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For results to be consistent in spirometry, FVC and FEV1 have to be within what percentage?





What is a normal FEV1?



What is a normal FEV1/FVC ratio?




What is FEF25-75%?



Mean expiratory flow over the mid 50% of expiration



Describe a normal flow volume loop.

Top loop is expiration

bottom loop inspiration

PEF = airflow in large airways

FEF25-75% = small airways, effort independent

FEV1 = middle airways


What does this flow volume loop indicate?



What does this flow volume loop indicate?

Slow start


What does this flow volume loop indicate?

False start


What does this flow volume loop indicate?

Early termination


What does this flow volume loop indicate?

Variable effort


What does this flow volume loop indicate?

Not at TLC prior to start


What does a reduction in FVC indicate?

  • Reduced lung size
  • Restrictive lung disease or
  • severe air flow limitation.


What does a reduction in FEV1 indicate?

Airflow limitation or severe restrictive process. [earliest change associated with airflow limitation seen in small airways (FEF: 75 then 25-50)]


What do changes in FEV1/FVC ratio indicate?

Proportion of Vital Capacity expired in 1 second.

Normal is 80%

FEV1/FVC ratio is decreased in obstructive lung disease.

If <70%, COPD can be diagnosed.

In restrictive lung disease, both FEV1 and FVC are reduced, therefore FEV1/FVC ratio should be approximately normal or increased.


10 yr old girl with persistant wheeze and cough.

FVC 98%

FEV1 76%


FEF 25-75 34%

FEF50 44%

PF 77%

FIF 50% 116

Inspiratory loop normal

Concave expiratory loop = obstructive.

FVC good

FEV1 reduced

FEV1/FVC reduced

FEF 25-75 reduced


Obstructive picture - asthma


What do you expect to see in an obstructive picture in spirometry?

  • Low FEV1
  • Low FEF 25-75
  • Normal FVC
  • FEV1/FVC
  • Flow volume loop: Concave
  • Normal large airways – can reach PEF


  • Airways chockablock – air comes out slower like blowing through a straw
  • Bronchodilator responsiveness: >12% increase FEV1


14 yo boy with severe extensive bronchiectasis

  • FVC 85%
  • FEV1 42%
  • FEV1/FVC 42
  • FEF 25-75 13%
  • FEF50 15%
  • PF 69%
  • TLC 122%


Mod to severe obstructive lung disease

  • PEF reduced
  • Concave expiratory loop
  • FVC almost normal
  • FEV1 reduced
  • FEV1/FVC reduced
  • FEF 25-75 reduced
  • TLC high indicating air trapping

(FEV1/FVC ratio is decreased in obstructive lung disease)


What are the three main obstructive conditions?


Cystic Fibrosis



What is the main parameter to indicate obstructive lung disease in spirometry?



  • Normal >Lower limit of normal
  • Mild >70%
  • Moderate >50%
  • Severe >35%
  • Very severe <35%

- CF: FEV1 30% = 50% two year survival ... transplant


In obstructive airways disease, what is the most useful long-term measure of disease progression?


FEV1 is the most reproducible, most commonly obtained, and possibly most useful pulmonary function tests.

• objective measure of airflow in obstructive disease.

• FEV1 as a percentage of predicted norms is one of six criteria used to determine asthma severity. It provides an objective measure of airflow in obstructive disease.

• Lung hyperinflation can be adjusted for by FVC, which is why FEV1/FVC ratio of <80% for airflow limitation is used.

• Bronchodilator response with an improvement of >12% in FEV1 indicates obstruction.

• FEF25-75 considered by some to be more sensitive than the FEV1 for detecting early airway obstruction, but it has a wider range of normal values.


2008A Q36

A ten-year-old boy with severe bronchiolitis obliterans presents to the Emergency Department with increasing exercise intolerance over the previous week.
A capillary blood gas shows the following picture:
pH    7.29   [7.35 - 7.45]

pCO2    97 mmHg  [36 – 44 mmHg]

Bicarbonate (HCO 3 -)  45 mmol/L  [21 – 30 mmol/L]

Base excess  +18 mmol/L  [-3 – +3 mmol/L]

This result is most consistent with which of the following?

A. Acute on chronic respiratory acidosis.

B. Acute respiratory acidosis.

C. Chronic respiratory acidosis.

D. Mixed metabolic and respiratory acidosis.

E. Uncompensated metabolic acidosis. 

A. Acute on chronic respiratory acidosis
pH is acidotic.
CO2 is elevated indicating respiratory acidosis.
HCO3- and base excess are elevated indicating compensation for respiratory acidosis, indicates more chronic picture.
pH being low despite chronic compensation shows an acute on chronic picture.
B is incorrect because compensation in place - chronic.
C is incorrect because if chronic with such strong compensation, pH should be better.
D and E are incorrect because HCO3- would be low for metabolic acidosis


2 most common systems in primary ciliary dyskinesia?

