Short Notes on Cardiovascular Pressures. Part 1 | Clinical Notes.
Ayinla Daniel, RN, Rctn.
‘Pressure’ is a very important physical phenomenon/force which plays vital roles in human physiology. In this article, I will try to make notes and include comments to help simplify cardiovascular pressures.
The human heart and the hearts of any other mammal (and advance life forms; amphibians, Pisces etc), all work on the basic scientific principles of pressures, volumes and contraction. The human heart functions like a ‘pump, ‘ an organic pump that gets its fuel from coordinated electrical activities that cause the heart muscles to squeeze out blood into a closed network of blood vessels (aided by specialised valves).
The blood present in this closed system/circuit moves around with the aid of pressure generated by the pumping heart and this pressure is affected by other physiological elements, which will include blood volume & composition, nature of blood networks/vessels (size, pathology etc) and other factors.
Abnormal increase or decrease in cardiovascular pressures can negatively affect overall physiology – since blood is needed by all parts of the human body.
The term “cardiac output, “ is used to describe the amount of blood that is pumped out the heart in one minute and it is estimated that about 5 litres of blood is pumped out of the heart every minute, while “stroke volume” on the other hand is used to describe the amount of blood pumped out of the heart per heartbeat. In the course of explaining these pressures, you will come across these terms often.
Below is a list of basic cardiovascular pressures:
- Central Venous Pressure
- Pulmonary Artery Pressure
- Arterial Pressure
- Cardiac Chamber Pressures
- Mean Arterial Pressure
- Pulse Pressure
I will make very brief notes and won’t bother about much details in this article. There are other parameters that can be used to describe cardiovascular pressures, but these are the major ones:
- Central Venous Pressure: CVP is the hydrostatic pressure of the blood entering the heart (from the superior vena cava and the inferior vena cava; the upper & lower extremities respectively), as measured by a catheter with its tip in the right atrium. The CVP is a major determining factor of the state of cardiac filling or preload and its also used to determine the ability of the heart to squeeze the blood into the arterial system
An alteration in CVP (ΔCVP) is deduced by the change in volume (ΔV) of blood within the thoracic (blood vessels) veins divided by the compliance (Cv) of these veins according to the following equation: ΔCVP = ΔV / Cv.
(More elaborate notes on Central Venous Pressure will be presented latter on).
- Pulmonary Artery Pressure: Blood flow to the lung is made possible by pressure produced in the left ventricles, which is the chamber directly responsible for creating a force that pushes blood into the lungs through the pulmonary artery, controlled by the pulmonic/pulmonary valves. The volume of blood that needs to be oxygenated by the lungs is made available by the pulmonary pressure created by the right ventricle during systole.
(More elaborate notes on Pulmonary Artery Pressure will be presented latter on).
° Medical Terms Used:
• Preload – Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling
• Stroke volume – The amount of blood pumped by the left ventricle of the heart in one contraction.
• Hydrostatic Pressure – Hydrostatic pressure is the pressure that is exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.
° Physiological Ranges:
• CVP – 8 – 12 mmhg.
• Stroke volume – 70ml per beat at rest.
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