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