Resp- Lecture 3&4 Flashcards by Amy Woody

Dalton’s Law of Partial Pressure states:

In a mixture of gasses each gas exerts a partial pressure proportional to its concnetration in the mixture

N is 79%*760 mmHg= 600 mmHg Pn2

O2 is 21%* 760 mmHg= 160 mmHg

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What does A stand for? a?

A=alveolus

a is for arterial

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Alveolar gas equation?

pAO₂= FiO₂ x (760-47)- pACO₂/R

pAO₂= Partial pressure of alveolar O2
FIO2= Fractional concentraiton of o2
760= total barometic pressure (local)
47= partial pressure water vapor in alveolus
pACO2= alveolar partial pressure of CO2
R= respiratory quotient (RQ)<– will be given, typically 0.8 BMR
- RQ= amount of CO2 generate/o2 molecule used

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What are nitrogen levels like along respiratory tract?

Nitrogen is major component and does not change much

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What happens to O2 partial pressure once in trachea?

Air automatically becomes saturated with water vapor, so it takes up some of room available in 760. PP h2o= 47 mmHg and PPO2=150 in trachea

21/100*760= 159.6 ppO2 at room air

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What are partial pressures like in alveolus?

pO2= 100 mmHg
pH2O= 47 mmHg
pCO2= 40 mmHg

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What are partial pressures like in artery?

pO2= 95 mmHg
pCO2= 40
pH2O=0

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What is difference between pAo2 and pao2? What is this called?

Alveolar-arterial gradient. Typically 5-10 mmHg

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What is primary reason for a-a gradient?

Return of deoxygenated blood to Left atrium from bronchial vasculature

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When might alveolar-arterial gradient increase?

When there is a diffusion problem

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Normal tidal volume?

500 mL

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Normal anatomical dead space?

150 mL

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Alveolar ventialtion flow?

5250 mL/min

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What is pulmonary capillary blood flow?

70 mL/beat; 70 beat/min

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Pulmonary blood flow?

5000 mL/min

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What is minute ventilation?

TV x RR

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What is vita capacity?

IRV + TV + ERV

inspiratory reserve volume + tidal volume+expiratory reserve volume

(everything you can move, full exertional effort)

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What is inspiratory capacity?

IRV +TV

Everything inhaled from rest.

Inspiratory reserve volume +tidal volume

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What is functional residual capacity?

ERV + RV

Everything left in lungs

Expiratory reserve volume + residual volume

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Total lung capacity is?

IRV + TV + ERV+ RV

Everything!

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Can you measure RV by spirometry?

Any value that includes residual value cannot be measure by simple spirometry (FRC, RV)

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What is forced vital capacity?

Forcing VC out quickly. Value ends up a little less than VC (you get less air out when forced)

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What is anatomic dead space?

Volume of conducting airways (150 mL)

Can be measured by measuring N2 concentraiton by “washout” using 100% o2
Measures volume of conducting airways down to midpoint of transition from dead space to alveolar gas

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What is physiological dead space?

Volume of gas that does not participate in gas exchange and does not eliminate CO2
Alveolar CO2 equilibrates with arterial blood
- co2 so soluble and diffuses so fast that pAco2= paco2
- can be measured by Bohr’s method
V_D =V_T x PaCO₂ – P_ECO__₂ where PaCO₂is arterial pCO₂
- PaCO₂
- PeCO2= Expired CO2
- paCO2= arterial co2
- VT= tidal volumd
- Vd= volume dead space

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Anatomic dead space and physiological dead space should be almost the ____ in healthy people

same

When might physiological dead space be increased?

Asthma

What is helium dilution method?

* Measures communicating gas, or ventilated lung volume * Subject connected to spirometer containing a known concentration of helium * subject breaths to equilibrate Helium in his lung as well as spirometer * Helium is insoluble in blood * new helium concnetration measured * C1V1= C2 (V1 +V2) * C1= concentration helium in jar * V1= volume of gas in jar * C2= concentration of helium in lung * V2= volume in lung= FRC can measure RV by combining with spirometry

How do you assess alveolar ventilation?

