Linshom respiratory monitoring device: a novel temperature-based respiratory monitor
Can J Anesth/J Can Anesth
Linshom respiratory monitoring device: a novel temperature-based respiratory monitor Le dispositif de monitorage respiratoire Linshom: un nouveau moniteur respiratoire base´ sur la tempe´rature
Jerrold Lerman 0 1 2 3 4 5 6
. Doron Feldman 0 1 2 3 4 5 6
. Ronen Feldman 0 1 2 3 4 5 6
BS . John Moser 0 1 2 3 4 5 6
BS . Leeshi Feldman 0 1 2 3 4 5 6
. Madhankumar Sathyamoorthy 0 1 2 3 4 5 6
. Kenneth Deitch 0 1 2 3 4 5 6
DO . Uri Feldman 0 1 2 3 4 5 6
0 J. Lerman, MD D. Feldman, MD State University of New York at Buffalo , Buffalo, NY , USA
1 J. Lerman, MD (&) Department of Anesthesia, Women and Children's Hospital of Buffalo , 219 Bryant St, Buffalo, NY 14209 , USA
2 Presented in part at the Annual Meeting of the European Society of Anaesthesiologists , Stockholm , Sweden
3 K. Deitch, DO Department of Emergency Medicine, Einstein Medical Center, Thomas Jefferson University , Philadelphia, PA , USA
4 M. Sathyamoorthy, MD Department of Anesthesiology, University of Mississippi Medical Center , Jackson, MS , USA
5 L. Feldman, MD Sackler Medical School , Tel Aviv , Israel
6 R. Feldman, BS J. Moser, BS U. Feldman , PhD Artep Incorporated, Ellicott City, MD , USA
Purpose We sought to develop a temperature-based respiratory instrument to measure respiration noninvasively outside critical care settings. Method Respiratory temperature profiles were recorded using a temperature-based noninvasive instrument comprised of three rapid responding medical-grade thermistors-two in close proximity to the mouth/nose (sensors) and one remote to the airway (reference). The effect of the gas flow rate on the amplitude of the tracings
was determined. The temperature-based instrument, the
Linshom Respiratory Monitoring Device (LRMD) was
mounted to a face mask and positioned on a mannequin
face. Respiratory rates of 5-40 breaths min-1 were then
delivered to the mannequin face in random order using
artificial bellows (IngMar Lung Model). Data from the
sensors were collected and compared with the bellows
rates using least squares linear regression and coefficient
of determination. The investigators breathed at fixed rates
of 0-60 breaths min-1 in synchrony with a metronome as
their respiratory temperature profiles were recorded from
sensors mounted to either a face mask or nasal prongs. The
recordings were compared with a contemporaneously
recorded sidestream capnogram from a CARESCAPE
GEB450 Monitor. The extracted respiratory rates from
the LRMD tracings and capnograms were compared using
linear regression with a coefficient of determination and a
Results The amplitude of the sensor tracings was
independent of the oxygen flow rate. Respiratory rates
from the new temperature-based sensor were synchronous
and correlated identically with both the artificial bellows
(r2 = 0.9997) and the capnometer mounted to both the face
mask and nasal prongs (r2 = 0.99; bias = -0.17; 95%
confidence interval, -2.15 to 1.8).
Conclusions Respiratory rates using the LRMD, a novel
temperature-based respiratory instrument, were consistent
with those using capnometry.
Objectif Nous avons tente´ de mettre au point un
instrument respiratoire se fondant sur la tempe´rature afin
de mesurer la respiration de fac¸on non invasive en dehors
des unite´s de soins critiques.
