Tidal Volume Measurements Research Articles

Non-invasive respiratory volume monitoring in patients with traumatic thoracic injuries

Background Respiratory decompensation is common after traumatic thoracic injuries such as multiple rib fractures and pulmonary contusions. A continuous, non-invasive, impedance-based respiratory volume monitor generates right and left tidal volume measurements, reflecting air exchange in the lungs and derives an instantaneous respiratory rate. The feasibility of using unilateral respiratory volume monitor–based tidal impedance measurements to monitor respiratory status in trauma patients is evaluated. Methods Three intensive care unit patients with three or more rib fractures following blunt trauma had continuous respiratory volume monitor measurements with a novel non-invasive impedance-based device (ExSpiron, Respiratory Motion Inc., Waltham, MA) and corresponding clinical data to permit analysis. Tidal impedance measurements were collected from both the injured and non-injured sides and converted into bilateral respiratory volume monitor measurements using advanced algorithms. Results In Patient 1, following evacuation of a pneumothorax, the respiratory volume monitor showed a significant increase in tidal measurements coupled with a compensatory decrease in tidal measurements on the uninjured side and a decrease in respiratory rate. In Patient 2, tidal measurements were only slightly decreased on both the injured side and uninjured side; respiratory rate remained unchanged. This patient remained stable and required no intervention. Patient 3 demonstrated a sustained decrease in tidal measurements on the injured side that corresponded with radiograph findings and clinical deterioration leading to the need for endotracheal intubation. Conclusions The results from these cases demonstrate that respiratory volume monitor can generate unilateral respiratory tidal measurements and respiratory rate in patients with traumatic thoracic injuries. Continuous respiratory volume monitor in patients with thoracic trauma has strong potential for application in the military, aeromedical, and other austere environments where respiratory monitoring is problematic. Future studies to investigate the utility of this technology are warranted.

The evaluation of a non-invasive respiratory volume monitor in surgical patients undergoing elective surgery with general anesthesia.

Continuous respiratory assessment is especially important during post-operative care following extubation. Respiratory depression and subsequent adverse outcomes can arise due to opioid administration and/or residual anesthetics. A non-invasive respiratory volume monitor (RVM) has been developed that provides continuous, real-time, measurements of minute ventilation (MV), tidal volume (TV), and respiratory rate (RR) via a standardized set of thoracic electrodes. Previous work demonstrated accuracy of the RVM versus standard spirometry and its utility in demonstrating response to opioids in postoperative patients. This study evaluated the correlation between RVM measurements of MV, TV and RR to ventilator measurements during general anesthesia (GA). Continuous digital RVM and ventilator traces, as well as RVM measurements of MV, TV and RR, were analyzed from ten patients (mean 62.6±7.4 years; body mass index 28.6±5.2 kg/m2) undergoing surgery with GA. RVM data were compared to ventilator data and bias, precision and accuracy were calculated. The average MV difference between the RVM and ventilator was -0.10 L/min (bias: -1.3%, precision: 6.6%, accuracy: 9.0%. The average TV difference was 40 mL (bias: 0.4%, precision: 7.3%, accuracy: 9.1%). The average RR difference was -0.22 breaths/minute (bias: -1.8%, precision: 3.7% accuracy: 4.1%). Correlations between the RVM traces and the ventilator were compared at various points with correlations>0.90 throughout. Pairing the close correlation to ventilator measurements in intubated patients demonstrated by this study with previously described accuracy compared to spirometry in non-intubated patients, the RVM can be considered to have the capability to provide continuity of ventilation monitoring post-extubation This supports the use of real-time continuous RVM measurements to drive post-operative and post-extubation protocols, initiate therapeutic interventions and improve patient safety.

