Association between distance-saturation product and clinical parameters in primary ciliary dyskinesia

<bold>Background:</bold> Distance-saturation product (DSP) is an indicator that predicts mortality in chronic lung diseases. It is determined as the product of the six-minute walk test (6MWT) distance and the lowest oxygen saturation (SpO₂) observed during the 6MWT. The associations between DSP and clinical parameters in primary ciliary dyskinesia (PCD) remain unknown. <bold>Objective:</bold> To investigate the associations between DSP and respiratory muscle strength, lung function, and sputum and cough severity in children with PCD. <bold>Methods:</bold> Twenty-three children with PCD (mean age=13.2±3.0 years) underwent a set of assessments, including lung function, maximal inspiratory and expiratory pressure, and the 6MWT. The SpO₂ was measured before, after, and during the 6MWT. Sputum and cough severity were assessed using the Visual Analog Scale (VAS). <bold>Results:</bold> The mean DSP was 534.5±63.8 m%, the 6MWT distance was 588.7±68.7 m, and the lowest SpO₂ during 6MWT was 90.8±3.6%. The DSP was associated with FEV₁ (r=0.418), FVC (r=0.440), FEV₁/FVC (r=0.480), PEF (r=0.683), FEF25-75% (r=0.565), maximal expiratory pressure (r=0.533), and sputum severity (r=-0.499, p<0.05). Maximal expiratory pressure (β=0.565, variance inflation factor [VIF]=1.003), sputum severity (β=-0.417, VIF=1.049), and FEV₁/FVC (β=0.423, VIF=1.052) were found to be independent predictors of DSP (R²=0.712, F_(3-19)=15.667, p<0.001). <bold>Conclusions:</bold> The DSP correlates with maximal expiratory pressure, lung function, and sputum severity in children with PCD. As a practical measure, the DSP can contribute to the understanding of the disease impact and prognosis of PCD.