Esophageal Balloon Catheter Research Articles

Quantifying Diaphragm Blood Flow With Contrast-Enhanced Ultrasound in Humans

Despite the known interplay between blood flow and function, to our knowledge, there is currently no minimally invasive method to monitor diaphragm hemodynamics. We used contrast-enhanced ultrasound to quantify relative diaphragm blood flow (Q˙DIA) in humans and assessed the technique's efficacy and reliability during graded inspiratory pressure threshold loading. We hypothesized that: (1) Q˙DIA would linearly increase with pressure generation, and (2) that there would be good test-retest reliability and interanalyzer reproducibility. Can we validate what is, to our knowledge, the first minimally invasive method to measure relative diaphragm blood flow in humans? Quantitative contrast-enhanced ultrasound of the costal diaphragm was performed in healthy participants (10 male participants, 6 female participants; mean age 28 ± 5 years; BMI 22.8 ± 2.0kg/m) during unloaded breathing and three stages of loaded breathing on two separate days. Gastric and esophageal balloon catheters measured transdiaphragmatic pressure. Ultrasonography was performed during a constant-rate IV infusion of lipid-stabilized microbubbles following each stage. Ultrasound images were acquired after a destruction-replenishment sequence and diaphragm specific time-intensity data were used to determine Q˙DIA by two individuals. Transdiaphragmatic pressure for unloaded and each loading stage were 15.2 ± 0.8, 26.1 ± 0.8, 34.6 ± 0.8, and 40.0 ± 0.8 percentage of the maximum, respectively. Q˙DIA increased with each stage of loading (3.1 ± 3.1, 6.9 ± 3.6, 11.0 ± 4.9, and 13.5 ± 5.4 acoustic units/s; P< .0001). The linear relationship between diaphragmatic flow and pressure was reproducible from day to day. Q˙DIA had good to excellent test-retest reliability (0.86 [0.77, 0.92]; P< .0001) and excellent interanalyzer reproducibility (0.93 [0.90, 0.95]; P< .0001) with minimal bias. Relative Q˙DIA measurements had valid physiological underpinnings, were reliable day-to-day, and were reproducible analyzer-to-analyzer. This study indicated that contrast-enhanced ultrasound is a viable, minimally invasive method for assessing costal Q˙DIA in humans and may provide a tool to monitor diaphragm hemodynamics in clinical settings.

Comparative analysis of novel esophageal pressure monitoring catheters versus commercially available alternatives in a biomechanical model of the thoracic cavity

Transpulmonary pressure can be estimated using esophageal balloon (EB) catheters, which come in a variety of manufacturing configurations. We assessed the performance of novel polyurethane EB designs, Aspisafe NG and NG+, against existing alternatives. We created a biomechanical model of the chest cavity using a plastic chamber and an ex-vivo porcine esophagus. The chamber was pressurized (− 20 and + 20 cmH2O) to simulate pleural pressures. We conducted tests with various EB inflation volumes and measured transesophageal pressure (TEP). TEP measurement was defined as accurate when the difference between pressure within the EB and chamber was 0 ± 1 cmH2O. We computed the minimal (Vaccuracy-min) and maximal (Vaccuracy-max) EB inflation volumes of accuracy. Inflation volumes were further validated using a surrogate method derived by the clinically validated positive pressure occlusion test (PPOT). When the esophageal balloons were filled with inflation volumes within the range provided by the manufacturers, the accuracy of TEP measurements was marginal. Our tests found median Vaccuracy-min across EB of 0.00–0.50 mL (p = 0.130), whereas Vaccuracy-max ranged 0.50–2.25 mL (p = 0.002). Post PPOT validation, median TEP was − 0.4 cmH2O (− 1.5 to 0.3) (p < 0.001 among catheters). The Aspisafe NG and NG+ were accurate in 81.7% and 77.8% of the measurements, respectively. We characterized two new EBs, which demonstrated good benchtop accuracy in TEP measurements. However, accuracy was notably influenced by the precise selection of EB inflation volumes.

Estimation of the transpulmonary pressure from the central venous pressure in mechanically ventilated patients

Transpulmonary pressure (PL) calculation requires esophageal pressure (PES) as a surrogate of pleural pressure (Ppl), but its calibration is a cumbersome technique. Central venous pressure (CVP) swings may reflect tidal variations in Ppl and could be used instead of PES, but the interpretation of CVP waveforms could be difficult due to superposition of heartbeat-induced pressure changes. Thus, we developed a digital filter able to remove the cardiac noise to obtain a filtered CVP (f-CVP). The aim of the study was to evaluate the accuracy of CVP and filtered CVP swings (ΔCVP and Δf-CVP, respectively) in estimating esophageal respiratory swings (ΔPES) and compare PL calculated with CVP, f-CVP and PES; then we tested the diagnostic accuracy of the f-CVP method to identify unsafe high PL levels, defined as PL>10 cmH2O. Twenty patients with acute respiratory failure (defined as PaO2/FiO2 ratio below 200 mmHg) treated with invasive mechanical ventilation and monitored with an esophageal balloon and central venous catheter were enrolled prospectively. For each patient a recording session at baseline was performed, repeated if a modification in ventilatory settings occurred. PES, CVP and airway pressure during an end-inspiratory and -expiratory pause were simultaneously recorded; CVP, f-CVP and PES waveforms were analyzed off-line and used to calculate transpulmonary pressure (PLCVP, PLf-CVP, PLPES, respectively). Δf-CVP correlated better than ΔCVP with ΔPES (r = 0.8, p = 0.001 vs. r = 0.08, p = 0.73), with a lower bias in Bland Altman analysis in favor of PLf-CVP (mean bias − 0.16, Limits of Agreement (LoA) -1.31, 0.98 cmH2O vs. mean bias − 0.79, LoA − 3.14, 1.55 cmH2O). Both PLf-CVP and PLCVP correlated well with PLPES (r = 0.98, p < 0.001 vs. r = 0.94, p < 0.001), again with a lower bias in Bland Altman analysis in favor of PLf-CVP (0.15, LoA − 0.95, 1.26 cmH2O vs. 0.80, LoA − 1.51, 3.12, cmH2O). PLf-CVP discriminated high PL value with an area under the receiver operating characteristic curve 0.99 (standard deviation, SD, 0.02) (AUC difference = 0.01 [-0.024; 0.05], p = 0.48). In mechanically ventilated patients with acute respiratory failure, the digital filtered CVP estimated ΔPES and PL obtained from digital filtered CVP represented a reliable value of standard PL measured with the esophageal method and could identify patients with non-protective ventilation settings.