Tidal ventilation distribution during pressure-controlled ventilation and pressure support ventilation in post-cardiac surgery patients

Inhomogeneous ventilation is an important contributor to ventilator-induced lung injury. Therefore, this study examines homogeneity of lung ventilation by means of electrical impedance tomography (EIT) measurements during pressure-controlled ventilation (PCV) and pressure support ventilation (PSV) using the same ventilation pressures. Twenty mechanically ventilated patients were studied after cardiac surgery. On arrival at the intensive care unit, ventilation distribution was measured with EIT just above the diaphragm for 15 min. After awakening, PCV was switched to PSV and EIT measurements were again recorded. Tidal impedance variation, a measure of tidal volume, increased during PSV compared with PCV, despite using the same ventilation pressures (P = 0.045). The distribution of tidal ventilation to the dependent lung region was more pronounced during PSV compared with PCV, especially during the first half of the inspiration. An even distribution of tidal ventilation between the dependent and non-dependent lung regions was seen during PCV at lower tidal volumes (< 8 ml/kg) and PSV at higher tidal volumes (≥ 8 ml/kg). In addition, the distribution of tidal ventilation was predominantly distributed to the dependent lung during PSV at low tidal volumes. In post-cardiac surgery patients, PSV showed improved ventilation of the dependent lung region due to the contribution of the diaphragm activity, which is even more pronounced during lower assist levels.

Non-invasive respiratory monitoring using long-period fiber grating sensors.

In non-invasive ventilation, continuous monitoring of respiratory volumes is essential. Here, we present a method for the measurement of respiratory volumes by a single fiber-grating sensor of bending and provide the proof-of-principle by applying a calibration-test measurement procedure on a set of 18 healthy volunteers. Results establish a linear correlation between a change in lung volume and the corresponding change in a local thorax curvature. They also show good sensor accuracy in measurements of tidal and minute respiratory volumes for different types of breathing. The proposed technique does not rely on the air flow through an oronasal mask or the observation of chest movement by a clinician, which distinguishes it from the current clinical practice.

Accuracy of tidal breathing measurement of floright compared to an ultrasonic flowmeter in infants

Monitoring breathing pattern is especially relevant in infants with lung disease. Recently, a vest-based inductive plethysmograph system (FloRight®) has been developed for tidal breathing measurement in infants. We investigated the accuracy of tidal breathing flow volume loop (TBFVL) measurements in healthy term-born infants and infants with lung disease by the vest-based system in comparison to an ultrasonic flowmeter (USFM) with a face mask. We also investigated whether the system discriminates between healthy infants and those with lung disease. Floright® measures changes in thoracoabdominal volume during tidal breathing through magnetic field changes generated by current-carrying conductor coils in an elastic vest. Simultaneous TBFVL measurements by the vest-based system and the USFM were performed at 44 weeks corrected postmenstrual age during quiet unsedated sleep. TBFVL parameters derived by both techniques and within both groups were compared. We included 19 healthy infants and 18 infants with lung disease. Tidal volume per body weight derived by the vest-based system was significantly lower with a mean difference (95% CI) of -1.33 ml/kg (-1.73; -0.92), P < 0.001. Respiratory rate and ratio of time to peak tidal expiratory flow over total expiratory time (tPTEF/tE) did not differ between the two techniques. Both systems were able to discriminate between healthy infants and those with lung disease using tPTEF/tE. FloRight® accurately measures time indices and may discriminate between healthy infants and those with lung disease, but demonstrates differences in tidal volume measurements. It may be better suited to monitor breathing pattern than for TBFVL measurements.

