bài giảng hô hấp ký
TRANSCRIPT
HÔ HẤP KÝ (SPIROMETRY)
GIỚI THIỆU
Hô hấp ký là một trong bốn xét nghiệm cơ bản của thăm dò CNHH (hô hấp ký, đo tổng dung lượng phổi, khả năng khuếch tán của phổi và khí trong máu).
Là tiêu chuẩn vàng để chẩn đoán COPD Là dụng cụ dùng để đo các thể tích hít
vào và thở ra theo thời gian. Giá trị lâm sàng của HHK phụ thuộc vào
chất lượng máy, kỹ thuật đo, và chọn giá trị dự đoán phù hợp.
CÁC LOẠI HÔ HẤP KÝ
Máy đo thể tích theo thời gian: Là loại cổ điển có chuông úp trên một
thùng nước hay dạng đèn xếp.
MÁY HHK ĐO THỂ TÍCH
CÁC LOẠI HÔ HẤP KÝ Máy đo lưu lượng theo thể tích phổi
Loại dùng bộ phận nhận cảm để đo khuynh áp từ đó tính ra lưu lượng và thể tích phổi
MÁY HHK ĐO LƯU LƯỢNG
MÁY HHK ĐIỆN TỬ ĐỂ BÀN
MÁY HHK XÁCH TAY
Các thể tích và dung tích phổi
4 thể tích: thể tích dự trữ hít vào, thể tích khí lưu thông, thể tích dự trữ thở ra, và thể tích khí cặn
4 dung tích: dung tích sống, dung tích hít vào, dung tích cặn chức năng, dung tích phổi toàn bộ
Các thể tích phổi Thể tích khí lưu thông
(Tidal Volume- TV): Thể tích khí của một lần hít vào hoặc thở ra bình thường
Thể tích dự trữ hít vào (Inspiratory Reserve Volume -IRV): Thể tích khí hít vào thêm khi gắng sức, sau khi đã hít vào bình thường
Thể tích khí dự trữ thở ra (Expiratory Reserve Volume -ERV): Thể tích khí thở ra thêm được khi gắng sức, sau khi đã thở ra bình thường
Các thể tích phổi
Thể tích khí cặn (Residual Volume -RV): Thể tích khí vẫn còn
ở trong phổi sau khi thở ra tối đa
Được đo trực tiếp (FRC-ERV) bằng phế thân kế (Body Plethysmography) hay pha loãng helium, không đo bằng spirometry
Các dung tích phổi Total Lung Capacity
(TLC): Tổng các thể tích trong phổi
Vital Capacity (VC): Thể tích lớn nhất mà người ta có thể huy động được bằng cách thở ra hết sức sau khi đã hít vào hết sức
Inspiratory Capacity (IC): Tổng của thể tích dự trữ hít vào và thể tích khí lưu thông
Các dung tích phổi (tt)
Dung tích cặn chức năng (Functional Residual Capacity - FRC): Tổng RV và ERV
hoặc thể tích khí của phổi ở cuối thì thở ra bình thường
Được đo bằng phế thân kế (Body Plethysmography) hay pha loãng helium, không đo bằng spirometry
CÁC CHỈ SỐ HÔ HẤP KÝ
FVC (Forced vital capacity):
Thể tích khí toàn bộ được thở ra gắng sức trong một lần thở
FEV1 (Forced expiratory volume in one second): Thể tích khí thở ra trong giây đầu
Tỉ số FEV1/FVC (chỉ số Gaensler); FEV1/VC ( chỉ số Tiffeneau):
Phân số khí được thở ra trong giây đầu liên quan với thể tích khí toàn bộ được thở ra
CÁC CHỈ SỐ HÔ HẤP KÝ
FEF 25-75% (Forced Expiratory Flow between 25% and 75% of the FVC)(L/s):Lưu lượng thở ra gắng sức trong khoảng 25 – 75% của dung tích sống gắng sức
PEF ( Peak Expiratory Flow)(L/s):Lưu lượng thở ra đỉnh
CÁC CHỈ SỐ HÔ HẤP KÝ (tt)
PIF ( Peak Inspiratory Flow)(L/s):Lưu lượng hít vào đỉnh: Lưu lượng cao nhất trong lúc hít vào, thường được dùng để đánh giá tắc nghẽn đường hô hấp trên.