1. respiratory

2. otological



A disorder characterized by the presence of a higher than normal level of methemoglobin (metHb, i.e., ferric [Fe3+] rather than ferrous [Fe2+] haemoglobin) in the blood.

Methemoglobin is a form of hemoglobin that contains ferric [Fe3+] iron and has a decreased ability to bind oxygen. However, the ferric iron has an increased affinity for bound oxygen.[1] The binding of oxygen to methemoglobin results in an increased affinity of oxygen to the three other heme sites (that are still ferrous) within the same tetrameric hemoglobin unit.

This leads to an overall reduced ability of the red blood cell to release oxygen to tissues, with the associated oxygen–hemoglobin dissociation curve therefore shifted to the left.


In a 10-year-old child with neuromuscular weakness, which of the following lung function tests best evaluates the degree of respiratory muscle weakness?

A. Forced expiratory volume in 1 second (FEV1).
B. Forced vital capacity (FVC).
C. FEV1/FVC ratio.
D. Functional residual capacity.
E. Maximal mid-expiratory flow

Forced vital capacity (FVC)

• Monitoring of patients with Duchenne Muscular Dystrophy includes 6 monthly pulmonary function testing, including FVC.

• FVC predicts development of hypercapnia and survival and a combination of FVC and blood gas results can be used to monitor disease progression.


Morquio's syndrome aka mucopolysaccharidosis IV

  • Abnormal heart development
  • Abnormal skeletal development
  • Hypermobile joints
  • Large fingers
  • Knock-knees
  • Widely spaced teeth
  • Bell-shaped chest (flared ribs)
  • Compression of spinal cord
  • Enlarged heart
  • Dwarfism
  • Heart Murmur
  • below average height for certain age


Oxygen dissociation curve - left shift(high affinity for O2)

1.Temperature decrease 

2. 2.3-DPG decrease 

3.p(CO2) decrease 

4.pH (Bohr effect) increase (alkalosis) 

5.type of hemoglobin fetal hemoglobin 



Oxygen dissociation curve - Right shift(low affinity for O2)

  1. Temp - Increase
  2. 2,3 DPG - Increase
  3. p(CO2) - Increase
  4. PH -Decrease(acidosis)
  5. Hgb- Adult Hgb


The calculation of Respiratory Compliance (Crs) in infants can be undertaken using the single-breath occlusion method. When using this technique, the most appropriate method of calculating respiratory compliance is:
A. the pressure at the airway opening recorded during occlusion, divided by flow.
B. the pressure at the airway opening recorded during occlusion, divided by total exhaled volume.
C. the time constant divided by the total exhaled volume.
D. the time constant divided by the airway opening pressure recorded during occlusion.
E. the total exhaled volume divided by pressure at the airway opening recorded during occlusion.

E. the total exhaled volume divided by pressure at the airway opening recorded during occlusion.


A 16-year-old girl is referred for evaluation of daytime tiredness.   She is reported to go to bed at 1.00 a.m. and to have difficulty rising in the morning for school.  At weekends she sleeps until early afternoon.  No medical or psychiatric symptoms are detectable. In addition to gradually advancing her bedtime to an earlier time, bright light therapy is recommended.
This is most effective if undertaken at which of the following time periods?

A. Early morning.
B. Late morning.
C. Mid afternoon.
D. Evening.
E. Prior to retiring.


A. Early morning.


Phototherapy — Exposure to bright light when awakening is an effective therapy for patients whose sleep onset insomnia is due to delayed sleep phase syndrome, a condition in which the onset of sleep is delayed because the individual's sleep-wake rhythm is longer than 24 hours.

Patients undergoing phototherapy sit in front of 10,000 lux light box (or a window with sunlight) for 30 to 40 minutes upon awakening (average indoor lighting is 300 to 500 lux, average sunny summer day is 100,000 lux). In addition, they markedly reduce their exposure to bright light in the evening (eg, they may keep their shades down and indoor lights dim). A response to therapy is generally evident after two to three weeks. Indefinite treatment is frequently necessary to maintain the benefits. In less severe cases, consistent awakening at a given time in the morning, followed by physical activity with exposure to outdoor light (eg, a walk outside, sitting next to a window with the shades and curtains open), may be sufficient even on a cloudy day.

Phototherapy may also be beneficial to patients whose insomnia is due to advanced sleep phase syndrome, a condition in which the individual desires sleep early and awakens early because their sleep-wake rhythm has shifted earlier. In this situation, exposure to bright light in the evening can help delay sleep onset.




2005, part b question 12

A nine-year-old girl with cystic fibrosis presents to clinic with a cough productive of brown sputum.  Her chest X-ray is shown opposite.
The most likely diagnosis is:

A. allergic bronchopulmonary aspergillosis.
B. atypical mycobacterium infection.
C. Burkholderia cepacia infection.
D. Staphylococcus aureus infection.
E. Stenotrophomonas maltophilia infection.


A. allergic bronchopulmonary aspergillosis.