General Physiology First Aid Extra Info

Question 1

Formula for determining Physiologic dead space

Answer 1

Taco Paco Peco Paco

Vt = Tidal Volume
PaCO2 = arterial PCO2
PECO2 = expired air PCO2
Vd = Physiologic dead space

Vd = Vt x (PaCO2 - PECO2)/(PaCO2)

Question 2

Minute Ventilation (VE)

Answer 2

Total volume of gas entering the lungs per minute

VE = Vt x RR

RR = Respiratory Rate

Question 3

Alveolar Ventilation (VA)

Answer 3

Volume of gas per unit time that reaches the alveoli

VA = (Vt - Vd) x RR

Question 4

There is a tendency for the lungs to ________ and for the chest wall to _____.

Answer 4

Lungs to collapse inward and the chest wall to spring outward

Question 5

At the FRC, what are the pressures of the lungs?

Answer 5

Inward pull of the lung is balanced by outward pull of chest wall and system pressure is atmospheric

Question 6

At FRC, airway and alveolar pressures are ____ and intrapleural pressure is ____ which prevents _____.

____ is at a minimum.

Answer 6

Zero, negative, pneumothorax, PVR

Question 7

2 forms of the hemoglobin chains

Answer 7

T = Taut form - Has low affinity for O2
R = Relaxed form - Has high affinity for O2 (300x)

Question 8

What favors the taut form of hemoglobin?

Answer 8

Increased Cl, H+, CO2, 2,3-BPG, and temperature since these shift the dissociation curve to the right, leading to increased O2 unloading

Question 9

Why does fetal hemoglobin have higher affinity for O2 and what are the chain type differences

Answer 9

Fetal Hb is made of 2a and 2y chains. This causes fetal hemoglobin to have a lower affinity for 2,3-BPG than adult Hb, and thus has higher affinity for O2.

Question 10

When is hemoglobin taut vs. relaxed?

Answer 10

Taut in Tissues

Relaxed in Respiratory tract

Question 11

What is methemoglobin?

Answer 11

Oxidized form of Hb (ferric, Fe3+) that does not bind O2 as readily, but has increased affinity for cyanide (iron in Hb usually is in a reduced state of Fe2+)

Question 12

How does methemoglobinemia present?

Answer 12

Cyanosis and chocolate colored blood

Question 13

How do you treat cyanide poisoning?

Answer 13

Use nitrites to oxidize Hb to methemoglobin, which binds cyanide. Use thiosulfate to bind this cyanide, forming thiocyanate, which is renally excreted

Question 14

Treatment of methemoglobinemia can be treated with what?

Answer 14

Methylene blue

Question 15

Nitrites cause poisoning by____________.

Answer 15

oxidizing Fe2+ to Fe3+

Question 16

What is carboxyhemoglobin and what does it do to normal hemoglobin?

Answer 16

CO bound to Hemoglobin which shifts the dissociation curve to the left due to a decreased O2 binding capacity, causing a decreased O2 unloading in tissues.

Question 17

What is PVR?

Answer 17

Pulmonary Vascular Resistance

PVR = (Pressure in pulmonary artery - Pulmonary wedge pressure or pressure in the left atrium) / Cardiac output

Question 18

What is the alveolar gas equation?

Answer 18

PAO2 = PIO2 - (PaCO2/R)

PIO2 = PO2 of inspired air
PaCO2 = arterial PCO2
R = respiratory quotient = CO2 produced/O2 consumed

We can also just do:
150 - PaCO2/0.8

Question 19

Calculate A-a gradient

Answer 19

PAO2 - PaO2 = 10-15mmHg

Question 20

When might we see an increased A-a gradient?

Answer 20

May occur in hypoxemia, causes include shunting, V/Q mismatch, fibrosis (impairs diffusion)

Question 21

When we have Hypoxemia but a normal A-a gradient, what could be the cause?

Answer 21

High altitude or hypoventilation

Question 22

When we have hypoxemia but an increased A-a gradient, what could be the cause?

Answer 22

V/Q mismatch, diffusion limitations, right to left shunt

Question 23

Causes of hypoxia

Answer 23

Decreased Cardiac output
hypoxemia
anemia
CO poisoning

Question 24

Causes of ischemia or loss of blood flow

Answer 24

Impeded arterial flow or a decreased venous drainage

Question 25

Ideal situation for V/Q?

Answer 25

V/Q = 1 which would indicate ventilationm atching perfusion for adequate gas exchange

Question 26

V/Q for the apex and what is indicates

Answer 26

= 3, which means wasted ventilation

Question 27

V/Q for the base of the lung and what it indicates

Answer 27

= 0.6 and indicates wasted perfusion

Question 28

What is true about ventilation and perfusion at the base of the lung?

Answer 28

They are both greatest there than at the apex

Question 29

With exercise there is _____ in apical capillaries resulting in a V/Q ratio that approaches ______.

Answer 29

Vasodilation, approaches 1

Question 30

Why does TB affect the upper lobes?

Answer 30

Thrive in high O2 conditions

Question 31

Discuss what a V/Q = 0 indicates and the effect of 100% O2 added to the system

Answer 31

Indicates a shunt = airway obstruction. In a shunt, 100% O2 does not improve PO2

Question 32

Discuss what a V/Q = infinite indicates and the effect of 100% O2 added to the system

Answer 32

Blood flow obstruction = dead space. Assuming <100% dead space, 100% O2 improves PO2