Cardiovascular system: Cardiac output Flashcards
What is the function of the heart?
To supply the right amount of O2 and nutrients to the body
What is the resting vs intrinsic heart rate of a normal heart?
Resting = 60-70, intrinsic = 90
What set the intrinsic heart rate?
The sinoatrial node
What lowers the normal resting heart rate?
parasympathetic nerves
What is the cardiac output (CO) formula?
Heart rate (HR) * Stroke volume (SV)
What is the cardiac output at rest?
4-5Lmin-1
What is venous return?
The volume of blood returning to the heart from the vasculature (vascular system of the body) every minute
What is the cardiac reserve?
The difference between resting CO and and max CO (i.e. rest = ~5Lmin-1, exercise = ~20Lmin-1 therefore cardiac reserve = 15Lmin-1)
How can the CO be regulated?
By regulating the heart rate and stroke volume
How is the stroke volume regulated?
By pre-load, after-load and contractility
What is pre-load?
The pressure of the blood retuning to the heart
How does pre-load affect the SV? What determines the affect?
The greater the pressure of the blood on the heart the more force the heart exerts to push it out therefore increasing stroke volume
The Frank-Starling law determines the relationship between pressure on the heart and how hard it contracts
What is after load?
The pressure that must be exceeded in order for blood to be moved into and out of the ventricle
How does after load affect stroke volume?
The greater the after load in the pulmonary artery, the more force the right ventricle needs to exert to pump blood into the pulmonary system
The great the after load in the aorta, the more force the left ventricle needs to exert to pump blood into the systemic circuit
What is contractility?
The strength of the contraction of the heart
How is contractility affected?
By the inotropic agents, i.e. an increase of positive inotropic agents causes an increase in contraction strength (and heart rate FYI), an increase in negative inotropic agents decreases contraction strength (and heart rate FYI) (FYI this strength is for all physiological levels of stretch in the heart)
What are some examples of positive inotropic agents? What do they do to increase contractility?
Norepinephrine and epinephrine, they increase Ca2+ release
How do negative inotropic agents decrease contractility?
Reducing Ca2+ flow therefore decreasing strength of the heart beat
What is the Frank - Starling law of the heart?
That the more blood that comes into the heart during diastole, the harder the contraction during systole OR the energy of contraction of the ventricle is a function of the initial length of ht muscle fibres comprising its walls
What happens when pre-load increase but stroke volume doesn’t change?
It causes an increase in pulmonary congesting (i.e. pooling of liquid in the venous system)
What is the ejection fraction?
The percentage of the max blood that is ejected per stroke (i.e. if volume of heart = 120ml and max ejected blood = 80ml, ejection fraction = 66%)
How does the ejection fraction change during heart failure?
The ejection fraction begins to decrease
What does a decreasing ejection fraction indicate about the heart?
A decreasing ejection fraction indicates that the heart is pumping out less per contraction which means that it will struggle to pump against the after load
Hw can the heart rate be affected?
Nervous system, chemicals, health and environment
How can the nervous system affect heart rate?
The sympathetic and parasympathetic stimulation affection the release of chemical and influence Ca2+ fluxes influencing the depolarisation of the SA and AV node
How can chemicals affect heart rate?
positive inotropic chemicals increase extracellular Ca2+ concentrations causing increase in heart rates
How can health affect heart rate?
Old/young, gender, fitness etc. all affect the resting heart rate based on the physiological needs on the body and the size and condition of the heart
How can the environment affect heart rate?
For example, increasing body temperatures causes an increase in heart rate for cooling purposes