Respiratory Volume Monitoring to Assess the Effect of Airway Maneuvers on Ventilation during Upper Endoscopy

Introduction: Propofol use during endoscopic procedures has become increasingly popular and assessing and maintaining airway patency is a significant challenge. Anesthesiologists often use airway maneuvers to maintain airway patency and ventilation during procedural sedation. A novel, non-invasive, Respiratory Volume Monitor (RVM) that provided continuous, real-time measurements of minute ventilation (MV), tidal volume (TV) and respiratory rate (RR) was used to monitor respiratory performance before, during, and after endoscopic procedures, quantify MV changes before and after airway maneuvers, and to quantify propofol-induced respiratory depression. Methods: RVM traces were obtained from 25 patients undergoing sedation for endoscopic procedures. Airway maneuvers were performed in 19/25 patients. All 25 patients received propofol as the primary sedative. Results: Forty-five airway maneuvers were performed. During these maneuvers, all respiratory parameters increased relative to pre-maneuver levels. On average, MV increased by 24% ± 5% (mean ± SEM), TV 14% ± 5% and RR: 17% ± 6%. The cohort average MVBASELINE was 9.5 ± 0.7 L/min (TV = 670 ± 60 ml, RR = 15 ± 0.7). Following propofol MV decreased transiently, reaching nadir five minutes after the last dose of propofol at 82% ± 10% of baseline (MV = 7.5 ± 1.0 L/min). The reduction in MV was driven by reduction in TV, not RR. Conclusions: Data demonstrated that RVM was able to track changes in ventilation and was able to quantify respiratory changes following airway maneuvers. All patients had a significant reduction in ventilatory volumes after propofol. Five minutes after the last dose of propofol, MV and TV were significantly reduced while RR was not, suggesting that monitoring respiratory rate alone was not a sufficient indicator of respiratory status.

In vitro and in vivo evaluation of a new large animal spirometry device using mainstream CO2 flow sensors

A spirometry device equipped with mainstream CO2 flow sensor is not available for large animal anaesthesia. To measure the resistance of a new large animal spirometry device and assess its agreement with reference methods for volume measurements. In vitro experiment and crossover study using anaesthetised horses. A flow partitioning device (FPD) equipped with 4 human CO2 flow sensors was tested. Pressure differences were measured across the whole FPD and across each sensor separately using air flows (range: 90-720 l/min). One sensor was connected to a spirometry monitor for in vitro volume (3, 5 and 7 l) measurements. These measurements were compared with a reference method. Five anaesthetised horses were used for tidal volume (VT) measurements using the FPD and a horse-lite sensor (reference method). Bland-Altman analysis, ANOVA and linear regression analysis were used for data analysis. Pressure differences across each sensor were similar suggesting equal flow partitioning. The resistance of the device increased with flow (range: 0.3-1.5 cmH2 O s/l) and was higher than that of the horse-lite. The limits of agreement for volume measurements were within -1 and 2% in vitro and -12 and 0% in vivo. Nine of 147 VT measurements in horses were outside of the ± 10% limits of acceptance but most of these erroneous measurements occurred with VTs lower than 4 l. The determined correction factor for volume measurements was 3.97 ± 0.03. The limits of agreement for volume measurements by the new device were within ± 10% using clinically relevant range of volumes. The new spirometry device can be recommended for measurement of VT in adult Warmblood horses.

Short- and long-term effects of a maternal low-protein diet on ventilation, O2/CO2chemoreception and arterial blood pressure in male rat offspring

Maternal undernutrition increases the risk of adult arterial hypertension. The present study investigated the short- and long-term effects of a maternal low-protein diet on respiratory rhythm, O₂/CO₂ chemosensitivity and arterial blood pressure (ABP) of the offspring. Male Wistar rats were divided into two groups according to their mothers' diets during gestation and lactation: control (NP, 17% of casein) and low-protein (LP, 8% of casein) groups. Direct measurements of ABP, respiratory frequency (RF), tidal volume (V T) and ventilation (VE), as well as hypercapnia (7% CO₂) and hypoxia (7% O₂) evoked respiratory responses were recorded from the awake male offspring at the 30th and 90th days of life. Blood samples were collected for the analyses of protein, creatinine and urea concentrations. The LP offspring had impaired body weight and length throughout the experiment. At 30 d of age, the LP rats showed a reduction in the concentrations of total serum protein (approximately 24%). ABP in the LP rats was similar to that in the NP rats at 30 d of age, but it was 20% higher at 90 d of age. With respect to ventilatory parameters, the LP rats showed enhanced RF (approximately 34%) and VE (approximately 34%) at 30 d of age, which was associated with increased ventilatory responses to hypercapnia (approximately 21% in VE) and hypoxia (approximately 82% in VE). At 90 d of age, the VE values and CO₂/O₂ chemosensitivity of the LP rats were restored to the control range, but the RF values remained elevated. The present data show that a perinatal LP diet alters respiratory rhythm and O₂/CO₂ chemosensitivity at early ages, which may be a predisposing factor for increased ABP at adulthood.

