Respiratory topic

1. Respiratory Physiology &
Pulmonary Function Tests

2. Mechanics of respiration
 Diaphragm
the principal pulmonary muscle—base of the thoracic cavity to descend 1.5–7 cm and
its contents (the lungs) to expand.
Diaphragmatic movement normally accounts for 75% of the change in chest volume.
 external intercostal muscles
 sternocleidomastoid,
 scalene,
 pectoralis muscles
Exhalation passive.
 may be facilitated by the abdominal muscles (rectus abdominis,
external and internal oblique, and transversus) and perhaps the
internal intercostal muscles

4. Controls of Respiration
Medullary Rhythmicity Area
Medullary Inspiratory Neurons
Main control of breathing
Pons neurons influence inspiration
Pneumotaxic area limiting inspiration
Apneustic area prolonging inspiration.
Lung stretch receptors limit inspiration from being too deep
Medullary Expiratory Neurons
Only active with exercise and forced expiration

5. Controls of rate and depth of respiration
Arterial PO2
When PO2 is VERY low, ventilation increases
Arterial PCO2
The most important regulator of ventilation, small
increases in PCO2, greatly increases ventilation
Arterial pH
As hydrogen ions increase, alveolar ventilation increases,
but hydrogen ions cannot diffuse into CSF as better as CO2

6. Nerve supply
 C3–C5 nerve roots. Unilateral phrenic nerve block or palsy only modestly
reduces pulmonary function (about 25%) in normal subjects.
 Accessory muscles may maintain ventilation in some people with bilateral
phrenic nerve palsies
 Cervical cord injuries above C5 are incompatible with spontaneous
ventilation because both phrenic and intercostal nerves are affected.
 Both sympathetic and parasympathetic autonomic innervation of bronchial
smooth muscle and secretory glands is present.
Vagal activity mediates bronchoconstriction and increases bronchial secretions
via muscarinic receptors.
Sympathetic activity (T1–T4) mediates bronchodilation and also decreases
secretions via β 2 -receptors.

7. Intra thoracic
pressures

8. Intra thoracic
pressures

9. • At end-expiration,
• intrapleural pressure –5 cm H 2 O,
• alveolar pressure is 0 (no flow),
• transpulmonary pressure is +5 cm H2O.
• Diaphragmatic and intercostal muscle activation
during inspiration expands the chest and decreases
intrapleural pressure from –5 cm H2O to –8 or –9 cm
H2O.
• alveolar pressure also decreases (between –3 and –4
cm H 2 O), and an alveolar–upper airway gradient is
established; gas flows from the upper airway into
alveoli.
• At endinspiration (when gas inflow has ceased),
alveolar pressure returns to zero, but intrapleural
pressure remains decreased; the new transpulmonary
pressure (5 cm H 2 O) sustains lung expansion.

10.  During expiration, diaphragmatic relaxation returns
intrapleural pressure to –5 cm H 2 O.
 Now the transpulmonary pressure does not support the new
lung volume, and the elastic recoil of the lung causes reversal
of the previous alveolar–upper airway gradient;
 gas flows out of alveoli, and original lung volume is restored

11. Lung Mechanics; elastance
 Chest has a tendency to expand outward,
 Lungs have a tendency to collapse
When the chest is exposed to atmospheric pressure(open
pneumothorax), it usually expands about 1 L in adults.
In contrast, when the lung is exposed to atmospheric pressure, it
collapses completely and all the gas within it is expelled.
 The elastic recoil of the lungs is due to their high content of elastin
fibers, and, even more important, the surface tension forces acting at
the alveoli.

12. Compliance
 The change in volume per unit change in pressure
 Lung compliance(Cl ) is defined as
Cl = Change in lung volume
Change in transpulmonary pressure
 Cl is normally 150–200 mL/cm H2O. A variety of factors,
including
 lung volume,
 pulmonary blood volume
 extravascular lung water
 pathological processes (eg, inflammation and fibrosis) affect Cl

13.  Chest wall compliance (Cw) = Change in chest volume
Change in transthoracic pressure
 where transthoracic pressure equals atmospheric pressure minus
intrapleural pressure.
 Normal chest wall compliance is 200 mL/ cm H2O.
 In the supine position, chest wall compliance (Cw) is reduced because
of the weight of the abdominal contents against the diaphragm.
 Total compliance (lung and chest wall together) is 100 mL/cm H2O
and is expressed by the following equation:
1 = 1 + 1
Ctotal Cw Cl

14. Lung volumes

15. Pulmonary Function Testing
Clinical Significances:
Lung function tests are valuable because they give some measure of
 Lung compliance or elasticity
 Airway resistance
 Respiratory muscle strength
These three factors determine how much air a person can move into
lungs per unit of time and this is what the pulmonary function
tests measure.

