1. Plethysmography

2. Standard PF Plethysmograph
Spirometry Spirometry
Diffusion Capacity Diffusion Capacity
Lung Volumes Lung Volumes
MIP/MEP MIP/MEP
Thoracic Gas Volume
Airways Resistance

3. Myths Plethysmography is too difficult for the patient.
Plethysmography is too expensive
Plethysmography is too complex and useful only as a research tool.
My it will be torture for my patients 3 3

5. 5 5

6. What does it measure?
Flow (Volume)
Mouth Pressure
Box Pressure 6 6

7. How does it measure? Mouth Pressure Xducer Pneumotachometer (Flow)
Box Pressure Transducer

8. How Does It Work?
As the patient pants against the closed shutter, pressure change is measured in the box and at the mouth 8 8

9. Assumptions Mouth Pressure (Pm) is equal to alveolar pressure (Palv)
Abdominal gas does not effect the measurement 9 9

10. Pascal’s Principle How Does It Work?
In a fluid or gas filled circuit, pressure applied at any point is felt equally throughout the circuit
This assumption must be true for results to be valid P3 P2 10 10

11. Why Calculate lung volumes
A restrictive ventilatory defect is characterized by a reduction in TLC
below the 5th percentile of the predicted value
Below the lower limits of normal

12. Why Determine Lung Volumes
ERS/ATS:
The presence of a restrictive ventilatory defect may be suspected when VC is reduced.
A reduced VC by itself does not prove a restrictive ventilatory defect. 12 12

13. Why Determine Lung Volumes
ERS/ATS:
A reduced FVC is associated with a low TLC only 50% of the time or less. 13 13

14. Lung Volumes
Thoracic Gas Volume (TGV) also called FRCpleth – the volume of air in the lungs at the end of a normal exhalation
We are after Total Lung Capacity (TLC); however, TLC is not measured directly. 14 14

15. Lung Volumes TLC = TGV (FRC) + Inspiratory Capacity (IC)
TLC = Residual Volume (RV) + VC
RV = TGV - ERV 15 15

16. Lung Volumes 16 16

17. Determination of FRC Multiple breath gas dilution Nitrogen Washout
Helium Dilution
TGV via Body Plethysmography
Imaging Techniques (radiology)
Planimetry
CT/MRI

18. Determination of FRC ACCP Scientific Section Recommendation:
In patients with airway obstruction the dilution method underestimates the thoracic gas volume to the extent that depends on the severity of the obstruction. The plethysmographic method measures the total compressible gas including that of poorly ventilated areas.
Murray, Crapo, et al ,1982 18 18

19. Determination of FRC
Dilution methods measure only communicating airways and therefore can significantly underestimate true lung volume.

20. FRC by Plethysmography = 2L
FRC by Dilution = 2L
FRC by Plethysmography = 2L

21. FRC by Plethysmography = 2L
Obstructed airway
FRC by Dilution = 1 L
FRC by Plethysmography = 2L

22. Determination of TLC via Single Breath
Single breath inert gas dilution (DLco)
Helium, Neon, Methane
Alveolar Volume (VA) approximates TLC
Single breath techniques further underestimate lung volume due to reduced time for equilibration. 22 22

23. Plethysmography vs. Dilution
Decreases test time –
One N2 washout or helium dilution can take up to 7-8 minutes. If you have to repeat, this takes an additional 7-8 minutes after waiting for gas to clear lungs
Plethysmography can perform several efforts in 3 minutes 23 23

24. Clinical Indications
To distinguish between restrictive and obstructive disease patterns, particularly in the presence of a reduced VC
To diagnose restrictive disease patterns
To provide an index of gas trapping (plethysmography vs gas dilution)
Assess response to therapeutic intervention
AARC Clinical Practice Guideline 24 24

25. TGV - How Does It Work? P P`
Boyle’s Law
P1V1 = P2V2 V` V

26. TGV - How Does It Work? Solving for P1 V1 = PB • (V / P) P1V1 = P2V2
P1 = barometric Pressure*
V1= thoracic gas volume
P2 = P1 + delta P
V2 = V1 - delta V
Solving for P1
V1 = PB • (V / P) 26 26

