Respiratory inductance plethysmography for the diagnosis of dysfunctional breathing in patients with severe asthma

Abstract

Rationale A pilot study of Respiratory Inductance Plethysmography (RIP) to diagnose disordered breathing in difficult asthma patients. Methods Six clinically stable patients attending the severe asthma clinic and 3 healthy volunteers were selected. In addition to their asthma diagnosis, 2 were known to hyperventilate, 2 to have thoraco-abdominal asynchrony (TAA) and 2 were not suspected to have any disordered breathing. Each was monitored with fixed volume calibrated RIP (Vivometrics inc) and were left in the sitting position for approximately one hour. Raw traces were selected for a period of quiet tidal breathing (QTB) and minimal motion artefact and then analyzed with the Vivologic system. Hyperventilation was assessed by calculating respiratory rate and minute volume. TAA was indicated by the phase angle of the rib cage and abdominal excursion plot. Results Compared to healthy volunteers patients with hyperventilation had higher mean minute volume (13.1 vs 9.2 lmin -1) and respiratory rate (19 vs 28 bpm) as expected. All study patients had markedly raised mean phase angles. Patients with TAA were greatest (41 o,54 o) compared to healthy volunteers (7 o,7 o,18 o), historical COPD controls (mean 32 o) and severe asthmatics not suspected of disordered breathing (21 o,25 o). Hyperventilation and TAA were seen in all patient groups whether suspected or not. Conclusions TAA exists in severe asthma as in other previously documented obstructive lung diseases. Hyperventilation and TAA can co-exist in the same patients and worsen the severity of TAA. RIP is a novel and suitable tool to detect disordered breathing in severe asthma.