Today's picture comes from the Official website for Kuwait University Medical Students - no kidding, here's the link http://kuwaitmd.hsc.edu.kw/main/btw, the images in these blogs can be clicked on to see them full size and you can right click on the images to open them up in a new window or tab.
Anyway - today's picture represents the cardiac cycle. Yup - we're still delving into the wonderful world of coronary carnage. If you spend a couple scant hours looking at the pic then some interesting things come to light (they did for me anyway).
At the top of this chart we have ventricular pressure in blue along with atrial and aortic pressure shown in gray. The middle part of the chart shows the electrocardiogram with our old friends, the P, QRS and T waves. The bottom portion shows the phonocardiogram and three sounds in the heart. The first two sounds are the most common that people know about, I think I read there are four sounds but the latter sounds are probably nothing that could be heard w/ a stethoscope. The first two sounds represent the familiar "lubb" "dup" sounds. The first sound comes from the closing of the atrioventricular valves and the second sound is from the semilunar valves.
When we get our blood pressure taken we're getting the pressure generated by our left ventricle. If you look at the chart of Pressure (mmHg) and follow the blue line, you'll notice on the ascending portion of the blue line that intersects with the opening of the aortic valve and follow that intersection over to the left we'll see it corresponds with a pressure of around 80mmHg. This corresponds to diastolic pressure ...it's kind of interesting to note that the diastolic pressure is obtained during systole (contraction) of the ventricle. Basically, it's the least amount of pressure needed in order for the ventricles to force open the semilunar valves. If you're a right ventricle, you'll be sending blood to the lungs to get refreshed and if you're a left ventricle, then you've got your work cut out for you because you'll be sending your blood throughout the entire body or systemic circulatory system. Once the left ventricle has squeezed out all the blood it can then the blood pressure in the aorta slams those semilunar valves shut and that's the second heart sound we hear ("dup")
When that blue line is at it's peak and we follow the peak over to the corresponding pressure we'll notice it's at about 120 mmHg. So, this graph represents a patient with a blood pressure reading of about 120/80 which is what we like to see :)
I am starting to learn a little more detail about the electrocardiogram readings. The QRS complex does involve depolarization of the ventricles but I'm thinking the sharp upward spike from Q to R is the depolarization along the interventricular septum (the part that separates the two ventricle) and the sharp downward reading from R to S is when the Purkinje fibers shoot the depolarization back up the ventricular myocardium. At least, that's how I'm seeing things for now.
I mentioned hyper (high) and hypo (low) kalemia and calcemia the other day. Those conditions can be seen on an EKG or ECG ....I've always heard EKG and learned from my readings that EKG comes from the German word - elektrocardiogram - I guess it's got a 'k' in there where us Americans put a C.
In cases with too much Potassium (K+, hyperkalemia) we can see high T-waves and Hypokalemia (low potassium) has a tendency to produce 'u' waves. I don't think U-waves are seen much under any normal circumstances.
High levels of calcium - hypercalcemia provides for a narrow QRS complex and I believe low levels of calcium widens the QRS complex.
There are abnormalities such when the conduction of the electrical impulses get stuck between the atria and ventricles - these are referred to as atrioventricular blocks or AV blocks and they come in three degrees - just like burns - and ...the severity rises with each degree.
In first degree blocks, there are simply longer intervals between the P and Q waves. This could be due to scarring of the myocardium or heart tissue. With 2nd degree blocks - you probably want to get your patient a shiny new Medtronics pacemaker and if a patient comes in with 3rd degree heart block then you want to make sure your malpractice insurance is up to date because they could die on the spot ...kind of makes you wonder how they get into the hospital in the first place?
Ventricular fibrillation is pretty bad also.
I think if I just get that chart memorized then I should be in pretty good shape for the test - at least regarding the cardiac cycle portion of the test. The chart in our (American) powerpoint is actually a bit more detailed. Regarding Systole and Diastole, there are sub-phases of each one. Systole includes a period of isovolumic contraction and a period of ejection while diastole involves a period of isovolumic relaxation, passive ventricular filling and active ventricular filling. There are other charts that go with that stuff as well.
Huh - I really wanted to talk about proprioception tonight but I guess all the cardio study caught me off guard.
Some personal interesting things I've learned about the heart ....
When pronouncing the words "systole" and "diastole" you pronounce the E at the end, it's a long e. I had always pronounced those words with a silent e.
More interesting - is that the heart has a fibrous skeleton that separates the top and the bottom of the heart. The fibrous skeleton partitions the atriums on top from the ventricles on the bottom. The fibrous skeleton even has a cool name - TRIGONES. We have a left and right fibrous trigone and the valves in the heart all have fibrous rings.
A big part of these trigones is to keep the electrical current passing throughout the heart in an orderly and coordinated manner. The sparkplug of the heart starts in the right atrium at a location called the sinoatrial node or SA node. When I see that letter S in SA I think "start" and it helps me keep straight where the spark starts. Next the impulse goes to the AV node or antrioventricular node, which is still in the atrium, then in order to get around the fibrous skeletal trigones there is a single path where the impulse gets to cross over, down into the ventricles called the Atrioventricular Bundle or AV bundle - this is also known as the Bundle of HIS - strange name but, it's pretty important so I guess it gets a special name. ....
now, we know a snake hisses and a snakes tongue is forked so, this Bundle of HIS also forks and becomes the right and left bundle branches which go down the ventricular dividing line known as the interventricular septum - those branches head all the way down the the bottom or apex of the heart where they meet the super fast and fun loving Purkinje Fibers - The SA and AV nodes are kind of slow pokes when it comes to electrical conduction - they fire away at a speed of about 2 inches per second but those darned Purkinje fibers blast away at better than 13 FEET per second! Those Purkinje fibers shoot the electrical impulse back up the outside walls of the ventricles. (recalling that the septum between the ventricles kind of runs down the middle of the heart)
Purkinje reminds me of Penske - you know, the race car people (http://www.penskeracing.com/)
So, it makes sense that Purkinje fibers are so fast ;)
I've got two more nights to study for this physio test - hoping for the best. We've also got our third microbiology exam on Wednesday along with a biochemistry quiz - I'll do what I can with each - tomorrow is a long day at school - 9 hours straight classes - no lunch break - might get out a bit early from micro lab and anatomy dissection sometimes gets out early - no worries - long days at chiro school are pretty good things to have in the big scheme of things.
btw - I brought my pocket sized Guytons physiology review book in when I went to the doctors office this past Friday and my MD doc commented that it was the same book he used way back when - and I think he graduated in '72. He mentioned that he thought Dr. Guyton was dead now but his books are still THE bible when it comes to physiology.
Thy Guytons practice quizzes will be the last thing I do in prepping for this test - it's kind of a formidable book. :)
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