3 - Cardiovascular Mechanics 2 Flashcards
What diagram is used to represent the cardiac cycle?
Wiggers diagram
What is used to measure preload on the left side of the heart?
- PAWP: Pulmonary Artery Wedge Pressure
- By measuring the pulmonary artery pressure you get an indirect measurement of the left atrial pressure
What three factors affect cardiac output?
- Preload
- Afterload
- Contractility
How does the Frank-Starling Relationship change with increased contractility?
The gradient of the ESV line changes
What are the phases of the cardiac cycle?
- atrial systole
- isovolumetric contraction
- rapid ejection
- reduced ejection
- isovolumetric relaxation
- rapid passive filling
- reduced passive filling
What are the systolic phases of the cardiac cycle?
- isovolumetric contraction
- rapid ejection
- reduced ejection
What are the diastolic phases of the cardiac cycle?
- atrial systole
- isovolumetric relaxation
- rapid passive filling
- reduced passive filling
What happens during atrial systole?
- P wave
- S4 (abnormal)
- contraction from top to bottom tops up blood volume in ventricles (atria almost full from passive filling)
What causes an S4 heart sound?
- congestive heart failure
- pulmonary embolism
- tricuspid incompetence
What happens during isovolumetic contraction?
- QRS complex
- S1 (lub - closure of AV valves)
- ventricular contraction, no volume change
What happens during rapid ejection?
- c wave
- semi-lunar valves open
- ventricular contraction causes greater ventricular pressure than aortic/pulmonary artery pressure so valves open
- ventricular volume decreases
What happens during reduced ejection?
- t wave (repolarisation of ventricles)
- semi-lunar valves start closing
- ventricular volume decreases more slowly
What happens during isovolumetric relaxation?
- v wave
- atrial pressure increases
- dichrotic notch (rebound pressure against aortic valve as aortic wall relaxes)
- S2 (dub - close of semilunar valves)
What happens during rapid passive filling?
- isoelectric ECG (ventricular pressure lower than atrial between cycles)
- AV valves open and blood flows into ventricles
- S3 (abnormal)
What causes the S3 heart sound?
- severe hypertension
- mitral incompetence
What happens during reduced passive filling?
- diastasis (middle of diastole)
- ventricular volume fills slower
- ventricles fill without atrial contraction
What is diastole?
- 2/3 beat
- ventricular relaxation
- ventricles fill with blood
What is systole?
- 1/3 beat
- ventricular contraction
- ventricles generate pressure then eject blood into arteries
What is the ejection fraction?
- stroke volume/end-diastolic volume
- proportion of blood pumped out of heart in a contraction
What are the average systemic and pulmonary circuit pressures?
- systemic: 120/80 mmHg (high)
- pulmonary 25/5 mmHg (low)
What are the labels of the Wiggers diagram?
- P
- Q
- R
- S
- T
- a
- c
- v
- S4
- S1
- S2
- S3
a. aorta
b. atrium
c. ventricle
What are the effects of sympathetic and parasympathetic stimulation on the SA node?
- parasympathetic: present at rest, slows SA node
- sympathetic: increases SA nde through hormonsl (adrenaline) and neural (noradrenaline) mechanisms
What are the effects of exercise on pressure-volume loops?
- increased skeletal muscle pump work in legs leads to increased venous return
- increased stretch so more blood enters ventricles (increased EDV so graph shifts to right)
- increased sympathetic heart activity so increased contractility (graph shifts to left)
- increased volume ejected, lower ESV so lower SV
- no pressure effects with preload change
What do the 4 points on a pressure-volume loop represent?
- end-diastolic volume (preload)
- after isovolumetric contraction (afterload)
- after isovolumetric relaxation
- end-systolic volume
