Esophageal Pressure Measurements Research Articles

The Acute Effects of Nasal Positive Pressure Ventilation in Patients With Advanced Cystic Fibrosis

To evaluate the acute effects of noninvasive positive pressure ventilation (NPPV) in patients with stable chronic respiratory failure secondary to cystic fibrosis. Eight patients (29+/-5 years of age) with severe airflow limitation (mean FEV1, 24+/-3% predicted) and chronic respiratory failure (PaO2=67+/-15 mm Hg and PaCO2=50+/-4 mm Hg) were evaluated. Tidal volume, respiratory rate, minute ventilation, oxygen saturation, and transcutaneous CO2 (TcCO2) measurements were made over a 20-min period before and after the application of NPPV (inspiratory pressure of 10 to 12 cm H2O and expiratory pressure of 4 to 6 cm H2O). NPPV increased saturation from 88+/-2% to 90+/-1% (p<0.05) and decreased TcCO2 from 51+/-3 mm Hg to 50+/-2 mm Hg (p<0.05). Tidal volume increased from 219+/-20 mL to 256+/-37 mL (p=not significant [NS]) and respiratory rate decreased from 24+/-2 to 18+/-1 (p<0.01). Minute ventilation decreased from 5.3+/-0.8 L/min to 4.6+/-0.6 L/min (p=0.08). There was no change in duty cycle (32+/-5% to 34+/-5%, p=NS). In two patients, esophageal pressure measurements were also recorded. There was a decrease in pressure from -21+/-1 cm H2O to -11+/-2 cm H2O and -14+/-1 cm H2O to -7+/-1 cm H2O. In patients with stable, severe cystic fibrosis, NPPV (1) acutely improves gas exchange, (2) decreases minute ventilation, suggesting either a reduction in CO2 production or an increase in alveolar ventilation, and (3) reduces work of breathing.

Airway dynamics, oesophageal pressure and cough.

This study hypothesizes that: peak supramaximal airflow during cough reflects expiratory muscle effort, and that expiratory muscle function during cough might be assessed from the airflow signal alone. We monitored airflow and oesophageal pressure (Poes) in normal subjects during cough generated under two conditions: 1) voluntarily from functional residual capacity (FRC); and 2) involuntarily after inhalation of citric acid (CA). Maximal expiratory cough flow was quantified as the quotient of maximal flow during a given cough divided by maximal flow at the matched volume of thoracic gas (Vtg) as identified on the maximal expiratory flow-volume curve. We found: flow ratios correlated poorly with Poes; the variance of flow ratios associated with a series of voluntary coughs was poorly explained by Poes. During CA inhalation, when the Vtg compressed during cough could not be controlled, correlation of Poes with flow ratio remained poor. We conclude that to study the motor limb of the cough reflex, measurements of both airflow and oesophageal pressure are required.

Pulmonary-locomotory interactions in exercising dogs and horses

In exercising quadrupeds, limb movement is often coupled with breathing frequency. This finding has lead some investigators to conclude that locomotory forces, associated with foot plant, abdominal visceral displacements or lumbo-sacral flexion, are the primary determinants of airflow generation. Analysis of respiratory muscle electrical activation (EMG) and contraction profiles in chronically instrumented dogs and horses, along with measurements of esophageal pressure (P es) changes and limb movements, provide evidence that each breath during the exercise hyperpnea is determined by respiratory neuromuscular events. Specifically: (1) Phasic diaphragmatic EMG and tidal shortening are always synchronous with decreases in P es; (2) decrements in P es are always associated with inspiratory flow generation; and (3) strict phase coupling between breathing and stride frequency is not obligatory. Thus, although locomotory-associated forces may minimally assist with flow generation, they are not the primary determinants of breathing during exercise.

Respiratory Effort During Obstructive Sleep Apnea: Role of Age and Sleep State

To evaluate the patients' individual characteristics predictive of the degree of respiratory effort developed during obstructive sleep apneas (OSAs). Prospective consecutive sample, collection of clinical and polysomnographic data. University teaching hospital. One hundred sixteen consecutive OSA patients with clinical symptoms of OSA and more than 20 apneas per hour of sleep. Anthropomorphic data, daytime blood gas values, and polysomnographic data. From esophageal pressure measurements during sleep, three indexes of respiratory effort during OSAs were derived: the maximal end-apneic esophageal pressure swing (PesMax), the increase in esophageal pressure swing (deltaPes) during the apnea, and its ratio to apnea duration (RPes). The indexes of respiratory effort were significantly lower in rapid eye movement (REM) than in non-REM sleep (PesMax: 50.9+/-2.5 vs 39.6+/-1.9 cm H2O, p<0.001; deltaPes: 30.9+/-1.7 vs 23.4+/-1.4 cm H2O, p<0.001; RPes: 1.05+/-0.05 vs 0.53+/-0.03 cm H2O/s, p<0.001); therefore, a separate analysis was conducted in non-REM and in REM sleep. Indexes were also significantly lower in subgroups of older as compared to younger patients (PesMax: 55.6+/-3.5 vs 40.0+/-2.2 cm H2O, p<0.001; deltaPes: 34.2+/-2.3 vs 24.1+/-1.6 cm H2O, p=0.001; RPes: 1.21+/-0.08 vs 0.8+/-0.05 cm H2O/s, p<0.001). The three indexes were closely correlated with each other and only PesMax correlation data are reported. In non-REM sleep, age was the most important single independent correlate of PesMax (r=-0.37, p=0.000). In REM sleep, the apnea-related hypoxemia, apnea duration, and age were the main contributors to the variance of PesMax. Respiratory effort in response to upper airway occlusion in OSA patients is lower in REM than in non-REM sleep and decreases with increasing age.

