Linshom thermodynamic sensor is a reliable alternative to capnography for monitoring respiratory rate


Monitoring ventilation accurately is a technically challenging, yet indispensable aspect of patient care in the intra- and post-procedural settings. A new prototypical device known as the Linshom Respiratory Monitoring Device (LRMD) has been recently designed to non-invasively, inexpensively, and portably measure respiratory rate. The purpose of this study was to measure the accuracy and variability of LRMD measurements of respiratory rate relative to the measurement of capnography. In this prospective study, participants were enrolled and individually fitted with a face mask monitored by the LRMD and capnography. With a baseline oxygen flow rate and digital metronome to pace their respiratory rate, the participants were instructed to breathe at 10 breaths per minute (bpm) for 3 min, 20 bpm for 3 min, 30 bpm for 3 min, 0 bpm for 30 s, and resume regular breathing for 30 s. Both sensors were connected to a computer for continuous temperature and carbon dioxide waveform recordings. The data were then retrospectively analyzed. Twenty-six healthy volunteers, mean (range) age 27.8 (23–37) and mean (range) BMI 23.1 (18.8–29.2) kg/m2 were recruited. There were 15 males (57.7%) and 11 females (42.3%). After excluding 3 subjects for technical reasons, 13,800 s of breathing and 4,140 expiratory breaths were recorded. Throughout the protocol, the average standard deviation (SD) for the LRMD and capnography was 1.11 and 1.81 bpm, respectively. The overall mean bias (±2SD) between LRMD and capnography was −0.33 (±0.1.56) bpm. At the lowest and intermediate breathing rates reflective of hypoventilation and normal ventilation, the LRMD variance was 0.55 and 1.23 respectively, compared to capnography with 5.54 and 7.47, respectively. At higher breathing rates indicative of hyperventilation, the variance of the test device was 4.52, still less than that of capnography at 5.73. This study demonstrated a promising correlation between the LRMD and capnography for use as a respiratory rate monitor. The LRMD technology may be a significant addition to monitoring vital signs because it offers a minimally intrusive opportunity to detect respiratory rate and apnea, without expensive or complex anesthetic equipment, before the need for life-saving resuscitation arises.

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Funding for this study was provided by internal department funds.

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Corresponding author

Correspondence to Richard D. Urman.

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Conflict of interest

Drs. Bhavani Kodali and Richard D. Urman received funding from Medtronic for unrelated research. Dr. James H. Philip has a financial interest in Respiratory Motion Incorporated. The remaining authors report no conflicts of interest.

Research Involving Human Participants

Institutional Review Board approval was obtained for subject recruitment and analysis of the data. The authors do not know of any ethical issues to declare.

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Informed consent was obtained from all study participants prior to study.

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Preiss, D., Drew, B.A., Gosnell, J. et al. Linshom thermodynamic sensor is a reliable alternative to capnography for monitoring respiratory rate. J Clin Monit Comput 32, 133–140 (2018).

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  • Ventilation
  • Respiratory rate
  • End-tidal carbon dioxide
  • Apnea
  • Monitoring
  • Post-operative