How Do PFTs and Dynamic CT Diagnose Airway Disease in RP?

When relapsing polychondritis (RP) affects your respiratory system, it can cause your airways to narrow or collapse. Doctors use two main tests—pulmonary function tests (PFTs) and dynamic computed tomography (CT) scans—to help suggest how and where your airways are affected. PFTs measure the physical flow of air in and out of your lungs, providing functional clues about airway obstruction ^[1]. Dynamic or expiratory CT scans provide a structural picture, capturing images of your airways while you actively breathe in and out to reveal exactly where the airway may be closing ^[2]. Together with your symptoms, these tests help your care team determine if you have fixed stenosis (narrowing that does not change as you breathe) or dynamic airway collapse, guiding individualized decisions about your care ^[3][4].

Urgent Safety Warning: If you experience rapidly worsening shortness of breath, stridor (a high-pitched whistling sound when breathing), blue or gray lips, fainting, inability to speak in full sentences, or severe respiratory distress, seek immediate emergency medical care. Do not wait for outpatient testing or a scheduled specialist appointment.

Pulmonary Function Tests: Measuring Your Airflow

PFTs involve blowing forcefully into a machine (a spirometer) that measures your lung capacity and airflow. In RP, these tests look for airflow limitation ^[5]. Doctors evaluate measures like your FEV1 (forced expiratory volume, or how much air you can forcefully exhale in one second), FVC (forced vital capacity, the total amount of air you can blow out), and your peak expiratory flow (the maximum speed of your exhale) ^[5][3].

PFTs may include testing your response to an asthma inhaler (a bronchodilator). The airway obstruction in RP often shows minimal or no improvement with inhalers, which can provide a clue that the issue stems from damaged cartilage rather than typical asthma ^[3]. However, this is not a definitive rule—some asthma patients do not show a response on a given test, and you can have both asthma and RP airway involvement.

Flow-Volume Loops: Fixed Narrowing vs. Collapse

The spirometer generates a graph called a flow-volume loop, plotting the speed of your breath against the volume of air. The shape of this loop can suggest different types of airway issues:

• Fixed Narrowing (Stenosis): If the airway is narrowed due to scarring, it restricts air evenly across the breathing cycle. The flow-volume loop may look flattened or truncated on both the top (exhaling) and bottom (inhaling) curves ^[6]. Note that “fixed” means relatively unchanged as you breathe, not necessarily untreatable.
• Dynamic Expiratory Airway Collapse: If RP has destroyed the stiff cartilage rings (tracheobronchomalacia), the airway becomes floppy. It might cave inward when you forcefully push air out, often showing up as a smooth flattening only on the expiratory curve ^[6][7].

It is important to know that flow-volume loops are highly effort-dependent and are considered a screening clue rather than a stand-alone diagnosis ^[8]. A normal or non-specific loop does not rule out significant airway disease.

CT Scans: Seeing the Airway in Motion

A standard CT scan takes images while you hold your breath (full inspiration). This gives an excellent structural view, showing if the walls of your trachea are thickened or calcified ^[2][9]. However, an inspiratory CT can look completely normal even if your airway collapses when you exhale.

Why Expiratory Views Matter

Because of this limitation, doctors often use additional CT techniques—such as a static end-expiratory breath-hold or a dynamic/cine CT that captures continuous motion as you forcefully exhale ^[2].

By comparing the airway’s size when breathing in versus breathing out, doctors can identify collapse ^[1]. A large reduction in airway size during exhalation may indicate cartilage malacia, though it must be carefully distinguished by specialists from normal physiology or excessive collapse of the airway’s posterior wall ^[4]. Because airway damage can happen before you develop noticeable breathing symptoms, some expert centers recommend expiratory or dynamic imaging at diagnosis and during follow-up, though repeat imaging is always tailored to balance clinical need and radiation exposure ^[10][2].

What These Tests Cannot Tell Us

While PFTs and dynamic CTs provide vital pieces of the puzzle, they have limitations:

• They don’t prove active inflammation: Thickened airway walls on a CT scan are non-specific; they can reflect active edema, chronic inflammation, or old scar tissue. Tests cannot definitively determine if inflammation is currently active on their own ^[4][11]. Airway cartilage destruction can also continue to progress even if wall thickening appears to improve on a scan ^[4].
• They don’t show the inside surface: CT scans cannot see if the inside lining of the airway is red, swollen, or bleeding. That requires a bronchoscopy, where a camera is passed into the lungs ^[12].

How Results Guide Your Care

Treatment for RP airway disease depends on combining these test results with your full clinical picture, symptoms, and physical exams:

• Medical Treatment: If the combined evidence suggests active RP inflammation, your doctor may recommend systemic corticosteroids or immunosuppressants ^[13]. In severe cases, biologic therapies (advanced medications targeting specific parts of the immune system) may be used, though these are individualized options directed by specialists ^[14].
• Airway Interventions: If tests reveal severe dynamic collapse or fixed stenosis, medications alone might not be enough ^[4]. You may be referred to a tertiary airway center—a specialized multidisciplinary team. They might suggest non-invasive support like a CPAP machine to help splint the airway open, though this does not treat the underlying inflammation ^[15]. Endoscopic or surgical options like balloon dilation or airway stents (tubes placed to hold the airway open) can improve breathing but carry meaningful risks, including mucus plugging, stent migration, infection, or the need for repeat procedures ^[16][14].
• Procedural Safety: Interventions like bronchoscopy allow doctors to directly visualize and treat the airway, but they carry risks, especially in severe RP. For instance, a severely reduced FVC percentage (low lung capacity) on your PFTs is a recognized risk factor for complications ^[17]. Your interventional pulmonology and anesthesia teams will use your PFT and CT results to evaluate your specific anatomy and gas exchange, creating a highly individualized safety and rescue plan before attempting any procedure ^[17].