27. Testing Sequence(1st Choice)
Measure ERV after the acquisition of the FRC measurement followed by slow IVC maneuvers that are linked
FRC reported – mean of technically acceptable FRC measurements (CV 5% = difference between highest and lowest values divided by the mean ≤ .05) linked to technically acceptable ERV and IC measurements used for calculating RV and TLC
Acceptable IC’s CV 5% +/- 3% (obstructed)

28. Testing Sequence 1ST Choice

29. Testing Sequence 2nd Choice
Perform IC immediately after the FRC measurement to TLC
This method might work better for those who have severe COPD
TLC = FRC + IC

30. Airways Resistance
(Raw)

31. Airways Resistance (Raw)
Airways Resistance can be thought of as how much work (driving pressure) the patient has to do simply to breath. 31 31

32. Airway Resistance (Raw)
Increased Raw is the primary finding in Obstructive Airways Disease
May be caused by bronchospasm, compression or consolidative filling 32 32

33. Airways Resistance (Raw)
Airways Resistance - Pressure
cmH2O/L/sec
Conductance (Gaw) – Flow
L/sec/cmH20
Gaw is the reciprocal of Raw
1/Raw 33 33

34. Airways Resistance (Raw)
Airways Resistance - Pressure
cmH2O/L/sec
sRaw (Raw relative to lung volume)
Raw x Vpant
Conductance (Gaw) – Flow
L/sec/cmH20
sGaw (Gaw relative to lung volume)
Gaw/Vpant 34 34

35. Airways Resistance (Raw)
COPD patient -
Raw
sRaw
sGaw
Compensatory Hyperinflation 35 35

36. Airway Resistance Effort independent assessment of airway caliber !
If pressure is constant which will conduct more flow?

37. Flow rate is proportional to the 4th power of a pipe’s radius.
Poiseuille’s Law
(Pdriving)(pi)(radius4)
Flow =
(8)(Length)(viscosity)
Flow rate is proportional to the 4th power of a pipe’s radius. 37 37

38. Poiseuille’s Law
You need 16 tubes to pass as much fluid as one tube twice their diameter. 38 38

39. Airway Resistance
Since resistance is related most strongly to total cross sectional area rather than length, the majority of resistance in normal lungs resides in the larger airways P1 P2
P3B
P3A
P3B2
P3A1
P3B1
P3A2

40. Airways Resistance
In summary, what proportion of the total airways resistance is in the larger airways?
What proportion of the airways resistance is in the smaller airways?
80% Larger
20% Smaller

41. Pleth Test Maneuver Door closed for ~1 min to allow for equilibration
Patient sitting up straight, nose clips
Hands supporting their cheeks
Elbows at their side 41 41

42. TGV Test Maneuver
Normal tidal breathing until stable respiratory pattern is achieved
At end expiration the shutter is closed
Patient is asked to “pant” against the closed shutter for 2 to 3 seconds.
After shutter reopens, perform an SVC 42 42

43. Thoracic Gas Volume – “Panting”
Pant Volume: ~50cc
Frequency: 0.5 – 1.0 Hz (30 to 60 bpm, although up to 90 is acceptable)
Emphasize this is NOT an MVV or MIP/MEP

44. Thoracic Gas Volume – “Panting”
Tidal Breathing
Shutter Closure 44 44

45. Mouth Pressure vs Box Pressure
How Does It Work?
Mouth Pressure vs Box Pressure
Mouth
Pressure
Box Pressure (pleth volume)

46. How Does It Work?
Mouth
Pressure
Box Pressure (pleth volume)
V / P is the relationship between mouth pressure and box pressure, and can be expressed as the tangent of the angle 46 46

47. Line of “Best Fit” 47 47

48. Importance of “pinned” SVC
Trying to measure TLC
TGV efforts can be variable
Performing an SVC with the TGV maneuver produces more repeatable TLC values

49. Importance of “pinned” SVC
TGV IC
TLC
3.00
1.50
4.50 L
2.50
2.00
3.50
1.00 49 49

50. Airway Resistance Test
Open Shutter Phase
Pant with shutter open to determine airway resistance
Closed Shutter Phase
Pant with shutter closed to measure lung volume – VPant (can be used to measure TGV)

