L9 Cardiovascular Responses to Stress Flashcards
What is the equation for cardiac output?
Cardiac output = Stroke Volume * Heart rate
What is the equation for mean systemic arterial pressure?
Mean Arterial Systemic Pressure = Total Peripheral Resistance * cardiac Output
What is the Frank-Starling Law?
Cardiac performance increases with sarcomere length until a point in which increasing sarcomere length leads to reduced cardiac performance. In order to increase sarcomere length you can increase the preload.
How is preload increased?
- Exercise means there is greater use fo the skeletal muscle pump and so greater venous return.
- Reduced venous compliance.
- Increased pulmonary and aortic pressure.
- Reduced heart rate.
- Activation of RAAS.
- Increasing central venous pressure for example by increasing fluid uptake.
- Increased ventricular compliance.
- Increased ventilation. the respiratory pump reduces the thoracic pressure making it easier for blood to enter the right side of the heart.
What is the Bowditch effect?
Increasing the heart rate will increase cardiac performance until a certain point at which further increase of heart rate decreases performance. This is independent of Frank-Starlings law as it does not effect sarcomere length. This is an intrinsic function.
What is the Bainbridge reflex?
Baroreceptors in the atria can detect stretch stimulating the sympathetic nervous system to increase heart rate. Greater venous return increases end diastolic volume and heart rate. This is involved in sinus arrythmia.
What is the effect of sympathetic action on the heart?
- Positive chronotropy
- Positive Ionotrophy
- Postive dromotrophy
- Positive lusitrophy
- Activation of RAAS
- Suprarenal stimulation leading to the release of catecholamines.
What is the relationship between iontrophy and cardiac performance?
As ionotrophy increases due to the sympathetic nervous system, or Dobutamine which mimics the SNS, the cardiac performance increases. This pattern is seen during exercise. This however occurs up to a point where further ion trophy leads to decreased cardiac performance.
What is the effect of RAAS on the heart?
RAAS acts to increase blood pressure at times of hypotension.
Angiotensin II causes vasoconstriction and increased water and sodium ion retention.
Aldosterone leads to sodium and therefore water retention.
Vasopressin (ADH) causes water retention.
The effect of RAAS causes an increase in central venous pressure. This means that preload increases and so cardiac performance.
What is the effect of epinephrine on the heart?
Epinephrine is a powerful vasoconstrictor, increasing mean systemic arterial pressure. It also acts to increase heart rate and stroke volume through renin secretion. This acts to increase cardiac output.
What is the effect of parasympathetic actions on the heart?
- Negative chronotropy
- Negative ionotropy in the atria, it does not seem to have much effect on the ventricles
- Negative dromotropy
- No effect on RAAS
- No effect on luistropy
How is a change in arterial pressure sensed in the body?
Baroreceptors are pressure receptors. There are some in the aortic arch and carotid bodies. The juxtaglomerular arch in the kidney can also adjust the flow to itself and the rest of the body. There are higher functions as well that can act to override this, such as fear.
How do baroreceptors affect the autonomic nervous system?
An increase in mean arterial systemic pressure causes the baroreceptors to fire more. This causes decreased. and increased parasympathetic tone.
Decreased mean arterial systemic pressure causes decreased firing of baroreceptors. This causes increased sympathetic tone and decreased parasympathetic tone.
What is the initial response in significant blood loss?
If you lose blood, there is decreased central venous pressure. This leads to less preload and a lower stroke volume initially. There is less cardiac output and so less blood pressure. This causes baroreceptors to activate sympathetic system and reduce the effect of parasympathetic system.
What is the effect of giving too much blood?
The cardiac output will fall. The blood pressure will therefore fall. The pressure will get transmitted to the lungs and so increased alveolar pressure. This will cause fluid to leak out of the capillaries and into the pulmonary space - pulmonary oedema. This will also cause a lower blood pressure due to the decreased stroke volume and so cardiac output.
In order to treat this, you would then give a diuretic such as Furosemide to lower central venous pressure and bring preload back to normal.
