Cardiovascular - First Aid Flashcards
Heart Embryology:
ascending aorta and pulmonary trunk
Truncus Arteriosus
Heart Embryology:
smooth parts (outflow tract) of left and right ventricles
Bulbus Cordis
Heart Embryology:
- atrial septum
- membranous interventricular septum
- AV and semilunar valves
Endocardial Cushion
Heart Embryology:
trabeculated part of left and right atria
Primitive Atrium
Heart Embryology:
trabeculated part of left and right ventricles
Primitive Ventricle
Heart Embryology:
smooth part of left atrium
Primitive Pulmonary Vein
Heart Embryology:
coronary sinus
Left Horn of Sinus Venosus
Heart Embryology:
smooth part of right atrium (sinus venarum)
Right Horn of Sinus Venosus
Heart Embryology:
superior vena cava (SVC)
- Right Common Cardinal Vein
- Right Anterior Cardinal Vein
The _____ is the first functional organ in vertebrate embryos.
heart
The heart beats spontaneously by _____ of development.
week 4
Cardiac Looping
- Primary heart tube loops to establish left-right polarity; begins in week 4 of gestation.
- Defect in left-right Dynein (involved in L/R asymmetry) can lead to Dextrocardia, as seen in Kartagener syndrome (1° ciliary Dyskinesia).
Septation of the Atria
- Septum primum grows toward endocardial cushions, narrowing foramen primum.
- Foramen secundum forms in septum primum (foramen primum disappears).
- Septum secundum develops as foramen secundum maintains right-to-left shunt.
- Septum secundum expands and covers most of the foramen secundum. The residual foramen is the foramen ovale.
- Remaining portion of septum primum forms valve of foramen ovale.
- Septum secundum and septum primum fuse to form the atrial septum.
- Foramen ovale usually closes soon after birth because of ↑ LA pressure.
_____ is caused by failure of septum primum and septum secundum to fuse after birth; most are left untreated. Can lead to paradoxical emboli (venous thromboemboli that enter systemic arterial circulation), similar to those resulting from an ASD.
Patent Foramen Ovale
Septation of the Ventricles
- Muscular interventricular septum forms. Opening is called interventricular foramen.
- Aorticopulmonary septum rotates and fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen.
- Growth of endocardial cushions separates atria from ventricles and contributes to both atrial septation and membranous portion of the interventricular septum.
_____ is the most common congenital cardiac anomaly.
Ventricular Septal Defect
VSD usually occurs in the _____.
membranous septum
Outflow Tract Formation
neural crest and endocardial cell migrations → truncal and bulbar ridges that spiral and fuse to form aorticopulmonary septum → ascending aorta and pulmonary trunk
Conotruncal Abnormalities Associated with
Failure of Neural Crest Cells to Migrate
- Transposition of Great Vessels
- Tetralogy of Fallot
- Persistent Truncus Arteriosus
Valve Development
- Aortic/Pulmonary: derived from endocardial cushions of outflow tract
- Mitral/Tricuspid: derived from fused endocardial cushions of the AV canal
Valvular anomalies may be _____.
- stenotic
- regurgitant
- atretic—tricuspid atresia
- displaced—Ebstein anomaly
Fetal Circulation
3 Important Shunts:
- Blood entering fetus through the umbilical vein is conducted via the ductus venosus into the IVC, bypassing hepatic circulation.
- Most of the highly oxygenated blood reaching the heart via the IVC is directed through the foramen ovale and pumped into the aorta to supply the head and body.
- Deoxygenated blood from the SVC passes through the RA → RV → main pulmonary artery → ductus arteriosus → descending aorta; shunt is due to high fetal pulmonary artery resistance (due partly to low O2 tension).
Blood in umbilical vein has a Po2 of ≈ _____ and is ≈ _____ saturated with O2.
- 30 mm Hg
- 80% O2
Transitional Circulation
At birth, infant takes a breath → ↓ resistance in pulmonary vasculature → ↑ left atrial pressure vs. right atrial pressure → foramen ovale closes (now called fossa ovalis); ↑ in O2 (from respiration) and ↓ in prostaglandins (from placental separation) → closure of ductus arteriosus.
_____ helps close PDA → ligamentum arteriosum (remnant of ductus arteriosus).
Indomethacin
Prostaglandins E1 and E2 kEEp PDA open.