Me´thode Les profils de tempe´rature respiratoire ont e´te´
enregistre´s a` l’aide d’un instrument non invasif se fondant
sur la tempe´rature et compose´ de trois thermistances de
qualite´ me´dicale a` re´ponse rapide – deux a` proximite´ de la
bouche et du nez (capteurs) et un troisie`me a` l’e´cart des
voies ae´riennes (re´fe´rence). L’effet du de´bit gazeux sur
l’amplitude des trace´s a e´te´ de´termine´. L’instrument fonde´
sur la tempe´rature, nomme´ment le dispositif de monitorage
respiratoire Linshom (LRMD), a e´te´ fixe´ a` un masque
facial et positionne´ sur le visage d’un mannequin. Des
fre´quences respiratoires de 5-40 respirations min-1 ont
ensuite e´te´ livre´es au visage du mannequin dans un ordre
ale´atoire a` l’aide de soufflets artificiels (mode`le de poumon
IngMar). Les donne´es des capteurs ont e´te´ collige´es et
compare´es aux fre´quences des soufflets a` l’aide d’une
me´thode de re´gression line´aire des moindres carre´s et d’un
coefficient de de´termination. Les chercheurs ont respire´ a`
des fre´quences fixes de 0-60 respirations min-1 en
synchronie avec un me´tronome pendant que leurs profils
de tempe´rature respiratoire e´taient enregistre´s par des
capteurs fixe´s a` un masque facial ou a` des canules nasales.
Les enregistrements ont e´te´ compare´s a` un trace´ de
capnogramme late´ral enregistre´ simultane´ment par un
moniteur CARESCAPE GEB450. Les fre´quences
respiratoires extraites des trace´s du LRMD et des
capnogrammes ont e´te´ compare´es a` l’aide d’une me´thode
de re´gression line´aire avec un coefficient de de´termination
et un graphique de Bland-Altman.
Re´sultats L’amplitude des trace´s des capteurs e´tait
inde´pendante du de´bit d’oxyge`ne. Les fre´quences
respiratoires du nouveau capteur base´ sur la tempe´rature
e´taient synchrones et identiquement corre´le´es aux soufflets
artificiels (r2 = 0,9997) et au capnome`tre fixe´ au masque
facial et aux canules nasales (r2 = 0,99; biais = -0,17;
intervalle de confiance 95 %, -2,15 a` 1,8).
Conclusion Les fre´quences respiratoires mesure´es a`
l’aide du LRMD, un nouvel instrument respiratoire fonde´
sur la tempe´rature, e´taient cohe´rentes a` celles mesure´es
Outside critical care settings,1-3 there is a paucity of
inexpensive and portable monitors that can deliver accurate
measurements, monitor respiratory rate and, in particular,
detect apnea in advance of desaturation. In many centres,
pulse oximetry is used as a surrogate monitor for
respiration, although the sensitivity of this monitor to
detect apnea is attenuated when oxygen is administered.4
Other monitors, such as capnography and
plethysmography, for tracking respiration during transport
and monitoring sedation on the ward have their limitations
(e.g., cost, size, weight, and reliability) which preclude
their routine use.5-7 We identified the need for a new
monitor based on simple physiological principles that
would track respiration in advance of apnea and address the
above shortcomings of the current monitors.
Previously, investigators attempted to monitor indices of
respiration by placing a thermistor adjacent to the airway and
measuring the changes in the temperature of the breath
during the respiratory cycle.8 These detectors did not
achieve any measure of clinical success, however, partly
because they had slow response times and could not
distinguish between the temperature of the exhaled breath
and that within the microenvironment of the face mask. The
former problem was remedied by the inclusion of
medicalgrade rapid responding thermistors, but the latter problem
persisted. We determined that we could address the latter
problem and increase the signal-to-noise ratio of
temperature within the face mask by implementing the
Peltier-based microbalance in the temperature controller. To
address this challenge, we sought to develop a
temperaturebased respiratory instrument that could reliably and
consistently measure the respiratory rate in humans.
In accordance with the conditions for acceptance by the
Journal during its editorial process, this investigation was
submitted post hoc to the Institutional Review Board (IRB)
at the State University of New York, Buffalo. The IRB
determined that this research did not involve human
subjects and that approval was not required (dated March
31, 2016). A temperature-based noninvasive instrument,
the Linshom Respiratory Monitoring Device (LRMD), was
developed to measure respiration. The instrument is
comprised of three rapid responding medical-grade
thermistors (1.5-mm diameter) with a unique control-loop
algorithm executed by a microcontroller.A The two primary
thermistors (sensors) are positioned near the mouth and/or
nose within a disposable oxygen face mask (Hudson RCI
Ref 1041, USA) (Fig. 1) or nasal prongs (Fig. 2) to
measure the temperature during respiration. The solitary
secondary (reference) thermistor is positioned outside the
face mask to measure and adjust for the ambient
temperature. The thermistor signals are converted from
analog to digital signals using analog-to-digital converters
and displayed. The sensors placed in the vicinity of the
nose and/or mouth respond precisely by keeping the
thermistor in thermal balance with a thermoelectric
cooler (TEC) utilizing the Peltier effect within a
controlA US Patents #8,579,829 and non-provisional approval of application
loop process. The TEC selects a temperature setpoint based
on ambient conditions and continuously operates to hold
the sensor’s temperature stable at that setpoint. As
respiration disrupts the thermal balance, the control loop
generates a feedback signal (i.e., an accurate signature
representation of the breath) which captures the subtle
detail of the breath cycle. After each breath, the control
loop returns the sensor to thermal balance with smooth
precision ready for the next breath.