16. indications
Used for the following:
Medical diagnosis
Surgery related evaluation
Disability evaluation
Public Health/Research
Studying the effects of exercise on the lungs

17. Contraindications
Recent abdominal, thoracic, or eye surgery
Hemodynamic instability
Symptoms of acute severe illness
Chest pain, nausea, vomiting, high fever, dyspnea
Recent hemoptysis
Pneumothorax
Recent history of abdominal, thoracic, or cerebral
aneurysm

18. Classification of Lung Defects
OBSTRUCTIVE
 Obstruction to Expiratory flow
 Decrease in expiratory flow rate throughout
expiration
 Anatomic site can be identified
 Diseases:
 Cystic fibrosis
 Bronchitis
 Asthma
 Bronchiectasis
 Emphysema
RESTRICTIVE
 Lung volumes are reduced
 Main feature is reduced lung volume
(mainly TLC and RV).
 Diseases:
 Neuromuscular
 Cardiovascular
 Pulmonary (interstitial fibrosis)
 Trauma/chest wall dysfunction
 Obesity
Pulmonary function testing primarily detects two abnormal
patterns:

19. Spirometry
 Is the first lung function test done. It measures how much and how
quickly you can move air out of your lungs.
 For this test, you breath into a mouthpiece attached to a recording
device (spirometer).

20. Spirometry
Volumes
 Tidal Volume
 Residual Volume
 Inspiratory Reserve Volume
 Expiratory Reserve Volume
Capacities
 Vital Capacity
 Inspiratory Capacity
Cannot measure
 Residual volume
 TLC
 FRC

21. Spirometer
 There are tow types of spirometer:
1- Mechanical devices:
(Incentive spirometer)
2- Electronic devices

22. Flow Measurements
 FEV1
 FEV3
 FEF200-1200 FEF 25-75%
 PEFR

23. FEV1
 Maximal volume exhaled during the first second of expiration
 Best indicator of obstructive lung disease
 Flow characteristics of the larger airways
 Best expressed as a percentage of the FVC (FEV1/FVC)
 Should be able to exhale 70% of the vital capacity in the first second
 Decreased in obstructive disorders

24. FEV3
 Evaluates flow 3 seconds into expiration
 Indicates flow in the smaller airways

25. Forced Expiratory Flow
FEF 25-75%
 Examines the middle 50% of
the exhaled curve
 Reflects degree of airway
patency/condition of the
medium to small airways
 Early indicator of
obstructive dysfunction
 Normal value is 4-5 L/sec

26. Forced Expiratory Flow
FEF 200-1200
 Average flow after the first
200ml is exhaled
 Good indicator of the
integrity of large airway
funtioning
 Decreased in obstructive
disorders
 Normal value is 6-7L/se

27. Peak expiratory flow (PEF):
 Is the maximum or peak rate (or velocity), in liters per minute, with
which air is expelled with maximum force after a deep inspiration.
 It can be measured by wright peak flow meter. The maximum
expiratory flow is much greater when the lungs are filled with a
large volume of air than when they are almost empty

28. Peak Expiratory Flow Rate
 Maximum flow rate achieved during an FVC
 Used in asthmatics to identify the severity of airway obstruction
and guide therapy
 Dependent on patient effort
 Normal value is 10L/sec (600L/min), decreases with age and
obstruction

29. Vital Capacity
Forced (FVC)
Requires proper coaching
Three distinct phases
Decreased in both obstructive
and restrictive diseases
Slow (SVC)
Helps avoid air trapping

30. Total Lung Capacity
Increased with obstructive disease
Decreased with restrictive disorders
Sum of the vital capacity and residual volume
Obtain RV by:
Body plethysmography
Nitrogen washout
Helium dilution

