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Pulmonary  Function  Tests  (BCM)  
 
PEFR  vs  Spirometry    
PEFR  (peak  expiratory  flow  rate)  
-­‐ Measures  large  airways  
-­‐ ONLY  done  for  asthma,  not  COPD  
o Bronchoconstriction  is  a  hallmark  of  asthma  
Spirometry:  
-­‐ Measures  both  small  and  large  airways  
-­‐ Useful  in  most  respiratory  disease  
 
Indications  for  Pulmonary  Function  Tests  
1) Physiological  assessment  leading  to  diagnosis  
2) Establishment  of  severity  
3) Monitoring  of  the  disease  process  and  response  to  therapy  
4) Brochoprovocation  
5) Pre-­‐operative  risk  assessment  
6) Pulmonary  disability  
7) Exercise  testing  
 
Evaluation  of  Pulmonary  Function  
1:  Flow  rates  –  spirometry,  flow-­‐volume  loops  
-­‐ Flow  rates:  flow  of  air  through  airways  
2:  Lung  volumes  
3:  Diffusing  capacity  
-­‐ This  is  the  ability  of  gas  to  cross  the  membrane  
-­‐ Usually  reduced  in  ILD  
4:  Blood  pCO2  and  pO2  levels    
 
Spirometry  
-­‐ Subject  inhales  to  Vmax  then  forcefully  exhales  
-­‐ Volume  leaving  the  lung  is  recorded  as  a  function  of  time  (spirometry)  
-­‐ Total  volume  which  leaves  the  lung  appears  as  a  maximum  deflection  on  
spirometer  
 

 

Expiration  is  usually  passive  whilst  inspiration  is  
active
...
MMF  =  FEF  
b
...
MMF  usually  decreases  with  FEV1  
d
...
e
...
g
...
g
...
Ability  of  gases  to  cross  the  alveolar-­‐capillary  membrane  
a
...
Carbon  monoxide  (CO  gas)  is  usually  used  to  quantify  the  diffusion  
capacity  
c
...
The  diffusion  limit  of  CO  =  DLCO;  usually  reported  in  PFTs  
a
...
Use  CO  in  very  low  doses  in  mixture  with  hydrogen  
c
...
Reduced  DLCO:    
i
...
Anaemia    
iii
...
Emphysema  (pure  chronic  bronchitis  maintains  relatively  
normal  DLCO):  emphysema  =  destruction  of  alveolar  septa  
1
...
Emphysema  à  nodes  in  lungs  
v
...
Loss  of  lung  parenchyma:  pneumonia,  pneumonectomy,  fibrosis  
etc
...
Pulmonary  vascular  disease  –  pulmonary  hypertension,  vasculitis  
 
Arterial  Blood  Gases  
Sampled  anaerobically  on  an  automated  analyzer  
Analysed  for  gas  tensions  and  pH  
Oxygen  saturation  of  Hgb  
Hgb  content  
Key  determinants  of  ABGs:  
-­‐ pO2:  inspired  oxygen  fraction,  ventilation  perfusion  matching  (including  shunt),  
cardiac  output,  systemic  oxygen  consumption,  alveolar  ventilation  
o Hypoxemia  (low  O2)  à  SOB;  low  cardiac  output  à  hypoxemia  
o pO2  determined  by  O2  intake  (e
...
 high  altitude)  
o Fever  and  septic:  patient  requires  increased  O2  
-­‐ pCO2:  alveolar  ventilation,  ventilation  perfusion  matching,  metabolic  CO2  
production  
-­‐ pH:  alveolar  ventilation,  metabolic  acid-­‐base  balance  
Clinical  usefulness  of  ABGs:  
-­‐ ABGs  =  endpoint  of  gas-­‐exchange  function  of  the  lung  
-­‐ Reflex  gas  exchange,  not  lung  mechanics  
-­‐ If  problem  is  one  of  the  lung  mechanics,  e
...
 asthma,  follow  the  lung  mechanics  
(spirometry)  as  well  as  gas  exchange  
 
Pre-­‐operative  evaluation  
History  and  physical  exam,  especially  of  the  respiratory  system  
ABG  if  O2  sat  <96%  or  suspect  CO2  retention  
CXR  in  all  patients  >65  or  known  lung  disease  
Spirometry  especially  prior  to  thoraco-­‐abdominal  operations  
 

Dyspnoea  in  post-­‐operative  patient  
Atelectasis/large  pleural  effusion  
LVF  due  to  fluid  overload/MI  
PE  usually  secondary  to  LE  DVT  
Post  operative  pneumonia?  Aspirate  
PTX  due  to  central  line/intercostal  block  
Sepsis  
 
 
 
Flow-­‐Volume  Curve  
Normal  

Findings    
FVC  ∞  TLC  –  RV  
E:I  volume  at  FVC50  >1  

 

Moderate  COPD  

Severe  Emphysema    

 

 

COPD  à  lose  hypoxic  
drive  à  retain  CO2  
TLC  and  RV  increased  
FVC  mild  decrease  
Concavity  increased  
 

RV  and  TLC  increased  
FEV1  severely  
decreased  
FVC  decreased  
Concavity  increased  
E:I  volume  @  FVC50  <1  
 

 



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