Systole vs Diastole Cardiac Output Guide

SimpleNursing Editorial Team Nov 5, 2018
Nurse talking to senior woman in hospital bed. She is measuring her blood pressure. Senior woman in hospital bed

Blood pressure is determined by two factors – systolic and diastolic pressure. In this discussion, we’ll go through the traffic jam that happens within the blood vessels, the factors that influence pressure increase, and how peripheral pressure heightens.

Jump to Sections


  1. Blood Pressure
  2. Systolic vs Diastolic Blood Pressure
  3. Pulse Pressure Narrowing

Blood Pressure (The Traffic Jam)

Think of your blood pressure as a morning drive with your car. If you’re driving on a freeway, there are only two things that matter to arrive at work on time – how many lanes are open and how many cars are on the freeway.

The most important between the two is the lanes that are open during that moment because, no matter how many cars there are, there wouldn’t be a traffic jam as long as the lanes opened are sufficient to sustain the volume.

On the other hand, if there is only one lane that’s open at that time, cars are going to be backed up, causing the traffic jam. A blocked freeway, or in this case, a blood vessel, can either be due to several reasons. Either way, limited passage will cause bottleneck, resulting in increased pressure.

Systolic vs Diastolic Blood Pressure

What is the difference between systolic and diastolic blood pressure? The systolic pressure is when a patient’s heart is pumping, and the diastolic pressure is when the heart is resting between beats. When either of these pressures goes up. It could be a sign that there is a complication with the heart or overall health.

Here’s the scoop on the difference between the two: systolic pressure is the amount of force in the arteries when your heart is squeezing, and diastolic pressure is the force in the arteries when your heart is chillin’ out between squeezes.

In a relaxed sitting position, a normal systolic pressure should be below 120 mmHg (that’s millimeters of mercury), while a normal diastolic pressure should be below 80 mmHg. If a patient’s systolic pressure is high, it’s usually because their arteries have gotten stiff. On the flip side, low diastolic pressure can sometimes happen if they’re dehydrated or experiencing severe bleeding.

When systolic pressure increases and diastolic pressure does not increase as much, the difference between them—pulse pressure—gets wider. The gap between the high systolic pressure and the lower diastolic pressure becomes greater. This widening of pulse pressure is often seen in conditions like high blood pressure, where narrowed arteries cause increased resistance to blood flow.

Pulse pressure is the difference between the systolic and diastolic blood pressure readings. It indicates how much force the heart exerts with each beat. When blood vessels get narrower, in the case of clogged arteries or other vascular diseases, it becomes harder for blood to flow through them. So, the heart has to work harder and pump with more force, resulting in a higher systolic pressure.

Pulse Pressure Narrowing (Factors that Shuts Down the Freeway)

There are four different factors that influence the closing down of lanes or the narrowing of the pathways of the blood vessels. These four areas are essential in the therapeutic clinical objectives when dealing with blood pressure issues. So, what are the reasons why the lanes of the freeway are narrowing or shutting down?

  1. Increase platelet congregation

Platelet congregation is simply platelets surrounding or attaching to the lining of the blood vessels. As platelets attach to the vessels, it causes narrowing. Furthermore, tissue damage will occur.

  1. Stress

Increased stress is element that increases the risk of a narrowed pathway, this is because stress influences the increase of adrenaline which stimulates the sympathetic nervous system or the fight and flight response; thus, severe vasoconstriction occurs.

  1. Injury

Critical injury to certain sites, especially to the blood vessels, is also a qualifying factor for the constriction of passageways. What causes injury to the freeway?

  • Smoking
  • Diabetes – insulin is a corrosive agent that damages the lining of the blood vessels, causing inflammation and constriction
  1. Fatty deposits

High level of fats or cholesterol is detrimental to the body. Fats, much like platelets, attach to the lining of the blood vessels, causing the narrowing of the freeway. To prevent this from happening, high density lipoproteins (HDL), or the good cholesterol, should be increased. Also, low density lipoprotein (LDL), or the bad cholesterol, should be decreased.

Plaque Formation

Now, we have laid down the four main causes of the shutting down or narrowing of the freeway, which results to an increase in peripheral pressure. To review, we have platelet congregations, stressors, injuries, and fatty deposits.

Plaque is another thing that you need to take note of when understanding blood pressure. Plaque is just an inflammation of the veins wherein deposits underneath the vein have broken through and has protruded. Plaque is said to be one of the primary reasons for increasing peripheral pressure.

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