Sample – ΔP = Flow x Resistance Practice


 

Next Step: Make Cards on the Automatic Key Concepts, and Vignettes

Remember, the more you automatically know what each sentence means on your test, the better you will do. There are 4 stages in making interpretation more automatic:

  • Stage 1: Unable to Make Pathophysiologic Chronologies in Either Timed or Untimed setting
  • Stage 2: Basic Pathophysiologic Chronologies, but with Significant Gaps
  • Stage 3: Detailed Pathophysiologic Chronology Without Time, but Unable to Consistently Generate PC During Timed Setting
  • Stage 4: Consistent Pathophysiologic Chronologies in Timed Setting

My goal with these vignettes is to help you reach Stage 4. How do you do so?

  • With the Automatic Key Concept cards, you can master the underlying information to move past Stages 1 + 2.
  • Then, with the Vignette/Pathophysiologic Chronology cards, you can teach yourself to make these connections on your exam.

summary of key concepts:

 

Pressure ischemia – what equation can you use to explain this phenomenon? Why would this make sense?

P1 – P2 = ΔP = Flow x Resistance

By putting external pressure on capillary beds → resistance ↑ → P1 ↑, P2 ↓, and flow ↓ → tissue hypoperfusion → ischemia → if prolonged, then necrosis

 

When you sit for a long time and you skin feels numb/tingling, what equation and concept can you use to explain this?

Equation: P1 – P2 = ΔP = Flow x Resistance

Concept: transient ischemia = dysfunction

Sitting for a long time → resistance ↑ → flow ↓ → transient nerve ischemia → transient dysfunction (e.g., numbness, paresthesias)

 

Pressure ulcers – what equation and concept can you use to explain this?

Equation: P1 – P2 = ΔP = Flow x Resistance

Concept: prolonged ischemia = necrosis

Long pressure on tissue → resistance ↑ → flow ↓ → prolonged tissue (muscle, skin) ischemia → necrosis → skin breakdown → ulceration

 

Heart murmurs – physiologically, what are the ways that a murmur volume can increase? Use an equation to explain

In a general sense, a heart murmur can occur when there is:

    • 1) A more diseased valve/portion of blood vessel, and/or
    • 2) Greater velocity of blood across that valve / vessel

For 2), you can use the equation ΔP = Flow x Resistance, with flow as a rough approximation of blood velocity for a fixed valve lesion

 

Using the equation P1 – P2 = Flow x Resistance, explain at what point the aortic valve opens?

P1 = LV pressure, P2 = aortic pressure

When (P1 – P2) is a positive number, flow is positive. Thus, it makes sense that the aortic valve would open when LV pressure > aortic pressure

 

Using the equation P1 – P2 = Flow x Resistance, explain at what point the mitral valve opens?

P1 = LA pressure, P2 = LV pressure

When (P1 – P2) is a positive number, flow is positive. Thus, it makes sense that the mitral valve would open when LA pressure > LV pressure

 

Aortic flow – RELATIVELY speaking, just after the aortic valve opens, what will be the flow across the aortic valve? Use an equation to make sense of this.

Recall: P1 – P2 = Flow x Resistance

For flow across the aortic valve:

P1 = LV pressure (blood coming FROM)

P2 = aortic pressure (blood going TO)

Resistance = aortic valve resistance

At the moment the aortic valve opens, P1 will be BARELY higher than P2. As such, flow will be positive (but barely)

 

Aortic flow – RELATIVELY speaking, at mid-systole, what will the flow be relative to the beginning of systole? Why?

Recall: P1 – P2 = Flow x Resistance

For flow across the aortic valve:

P1 = LV pressure (blood coming FROM)

P2 = aortic pressure (blood going TO)

Resistance = aortic valve resistance

At the moment the aortic valve opens, P1 will be BARELY higher than P2. As such, flow will be positive (but barely)

Near mid-systole, however, (P1 – P2) ↑ → flow ↑

 

Aortic stenosis – using an equation, explain what the character of the murmur will be (e.g., holosystolic, decrescendo, crescendo-decrescendo). Why does this make sense?

Crescendo-decrescendo

Recall: P1 – P2 = Flow x Resistance

For flow across the aortic valve:

P1 = LV pressure (blood coming FROM)

P2 = aortic pressure (blood going TO)

Resistance = aortic valve resistance

As the LV contracts → P1 ↑. Initially, (P1 – P2) ↑ → flow ↑ → murmur will crescendo (get louder) earlier.

However, as near the end of systole, (P1 – P2) ↓ → flow ↓ → murmur will decrescendo (get softer)

 

Aortic regurgitation – using an equation, explain when will the regurgitant flow be the greatest across the aortic valve?

Regurgitant flow will be highest after the mitral valve opens

Recall: P1 – P2 = Flow x Resistance

In this case, because it is blood REGURGITATION (the reverse of normal):

P1 = aortic pressure (blood coming FROM)

P2 = LV pressure (blood going TO)

Just after the mitral valve opens:

    • P1 is relatively high (before much blood has been distributed to the rest of the body)
    • P2 is at the lowest (it has just ejected its stroke volume, and hasn’t been filled up by the LA / aorta yet)

In other words, the moments after the mitral valve opens (P1 – P2) highest → flow highest

 

Aortic regurgitation – using an equation, explain what the character of the murmur will be (e.g., holosystolic, decrescendo, crescendo-decrescendo). Why does this make sense?

Decrescendo

Recall: P1 – P2 = Flow x Resistance

In this case, because it is blood REGURGITATION (the reverse of normal):

P1 = aortic pressure (blood coming FROM)

P2 = LV pressure (blood going TO)

Just after the mitral valve opens:

    • P1 is relatively high (before much blood has been distributed to the rest of the body)
    • P2 is at the lowest (it has just ejected its stroke volume, and hasn’t been filled up by the LA / aorta yet)

In other words, the moments after the mitral valve opens (P1 – P2) highest → flow highest → murmur loudest early → as (P1-P2) ↓ → regurgitant flow ↓ → murmur softer later in the cycle

 

references:

GERD.png. (2020, October 7). Wikimedia Commons, the free media repository. Retrieved 02:02, April 27, 2021 from https://commons.wikimedia.org/w/index.php?title=File:GERD.png&oldid=483203113.

Pulmonary artery catheter english.JPG. (2020, October 18). Wikimedia Commons, the free media repository. Retrieved 02:20, April 2, 2021 from https://commons.wikimedia.org/w/index.php?title=File:Pulmonary_artery_catheter_english.JPG&oldid=493462725.

Circulation of blood through the heart.png. (2020, December 23). Wikimedia Commons, the free media repository. Retrieved 04:13, April 2, 2021 from https://commons.wikimedia.org/w/index.php?title=File:Circulation_of_blood_through_the_heart.png&oldid=520574500.

Radial artery catheterization.jpg. (2020, October 7). Wikimedia Commons, the free media repository. Retrieved 05:01, April 2, 2021 from https://commons.wikimedia.org/w/index.php?title=File:Radial_artery_catheterization.jpg&oldid=483583496.

Phonocardiograms from normal and abnormal heart sounds.png. (2020, October 3). Wikimedia Commons, the free media repository. Retrieved 06:06, April 2, 2021 from https://commons.wikimedia.org/w/index.php?title=File:Phonocardiograms_from_normal_and_abnormal_heart_sounds.png&oldid=478934031.

Wiggers Diagram.svg. (2020, September 12). Wikimedia Commons, the free media repository. Retrieved 06:07, April 2, 2021 from https://commons.wikimedia.org/w/index.php?title=File:Wiggers_Diagram.svg&oldid=456197904.

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