INSPIRATORY PRESSURE PATTERN AFFECTS RESPIRATORY MUSCLE FATIGUE DURING RESISTIVE BREATHING

Abstract

TYPE: Late Breaking Abstract TOPIC: Pulmonary Physiology PURPOSE: The esophageal pressure (Peso) based tension-time index (TTI) is the reference technique for breathing effort assessment (Bellemare and Grassino. J Appl Physiol, 1982). TTI estimation entails measurement of the timing and effort of breathing and predicts time to fatigue during resistive breathing (Tlim). Effect of TTI on Tlim has been estimated using pressure square wave breathing. This cross-over study compares Tlim between square wave and more natural triangle wave breathing. METHODS: Four healthy subjects (W=70±9kg, H=176±4cm, age=31.7±6yr) were enrolled after informed consent. Subjects were fitted with a double-balloon nasogastric catheter. Two trials were performed, separated by >4 days of rest. Subjects were randomized to Peso square or triangle wave breathing with a target of mean 50% maximal inspiratory pressure (Pmax), Vt∼800ml, 12b/min, ti/ttot of 0.5 and through a resistance. Pmax was determined using magnetic phrenic nerve stimulation. Subjects reported modified Borg (0-10) every 5min. Tlim was decided when subjects could not maintain Peso target. RESULTS: Mean Tlim was 30.8min and 40.1min for square to triangle wave breathing, with a triangle-square difference of 9.2min (range:3-18.5min). Mean Borg was 5.2, 7 and 8.2 and 4.7, 7, 8.2 for square and triangle wave. CONCLUSIONS: Healthy subjects are able to sustain resistive breathing at the same average load for longer during a more natural breathing pattern compared to square wave breathing. CLINICAL IMPLICATIONS: If TTI is used to evaluate breathing effort, as preformed during weaning from mechanical ventilation or readiness to extubation, current TTI thresholds defined from square wave breathing might underestimate the patients’ ability to perform breathing. DISCLOSURE: No significant relationships. KEYWORD: Respiratory Muscle Fatigue