Cardiology Flashcards
Define preload
The force imposed on a resting muscle that stretches the muscle to a new length.
What principle is described in the definition
The force imposed on a resting muscle that stretches the muscle to a new length.
Preload
What determines preload in the heart
End diastolic ventricular volume
State the Frank-Starling relationship
In the normal heart, diastolic volume is the principle factor governing the strength of ventricular contraction
What surrogate measure is used in clincal practice to estimate right ventricular end-diastolic volume (and therefore preload)?
Central venous pressure
What surrogate marker is used to estimate left ventricular end-diastolic volume in clinical practice?
Pulmonary artery occlusion pressure
NB: pulmonary artery wedge pressure is a misnomer unless catheter is actually being wedged into capillaries
What equation describes ventricular compliance?
Compliance = ∆EDV / ∆EDP
Where EDV = end diastolic volume; EDP = end-diastolic pressure
How will decreased ventricular compliance affect the estimation of end-diastolic ventricular volume by measurement of end-diastolic pressure?
It will cause an overestimation of end-diastolic volume
Contrast heart failure with normal and reduced ejection fractions in terms of:
- end diastolic pressure
- end diastolic volume
Preserved ejection fraction:
- high EDP
- low EDV
Reduced ejection fraction:
- high EDP
- high EDV
Define afterload
The force equivalent to the peak tension developed across the walls of the ventricle during systole
State the Laplace equation.
Wall tension = (pressure x radius) / (2 x wall thickness)
What four factors contribute to ventricular afterload?
- Pleural pressure
- End diastolic volume
- Aortic impedance
- Systemic vascular resistance
What is vascular impedance?
The force that opposes the rate of change in pressure and flow; that is, the force that opposes pulsatile flow.
What vessels predominantly determine vascular impedance?
Proximal arteries (e.g., aorta, pulmonary arteries)
What vessels determine vascular resistance?
Arterioles, capillaries
What is vascular resistance?
The force opposing non-pulsatile flow.
State the general equation describing resistance to flow in a hydraulic circuit
R = (PIN - POUT) / Q
Where R = resistance; Q = flow
State the equation describing systemic vascular resistance
R = (MAP - CVP) / CO
State the equation describing pulmonary vascular resistance
R = PAP - LAP / CO
What equation describes the determinants of steady flow through small tubes
Hagen-Pouseuille equation
(Q = ∆P x (πr4/8µL)
State the equation describing resistance to flow in small tubes
R = 8µL / πr4
Where R = resistance; µ = viscosity; L = tube lenght; r = tube radius
What is the effect of positive pleural pressure on ventricular emptying?
Increased emptying
What is the effect of negative pleural pressure on ventricular emptying?
Reduced ventricular emptying
What component force affecting ventricular afterload cannot be measured?
Vascular impedance
At what phase of respiration should central venous pressure be transduced?
End expiration
When measuring CVP in ventillated patients, what ventillator setting must be accounted for?
positive end expiratory pressure (PEEP
What four factors cause a right shift in the oxyhaemoglobin dissociation curve? What is the consequence of this?
- Acidaemia
- High temperature
- Decreased CO2
- Increased 2,3 DPG
Consequence: reduced oxygen-haemoglobin affinity for a given PO2
What five factors cause a left shift in the oxyhaemoglobin dissociation curve? What is the effect of left shift?
- Alkalaemia
- Low temperature
- Decreased CO2
- Decreased 2,3 DPG
- Increased CO
Effect: increased affinity betwen oxygen and haemoglobin for a given pO2
Define the Bohr effect
Haemoglobin oxygen-binding capacity is inversely related to the acidity and the partial pressure of CO2in the solution
State the equation describing haemoglobin-bound oxygen content in blood
HbO2 = 1.34 x [Hb] x SO2
State the equation describing dissolved oxygen content in blood
Dissolved O2 = 0.003 x pO2 (mL/dL)
State the equation describing arterial oxygen content
CaO2 = (1.34 x [Hb] x SaO2) + (0.003 x PaO2)
Define dysoxia
The state where nutrient metabolism is limited by the availability of oxygen
What are the two causes of dysoxia?
- Hypoxia (inadequate supply to tissues)
- Cytopathic hypoxia (defective oxygen utilization)
What adrenergic receptors predominate myocardium?
Beta 1
What are the diagnostic criteria for systemic inflammatory response syndrome (SIRS)
At least two of:
- Resp. rate >20 or PCO2 <32mmHg
- Pulse >90 beats/min
- Temperature >38 or <36
- WCC >12x103/mm3, <4x103/mm3; or >10% immature neutrophils
Define sepsis
SIRS plus evidence of infection
Define is Wellens’ syndrome?
Wellens’ syndrome is a pattern of deeply inverted or biphasic T waves in V2-3, which is highly specific for a critical stenosis of the left anterior descending artery (LAD)
What are the Brugada criteria? Describe them.
For differentiating SVT with aberrancy and VT
