Blood Pressure and Blood Flow Help
Introduction to the Cardiac Cycle
After the chambers of the heart are excited, they go into a state of systole ( SIS -toh- lee ) or “contraction” and emptying. It is during systole that the blood is pumped from each of the ventricles, and out into their major arteries. After systole, comes diastole (die- AH -stoh- lee ) or “relaxation” and filling. While the atria are still contracting in systole, the ventricles below them are in a state of diastole, so that they receive blood through the right and left atrioventricular valves.
The Cardiac Cycle is one heart beat or one complete cycle of contraction (systole) plus relaxation (diastole) of all four chambers of the heart. There are also at least two heart sounds that can be heard through a stethoscope placed onto the chest or back. The 1st heart sound is commonly described as “lubb.” It is due to closure of both A-V valves, which occurs when the ventricles start going into systole. The ventricles push the A-V valve flaps shut from below. As a result, a back-flow of blood from the ventricles, and back up into the atria, is usually prevented.
The 2nd heart sound is usually represented as “dupp.” This sound occurs because of the closing of both semilunar valves at the beginning of ventricular diastole. The blood in the common pulmonary artery/aortic arch above each ventricle starts to fall back downward, due to the force of gravity. As the blood falls down, it catches the semilunar valve flaps and slams them shut, thereby preventing a back-leak into the ventricles. Glance back to Fig. 16.3, to help you visualize what’s happening during the two heart sounds.
Sometimes the heart valve flaps do not fit tightly together. Consider what may happen after bacterial endocarditis ( en -doh-car- DIE -tis). This disease involves an “inflammation of” (-itis) the “inner” (endo-) lining of the “heart” (cardi), due to infection with bacteria. During the process of inflammation, the flaps of certain valves (especially those of the left A-V valve) become swollen. When the inflammation finally heals, the valve flaps may become pulled back and distorted.
Thus, there is a turbulent ( TUR -byuh-lunt) back-flow of blood – a back-flow which is highly disorderly and in a state of “turmoil”– through the distorted and ill-fitting heart valve flaps. The resulting noisy, abnormal heart sounds are called a heart murmur.
In general, blood pressure (BP) is a pushing force exerted against the blood and against the walls of the blood vessels (see Figure 16.4). The blood pressure (BP) is at its highest in the major arteries attached directly to the heart (such as the aortic arch and common pulmonary artery). The BP then progressively decreases with greater distance from the heart.