Fetal-Postnatal Derivatives:
Median Umbilical Ligament
Allantois → Urachus
Urachus is part of allantoic duct between bladder and umbilicus.
Fetal-Postnatal Derivatives:
Ligamentum Arteriosum
Ductus Arteriosus
Fetal-Postnatal Derivatives:
Ligamentum Venosum
Ductus Venosus
Fetal-Postnatal Derivatives:
Fossa Ovalis
Foramen Ovale
Fetal-Postnatal Derivatives:
Nucleus Pulposus
Notochord
Fetal-Postnatal Derivatives:
Medial Umbilical Ligaments
Umbilical Arteries
Fetal-Postnatal Derivatives:
Ligamentum Teres Hepatis (Round Ligament)
Umbilical Vein
*contained in falciform ligament
Anatomy of the Heart
- Right-Dominant Circulation (85%) = PDA arises from RCA
- Left-Dominant Circulation (8%) = PDA arises from LCX
- Codominant Circulation (7%) = PDA arises from both LCX and RCA
The SA node is commonly supplied by the _____ (blood supply independent of dominance).
RCA
The AV node is supplied by the _____.
PDA
Coronary artery occlusion most commonly occurs in the _____.
LAD
Coronary blood flow peaks in _____.
early diastole
The most posterior part of the heart is the _____. Its enlargement can cause dysphagia (due to compression of the esophagus) or hoarseness (due to compression of the left recurrent laryngeal nerve, a branch of the vagus nerve).
left atrium
Pericardium Layers
Outer → Inner:
- Fibrous Pericardium
- Parietal Layer of Serous Pericardium
- Visceral Layer of Serous Pericardium
The pericardial cavity lies between parietal and visceral layers.
The pericardium is innervated by the _____.
phrenic nerve
Pericarditis can cause referred pain to the _____.
shoulder
Cardiac Output
CO = stroke volume (SV) × heart rate (HR)
Fick Principle
Mean Arterial Pressure
MAP = CO × total peripheral resistance (TPR)
MAP (at resting HR)
MAP (at resting HR) = ⅔ diastolic pressure + ⅓ systolic pressure
Pulse Pressure
Pulse Pressure = systolic pressure – diastolic pressure
Pulse pressure is proportional to SV, and inversely proportional to arterial compliance.
Stroke Volume
SV = end-diastolic volume (EDV) − end-systolic volume (ESV)
During the early stages of exercise, CO is maintained by _____.
- ↑ HR
- ↑ SV
During the late stages of exercise, CO is maintained by _____ only.
↑ HR
*SV plateaus
Diastole is preferentially shortened with _____ → less filling time → ↓ CO (eg. ventricular tachycardia).
↑ HR
↑ Pulse Pressure
- hyperthyroidism
- aortic regurgitation
- aortic stiffening (isolated systolic hypertension in elderly)
- obstructive sleep apnea (↑ sympathetic tone)
- anemia
- exercise (transient)
↓ Pulse Pressure
- aortic stenosis
- cardiogenic shock
- cardiac tamponade
- advanced heart failure (HF)
Stroke Volume is affected by _____.
SV CAP
- Contractility
- Afterload
- Preload
A failing heart has ↓ SV (systolic and/or diastolic dysfunction)
↑ SV
- ↑ Contractility (eg. anxiety, exercise)
- ↑ Preload (eg. early pregnancy)
- ↓ Afterload
↑ Contractility and SV
- Catecholamine Stimulation via β1 Receptor:
- Ca2+ channels phosphorylated → ↑ Ca2 entry → ↑ Ca2+-induced Ca2+ release and ↑ Ca2+ storage in sarcoplasmic reticulum
- Phospholamban phosphorylation → active Ca2+ ATPase → ↑ Ca2+ storage in sarcoplasmic reticulum
- ↑ intracellular Ca2+
- ↓ extracellular Na+ (↓ activity of Na+/Ca2+ exchanger)
- Digitalis (blocks Na+/K+ pump → ↑ intracellular Na+ → ↓ Na+/Ca2+ exchanger activity → ↑ intracellular Ca2+)
↓ Contractility and SV
- β1-blockade (↓ cAMP)
- HF with systolic dysfunction
- Acidosis
- Hypoxia/Hypercapnia (↓ Po2/ ↑ Pco2)
- Non-Dihydropyridine Ca2+ Channel Blockers
Preload is approximated by _____.
ventricular EDV
Preload depends on _____.
