Cardiac Cycle and Pressures Flashcards
Steps of Cardiac Cycle
- Atrial Contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- rapid filling
- Reduced filling
S1
Closure of AV valves, beginning of systole
S2
Passive closure of aortic, pulmonic valves
S3
Rapid passive ventricular filling, ventricular gallop rhythm in LV heart failure
Can be normal finding in LA, may also be normal in some cats with gallop rhythm
S4
atrial contraction vibrates stiff walls of ventricles during filling: atrial gallop rhythm indicative of cardiac dz
RA Pressures
0-2
RV Pressures
SAP 15-30, Diastolic 2-8
PAP
15mm Hg MAP
Pulmonary Capillaries
10mm Hg
Pulmonary Venous pressure
8mm Hg
LA P
2-5mm Hg
LV pressures
100-140 SAP
DAP 3-12
Aorta, large arteries
100mm Hg
Arterioles
50mm Hg
Capillaries
20mm Hg
Vena Cava
4mm Hg
Critical DO2
5-7mL/kg/min
Critical HGB
4g/dL
Cyanosis at 5
Critical O2ER
0.6(60%)
CO - kidney
20-25%
CO-liver
20-25%
CO brain
10-15%
CO heart (coronary BF)
5%
CO - GIT
25%
CO - skin
5%
O2 ER: heart
10-12%
O2 ER: SkM
2-5%
O2ER kidney
2-3%
O2ER:
GIT 4-6%
Myocardial Oxygen Extraction
70-80%
Why first thing to get upset with anemic patient or hypoxemic patients
L anterior descending coronary artery + branches
largest mass in humans, swine, rats, non-human primates
Circumflex coronary artery
largest mass in dogs, cats, horses, cattle
Dogs = extensive collateral circulation pigs, primates do not
Thebesian veins
present t/o heart, drain directly to cardiac chambers (4% venous return)
What determines BF to myocardium
extravascular compression of intramural coronary vessels (30-40% of total resistance), contractile state of myocardium, HR
Coronary blood flow determined by oxygen demand
Cerebral Perfusion
autoregulation (50mL/100g/min) btw 60-150 mmHg CPP
o Most important VD = CO2
Bronchial Circulation
o Bronchial arteries carry oxygenated blood to lungs pulmonary capillaries (exchange occurs here) bronchial veins (minimal) pulmonary veins (majority)
Pulmonary Circulation
Enter CO from RV: 10-15% blood vol (reservoir to stabilize LV ESV, systemic blood volume)
low-pressure system has limited ability to control regional distribution of BF –> pulm capillaries can collapse if significant decrease in BP
HPV
Alveolar hypoxia = most important stimulus for HPV
Site of action = extra-alveolar vessels
Hypoxic conditions: pulm vessels constrict: increase pulmonary artery pressure –> distends, recruits under-perfused pulmonary vessels ==> shunting of blood to better ventilated alveoli = improvement in VQ ratio
Splanchnic Circulation
o 25% CO, contains 20% blood vol
o Splanchnic arteries = all arterial walls of preportal organs
o Splanchnic veins = highly compliant, lrg vol reservoir, high population of a1/a2 R
Spleen
Also has high population of a1/a2 receptors
Highly sensitive to adrenergic stimulation or blockade, spleen can hold significant reservoir of blood
Role of Axs in Splanchnic Circulation
blunt/abolish ability of splanchnic circulation to mobilize blood
How Splanchnic vasculature mobilizes volume
Volume mobilization = result of active VC, passive elastic recoil of splanchnic veins secondary to decrease arterial inflow
Can compensate for up to 50-60% blood loss after moderate hemorrhage
Active mobilization of splanchnic blood vessels = b2, a R activation –> act in concert to shift blood from splanchnic vasculature into systemic circulation via VC, decreased splanchnic vascular capacitance, decreased intrahepatic vascular resistance
