Can Diaphragmatic Hernia Cause FEV1 Decline on PFT?
Yes, diaphragmatic hernia can cause a decline in FEV1 on pulmonary function testing, primarily through restrictive physiology that reduces lung volumes, though the pattern typically shows reduced FVC with a preserved or elevated FEV1/FVC ratio rather than isolated FEV1 decline. 1
Mechanism of Pulmonary Impairment
Diaphragmatic hernias cause a 25-50% decrease in pulmonary function due to herniation of abdominal contents into the thoracic cavity, which compresses lung tissue and restricts lung expansion 1
The primary physiological pattern is restrictive, characterized by reduced total lung capacity (TLC) below the 5th percentile with a normal or elevated FEV1/FVC ratio, not isolated obstructive disease 1
Both FEV1 and FVC decline proportionally in restrictive disease, so while FEV1 does decrease, the FEV1/FVC ratio remains normal (>0.70) or is actually increased (>0.85-0.90) 1
Clinical Evidence in Diaphragmatic Hernia Populations
In children and adolescents with congenital diaphragmatic hernia (CDH), mean FEV1 z-scores are significantly reduced (-2.21±1.68, below normal range), and FVC z-scores are also reduced (-1.32±1.39) 2
The degree of FEV1 impairment correlates with severity markers including need for patch closure, ECMO, pulmonary vasodilators, and duration of mechanical ventilation 3
Pulmonary function abnormalities persist throughout the first 3 years of life in CDH survivors, with forced expiratory flows remaining below normal despite total lung capacity being normal 3
Distinguishing the Pattern from Obstructive Disease
Critical pitfall: A reduced FEV1 alone does not indicate obstruction—you must evaluate the FEV1/FVC ratio first 1, 4
In diaphragmatic hernia, expect both FEV1 and FVC to be reduced proportionally with FEV1/FVC ratio preserved or elevated, indicating restriction rather than obstruction 1
True restrictive defects require TLC measurement below the 5th percentile for confirmation, as reduced VC alone has poor positive predictive value for restriction (associated with low TLC only 50% of the time) 1
Respiratory Symptoms and Functional Impact
Patients with diaphragmatic hernia commonly present with dyspnea (86% in traumatic cases) and respiratory symptoms (58% in Morgagni hernia cases) that correlate with the degree of lung compression 1, 5
The herniation creates both circulatory and respiratory effects, with the mechanical compression being the primary driver of reduced lung volumes 1
Gastrointestinal symptoms (pain, obstruction, reflux) often coexist with respiratory complaints in symptomatic diaphragmatic hernias 1, 5
Diagnostic Approach When Suspecting Diaphragmatic Hernia
In patients without trauma history presenting with respiratory symptoms, chest X-ray (anteroposterior and lateral) is the recommended first diagnostic study 1
For stable patients with suspected diaphragmatic hernia and non-specific symptoms, CT scan with contrast enhancement of chest and abdomen is recommended for definitive diagnosis 1
When PFTs show reduced FEV1 and FVC with preserved ratio, measure TLC to confirm restriction and consider imaging to evaluate for space-occupying thoracic pathology like diaphragmatic hernia 1
Severity Grading and Prognosis
Using the European Respiratory Society classification, FEV1 percent predicted grades severity: mild (≥70%), moderate (60-69%), moderately severe (50-59%), severe (35-49%), and very severe (<35%) 4
However, FEV1 may not correlate well with symptoms in individual patients with diaphragmatic hernia, as mechanical compression effects vary 1
The degree of pulmonary hypoplasia and intensity of neonatal therapies in congenital cases predict long-term lung function impairment 3