Evaluation of Optimal Esophageal Catheter Balloon Inflation Volume in Mechanically Ventilated Children.

Accuracy of esophageal pressure measured by an air-filled esophageal balloon catheter is dependent on balloon filling volume. However, this has been understudied in mechanically ventilated children. We sought to study the optimal filling volume in children receiving ventilation by using previously reported calibration methods. Secondary objectives included to examine the difference in pressure measurements at individualized optimal filling volume versus a standardized inflation volume and to study if a static hold during calibration is required to identify the optimal filling volume. An incremental inflation calibration procedure was performed in children receiving ventilation, <18 y, instrumented with commercially available catheters (6 or 8 French) who were not breathing spontaneously. The balloon was manually inflated by 0.2 to 1.6 mL (6 French) or 2.6 mL (8 French). Esophageal pressure (Pes) and airway pressure tracings were recorded during the procedure. Data were analyzed offline by using 2 methods: visual determination of filling range with the calculation of the highest difference between expiratory and inspiratory Pes and determination of a correctly filled balloon by calculating the esophageal elastance. We enrolled 40 subjects with median (interquartile range [IQR]) age 6.8 (2-25) months. The optimal filling volume ranged from 0.2 to 1.2 mL (median [IQR] 0.6 [0.2-1.0] mL) in the subjects with a 6 French catheter and 0.2-2.0 mL (median [IQR] 0.7 [0.5-1.2] mL) for 8 French catheters. Inflating the balloon with 0.6 mL (median computed from the whole cohort) gave an absolute difference in transpulmonary pressure that ranged from -4 to 7 cm H2O compared with the personalized volume. Pes calculated over 5 consecutives breaths differed with a maximum of 1 cm H2O compared to Pes calculated during a single inspiratory hold. The esophageal elastance was correlated with weight, age, and sex. The optimal balloon inflation volume was highly variable, which indicated the need for an individual calibration procedure. Pes was not overestimated when an inspiratory hold was not applied.

Esophageal balloon catheter system identification to improve respiratory effort time features and amplitude determination

Objective. Understanding a patient’s respiratory effort and mechanics is essential for the provision of individualized care during mechanical ventilation. However, measurement of transpulmonary pressure (the difference between airway and pleural pressures) is not easily performed in practice. While airway pressures are available on most mechanical ventilators, pleural pressures are measured indirectly by an esophageal balloon catheter. In many cases, esophageal pressure readings take other phenomena into account and are not a reliable measure of pleural pressure. Approach. A system identification approach was applied to provide accurate pleural measures from esophageal pressure readings. First, we used a closed pressurized chamber to stimulate an esophageal balloon and model its dynamics. Second, we created a simplified version of an artificial lung and tried the model with different ventilation configurations. For validation, data from 11 patients (five male and six female) were used to estimate respiratory effort profile and patient mechanics. Main results. After correcting the dynamic response of the balloon catheter, the estimates of resistance and compliance and the corresponding respiratory effort waveform were improved when compared with the adjusted quantities in the test bench. The performance of the estimated model was evaluated using the respiratory pause/occlusion maneuver, demonstrating improved agreement between the airway and esophageal pressure waveforms when using the normalized mean squared error metric. Using the corrected muscle pressure waveform, we detected start and peak times 130 ± 50 ms earlier and a peak amplitude 2.04 ± 1.46 cmH2O higher than the corresponding estimates from esophageal catheter readings. Significance. Compensating the acquired measurements with system identification techniques makes the readings more accurate, possibly better portraying the patient’s situation for individualization of ventilation therapy.

The calibration of esophageal pressure by proper esophageal balloon filling volume: A clinical study.

