6. lung anatomy and spirometers(2)
DESCRIPTION
spirometerTRANSCRIPT
BG 3105 Biomedical Instrumentation
Lung Anatomy and Spirometers
Asst Prof Manojit Pramanik School of Chemical and Biomedical Engineering
Nanyang Technological University
[email protected] Office: N1.3-B2-11
Respiratory System and Measurements
1 Introduction 2 Lung volume 3 Respiratory system measurements 3.1 Flow measurement 3.2 Spirometer 3.3 Nitrogen-washout estimate of lung volume
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1. Introduction
β’ Respiration (= breathing) is the interchange of gases.
β’ The purpose is to deliver oxygen to the body and to take away carbon dioxide.
β’ The main organ of the respiratory system are the lungs.
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β’ Lungs consists of 2 spongy organ.
β’ It contains 300 million alveoli (air sac).
β’ Each sac with 0.2 mm in diameter.
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Lungs
Trachea
β’ The trachea filters the air we breathe and branches into the bronchi.
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Bronchi
β’ The bronchi are two air tubes that branch of the trachea and carry air directly into the lungs.
Diaphragm
β’ The diaphragm is the main muscle involved in breathing.
β’ It is a dome-shaped muscle at the bottom of the lungs. β’ Breathing starts from diaphragm.
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β’ When you breathe in, the diaphragm contracts. When it contracts it flattens out and pulls downward. This movement enlarges the space and pulls air into the lungs.
β’ When you breathe out, the diaphragm expands reducing the amount of space for the lungs and forcing air out.
β’ The red blood cells pick up the oxygen in the lungs (alveoli) and carry the oxygen to all the body.
β’ The red blood cells transport the carbon dioxide back to the lungs (alveoli).
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Alveoli
β’ Capillaries are small blood vessel with thin walls, and are wrapped around these alveoli.
β’ The walls are so thin and close to each other that the air easily seeps through.
β’ Oxygen seeps through into the bloodstream and carbon dioxide, in the bloodstream, seeps through into the alveoli.
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Capillaries
The effect of blood PCO2 and PO2 on the respiration rate
β’ An increase in PCO2 increases the breathing rate.
β’ An increase in PO2 slows down the breathing rate.
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Internal respiration
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β’ Internal respiration is the exchange of gases between the bloodstream and nearby cells.
External respiration
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β’ External respiration is the exchange of gases between the lungs and bloodstream.
External respiration
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β’ External respiration includes: Inspiration β intake of air
79% nitrogen (N) 20.96% oxygen (O2) 0.04% carbon dioxide (CO2)
Expiration β exhaust of waste gases
79% nitrogen (N) 17% oxygen (O2) 4% carbon dioxide (CO2)
2. Lung volume
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TV: Tidal volume IRV: Inspiratory reserve volume ERV: Expiratory reserve volume VC: Vital capacity RV: Residual volume FRC: Functional residual capacity TLC: Total lung capacity
Lung Volume
β’ Dead Space (150 ml) β the volume of air that is not available for gas exchange with the blood. Air in air way Air in trachea Air in bronchi
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Lung Volume
β’ Tidal volume (TV) (500 ml) β is the volume of gas inspired or expired during each normal respiratory cycle. At rest condition For normal adults
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Lung Volume
β’ Residual volume (RV) (1200 ml) β is the amount of gas remaining in the lungs at the end of maximal expiration.
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Lung Volume
β’ Functional residual capacity (FRC) (2400 ml) β is the amount of gas remaining in the lungs at the resting expiration level.
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Lung Volume
β’ Vital capacity (VC) (4800 ml) β is the maximum amount of gas expelled from the lungs by forceful effort from maximal inspiration.
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Lung Volume
β’ Total lung capacity (TLC) (6000 ml) β is the amount of gas contained in the lungs at the end of maximal inspiration.
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Lung Volume β food for thoughts
Can this guy breathe comfortably?
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3. Respiratory system and measurements
3.1 Air flow measurement A strain-gauge wire mesh is used to measure air
flow
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Air flow measurement
β’ The strain-gauge is a component of a Wheatstone bridge
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A circuit for measuring airflow rate and volume
Air flow measurement
β’ Here the change in resistance βπΉ is proportional to the airflow rate π = πβπΉ, where π is pneumotach coefficient.
β’ Given Wheatstone bridge voltage π½π©π©, we have
β’ The circuit may be designed so that πΉ β« βπΉ, then we have
β’ π½π is proportional to flow π. Biomedical Instrumentation - wk 6 23
ππ΄π΄ =π
π + βπ + π βπ 2π
ππ΄π΄ =βπ βπ
4π 2 + 2π βπ ππ΄π΄
ππ΄π΄ =βπ βπ
4π 2 + 2π βπ ππ΄π΄ β
βπ βπ 4π 2
ππ΄π΄ =ββπ 4π
ππ΄π΄
ππΉ = π΄π·ππ΄π΄ = βπ΄π·βπ 4π
ππ΄π΄ =βπ΄π·ππ΄π΄
4ππ πΉ
3.2 Spirometer
β’ Spirometer is used to measure lung volume under conditions Constant temperature Constant pressure
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Spirometer
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Mouthpiece & Spirometer
LCD Display graph and data
Spirometer
β’ The spirometer consists of An upright water filled cylinder An inverted floating drum An mechanical linkage
β’ How to operate?
