Aims Pulse oximetry is widely used to identify children with OSA but lacks sensitivity compared to polysomnography. Previous studies have shown the utility of pulse transit time (PTT) at detecting arousals in children with OSA but values likely to be indicative of disease have not been established.1 PTT is the time taken for the pulse pressure wave to travel from the aortic valve to the periphery and is a non-invasive marker of blood pressure. It provides a quantitative measurement of inspiratory effort in patients with sleep-related breathing disorders. We aim to investigate if a correlation exists between PTT indices (PTT arousals, respiratory swing) and oximetry results to ascertain its usefulness or otherwise in the assessment of children with suspected OSA.
Methods A retrospective review was carried out of 176 paediatric inpatient sleep studies undertaken at a district general hospital between Dec 2013–Dec 2014. Data were obtained from a database and patient notes. Sleep studies were carried out using VISILAB equipment incorporating ECG, audio, video, PTT and oximetry. Statistical analysis was performed using an unpaired, 1-tailed students t test.
Results Our data showed an upward trend in average PTT arousals when OSA severity was determined using pulse oximetry or by sleep study based diagnosis. Positive studies had an average PTT over 49/hour (Figures 1 and 3). This upward trend is also the case for respiratory swing (Figure 2), with positive studies having a mean respiratory swing over 24 ms. There is a highly significant difference in mean PTT and respiratory swing between normal/borderline and abnormal oximetry categories (p = < 0.005 for both) and between normal (including primary snoring) and abnormal sleep study categories (p = < 0.005 for both). However, the trends are not discriminatory enough to be used as stand-alone measurements of degree of OSA as there is significant overlap between the categories (p values = > 0.05).
Conclusion PTT is not sufficiently discriminatory if used in isolation for assessment of OSA in children, but is a useful addition when combined with pulse oximetry and other parameters.
Katz ES, Lutz J, Black C, Marcus CL. Pulse transit time as a measure of arousal and respiratory effort in children with sleep-disordered breathing. Pediatr Res. 2003;53:580–588
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