Predictive value of sleep apnea screenings in cardiac surgery patients.

INTRODUCTION: Obstructive sleep apnea (OSA) is a highly prevalent disorder associated with increased cardiovascular risks. We explored the predictive value of OSA screening instruments in cardiac disease patients awaiting cardiac surgery. METHODS: In this prospective cohort, 107 participants awaiting cardiac surgery from Cleveland Clinic and Johns Hopkins underwent polysomnography after completing Epworth Sleepiness Scale (ESS), Sleep Apnea/Sleep Disorder Questionnaire (SA/SDQ), STOP, STOPBAG2 and Berlin questionnaires. Score comparisons between groups based on apnea-hypopnea index (AHI) ≥15 were performed. Logistic regression with receiver operating characteristic (ROC) analysis was used to investigate optimal threshold. RESULTS: Prevalence of OSA (AHI ≥5) was 71.9% (77/107) and 51 (47.7%) had moderate-to-severe disease (AHI ≥15). Participants were primarily male (57%) and Caucasian (76.6%). Mean age was 67.3 ± 13.3 years and BMI was 26.5 ± 6.6. Of the five screening tools, STOPBAG2 with a cut-point of 0.381 provided 78% sensitivity and 38% specificity (AUC 0.66, 95%CI 0.55-0.77). SA/SDQ yielded a cut-point of 32 for all subjects (AUC: 0.62, 95%CI 0.51-0.73) with sensitivity and specificity of 60% and 62% respectively, while STOP score ≥2 provided sensitivity and specificity of 67% and 52% respectively (AUC: 0.61, 95%CI 0.51-0.72). Among STOP items, "observed apnea" had the strongest correlation with AHI ≥15 (OR 3.67, 95%CI 1.57-8.54, p = 0.003). The ESS and Berlin were not useful in identifying moderate-to-severe OSA. CONCLUSION: Common screening tools had suboptimal performance in cardiac surgery patients. STOPBAG2 was better at predicting the probability of moderate-to-severe OSA in patients undergoing cardiac surgery compared to ESS, SA/SDQ, STOP and Berlin questionnaires.

An implantable impedance pneumograph monitor for detection of diaphragm contraction and airway obstruction during diaphragm pacing.

Impedance pneumography signals were characterised during diaphragm pacing using stimulating and recording electrodes placed on the abdominal surface of the diaphragm. These measurements were useful for the detection of muscle contraction without confounding effects from stimulus artifacts. Impedance pneumography signals were measured using 23 epimysial electrodes implanted in seven dogs with 1-5 experiments on each electrode. The polarity of the change in impedance associated with diaphragm pacing differed for each recording electrode and its configuration. Thirty-four of 57 cases produced increased impedance, 11 produced decreased impedance and the remaining 12 depended on the level of diaphragm activation. Impedance pneumography signals were useful for detecting complete airway obstruction. The mean difference between the impedance measured during open and obstructed airway conditions was 80% of the open airway impedance signal. The difference between open and obstructed airway impedance measurements was a mean of 2.3 times larger with a recording electrode on the same hemidiaphragm as the stimulating electrode, compared to an electrode placed on the opposite hemidiaphragm (p < 0.05, paired t test, four dogs). In addition, the differences between open and completely obstructed airways were a mean of 2.8 times larger when the second recording electrode was placed on the thorax at the fifth intercostal space, compared to the ninth intercostal space (p < 0.05, two-factor ANOVA, one dog, two replicates). It was concluded that impedance pneumograph circuitry could be incorporated into an existing diaphragm pacer using electrodes placed on the diaphragm to provide valuable measurements of the function of the device.

Effects of applied currents on epileptiform bursts in vitro.

In this study, results show that applied electric currents can be effective to control the neuronal bursting that characterizes epileptic activity. Recordings from the CA1 region of rat hippocampus treated with penicillin show that local inhibition of epileptiform bursts is possible by short anodic current pulses (50 ms duration) applied extracellularly. Inhibition was evidenced by a large reduction (greater than 90%) in the amplitude of field potential. Data collected from 20 slices with moderate field potentials (50-80% of maximum) showed that current needed for complete inhibition was on the order of 42 +/- 3 microA. Intracellular recordings in CA1 cells (n = 13) showed that the decrease in field potential amplitude was accompanied by suppression of intracellular neuronal firing caused by somatic hyperpolarization as measured by transmembrane potentials. The resulting hyperpolarization was on the order of 13 mv below resting potential for weakly epileptiform responses (less than 50% of maximum response), and 50 mv below resting potential for strongly epileptiform activity (greater than 50% of maximum response). These results reveal the existence of a stimulation window within which inhibition of neuronal elements can be achieved without simultaneous excitation.