Cardiovascular Flashcards
Explain the elecrophysiological changes that cause the ST segment elevation seen in a myocardial infarction?
- Abnormally rapid repolarisation of the infarcted muscle (accelerated opening of K+ channels). Current flow out of infarct (normal region negative relative to infarct). Occurs within seconds of infarction and lasts a few minutes.
- Decreased resting membrane potential (due to loss of intracellular K+). Begins in first few minutes secondary to process above. Current flow into infarct during diastole (ECG configured to record as ST elevation).
- Slowed depolarisation of affected cells compared to normal cells. Occurs at 30mins into infarct process. Current flow out of infarct.
What are baroreceptors and where are they located?
Baroreceptors are stretch receptors that sense the blood pressure. They are found in the adventitia of the carotid sinus and aortic arch. In the low-pressure circulation, there are baroreceptors in the atria at the entrance points of the IVC and SVC, and also in the pulmonary circulation.
(Bold + 2 locations to pass)
What stimulates the baroreceptors?
Stretch / distension of the vascular walls.
What are the effects of baroreceptor stimulation?
Inhibits the tonic sympathetic drive, and increases vagal tone. Allows rapid adjustments in BP. Causes:
- Reduced BP
- Reduced heart rate
- Reduced CO
- Vasodilation
(3 bold to pass)
Describe the mechanisms of venous return to the heart.
Thoracic pump - inspiration results in negative pressure to the thorax and positive pressure in the abdomen.
Effect of heart beat - pulls AV valves
Skeletal muscle pump
Lower resistance in large proximal veins, higher resistance in small peripheral veins
(Bold + 1 other)
What factors affect central venous pressure?
Decrease CVP: hypovolaemia
Increase CVP: congestive cardiac failure, tricuspid regurgitation, excessive fluid replacement
(1 example from each to pass)
What is the normal value of the mean CVP in adults?
6-8 cm H2O
or approx 5mmHg
