Effects of the Elevation Training Mask® 2.0 on dyspnea and respiratory muscle mechanics, electromyography, and fatigue during exhaustive cycling in healthy humans.

OBJECTIVES: Examine the effects of the Elevation Training Mask® 2.0 (ETM) on dyspnea, and respiratory muscle function and fatigue during exercise. DESIGN: Randomized crossover. METHODS: 10 healthy participants completed 2 time-to-exhaustion (TTE) cycling tests while wearing the ETM or under a sham control condition. During the sham, participants were told they were breathing air equivalent to "9000 ft" (matched to the selected resistance valves on the ETM according to the manufacturer), but they were breathing room air. Dyspnea and leg discomfort were assessed using the modified 0-10 category-ratio Borg scale. Qualitative dyspnea descriptors at peak exercise were selected from a list of 15. Crural diaphragmatic electromyography (EMGdi) and transdiaphragmatic pressure (Pdi) were measured via a multipair esophageal electrode balloon catheter. Participants performed maximal respiratory maneuvers before and after exercise to estimate the degree of respiratory muscle fatigue. RESULTS: Exercise with the ETM resulted in a significant decrease in TTE (p = 0.015), as well as increased dyspnea at baseline (p = 0.032) and during the highest equivalent submaximal exercise time (p = 0.0001). The increase in dyspnea with the ETM was significantly correlated with the decrease in exercise time (r = 0.73, p = 0.020). EMGdi and Pdi were significantly increased with the ETM at all time points (all p < 0.05). There was a significant increase in the selection frequency of "my breath does not go in all the way" at peak exercise with the ETM (p = 0.02). The ETM did not induce respiratory muscle fatigue. CONCLUSIONS: Exercising with the ETM appears to decrease exercise performance, in part, by increasing the sensation of dyspnea.

The Effect of Low-Dose Intraoperative Ketamine on Closed-Loop-Controlled General Anesthesia: A Randomized Controlled Equivalence Trial.

BACKGROUND: Closed-loop control of propofol-remifentanil anesthesia using the processed electroencephalography depth-of-hypnosis index provided by the NeuroSENSE monitor (WAVCNS) has been previously described. The purpose of this placebo-controlled study was to evaluate the performance (percentage time within ±10 units of the setpoint during the maintenance of anesthesia) of a closed-loop propofol-remifentanil controller during induction and maintenance of anesthesia in the presence of a low dose of ketamine. METHODS: Following ethical approval and informed consent, American Society of Anesthesiologist (ASA) physical status I-II patients aged 19-54 years, scheduled for elective orthopedic surgery requiring general anesthesia for >60 minutes duration, were enrolled in a double-blind randomized, placebo-controlled, 2-group equivalence trial. Immediately before induction of anesthesia, participants in the ketamine group received a 0.25 mg·kg-1 bolus of intravenous ketamine over 60 seconds followed by a continuous 5 µg·kg-1·min-1 infusion for up to 45 minutes. Participants in the control group received an equivalent volume of normal saline. After the initial study drug bolus, closed-loop induction of anesthesia was initiated; propofol and remifentanil remained under closed-loop control until the anesthetic was tapered and turned off at the anesthesiologist's discretion. An equivalence range of ±8.99% was assumed for comparing controller performance. RESULTS: Sixty patients participated: 41 males, 54 ASA physical status I, with a median (interquartile range [IQR]) age of 29 [23, 38] years and weight of 82 [71, 93] kg. Complete data were available from 29 cases in the ketamine group and 27 in the control group. Percentage time within ±10 units of the WAVCNS setpoint was median [IQR] 86.6% [79.7, 90.2] in the ketamine group and 86.4% [76.5, 89.8] in the control group (median difference, 1.0%; 95% confidence interval [CI] -3.6 to 5.0). Mean propofol dose during maintenance of anesthesia for the ketamine group was higher than for the control group (median difference, 24.9 µg·kg-1·min-1; 95% CI, 6.5-43.1; P = .005). CONCLUSIONS: Because the 95% CI of the difference in controller performance lies entirely within the a priori equivalence range, we infer that this analgesic dose of ketamine did not alter controller performance. Further study is required to confirm the finding that mean propofol dosing was higher in the ketamine group, and to investigate the implication that this dose of ketamine may have affected the WAVCNS.