Pulmonary Mechanics Flashcards
1
Q
Lung is Negative Pressure Pump
A
- the lung is like a balloon can be inflated artifically by raising the pressure inside or like normal breathing by reducing the pressure on the outside
- during normal quiet breathing the contraction of the diaphragm exerts an expansive force on the intrapleural space- the space outside of the lung but within the chest wall
- the resultant pressure in the intrapleural space decreases, the drop in intrapleural pressure causes the lung to inflate
- when the diaphragm stops contracting, and starts to relax, then the passive elastic recoil of the lung results in deflation
- when resp muscles relaxed the pressure in intrapleural space is less than atmospheric pressure by about 5 cm H2O
- with wound the intrapleural pressure rises up to atmosperic pressure and the lung collapses. Mainttenance of lung inflation depends critically on the maintenance of neg pressure in the space between lung and chest wall. Atmospheric pressure in intrapleural space is pneumothorax
2
Q
Eupnea
A
- quiet breathing (with a ventilation of about 7/5 L/min), the diaphragm may be the only active inspiratory muscle, enlarging the thoracic cavity by moving downward by as much as 10 cm
- expiration is due to the passive recoil of the lung and the chest wall without the participation of expiratory muscles
- thus during eupneic breathing inspiration is active while expiration is passive
3
Q
Hyperpnea
A
- active breathing during exercise, inspiration is aided by the contraction of the external intercostals, which lift the ribs upwards and outward to expand the chest cavity to accommodate the larger volumes of air
- during strenuous exercise the accessory muscles of the chest and neck are used to reduce the resistance to airflow
- when ventilation exceeds about 40 L/min, expiration is aided by contraction of the internal intercostals which depress the ribs downward and inward
- four major abdominal muscles contract to increase abdominal pressure to force the diaphragm upward, thus increasing the positive alveolar pressure which expels air out of the lung. Thus during hyperpneic breathing, both inspiration and expiration are active
4
Q
Muscles of Inspiration
A
- Diaphragm: primary muscle of inspiration
- Accessory: Sternomastoid- lifts sternum scalene- lifts upper ribs, others- facial, neck, head
- External Intercostals: lifts ribs up and forward; increases anterior-posterior dimension of chest cavity; adds tone to chest wall
5
Q
Muscles of Expiration
A
- Internal Intercostals- lower ribs
- abdominal: depresses lower ribs; compresses abdominal cavity and pushes up diaphragm
- rectus abdominus, external oblique, internal oblique, transversus abdominus
6
Q
Tachypnea
A
-more rapid than normal
7
Q
Hypoventilation
A
- muscular dystrophy, respiratory muscle paralysis
- leads to alveolar hypoxia and hypercapnea respiratory acidemia
8
Q
Hyperventilation
A
- anxiety, panic attack
- breathing faster than required for oxygenation leads to alveolar hypocapnea respiratory alkalosis
9
Q
Alveolar Pressure
A
- Palv, varies during the breathing cycle
- air movement requires a pressure gradient
- during inspiration Palv < Patm
- during expiration Palv > Patm
- if the breath is held at any lung volume with no air moving, and with the mouth and glottis open, then Palv= Patm
10
Q
Intrapleural Pressure
A
- Ppl is the pressure in the space outside the lung but within the chest wall
- the intrapleural space is fluid-filled and is only about 10 microns thick, holding a few ml in volume
- the lung is in close apposition to the inner chest wall; the movements of the two elastic vessels are lubricated by fluid in the intrapleural space
- contraction of the diaphragm exerts an expansive force on the intrapleural space, thus decreasing its pressure, making it more negative, and acting to inflate the lung
- can measure esophageal balloon provides a good estimate of changes in Ppl because the esophagus is a thin walled tube which has little tone
11
Q
External pressure
A
- usually atmospheric pressure, or Patm, which is constant during the respiratory cycle
- f weight is placed on the chest, then the external pressure on the chest wall is greater than Patm and is referred to as body surface pressure
12
Q
Transmural Pressures
A
-Ptm
-across an elastic vessel is defined as internal minus external pressure
Ptm= Pinternal - Pexternal
13
Q
Lung pressure
A
- Pl is the transmural pressure across the lung and is the difference between alveolar and intrapleural pressures
- sets the degree of lung inflation and must always be positive to maintain inflation
- Pl = Palv- Ppl
14
Q
Chest wall pressure
A
- Pc
- the transmural pressure across the chest wall, and is the difference in pressure between the intrapleural space and atmospheric or body surface pressure
- sets degree of inflation of chest wall
- negative at rest
- Pc= Ppl- Palv
15
Q
Total transmural pressure
A
- also called relaxation pressure, is the total transmural pressure across the lung and the chest wall
- the total pressure is the difference between alveolar and atmospheric pressure and is equal to the sum of the lung presure and the chest wall pressure
- Pt= Palv- Patm = Pc + PL
- at rest the positive outward lung pressure is balanced by the inward passive elastic recoil pressure of the lung
- the negative inward chest wall pressure is balanced by the passive outward elastic recoil pressure of the chest wall