31. Body Plethysmography
Uses the “body box”
Boyles Law
Unknown lung gas vol = Gas pressure of the box
Known box gas vol Gas pressure of the lungs

32. In body plethysmography, the patient sits inside
an airtight box, inhales or exhales to a
particular volume (usually FRC),
then a shutter drops across their breathing
valve. The subject makes respiratory efforts
against the closed shutter causing their
chest volume to expand and decompressing
the air in their lungs.
The increase in their chest volume slightly
reduces the box volume and thus increases
the pressure in the box.
This method of measuring FRC actually
measures all the conducting pathways
including abdominal gas; the actual
measurement made is VTG (Volume of
Thoracic gas).

33. Nitrogen Washout
 Open circuit method
 Patient breathes
100% oxygen while
the nitrogen washed
out of the lungs is
measured
 Assumes 79% of lung volume
is nitrogen
 Several “problems” with this
test

34. Helium Dilution
 Closed system
 Known volume and
concentration of He added and
it will be diluted in proportion to
the size of the lung volume

35. Flow Volume Loops
 Identify inspiratory and
expiratory components –
opposite from ventilator
waveforms!
 Reveals a pattern typical for
certain diseases

36. Graphic Representation of Values

37. Flow Volume Loops
Restrictive Obstructive

38. Figure 08-07. Flow volume loop. These flow volume loops are typical
patterns seen with (A) normal, (B) restrictive lung diseases, (C) upper airway
obstruction, and (D) severe chronic obstructive lung disease

39. Diffusion Capacity (DL)
 Represents the gas
exchange capabilities of
the lungs
 Measures the ability of gas
to diffuse across the
alveolar-capillary
membrane using carbon
monoxide: DLCO

40. DLCO
 Diseases that reduce surface area –
DL
 emphysema
 Interstitial altering of the membrane
integrity - DL
 Pulmonary fibrosis, Asbestosis,
Sarcoidosis

41. Other Studies
 Airway Resistance
 Quantifying allows understanding of
the severity of the disease
 Measured using plethysomograph
 Compliance Studies
 Identifies the relative stiffness of the
lung
 Esophageal balloon catheter
 Nitrogen Washout
 Determines if there is gross
maldistribution of ventilation
 Closing Volume
 Used for diagnosis of small airway
obstruction
 Respiratory Quotient
 Determines the amount of carbon
dioxide produced and oxygen
consumed

42. Exercise Testing
 6 minute walk test
 Anaerobic threshold
 Exercise challenge
 Ventilatory Capacity

43. Evaluation/Interpretation of PFT’s
INTERPRETATION CRITERIA
TEST NORMAL MILD MODERATE SEVERE
FVC>80% 61-80% 50-60% <50% Restriction
FEV1 >80% 61-80% 50-60% <50% Obstruction
PEFR >80% 61-80% 50-60% <50%
FEF25-75 >80% 61-80% 50-60% <50% Small Airway
Disease
FEV1/FVC 70-75% 60-69% 50-59% <50% Obstruction
POSITIVE RESPONSE TO BRONCHODILATOR
1. FVC: increase greater than 10%
2. FEV1: increase of 200cc or 15% over baseline
3. FEF25-75: 20% increase
4. 2 out of 3 should improve to indicate a positive response

44. Evaluation of Results
Evaluation of the Vital Capacity
 can be reduced in obstructive and
restrictive disease
 if VC is reduced, evaluate the TLC
 if the TLC is increased = obstruction
 if the TLC is decreased = restriction
 if VC is normal, evaluate the TLC
 if the FVC is greater than 90% of the SVC
= normal
 if the FVC is less than 90% of the SVC =
obstruction
 Evaluation of the FEV1/FVC
 if the FEV1/FVC is normal then
the lungs are normal or
restrictive
 if the FEV1/FVC is reduced =
obstruction

45. Evaluation of Results
 Evaluation of FEF 25-75%
 if normal then normal lungs
or possible restriction
 if reduced = peripheral
obstruction
 Evaluation of the Total Lung
Capacity: % pred.
 increased =hyperinflation present
evaluate the FEV1
Normal = normal lungs
Decreased = obstruction
 Decreased
evaluate the FEV1
Normal = restrictive
Decreased = obstructive and restrictive

46. Questions/ Comments