Respiratory rate monitoring goes sensorless

Depth-sensing cameras provide a promising approach to continuous, no-contact measurement of respiratory rate, a team of researchers reported.

Cameras equipped with depth-based technology use a depth matrix that represents the distances to all objects within the camera’s field of view, they noted. Visualization of this matrix allows the tracking of changes in depth caused by breathing, particularly within the torso. These variations in depth are then used to generate a signal reflecting the respiratory rate.

In a study, the researchers tested the accuracy of a depth-sensing camera system for the continuous measurement of respiratory rate across a breathing range of 4–40 breaths/min in 30 adult volunteers. The camera was positioned above the bed to capture depth information from the torso region. The resulting calculation in respiratory rate was compared with a reference rate obtained from a manually scored capnograph.

The depth-sensing camera system accurately measured respiratory rate across the entire breathing range, with a root mean squared difference (RMSD) of 0.77 breaths/min from the reference measurement. The camera slightly overestimated the rate by an average of 0.05 breaths/min. [Respir Med 2023:220:107463]

On further analysis, the accuracy of the camera remained consistent across the predefined respiratory rate ranges (≤7, >7–10, >10–20, >20–30, and >30 breaths/min), with an RMSD of less than 1.00 breaths/min relative to the reference measurement.

The camera also performed well even when measuring spontaneous breathing during the study, with an RSMD accuracy of 1.20 breaths/min, with individual subranges maintaining accuracies within ≤1.30 breaths/min.

“[The performance of the camera] corresponds well with that achieved in previous smaller scale studies conducted by our group in healthy volunteers during a breathe-down study and in a longitudinal study of respiratory rate with a ventilator reference,” the researchers noted. [J Clin Monit Comput 2020;34:1025-1033; J Clin Monit Comput 2022;36:657-665]

Neglected vital sign

“Respiratory rate is a commonly used vital sign … [and] serves as a crucial marker of acute health issues… [A]ny significant alteration in respiratory rate may be an early warning sign of major issues such as infections in the respiratory tract, respiratory failure, or cardiac arrest,” the researchers said.

However, previous studies suggest that measuring respiratory rate is often overlooked due to several factors. Firstly, healthcare professionals may skip assessments based on subjective judgments about patient appearance or behaviour. Secondly, proper evaluation is hindered by inadequate training and lack of confidence in accurate measurement techniques. Time constraints and demanding workloads, coupled with the absence of automated solutions, further limit dedicated attention to the measurement of respiratory rate. [Int Arch Nurs Health Care 2016;2:050]

According to the researchers, such underestimation and inconsistency in measurement can lead to missed diagnoses and potential complications. It also does not help that the lack of accountability measures in healthcare settings discourage meticulous and consistent monitoring.  [Joint Comm J Qual Patient Saf 2018;44:494-499; ERJ Open Res 2020;6:1-8]

“The depth-sensing respiratory monitoring system … can address many of the issues … causing the poor measurement and recording of this important parameter in current practice. The system has potential for continuous monitoring in a variety of clinical settings including the general care floor, postanaesthesia care unit, nonvented ICU patients, elderly care facilities, sleep facilities, and at-home sleep studies,” the researchers said.

“It may also be a valuable monitoring modality for controlling infection during pandemics, such as influenza and coronavirus, as the method requires minimal interaction with the patient while providing a reliable measurement,” they added. [Best Pract Res Clin Anaesthesiol 2020;34:345-351; Front Physiol 2020;11:1-4]

The researchers believe that the use of a depth-based no-contact camera system to measure respiratory rate is a realistic possibility. They shared that they are looking into the viability of various form factors of the technology, including systems that are trolley or stand-based, attached to the bed, or attached to the wall or ceiling.