When the investigators (J.L., R.F., J.M.) self-applied the
face masks, data were acquired from the LRMD sensors
mounted in the masks, and the extracted data were stored
on a laptop using a custom program.
To determine the effect of the oxygen flow rate (2, 4, 6,
or 10 L min-1) on the readings of the LRMD sensor, the
investigators breathed 12-30 breaths min-1 through the
oxygen face mask at each of the four oxygen flow rates
while the LRMD responses were recorded electronically.
The amplitude of the tracings from the nadir of the signal at
end-inspiration until the peak at end-exhalation was
recorded for each breath at the respective gas flow rate.
A bench test was designed to determine whether this
novel sensor could track respiration delivered by calibrated
mechanical bellows (IngMar Medical Adult/Pediatric
Demonstration Lung Model; IngMar Medical, Pittsburgh,
PA, USA). An oxygen face mask fitted with a LRMD
sensor was placed over the mannequin’s mouth. The
bellows delivered breaths to the mannequin’s mouth via a
single tube at respiratory rates of 5-40 breaths min-1 (with
corresponding lung volumes of 120-300 mL breath-1) in a
randomized sequence (using www.random.org). The gas
flow cooled the sensor during each breath, and when the
breath ended, the TEC automatically returned the
thermistor to its setpoint, creating a sinusoidal breathing
pattern. Data were collected from the sensor for 30-60 sec
at a time depending on the respiratory rate of the bellows.
The respiratory rates measured from the tracings detected
by the sensor were plotted against those set on the bellows
and analyzed using linear regression and the coefficient of
determination (r2) using Prism 6.0d software (GraphPad,
La Jolla, CA, USA).
Respiratory rate was evaluated while one of the
investigators breathed oxygen through an oxygen face
mask fitted with a LRMD sensor and operational
sidestream capnography. The LRMD sensor was mounted
across from the mouth/nose in the mask while data were
collected. The end-tidal carbon dioxide tension was
measured via nasal prongs and a CARESCAPE GEB450
Monitor (GE Healthcare, Chicago, IL, USA, hereafter
referred to as GEB450). The investigator breathed at
constant rates of *7.5-60 breaths min-1 for two-minute
periods in synchrony with a metronome. The sinusoidal
tracings from the LRMD sensor and the GEB450 were
compared after three manipulations were applied to the
LRMD data. Differences in the latency between the two
instruments were corrected by digitizing the upstrokes of
the initial breath from each monitor and synchronizing
them to begin at time 0. These differences were attributed
in part to the capacity of the LRMD sensor to detect breaths
more rapidly than the capnogram. To ensure a
stable breathing pattern, the breath-to-breath interval was
determined after at least the third breath in each sequence.
Differences in the amplitude of the tracings between the
two instruments were adjusted by first normalizing the data
from the LRMD sensor by amending each data point by the
offset between the minimum value and 0 and then
converting the GEB450 values to SI units. Differences in
the rate of data acquisition were adjusted by halving the
speed of the tracings from the LRMD sensor and then
superimposing the tracings from the two instruments. A
sample tracing was extracted to illustrate the congruity of
the respirations detected by the LRMD and the capnogram.
The derived respiratory rates from the two instruments
were plotted using linear regression and r2.
The LRMD sensor, with dimensions of 25 mm 9 20 mm
9 15 mm (length 9 width 9 height) and a weight of 10 g,
was adapted to nasal prongs (Fig. 2). To evaluate
simultaneous recordings of the nasal LRMD tracing and
nasal capnometry (GEB450), one investigator breathed
2040 breaths min-1 in synchrony with a metronome in
random order (predetermined using www.random.org), and
the signals were recorded simultaneously. The derived
respiratory rates from the two instruments were plotted
using a Bland-Altman plot.
