Ruhle and colleagues suggested in a recent review that upper airway impedance measurements using the forced oscillation technique may be useful as a surrogate of Pes in the diagnosis of UARS. With this technique, an airflow of 2 L/min is applied to a conventional nCPAP mask at an oscillatory frequency of 20 Hz. The researchers studied 25 nono-bese patients with EDS and a mean RDI of 3.4, Although the majority of arousals could not be explained on the basis of standard polysomnographic measurements, this technique showed IUAR in over half of these unexplained events. These authors also suggested that the pulse transit time (the time between the ECG R wave and the fingertip pulse shock wave) correlated with subtle changes in both the Pes and the arousals Reading here asthma medications inhalers. They also discussed changes in BP as a marker of IUAR because more negative intrathoracic pressure would decrease BP and arousal would increase BP.
With the inclusion of frontal leads, O’Malley and colleagues demonstrated an improved detection of EEG arousals in five UARS patients and five CPAP-treated OSAS patients. Using 1992 ASDA criteria, brief arousals in the central and occipital leads were noted to accompany 73% of the respiratory events defined as an airflow reduction of > 50% for > 10 s or a flattening of the inspiratory flow tracing (suggesting flow limitation). Of the remaining respiratory events, 22% were associated with arousal seen only in the frontal leads, suggesting that unexplained daytime symptoms in UARS or treated OSAS may be accounted for by the detection of previously unexplained arousals.
Although patterns of snoring, arousals, airflow by thermistry, and abdominal/thoracic plethysmography from conventional polysomnography may, at times, suggest the diagnosis of UARS, they are by no means definitive or confirmatory measurements. Some of the newer, more technically advanced measurement techniques reviewed hold promise as reliable, non-invasive modalities for UARS diagnosis, but testing in larger populations is required to compare these advancements with standard diagnostic methods.