Influence of the Hand Squeeze and Mask Distensibility on Tidal Volume Measurements during Neonatal Mask Ventilation

Background: During mask ventilation, the mask volume can vary as it is pressurized or when it is squeezed. The change in volume of the mask may affect tidal volumes delivered and difference in inspired (V_ti) and expired tidal volumes (V_te). Objectives: To investigate whether hand squeeze and distensibility of the mask during ventilation influences tidal volume measurements. Methods: For both experiments, we ventilated a leak-free mask ventilation model using pressures of 25/5 cm H₂O through a t-piece. V_ti and V_te were measured. (A) Two consultants performed mask ventilation with (1) consistent hand squeeze, (2) release during inflation and squeeze during expiration, (3) squeeze during inflation, release during expiration, and (4) gentle squeeze. Results: (B) Thirty caregivers performed mask ventilation. Experiment A: V_ti was different during consistent hold (1) 8.1 ml (0.4) and loose grip (4) 8.2 ml (0.3), compared to squeezing during inflation (2) 18.9 ml (1.9), or expiration (3) 6.4 ml (3.5). Variance in difference between V_ti and V_te occurred only when the mask was squeezed during inflation (-47.4% (101.5)). Experiment B: volumes measured were consistent (intraindividual CV 3-5%, interindividual CV 9-10%). When comparing gas flow rate of 6-10 l/min, volumes increased by approximately 8%, differences in V_ti and V_te were small with both flow settings (-0.9% (-3.9-1.4) and -0.6% (-3.3-1.8); n.s.). Conclusion: Variation in mask hold during mask ventilation can influence volume measurement, but this hardly occurs when testing caregivers.

Tidal Volume Measurement Through Non-Contact Doppler Radar With DC Reconstruction

This paper describes the calibration technique for a non-contact Doppler radar to monitor respiration and tidal volume in human subjects. The detected change in sensor output, reflecting the displacement of lung movement, is found to relate linearly to tidal volume. The DC reconstruction and calibration techniques are used to extract the tidal volume measurement from the radar signal. Comparison of the radar prediction and reference tidal volumes shows the average mean difference (d) to be -38.9 ml in seated subjects and 23.5 ml in supine subjects. Other chest wall displacement measurements from piezo-electric sensors at the upper and lower torso reports worse d:-40.6 ml and -54.8 ml in seated subjects and 246.6 ml and 68.5 ml in supine subjects. The predicted volumes are not significantly affected by either frequency of respiration or variation in subjects. The results in this paper show that Doppler radar could provide a valuable tool for the noncontact and unobtrusive measurement of tidal volume in human subjects.

Evaluation of a Novel Noninvasive Respiration Monitor Providing Continuous Measurement of Minute Ventilation in Ambulatory Subjects in a Variety of Clinical Scenarios

