Week 5/6 - A -Restrictive lung disease - Definitions, L.F.Ts (Spirometry, Lung volumes, D.L.C.O), V/Q mismatch, Cor pulmonale Flashcards
What is the normal FEV1, FVC and forced expiratory ratio (FEV1/FVC)?
* Normal FEV1 (forced expiratory volume in 1 second) >80% predicted * Normal FVC (forced vital capacity -total volume exhaled) >80% predicted Normal FEV1/FVC (forced expiratory ratio) >70%
Explain the results of an obstructive spirometry test result and why it occurs State which diseases would cause an obstructive spirometry result
Obstructive lung diseases cause - because of damage to the lungs are narrowing of the airways, exhaled air comes out slower. FEV1 <80%, FVC normal/low FEV1/FVC <70% (inability to exhale 70% of vital capacity in one second) Diseases - asthma, COPD, bornchiectasis, CF
Explain the results of a restrictive spirometry test result and why it occurs State which diseases would cause an restrictive spirometry result
Restrictive lung diseases restrict the lung from fully expanding and therefore the vital capacity of the lung is reduced Both FEV1 and FVC are reduced ( 70% Diseases - Interstitial lung diseases or external diseases restricting the lung (eg pleural effusion or kyphoscoliosis)
Lung function tests are a useful way in distinguishing between obstructive and restrictive lung disease - includes spirometry ( been discussed), peak expiratory flow, lung volumes, diffusion capacity of the lungs for carbon monoxide etc What is the difference in lung volume measurements in obstructive and restrictive lung disease?
Total lung capacity may be normal or increased in obstructive lung disease (ie emphysema where alveolar walls are destroyed and therefore no elastic recoil) Residual volume (total volume of air left after maximal expiration) may also be normal or increased in obstructive lung disease Both total lung capacity and residual volume are decreased in restrictive lung diseases
As said restrictive lung diseases can be intrinsic or extrinsic Intrinsic is disease of the lung itself Extrinsic is diseases that essentially compress the lung ie obestiy, pleural effusion etc How do interstitial lung diseases affect the lung?
Th intersitial lung diseases affect the lung intersitium (tissue and space around the alveoli) causing various degrees of fibrosis or inflamamtion They also cause alveolar inflammation - can cause oedema, haemorrhage or infection
When intrinsic disease affect the alveolar walls/lumen, how does this impair gas exchange? Which type of respiratory failure does this lead to?
Diseases affecting the alveolar walls/lumen cause a ventilation/perfusion mismatch - in interstitial lung diseases, the inflamed alveoli are not adequately ventilated as their is a barrier to O2 meaning patient becomes hypoxaemic CO2 exhange unimpaired as it readily diffuses and is exhaled Leads to Type 1 resp failure - low O2, normal CO2
DLCO (diffusion capacity of the lungs for carbon monoxide (CO)) is the extent to which oxygen passes from the air sacs of the lungs into the blood. What does this test rely on the measurement of?
DLCO (diffusing capacity) - involves measuring the difference in partial pressure of inspired and expired carbon monoxide - It relies on the strong affinity and large absorption capacity of red blood cells for carbon monoxide
What conditions would affect the diffusing capacity of the lungs for carbon monoxide (increase or decrease)?
DLCO is decreased in any condition which affects the effective alveolar surface area - ie interstital lung disease or emphysema DLCO is increased if there is an increased red blood cell supply to the lungs - eg in polycythaemia or alveolar haemorrhage
What is useful for monitoring treatment response in interstitial lung disease?
DCLO is useful for monitoring treatment response in ILD (it is more sensitive than FVC)
Extrinsic diseases can also cause a restrictive defect in the lungs Name some conditions?
Thoracic/extrathoracic - eg obestiy, kyphoscoliosis, ascites Neuromuscular diseases - eg motor neurones and myasthenia gravis Pleural diseases - diffuse pleura; thickening, mesothelioma, large pleural effusions
Hypoventilation means impaired alveolar ventilation which means a rise in paCO2 and reduced paO2 What two conditions reduce the chest wall compliance (ability of the chest wall to expand) leading to a reduced tidal volume?
Obesity and kyphoscoliosis are two extrinsic restrictive lung diseases which reduce the chest wall compliance - Can lead to a reduced tidal volume as lungs cannot expand fully
How can the low blood oxygen level seen in obesity hypoventilation syndrome/obstructive sleep apnoea lead to cor pulmonale? (this question tbf applies to any restrictive lung disease - intrinsic or extrinsic, can also apply to eg COPD)
The low blood oxygen level will lead to physiological constriction of the pulmonary arteries to correct the ventilation -perfusion mismatch This puts excessive strain on the right side of the heart to pump blood through the lungs - the right heart failure caused by chronic pulmonary arterial hypertension is known as cor pulmonale
What conditions can cause cor pulmonale?
Caused by Lung disease - COPD, pulmonary fibrosis, pulmonary emboli Neuromuscular diseases - affecting inspirtory muscles Obesity and kyphoscoliosis - reduce chest wall compliance These can all affect the ventilation/perfusion of the lung - a V/Q mismatch can cause pulmonary hypertension leading to cor pulmnale
What are the symptoms of cor pulmonale - the right sided heart failure due to chronic pulmonary arterial hypertension?
Symptoms include Shortness of breath Fatigue Cyanosis Raised JVP Ascites Leg oedema RVH
Therapy for interstitial lung diseases can be * medical therapy (treating the inflammation/fibrosis/neuromuscular disease) * surgical therapy * supportive therapy - eg for OSA Also remove any trigger factor, and weight loss * What medical therapies can be given for inflamamtion, fibrosis? * When is surgical therapy used? * What can be used for OSA?
Inflammation - steroids and/or azathioprine Surgical therapy - used for eg * corrective spinal surgery * Pulmonary fibrosis (lung transplant) * OSA - LOSE WEIGHT, CPAP (continous positive airway pressure) - keeps airway open at night
