Wednesday, May 17, 2017

Flow volume loop notes and mnemonics

Here are my notes on the flow volume loops!
(Video on this topic here)

Obstructive lung disease
Flow volume loop: TLC and RV increased - Flow volume loop shifts towards left. Concave upward or "scooped-out," or "coved" pattern on the expiratory portion.
Pathophysiology: Characterized by airway obstruction, resulting in air trapping in the lungs.There is an increased compliance due to the loss of alveolar and elastic tissue.
Seen in:
Chronic bronchitis

Restrictive lung diseases
Flow volume loop: Decrease in vital capacity, shift to the right.
Pathophysiology: Characterized by restriction of lung expansion. Reduced compliance - Lungs become fibrotic, lose their distensibility and become stiffer.
Seen in:
Pulmonary fibrosis

Variable extrathoracic obstruction
Flow volume loop: Flattening of maximal inspiratory curve is seen.
Pathophysiology: During thoracic expansion with inspiration, the combination of atmospheric extraluminal pressure and negative (subatmospheric) intraluminal pressure results in decreased luminal size of the extrathoracic portion of the upper airway, thus accentuating the effect of any obstructive lesion in this region.
Seen in:
Laryngomalacia and tracheomalacia of the extrathoracic trachea
Structural or functional vocal cord abnormalities

Variable intrathoracic obstruction
Flow volume loop: Flattening of maximal expiratory curve is seen.
Pathophysiology: The pleural pressure surrounding the intrathoracic trachea is negative relative to the intratracheal pressure during inspiration, thereby producing no restraint to inspiratory airflow. In contrast, flow limitation is encountered during forced expiration, when the pleural pressure becomes positive relative to airway pressure, and the effect of any obstructive lesion in this region is accentuated
Seen in:
Tracheomalacia of the intrathoracic airway
Bronchogenic cysts
Tracheal lesions (often malignant)

Fixed upper airway obstruction 
Flow volume loop: Flattening of both limbs of the flow-volume loop.
Pathophysiology:  Firm tracheal lesions limit the modulating effect of transmural pressures on airway luminal diameter.
Seen in:
Tracheal stenosis (as from prolonged intubation)
Goiter compressing the trachea
Laryngeal edema (anaphylaxis)

That's all!

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