Alveolar ventilation (Va)= tidal volume- dead space x rate CO2 concentration in expired gas may be used to measure alveolar ventilation VCO2= Va x FCO2 x K (constant) Fractional CO2= % CO2/100 Va= VCO2/pCO2 x K

What does total body plethysmography do?

Measure volume of chest cavity.

If ventilation is halved, CO2 \_\_\_\_\_

doubles

Normal Po2 /Pco2 in alveolus?

Po2= 100 mmhg PCO2= 40 mmHg

Normal Po2/Pco2 in pulmonary veins?

Po2= 100 mmHg Pco2= 40 mmHg

Normal po2/pco2 in pulmonary artery?

pO2= 40 mmHg pco2= 46 mmHg

Diffusion of CO2 is ____ faster than O2

20 times

How do you assess diffusion?

Carbon monoxide * CO immediatly binds to blood Hgb * Concentration in solution doesn't build up. Always has same delta P * Transfer is truly limited by diffusion * Allows to evaluate ability of patient to diffuse gases * Vgas= A x D( P1-P2)/T * Ax Dco (P1co-p2co)/T * DLco= (A/T) x Dco * DLco= Vco/PAco

1. At high altitudes, alveolar pO2 is reduced and the gradient between air and blood is less, so rise in pO₂ along the capillary is relatively

slow

How to find ambient O2?

21/100 x ambient pressure

How to find inspired o2?

21/100 x (ambient pressure-water vapor [47])

How to find alveolar o2?

Inspired o2- (Pco2/RQ)

Causes of hypoventilation?

- Drugs - Damage to chest wall - Weakness R muscles Increased resistance to airflow

What does hyhpoventilation increase?

pAco2 and paCO2 (fraction o2 going down so CO2 will take up more space, therefore increase % co2)

Diffusion can be limited by?

Interstitial disease

What is easiest factor to change in fick's law to influence diffusion?

Change in P - Increase pO2 in alveolus will increase gradient and increase arterial po2

Shunt refers to what?

* Refers to blood that enters arterial system without going through ventilated areas of the lung * v/q=0 * Perfusion without ventilation * SHunt fraction Qs/ Qt = _CcO__₂__- CaO__₂_ CcO₂ – CvO₂

Can a shunt be fixed by giving 100% O2?

No, shunted blood is not xposed to high concentration of O2 However, giving O2 will increase alveolar O2, but this **will not reach the blood**

What is physiological dead space?

* When an area of lung is ventilated but not perfused * Va/Qc= infinity * Ventilation without perfusion

What is shunt flow?

Perfusion without ventilation (shunted blood returning to left heart that has not been exposed to ventilated alveoli)

What is a physiological shunt?

Alveolar capillaries are perfused in an area of lung that is not ventilated (i.e. blocked aiway) * Va/Qc= 0 * Can also be anatomic * ex- blood from bronchopulmonary circulation returning to L heart * Contributes to small alveolar to systemic arterial Po2 gradient

What could cause V/Q to = infinity?

Pulmonary embolism

What can cause V/Q to =0?

Airway obstruction, shunt

What can cause V/Q \<1?

hypoxemia

Normal V/Q is?

When could A-a gradient be normal but hypoxemia present?

Low inspired O2 (high altitude) Hypoventilation Both can be aliveated by providing extra o2

When can hypoxemia be present with A-a increased?

Diffusion limitation (o2 will help) Ventilation-perfusion inequality (o2 will help) Shunt (o2 will not help)

Blood flow distribution in Zone one?

Blood flow is lowest Pressure driving blood flow: P_A(alveolar)\>Pa(arterial) \>Pv

Blood flow distribution in zone 2?

Medium blood flow Pa\> PA\> pv a= arterial A= alveolar P= pressure

Blood flow distribtuion in zone 3?

Blood flow is highest Pa\> Pv\> PA a= arteriole, v= venous A= alveolar

Ventilation/unit volume is ______ at base vs apex

increased

Describe the venitlation-perfusion relationship in the lung

* Both blood flow (Q) and ventilation (V) go down moving from bottom to top of lung * But Q (flow) goes down faster than V and Q is denominator, so V/Q goes **up** (as you go up the lung)