- venous tone
- circulating blood volume
↓ Preload
Venous Vasodilators (eg. nitroglycerin)
Afterload approximated by _____.
MAP
Laplace’s Law
↑ afterload → ↑ pressure → ↑ wall tension per
LV compensates for ↑ afterload by _____ in order to ↓ wall tension.
thickening (hypertrophy)
↓ Afterload
Arterial Vasodilators (eg. hydralazine)
↓ Preload and Afterload
- ACE Inhibitors
- ARBs
Chronic Hypertension ( ↑ MAP) → _____
LV Hypertrophy
↑ Myocardial O2 Demand
MyoCARDial O2:
- ↑ Contractility
- ↑ Afterload (proportional to arterial pressure)
- ↑ Heart Rate
- ↑ Diameter of ventricle (↑ wall tension)
Cardiac wall tension follows _____.
Laplace’s Law
Wall Tension
Wall Tension = Pressure × Radius
Wall Stress
Ejection Fraction
- Left Ventricular EF is an index of ventricular contractility.
- EF is ↓ in systolic HF.
- EF is normal in HF with preserved ejection fraction.
Starling Curve
- Force of contraction is proportional to end-diastolic length of cardiac muscle fiber (preload).
- ↑ contractility with catecholamines, positive inotropes (eg. digoxin).
- ↓ contractility with loss of myocardium (eg. MI), β-blockers (acutely), non-dihydropyridine Ca2+ channel blockers, dilated cardiomyopathy.
Resistance, Pressure, Flow
- Pressure gradient drives flow from high pressure to low pressure.
- Compliance = ΔV/ΔP
_____ have the highest total cross-sectional area and the lowest flow velocity.
Capillaries
_____ account for most of TPR.
Arterioles
_____ provide most of the blood storage capacity.
Veins
Viscosity depends mostly on _____.
Hematocrit
- ↑ in hyperproteinemic states (eg. multiple myeloma) and polycythemia
- ↓ in anemia
Cardiac and Vascular Function Curves
- Intersection of Curves = Operating Point of the Heart (ie. venous return and CO are equal)
- Changes often occur in tandem, and may be reinforcing (eg. exercise ↑ inotropy and ↓ TPR to maximize CO) or compensatory (eg, HF ↓ inotropy → fluid retention to ↑ preload to maintain CO).
Inotropy
Changes in contractility → altered CO for a given RA pressure (preload).
- catecholamines, digoxin ⊕, exercise
- HF with reduced EF, narcotic overdose, sympathetic inhibition ⊝
Venous Return
Changes in circulating volume or venous tone → altered RA pressure for a given CO. Mean systemic pressure (x-intercept) changes with volume/venous tone.
- fluid infusion, sympathetic activity ⊕
- acute hemorrhage, spinal anesthesia ⊝
Total Peripheral Resistance
At a given mean systemic pressure (x-intercept) and RA pressure, changes in TPR → altered CO.
- vasopressors ⊕
- exercise, AV shunt ⊝
Pressure-Volume Loops
Phases—Left Ventricle:
- Isovolumetric Contraction—period between mitral valve closing and aortic valve opening; period of highest O2 consumption
- Systolic Ejection—period between aortic valve opening and closing
- Isovolumetric Relaxation—period between aortic valve closing and mitral valve opening
- Rapid Filling—period just after mitral valve opening
- Reduced Filling—period just before mitral valve closing
Cardiac Cycle
Phases—Left Ventricle:
- Isovolumetric Contraction—period between mitral valve closing and aortic valve opening; period of highest O2consumption
- Systolic Ejection—period between aortic valve opening and closing
- Isovolumetric Relaxation—period between aortic valve closing and mitral valve opening
- Rapid Filling—period just after mitral valve opening
- Reduced Filling—period just before mitral valve closing
Heart Sounds
- S1—mitral and tricuspid valve closure. Loudest at mitral area.
- S2—aortic and pulmonary valve closure. Loudest at left upper sternal border.
- S3—in early diastole during rapid ventricular filling phase. Associated with ↑ filling pressures (eg. mitral regurgitation, HF) and more common in dilated ventricles (but can be normal in children, young adults, and pregnant women).