Esophageal pressure (Pes) can be used as a reliable surrogate for pleural pressure, especially in critically ill patients requiring personalized mechanical ventilation strategies. How to choose the proper esophageal balloon filling volume and then find the optimal value of esophageal pressure remains a challenge. The study aimed to assess the feasibility of catheters for Pes monitoring in mechanically ventilated patients. Twelve patients under pressure-controlled mechanical ventilation were included in this study. Raw esophageal pressure was recorded at different balloon filling volumes. Then, the P-V curves were determined. V WORK was the intermediate linear section on the end-expiratory P-V curve, and V BEST was the filling volume providing the maximum difference between Pes at end-inspiration and end-expiration. The raw value of Pes was recorded, and the calibrated values of Pes were calculated by calculating the esophageal wall pressure (Pew) and esophageal elastance (Ees). Twenty-four series of Pes measurements were performed. The mean V MIN and V MAX were 2.17 ± 0.49 ml (range, 1.0-3.0 ml) and 6.79 ± 0.83 ml (range, 5.0-9.0 ml), respectively, whereas V BEST was 4.69 ± 0.16 ml (range, 2.0-8.0 ml). Ees was 1.35 ± 0.51 cm H2O/ml (range, 0.26-2.38 cm H2O/ml). The estimated Pew at V BEST was 3.16 ± 2.19 cm H2O (range, 0-7.97 cm H2O). Patients with a body mass index (BMI) ≥ 25 kg/m2 had a significantly lower V MAX (5.88 [5.25-6] vs. 7.25 [7-8] ml, p = 0.006) and a significantly lower V BEST (3.69 [2.5-4.38] vs. 5.19 [4-6] ml, p = 0.036) than patients with a BMI < 25 kg/m2. Patients with positive end-expiratory pressure (PEEP) ≥ 10 cm H2O had a lower V MIN and V BEST than patients with PEEP < 10 cm H2O, P > 0.05. Patients in the supine position had a higher esophageal pressure than those in the prone position with the same balloon filling volume. Calibration of esophageal pressure to identify the best filling volume of esophageal balloon catheters is feasible. The esophageal pressure can be influenced by BMI, PEEP, and position. It is necessary to titrate the optimal inflation volume again when the PEEP values or the positions change.

The Effect Of Sex On The Mechanical Cost And Work Of Breathing During Exercise

Sex differences in pulmonary system structure and function lead to differences in respiratory mechanics during exercise. Specifically, women incur a greater power of breathing (Pb) during exercise than men. However, women typically display a more rapid breathing pattern at a given minute ventilation during exercise and, as such, it remains unclear whether previously reported sex differences in Pb are due to higher respiratory frequencies (i.e., more breaths per minute), or if the work of breathing (Wb) is indeed greater per breath in women compared with men. Moreover, it remains unclear whether differences exist between sexes when the Wb during exercise is converted to a mechanical cost of breathing (i.e., J·L-1). PURPOSE: To examine differences in the Wb (J·breath-1) and the mechanical cost of breathing (J·L-1) between men and women during incremental cycling. METHODS: Forty-two healthy participants (29 ± 15 yrs) completed a graded exercise test on a cycle ergometer. During the test, participants were instrumented with an esophageal balloon catheter to measure esophageal pressure as a surrogate of pleural pressure. Chest wall compliance was measured at rest before exercise via the two-point method. The Wb was determined via the modified Campbell diagram. The mechanical cost was computed as Wb divided by tidal volume. To compare the Wb (and components) and the mechanical cost between sexes we used a generalized additive mixed model (GAMM) approach. Values are reported as the mean and 95% confidence interval. RESULTS: The total Wb was greater in men than women at ventilations >140 L·min-1 (men = 12.9 J·breath-1 [11.8, 14.1]; women = 11.4 J·breath-1 [10.2, 12.5]; p < 0.05). The mechanical cost of breathing was greater in women at ventilations >95 L·min-1 (men = 2.7 J·L-1 [2.3, 3.2]; women = 3.4 J·L-1 [2.9, 3.8]; p < 0.05). CONCLUSIONS: Wb (J·breath-1) is effectively no different between sexes across all ventilations attained by the women in our study (up to 120 L·min-1). Even when tidal volume is taken into consideration, the mechanical cost of breathing is not greater in women until high ventilations suggesting that differences in the Pb are due to sex differences in breathing pattern rather than differences in the mechanical cost of breathing.

Influence of respiratory loading on left-ventricular function in cervical spinal cord injury.

Cervical spinal cord injury (C-SCI) negatively impacts cardiac and respiratory function. As the heart and lungs are linked via the pulmonary circuit these systems are interdependent. Here, we utilized inspiratory and expiratory loading to assess whether augmenting the respiratory pump improves left-ventricular (LV) filling and output in individuals with motor-complete C-SCI. We hypothesized LV end-diastolic volume (LVEDV) would increase and decrease with inspiratory and expiratory loading, respectively. Participants (C-SCI: 7M/1F, 35±7years; able-bodied: 7M/1F, 32±6years) were assessed under five conditions during 45° head-up tilt; unloaded, inspiratory loading with -10 and -20cmH2 O oesophageal pressure (Poes ) on inspiration, and expiratory loading with +10 and +20cmH2 O Poes on expiration. An oesophageal balloon catheter monitored Poes , and LV structure and function were assessed by echocardiography. In C-SCI only, (1) +20cmH2 O reduced LVEDV vs. unloaded (81±15 vs. 88±11ml, P=0.006); (2) heart rate was higher during +20cmH2 O compared to unloaded (P=0.001) and +10cmH2 O (P=0.002); (3) cardiac output was higher during +20cmH2 O than unloaded (P=0.002); and (4) end-expiratory lung volume was higher during +20cmH2 O vs. unloaded (63±10 vs. 55±13% total lung capacity, P=0.003) but was unaffected by inspiratory loading. In both groups, -10 and -20cmH2 O had no significant effect on LVEDV. These findings suggest greater expiratory positive pressure acutely impairs LV filling in C-SCI, potentially via impaired venous return, mediastinal constraint and/or direct ventricular interaction subsequent to dynamic hyperinflation. Inspiratory loading did not significantly improve LV function in C-SCI and neither inspiratory nor expiratory loading affected cardiac function or lung volumes in able-bodied participants. KEY POINTS: Cervical spinal cord injury (C-SCI) alters both the cardiac and the respiratory system, but little is known about how these systems interact following injury. Here, we manipulated inspiratory or expiratory intrathoracic pressure (ITP) to mechanistically test the role of the respiratory pump in circulatory function in highly trained individuals with C-SCI and an able-bodied reference group. In individuals with C-SCI, greater ITP during expiratory loading caused dynamic hyperinflation that was associated with impaired left-ventricular filling. More negative ITP during inspiratory loading did not significantly alter left-ventricular volumes in either group. Interventions that prevent dynamic hyperinflation and/or enhance the ability to generate expiratory pressures may help preserve left-ventricular filling in individuals with C-SCI.