MVV ( Maximal Volumtary Ventilation)(L/phút)Thể tích thông khí tự ý tối đa
GIẢN ĐỒ THỂ TÍCH THEO THỜI GIAN
ĐƯỜNG CONG LƯU LƯỢNG THỂ TÍCH
KẾT QUẢ HÔ HẤP KÝ
Bình thường
Tắc nghẽn
Hạn chế
Dạng hỗn hợp
HÔ HẤP KÝ
CÁC GIÁ TRỊ BÌNH THƯỜNG
CÁC GIÁ TRỊ BÌNH THƯỜNG ĐƯỢC DỰ ĐOÁN
Tuổi
Chiều cao
Giới
Chủng tộc
Phụ thuộc vào:
CÁC GIÁ TRỊ BÌNH THƯỜNG ĐƯỢC DỰ ĐOÁN (tt)
Được dựa trên các khảo sát trong dân số lớn
Các giá trị được dự đoán là các giá trị trung bình lấy từ kết quả khảo sát
Không có các khảo sát trong dân số người già
Tiêu chuẩn cho một hô hấp ký bình thường sau dãn phế quản
FEV1: % dự đoán > 80%
FVC: % dự đoán > 80%
FEV1/FVC: > 0.7
Đường cong lưu lượng - thể tíchvà thể tích theo thời gian của một người bình thường
HÔ HẤP KÝ
BỆNH PHỔI TẮC NGHẼN
Tiêu chuẩn chẩn đoán hội chứng tắc nghẽn trên hô hấp ký
FEV1:%dự đoán < 80
FVC:%dự đoán > 80 hoặc < 80
FEV1/FVC:< 0.7
Đường cong chỉ sự tắc nghẽn
HÔ HẤP KÝ
BỆNH PHỔI HẠN CHẾ
Tiêu chuẩn bệnh phổi hạn chế
FEV1: % dự đoán > 80 hoặc < 80
FVC: % dự đoán < 80
FEV1/FVC: > 0.7
Đường cong chỉ sự hạn chế
RỐI LOẠN THÔNG KHÍ HỔN HỢP
FEV1: % dự đoán < 80%
FVC: % dự đoán < 80%
FEV1 /FVC: < 0.7
Đường cong chỉ rối loạn thông khí kiểu hổn hợp
Th
ể t
ích
, lí
t
Thời gian, giây
Bình thường
Tắc nghẽn + hạn chế
HÔ HẤP KÝ
ĐƯỜNG CONG LƯU LƯỢNG - THỂ TÍCH
ĐƯỜNG CONG LƯU LƯỢNG -THỂ TÍCH
chuẩn cho hầu hết các máy hô hấp ký để bàn
Cung cấp thông tin thêm vào đường cong thể tích theo thời gian
Không quá khó để giải thích kết quảPhát hiện tốt hơn khi có sự tắc nghẽn
luồng khí nhẹ
Các dạng đường cong lưu lượng thể tích
CHỈ ĐỊNH
Đánh giá các triệu chứng, các dấu hiệu bệnh phổi
Đánh giá sự tiến triển của bệnh phổi Theo dõi hiệu quả điều trị Đánh giá nguy cơ hô hấp trước phẫu thuật Giám định y khoa về sức khỏe hô hấp Tầm soát các đối tượng có nguy cơ bệnh phổi Theo dõi tác dụng độc hại của một số thuốc,
hóa chất
CHỐNG CHỈ ĐỊNH
Tình trạng tim mạch không ổn định Nhồi máu cơ tim gần đây Phẫu thuật mắt, ngực, bụng gần đây Tràn khí màng phổi Phình động mạch chủ Ho ra máu Các tình trạng cấp tính như chóng mặt,
viêm phổi
CÁC BIẾN CHỨNG
Ngất, chóng mặt, nhức đầu nhẹ Co thắt phế quản Ho Giảm độ bão hòa oxy nếu điều trị
oxy bị gián đoạn Áp lực nội sọ tăng Tràn khí màng phổi Đau ngực Nhiễm trùng
Hết
Spirometry and Related Tests
RET 2414Pulmonary Function TestingModule 2.0
SPIROMETRY AND RELATED TESTS
Learning Objectives
Determine whether spirometry is acceptable and reproducible
Identify airway obstruction using forced vital capacity (FVC) and forced expiratory volume (FEV1)
Differentiate between obstruction and restriction as causes of reduced vital capacity
SPIROMETRY AND RELATED TESTS
Learning Objectives
Distinguish between large and small airway obstruction by evaluating flow-volume curves
Determine whether there is a significant response to bronchodilators
Select the appropriate FVC and FEV1 for reporting from series of spirometry maneuvers
Predicted Values
Laboratory Normal Ranges
Laboratory tests performed on a large number of normal population will show a range of results
Predicted Values
Laboratory Normal Ranges
Predicted Values
Laboratory Normal Ranges
Most clinical laboratories consider two standard deviations from the mean as the normal range since it includes 95% of the normal population.