- S4—in late diastole (“atrial kick”). Best heard at apex with patient in left lateral decubitus position. High atrial pressure. Associated with ventricular noncompliance (eg. hypertrophy). Left atrium must push against stiff LV wall. Consider abnormal, regardless of patient age.
Jugular Venous Pulse (JVP)
- a wave—atrial contraction. Absent in atrial fibrillation (AF).
- c wave—RV contraction (closed tricuspid valve bulging into atrium).
- x descent—downward displacement of closed tricuspid valve during rapid ventricular ejection phase. Reduced or absent in tricuspid regurgitation and right HF because pressure gradients are reduced.
- v wave—↑ right atrial pressure due to filling (“villing”) against closed tricuspid valve.
- y descent—RA emptying into RV. Prominent in constrictive pericarditis, absent in cardiac tamponade.
Heart Sounds:
Normal Splitting
- inspiration → drop in intrathoracic pressure → ↑ venous return → ↑ RV filling → ↑ RV stroke volume → ↑ RV ejection time → delayed closure of pulmonic valve
- ↓ pulmonary impedance (↑ capacity of the pulmonary circulation) also occurs during inspiration, which contributes to delayed closure of pulmonic valve
Heart Sounds:
Wide Splitting
- seen in conditions that delay RV emptying (eg. pulmonic stenosis, right bundle branch block)
- causes delayed pulmonic sound (especially on inspiration)
- an exaggeration of normal splitting
Heart Sounds:
Fixed Splitting
- heard in ASD
- ASD → left-to-right shunt → ↑ RA and RV volumes → ↑ flow through pulmonic valve such that, regardless of breath, pulmonic closure is greatly delayed
Heart Sounds:
Paradoxical Splitting
- heard in conditions that delay aortic valve closure (eg. aortic stenosis, left bundle branch block)
- normal order of valve closure is reversed so that P2 sound occurs before delayed A2 sound
- on inspiration, P2 closes later and moves closer to A2, thereby “paradoxically” eliminating the split (usually heard in expiration)
Auscultation of the Heart
Besdside Maneuvers:
- ↑ venous return to right atrium
- ↑ intensity of right heart sounds
Inspiration
Besdside Maneuvers:
- ↑ afterload
- ↑ intensity of MR, AR, and VSD murmurs
- ↓ hypertrophic cardiomyopathy and AS murmurs
- MVP: later onset of click/murmur
Hand Grip
Besdside Maneuvers:
- ↓ intensity of most murmurs (including AS)
- ↑ intensity of hypertrophic cardiomyopathy murmur
- MVP: earlier onset of click/murmur
- Valsalva (phase II)
- standing up (↓ preload)
Besdside Maneuvers:
- ↑ venous return, preload, and afterload
- ↓ intensity of hypertrophic cardiomyopathy murmur
- ↑ intensity of AS, MR, and VSD murmurs
- MVP: later onset of click/murmur
Rapid Squatting
Systolic Murmurs
- Aortic/Pulmonic Stenosis
- Mitral/Tricuspid Regurgitation
- VSD
- MVP
- Hypertrophic Cardiomyopathy.
Diastolic Murmurs
- Aortic/Pulmonic Regurgitation
- Mitral/Tricuspid Stenosis
Systolic Murmurs:
- crescendo-decrescendo systolic ejection murmur and soft S2 (ejection click may be present)
- LV >> aortic pressure during systole
- loudest at heart base; radiates to carotids
- pulsus parvus et tardus
- can lead to syncope, angina, and dyspnea on exertion
- most commonly due to age-related calcification in older patients (> 60 years old) or in younger patients with early-onset calcification
Aortic Stenosis
SAD:
