From the Guidelines
When FVC and FEV1 are more than 2 standard deviations above predicted z-scores but Peak Inspiratory Flow (PIF) is low, this suggests an upper airway obstruction rather than a problem with the lung tissue itself, and thus, a full pulmonary function test with flow-volume loops and direct visualization of the upper airway via laryngoscopy during inspiration are essential for diagnosis and treatment planning. This pattern is indicative of normal or above-normal lung capacity with a specific limitation in inspiratory airflow. The most common causes include vocal cord dysfunction, laryngeal stenosis, tracheal stenosis, or other forms of extrathoracic airway obstruction 1.
For evaluation, a full pulmonary function test with flow-volume loops is recommended, as it can show the characteristic flattening of the inspiratory limb, which is crucial for diagnosing upper airway obstruction. Direct visualization of the upper airway via laryngoscopy during inspiration is also essential to identify structural abnormalities or paradoxical vocal cord movement. The standardization of spirometry, as outlined in the European Respiratory Journal 1, should be followed to ensure accurate and reliable results.
Treatment depends on the underlying cause - vocal cord dysfunction may respond to speech therapy techniques, while structural obstructions might require surgical intervention. Inhaled bronchodilators typically won't help since the issue isn't in the lower airways. If symptoms are severe, consultation with both pulmonology and otolaryngology specialists is warranted. The discrepancy between excellent expiratory measures and poor inspiratory flow occurs because expiration is largely passive and depends on elastic recoil, while inspiration requires active muscle contraction to overcome any upper airway resistance.
Key considerations in the management of this condition include:
- Accurate diagnosis through pulmonary function tests and laryngoscopy
- Identification of the underlying cause of the upper airway obstruction
- Appropriate treatment, which may include speech therapy, surgical intervention, or other modalities
- Collaboration with specialists in pulmonology and otolaryngology to ensure comprehensive care.
From the Research
FVC and FEV1 More Than 2 SD Above Predicted Z-Score But Low PIF
- The provided studies do not directly address the scenario of FVC and FEV1 being more than 2 SD above the predicted z-score but with low PIF 2, 3, 4, 5, 6.
- However, some studies discuss the effects of inspiratory muscle training on pulmonary functions, which may be relevant to understanding the relationship between FVC, FEV1, and PIF:
- A study on sedentary hemodialysis patients found significant improvement in FVC%, FEV1%, and PEF% after 12 weeks of inspiratory muscle training 2.
- Another study on critically ill adults found that inspiratory muscle training improved maximal inspiratory pressure and maximal expiratory pressure, and was associated with a shorter duration of ventilation and weaning 3.
- The studies also discuss the effects of different training programs on lung functions in patients with various conditions, such as Parkinson's disease 5 and chronic obstructive pulmonary disease (COPD) 4.
- Additionally, a study on the general population found that the odds for any respiratory symptom decreased with higher FEV1/FVC ratios, reaching a minimum around 0.80-0.85 6.
- There is no direct evidence to explain the specific scenario of FVC and FEV1 being more than 2 SD above the predicted z-score but with low PIF, and further research would be needed to understand this phenomenon.