Ultrasound Imaging for the Examination of Diaphragm Thickness in Females With Breathing Pattern Disorders

Abstract

This research examined diaphragm thickness and diaphragm thickening fraction, using ultrasound imaging (USI), in females with breathing pattern disorders (BPD) and healthy female controls. The diaphragm is the key muscle of respiration, and people with BPD present with breathing that has increased accessory, chest and neck muscles use and decreased use of the diaphragm, and diaphragm wasting is hypothesised to occur over time. Establishing a clear diagnosis of BPD is difficult and USI has been proposed as a useful tool in respiratory physiotherapy for measurement of diaphragm morphology. The primary aim of this study was to answer the question: ‘Does diaphragm thickness at tidal exhalation, as measured by USI, differ in females with BPD, when compared with healthy controls?’ A female BPD group (n=19) and female control group (n=18) with normal body mass index (BMI) were recruited in an outpatient setting. A second cohort of females (BPD group n=6, female control group n= 4) was recruited with an elevated BMI (BMI+). The inclusion criteria for the BPD group consisted of: elevated Nijmegen Questionnaire (NQ) score, elevated respiratory rate, dominant apical breathing pattern on the Hi-Lo test, and poor breath hold time. Diaphragm thickness was assessed by ultrasound imaging. Diaphragm thickness was measured at four points during the breathing cycle: tidal exhalation (Tvex), tidal inhalation (Tvin), maximum inhalation (Tmax), and exhalation to residual volume (Tmin). The diaphragm thickening fraction (TF) was then calculated by the formula TF = (Tmax – Tvex) / Tvex. Results indicated significant differences in the primary measure of diaphragm thickness between the BPD and control groups at Tvex on the left side (BPD 1.583±0.341 mm, n=19; control 2.003±0.584, n=18; p=0.011) and on the right side (BPD 1.650±0.369, n=19; control 2.013±0.617, n=18; p=0.032). Other variables showed statistical significance for diaphragm thickness at Tvin, Tmax and TF on the left side, and at Tvin on the right side (p<0.05). Parametric statistical testing was unable to be performed due to inadequate sample size in the BMI+ groups. A trend of paradoxical diaphragm thickening was observed in both the BPD and BPD BMI+ groups from the Tvex to Tmin measurements on both the left and right sides. These findings suggest that in females with a healthy BMI, diaphragm thickness is reduced in females with BPD compared with controls. USI is useful to quantify diaphragm atrophy in females with BPD, and future research in BPD should be directed towards replicating these results in a male BPD population, and in a BPD population with a >25kg/m2 BMI sample. Based on these findings, patients with BPD should be assessed with USI to allow for identification of diaphragm atrophy, and treatment should focus on improving the morphology of the diaphragm with strengthening exercises.