PFT Reports
o When performing PFT’s three values are reported:
o Actual – what the patient performed
o Predicted – what the patient should have performed based on Age, Height, Sex, Weight, and Ethnicity
o % Predicted – a comparison of the actual value to the predicted value
PFT Reports
Example
Actual Predicted %Predicted
VC 4.0 5.0 80%
SPIROMETRY
Vital Capacity
The vital capacity (VC) is the volume of gas measured from a slow, complete expiration after a maximal inspiration, without a forced effort.
SPIROMETRY
Vital Capacity
SPIROMETRY
Vital Capacity
Valid VC measurements important IC and ERV used to calculate
RV and TLC
Example: RV = FRC - ERV TLC = IC + FRC
SPIROMETRY
VC: Criteria for Acceptability
1. End-expiratory volume varies by less than 100 ml for three preceding breaths
2. Volume plateau observed at maximal inspiration and expiration
SPIROMETRY
VC: Criteria for Acceptability
3. Three acceptable VC maneuvers should be obtained; volume within 150 ml.
4. VC should be within 150 ml of FVC value
SPIROMETRY
VC: Selection Criteria
The largest value from at least 3 acceptable maneuvers should be reported
SPIROMETRY
VC: Significance/Pathophysiology
Decreased VC Loss of distensible lung tissue
Lung CA Pulmonary edema Pneumonia Pulmonary vascular congestion Surgical removal of lung tissue Tissue loss Space-occupying lesions Changes in lung tissue
SPIROMETRY
VC: Significance/Pathophysiology
Decreased VC Obstructive lung disease Respiratory depression or
neuromuscular disease Pleural effusion Pneumothorax Hiatal hernia Enlarged heart
SPIROMETRY
VC: Significance/Pathophysiology
Decreased VC Limited movement of diaphragm
Pregnancy Abdominal fluids Tumors
Limitation of chest wall movement Scleraderma Kyphoscoliosis Pain
SPIROMETRY
VC: Significance/Pathophysiology
If the VC is less than 80% of predicted: FVC can reveal if caused by obstruction
SPIROMETRY
VC: Significance/Pathophysiology
If the VC is less than 80% of predicted: Lung volume testing can reveal if caused by restriction
SPIROMETRY
Forced Vital Capacity (FVC)
The maximum volume of gas that can be expired when the patient exhales as forcefully and rapidly as possible after maximal inspiration (sitting or standing)
SPIROMETRY
FVC (should be within 150 ml of VC)
SPIROMETRY
FVC: Criteria for Acceptability1. Maximal effort; no cough or glottic closure
during the first second; no leaks or obstruction of the mouthpiece.
2. Good start-of-test; back extrapolated volume <5% of FVC or 150 ml, whichever is greater
SPIROMETRY
FVC: Criteria for Acceptability
3. Tracing shows 6 seconds of exhalation or an obvious plateau (<0.025L for ≥1s); no early termination or cutoff; or subject cannot or should not continue to exhale
SPIROMETRY
FVC: Criteria for Acceptability
4. Three acceptable spirograms obtained; two largest FVC values within 150 ml; two largest FEV1 values within 150 ml
SPIROMETRY
FVC: Selection Criteria
The largest FVC and largest FEV1 (BTPS) should be reported, even if they do not come from the same curve
SPIROMETRY
FVC: When to call it quits !!!
