No abstract

Noninvasive alternatives to esophageal pressure (Pes) are needed to evaluate respiratory effort during sleep. Pulse transit time (PTT) is the time taken for pulse pressure to travel from the aortic valve to the periphery. PTT has been shown to be inversely correlated with blood pressure, and can reveal acute changes generated by high pleural pressure swings during pulsus paradoxus. A close relationship has been demonstrated between the increase in Pes and a progressive rise in the amplitude of PTT oscillations. The aim of the present study was to assess the accuracy of PTT for the classification of sleep respiratory events as central or obstructive. Respiratory events occurring during sleep were randomly chosen from 13 unselected male patients (mean apnea-hypopnea index [AHI] = 25.1 per hour of sleep; age = 47.3 yr, body mass index [BMI] = 27.1 kg/m2). Two observers experienced in polysomnography classified 177 events on the basis of the "gold standard method": the measurement of Pes. For 167 events about which the observers agreed, the PTT signal was analyzed visually and independently by the two observers blinded to Pes, in order to reclassify the same sleep respiratory events. The two observers were in agreement for 94.6% of the events scored visually on PTT recordings. We evaluated sensitivity (Se) (Observer 1: 94%, Observer 2: 91%), specificity (Sp) (97% and 95%, respectively), negative predictive value (NPV) (95% and 92%, respectively), and positive predictive value (PPV) (96% and 94%, respectively), of PTT with Pes as the reference. Misclassifications of respiratory episodes were usually due to artifacts or baseline variations of the PTT signal (57%), and occurred during rapid eye movement (REM) sleep (42.8%). PTT has shown a high sensitivity and specificity in differentiating obstructive and central respiratory events, and may become the reference noninvasive tool for this purpose.

Obstructive nonapneic respiratory events (ONAREs) are much more difficult to detect and classify than apneas unless sensitive measures of respiratory effort and airflow are employed. The aim of this study was to compare two measures of respiratory effort, esophageal pressure monitoring (Pes) and pulse transit time (PTT), for scoring of ONAREs by visual analysis. Nine men (age 49 +/- 10 yr) with mild to moderate sleep apnea syndrome (AHI of 25.1 +/- 10. 8/h) were studied and 340 ONAREs (hypopneas and upper airway resistance episodes) were randomly selected for scoring by two experienced observers. Each observer blindly scored each ONARE twice (once with Pes and once with PTT) with a concurrent pneumotachography trace available for airflow quantification. This permitted the respiratory events scored with PTT to be compared with those scored with Pes, and in addition interobserver variability could be assessed for each signal. Even though standard criteria were used for scoring, there was significant interobserver variability for both Pes (29.7%) and PTT (37.1%). Taking those events for which there was agreement between the observers, PTT had a sensitivity of 79.9% and a positive predictive value of 91.2% (using Pes as the gold standard). In those ONAREs for which there was agreement between the two observers there was a larger percentage reduction in airflow compared to ONAREs that did not concur (51 versus 30.3%, p < 0.001), a larger increase in respiratory effort as assessed by PTT (slope of PTT: 23.1 versus 14. 3 arbitrary units, p < 0.01), and a higher incidence in autonomic microarousals detected with PTT (90 versus 45% of ONAREs, p < 0.006). Subtle respiratory events are more difficult to detect than apneas or frank hypopneas. When comparing PTT with esophageal pressure in detecting those events the sensitivity of PTT is good but limited when the reduction in airflow, the increase in respiratory effort, or the arousal reaction is the less clear. However, PTT appears to be a good noninvasive alternative to Pes in the detection of nonapneic obstructive respiratory events, and its ability to detect autonomic arousal gives this physiological signal added clinical usefulness.

Aims of the study were 1) to compare Hudgel's hyperbolic with Rohrer's polynomial model in describing the pressure-flow relationship, 2) to use this pressure-flow relationship to describe these resistances and to evaluate the effects of sleep stages on pharyngeal resistances, and 3) to compare these resistances to the pressure-to-flow ratio (DeltaP/V). We studied 12 patients: three with upper airway resistance syndrome (UARS), four with obstructive sleep hypopnea syndrome (OSHS), three with obstructive sleep apnea syndrome (OSAS), and two with simple snoring (SS). Transpharyngeal pressures were calculated between choanae and epiglottis. Flow was measured by use of a pneumotachometer. The pressure-flow relationship was established by using nonlinear regression and was appreciated by the Pearson's square (r(2)). Mean resistance at peak pressure (Rmax) was calculated according to the hyperbolic model during stable respiration. In 78% of the cases, the value of r(2) was greater when the hyperbolic model was used. We demonstrated that Rmax was in excellent agreement with P/V. UARS patients exhibited higher awake mean Rmax than normal subjects and other subgroups and a larger increase from wakefulness to slow-wave sleep than subjects with OSAS, OSHS, and SS. Analysis of breath-by-breath changes in Rmax was also a sensitive method to detect episodes of high resistance during sleep.