The Respiratory Cycle

Question 1

Diaphragm

Answer 1

Innervated by phrenic n.
Contraction causes flattening and moves down the diaphragm.
Increases volume of thorax when contracting, decreasing the pressure inside.

Question 2

Main muscles in inspiration

Answer 2

External intercostal ms.
Between ribs, slope downward and forward.
Raise the ribs when contracted (bucket-handle).

Question 3

Minor muscles in inspiration

Answer 3

Scalene ms. - raise the 1st and 2nd ribs.

Sternocleidomastoid m. - raise sternum.

Question 4

Events in inspiration

Answer 4

1. Contraction of inspiratory muscles increases thoracic volume, decreasing the pressure.
2. Intrapleural pressure decreases to -8 cm from -5 cm.
3. Thorax and lungs expand.
4. Alveolar pressure decreases.
5. When alveolar pressure drops below atmospheric, air flows into the lungs.

Question 5

Main muscles involved in expiration

Answer 5

Abdominal ms. - push into abdomen and displace diaphragm upward.
Internal intercostal ms. - perpendicular to external intercostal ms. Decrease the A/P diameter of the thorax.
*lungs generally want to get smaller.

Question 6

Events in expiration

Answer 6

1. Inspiratory muscles relax causing the volume of thorax to decrease and diaphragm and ribcage return to starting positions.
2. Decrease in volume (increase in pressure) causes an increase in intrapleural pressure.
3. Alveolar pressure increases due to action of ribcage.
4. Pressure gradient reached and produces an outflow of air from the lungs, causing a decrease in volume.
5. As expiration proceeds, alveolar pressure begins to return to 0 cm. Eventually all air that entered is exhaled.

Question 7

Minute ventilation

Answer 7

= V(dot) = Vt x frequency (RR)

Question 8

Anatomical dead space

Answer 8

First 16 generations of airway does not have any alveoli. Does not participate in gas exchange.
Estimated by pt’s weight in lbs.

Question 9

Minute alveolar ventilation

Answer 9

Amount of air actually getting to lungs.

Valv = Vt - Vds

Question 10

Volume change graph

Answer 10

Begins at 0, peaks at +0.5 (end of inspiration) and finish at 0 (end of expiration).

Question 11

Alveolar pressure graph

Answer 11

Begins at 0, goes to -1, goes to 0, goes to +1, finished at 0. Hits -1 and +1 at midpoint of inspiration/expiration.

Question 12

Intrapleural pressure graph

Answer 12

Begins at -5, goes to -8 (end of inspiration) and returns to -5 (end of expiration).

Question 13

Air flow graph

Answer 13

Mimics alveolar pressure graph.