Single Lung Function Test Finds Hyperinflation in CF Children

Patricia Inácio, PhD avatar

by Patricia Inácio, PhD |

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Hyperinflation test


Functional residual capacity (FRC), a measure of the volume of air left in the lungs at the end of a normal exhalation, may help detect lung disease in children diagnosed with cystic fibrosis (CF) via newborn screening, a study suggests.

Also, a cut-off value of 36 breaths per minute may help identify children with hyperinflated lungs, which occurs when the lungs are overinflated due to trapped air.

The study, “Hyperinflation is associated with increased respiratory rate and is a more sensitive measure of cystic fibrosis lung disease during infancy compared to forced expiratory measures,” was published in the journal Pediatric Pulmonology.

Even with the availability of newborn screening, measures of lung function in children are key for prompt treatment intervention and to slow disease progression.

However, assessing lung function in infants is challenging because current methods, such as chest CT scans, require sedation and expose the child to radiation.

FRC has been used in this patient population, but limited data exist in infants diagnosed via newborn screening.

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In this study, a group of researchers at Indiana University School of Medicine and colleagues measured FRC and compared it to other lung tests in children diagnosed with CF as newborns.

They analyzed two sets of data from a total of 45 children, collected retrospectively (35 patients) and prospectively — meaning collected over time — (10 patients).

The retrospective data were from 23 infants who underwent a lung function test while hospitalized at the Riley Hospital for Children in Indianapolis (data collected from 2012 to 2018); and from 12 children who underwent the tests as part of two clinical trials assessing the impact of early viral infections in CF (NCT01973192 and NCT04026360).

The prospective data came from 10 children recruited to perform the lung tests at the CF Center at Riley.

Lung tests included forced vital capacity (FVC), forced expiratory volume in 0.5 seconds (FEV0.5), forced expiratory flow (FEF), and FRC.

FVC measures the amount of air that can be forcibly exhaled from the lungs after taking the deepest breath possible. FEV0.5 refers to how much air can be exhaled in half a second after a deep inhaled breath. FEF assesses the flow of air coming out of the lung during the middle portion of a forced expiration (exhalation). FEF was measured by the rapid thoracoabdominal technique, during which pressure is applied at the thorax and abdomen at the end of a normal inspiration (inhalation).

Results showed that the FEV0.5 and FEF scores were within the normal limits, while the mean FVC score was reduced, indicative of worsening lung function.

The FRC score was 2.18, which according to the researchers’ criteria (FRC score above 2), was indicative of hyperinflated lungs. Hyperinflation was seen in 44% of the children and was significantly higher in children with a diminished FEV0.5.

Also, the mean respiratory rate (RR) — the number of breaths taken per minute — was elevated in these children and showed a positive correlation with the FRC scores.

The researchers found that a cut-off RR of 36 breaths per minute was indicative of hyperinflation with a 92% sensitivity and 32% specificity. Notably, a test’s sensitivity is its ability to correctly identify those with a given condition, while specificity refers to correctly identifying those without it.

Overall, these findings suggest that “FRC is a more sensitive measure of early CF lung disease and that measurement of RR may be a simple, noninvasive clinical marker to identify CF [newborn screening] infants with hyperinflation,” the scientists concluded.

As to study limitations, they mentioned the relatively small size of the group and that this was a single-center study, which may limit generalizing the results.

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