Reproducible determination of transpulmonary pressures

Oesophageal pressures, as measured in an oesophageal balloon catheter, are a validated substitute for pleural pressures.Transpulmonary pressures, indispensable to improve our understanding of ventilatory physiology, are therefore typically calculated as the difference between airway and oesophageal pressures.The oesophageal pressure signal, however, features a superimposed oscillation due to cardiac motion, not representative for pleural pressure. Additionally, oesophageal contractions or surgical manipulation can alter the signal. In practice, transpulmonary pressures are therefore manually determined from the pressure-time graphic by visual inspection of the waves and averaging a limited number of samples.We suggest an approach to extract the end-expiratory transpulmonary pressure from the raw monitoring data.•Our approach reproducibly determines end-expiratory transpulmonary pressures at a given level of set positive end-expiratory pressure at the ventilator.•Our approach ignores surgical disturbance and cardiac oscillations in the oesophageal pressure signal.

Surface EMG-based quantification of inspiratory effort: a quantitative comparison with Pes

BackgroundInspiratory patient effort under assisted mechanical ventilation is an important quantity for assessing patient–ventilator interaction and recognizing over and under assistance. An established clinical standard is respiratory muscle pressure textit{P}_{mathrm{mus}}, derived from esophageal pressure (textit{P}_{mathrm{es}}), which requires the correct placement and calibration of an esophageal balloon catheter. Surface electromyography (sEMG) of the respiratory muscles represents a promising and straightforward alternative technique, enabling non-invasive monitoring of patient activity.MethodsA prospective observational study was conducted with patients under assisted mechanical ventilation, who were scheduled for elective bronchoscopy. Airway flow and pressure, esophageal/gastric pressures and sEMG of the diaphragm and intercostal muscles were recorded at four levels of pressure support ventilation. Patient efforts were quantified via the textit{P}_{mathrm{mus}}-time product ({mathrm{PTP}}_{mathrm{mus}}), the transdiaphragmatic pressure-time product ({mathrm{PTP}}_{mathrm{di}}) and the EMG-time products (ETP) of the two sEMG channels. To improve the signal-to-noise ratio, a method for automatically selecting the more informative of the sEMG channels was investigated. Correlation between ETP and {mathrm{PTP}}_{mathrm{mus}} was assessed by determining a neuromechanical conversion factor textit{K}_{mathrm{EMG}} between the two quantities. Moreover, it was investigated whether this scalar can be reliably determined from airway pressure during occlusion maneuvers, thus allowing to quantify inspiratory effort based solely on sEMG measurements.ResultsIn total, 62 patients with heterogeneous pulmonary diseases were enrolled in the study, 43 of which were included in the data analysis. The ETP of the two sEMG channels was well correlated with {mathrm{PTP}}_{mathrm{mus}} (textit{r}={0.79pm 0.25} and textit{r}={0.84pm 0.16} for diaphragm and intercostal recordings, respectively). The proposed automatic channel selection method improved correlation with {mathrm{PTP}}_{mathrm{mus}} (textit{r}={0.87pm 0.09}). The neuromechanical conversion factor obtained by fitting ETP to {mathrm{PTP}}_{mathrm{mus}} varied widely between patients (textit{K}_{mathrm{EMG}}= {4.32pm 3.73},{hbox {cm}hbox {H}_{2}hbox {O}/upmu hbox {V}}) and was highly correlated with the scalar determined during occlusions (textit{r}={0.95}, textit{p}<{.001}). The occlusion-based method for deriving {mathrm{PTP}}_{mathrm{mus}} from ETP showed a breath-wise deviation to {mathrm{PTP}}_{mathrm{mus}} of {0.43pm 1.73},{hbox {cm}hbox {H}_{2}hbox {O},hbox {s}} across all datasets.ConclusionThese results support the use of surface electromyography as a non-invasive alternative for monitoring breath-by-breath inspiratory effort of patients under assisted mechanical ventilation.