Currently there is no technology that noninvasively measures the adequacy of ventilation in nonintubated patients. A novel, noninvasive Respiratory Volume Monitor (RVM) has been developed to continuously measure and display minute ventilation (MV), tidal volume (TV), and respiratory rate (RR) in a variety of clinical settings. We demonstrate the RVM's accuracy and precision as compared with a standard spirometer under a variety of clinically relevant breathing patterns in nonintubated subjects. Thirty-one voluntary subjects completed the primary study. MV, TV, and RR measurements were collected from the RVM and spirometer simultaneously for each participant on day 1 and day 2 and analyzed to determine accuracy, precision, and bias for normal, fast, slow, irregular, and closed-glottis breathing. Data demonstrated that RVM and spirometer measurements of MV and TV are equivalent in a wide range of ambulatory subjects with an average error <10% (95% confidence interval for accuracy <16%, precision <12%, and bias <11%). Repeated measures analysis of variance found no significant difference between spirometry and RVM individual measurements of MV, TV, and RR (P > 0.7), whereas a paired-difference equivalent test demonstrated, with 99% power, that both MV and TV measurements from the 2 devices are equivalent within ±15%. This study demonstrates RVM's clinically relevant accuracy and precision in measuring MV, TV, and RR over a 24-hour period and during various breathing patterns.

Closing the Loop on Relaxant Reversal

To the Editor:We read with interest the article by Thilen et al.1 pertaining to residual paralysis. We commend the authors for clarifying the pitfalls of monitoring the periorbital muscles as opposed to the adductor pollicis muscle. However, we are curious as to how adequate reversal of neuromuscular blockade was assessed prior to extubation. Depending on the density of the block, complete reversal after an intermediate duration neuromuscular blocker may be rapid, but could take up to roughly 50min.2 Due to the variability and the danger of respiratory complications with residual paralysis, we consider it essential to document that adequate reversal has in fact occurred. As Plaud et al.3 highlight in their excellent review article, subjective assessment of train-of-four strength and measurement of tidal volume, two often mentioned parameters, are wholly inadequate to assess adequate reversal. Without quantitative train-of-four monitoring intraoperatively, 5 s head lift and sustained tetanus with 100 Hz are the best available parameters, although even these are not completely adequate. We question which measures were used in this study.The authors state that the time interval from neostigmine administration to train-of-four ratio measurement was not significantly different between the two groups. Given the different degrees of neuromuscular blockade at the time of reversal (based on similar train-of-four at the two different sites), it is possible that the decision to extubate was based on time elapsed from neostigmine administration rather than specific measures of strength. The time pressure of getting patients extubated as well as reliance on less reliable measures such as tidal volume may explain this finding. While most patients will not be harmed (as shown in this study) by extubating with a train-of-four ratio less than 90, these patients are likely at increased risk of respiratory complications.4 As such, we encourage practitioners to confirm that the reversal drug has had the desired effect. To not do so makes an assumption which will be incorrect in a small but real percentage of patients.

Comparing the Effects of Rise Time and Inspiratory Cycling Criteria on 6 Different Mechanical Ventilators

Inspiratory rise time and cycling criteria are important settings in pressure support ventilation. The purpose of this study was to investigate the impact of minimum and maximum rise time and inspiratory cycling criteria settings on 6 new generation ventilators. Our hypothesis was there would be a difference in the exhaled tidal volume, inspiratory time, and peak flow among 6 different ventilators, based, on change in rise time and cycling criteria. The research utilized a breathing simulator and 4 different ventilator models. All mechanical ventilators were set to a spontaneous mode of ventilation with settings of pressure support 8 cm H2O and PEEP of 5 cm H2O. A minimum and maximum setting for rise time and cycling criteria were examined. Exhaled tidal volume, inspiratory time, and peak flow measurements were recorded for each simulation. Significant (P < .001) differences were found when comparing minimum and maximum rise time and minimum and maximum cycling criteria for each ventilator. Significant differences in exhaled tidal volume, inspiratory time, and peak flow were observed by adjusting rise time and cycling criteria. This research demonstrates that during pressure support ventilation strategy, adjustments in rise time and/or cycling criteria can produce changes in inspiratory parameters. Obviously, this finding has important implications for practitioners who utilize a similar pressure support strategy when conducting a ventilator wean. Additionally, this study outlines major differences among ventilator manufacturers when considering inspiratory rise time and cycling criteria.

