Respiratory Function Test

Department of internal medicine

Chen Yu

Respiratory Function Test

Lung volumes Ventilation function Gas exchange Blood flow Respiratory motive force

Lung Volume and Subdivisions

VT

IRV

ERV

RV

IC

FRC

VC

RV

TLC

Basal Lung Volume

VT (tidal volume): 500ml IRV (inspiratory reserve volume) ERV (expiratory reserve volume) RV (residual volume)

Basal Lung Capacity

IC (inspiratory capacity): VT+ IRV FRC (functional residual capacity):

ERV + RV VC (vital capacity) : IC + ERV

normal men: 4217ml

women: 3105ml TLC (total lung capacity): VC + RV

Some Explanatory Points

Lung volume is to describe the changes of the lung volume during one breathing at static conditions, also called static lung volume.

VT, VC, TLC are used at clinical. VT and VC are determined by Spirometric trace , but FRC and RV by indirect method: Helium or Nitrogen analyses method.

Clinical Significance

VC depends on sex, age and height. VC% < 80% is abnormal. VC : restrictive ventilation disorder

severe obstructive ventilation disorder

Clinical Significance

RV/TLC% (residual air rate)

normal : < 35%

emphysema: > 40 %

old person can be 50%. FRC : emphysema FRC : interstitial pulmonary fibrosis

Ventilation Function Test

It is called as dynamic lung volumes.

Fast spirometric trace to illustrate timed ventilation tests (air volume and air flow during breathing).

Ventilation Function Test

Lung ventilation volume

VE and MVV Forced vital capacity (FVC) Maximal mid-expiratory flow (MMEF.

MMF) Alveolar ventilation (VA)

·

VE ( minute ventilation):

= VT×RR/min

normal : 4—6 liter

< 3L : hypoventilation

>10L: hyperventilation

MVV ( maximal voluntary ventilation): ventilative volume at the most rate and

most breathing deep during a minute Normal : 80—100L abnormal: < 70L MVV%=(MVV—VE)/MVV % Normal: >95% ventilation storage : <86%

FVC (Forced Vital Capacity)

The volume that after full inspiration, to expire with the most force and the most rate.

FEV1 (forced expiratory volume in the first second)

FEV1/FVC% ( the first rate)

FEV1/FVC%: 83%

FEV2/FVC%: 96%

FEV3/FVC%: 99%

Normal: > 80%

<70%: obstructive ventilation disorder

MMEF (maximal mid-expiratory flow)

The mean flow between 25% and 75% forced expiration.

Significance: to evaluate the small airway obstruction in early stage

VA (alveolar ventilation)

The air volume entered respiratory bronchioli and the alveoli during a minute.

VD (dead space )=150ml VA = (VT –VD) ×RR/min Normal VD/VT=0.3-0.4

VD/VT : effective ventilation increased

VD/VT : effective ventilation decreased

Clinical Values of Ventilation Test

Air rate index =

Normal : =1

MVV active/predictive%

VC active/predictive%

Degrees of Lung Disfunction

VC or MVV act/pre% FEV1%

Normal >80 >70

Mild reduce 80-71 70-61

Mediate reduce 70-51 60-41

Severe reduce 50-21 <=40

Respiratory failure <=20

Classification of Ventilative Function Disorder

obstruction restriction mix

FEV1/FVC N or

MVV or N

VC N or

Rate index <1.0 >1.0 =1.0

RV N or uncertain

TLC N or uncertain

Degrees of Obstructive Emphysema

RV/TLC (%)

Normal <=35%

Mild emphysema 36-45

Mediate emphysema 46-55

Severe emphysema >=56

Bronchial Dilation Test

Method: to determine FEV1 and FEV1/FVC% before and after ß2-agonist inhalation

Result: improved rate=

Positive: >15% Reversible limitation: asthma

>15% and improved volume>200ml

After-before

before× 100%

PEF Variable Rate

PEF (peak expiratory flow): the most flow during forced expiration. It indicates the force of respiratory muscle and airway obstruction.

PEF variability=

PEF variability≥20% : asthma

PEFmax-PEFmin

1/2 (PEFmax+PEFmin)× 100%

Bronchial Provocation Test

Method : to inhale histamine from low to high concentration till the FEV1 decrease ≥20%. Calculate drug volume (PD20FEV1).

Positive: PD20FEV1<7.8umol indicate airway hyperresponsiveness asthma

Gas Exchange Test

Gas distribution: Nitrogen concentration method

normal < 2.5% Ventilation/perfusion ratio (V/Q) : 0.4

P(A-a)O2: 5-15mmHg

Diffusion capacity (DL): CO method

· ·

Small Airway Function Test

Small airway: diameter ≤2mm Closing volume (CV): N2 or He method

Maximum expiratory flow-volume curve (MEFV):

indicate disease from the curve shape

Thank you!