- Syncope
- Angina
- Dyspnea on exertion
_____ are pulses that are weak with a delayed peak.
Pulsus Parvus et Tardus
Systolic Murmurs:
- holosystolic, high-pitched “blowing murmur”
- Mitral—loudest at apex and radiates toward axilla, often due to ischemic heart disease (post-MI), MVP, LV dilatation
- Tricuspid—loudest at tricuspid area, commonly caused by RV dilatation
- rheumatic fever and infective endocarditis can cause either
Mitral/Tricuspid Regurgitation
Systolic Murmurs:
- late systolic crescendo murmur with midsystolic click (MC; due to sudden tensing of chordae tendineae)
- most frequent valvular lesion
- best heard over apex
- loudest just before S2
- usually benign
- can predispose to infective endocarditis
- can be caused by myxomatous degeneration (1° or 2° to connective tissue disease such as Marfan or Ehlers-Danlos syndrome), rheumatic fever, chordae rupture
Mitral Valve Prolapse
Systolic Murmurs:
- holosystolic, harsh-sounding murmur
- loudest at tricuspid area
Ventricular Septal Defect
Diastolic Murmurs:
- high-pitched “blowing” early diastolic decrescendo murmur
- long diastolic murmur, hyperdynamic pulse, and head bobbing when severe and chronic
- wide pulse pressure
- often due to aortic root dilation, bicuspid aortic valve, endocarditis, rheumatic fever
- progresses to left HF
Aortic Regurgitation
Diastolic Murmurs:
- follows opening snap (OS; due to abrupt halt in leaflet motion in diastole, after rapid opening due to fusion at leaflet tips)
- delayed rumbling mid-to-late diastolic murmur (↓ interval between S2 and OS correlates with ↑ severity)
- LA >> LV pressure during diastole
- often a late (and highly specific) sequela of rheumatic fever
- chronic disease can result in LA dilatation → dysphagia/hoarseness via compression of esophagus/left recurrent laryngeal nerve, respectively
Mitral Stenosis
Continuous Murmurs:
- machine-like murmur
- best heard at left infraclavicular area
- loudest at S2
- often due to congenital rubella or prematurity
Patent Ductus Arteriosus
Myocardial Action Potential
- Phase 0 = rapid upstroke and depolarization—voltage-gated Na+ channels open.
- Phase 1 = initial repolarization—inactivation of voltage-gated Na+ channels. Voltage-gated K+ channels begin to open.
- Phase 2 = plateau—Ca2+ influx through voltage-gated Ca2+ channels balances K+ efflux. Ca2+ influx triggers Ca2+ release from sarcoplasmic reticulum and myocyte contraction.
- Phase 3 = rapid repolarization—massive K+ efflux due to opening of voltage-gated slow K+ channels and closure of voltage-gated Ca2+ channels.
- Phase 4 = resting potential—high K+ permeability through K+ channels.
*also occurs in bundle of His and Purkinje fibers
In contrast to skeletal muscle, cardiac muscle _____.
- cardiac muscle action potential has a plateau, which is due to Ca2+ influx and K+ efflux
- cardiac muscle contraction requires Ca2+ influx from ECF to induce Ca2+ release from sarcoplasmic reticulum (Ca2+-induced Ca2+ release)
- cardiac myocytes are electrically coupled to each other by gap junctions
Pacemaker Action Potential
Occurs in the SA and AV nodes.
- Phase 0 = upstroke—opening of voltage-gated Ca2+ channels. Fast voltage-gated Na+ channels are permanently inactivated because of the less negative resting potential of these cells. Results in a slow conduction velocity that is used by the AV node to prolong transmission from the atria to ventricles.
- Phases 1 and 2 are absent.
- Phase 3 = repolarization—inactivation of the Ca2+ channels and ↑ activation of K+ channels → ↑ K+ efflux.
- Phase 4 = slow spontaneous diastolic depolarization due to If (“funny current”). If channels responsible for a slow, mixed Na+/K+ inward current; different from INa in phase 0 of ventricular action potential. Accounts for automaticity of SA and AV nodes. The slope of phase 4 in the SA node determines HR. ACh/adenosine ↓ the rate of diastolic depolarization and ↓ HR, while catecholamines ↑ depolarization and ↑ HR. Sympathetic stimulation ↑ the chance that If channels are open and thus ↑ HR.
Conduction Pathway
SA node → atria → AV node → bundle of His → right and left bundle branches → Purkinje fibers → ventricles
*left bundle branch divides into left anterior and posterior fascicles
_____ “pacemaker” inherent dominance with slow phase of upstroke.
SA Node
The AV node is located in the _____.
