L04- The cardiac cycle Flashcards
What is the largest part of the cardiac cycle and how does this change when HR inceases?
Diastole is the largest part of the cardiac cycle and it shortens when HR increases. hence the filling phase reduces.
Which is the dominant nervous system in resting heart rate?
Parasympathetic
What are the lub dub heart sounds representing?
The initial lub is the sound of the atrioventricular valves closing as the pressure in the ventricles exceed the pressure in the atria at the start of systole.
The dub sound is the aortic valve closing as the pressure in the aorta exceeds that of the left ventricle at the end of systole
What is stroke volume equal to?
SV=EDV-ESV
What is the ejection fraction?
The percentage of blood pumped out of the ventricles with each contraction
A patient has a blood pressure of 82/52 mmHg. What is the mean blood pressure and is this in the cerebral autoregulatory range?
Mean blood pressure 62mmHg
Yes as the cerebral autoregulatory range is 60-180mmHg
What is the shape of the P-V loop that shows starlings effect?
Stretched right as it has a larger EDV which results in an increased SV
What would result in a P-V loop with a greater pressure (taller)
Greater afterload to pump against as this will not change the volume being pumped but as it is harder it will require a greater pressure
What is the normal range for HR?
60-100bpm
What is the intrinsic pacemaker rate of the heart and what changes this?
The intrinsic rate of the SA node is 100bpm. Vagal tone reduces this.
what is the normal amplitude of the QRS section of an ECG?
2.5-3.0mV
What is the normal QRS interval?
0.06-0.12 secs
Which valves are open for the longest period of time during the cardiac cycle?
The AV valves as they are open for 2 thirds of the cycle as the ventricles fill whereas the aortic and pulmonary valves are only open during ventricular contraction
What is the equation for average blood pressure?
ABP=COxTPR
What is the equation for cardiac work?
Cardiac work=SV x mabp