If reproducible values cannot be obtained after eight attempts, testing may be discontinued
SPIROMETRY
FVC: Significance and Pathophysiology
FVC equals VC in healthy individuals
FVC is often lower in patients with obstructive disease
SPIROMETRY
FVC: Significance and Pathophysiology
FVC can be reduced by:
Mucus plugging Bronchiolar narrowing Chronic or acute asthma Bronchiectasis Cystic fibrosis Trachea or mainstem bronchi obstruction
SPIROMETRY
FVC: Significance and Pathophysiology
Healthy adults can exhale their FVC within 4 – 6 seconds
Patients with severe obstruction (e.g., emphysema) may require 20 seconds, however, exhalation times >15 seconds will rarely change clinical decisions
SPIROMETRY
FVC: Significance and Pathophysiology
FVC is also decreased in restrictive lung disease
Pulmonary fibrosis dusts/toxins/drugs/radiation
Congestion of pulmonary blood flow pneumonia/pulmonary hypertension/PE
Space occupying lesions tumors/pleural effusion
SPIROMETRY
FVC: Significance and Pathophysiology
FVC is also decreased in restrictive lung disease
Neuromuscular disorders, e.g, myasthenia gravis, Guillain-Barre
Chest deformities, e.g, scoliosis/kyphoscoliosis
Obesity or pregnancy
SPIROMETRY
Forced Expiratory Volume (FEV1)
The volume expired over the first second of an FVC maneuver
SPIROMETRY
Forced Expiratory Volume (FEV1) May be reduced in obstructive or
restrictive patterns, or poor patient effort
SPIROMETRY
Forced Expiratory Volume (FEV1)
In obstructive disease, FEV1 may be decreased because of:
Airway narrowing during forced expiration emphysema
Mucus secretions Bronchospasm Inflammation (asthma/bronchitis) Large airway obstruction
tumors/foreign bodies
SPIROMETRY
Forced Expiratory Volume (FEV1)
The ability to work or function in daily life is related to the FEV1 and FVC
Patients with markedly reduced FEV1 values are more likely to die from COPD or lung cancer
SPIROMETRY
Forced Expiratory Volume (FEV1)
FEV1 may be reduced in restrictive lung processes
Fibrosis Edema Space-occupying lesions Neuromuscular diseases Obesity Chest wall deformity
SPIROMETRY
Forced Expiratory Volume (FEV1)
FEV1 is the most widely used spirometric parameter, particularly for assessment of airway obstruction
SPIROMETRY
Forced Expiratory Volume (FEV1)
FEV1 is used in conjunction with FVC for:
Simple screening Response to bronchodilator therapy Response to bronchoprovocation Detection of exercise-induced
bronchospasm
SPIROMETRY
Forced Expiratory Volume Ratio (FEVT%)
FEVT% = FEVT/FVC x 100
Useful in distinguishing between obstructive and restrictive causes of reduced FEV1 values
SPIROMETRY
Forced Expiratory Volume Ratio (FEVT%)
Normal FEVT% Ratios for Health Adults
FEV 0.5% = 50%-60%
FEV 1% = 75%-85%
FEV 2% = 90%-95%
FEV 3% = 95%-98%
FEV 6% = 98%-100%
Patients with obstructive disease have reduced FEVT% for each interval
SPIROMETRY
Forced Expiratory Volume Ratio (FEVT%)
A decrease FEV1/FVC ratio is the “hallmark” of obstructive disease
FEV1/FVC <75%
SPIROMETRY
Forced Expiratory Volume Ratio (FEVT%)
Patients with restrictive disease often have normal or increased FEVT% values
FEV1 and FVC are usually reduced in equal proportions
The presence of a restrictive disorder may by suggested by a reduced FVC and a normal or increased FEV1/FVC ration
SPIROMETRY
Forced Expiratory Flow 25% - 75%(maximum mid-expiratory flow)
FEF 25%-75% is measured from a segment of the FVC that includes flow from medium and small airways
Normal values: 4 – 5 L/sec
SPIROMETRY
Forced Expiratory Flow 25% - 75%
In the presence of a borderline value for FEV1/FVC, a low FEF 25%-75% may help confirm airway obstruction
SPIROMETRY
Flow – Volume Curve AKA: Flow–Volume Loop (FVL)
The maximum expiratory flow-volume (MEFV) curve shows flow as the patient exhales from maximal inspiration (TLC) to maximal expiration (RV)
FVC followed by FIVC
SPIROMETRY
FVL X axis: Volume
Y axis: Flow
PEF (Peak Expiratory Flow)
PIF (Peak Inspiratory Flow) .
