CV Lab Flashcards
Blood pressure can be influenced primarily by:
cardiac output, peripheral resistance, and blood volume. Body position, exercise, and other factors may affect some of these variables.
Systolic pressure is
the maximum pressure in an artery during ventricular contraction.
Diastolic pressure is the
minimum pressure in an artery during ventricular relaxation.
Blood pressure is manually determined using a
sphygmomanometer (blood pressure cuff) along with a stethoscope.
The sphygmomanometer is placed around an artery (typically the
brachial artery of the arm), and the stethoscope is placed distal to the cuff.
The cuff is oriented such that the
tubing is facing anterior and exits the cuff distally.
Inflation of the cuff blocks blood flow
distally in the artery.
Slow deflation of the cuff allows blood to
slowly flood back into the artery. The practitioner can determine systolic and diastolic pressure by listening to the blood pressure (Korotkoff) sounds(see image below).
Korotkoff sounds are heard from an artery as
pressure is applied by a sphygmomanometer below systolic pressure.
Blood pressure is recorded using two numbers, one on top of the other. The top number is the
systolic pressure, and the bottom number is the diastolic pressure.
Normal adult blood pressure for those between the ages of 20-40 is
115/70. Blood pressure is lower as an adolescent, and higher as we age.
Chronically elevated blood pressure over 130/80 is called
hypertension.
Chronically low blood pressure less than 90/60 is called
hypotension.
Cardiac muscle cells contract in response to a rapid series of
electrical potential changes that travel through the heart along the conduction system.
Under normal conditions, electrical activity of the heart is spontaneously generated by the
sinoatrial (SA) node, the heart’s physiological pacemaker.
This electrical impulse is propagated throughout the
right and left atria, stimulating the myocardium of the atria to contract.
The electrical activity propagates throughout the atria from the
SA node to the atrioventricular (AV) node.
The AV node functions as a
critical delay in the conduction system.
This prevents the atria and ventricles from contracting at
the same time, and provides time for blood to flow from the atria to the ventricles.
The distal portion of the AV node is known as the
AV bundle (bundle of His), which splits into right and left bundle branches in the interventricular septum.
Both bundle branches taper out into the
subendocardiac conducting network (Purkinje fibers) that stimulate individual groups of ventricular myocardial cells to contract.
As the electrical current passes through the heart,
the cardiac muscle tissue is electrically excited, causing it to contract.
After contracting, the muscle cells relax again until the
next electrical current passes through, and the cycle is repeated.
An electrocardiogram (ECG) is an interpretation of the
electrical activity (depolarization and repolarization) of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body.
Einthoven’s triangle is formed by the use of the
left arm (LA), right arm (RA), and left leg (LL) electrodes to form the three pairs LA + RA, LA + LL, and RA + LL.
The output from each pair is known as
a lead.
The ECG recorder detects and amplifies the
tiny electrical changes on the skin from each pair caused when the heart muscle depolarizes during each heartbeat and compiles them as a recording that we call an electrocardiogram (ECG).
During each heartbeat, a healthy heart will have an orderly progression of a wave of depolarization triggered by the of the ventricles (T wave).
SA node (P wave) across the atria, passing through the AV node, and then spreading all over the ventricles (QRS complex) followed by repolarization
The ECG is made up of a s
traight baseline and waves. The waves can either move over or under the baseline. See an example in figure 1.
A segment is the area
between two waves. See an example in figure 2.
An interval is a
straight line and one or more waves. See an example in figure 3.
A complex is more than
one wave appearing in succession of one another. See the “QRS complex” in figure 4.
Brachial artery
Palpated within the front of the elbow (antecubital region)