Acetazolamide Attenuates the Ventilatory Response to Arousal in Patients with Obstructive Sleep Apnea

The magnitude of the post-apnea/hypopnea ventilatory overshoot following arousal may perpetuate subsequent respiratory events in obstructive sleep apnea (OSA) patients, potentially contributing to the disorder's severity. As acetazolamide can reduce apnea severity in some patients, we examined the effect of acetazolamide on the ventilatory response to spontaneous arousals in CPAP-treated OSA patients. We assessed the ventilatory response to arousal in OSA patients on therapeutic CPAP before and after administration of acetazolamide for 7 days. Sleep research laboratory. 12 (7M/5F) CPAP-treated OSA patients. Sustained-release acetazolamide 500 mg by mouth twice daily for one week. A blinded investigator identified spontaneous arousals (3-15 s) during NREM sleep. Breath-by-breath measurements of minute ventilation, end-tidal CO(2), tidal volume, expiratory/inspiratory-time, and total breath duration were determined (4-s intervals) 32 s prior and 60 s following each arousal. Acetazolamide significantly increased resting ventilation (7.3 ± 0.2 L/min versus 8.2 ± 0.4 L/min; P < 0.05) and attenuated the percent increase in ventilation following arousal by ~2.5 fold (122.0% ± 4.4% versus 108.7% ± 3.5% pre-arousal level; P < 0.05). There was a positive correlation between the mean increase in ventilatory response to arousal and mean AHI (r(2) = 0.44, P = 0.01). However, absolute peak levels of ventilation following arousal remained unchanged between conditions (8.8 ± 0.4 L/min versus 8.9 ± 0.1 L/min). Acetazolamide substantially attenuates the increase in ventilation following spontaneous arousal from sleep in OSA patients. This study suggests an additional mechanism by which acetazolamide may contribute to the improvement in ventilatory instability and OSA severity. The data also provide support for reinforcing the importance of ventilatory control in OSA pathogenesis.

Measurement of tidal volume using Respiratory Ultrasonic Plethysmography in anaesthetized, mechanically ventilated horses

ObjectiveTo compare tidal volume estimations obtained from Respiratory Ultrasonic Plethysmography (RUP) with simultaneous spirometric measurements in anaesthetized, mechanically ventilated horses. Study designProspective randomized experimental study. AnimalsFive experimental horses. MethodsFive horses were anaesthetized twice (1 week apart) in random order in lateral and in dorsal recumbency. Nine ventilation modes (treatments) were scheduled in random order (each lasting 4 minutes) applying combinations of different tidal volumes (8, 10, 12 mL kg−1) and positive end-expiratory pressures (PEEP) (0, 10, 20 cm H2O). Baseline ventilation mode (tidal volume = 15 mL kg−1, PEEP = 0 cm H2O) was applied for 4 minutes between all treatments. Spirometry and RUP data were downloaded to personal computers. Linear regression analyses (RUP versus spirometric tidal volume) were performed using different subsets of data. Additonally RUP was calibrated against spirometry using a regression equation for all RUP signal values (thoracic, abdominal and combined) with all data collectively and also by an individually determined best regression equation (highest R2) for each experiment (horse versus recumbency) separately. Agreement between methods was assessed with Bland-Altman analyses. ResultsThe highest correlation of RUP and spirometric tidal volume (R2 = 0.81) was found with the combined RUP signal in horses in lateral recumbency and ventilated without PEEP. The bias ± 2 SD was 0 ± 2.66 L when RUP was calibrated for collective data, but decreased to 0 ± 0.87 L when RUP was calibrated with individual data. Conclusions and clinical relevanceA possible use of RUP for tidal volume measurement during IPPV needs individual calibration to obtain limits of agreement within ± 20%.

