All mammals breath by actively ventilating their lungs. Inhalation is essential for the delivery of oxygen, but also of airborne odorants that direct our sense of smell. Thus, accurate measurement of respiratory rate is indispensable for a broad range of biomedical research questions and of course in clinical practice.
Most existing respiration measurement techniques require either surgical implantation of sensors (in the case of animal models), or attachment of uncomfortable sensors for patients in a clinical setting. However, the Haesler lab has previously developed a contactless approach to assess respiration rate, based on infrared (IR) thermography. The fact that IR themography is noninvasive is a clear advantage, but reliably extracting all respiration signals from videos can be challenging, especially if the videos have low contrast or their focus is suboptimal. Now they have developed a new algorithm to address this limitation.
An important step forward
The algorithm extracts respiration signals based on pixel time series, removing the need for nose-tracking and image segmentation. The researchers validated the algorithm in mice and in humans and found that it reliably detects inhalation onsets with high temporal precision.
Kadir Mutlu, PhD student in the Haesler lab, explains: "The current standard practice for measuring respiration based on intranasal airflow involves implanting a cannula in the nasal cavity. This procedure is invasive and requires surgical skills. Measurements also frequently fail after a short time because of mucus aggregation or tissue regrowth. Our validation experiments in head-restrained mice demonstrate that IR thermography can be used to reliably monitor respiration in the same animal over long time periods in a simple, efficient way."
Better for mice, better for humans
Method development is essential to push research forward, but in this case also out of ethical considerations. Sebastian Haesler: "By removing the need for invasive surgery, IR thermography addresses the requirement for more refined animal experimentation according to the ‘3Rs’ principle (‘Refine, Reduce, Replace’) that guides animal research."
The new algorithm also benefits human research and clinical practice, as it allows for the improved measurement of different respiratory parameters. Haesler: "While various algorithms have been developed for determining respiration rate from human thermal videos, to the best of our knowledge, this paper is the first to extract inhalation onsets."
Mutlu K, Rabell JE, Martin Del Olmo P & Haesler S. IR thermography-based monitoring of respiration phase without image segmentation. J Neurosci Methods. 2018 Mar 1;301:1-8. doi: 10.1016/j.jneumeth.2018.02.017