what is the normal PP

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Here is a complete overview of normal pulse pressure based on authoritative medical textbooks:

Pulse Pressure (PP)

Definition & Formula

PP = Systolic BP - Diastolic BP

Example: BP of 120/80 mmHg → PP = 40 mmHg

Normal Value

Parameter	Value
Normal PP	40 mmHg
Normal range	30-50 mmHg
Approximately	~25-30% of systolic BP

Abnormal Pulse Pressure

Wide (increased) PP - ≥60 mmHg:

Aortic regurgitation
Arteriosclerosis (stiff, non-compliant arteries)
Patent ductus arteriosus (PDA)
Hyperthyroidism
Anemia
Arteriovenous fistula
Increased intracranial pressure
Exercise (physiologic, transient)

Narrow (decreased) PP - ≤20 mmHg:

Hypovolemia / reduced central blood volume
Aortic stenosis (reduced stroke volume)
Pericardial tamponade
Early septic shock (increased peripheral vascular resistance)
Decreased stroke volume of any cause

Physiological Basis

Pulse pressure is determined by two main factors (Guyton & Hall):

Stroke volume - more volume ejected = wider PP
Arterial compliance - stiffer arteries = wider PP (PP = stroke volume / compliance)

This is why PP is a clinical surrogate for stroke volume. Pulse pressure is highest in the large arteries (slightly augmented from the aorta due to pressure wave reflection) and progressively dampened in smaller arteries, becoming virtually absent in arterioles and completely gone in capillaries and veins.

Clinical Pearl: Pulse Pressure Variation (PPV)

In mechanically ventilated patients, a PPV >13% (max PP - min PP / mean PP over one respiratory cycle) is highly predictive of fluid responsiveness.

Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 43
Costanzo Physiology, 7th Edition - Arterial Pressure section
Guyton and Hall Textbook of Medical Physiology - Arterial Pressure Pulsations

Explain me the vascular function like I am 5. The graph is like pointing downwards. There a shift to the right, a shift to the down, a shift to the up, maybe right or left. So explain me.

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Perfect - I have all three textbook diagrams. Here is the full simple explanation:

The Vascular Function Curve - Explained Like You're 5

First, what is this graph even about?

Think of the heart and blood vessels like a garden hose and a pump.

The Y-axis (up-down) = Venous Return - how much blood is flowing BACK to the heart per minute (L/min)
The X-axis (left-right) = Right Atrial Pressure (RAP) - how much pressure is building up at the door of the heart

The big idea is simple: the more pressure piling up at the heart's door, the LESS blood can flow back in. That's why the line goes downhill - higher RAP = less venous return.

The Basic Curve

Look at this graph. Two key points:

Point	What it means
Point B (where it hits zero, ~7 mmHg)	The Mean Systemic Filling Pressure (MSFP) - if the heart stopped completely, pressure would equalize everywhere at this number. No flow.
Point A (middle of the slope)	Normal operating state - RAP ~2 mmHg, venous return ~5 L/min
Flat part (left side)	Veins collapse when RAP goes too negative, so flow can't increase anymore even if you pull harder

Simple rule: Lower RAP = heart is "sucking" harder = more blood flows back. Higher RAP = congestion = less blood flows back.

Shift to the RIGHT (more blood volume)

Imagine you add more water to the hose system (blood transfusion, IV fluids, venoconstriction).

The whole curve slides to the right
MSFP goes UP (e.g., from 7 to 9 mmHg) - there is more pressure everywhere because the system is fuller
At any given RAP, venous return is now higher
The slope does NOT change - the curve just moves right, parallel to the original

Real life: IV fluids, blood transfusion, venoconstriction (like in sympathetic activation - veins squeeze and push blood forward)

Opposite - shift to the LEFT = hemorrhage, dehydration, venodilation (less blood in the system, MSFP falls, curve slides left)

Shift Up/Down = Change in SLOPE (arteriolar tone)

Now imagine the arterioles - the tiny resistance vessels - open up or clamp down. These contain very little blood, so they don't move the MSFP (x-intercept stays the same at ~7 mmHg). But they change how easily blood flows from arteries to veins.

Change	What happens	Why
Vasodilation (arterioles open)	Curve rotates upward/steeper	Blood flows easily from artery side to vein side - more venous return at every RAP
Vasoconstriction (arterioles clamp)	Curve rotates downward/flatter	Blood gets stuck on the artery side - less venous return at every RAP

Notice both curves still cross the x-axis at the same MSFP (~7 mmHg) - because you didn't change how much total blood is in the system, just how easily it moves.

