The Science Journal of the American Association for Respiratory Care

2010 OPEN FORUM Abstracts

COMPARING BREATHING INTOLERANCE INDEX PRE- AND POST-DIAPHRAGMATIC MUSCLE FATIGUE IN HEALTHY ADULTS.

Dawn Marie Axness, Junko Morikawa, Chontel Ross, Dione Harrod, Lonny Ashworth; Boise State University, Boise, ID

Background: Breathing Intolerance Index (BIT Index) was proposed by Dr. Toshihiko Koga as an alternative to measuring the Tension Time Index of the diaphragm (TTIdi) to measure diaphragmatic fatigue. BIT Index is defined as Inspiratory Time/Total Time multiplied by Tidal Volume/Vital Capacity: (Ti/Ttot) x (Vt/VC). Dr. Koga previously found that subjects who used NPPV at night for OSA had a higher BIT Index when compared to healthy adults. Presently, there is no clinical scale for the BIT Index and there is no evidence to show that an individual’s BIT Index can be altered. The purpose of this study was to measure the baseline BIT Index in healthy individuals, then to induce diaphragmatic muscle fatigue, and see if the BIT Index changes. Methods: Following IRB approval, four subjects’ baseline Vt, VC, Ti, Ttot and MIP were measured using the METEOR Respiratory Mechanics Handheld Monitor. The baseline BIT Index was calculated for each subject. Next, each subject used an Inspiratory Muscle Trainer set at 40% of their MIP. Each subject’s heart rate, respiratory rate and level of dyspnea (using the Modified Borg Scale) were monitored every three minutes. Each subject continued the use of the Inspiratory Muscle Trainer until a 10 (maximal) was reached on the Modified Borg Scale. At this point, the MIP was immediately re-measured and spirometry measurements were repeated to obtain new data points for the BIT Index. Results: Inducing diaphragmatic fatigue proved difficult, but when it was achieved, the BIT Index increased in two of the four subjects. Two of the subjects’ BIT Index increased, in one subject the BIT Index decreased and the BIT Index of the final subject did not change. For the subjects whose BIT Index increased, the MIP decreased, while Vt and Vt/VC increased. For the two subjects whose BIT Index did not change or decreased, MIP increased, while Vt and Vt/VC decreased. Conclusions: The two subjects who had an increase in their BIT Index reached a 10 on the Modified Borg Scale in less than forty minutes. The subject whose BIT Index decreased used the inspiratory muscle trainer for seventy-seven minutes. The subject who had no change in BIT Index ended the testing period in a tripod position. Further studies are needed to evaluate alternate methods of inducing muscle fatigue and to evaluate the BIT Index for patients with muscle fatigue and/or muscle weakness. Sponsored Research - None Breathing Intolerance Index Before and After Inducing Muscle Fatigue