Novel method of transpulmonary pressure measurement with an air-filled esophageal catheter

BackgroundThere is a strong rationale for proposing transpulmonary pressure-guided protective ventilation in acute respiratory distress syndrome. The reference esophageal balloon catheter method requires complex in vivo calibration, expertise and specific material order. A simple, inexpensive, accurate and reproducible method of measuring esophageal pressure would greatly facilitate the measure of transpulmonary pressure to individualize protective ventilation in the intensive care unit.ResultsWe propose an air-filled esophageal catheter method without balloon, using a disposable catheter that allows reproducible esophageal pressure measurements. We use a 49-cm-long 10 Fr thin suction catheter, positioned in the lower-third of the esophagus and connected to an air-filled disposable blood pressure transducer bound to the monitor and pressurized by an air-filled infusion bag. Only simple calibration by zeroing the transducer to atmospheric pressure and unit conversion from mmHg to cmH2O are required. We compared our method with the reference balloon catheter both ex vivo, using pressure chambers, and in vivo, in 15 consecutive mechanically ventilated patients. Esophageal-to-airway pressure change ratios during the dynamic occlusion test were close to one (1.03 ± 0.19 and 1.00 ± 0.16 in the controlled and assisted modes, respectively), validating the proper esophageal positioning. The Bland–Altman analysis revealed no bias of our method compared with the reference and good precision for inspiratory, expiratory and delta esophageal pressure measurements in both the controlled (largest bias −0.5 cmH2O [95% confidence interval: −0.9; −0.1] cmH2O; largest limits of agreement −3.5 to 2.5 cmH2O) and assisted modes (largest bias −0.3 [−2.6; 2.0] cmH2O). We observed a good repeatability (intra-observer, intraclass correlation coefficient, ICC: 0.89 [0.79; 0.96]) and reproducibility (inter-observer ICC: 0.89 [0.76; 0.96]) of esophageal measurements. The direct comparison with pleural pressure in two patients and spectral analysis by Fourier transform confirmed the reliability of the air-filled catheter-derived esophageal pressure as an accurate surrogate of pleural pressure. A calculator for transpulmonary pressures is available online.ConclusionsWe propose a simple, minimally invasive, inexpensive and reproducible method for esophageal pressure monitoring with an air-filled esophageal catheter without balloon. It holds the promise of widespread bedside use of transpulmonary pressure-guided protective ventilation in ICU patients.

Effects of the Elevation Training Mask® 2.0 on dyspnea and respiratory muscle mechanics, electromyography, and fatigue during exhaustive cycling in healthy humans

ObjectivesExamine the effects of the Elevation Training Mask® 2.0 (ETM) on dyspnea, and respiratory muscle function and fatigue during exercise. DesignRandomized crossover. Methods10 healthy participants completed 2 time-to-exhaustion (TTE) cycling tests while wearing the ETM or under a sham control condition. During the sham, participants were told they were breathing air equivalent to “9000 ft” (matched to the selected resistance valves on the ETM according to the manufacturer), but they were breathing room air. Dyspnea and leg discomfort were assessed using the modified 0–10 category-ratio Borg scale. Qualitative dyspnea descriptors at peak exercise were selected from a list of 15. Crural diaphragmatic electromyography (EMGdi) and transdiaphragmatic pressure (Pdi) were measured via a multipair esophageal electrode balloon catheter. Participants performed maximal respiratory maneuvers before and after exercise to estimate the degree of respiratory muscle fatigue. ResultsExercise with the ETM resulted in a significant decrease in TTE (p = 0.015), as well as increased dyspnea at baseline (p = 0.032) and during the highest equivalent submaximal exercise time (p = 0.0001). The increase in dyspnea with the ETM was significantly correlated with the decrease in exercise time (r = 0.73, p = 0.020). EMGdi and Pdi were significantly increased with the ETM at all time points (all p < 0.05). There was a significant increase in the selection frequency of “my breath does not go in all the way” at peak exercise with the ETM (p = 0.02). The ETM did not induce respiratory muscle fatigue. ConclusionsExercising with the ETM appears to decrease exercise performance, in part, by increasing the sensation of dyspnea.

Partitioning The Work Of Breathing During Running And Cycling Using Optoelectronic Plethysmography

Work of breathing (B) derived from a single lung volume and pleural pressure is limited and does not fully characterize the mechanical work done by the respiratory musculature. It has long been known abdominal activation increases with increasing exercise intensity, yet the mechanical work done by these muscles is not reflected in B. Optoelectronic plethysmography (OEP) is a 3-dimentional motion analysis tool that measures the positions and displacements of reflective markers on the thorax and abdomen to calculate volume changes. Importantly, OEP permits an assessment of the ribcage and abdominal contribution to volume changes during breathing. PURPOSE: We sought to: (1) show the volumes measured using OEP (VCW) were comparable to volumes from flow integration (Vt) during cycling and running, and (2) to demonstrate that partitioned ribcage and abdominal volume from OEP could be utilized to quantify the mechanical work done by the ribcage (BRC) and abdomen (BAB) during exercise. METHODS: We fit 11 subjects (6 males/5 females; age, 26 ± 3 years; body mass, 73 ± 10 kg; height, 177 ± 6 cm; maximal oxygen uptake, 55.2 ± 9.8 ml/kg/min) with 89 reflective markers, and esophageal and gastric balloon catheters. Subjects completed an incremental cycling test to exhaustion and a series of submaximal treadmill running trials. RESULTS: We found good agreement between VCW vs. Vt during cycling (bias = 0.002) (p > 0.05) and running (bias = 0.016) (p > 0.05). From rest to maximal-exercise, BAB increased by 84% (range: 30-99%; BAB: 1 ± 1 J/min to 61 ± 52 J/min). The relative contribution of the abdomen increased from 17 ± 9% at rest to 26 ± 16% during maximal-exercise. CONCLUSION: Our study highlights and provides a quantitative measure of the role of the abdominal muscles during exercise. Incorporating the work done by the abdomen allows for a greater understanding of the mechanical tasks required by the respiratory muscles under physiologically relevant conditions such as exercise. Moreover, our approach could be used to gain insight into how the respiratory system functions under pathophysiological conditions and injury.

