle; onset 3 to 4 hrs post myocardial damage
- b type natriuretic peptide (BNP) - for heart failure; released from ventricles when preload is increased; normal=100
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diagnostic procedures to assess CO
- CXR
- ECG and stress ECG
- echo and TEE
- cardiac cath
- electrophysiology study
- nuclear perfusion imaging
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pulmonary artery catheter
- Swan-Ganz or right heart catheter
- measures pulmonary artery systolic and diastolic pressures
- wedge pressure (pulmonary artery occlusion)
- cardiac output
- central venous pressure
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central venous pressure (CVP)
- measures filling pressures of right heart and measures fluid status
- normal CVP : 2-6
- low CVP : hypovolemia, dehydration, bleeding, vasodilation, diuresis
- high CVP : fluid overload, CHF, acute MI, renal failure
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PA Pressures
- normal : 20-30/8-15
- measures systolic and diastolic pressures of pulmonary artery
- reflects state of right ventricle and lung
- low PA : hypovolemia
- high PA : fluid overload/CHF, mitral stenosis, lung disease/COPD, pulmonary embolus, idiopathic pulmonary hypertension
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pulmonary artery wedge pressure
- normal: 4-12
- reflects blood pressure in the left ventricle at end diastole
- low wedge : hypovolemia
- high wedge : fluid overload, MI/cardiogenic shock, CHF
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Cardiac output (CO)
- amount of blood ejected by the heart per minute
- normal : 4-8L/min
- CO= HR x stroke volume
- stroke volume - amount of blood ejected by heart per beat
- normal stroke volume : 50-100mL
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Cardiac Index (CI)
- normal : 2.4 to 4
- CI < 2 indicates shock state
- CI=CO/ body surface area
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septic shock
- bacterial endotoxins produce massive arterial vasodilation
- severe decrease of BP
- decreased SVR
- increased HR, contractility, CO
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Cardiogenic shock
- nonfunctioning ventricular wall and heart loses pumping ability
- severe decrease in BP
- decreased CO
- increased SVR
- vasoconstriction
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complications of swan-ganz catheter
- pneumothorax
- infection
- balloon rupture
- pulmonary infarction
- pulmonary artery rupture
- v tach
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