EXAM #1: CORONARY & PULMONARY CIRCULATION Flashcards
What is WPW Syndrome?
An accessory pathway linking atrial to ventricular tissue, bypassing the AV node
What normally prevents re-entry?
Depolarization circuit encounters tissue in the absolute refractory period
What two mechanisms can lead to the development of re-entry circuits?
1) Reduced refractory period– propagating waveform and re-enter a previously blocked path
2) Reduced conduction velocity
What is a passive arrhythmia?
Conduction abnormality that arises from an abnormality in tissue structure
List examples of tissue structure changes that can lead to the development of a passive arrhythmia?
- Gap junction changes
- Fat deposition
- Fibrosis
- Changes in cell size
What is the source-sink concept in arrhythmogenesis?
Source= strength of an impulse Sink= amount of tissue that must be excited
How does the APD change the source-sink relationship if there is an area of inexctiable tissue?
- Source does NOT change (same impulse strength)
- Propagates on a relative smaller area (sink)
Strength is relative greater and the APD shortens.
What part of the heart is supplied by the RCA?
Posterior LV, and RV
What are the two major branches of the LCA?
- LAD
- Left circumflex artery
What does the LAD supply?
Anterior LV
What does the left circumflex supply?
Lateral LV
When is blood flow highest through the coronary arteries?
Early diastole
*B/c of some retrograde flow from the aorta
What part of the heart is more subject to phasic changes in blood flow?
Left heart b/c of higher ventricular wall pressure
What is autoregulation of coronary blood flow?
Changes in vascular resistance to maintain constant blood flow
What are the mechanisms of autoregulation?
1) Myogenic
2) Metabolic
Define myogenic autoregulation.
- Activation of stretch receptors
- Stretch receptors alter ion channels
- Can cause depolarization and contraction of vascular smooth muscle in response to changes in pressure
What is metabolic autoregulation?
The effects of metabolites on coronary autoregulation
What is coronary reserve?
Ability of the coronary vasculature to respond to a vasodilatory stimulus
An inability to vasodilate in conditions of increased metabolic demand= reduced coronary reserve
What disease states can reduce the coronary reserve?
1) Thrombus/ plaque formation= physical impedence to full luminal diameter
2) Heart Failure/DM= inability to properly respond to vasodilatory stimuli
What is the sequence of events that happens to coronary blood flow in hypoxia?
1) Less O2
2) ATP depletion leads to Adenosine release
3) Adenosine binds A2 receptors
Outcome is vasodilation
Describe the influence of the SNS on coronary blood flow.
SNS has a BIPHASIC effect on coronay circulation
- First, alpha activation leads to VASOCONSTRICTION
- Vasoconstriction= hypoxia
- METABOLIC response= VASODILATION in a second phase
How does the resistance of the pulmonary circulation compare to the systemic circulation?
Pulmonary circulation has DECREASED resistance compared to systemic circulation
How do the pulmonary vessels compare to the systemic vessels?
1) More elastic with less smooth muscle
2) Larger lumen and shorter length
3) More distensible and compressible
4) Blunted myogenic mechanisms
What is ventilation: perfusion matching? What is the normal V:Q ratio?
Supplying blood to well oxygenated lung tissue
*Normal= 0.8 to 1.0
What are the passive mechanisms that regulate pulmonary blood flow?
1) Gravity
2) Body position
3) Extravascular pressure
4) Intravascular pressure
Generally, speaking how does gravity effect pulmonary perfusion? From a disease standpoint what is the outcome of gravity?
- Blood must work AGAINST gravity to reach the APEX
- Blood flows with gravity to reach the base
Increased hydrostatic pressure is developed in the base of the lung, which more readily leads to pulmonary edema in the bases
What are recruitment and distension as passive mechanisms that alter pulmonary blood flow?
Recruitment= opening of previously closed capillaries to accommodate increased blood flow
Distension= widening of already open capillaries to accommodate increased blood flow
What is the most important active mechanism to regulate pulmonary blood flow?
Hypoxic VASOCONSTRICTION
Note that this is OPPOSITE compared to the coronary vessels
What is the outcome of hypoxic vasoconstriction?
Diversion of pulmonary blood flow from hypoxic lung regions
What is the normal pressure of the pulmonary artery?
20 mmHg
What pressure defines pulmonary artery HTN?
25 mmHg
What is extravascular compression (heart)?
Compression of the coronary arteries with increased chamber pressure during systole
What are the three major mechanisms that alter coronary blood flow?
1) Extravascular compression
2) Autoregulation
3) Autonomic input
What is phasic blood flow in regards to the coronary arteries?
- The undulating or phasic flow of blood through the coronary arteries
- This is a pressure dependent phenomenon; flow is high during diastole and low during systole
What is the consequence of severe/prolonged hypoxia?
- Hypoxic vasoconstriction that INCREASES pulmonary vascular resistance
- Causing PULMONARY ARTERY HTN
What determines pulmonary artery pressure?
CO and pulmonary vascular resistance (PVR)
What normally happens as CO increased to maintain a constant pulmonary artery pressure?
Decreased PVR
What are some diseases that will increase PVR leading to PAH?
1) PE
2) LVH
What is the consequence of prolonged PAH?
RVH