Reverse Trigger in Ventilated Non-ARDS Patients: A Phenomenon Can Not Be Ignored!

IntroductionThe role of reverse trigger (RT) was unknown in ventilated non-acute respiratory distress syndrome (ARDS) patients. So we conducted a retrospective study to evaluate the incidence, characteristics and physiologic consequence of RT in such population.MethodSix ventilated non-ARDS patients were included, the esophageal balloon catheter were placed for measurements of respiratory mechanics in all patients. And the data were analyzed to identified the occurrence of RT, duration of the entrainment, the entrainment pattern or ratio, the phase difference (dP) and the phase angle (θ), phenotypes, Effects and clinical correlations of RT.ResultRT was detected in four patients of our series (66.7%), and the occurrence of RT varying from 19 to 88.6% of their recording time in these 4 patients. One patient (No.2) showed a stable 1:1 ratio and Mid-cycle RT was the most common phenotype. However, the remained patients showed a mixed ratios, and Late RT was the most common phenotype, followed by RT with breath stacking. The average values of mean phase delay and phase angles were 0.39s (0.32, 0.98) and 60.52° (49.66, 102.24). Mean phase delay and phase angles were shorter in early reverse triggering with early and delayed relaxation, and longer in mid, late RT and RT with breath stacking. Pmus was variable between patients and phenotypes, and larger Pmus was generated in Early RT, Delayed Relaxation and mid cycle RT. When the RT occurred, the Peso increased 17.27 (4.91, 19.71) cmH2O compared to the controlled breathing, and the average value of incremental ΔPeso varied widely inter and intra patients (Table 3B and Figure 1). Larger ΔPeso was always generated in Early RT, Delayed Relaxation and mid cycle RT, accompanied by an significant increase of PL with 19.12 (0.75) cmH2O and 16.10 (6.23) cmH2O.ConclusionRT could also be observed in ventilated non-ARDS patients. The characteristics of pattern and phenotype was similar to RT in ARDS patients to a large extent. And RT appeared to alter lung stress and delivered volumes.

Effects of Dynamic Hyperinflation on Left Ventricular Diastolic Function in Healthy Subjects - A Randomized Controlled Crossover Trial.

Objective: Diastolic dysfunction of the left ventricle is common in patients with chronic obstructive pulmonary disease (COPD). Dynamic hyperinflation has been suggested as a key determinant of reduced diastolic function in COPD. We aimed to investigate the effects of induced dynamic hyperinflation on left ventricular diastolic function in healthy subjects to exclude other confounding mechanisms associated with COPD.Design: In this randomized controlled crossover trial (NCT03500822, https://www.clinicaltrials.gov/), we induced dynamic hyperinflation using the validated method of expiratory resistance breathing (ERB), which combines tachypnea with expiratory resistance, and compared the results to those of tachypnea alone. Healthy male subjects (n = 14) were randomly assigned to the ERB or control group with subsequent crossover. Mild, moderate, and severe hyperinflation (i.e., ERB1, ERB2, ERB3) were confirmed by intrinsic positive end-expiratory pressure (PEEPi) using an esophageal balloon catheter. The effects on diastolic function of the left ventricle were measured by transthoracic echocardiographic assessment of the heart rate-adjusted transmitral E/A-ratio and E/e'-ratio.Results: We randomly assigned seven participants to the ERB group and seven to the control group (age 26 [24-26] vs. 24 [24-34], p = 0.81). Severe hyperinflation decreased the E/A-ratio compared to the control condition (1.63 [1.49–1.77] vs. 1.85 [0.95–2.75], p = 0.039), and moderate and severe ERB significantly increased the septal E/e'-ratio. No changes in diastolic function were found during mild hyperinflation. PEEPi levels during ERB were inversely correlated with the E/A ratio (regression coefficient = −0.007, p = 0.001).Conclusions: Our data indicate dynamic hyperinflation as a determinant of left ventricular diastolic dysfunction in healthy subjects. Therapeutic reduction of hyperinflation might be a treatable trait to improve diastolic function in patients with COPD.

Sex differences in post‐inspiratory inspiratory activity and evolution of net respiratory muscle pressures during incremental exercise

