Coronary Blood Flow Flashcards
Metabolic cost of a HB
Will inc in HTN because of the decreased afterload
Will inc in exercise bc of tachycardia
Special aspects of coronary circulation
Never has an opportunity to repay metabolic debt…must supply O2 as rapidly as consumed
Vessels are surrounded by contracting muscle…coronary flow to LV will peak during diastole
Extraction ratio is very high - myocardium cannot obtain more O2 by inc extraction
Healthy coronary circulation
Blood flow adjusted to match metabolic demand
Metabolic factors
Match between CBF and MVo@ is achieved becyase they change in proportion to demand
Po2, H, and K
Systolic compression
Flow is lower during systole due to throttle effect from myocardial contraction
Concept of trnasmural pressure…external pressure will exceed internal pressure during systole due to muscle
Thorttle effect accentuated by
Tachycardia
Inc extra-luminal pressure (compressive form muscle contraction)
Positive inotropism
Coronary artery dz
HR inc
BP inc
High symp
Diastole is smaller % of cycle
Thorttle effect accentuated
Myocardial metabolic demand elevated
More likely to expereince myocardial ischemia
Why is sub-ednocardium more susceptible to ischemia
Systolic compression/throttle effect inc as one descends deepter
Elevated preload constitituee another mechanical compression
Intrinsic and autoreg factors
Coronary flow does NOT change linearly with arterial perfusion pressure
Myogenic mech - inc strethc means inc contraction
Direct particpation of endothelium in controlling flow
Severe hypoxia/anoxia
Adenosine will contribute to coronary vasdoailtio
Inc cardiac symp
Will directly vasoconstrict but net effect vasodilation due to increase in metabolites from inc contractility
Advanced coronary artery dz and inc sympthatietc activity
Symp activity may limited blood flow in those who have exhausted their metabolibc reserve
Contractile forces in ischmic
Above occlusion - force will inc due to inc symp
Below occlusion - force will dec due to lack of O2
PVC characteristics
Not preceded by a P wave
Premature
Bizarre QRS
Systolic pressure lower for the beat and may not even open aortic valve
Compensatory pause prior to next beat
