Week 1: Physiology part 2

Question 1

Describe differences in Pa and PA throughout the lung

Answer 1

• at apices, PA is greater than Pa. Alveoli are distended at the apices and squish the capillaries
• at base of lung Pa>PA

Question 2

When is pulmonary vascular resistance lowest?

Answer 2

-at FRC: end of expiration, where alveoli are most collapased

Question 3

When is airway resistance the lowest?

Answer 3

-at TLC, alveoli are most distended at end of inspiration

Question 4

Pulsus paradoxus

Answer 4

1. physiological
   - during inspiration, intrathoracic pressure becomes more negative, leading to greater venous return to the heart. Blood pulls in pulmonary vasculature (also due to negative pressure). Decreased LA filling leads to decreased SV and CO.
   - causes drop in bp and increase in hr
2. PPV
   - inspiration leads to decreased venous return to the right heart and decreased CO
3. pathology: cardiac tamponade: decreases venous return to heart

Question 5

Bainbridge Reflex aka atrial reflex

Answer 5

• increase in heart rate due to an increase in central venous pressure
• increased blood volume is detected by stretch receptors in atria and veno-atrial junctions
• is dominant when blood volume is increased, whereas baroreceptor reflex is dominant when blood volume is decreased.

Question 6

Pneumothorax

Answer 6

• intrapleural pressure increases to equal atmospheric pressure
• chest wall expands
• (when air can’t go out, have increase intrapleural pressure)

Question 7

Components of lung recoil

Answer 7

1. Lung tissue: collagen and elastim fibers
2. surface tension forces in the fluid lining the alveoli
   - Laplace’s law: as radius of sphere decreases, pressure inside increases. Smaller alveoli collapse since higher pressure flows into lower pressure larger alveoli

Question 8

3 main functions of surfactant

Answer 8

1. lowers surface tension in alveoli: increases compliance
2. promotes stability among alveoli of different sizes by decreasing tendency of small alveoli to collapse
3. reduces capillary filtration and thus reduces tendency to develop pulmonary edema.

Question 9

Infant RDS and Atelectasis

Answer 9

• premature infants may have a deficiency of surfactant

- infants with respiratory distress syndrome have a very high surface tension