the coronary circulation 2015.ppt - amazon s3 · the coronary circulation guyton chapter 21...
Post on 20-May-2020
6 Views
Preview:
TRANSCRIPT
11/1/2014
1
The Coronary Circulation
Guyton Chapter 21
Coronary Circulation
� Heart blood
flow second only to kidney
on per gram
basis
� Heart weighs ~300 gms
� CBF ≈
250cc/min
Cardiac Hemodynamics
Region Mass
(kg)
Blood
flow
mL/m
Blood
flow mL/100
gm/m
O2
mL/100
g/m
%
Cardiac Output
% O2
Use
Brain 1.5 750 50-55 3.5 15% 20%
Kidneys 0.3 1240 420 6.0 25% 7%
Liver 2.6 1500 58 2.0 28% 20%
Heart 0.3 250 84 9.7 5% 12%
Whole
Body
63 5500 8.6 0.4 100% 100%
11/1/2014
2
Coronary Arteries
� Two main coronary arteries arise from root of aorta
� Large, low resistance
� Lie on surface of the heart (epicardium) –penetrate into cardiac muscle
Coronary Arteries
Left coronary a. supplies the LA, the anterior and lateral LV, and the right and left bundle branches
1. Left coronary artery
� anterior descending
� circumflex
Coronary Arteries
Right coronary a. supplies the RA, RV, posterior LV, SA node (60%), AV node (90%), and AV bundle
2. Right coronary artery
11/1/2014
3
Coronary Venous Blood
� Coronary Sinus
� Collects 75% of total
CBF; empties into RA
� Anterior Cardiac Vein
� Collects venous blood from RV; empties into
RA
� Thebesian Veins
� Collect blood from all
over the heart; empty directly into chambers
� Contributes to venous
admixture
Coronary Perfusion Pressure (CPP)
� Coronary arteries are perfused during diastole
Normal
Why does coronary perfusion occur
during diastole?
� CBF to LV falls during systole (opposite all other vascular beds)
� Why? Strong compression of LV muscle around coronary a. during contraction
� During diastole, cardiac muscle relaxes completely ⇒ ↑ blood flow
Note, still some blood flowduring systole i.e. flow doesnot decline to 0
11/1/2014
4
Epicardial vs. Subendocardial Blood
Flow
� During systole a pressure gradient develops within the heart muscle ⇒ highest pressure at endocardium and lowest pressure at epicardium
� Endocardium gets full force of all muscle layers and subendocardial vessels are compressed to the greatest degree
Subendocardial arterialplexus most extensive
blood vessel network
Epicardial vs. Subendocardial Blood Flow
� Subendocardial vessels are most vulnerable to decreases in coronary blood flow
Epicardial vs. Subendocardial Blood Flow
What factors impair subendocardial blood flow?
1. Low diastolic BP2. High LVEDP
• Direct compression of subendocardial vessels
• Decreased CPP due to higher opposing pressure to diastolic
pressure
11/1/2014
5
Control of Coronary Blood Flow
� Primary controller of coronary vessel resistance is locally generated metabolites
� Coronary blood flow ∝∝∝∝ metabolism
Cardiac Muscle
Metabolism
� Heart has the highest
metabolic rate (and ATP requirements) in body
� Normal basal myocardial O2
consumption 8-10
mL/100gm/min
� Normal O2 delivery 8-10 mL/100gm/min
� ↑ myocardial O2 demand met
by ↑ coronary blood flow, not by ↑ O2 extraction
Cardiac O2 supply vs. O2 Demand
O2 supply determined by:
� Diameter of coronary arteries
� LVEDP
� Aortic diastolic pressure
� Arterial O2 content
� Heart rate
� Diastolic time
O2 demand determined by:
� Heart rate
� Wall tension
� Preload (“volume work”)
� Afterload (“pressure work”)
� Myocardial contractility
11/1/2014
6
Cardiac O2 Supply vs. O2 Demand
Cardiac O2 Supply vs. O2 Demand
Anesthetic considerations
� Volatile agents in general are considered “cardioprotective”
� Coronary artery vasodilators (Isoflurane most)
� Decrease myocardial O2 requirements (↓metabolism)
� Vasodilation: ↓ preload, ↓ afterload
� May precondition the heart and reduce postoperative ischemia
top related