A proportional assist ventilator to unload respiratory muscles experimentally during exercise in humans

Abstract

New Findings r What is the central question of this study?Can a modern proportional assist ventilator (PAV) function sufficiently well to unload the respiratory muscles during exercise? r What is the main finding and its importance?A PAV can be constructed with contemporary hardware and software and be used at all exercise intensities to unload the respiratory muscles by up to 70%. Previously, PAVs have allowed researchers to address many fundamental physiological problems in clinical and healthy populations, but those versions are no longer functional or available. We describe the creation of a PAV that permits researchers to use it as an experimental tool.Manipulation of the normally occurring work of breathing (WOB) during exercise can provide insights into whole-body regulatory mechanisms in clinical patients and healthy subjects. One method to reduce the WOB uses a proportional assist ventilator (PAV). Suitable commercially available units are not capable of being used during heavy exercise. This investigation was undertaken in order to create a PAV and assess the degree to which the WOB could be reduced during exercise. A PAV works by creating a positive mouth pressure (P m ) during inspiration, which consequently reduces the WOB. Spontaneous breathing patterns can be maintained, and the amplitude of P m is calculated using the equation of motion and predetermined proportionality constants. We generated positive P m using a breathing apparatus consisting of rigid tubing, solenoid valves to control the airflow direction and a proportional valve connected to compressed gas. Healthy male and female subjects were able to use the PAV successfully while performing cycling exercise over a range of intensities (50-100% of maximal workload) for different durations (from 30 s to 20 min) and different protocols (constant versus progressive workload). Inspiratory WOB was reduced up to 90%, while total WOB was reduced by 70%. The greatest reduction in WOB (50-75%) occurred during submaximal exercise, but at maximal ventilations (>180 l min −1 ) a 50% reduction was still possible. The calculated change in WOB and subsequent reduction in respiratory muscle oxygen consumption resulted in equivalent reductions in whole-body oxygen consumption. With adequate familiarization and practice, our PAV can consistently reduce the WOB across a range of exercise intensities.

Effects of respiratory muscle work on respiratory and locomotor blood flow during exercise

“…We have previously described and used the PAV (Dominelli et al . , ), and it is comparable to the devices used by others (Gallagher & Younes, ; Romer et al . ).…”

“…Metabolic volumes [oxygen uptake () and carbon dioxide production ()] are expressed as STPD, whereas all other volumes are shown as BTPS. To determine tidal pressure–volume loops, ∼15 s of data before and after ICG injection were composite averaged, and the WOB was determined as previously described (Dominelli & Sheel, , ).…”

Engineering a solution to explore the cardiorespiratory limits to exercise performance: take a load off!

“…Thereafter, Dominelli et al . () recruited endurance‐trained and recreational athletes and conducted assisted ventilation trials in multimodal exercise bouts of varying intensities up to 90% maximal oxygen uptake.…”

“…This was readily achieved during stationary cycle ergometry in the study by Dominelli et al . (), but would prove more difficult during treadmill running, which introduces movement artefact. Perhaps most significant in terms of limits is the fact that each subject must learn to tolerate the sensation of ventilatory support, accepting the inspiratory assistance provided by the ventilator by relaxing their respiratory muscles; no small task at any time and especially during exercise to exhaustion.…”

“…The system performed flawlessly during a simulation wherein a cleverly constructed motor substitute breathed life into the authors' ambitions to scale the project up to human subjects. Thereafter, Dominelli et al (2016) recruited endurance-trained and recreational athletes and conducted assisted ventilation trials in multimodal exercise bouts of varying intensities up to 90% maximal oxygen uptake.…”