I. Answers B and C are true statements, whereas A, D and E are false.
II. Answers A, B, D and E are true statements, whereas C is false.
1. Original volume of metabolic ratemeter:
VSTPD×760/273 = n×R = VATPS×(PB-Pwater)/(273+t).
VSTPD×760/273 = 50×(760-18)/(293).
VSTPD = 45.5 l STPD.
2. Safety period until the oxygen concentration was 14%:
The metabolic ratemeter contained at the start: (45.5× 0.21) = 9.56 l STPD of oxygen for use. Safety period: 9.56/(3*0.333) = 9.6 min. – Never breathe in a metabolic ratemeter with atmospheric air (21% oxygen)!
1. For the small alveolus the transmural pressure must be:
DP = 2T/r = (2 × 0.07)/0.00004 = 3500 Pa.
With the double radius the transmural pressure necessary to avoid collapse is only: 3500/2 = 1750 Pa.
2. Small alveoli must empty into larger alveoli and then collapse because they all communicate. The distending pressure is essentially the same in the 300 million basically spherical alveoli of different size. This implies that the alveolar wall tension must change commensurate with the change in alveolar radius, otherwise the small alveoli will collapse.
3. Yes, normally we produce surfactant from the type 2 cells of the alveoli. Surfactant can change the alveolar wall tension (the part that is due to surface tension). Let us assume the same surfactant density in the liquid film covering all alveoli. During expiration, surfactant molecules are packed tightly together, so that the surfactant separates the water molecules and reduces the total alveolar wall tension. When the radius is large (or during inspiration), surfactant is scattered, and thus the attractive forces between water molecules will increase (increasing surface tension).
4. 0.5/3 = 0.167 l BTPS per cm of water at FRC. The ratio to FRC is: 0.167/2.5 = 0.067. The normal value is 2 ml per Pascal or 0.2 L BTPS per cm of water at FRC.
5. The pressure applied for sufficient effect must be at least 1 l divided by the total compliance of this person. 1/Ctotal = 1/Clung + 1/Cchest wall = 1/0.167 + 1/0.15 = 12.65 cm of water per l BTPS.