ACOUSTIC PLETHYSMOGRAPH FOR MEASURING PULMONARY FUNCTION

The present disclosure concerns embodiments of an acoustic plethysmograph for measuring pulmonary function of an animal, such as a mouse. The plethysmograph in exemplary embodiments can measure thoracic tidal volume of an unrestrained animal. The plethysmograph in exemplary embodiments acoustically excites the chamber containing the animal and detects changes in the acoustic pressure in the chamber, which correlate to the thoracic tidal volume of the animal. Unlike the conventional whole-body plethysmograph, this acoustic plethysmograph provides a direct measure of thoracic tidal volume. The plethysmograph also can be configured to measure chamber flow (the flow of air into and out of the chamber). Specific airway resistance of the animal can then be determined from the thoracic tidal volume and plethysmograph flow measurements.

Expiratory time constant for determinations of plateau pressure, respiratory system compliance, and total resistance

IntroductionWe hypothesized the expiratory time constant (ƬE) may be used to provide real time determinations of inspiratory plateau pressure (Pplt), respiratory system compliance (Crs), and total resistance (respiratory system resistance plus series resistance of endotracheal tube) (Rtot) of patients with respiratory failure using various modes of ventilatory support.MethodsAdults (n = 92) with acute respiratory failure were categorized into four groups depending on the mode of ventilatory support ordered by attending physicians, i.e., volume controlled-continuous mandatory ventilation (VC-CMV), volume controlled-synchronized intermittent mandatory ventilation (VC-SIMV), volume control plus (VC+), and pressure support ventilation (PSV). Positive end expiratory pressure as ordered was combined with all aforementioned modes. Pplt, determined by the traditional end inspiratory pause (EIP) method, was combined in equations to determine Crs and Rtot. Following that, the ƬE method was employed, ƬE was estimated from point-by-point measurements of exhaled tidal volume and flow rate, it was then combined in equations to determine Pplt, Crs, and Rtot. Both methods were compared using regression analysis.ResultsƬE, ranging from mean values of 0.54 sec to 0.66 sec, was not significantly different among ventilatory modes. The ƬE method was an excellent predictor of Pplt, Crs, and Rtot for various ventilatory modes; r2 values for the relationships of ƬE and EIP methods ranged from 0.94 to 0.99 for Pplt, 0.90 to 0.99 for Crs, and 0.88 to 0.94 for Rtot (P <0.001). Bias and precision values were negligible.ConclusionsWe found the ƬE method was just as good as the EIP method for determining Pplt, Crs, and Rtot for various modes of ventilatory support for patients with acute respiratory failure. It is unclear if the ƬE method can be generalized to patients with chronic obstructive lung disease. ƬE is determined during passive deflation of the lungs without the need for changing the ventilatory mode and disrupting a patient's breathing. The ƬE method obviates the need to apply an EIP, allows for continuous and automatic surveillance of inspiratory Pplt so it can be maintained ≤ 30 cm H2O for lung protection and patient safety, and permits real time assessments of pulmonary mechanics.

Abstract 19585: Tidal Volume and Minute Ventilation Measurement at High, Low, and Erratic Respiratory Rates by a Non-Invasive Respiratory Monitoring System

