Breath-by-breath Analysis of a Rat Model of Pompe Disease Exposes Deficits in High-frequency Behaviors

Abstract

Pompe disease (PD) is caused by a loss of function of the enzyme acid-α-glucosidase (GAA) leading to glycogen accumulation, neuromuscular dysfunction, and breathing failure. Here, we characterized longitudinal changes in breathing of GAA null ( Gaa−/−) rats on a breath-by-breath basis using a novel respiratory event detection algorithm. Adult Pompe (n = 5) and Sprague Dawley (n = 5) rats were implanted with chronic diaphragm EMG electrodes. Once a month from 4-10 months of age, full body plethysmography with concurrent EMG was used to record respiratory waveforms under room air and hypoxia. Waveforms were analyzed by the Adjustable Baselines Respiratory Analysis Program (ABRAP) algorithm. An adaptive threshold identified “respiratory events” defined as crossings of a threshold set between the recent maxima and minima of the waveform. After event identification, a range of waveform characteristics are calculated and tagged to that event. Averages of each characteristic were taken for all events and then analyzed based on respiratory rate in breaths/minute (bpm): low (<120 bpm, ‘quiet breathing’), medium (between 120 and 240 bpm) and high (>240 bpm, ‘high frequency sniffng’). In room air, Pompe rats had a lower breathing rate than wildtype rats by month 10 (173 vs 285 bpm, standard error of the difference (SE of diff.) 37, p=0.03). This decrease in frequency was driven by the high rate events as there were no differences in the mean rate of low rate events at month 10 (80 vs 83 bpm, SE of diff. 3) while the frequency of high rate events was significantly lower by 9 months (mo 9: 393 vs 440 bpm, SE of diff. 16, p=0.04, mo 10: 383 vs 440 bpm, SE of diff. 17, p=0.008). Not only was the breathing frequency of high-rate events impaired in Pompe rats, but there was a trend towards decrease in the proportion of events falling in the high rate category indicating less time spent in high rate breathing behaviors (mo 4: 52 vs 59%, SE of diff. 6, mo 10: 25 vs 52%, SE of diff. 9) with a concomitant increase in the proportion of low frequency events. Additionally, there was a main effect of genotype on the latency between diaphragm activation and onset of inspiratory flow during hypoxia with Pompe rats having a longer latency across all months and frequency bands. This difference was most pronounced in the medium (44 vs 29 ms, SE of diff. 4 ms, p=0.003) frequency events. Active expiration was impaired in Pompe animals with peak post-event airflow (maximum positive pressure reached before the next inspiratory effort) blunted across all months. This effect was pronounced in the high frequency events (0.16 mL vs 0.24 mL, SE of diff. 0.01, p=0.0001). These deficits in high frequency events are consistent with progressive neuromuscular diaphragm weakness. We conclude that comprehensive analyses of all respiratory events over extended recording periods enables detection of altered breathing behaviors that may be missed when assessing only short periods of quiet breathing. In turn, this may help uncover a respiratory signature of disease progression in Pompe disease or other neuromuscular conditions. 2R01HD052682-11A1 (DDF, BJB), T32HL134621 (AM), R01HL153102 (ED), SPARC OT2OD023854 (ED), Craig H. Neilsen Pilot Grant (ED). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.