The volume of gases inside spirometer will change as the patient breathes through the mouthpiece
This volume change is proportional to lung volume change
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Spirometer
When no breathing
When inhaling
When exhaling This motion is recorded on a rotating drum through direct mechanical linkage
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Spirometer
β’ The spirometer can only measure the gas volume inspired and expired, i.e., a change in volume, for example TV.
β’ It cannot measure gas volume remaining inside lungs, for example, FRC (Function Residual Capacity), RV (Residual Volume).
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3.3 Nitrogen-washout estimate of lung volume
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Nitrogen-washout estimate of lung volume
β’ Where π½π³ is lung volume π»π³ is lung temperature (in K) ππ³π³π is π³π molar fraction in lung π½π is spirometer volume π»π is spirometer temperature (in K) ππΊπ³π is π³π molar fraction in spirometer
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Nitrogen-washout estimate of lung volume
β’ It is a modified spirometer Two one-way valves are connected in air tube The mouthpiece is in between the valves A Nitrogen analyzer used to measure the fraction of
Nitrogen is installed
β’ So that When the patient starts breathing through the
mouthpiece, he can only inhale pure πΆπ But, he exhales the mixture of πΆπ, π³π, and πͺπΆπ, as
his lung initially contains πΆπ, π³π, and πͺπΆπ And the expired mixture enters into spirometer
through one-way valve Biomedical Instrumentation - wk 6 31
Nitrogen-washout estimate of lung volume
β’ What happens to π³π in lungs after multiple-breathing? β’ The amount of π³π is gradually decreasing
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Nitrogen-washout estimate of lung volume
β’ What can it measure? Functional residual capacity (FRC) Residual volume (RV)
β’ At the beginning ππ, total number of π³π moles in lungs is given by
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π³π ππππππππ = ππ³π³π πππ½π³ πππ»π³
π·πΉ
Note: ππ³π³π =π½π³π³ππ½π³
, π½π³π³πππ πππππππ ππππππππ ππππππ,π½π³ ππ πππππ ππππ ππππππ
π·π½ = π³πΉπ» β π³ =π·π½πΉπ»
π³π ππππππππ =π·πΉπ½π³π³ππ»π³
=π·πΉππ³π³π ππ π½π³ ππ
π»π³
Nitrogen-washout estimate of lung volume
β’ At the beginning ππ, total number of π³π moles in spirometer is assumed
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π³π ππππππππππππππ = πππ³π πππ½π πππ»π
π·πΉ
= π
β’ After multiple-breathing from the mouthpiece, at time ππ, the number of π³π moles in lungs become
ππ³π³π πππ½π³ πππ»π³
π·πΉ
Decreased!
Where the left side is change of π³π mole in lungs and right is change of π³π in spirometer
ππ³π³π πππ½π³ πππ»π³
π·πΉβ ππ³π³π ππ
π½π³ πππ»π³
π·πΉ
= πππ³π πππ½π πππ»π
π·πΉ
Mass balance
Nitrogen-washout estimate of lung volume
β’ Suppose ππ and ππ are as follows
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Then, we have π½π³ ππ β ππΉπͺ,π½π³ ππ = ππΉπͺ
Nitrogen-washout estimate of lung volume
β’ If the beginning time ππ is shifted
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Then, we have π½π³ ππ = ππΉπͺ,π½π³ ππ = π½π³ ππ = ππΉπͺ
Nitrogen-washout estimate of lung volume
β’ Therefore,
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ππ³π³π ππππΉπͺπ»π³
β ππ³π³π ππππΉπͺπ»π³
= πππ³π πππ½π πππ»π
ππΉπͺ =π»π³π»π
πππ³π ππ π½π ππππ³π³π ππ β ππ³π³π ππ
FRC can be measured using the above formulation
Nitrogen-washout estimate of lung volume
β’ Procedure: At the beginning, measure initial ππ³π³π ππ using
Nitrogen analyzer (sensor). Start at π½π³ ππ = ππΉπͺ
At the end, measure ππ³π³π ππ and πππ³π ππ . End at π½π³ ππ = ππΉπͺ
Measure π»π³ and π»π (both are constant).
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Nitrogen-washout estimate of lung volume
β’ Similarly, we can measure RV, by setting π½π³ ππ =π½π³ ππ = πΉπ½
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πΉπ½ =π»π³π»π
πππ³π ππ π½π ππππ³π³π ππ β ππ³π³π ππ
Nitrogen-washout estimate of lung volume
β’ Example: a π³πβwashout experiment is carried out. At beginning, π½π ππ = π ππππππ, πππ³π ππ = π. At the end π½π ππ = ππ ππππππ, πππ³π ππ = π.πππ and fraction of π³π for the patient has decreased by π.π. What is the lung volume at which the patient is
breathing?
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β’ Solution: At the beginning of experiment π»π³ = ππ + πππ = πππ π²,
At the end of experiment π½π ππ = ππ ππππππ
πππ³π ππ = π.πππ ππ³π³π ππ β ππ³π³π ππ = π.π π»π = πππ π²
Nitrogen-washout estimate of lung volume
With assumption of π½π³ ππ = π½π³ ππ = π½π³,
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π½π³ =π»π³π»π
πππ³π ππ π½π ππππ³π³π ππ β ππ³π³π ππ
=ππππππ
Γπ.πππ Γ ππ
π.π= π.ππ ππππππ