Cardiovascular Response to Stress Flashcards
What is systemic arterial blood pressure?
What is the equation for ‘mean systemic arterial pressure’?
Refers to the pressure measured within large arteries in the systemic circulation (pressure exerted upon arteries during heart contractions). This number splits into systolic blood pressure and diastolic blood pressure.
Cardiac Output x Total Peripheral Resistance
What does the Frank-Starling curve say about preload?
- Increase in preload increases stroke volume - Decrease in preload decreases stroke volume - High levels of preload eventually leads to decreased stroke volume (downstroke of curve)
What is preload best measured as?
End diastolic volume (echo)
What can preload be defined as?
The initial stretching of the cardiac myocytes prior to contraction related to ventriuclar filling. (i.e. strength of ventricular contraction increased when ventricle stretched prior to contraction)
How does increased venous return to the heart affect the stroke volume?
- Increasing venous return increases filling pressure of ventricle (LVEDP: left ventricular end diastolic pressure) –> this stretches sacromeres and increases preload
- Leads to increased stroke volume
What factors increase preload?
- Increased central venous pressure that can result from decreased venous compliance or increased thoracic blood volume 2. Increased ventricular compliance 3. Increased atrial force of contraction / increased filling of atria 4. Reduced heart rate 5. Increased aortic / pulmonary pressure
What can decreased venous compliance be caused by?
Sympathetic activation of venous smooth muscle
How does increased ventricular compliance lead to increased preload?
Greater expansion of the chamber during filling at a given filling pressure
What can cause increased atrial force of contraction?
Sympathetic stimulation of the atria or from increased filling of the atria
How can reduced heart rate increase preload?
Prolongs diastole
How does increased aortic pressure increase preload?
Increases the afterload on the ventricle, reduces stroke volume by increasing end-systolic volume, and leads to a secondary increase in ventricular preload
How does the ‘Bowditch Effect’ relate to heart rate?
- Increase in heart rate increases force of contraction - Decrease in heart rate decreases force of contraction - High levels of heart rate eventually leads to decreased force of contraction
Why is the Bowditch (Treppe) Effect independent of Frank-Starling?
Length of muscle not affected
What is the Bainbridge reflex?
An increase in heart rate due to an increase in central venous pressure
What are baroreceptors? What do they detect?
Stretch receptors –> detect increased stretch (caused by increase in blood volume) Many individual baroreceptors are inactive at normal resting pressures and only become activated when their stretch or pressure threshold is exceeded.
What is effect of baroreceptors in atria detecting increased stretch?
Heart rate increased via sympathetic simulation to SA node
What are direct cardiac sympathetic actions?
- Positive chronotropy (speeds up heart rate) 2. Positive dromotropy (increases speed of conduction) 3. Positive ionotropy (better contraction) 4. Positive lusitropy (better relaxation of ventricles and atria)
What is effect of dobutamine? How does it work? What type of drug is it? What is it used to treat?
- B-agonist
- A cardiac stimulant which acts on beta1 receptors in cardiac muscle, and increases contractility.
Activates sympathetic system (acts as mimic), increasing heart rate and force of contraction
Used to treat: cardiogenic shock and severe heart failure
How does activation of RAAS affect central venous pressure?
Increases central venous pressure –> increases stroke volume
Describe RAAS
- Angiotensinogen produced in liver 2. Angiotensiogen converted to angiotensin I by renin (produced by kidney) 3. Angiotensin I converted to angiotensin II by ACE (in lungs and kidneys) 4. Angiotensin II stimulates release of aldosterone by adrenals
What is effect of angiotensin II on: 1. Arterioles 2. Kidneys 3. Sympathetic nervous system 4. Adrenals 5. Hypothalamus
- Vasoconstriction 2. Increased Na+ and H20 reabsorption 3. Increased release of noradrenaline 4. Aldosterone 5. Stimulates anti-diuretic hormone (ADH) release
What are the effects of increased aldosterone?
Increased Na+ and H20 retention
What is vasopressin? What is its effect?
ADH - promotes H20 retention