alveolar ventillation, lung volumes and capacities, measurement of lung volumes and capacities

1. RESPIRATORY PHYSIOLOGY
MECHANICS OF BREATHING
DR KIRAN KUMAR C
MBBS.,MD.,FAGE.,C DIAB
ASSISTANT PROFESSOR

3. MECHANICS OF BREATHING
• Air tends to move from a region of higher pressure to a region of lower
pressure—that is, down a pressure gradient
• Air flows into and out of the lungs during breathing
• By reversing pressure gradients between the alveoli and the atmosphere by cyclic
respiratory muscle activity.

4. PRESSURE IMPORTANT IN RESPIRATION
• THREE PRESSURE IMPORTANT FOR RESPIRATION
1.1 Atmospheric pressure(Barometric pressure)
1.2 Intra Alveolar pressure
1.3 Intra Pleural pressure

6. Applied aspect
• Pneumothorax

7. Muscles of respiration
• Muscles of Inspiration
Primary muscles of Inspiration
- Diaphargm
- External intercostal
Accessory muscles of Inspiration
- Strernocleidomastoid
- Scelene

8. • Muscles of Expiration
- Abdominal muscles
1. Rectus abdominus
2. Transverse abdominus’
3. Internal and external oblique
- Internal intercosrtal

10. Pump handle/Bucket handle movement

14. INSPIRATION

16. Respiratory centre initiates stimuli for respiration
Impulses carried via nerve to the respiratory muscles
The diaphragm and other muscles contract
Chest wall expands increases the volume of the thorax

17. Intrapleural pressure becomes more negative
Alveolar pressure decreases below atmospheric pressure
The alveoli inflate as air flow into them until the alveolar
pressure reaches atmospheric pressure

18. EXPIRATION

19. Respiratory centre stops stimuli for respiration
No Impulses carried to the respiratory muscles
The diaphragm and other muscles relax
Chest wall contracts decreases the volume of the thorax

20. Intrapleural pressure becomes more positive
Alveolar pressure increases above atmospheric pressure
The alveoli deflate as air flow out until the alveolar pressure
reaches atmospheric pressure

21. LUNG VOLUME & CAPACITIES

26. Lung volumes and capacities

27. Lung volumes Lung Capacities
• Tidal volume(TV)
• Inspiratory Reserve volume(IRV)
• Expiratory Reserve volume(ERV)
• Residual Volume(RV)
• Functional Residual Capacity(FRC)
• Inspiratory Capacity(IC)
• Expiratory Capacity(EC)
• Total Lung Capacity(TLC)

28. Lung Volumes
1. Tidal volume(TV)
2. Inspiratory Reserve volume(IRV)
3. Expiratory Reserve volume(ERV)
4. Residual Volume(RV)

29. Lung Volumes
• Tidal Volume: is the volume of air entering or leaving the nose or mouth
per breath.
• It is determined by the activity of the respiratory control centres in the
brain as they affect the respiratory muscles and by the mechanics of the
lung and the chest wall.
• During normal, quiet breathing (eupnea) the TV of a 70-kg adult is
about 500 mL per breath, but this volume can increase dramatically,
eg; during exercise

30. • THE INSPIRATORY RESERVE VOLUME
• Is the volume of gas that is inhaled into the lungs during a maximal
forced inspiration starting at the end of a normal tidal inspiration.
• It is determined by the strength of contraction of the inspiratory
muscles, the inward elastic recoil of the lung and the chest wall,
• The IRV of a normal 70-kg adult is about 2.5 L.

31. • THE EXPIRATORY RESERVE VOLUME
• The expiratory reserve volume (ERV) is the volume of gas that is
expelled from the lungs during a maximal forced expiration that starts
at the end of a normal tidal expiration.
• The ERV is about 1.5 L in a healthy 70-kg adult.

32. • THE RESIDUAL VOLUME
• The residual volume (RV) is the volume of gas left in the lungs after a
maximal forced expiration.
• The RV of a healthy 70-kg adult is about 1.5 L,
• The RV is important to a healthy person because it prevents the lungs
from collapsing at very low lung volumes.
• Such collapsed alveoli would require extremely great inspiratory
efforts to re inflate.

34. Lung Capacities
• Functional Residual Capacity(FRC)
• Inspiratory Capacity(IC)
• Expiratory Capacity(EC)
• Total Lung Capacity(TLC)

35. • THE FUNCTIONAL RESIDUAL CAPACITY
• The functional residual capacity (FRC) is the volume of gas remaining
in the lungs at the end of a normal tidal expiration
• Normal value: about 3 L in a healthy 70-kg adult.

36. • THE INSPIRATORY CAPACITY
• The inspiratory capacity (IC) is the volume of air that is inhaled into
the lungs during a maximal inspiratory effort that begins at the end of
a normal tidal expiration.
• The IC of a normal 70-kg adult is about 3 L.

37. • THE VITAL CAPACITY
• The vital capacity (VC), is the volume of air expelled from the lungs
during a maximal forced expiration starting after a maximal forced
inspiration.
• About 4.5 L in a healthy 70-kg adult.

38. • THE TOTAL LUNG CAPACITY
• The total lung capacity (TLC) is the volume of air in the lungs after a
maximal inspiratory effort.
• About 6 L in a healthy 70-kg adult.

40. Measurement of lung volumes and capacities
• Lungs volumes
- Spirometer

41. • FRC, RV and TLC cannot be measured by spirometer
• Nitrogen washout technique
• Helium dilution technique
• Body plethysmography

43. • We begin with a spirometer containing air with 10% He—this
is the initial helium concentration, [He]initial = 10%
• The initial spirometer volume, Vs(initial), including all air up to
the valve at the subject’s mouth, is 2 L.
• The amount of He in the spirometer system at the outset of
our experiment is thus
• [He]initial × Vs(initial), or (10%) × (2 L) = 0.2 L.

44. • We now open the valve at the mouth and allow the subject to breathe
spirometer air until the He distributes evenly throughout the
spirometer and airways.
• After equilibration, the final He concentration ([He]final) is the same in
the airways as it is in the spirometer.
• The volume of the “system”—the spirometer volume (VS) plus lung
volume (VL)—is fixed from the instant that we open the valve between
the spirometer and the mouth.

45. • When the subject inhales, VL increases and VS decreases by equal
amounts When the subject exhales, VL decreases and VS increases,
• (VL + VS) remains unchanged.
• Because the system does not lose He,
• The total He content after equilibration must be the same as it was at
the outset.
• In our example, we assume that [He]final is 5%.
• If the spirometer and lung volumes at the end of the experiment are
the same as those at the beginning

47. • VL corresponds to the lung volume at the instant we open the valve
and allow He to begin equilibrating.
• If we wish to measure FRC, we open the valve just after the
completion of a quiet expiration.
• If we open the valve after a maximal expiration, then the computed
VL is RV.

48. Nitrogen Washout Technique

51. • What particular lung volume or capacity does VL represent?
• The computed VL is the lung volume at the instant the
subject begins to inhale the 100% O2.
• Therefore, if the subject had just finished a quiet expiration
before beginning to inhale the O2, VL would be FRC; if the
subject had just finished a maximal expiratory effort, VL
would represent RV.

52. THE PLETHYSMOGRAPH, TOGETHER WITH
BOYLE’S LAW, IS A TOOL FOR
ESTIMATION OF RESIDUAL VOLUME