Assessment of Lung function II

Question 1

Describe DICO or TICO

Answer 1

• Transfer or diffusion of CO (carbon monoxide) across the lung in a single breath manoeuvre (2 step process)
  
  • Rate of uptake of CO (ml/min) divided by the driving pressure (mm/Hg)
  • The alveolar volume (VA) – accessible lung volume seen by the gas exchange surface (participating in gas exchange)
• Total diffusing capacity of the whole lung = diffusing of the pulmonary membrane component plus capacity of the pulmonary capillary blood volume

Question 2

Describe how DICO works

Answer 2

FICKS LAW
- Diffusivity or driving pressure of the gas (the difference in partial pressure between the two sides of the tissue)
- Tissue area (volume) of lungs participating in gas exchange
- Thickness of the tissue
- Diffusion constant (D) which is proportional to the solubility and inversely proportional to the square root of MW

Pulmonary capillary volume

Integrity of capillary vascular bed

Haemogolobin concentration and reactivity

Alveolar concentration fo CO not same as inspired, as it is diluted in the air in the lungs at residual volume:
- The concentration of CO at alveoli is calculated by the amount that the inert gas diluted in the residual volume

Question 3

Describe the procedure of gas transfer techniques

Answer 3

Test performance
- Patient exhales to residual volume
- Maximal inspiration to TLC during which a volume of test gas is inhaled
- The test gas is held in the lungs for approximately 10 seconds
- A portion of exhaled air/gas mix is discarded to wash out the mechanical and anatomical dead space not associated with gas transfer
- A portion of exhaled alveolar volume is analysed to calculate the TLCO and VA

Question 4

Describe how gas transfer is interpreted

Answer 4

Comparison of TLCO against LLN and severity based on %predicted
* > 60% and < LLN : Mild gas transfer impairment
* > 40% and < 60%: Moderate
* < 40%: Severe

Consider correction for haemoglobin and Carboxyhaemoglobin

Increase in TLCO > ULN, but remember this can still be normal!

Serial Change (Trend)
- TLCO change > ± 4.78mmol/min/mmHg in 1 week is considered to be significant
- 10% change over 1 year is considered to be significant for TLCO

Question 5

Describe reasons for TlCO decrease

Answer 5

• emphysema and reduction in alveolar surface area
  
  • anemia, due to reduced haemoglobin and elevated CO-Hb
  • PE due to reduction in capillary blood volume
  • Fibrosis or pneumonitis due to increased thickness of alveolar membrane
  • Volume loss pneumonectomy or atelectasis due to reduction in alveolar membrane SA

Note: Valsalva Manoeuvre – increase in positive pressure decreases pulmonary capillary blood volume in thoracic cavity

Note 2: changes in gas composition in lung: PIO2

Question 6

Provide examples of OLD causing DLCO decrease

Answer 6

 Emphysema (decreased surface area)
 Cystic Fibrosis (increased thickness of alveolar – capillary membrane)

Question 7

Provide examples of parenchymal disease causing DLCO decrease

Answer 7

Parenchymal Lung Diseases (increased thickness of alveolar – capillary membrane)
 Interstitial lung disease
 Idiopathic
 Sarcoidosis
 Asbestosis

Question 8

List some examples of Pulmonary involvement in Systemic Diseases causing DLCO decrease

Answer 8

Pulmonary involvement in Systemic Diseases (increased thickness of alveolar – capillary membrane)
 Systemic lupus erythematosus
 Rheumatoid arthritis
 Scleroderma
 Wegener’s granulomatosis

Question 9

Describe other causes of decreased DLCO

Answer 9

Anaemia

But also,

Cardiovascular diseases
 Acute and recurrent pulmonary thromboembolism (decreased perfusion surface area)
 Pulmonary oedema (increased thickness of alveolar-capillary membrane)
 Pulmonary Hypertension (decreased capillary volume)

Lung resection
- Pneumonectomy (decreased surface area)

Other
 Cigarette smoking prior to testing
 Marijuana
 Pregnancy
 Oxygen supplementation
 Valsalva manoeuvre

Question 10

Describe cases of DLCO increase

Answer 10

Increases occur in
* Low PIO2 due to altitude: due to changes in gas composition in lung
* Exercise, redistribution of blood flow due to pneumonectomy, Mueller manoeuvre: due to increase in capillary blood flow
* Impaired gas exchange: due to polycytehamia
* Pulmonary haemorrhage: blood in alveolar spaces
* Supine Posture

Question 11

Descrube exercise testing

Answer 11

6 Minute Walk Test
 Measure of overall physical functioning and prognosis
 Measures walk distance, oximetry & dyspnoea perception
 Responsive to change
 Less technical equipment needed
 Standards needed to minimise variability

Question 12

Describe the clinical utility of 6MWT

Answer 12

Clinical Utility in pre and post treatment including:
 Lung transplantation
 Lung resection
 Lung volume reduction surgery
 Pulmonary rehabilitation in COPD and Congestive Heart failure
 Therapeutic response for Pulmonary Arterial Hypertension

Question 13

Describe cardio-pulmonary tests

Answer 13

A test of integrated function under stressful conditions using increasing workload
- Measures:
- Ventilatory parameters
- Cardiac parameters including ECG
- Metabolic parameters

Determine underlying course of dyspnoea or reduced exercise tolerance; e.g. lungs, heart, vascular, perception
- Can be used to monitor treatment
- Resource intensive (As compared to 6MWT)