The respiratory muscle pressure (Pmus) waveform allows observation of net inspiratory andexpiratory muscle recruitment under a wide variety of conditions, including mechanical ventilation, spontaneous breathing, and during exercise. Observation of the Pmus waveform during incremental and constant work rate cycling reveals that inspiratory and expiratory muscle recruitment systematically increase with rising minute ventilations. Additionally, measuring Pmus allows one to assess the post-inspiratory inspiratory muscle activity (PIIA), whereby the inspiratory muscles “brake” some or all of expiration to allow for a smoother transition in muscle recruitment. In recent years, it has become increasingly evident that the work of breathing is systematically higher for women compared with men at a given minute ventilation during exercise. It is possible that a greater evolution of net respiratory pressures, as well as longer PIIA duration, may be a contributing factor to the greater work of breathing observed in women during exercise. However, to date, no study has examined the potential sex differences in Pmus, nor PIIA, during exercise. Thus, a comprehensive assessment of the Pmus and PIIA during exercise between sexes is warranted. PURPOSE To compare PIIA and inspiratory and expiratory Pmus between men and women during incremental cycling. METHODS Fifteen women (21 ± 2 yrs; 167 ± 7 cm; 62 ± 7 kg) and 19 men (24 ± 4 yrs; 182 ± 5 cm; 81 ± 10 kg) visited the laboratory on two separate occasions. The first occasion was used to obtain informed consent and to screen participants for normal pulmonary function (>85% age-predicted). On the second visit, participants were instrumented with an esophageal balloon catheter to estimate variations in pleural pressure (Ppl). Quasi-static relaxation curves were obtained to measure chest wall recoil pressure (Pcw). Participants then completed an incremental cycling protocol until volitional exhaustion. Pmus was calculated at given minute ventilations during the exercise protocol as follows: Pmus = Pcw – Ppl. RESULTS Total Pmus (sum of average inspiratory and expiratory Pmus) was greater in women than men (P < 0.05). Peak inspiratory Pmus was similar between sexes, but peak expiratory Pmus was greater in women. The average rates of change (slope) in Pmus during inspiration and expiration were significantly faster in women than men at a given minute ventilation (P < 0.05). Finally, the duration of PIIA (expressed as a fraction of expiratory time) gradually decreased with increasing minute ventilation during exercise in both sexes (P < 0.05), but the decrease was comparable between sexes (P > 0.05). CONCLUSION The primary finding of this study was that the pattern of respiratory muscle recruitment was different between sexes during incremental cycling, given that women displayed systematically faster rates, and greater magnitude, of net inspiratory and expiratory pressure-development compared with men at matched ventilations. Additionally, the duration of PIIA was similar in both women and men, which implies no difference in the pattern of transition from inspiration to expiration between sexes.

Estimation of change in pleural pressure in assisted and unassisted spontaneous breathing pediatric patients using fluctuation of central venous pressure: A preliminary study.

It is important to evaluate the size of respiratory effort to prevent patient self-inflicted lung injury and ventilator-induced diaphragmatic dysfunction. Esophageal pressure (Pes) measurement is the gold standard for estimating respiratory effort, but it is complicated by technical issues. We previously reported that a change in pleural pressure (ΔPpl) could be estimated without measuring Pes using change in CVP (ΔCVP) that has been adjusted with a simple correction among mechanically ventilated, paralyzed pediatric patients. This study aimed to determine whether our method can be used to estimate ΔPpl in assisted and unassisted spontaneous breathing patients during mechanical ventilation. The study included hemodynamically stable children (aged <18 years) who were mechanically ventilated, had spontaneous breathing, and had a central venous catheter and esophageal balloon catheter in place. We measured the change in Pes (ΔPes), ΔCVP, and ΔPpl that was calculated using a corrected ΔCVP (cΔCVP-derived ΔPpl) under three pressure support levels (10, 5, and 0 cmH2O). The cΔCVP-derived ΔPpl value was calculated as follows: cΔCVP-derived ΔPpl = k × ΔCVP, where k was the ratio of the change in airway pressure (ΔPaw) to the ΔCVP during airway occlusion test. Of the 14 patients enrolled in the study, 6 were excluded because correct positioning of the esophageal balloon could not be confirmed, leaving eight patients for analysis (mean age, 4.8 months). Three variables that reflected ΔPpl (ΔPes, ΔCVP, and cΔCVP-derived ΔPpl) were measured and yielded the following results: -6.7 ± 4.8, - -2.6 ± 1.4, and - -7.3 ± 4.5 cmH2O, respectively. The repeated measures correlation between cΔCVP-derived ΔPpl and ΔPes showed that cΔCVP-derived ΔPpl had good correlation with ΔPes (r = 0.84, p< 0.0001). ΔPpl can be estimated reasonably accurately by ΔCVP using our method in assisted and unassisted spontaneous breathing children during mechanical ventilation.

Fiber optic endoscopic optical coherence tomography (OCT) to assess human airways: The relationship between anatomy and physiological function during dynamic exercise.

Airway luminal area (Ai) influences respiratory mechanics during dynamic exercise; however, previous studies have investigated the relationship between airway anatomy and physiological function in different groups of individuals. The purpose of this study was to determine the effect of Ai on respiratory mechanics by making in vivo measures of airway dimensions and work of breathing (Wb) in the same individuals. Healthy participants (3F/2M; 23–45 years) completed a cycle exercise test to exhaustion. During exercise, Wb was assessed using an esophageal balloon catheter, while simultaneously assessing minute ventilation (V˙ E). On a separate day, subjects underwent a bronchoscopy procedure to capture optical coherence tomography (OCT) measures of three airways in the right lung. Each participant's Wb‐V˙ E data were fit to a non‐linear regression equation (Wb = a V˙ E 3 + b V˙ E 2) that partitions Wb into its turbulent resistive (a) and viscoelastic (b) components. Measures of Ai and luminal diameter were made for the 4th–6th airway generations. A composite index of airway size was calculated as the sum of the Ai for each generation and the total area of the 4th–6th generation was calculated based on Weibel's model. Constant a was significantly correlated to the Weibel model total airway area (r = −0.94, p = 0.017) and index of airway size (r = −0.929, p = 0.023), whereas constant b was not associated with either measure (both p > 0.05). We found that individuals who had the smallest Ai had the highest resistive Wb and our findings provide the basis for further study of the relationship between airway size and respiratory mechanics during exercise.