Vmax 75 or FEF 25% FVC Remaining or Percentage FVC exhaled
.
Vmax 50 or FEF 50% .
Vmax 25 or FEF 75%
FEF 25% or Vmax 75
FEF 75% or Vmax 25%
SPIROMETRY
FVL
FEVT and FEF% can be read from the timing marks (ticks) on the FVL
SPIROMETRY
FVL Significant decreases in flow or volume
are easily detected from a single graphic display
SPIROMETRY
FVL: Severe Obstruction
SPIROMETRY
FVL: Bronchodilation
SPIROMETRY
Peak Expiratory Flow (PEF)
The maximum flow obtained during a FVC maneuver
Measured from a FVL In laboratory, must perform a
minimum of 3 PEF maneuvers Largest 2 of 3 must be within 0.67
L/S (40 L/min) Primarily measures large airway
function Many portable devices available
SPIROMETRY
Peak Expiratory Flow (PEF)
When used to monitor asthmatics
Establish best PEF over a 2-3 week period
Should be measured twice daily (morning and evening)
Daily measurements are compared to personal best
SPIROMETRY
Peak Expiratory Flow (PEF) The National Asthma Education Program
suggests a zone system Green: 80%-100% of personal best
Routine treatment can be continued; consider reducing medications
Yellow: 50%-80% of personal best Acute exacerbation may be present Temporary increase in medication may be
needed Maintenance therapy may need increases
Red: Less than 50% of personal best Bronchodilators should be taken immediately;
begin oral steroids; clinician should be notified if PEF fails to return to yellow or green within 2 – 4 hours
SPIROMETRY
Peak Expiratory Flow (PEF) PEF is a recognized means of
monitoring asthma
Provides serial measurementsof PEF as a guide to treatment
ATS Recommended Ranges 60-400 L/min (children) 100-850 L/min (adults)
SPIROMETRY
Maximum Voluntary Ventilation (MVV)
The volume of air exhaled in a specific interval during rapid, forced breathing
SPIROMETRY
MVV Rapid, deep breathing VT ~50% of VC For 12-15 seconds
SPIROMETRY
MVV
Tests overall function of respiratory system
Airway resistance
Respiratory muscles
Compliance of lungs/chest wall
Ventilatory control mechanisms
SPIROMETRY
MVV At least 2 acceptable maneuvers should be
performed
Two largest should be within 10% of each other
Volumes extrapolated out to 60 seconds and corrected to BTPS
MVV is approximately equal to 35 time the FEV1
SPIROMETRY
MVV Selection Criteria
The highest MVV (L/min, BTPS) and MVV rate (breaths / min) should be reported
SPIROMETRY
MVV
Decreased in:
Patients with moderate to severe obstructive lung disease
Patients who are weak or have decreased endurance
Patients with neurological deficits
SPIROMETRY
MVV
Decreased in:
Patients with paralysis or nerve damage
A markedly reduced MVV correlates with postoperative risk for patients having abdominal or thoracic surgery
SPIROMETRY
Before/After Bronchodilator
Spirometry is performed before and after bronchodilator administration to determine the reversibility of airway obstruction
SPIROMETRY
Before/After Bronchodilator
An FEV1% less than predicted is a good indication for bronchodilator study
In most patients, an FEV1% less than 70% indicates obstruction
SPIROMETRY
Before/After Bronchodilator
Any pulmonary function parameter may be measured before and after bronchodilator therapy
FEV1 and specific airway conductance (SGaw) are usually evaluated
SPIROMETRY
Before/After Bronchodilator
Lung volumes should be recorded before bronchodilator administration
Lung volumes and DLco may also respond to bronchodilator therapy
SPIROMETRY
Before/After Bronchodilator
Routine bronchodilator therapy should be withheld prior to spirometry
Ruppel 9th edition, pg. 66: Table 2-2
Short-acting β-agonists 4 hours Short-acting anticholinergic 4 hours Long-acting β-agonists 12 hours Long-acting anticholinergic 24 hours Methylxanthines (theophyllines) 12 hours Slow release methylxanthines 24 hours Cromolyn sodium 8-12 hours Leukotriene modifiers 24 hours Inhaled steroids Maintain dosage
SPIROMETRY
Before/After Bronchodilator