Introduction: Changes in minute ventilation (MV) &amp; tidal volume (TV) signal the beginning of respiratory compromise which often precedes cardiopulmonary arrest. Currently, respiratory monitoring in non-intubated patients lacks objective &amp; quantitative methodology for determining the adequacy of ventilation. A non-invasive, Respiratory Volume Measurement (RVM) system has been developed to measure MV, TV and respiratory rate (RR) continuously. Previous work has demonstrated clinically acceptable accuracy and precision of RVM monitoring across normal respiratory patterns and rates. Hypothesis: RVM monitoring accurately yields tidal volume &amp; minute ventilation across abnormal breathing rates, and erratic patterns. Methods: We studied 51 adult subjects (93 visits, 2252 tests) at low (4 - 6 bpm), normal (8 - 20 bpm), and high (30 - 40 bpm) respiratory rates and during erratic breathing. TV, RR and MV were measured simultaneously with an impedance-based RVM system (ExSpiron, Respiratory Motion, Inc., Waltham, MA) and a dry rolling seal spirometer (Morgan Scientific Inc., Haverhill, MA). Advanced data processing algorithms displayed a real time respiratory curve and calculated RVM measurements. Results: Throughout the range of 4 bpm to 40 bpm and during erratic breathing, RVM measurements are highly-correlated with spirometer measurements, with an average MV and TV correlation coefficient of 0.96, 95% CI 0.93 to 0.99 (Fig 1). Across all subjects, median correlation coefficients ranged from 0.91 to 0.99. Conclusions: High correlation (r = 0.96) between spirometric measurements and RVM signals concludes that the RVM system is capable of monitoring respiratory status during normal and erratic breathing, and at high and low breathing rates. As a passive, continuous, non-invasive system, RVM monitoring of non-intubated patients could provide earlier indications of respiratory decline potentially permitting interventions to prevent cardiopulmonary arrest.

Effects of Nasal High Flow on Ventilation in Volunteers, COPD and Idiopathic Pulmonary Fibrosis Patients

Background: A high flow of air applied by large bore nasal cannulae has been suggested to improve symptoms of chronic respiratory insufficiency. In pediatric patients, nasal high-flow (nHF) ventilation was similarly effective compared to noninvasive ventilation with a face mask. Objectives: The aim of this study was to describe changes in respiratory parameters. Methods: We measured pressure amplitudes during the respiratory cycle and mean pressures in patients with idiopathic pulmonary fibrosis (IPF) and COPD. In order to achieve tidal volume and minute volume measurements, we used a polysomnography device. Capillary blood was taken for blood gas analysis before and after nHF breathing (8 h). Results: nHF led to an increase in pressure amplitude and mean pressure in healthy volunteers and in patients with COPD and IPF in comparison with spontaneous breathing. In COPD, nHF increased tidal volume, while no difference in tidal volume was observed in patients with IPF. Interestingly, tidal volume decreased in healthy volunteers. Breathing rates and minute volumes were reduced in all groups. Capillary pCO₂ decreased in patients with IPF and COPD. Conclusions: nHF resulted in significant effects on respiratory parameters in patients with obstructive and restrictive pulmonary diseases. The rise in pressure amplitude and mean pressure and the decrease in breathing rate and minute volume will support inspiratory efforts, helps to increase effectiveness of ventilation and will contribute to a reduction in the work of breathing. A CO₂ wash-out effect in the upper airway part of the anatomical dead space may contribute to the beneficial effects of the nHF instrument.

Optoelectronic plethysmography compared to spirometry during maximal exercise

The purpose of this study was to compare simultaneous measurements of tidal volume (Vt) by optoelectronic plethysmography (OEP) and spirometry during a maximal cycling exercise test to quantify possible differences between methods.Vt measured simultaneously by OEP and spirometry was collected during a maximal exercise test in thirty healthy participants. The two methods were compared by linear regression and Bland–Altman analysis at submaximal and maximal exercise. The average difference between the two methods and the mean percentage discrepancy were calculated.Submaximal exercise (SM) and maximal exercise (M) Vt measured by OEP and spirometry had very good correlation, SM R=0.963 (p<0.001), M R=0.982 (p<0.001) and high degree of common variance, SM R2=0.928, M R2=0.983. Bland–Altman analysis demonstrated that during SM, OEP could measure exercise Vt as much as 0.134L above and −0.025L below that of spirometry. OEP could measure exercise Vt as much as 0.188L above and −0.017L below that of spirometry. The discrepancy between measurements was −2.0±7.2% at SM and −2.4±3.9% at M.In conclusion, Vt measurements at during exercise by OEP and spirometry are closely correlated and the difference between measurements was insignificant.