To demonstrate that the LRMD sensor responds rapidly
to apneas, one investigator breathed through an oxygen
face mask until a stable respiratory pattern was detected.
The respiratory rate was detected using nasal capnometry
and the LRMD monitor mounted to the nasal prongs.
Periodic breath holds (apneas) were then performed to
demonstrate whether LRMD and the capnometer detected
The respiratory rates with each oxygen flow rate were
compared using one-way analysis of variance. The
closeness of fit between the programmed bellows
respiratory rate or the GEB450 and that determined by
LRMD was compared using least squares regression
analysis and the coefficient of variation (r2). A
BlandAltman plot was constructed to show the average
respiratory rate from the nasal LRMD and GEB450
capnometer sensors vs the difference in the respiratory
rates between the two sensors. All reported P values are
The data from the LRMD sensor were unaffected by
oxygen flow rates of 2-10 L min-1 (P = 0.19) (Fig. 3).
Although the shape and maximum end-tidal pCO2 of the
GEB450 tracings were fairly consistent (i.e., a constant
end-tidal pCO2), the amplitude of the LRMD tracings
varied by up to 50% (Fig. 5). The latter variability was
attributed to variations in the relative tidal volume.B
Respiratory rates determined by the LRMD monitor
B Sathyamoorthy M, Lerman J, Feldman D, et al. Linshom. a new
respiratory monitor. American Society of Anesthesiologists’ Meeting,
San Francisco, CA. 2013: A5032
correlated one-to-one with those from the GEB450 (r2 =
0.99) (Fig. 6).
With the LRMD monitor mounted to a nasal cannula, a
Bland-Altman plot of the average respiratory rates detected
by the LRMD and GEB450 monitors yielded a bias of
-0.17 with a 95% confidence interval of -2.15 to 1.8
To illustrate the ability of the LRMD monitor to detect
apneas, the respiratory rate was recorded with the LRMD
mounted to nasal prongs and by nasal capnometry while
the investigator performed several breath holds (Fig. 8).
Both instruments detected the apneas interspersed amongst
a regular breathing pattern.
The primary purpose of this preliminary investigation was
to evaluate whether a thermodynamic temperature-based
inexpensive and portable instrument (LRMD) could
accurately track the respiratory rate outside the intensive
care setting. First, we determined that the LRMD
measurements were independent of the oxygen flow rate.
Second, we determined that, whether the LRMD sensor
was mounted to a face mask or nasal prongs, the tracings
were synchronous and congruous with contemporaneous
capnograms obtained using nasal capnometry.
The notion that a temperature-based instrument could
measure indices of respiration is not a novel concept, but
previous attempts to develop a viable instrument have
failed for several reasons. First, rapidly responding
inexpensive thermistors operating in a thermal balance
circuit were not widely available in the past, thus limiting
the ability of investigators to detect minute changes in
temperature during the respiratory cycle. Second, the
temperature profile during the respiratory cycle becomes
progressively more attenuated within the
microenvironment of a face mask as thermal equilibrium
is reached. The blunted signal rendered a
temperaturebased instrument ineffective. To overcome this problem,
we added a second thermistor within the thermal balance
circuit to detect temperature changes throughout the
respiratory cycle that were independent of the
microenvironment. We then added a reference thermistor
outside the face mask or nasal prongs to account for gross
fluctuations in the ambient temperature. When combined
with a responsive algorithm, temperature-based
measurements of respiration were reliable and precise.
Currently, respiration is not widely monitored once
patients leave critical care settings such as the operating
room. This is a major risk for hypoxia-induced adverse
outcomes. The technology available to monitor respiration
suffers several limitations, including the size and cost of
existing monitors. The LRMD is a lightweight instrument
that may weigh as little as 10 g. The incremental disposable
cost of the LRMD is approximately US$4, with an estimate
for a freestanding monitor, based on the production of
1,000 units, of approximately US$250. A decrease in the
cost of respiratory monitoring by several orders of
magnitude, as we expect with LRMD, may introduce a
paradigm shift in the ubiquity of such monitors outside the
It may seem paradoxical that this temperature-based
respiratory sensor could detect ‘‘respiration’’ using
laboratory bellows with gas flowing at room temperature.