Minimum of 10 minutes, up to 15 minutes, between administration and repeat testing is recommended (30 minutes for short-acting anticholinergic agents)
FEV1, FVC, FEF25%-75%, PEF, SGaw are commonly made before and after bronchodilator administration
SPIROMETRY
Before/After Bronchodilator
Percentage of change is calculated
%Change = Postdrug – Predrug X 100Predrug
SPIROMETRY
Before/After Bronchodilator
FEV1 is the most commonly used test for quantifying bronchodilator response
FEV1% should not be used to judge bronchodilation response
SGaw may show a marked increase after bronchodilator therapy
SPIROMETRY
Before/After Bronchodilator
Significance and Pathophysiology
Considered significant if:
FEV1 or FVC increase ≥12% and ≥200 ml
SGaw increases 30% - 40%
SPIROMETRY
Before/After Bronchodilator
Significance and Pathophysiology
Diseases involving the bronchial (and bronchiolar) smooth muscle usually improve most from “before” to “after”
Increase >50% in FEV1 may occur in patients with asthma
SPIROMETRY
Before/After Bronchodilator
Significance and Pathophysiology
Patients with chronic obstructive diseases may show little improvement in flows
Inadequate drug deposition (poor inspiratory effort)
Patient may respond to different drug Paradoxical response <8% or 150 ml not
significant
SPIROMETRY
Maximal Inspiratory Pressure (MIP)
The lowest pressure developed during a forceful inspiration against an occluded airway
Primarily measures inspiratory muscle strength
SPIROMETRY
MIP
Usually measured at maximal expiration (residual volume)
Can be measured at FRC
Recorded as a negative number in cm H20 or mm Hg, e.g. (-60 cm H2O)
SPIROMETRY
MIP
SPIROMETRY
MIP
Significance and Pathophysiology
Healthy adults > -60 cm H2O Decreased in patients with:
Neuromuscular disease
Diseases involving the diaphragm, intercostal, or accessory muscles
Hyperinflation (emphysema)
SPIROMETRY
MIP
Significance and Pathophysiology
Sometimes used to measure response to respiratory muscle training
Often used in the assessment of respiratory muscle function in patients who need ventilatory support
SPIROMETRY
Maximal Expiratory Pressure (MEP)
The highest pressure developed during a forceful exhalation against an occluded airway
Dependent upon function of the abdominal muscles, accessory muscles of expiration, and elastic recoil of lung and thorax
SPIROMETRY
MEP
Usually measured at maximal inspiration (total lung capacity)
Can be measured at FRC
Recorded as a positive number in cm H20 or mm Hg
SPIROMETRY
MIP and MEP
SPIROMETRY
MEP
Significance and Pathophysiology
Healthy adults >80 to 100 cm H2O Decreased in:
Neuromuscular disorders
High cervical spine fractures
Damage to nerves controlling abdominal and accessory muscles of inspiration
SPIROMETRY
MEP
Significance and Pathophysiology
A low MEP is associated with inability to cough
May complicate chronic bronchitis, cystic fibrosis, and other diseases that result in excessive mucus production
SPIROMETRY
Airway Resistance (Raw)
The drive pressure required to create a flow of air through a subject’s airway
Recorded in cm H2O/L/sec
When related to lung volume at the time of measurement it is known as specific airway resistance (SRaw)
SPIROMETRY
Raw
Measured in a plethysmograph as the patient breathes through a pneumo-tachometer
SPIROMETRY
Raw Criteria of Acceptability
Mean of three or more acceptable efforts should be reported; individual values should be within 10% of mean
SPIROMETRY
Airway Resistance (Raw)
Normal Adult Values
Raw 0.6 – 2.4 cm H2O/L/sec
SRaw 0.190 – 0.667 cm H2O/L/sec/L
SPIROMETRY
Airway Resistance (Raw)
May be increased in:
Bronchospasm Inflammation Mucus secretion Airway collapse Lesions obstructing the larger airways
Tumors, traumatic injuries, foreign bodies
SPIROMETRY
RawSignificance and Pathology
Increased in acute asthmatic episodes
Increased in advanced emphysema because of airway narrowing and collapse
