Wednesday, July 28, 2010

Blood Pressure

So I know I skipped a few chapters, but I thought I'd try handwriting everything and see how that affected my grade.. it went down by just handwriting, so I decided to pick back up the blogs and hopefully I can pull up my grade :) cheers!

During systole our ventricles of the heart contracts compared to diastole when the ventricles relax.  One cardiac cycle occurs after both diastole and systole have occurred, which includes both atrial and ventricular contractions.  AV valves are closed during the ventricular systole; this makes sense because the AV valves lead from the atrials to the ventricles and you wouldn't want to add blood to the ventricles when they are contracting.  You can also look at why the AV valves are closed because the atrial pressure is less than ventricular pressure.  The semilunar valves are closed during ventricular relaxation and atrial contraction.  Both sets of valves can be closed at the same time, but not open.  They are briefly both closed after atrial contraction and ventricular systole. Cardiac pressure is highest during ventricular systole and lowest during ventricular diastole. The dicrotic notch is the result of a momentary increase in aortic pressure that occurs when its semilunar valve snaps shut. 

The normal length of the cardiac cycle is 0.8 seconds.  The time of atrial systole is just 0.1 seconds, while ventricular systole is 0.3 seconds.  The pause is approximately 0.4 seconds.  

When an individual has an increased heart rate, the quiescent period is shorter.  If you have a heart rate of 80 beats per minute, the cardiac cycle lasts approximately 0.75 seconds. 

Two main factors promote the movement the movement of blood through the heart.  Diastole and systole of both the atrials and ventricles (myocardium relaxation and contraction) will move blood.  The other factor is the opening and closing of valves which changes the pressure gradients. 

A pulse is the pressure that surges in an artery occurring during each contraction and relaxation of the left ventricle.  To measure a pulse, place 2-3 fingertips of one hand over an arterial pressure point.  Compress firmly and then release the pressure slightly to feel the pulse.  There are arterial pulses all over the body.  The temporal artery is located just in front of the ear.  The facial artery is just below the ear.  The common carotid artery is in the neck.  The brachial artery is on the anterior side of the elbow.  The radial artery is in the wrist.  The femoral artery is on the inside of the thigh.  The popliteal artery is found on the back of the knee.  The posterior tibial artery is on the ankle and the dorsalis pedis artery is in the foot. 

The carotid artery had the greatest amplitude because it is the major artery delivering blood to the brain and its closest to the heart.  To tell the difference between if a bleed is arterial or venous, look for if it is spurting or flowing.  Arterial bleeds will spurt because they have the pressure of "new" blood coming from the heart.  Venous bleeds just flow because there isn't as much pressure, or smooth muscle to push it along. 

Blood pressure is the pressure against the walls of blood vessels by blood.  Systolic pressure is measured during the systole and diastolic during diastole.  A sphygmomanometer is the instrument used to compress the artery so that we can record pressures in the ausculatory method of determining blood pressure.   The sounds of Korotkoff are the sounds that can be auscultated over a partially occluded artery.  The systolic sound is caused by turbulent blood flow as it first begins to move through the constricted artery.  The sound disappears when blood flows freely again.  Pulse pressure is systolic pressure minus diastolic pressure.  Venous pressures are lower than arterial pressures because veins are farther away from the heart. 

Blood pressure can be decreased by an increased diameter of arterioles or a hemorrhage.  Blood pressure might be increased by an increased blood viscosity, cardiac output, or pulse rate or arteriosclerosis.   Our blood pressure is normally highest while standing and lowest while reclining.  When you stand up, your blood pressure drops initially and then raises because of the gravitational pull of blood.  When you stand still for three minutes, your blood pressure will drop again because the sympathatic nervous system isn't pumping.