When humans breathe, the sensor detects the warm
temperature in the exhaled breath as respiration.
Nevertheless, we observed that, when the sensor was
mounted to the face mask, the temperature within the mask
equilibrated with that of the exhaled breath after several
breaths, obscuring the signal detected by the sensor. To
ensure that the sensor could detect respiration in the long
term, we applied the Peltier-based microbalance to our
sensor design. This offsets the temperature setpoint to ensure
a detectable response to breathing irrespective of the ambient
temperature. Hence, when air at room temperature flowed
past the sensor, the Peltier effect ensured that the sensor
detected respiration irrespective of the local temperature.
This study suffers from several limitations. First, these
are preliminary laboratory data that serve to establish the
feasibility and scope of respiratory monitoring with an
instrument using a temperature-based monitoring system.
Second, we studied the LRMD sensor in several
investigators, not in patients. To validate this novel
instrument, clinical studies are required in patients with a
wide range of diseases and during a range of procedures.
Currently, four clinical studies in various stages of
completion are being conducted to evaluate the reliability
and accuracy of the LRMD to monitor respiration in
patients—one such study has been presented.C Third,
variation in human physiology, including age, weight, and
breathing patterns, must be investigated to ensure the
current sensor is sufficiently robust to track respiration.
Fourth, although we have preliminary evidence that the
signal from the LRMD sensor is very stable during rapid
movement and for prolonged periods (www.
Linshomforlife), additional testing is needed to verify
C Preiss D, Drew B, Gosnell J, Kodali BS, Philip JH. A
thermodynamic breathing sensor—a new non-invasive monitor of
respiration. American Society of Anesthesiologists, San Diego,
October 2015, BOC09.
these findings in patients. Many of these limitations will be
addressed in the clinical studies that are underway.
In summary, this concept paper presents preliminary
data to show that this novel temperature-based respiratory
instrument, the Linshom Respiratory Monitoring Device,
tracks respiration noninvasively. Our results show that,
when the LRMD sensor is mounted to a face mask or nasal
prongs, the instrument can accurately measure the
respiratory rate over a wide range. These findings warrant
corroboration in clinical trials and in patients under diverse
Funding No external funding was received for conducting this
investigation or for analyzing these data.
Conflicts of interest Five authors (J. Lerman, D. Feldman, R.
Feldman, J. Moser, and U. Feldman) jointly hold two patents in the
U.S.A. that were issued for this device: #8,579,829 and
nonprovisional patent approved #13/553,070. The remaining authors do
not hold any interests in this instrument that might be perceived as
conflicts of interest.
Author contributions Jerrold Lerman, Doron Feldman, Ronen
Feldman, Kenneth Deitch, and Uri Feldman participated in the study
design. Jerrold Lerman, Doron Feldman, Ronen Feldman, John
Moser, Leeshi Feldman, Madhankumar Sathyamoorthy, and Uri
Feldman participated in the study execution. Jerrold Lerman, Doron
Feldman, Ronen Feldman, Leeshi Feldman, Madhankumar
Sathyamoorthy, and Uri Feldman participated in data acquisition.
Jerrold Lerman, Ronen Feldman, John Moser, and Uri Feldman
participated in the data analysis. Jerrold Lerman, Doron Feldman,
Ronen Feldman, John Moser, Kenneth Deitch, and Uri Feldman
participated in study interpretation. Jerrold Lerman and Ronen
Feldman participated in figure production. Jerrold Lerman, Doron
Feldman, Ronen Feldman, and John Moser participated in manuscript
writing. Jerrold Lerman, Doron Feldman, Ronen Feldman, John
Moser, Leeshi Feldman, Madhankumar Sathyamoorthy, Kenneth
Deitch, and Uri Feldman participated in manuscript editing. John
Moser participated in the hardware design. Uri Feldman participated
in development of the algorithm. Jerrold Lerman takes full
responsibility for the integrity of the data/analyses presented.
Editorial responsibility This submission was handled by Dr.
Gregory L. Bryson, Deputy Editor-in-Chief, Canadian Journal of
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