51. Airway Resistance Test
Patient performance criteria
Small breaths (~50)
Consistent, gentle efforts efforts/sec (60 – 90 efforts/min)
Emphasize this is NOT an MVV
Provide continuous feedback on performance

52. Airways Resistance – “Quiet Breathing”
Volume: ~50cc
Frequency: 0.5 cycle/sec (30 BPM)
Glottis opens and closes with each breath, causing Raw to increase
Most Raw predicted numbers are based on panting efforts 52 52

53. Airway Resistance Test53 53

54. Slope (pressure/volume)
Airway Resistance
Slope (pressure/volume)
Raw =
Slope (flow/volume)

55. Airway Resistance In the Lung: Flow = Pressure/ Resistance or
Resistance = Pressure/ Flow
Slope of the line is
Flow / Box Pressure F L O W
BOX PRESSURE

56. Resistance
What pressure (cmH20/L/S) does it take to create a certain flow?
What pressure does it take to create a standardized flow of .5 L/S?
R=Pressure/Flow

57. Line of “Best Fit” In the Lung: Flow = Pressure/ Resistance or
Resistance = Pressure/ Flow
Zero Flow
0.5 L/sec F L O W
BOX PRESSURE

58. Airway Resistance
a) Normal, b) Increased large airway Raw, c) COPD, d) Upper airway obstruction

59. Airway Resistance
Airway Collapse Patterns may be better represented by separating Inspiratory and Expiratory Raw.

60. Airway Resistance

61. Airways Resistance and Airway Reactivity
Airways resistance measures significant changes in airway caliber during bronchodilator and bronchoprovocation trials which might not be reflected in spirometry.
Airways resistance explains patient’s “perceived” response in the absence of spirometric changes.

62. Bronchodilators with Spirometry
Masking the response of bronchodilators
Lung memory and the broncho-dilatory effect of deep inhalations
Possible closure of intra-thoracic airways during forced exhalation
PRE
POST
Blast it out!!!!

63. Airways Resistance and Airway Reactivity
From National Jewish Medical Center in Denver:
Subjects often report subjective benefit from bronchodilators without demonsting improvement in spirometry

64. Determination of Airflow Obstruction
Flows determined by spirometry inherently incorporate driving pressure and therefore:
are effort dependent
are insensitive to early obstructive changes especially in a young, motivated subject
reflect true obstruction only after significant compromise of airway radius, well beyond the development of symptoms
Can overcome obstruction with more force

65. Determination of Airflow Obstruction
Determination of Airways Resistance and Conductance:
is effort independent
can identify early obstructive changes throughout the tracheobronchial tree
will identify obstructive changes, which increase work of breathing, and cause dyspnea, that might otherwise not be identified using spirometry

66. Artificial Resistance
Airflow
&
Artificial Resistance

67. Determination of Airflow Obstruction
Spirometry
Pred
Baseline
+1.5 cm/H2O/L/s
% Change
FVC
4.88
4.64
4.58 -1
FEV1
3.84
3.31
3.19 -4
FEV1/FVC 79 72 70 -3
FEFmax
8.99
8.81
6.62
-25
FEF25-75
3.78
2.46
2.28 -7

68. Spirometry
Pred
Baseline
+1.5 cm/H2O/L/s
% Change
FVC
4.88
4.64
4.58 -1
FEV1
3.84
3.31
3.19 -4
FEV1/FVC 79 72 70 -3
FEFmax
8.99
8.81
6.62
-25
FEF25-75
3.78
2.46
2.28 -7
Airway Mechanics
Raw
1.95
3.31
4.82 46
Gaw
1.03
.30
.21
-30
sGaw
.25
.08
.05
-38

69. Spirometry
Pred
Baseline
+1.5 cm/H2O/L/s
% Change
+4.0
FVC
4.88
4.64
4.58 -1
4.59
FEV1
3.84
3.31
3.19 -4
FEV1/FVC 79 72 70 -3 69
FEFmax
8.99
8.81
6.62
-25
6.09
-31
FEF25-75
3.78
2.46
2.28 -7