Other obstructive disease, e.g., bronchitis may cause increase in Raw proportionate to the degree of obstruction in medium and small airways
SPIROMETRY
Airway Conductance (Gaw)
A measure of flow that is generated from the available drive pressure
Recorded in L/sec/cm H2O
Gaw is the inverse of Raw
When related to lung volume at the time of measurement it is known as specific airway conductance (SGaw)
SPIROMETRY
Gaw
Measured in a plethysmograph as the patient breathes through a pneumo-tachometer
SPIROMETRY
Gaw Criteria of Acceptability
Mean of three or more acceptable efforts should be reported; individual values should be within 10% of mean
SPIROMETRY
Airway Conductance (Gaw)
Normal Adult Values
Gaw 0.42 – 1.67 L/sec/cmH2O
SGaw 0.15 – 0.20 L/sec/cm H2O/L
SPIROMETRY
Airway Conductance (Gaw)
Significance and Pathology
SGaw Values <0.15 – 0.20 L/sec/cm H2O/L are consistent with airway obstruction
Quiz Practice
Most clinical laboratories consider two standard deviations from the mean as the normal range when determining predicted values since it includes 95% of the normal population.a. Falseb. Only for those individuals with lung
diseasec. This applies only to cigarette smokersd. True
Quiz Practice
Vital capacity is defined as which of the following?a. The volume of gas measured from a slow,
complete exhalation after a maximal inspiration, without a forced effort
b. The volume of gas measured from a rapid, complete exhalation after a rapid maximal inspiration
c. The volume of gas measured after 3 seconds of a slow, complete exhalation
d. The total volume of gas within the lungs after a maximal inhalation
Quiz Practice
Which of the following statements are true regarding the acceptability criteria for vital capacity measurement?
I. End-expiratory volume varies by less than 100 ml for three preceding breaths
II. Volume plateau observed at maximal inspiration and expiration
III. Three acceptable vital capacity maneuvers should be obtained; volume within 150 ml
IV. Vital capacity should be within 150 ml of forced vital capacity in healthy individuals
a. I, II, and IVb. II, III, and IVc. III and IVd. I, II, III, IV
Quiz Practice
Which of the following best describes the Forced Vital Capacity (FVC) maneuver?
a. The volume of gas measured from a slow, complete exhalation after a maximal inspiration, without a forced effort
b. The volume of gas measured from a slow, complete exhalation after a rapid maximal inspiration
c. The volume of gas measured after 3 seconds of a rapid, complete exhalation
d. The maximum volume of gas that can be expired when the patient exhales as forcefully and rapidly as possible after maximal inspiration
Quiz Practice
All of the following are true regarding the acceptability criteria of an FVC maneuver EXCEPT?
a. Maximal effort, no cough or glottic closure during the first second; no leaks of obstruction of the mouthpiece
b. Good start of test; back extrapolated volume less than 5% of the FVC or 150 ml
c. Tracing shows a minimum of 3 seconds of exhalation
d. Three acceptable spirograms obtained; two largest FVC values within 150 ml; two largest FEV1 values within 150 ml
Quiz Practice
The FEV1 is the expired volume of the first second of the FVC maneuver.
a. Trueb. Falsec. Only when done slowlyd. Only when divided by the FVC
Quiz Practice
Which of following statements is true regarding FEV1?
a. FEV1 may be larger than the FVCb. FEV1 is always 75% of FVCc. May be reduced in obstructive and
restrictive lung diseased. Is only reduced in restrictive disease
Quiz Practice
The FEV1% is useful in distinguishing between obstructive and restrictive causes of reduced FEV1 values
a. Trueb. Falsec. Only helps to distinguish obstructive
lung diseased. Only helps to distinguish restrictive
lung disease
Quiz Practice
Which statements are true regarding the FEV 1%, also known as the FEV1/FVC?