Respiratory mechanic evaluation using an esophageal balloon catheter in patient receiving lung transplantation. Observational study. Preliminary results

Introduction Mechanical ventilation (MV) plays a crucial role during the early post-operative period of lung transplantation (LTx). An accurate setting of MV is important in order to prevent ventilation-induced lung injury, which may lead to Primary Graft Dysfunction (PDG), and to set a protective ventilation strategy whenever this complication occurs. Unfortunately, respiratory mechanics may be unpredictable: these patients receive lungs which may not perfectly match their chest walls, causing a patient-donor size-mismatch, is conventionally defined by the ratio between recipient and donor lungs predicted-Total Lung Capacity (r-pTLC and d-pTLC, respectively) and may modify the distribution of pressures inside the respiratory system between lung and chest wall. In order to improve our understanding of the LTx respiratory mechanics and to evaluate whether ventilation setting was dangerous for the transplanted lungs, we placed an Esophageal Balloon Catheter (EBC) and analysed the esophageal pressure (Pes) in the early post-operative period of patients receiving bilateral sequential single LTx (BSSLTx). Methods We observed the respiratory mechanics of patients receiving BSSLTx over 1-year period at Molinette Hospital (Ospedale Molinette, Citta della Salute e della Scienza, Turin, Italy). For each patient respiratory mechanics was evaluated at least two times in the post-transplant period: intraoperatively (T0), just before the chest closure, and post-operatively (T1), in ICU. Patients and donors data, recipient-donor size-matching and outcomes were compared with respiratory mechanics. Results Between November 2018 and October 2019, we included 22 patients receiving LTx. Among them, 9 were excluded: 6 were single LTx, 1 was a paediatric patient and 2 patients had incomplete data. Among the 13 patients included, 3 (23%) developed PGD: 5 patients were best matched (d/pTLC 0,9 – 1,1; 5/13, 38,4%), 6 were undersized (d/pTLC 1,1; 2/13, 15,3%) but no correlation was found between size-matching and incidence of high-grade PGD (PGD grade 2 or 3) (Fig.1). We found no statistically significant difference in transpulmonary pressure (PTP i, PTP e, PTP drive), transpulmonary compliance (CTP) or chest elastance (ECW) at T0 or T1 in patients who developed PGD compared to those without PGD. However, we noticed an early raise of PTP i in patients who were going to develop PGD (no PGD δ% t0-t1 PTP i – 14,6% vs PGD δ% t0-t1 PTP i + 14,0%; p=0,1402) (Fig. 2). Moreover, we found that this early raising in PTP i (δ% t0-t1 PTP i) was statistically related with the ICU-length-of-stay (ICU-LOS) (r2=0,57; p=0,050) (Fig. 3) Discussion The overall incidence of PGD in our centre was 23%, however no correlation with patient-donor size-matching. An early raise of transpulmonary pressure was observed among patients who developed PGD and it was statistically correlated with higher ICU-LOS.

Expiratory Pressure Generation In Adult Survivors Of Preterm Birth

Adult survivors of preterm birth (PRE) have arrested lung development resulting in lower pulmonary function compared to their counterparts born at full term (CON). PRE have normal lung volumes, but lower expiratory airflow, which could be caused, in part, by a lesser driving (alveolar) pressure. During forced expiration alveolar pressure is the sum of pleural pressure, a function of respiratory muscle effort/strength, and lung recoil pressure. Whether or not PRE have normal respiratory muscle strength and/or lung compliance (CL) has not yet been explored. PURPOSE: The purpose of this study was to quantify respiratory muscle strength and CL in PRE and CON. Based upon the existing literature, we hypothesized that PRE and CON will have equivalent respiratory muscle strength and CL. METHODS: To date, n = 8 PRE and n = 5 CON, visited the lab on two occasions. First, subjects performed standard spirometry (e.g. fast and slow vital capacity maneuvers). Next, to assess respiratory muscle strength, subjects performed maximal inspiratory and maximal expiratory pressure maneuvers (MIP and MEP, respectively). For MIP, subjects inhaled maximally against an occluded mouthpiece at residual volume. For MEP, subjects exhaled exhale maximally against an occluded mouthpiece at total lung capacity. Each maneuver was performed 3-5 times. On the second visit, CL was measured. To do so, subjects were instrumented with an esophageal balloon catheter and performed quasi-static expiratory deflation curves (i.e., very slow exhalations from total lung capacity to residual volume). To test for differences in MIP, MEP, and CL between groups we computed multiple independent samples t-tests with significance set to p<0.05. RESULTS: We found no difference in MIP (-130.6 ± 29.3 vs. -106.5 ± 36.1 cm H2O; p = 0.24) or MEP (165.7 ± 42.9 vs.121.0 ± 51.6 cm H2O; p = 0.14) between CON and PRE, respectively. Likewise, CL was comparable between CON (0.29 ± 0.11 L/cm H2O) and PRE (0.33 ± 0.10 L/cm H2O; p = 0.53). CONCLUSION: Our data suggests no effect of birth status on the ability to generate expiratory pressure during forced expiration. Likewise, results suggest that the lower pulmonary function in PRE is not the result of a lesser driving pressure, but instead may be the result of excessive airflow resistance. Support: Hooper Undergraduate Research Award from NAU.