Quick Cheat Sheet Summary

What changes	Effect on curve
↑ Blood volume / venoconstriction	Shift RIGHT (parallel, MSFP ↑)
↓ Blood volume / venodilation	Shift LEFT (parallel, MSFP ↓)
Arteriolar dilation (↓ TPR)	Rotate UP (steeper, same x-intercept)
Arteriolar constriction (↑ TPR)	Rotate DOWN (flatter, same x-intercept)

The golden rule to remember:

Blood volume changes = slide the whole curve left or right
Arteriolar resistance changes = rotate the curve up or down around the x-intercept
Costanzo Physiology, 7th Edition - Vascular Function Curve section
Medical Physiology (Boron & Boulpaep) - Chapter 23, Figures 23-9 and 23-10

How does this curve match with the cardiac function curve to determine heart output?

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Great images retrieved. Here is the full explanation:

Matching the Cardiac and Vascular Function Curves

First - why are they opposites?

Remember from before:

Vascular curve goes downhill - higher RAP = less venous return
Cardiac curve goes uphill - higher RAP = more filling = more cardiac output (Frank-Starling)

They are like two kids on a seesaw, always fighting each other. The only point where they agree - where the heart's output exactly matches what the veins are sending back - is where they cross.

The Equilibrium (Operating) Point

Point A is the steady-state operating point (~RAP 2 mmHg, ~5 L/min). This is normal resting cardiac output. At this single point:

Cardiac output = Venous return (both = 5 L/min)
The system is in balance

What happens if something disturbs balance? The graph shows this beautifully. If RAP suddenly rises to 4 mmHg (say, you gave a fluid bolus briefly):

The heart is now at point B (pumps more - 7.5 L/min, Frank-Starling)
But the vascular system is at point B' (sends back less - only 3 L/min because RAP is high)
Mismatch! Heart pumps out more than veins return, so RAP starts falling
The system spirals back through C/C' and settles at Point A again

The system is self-correcting. It always snaps back to the intersection.

Scenario 1: Shift the VASCULAR curve (blood volume change)

Give a blood transfusion: the vascular curve shifts right (more blood in the system, MSFP rises).

Old intersection = Point A (RAP ~2, CO ~5 L/min)
New intersection = Point B (RAP ~3, CO ~6.5 L/min)

Result: Both cardiac output AND RAP go up. The heart pumps more because it gets more filling (Frank-Starling does the work automatically - you didn't change the heart at all).

Opposite with hemorrhage: vascular curve shifts left, new intersection is down and to the left = lower CO and lower RAP.

Scenario 2: Shift the CARDIAC curve (contractility change)

Positive inotrope shifts cardiac curve up

Give digoxin (positive inotrope): the cardiac curve shifts upward - the heart squeezes harder at every RAP level. The vascular curve does NOT move.

Old intersection = Point A (RAP ~2, CO ~5 L/min)
New intersection = Point B (RAP ~0.5, CO ~6.5 L/min)

Result: Cardiac output goes UP, but RAP goes DOWN. Why? Because the stronger heart empties itself so well that less blood backs up at the right atrium. This is why giving digoxin to a heart failure patient drops their venous congestion - the RAP falls.

Opposite with negative inotrope (like beta-blocker overdose): cardiac curve shifts down, new intersection = lower CO, higher RAP (more congestion).

The Master Summary Table

Change	Which curve moves	New operating point
Blood transfusion / IV fluids	Vascular → right	↑ CO, ↑ RAP
Hemorrhage / dehydration	Vascular → left	↓ CO, ↓ RAP
Positive inotrope (digoxin)	Cardiac → up	↑ CO, ↓ RAP
Negative inotrope (beta blocker)	Cardiac → down	↓ CO, ↑ RAP
Vasodilation (↓ TPR)	Vascular rotates steeper	↑ CO, ↓ RAP
Vasoconstriction (↑ TPR)	Vascular rotates flatter	↓ CO, ↑ RAP

The One-Line Rule to Remember

"The operating point is where the two curves cross. To change cardiac output, you either slide the vascular curve (change volume) or rotate the cardiac curve (change contractility)."

Costanzo Physiology, 7th Edition - Combining Cardiac and Vascular Function Curves
Medical Physiology (Boron & Boulpaep) - Figure 23-11

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