Gas Laws

Question 1

Charles’ Law

Answer 1

Volume of gas varies directly with the absolute temperature @ constant P

=> volume of a fixed mass of gas @ constant P increases as temp increases

Question 2

What is the ideal gas law

Answer 2

PV = nRT

P₁V₁/T₁ = P₂V₂/T₂

Question 3

What is P_atm and P_alv before inspiration

Answer 3

0

Question 4

What is Pip before inspiration

Answer 4

• 4 mmHg

Question 5

What is the functional residual capacity

Answer 5

Volume of air left in lungs after passive expiration

Question 6

DURING INSPIRATION

1. Patm
2. Pip
3. Ptp (Palv - Pip)

Answer 6

1. 0
2. Increasing as thorax expands
3. increases above opposing inward lung recoil force causing expansion of lungs

Question 7

What happens to Palv @ mid-inspiration

Answer 7

Becomes -ve - reaches -1 mmHg

Question 8

What is tidal volume

Answer 8

Amount of air that flows into lungs during quiet breathing - 500 ml

Question 9

END OF INSPIRATION

1. Patm
2. Pip
3. Ptp
4. Palv

Answer 9

1. 0
2. @ most -ve (-7 mmHg) due to max thorax volume
3. = to opposing inward lung recoil force
4. equilibrate with Patm

no air flows in or out of lungs

Question 10

DURING EXPIRATION

1. Patm
2. Pip
3. Ptp
4. Palv

Answer 10

1. 0
2. Pip increases as chest wall recoils
3. decreases below inward lung recoil force => decrease in lung volume
4. Rises above Patm

Question 11

Values for

1. Palv
2. Pip

When air flows out of the lungs

Answer 11

1. Palv = 0
2. Pip = -4mmHg

Question 12

What is minute ventilation

Answer 12

Total ventilation per min

Tidal volume x resp rate (per min)

6000ml/min = 500ml x 12

Question 13

What is alveolar ventilation

Answer 13

Portion of V_E that reaches the alveoli

Remainder ventilates the conducting airways => not available for gas exchange

Question 14

What is anatomic dead space

Answer 14

1 ml for every pound of BW

Question 15

What is physiological dead space

Answer 15

Anatomic and any alveoli not involved in gas exchange

Question 16

Alveolar ventilation (V_A)

Answer 16

Total volume of fresh air entering the alveoli/min

=> portion of VE available for gas exchange

V_A = V_T - V_D x f

= (500 - 150) x 12

= 4200 ml

V_A is more important in effectiveness of gas exchange

Question 17

What influence do breathing patterns have

Answer 17

Have a marked influence on V_A and thus effectiveness of gas exchange

Question 18

What is Dalton’s Law of partial pressures

Answer 18

Atm P = 760 mmHg

Each gas contributes to total P

Individual gas’ contribution is proportional to number of molecules

* In a mixture of gases, each gas exerts same pressure as if it filled the container alone

Question 19

What does the equilibrium of gases imply

Answer 19

Rate of back diffusion = rate of diffusion of plasma => PO₂ plasma = PO₂ room air

Question 20

Henry’s Law

Answer 20

When gas under pressure comes in contact with liquid, gas dissolves in liquid until equilibrium is reached

@ a given temp, amount of gas in solution is proportional to partial pressure of that gas

Question 21

What is the magnitude of water vapour P proportional to

Answer 21

Temperature

@ body temp = 47 mmHg

Question 22

Name gases in blood in terms of DECREASING solubility

Answer 22

1. CO2
2. O2
3. N2

Question 23

PO2

1. Dry air
2. Alveolar gas
3. Arterial blood
4. Mixed venous blood

Answer 23

1. 159
2. 104
3. 100
4. 40

Question 24

PCO2

1. Dry air
2. Alveolar gas
3. Arterial blood
4. Mixed venous blood

Answer 24

1. 0.03
2. 40
3. 40
4. 46

Question 25

PH2O - alveolar gas

Answer 25

47

Question 26

P total

1. Dry air
2. Alveolar gas

Answer 26

1. 760
2. 760