posteroinferior part of the interatrial septum
_____ delay from the AV node allows time for ventricular filling.
100-msec
Pacemaker Rates
SA > AV > bundle of His/Purkinje/ventricles
Speed of Conduction
Purkinje > atria > ventricles > AV node
Electrocardiogram
- P wave—atrial depolarization, atrial repolarization is masked by QRS complex
- PR interval—time from start of atrial depolarization to start of ventricular depolarization (normally < 200 msec)
- QRS complex—ventricular depolarization (normally < 120 msec)
- QT interval—ventricular depolarization, mechanical contraction of the ventricles, ventricular repolarization
- T wave—ventricular repolarization, T-wave inversion may indicate ischemia or recent MI
- J point—junction between end of QRS complex and start of ST segment
- ST segment—isoelectric, ventricles depolarized
- U wave—prominent in hypokalemia (think hyp“U”kalemia), bradycardia
Dysrhythmias:
- polymorphic ventricular tachycardia
- characterized by shifting sinusoidal waveforms on ECG
- can progress to ventricular fibrillation (VF)
- long QT interval predisposes to _____
- caused by drugs, ↓ K+, ↓ Mg2+, and congenital abnormalities
Torsades de Pointes
Drug-Induced Long QT
ABCDE:
- AntiArrhythmics (class IA, III)
- AntiBiotics (eg. macrolides)
- Anti“C”ychotics (eg. haloperidol)
- AntiDepressants (eg. TCAs)
- AntiEmetics (eg. ondansetron)
Torsades de Pointes is treated with _____.
Magnesium Sulfate
_____ is an inherited disorder of myocardial repolarization, typically due to ion channel defects; ↑ risk of sudden cardiac death (SCD) due to torsades de pointes.
Congenital Long QT Syndrome
Congenital Long QT Syndrome:
- autosomal dominant
- pure cardiac phenotype (no deafness)
Romano-Ward Syndrome
Congenital Long QT Syndrome:
- autosomal recessive
- sensorineural deafness
Jervell and Lange-Nielsen Syndrome
_____ is an autosomal dominant disorder most common in Asian males. ECG pattern of pseudo-right bundle branch block and ST elevations in V1-V3. ↑ risk of ventricular tachyarrhythmias and SCD. Prevent SCD with implantable cardioverter-defibrillator (ICD).
Brugada Syndrome
_____ is the most common type of ventricular preexcitation syndrome. Abnormal fast accessory conduction pathway from atria to ventricle
(bundle of Kent) bypasses the rate-slowing AV node → ventricles begin to partially depolarize earlier → characteristic delta wave with widened QRS complex and shortened PR interval on ECG. May result in reentry circuit → supraventricular tachycardia.
Wolff-Parkinson-White Syndrome
Dysrhythmias:
- chaotic and erratic baseline with no discrete P waves in between irregularly spaced QRS complexes
- irregularly irregular heartbeat
- most common risk factors include hypertension and coronary artery disease (CAD)
- can lead to thromboembolic events, particularly strok
- treatment includes anticoagulation, rate control, rhythm control, and/or cardioversion
Atrial Fibrillation
Dysrhythmias:
- a rapid succession of identical, back-to-back atrial depolarization waves
- the identical appearance accounts for the “sawtooth” appearance of the flutter waves
- treat like atrial fibrillation
- definitive treatment is catheter ablation
Atrial Flutter
Dysrhythmias:
- a completely erratic rhythm with no identifiable waves
- fatal arrhythmia without immediate CPR and defibrillation
Ventricular Fibrillation
AV Blocks:
- the PR interval is prolonged (> 200 msec)
- benign and asymptomatic
- no treatment required
First-Degree AV Block
AV Blocks:
- progressive lengthening of PR interval until a beat is “dropped (a P wave not followed by a QRS complex)
- usually asymptomatic
- variable RR interval with a pattern (regularly irregular)
Second-Degree AV Block
Mobitz Type I (Wenckebach)
AV Blocks:
- dropped beats that are not preceded by a change in the length of the PR interval (as in type I)
- may progress to 3rd-degree block
- often treated with pacemaker
Second-Degree AV Block
Mobitz Type II
AV Blocks:
- the atria and ventricles beat independently of each other
- P waves and QRS complexes not rhythmically associated
- atrial rate > ventricular rate
- usually treated with pacemaker
- can be caused by Lyme disease
Third-Degree (Complete) AV Block
_____ is released from atrial myocytes in response to ↑ blood volume and atrial pressure. Acts via cGMP. Causes vasodilation and ↓ Na+ reabsorption at the renal collecting tubule. Dilates afferent renal arterioles and constricts efferent arterioles, promoting diuresis and contributing to “aldosterone escape” mechanism.