70. Spirometry
Pred
Baseline
+1.5 cm/H2O/L/s
% Change
+4.0
FVC
4.88
4.64
4.58 -1
4.59
FEV1
3.84
3.31
3.19 -4
FEV1/FVC 79 72 70 -3 69
FEFmax
8.99
8.81
6.62
-25
6.09
-31
FEF25-75
3.78
2.46
2.28 -7
Airway Mechanics
Raw
1.95
3.31
4.82 46
6.66
101
Gaw
1.03
.30
.21
-30
0.15
-50
sGaw
.25
.08
.05
-38
0.04

71. Case Study

72. Young Asthmatic Age: 16
Height: 75 in Weight: 268 Sex: M
Spirometry
Predicted
Actual Pre
% Predicted
FVC
5.54
4.70 85
FEV1
4.79
3.13 65
FEV1/FVC 86 67
FEF25-75%
5.27
2.08 40
FEFmax
9.46
6.27 66

73. Young Asthmatic Age: 16
Height: 75 in Weight: 268 Sex: M
Spirometry
Predicted
Actual Pre
% Predicted
FVC
5.54
4.70 85
FEV1
4.79
3.13 65
FEV1/FVC 86 67
FEF25-75%
5.27
2.08 40
FEFmax
9.46
6.27 66
Airway Mechanics
Raw
1.51
7.17
474
Gaw
0.66
0.14 21
sGaw
.019
0.02 11

74. Young Asthmatic Age: 16
Height: 75 in Weight: 268 Sex: M
Spirometry
Predicted
Actual Pre
% Predicted
Actual Post
% Change
FVC
5.54
4.70 85
4.73 1
FEV1
4.79
3.13 65
3.40 9
FEV1/FVC 86 67 72 8
FEF25-75%
5.27
2.08 40
2.54 22
FEFmax
9.46
6.27 66
6.32

75. Spirometry
Predicted
Actual Pre
% Predicted
Actual Post
% Change
FVC
5.54
4.70 85
4.73 1
FEV1
4.79
3.13 65
3.40 9
FEV1/FVC 86 67 72 8
FEF25-75%
5.27
2.08 40
2.54 22
FEFmax
9.46
6.27 66
6.32
Airway Mechanics
Raw
1.51
7.17
474
0.96
-87
Gaw
0.66
0.14 21
1.04
643
sGaw
.019
0.02 11
0.25
1150

79. Airways Resistance and Airway Reactivity
What is a clinically significant response?
Raw and SRaw: %
SGaw : %
Current ATS/ERS Standards use 12% and 200 ml for FVC and/or FEV1 for bronchodilator response

80. Implications Without Airways Resistance:
Patient may not have been correctly diagnosed with reversible airway obstruction.
Prescription of inhaler may not have been clinically justified.

81. Airway Resistance Spirometry alone:
May not accurately determine the presence or absence of obstruction
May not adequately evaluate airway response to stimuli

82. Airways Resistance and Airway Reactivity
“We conclude that spirometry alone fails to identify reversibility in approximately 15 percent of patients, and most of these patients can be identified by additional plethysmographic measurements…”
Smith HR, Irvin CG, Cherniak RM. The Utility of Spirometry in the Diagnosis of Reversible Airway Obstruction. Chest 1992; 101:1577

83. Asthma Management
The use of airways resistance to diagnose and monitor the asthmatic can improve the patient’s quality of life and reduce the associated cost of care.

84. Plethysmography: The Benefits
Rapid, accurate functional measurement
Multiple measurements < 5 min
Quantifies Non-Ventilated Lung
TGV-FRC
Non-Ventilated lung contributes to
Hypoxemia (Resting/Exercise)
Dyspnea

85. Plethysmography: The Benefits
Enhances diagnosis and treatment of obstructive disorders
More accurate Lung Volumes compared to lung dilution methods
Differential Diagnosis
Restriction/Hyperinflation is based on TLC 85 85

86. Plethysmography: The Benefits
More sensitive in diagnosis of airways disease
Earlier detection of airways disease
More accurate evaluation of airway reactivity (bronchodilation and bronchoprovocation)
Enhanced evaluation of upper airway lesions

87. AARC Clincal Practice Guidelines
ATS/ERS Guidelines 87 87

88. Thank You Patrick G Burns Director of Marketing MGC Diagnostics 88 88