I. A decreased FEV1/FVC is the hallmark of obstructive disease
II. Patients with restrictive lung disease often have normal or increased FEV1/FVC ratios
III. The presence of a restrictive disorder may be suggested by a reduced FVC and a normal or increased FEV1/FVC ratio
IV. A normal FEV1/FVC ratio is between 75% - 85%
a. I and IIb. I, II and IIIc. II, III and IVd. I, II, III and IV
Quiz Practice
What test is represented by the graph to the right?
a. Forced Vital Capacityb. Flow-Volume Loopc. Slow Vital Capacityd. Total Lung Capacity
Maneuver
Quiz Practice
What type of pulmonary disorder is represented by the graph below?
a. Obstructive lung diseaseb. Restrictive lung diseasec. Upper airway obstructiond. Normal lung function
(The dotted lines represent the predicted values)
Quiz Practice
Which is true regarding Peak Expiratory Flow (PEF)?
I. Primarily measures large airway functionII. Is a recognized means of monitoring
asthmaIII. Serial measurements of PEF are used a
guide to treat asthmaIV. When less than 50% of personal best, it is
an indication that immediate treatment is required
a. I onlyb. II and IIIc. II, III, and IVd. I, II, III, and IV
Quiz Practice
MVV is decreased in patients with which of the following disorders?
I. Moderate to severe obstructive lung disease
II. Weak or with decrease enduranceIII. Neurological defectsIV. Paralysis or nerve damage
a. I and IVb. II and IIIc. III and IVd. I, II, III, and IV
Quiz Practice
Spirometry before and after bronchodilator therapy is used to determine which of the following?
a. Reversibility of airway obstructionb. The severity of restrictive disordersc. The rate at which CO diffuses through the lung
into the bloodd. If the patient has exercised induced asthma
Quiz Practice
What is the minimum amount of time between administration of bronchodilator therapy and repeat pulmonary function testing?
a. 5 minutesb. 10 minutesc. 30 minutesd. 60 minute
Quiz Practice
Bronchodilation is considered significant when which of the following occurs?
a. FEV1/FVC increases by 12%b. SGaw increases by 12%c. FVC and/or FEV1 increases by 12% and 150 mld. DLco increases by 12%
Quiz Practice
Which of the following is true regarding Maximal Inspiratory Pressure (MIP)?
I. Primarily measures inspiratory muscle strength
II. Measures airway resistance during inspiration
III. Is decreased in patients with neurological disease
IV. Often used in the assessment of respiratory muscle function in patients who need ventilatory support
a. I, II, and IIIb. I, III, and IVc. II and IIId. II, III, and IV
Quiz Practice
Airway resistance (Raw) is the drive pressure required to create a flow of air through a subject’s airway.
a. Trueb. Falsec. Only in patients with COPDd. Only in patients with restrictive
disorders
Quiz Practice
Airway resistance may be increased in which of the following patients?
I. Purely restrictive lung disordersII. Acute asthmatic episodesIII. Mucus secretionIV. Lung compliance changes
a. I onlyb. I and IVc. II and IIId. I, II, III, and IV
Quiz Practice
Airway Conductance (Gaw) is a measure of flow that is generated from the available drive pressure.
a. Trueb. Falsec. Only in patients with COPDd. Only in patients with restrictive
disorders
Quiz Practice
A patient’s pulmonary function tests reveal the following:
Actual Predicted %Predicted FVC 4.01 L 4.97 L 81 FEV1 2.58 L 3.67 L 56 FEV1% 51 >75 _
Select the correct interpretationa. Restrictive patternb. Obstructive patternc. Inconclusived. Normal
Quiz Practice
A patient’s pulmonary function tests reveal the following:
Actual Predicted %PredictedFVC 3.75 L 4.97 L 75FEV1 2.80 L 3.67 L 76FEV1% 75 >/=75 _
Select the correct interpretationa. Restrictive patternb. Obstructive patternc. Inconclusived. Normal