Atrial Natriuretic Peptide
_____ is released from ventricular myocytes in response to ↑ tension. Similar physiologic action to ANP, with longer half-life. _____ blood test is used for diagnosing HF (very good negative predictive value). Available in recombinant form (nesiritide) for treatment of HF.
B-Type (Brain) Natriuretic Peptide
Cardiovascular Receptors
- Aortic arch transmits via vagus nerve to solitary nucleus of medulla (responds to ↓ and ↑ in BP).
- Carotid sinus (dilated region at carotid bifurcation) transmits via glossopharyngeal nerve to solitary nucleus of medulla (responds to ↓ and ↑ in BP).
Cardiovascular Baroreceptors
- Hypotension—↓ arterial pressure → ↓ stretch → ↓ afferent baroreceptor firing → ↑ efferent sympathetic firing and ↓ efferent parasympathetic stimulation → vasoconstriction, ↑ HR, ↑ contractility, ↑ BP. Important in the response to severe hemorrhage.
- Carotid Massage—↑ pressure on carotid sinus → ↑ stretch → ↑ afferent baroreceptor firing → ↑ AV node refractory period → ↓ HR.
- Component of Cushing Reflex (triad of hypertension, bradycardia, and respiratory depression)—↑ intracranial pressure constricts arterioles → cerebral ischemia → ↑ pCO2 and ↓ pH → central reflex sympathetic ↑ in perfusion pressure (hypertension) → ↑ stretch → peripheral reflex baroreceptor–induced bradycardia.
Cardiovascular Chemoreceptors
- Peripheral—carotid and aortic bodies are stimulated by ↓ Po2 (< 60 mm Hg), ↑ Pco2, and ↓ pH of blood.
- Central—are stimulated by changes in pH and Pco2 of brain interstitial fluid, which in turn are influenced by arterial CO2. Do not directly respond to Po2.
Normal Cardiac Pressures
Pulmonary capillary wedge pressure (PCWP; in mm Hg) is a good approximation of left atrial pressure. In mitral stenosis, PCWP > LV end diastolic pressure. PCWP is measured with pulmonary artery catheter (Swan-Ganz catheter).
Cardiovascular Autoregulation:
Heart
Local Metabolites (Vasodilatory):
- adenosine
- NO
- CO2
- ↓ O2
Cardiovascular Autoregulation:
Brain
Local Metabolites (Vasodilatory):
CO2 (pH)
Cardiovascular Autoregulation:
Kidneys
- Myogenic Feedback
- Tubuloglomerular Feedback
Cardiovascular Autoregulation:
Lungs
Hypoxia → Vasoconstriction
The pulmonary vasculature is unique in that alveolar hypoxia causes vasoconstriction so that only well ventilated areas are perfused. In other organs, hypoxia causes vasodilation.
Cardiovascular Autoregulation:
Skeletal Muscle
CHALK (exercise):
- CO2
- H+,
- Adenosine
- Lactate
- K+
At Rest: sympathetic tone
Cardiovascular Autoregulation:
Skin
Sympathetic stimulation is the most important mechanism for temperature control.
Capillary Fluid Exchange
Starling Forces determine fluid movement through capillary membranes:
- Pc = capillary pressure—pushes fluid out of capillary
- Pi = interstitial fluid pressure—pushes fluid into capillary
- πc = plasma colloid osmotic (oncotic) pressure—pulls fluid into capillary
- πi = interstitial fluid colloid osmotic pressure—pulls fluid out of capillary
- Jv = net fluid flow = Kf [(Pc − Pi) − σ(πc − πi)]
- Kf = capillary permeability to fluid
- σ = reflection coefficient (measure of capillary permeability to protein)
Capillary Fluid Exchange: Edema
Excess fluid outflow into interstitium is commonly caused by:
- ↑ capillary pressure (↑ Pc; eg. HF)
- ↓ plasma proteins (↓ πc; eg. nephrotic syndrome, liver failure, protein malnutrition)
- ↑ capillary permeability (↑ Kf ; eg. toxins, infections, burns)
- ↑ interstitial fluid colloid osmotic pressure (↑ πi; eg. lymphatic blockage)
Congenital Heart Diseases:
- early cyanosis—“blue babies”
- often diagnosed prenatally or become evident immediately after birth
- usually require urgent surgical treatment and/or maintenance of a PDA
R → L Shunts (Cyanotic)
Right-to-Left Shunts: eaRLy cyanosis