Vagal and sympathetic influences on the ferret lower oesophageal sphincter

This study has investigated the relative involvement of cholinergic, adrenergic, nitric oxide and tachykininergic transmission in extrinsic neural influences on the lower oesophageal sphincter (LOS) in urethane anaesthetized ferrets. A micromanometric assembly (OD 1.75 mm) incorporating a sleeve sensor was used for high-fidelity oesophageal, LOS and gastric pressure measurement at low perfusion rates (<0.1 ml/min). The LOS response to vagal and splanchnic nerve stimulation (0.5 ms pulse width, 10 s duration) was frequency- and voltage-dependent. LOS responses to stimulation at 20 V, 10 Hz were investigated in separate groups of animals with either l-NAME (100 mg/kg), hexamethonium (15 mg/kg), guanethidine (5 mg/kg), CP96,345 (NK-1 antagonist, 4 mg/kg), atropine (0.4 mg/kg) or propranolol (1 mg/kg). Propranolol treatment was followed by yohimbine (1 mg/kg) and prazosin (0.25 mg/kg). Vagal stimulation caused an immediate decrease in LOS pressure, followed by increase on cessation of stimulation, followed by a prolonged decrease (77±2%) for up to 5 min. l-NAME did not affect inhibition, but increased excitation 4-fold ( p<0.001). Guanethidine and CP96,345 had no major effect. Hexamethonium decreased the inhibitory ( p<0.05) and excitatory ( p<0.01) responses. Atropine reduced the excitatory response ( p<0.05). Some inhibition still remained if all treatments were combined. Splanchnic stimulation reduced LOS pressure by 70±6% for 101±17 s. l-NAME, guanethidine, hexamethonium and CP96,345 all independently significantly reduced inhibition. The combination of guanethidine and CP96,345 usually abolished splanchnic-induced inhibition. Atropine was without effect. Propranolol (1 mg/kg) changed the splanchnic-induced response from mainly inhibition to excitation (100±44% increase). LOS responses to noradrenaline (1–10 μg close IA) showed similar features to responses to splanchnic stimulation. We conclude that vagal stimulation evokes LOS relaxation via activation of established cholinergic and NANC mechanisms and other, unidentified mechanisms. Splanchnic stimulation activates adrenergic neurones probably via nicotinic and non-nicotinic ganglionic mechanisms, which in turn elicit β adrenergic inhibitory effects on the LOS. Splanchnic stimulation also antidromically activates spinal afferent fibres. These may release substance P from peripheral myenteric plexus and prevertebral ganglionic endings causing activation of myenteric NANC inhibitory neurones and sympathetic neurones, respectively.

Esophageal Pressure Measurements in Cardiopulmonary Exercise Testing

We sought to determine the adaptability and effectiveness of a new esophageal balloon technique to measure changes in esophageal pressure (Pes) as a reflection of pleural pressure with progressive incremental exercise testing in normal subjects. An 8F (0.9 cm) esophageal balloon catheter (Smart Cath; Allied Health Products; Riverside, Calif), a CP-100 pulmonary monitor (BiCore Monitoring Systems PC-100; Irvine, Calif), and a flow transducer (Var flex; Allied Health Products; Riverside, Calif) were connected to a breathing valve (model 2700; Hans-Rudolph Inc; Kansas City, Mo). This apparatus was then used to measure Pes during a graded cardiopulmonary exercise test (CPX) to symptom limitation. University-affiliated Veterans Affairs Hospital. Eight nonsmoking volunteers with normal results of pulmonary function tests. Plots of deltaPes against pressure time product (PTP), minute ventilation (VE), and oxygen consumption (VO2) were obtained. Pes at baseline, anaerobic threshold (AT), and maximum oxygen consumption (VO2max) were obtained by comparing the Pes measurements from the computer printout to the corresponding breath-by-breath measurements on the CPX. The flow transducer (Varflex) connection added only 20 mL of dead space to the standard mouthpiece apparatus. The mean maximum work performance was 203+/-32 W. The mean VO2max was 29+/-9 mL/kg/min. The Pes at AT was 16+/-3 cm H2O. The Pes at maximal exercise was 42+/-16 cm H2O. The small esophageal balloon was well tolerated by all subjects. Plots of deltaPes vs PTP, VE, and VO2 demonstrated a linear correlation. This apparatus could be added to the standard CPX to assess the contribution of the diaphragm and respiratory muscles in patients with dyspnea.

Lung mechanical behavior during one-lung ventilation

Objective: Switching from two-lung to one-lung ventilation would be expected to have large effects on lung mechanical properties, and these effects may depend on tidal volume and respiratory frequency. These changes in lung mechanics with one-lung ventilation may be similar to pulmonary edema. Deteriorating lung mechanics during pulmonary edema have been attributed to a loss of ventilated lung units. Therefore, changes in lung mechanics caused by one-lung ventilation were measured and compared with those previously seen during pulmonary edema. Design: Prospective study. Setting: Research laboratory. Interventions: After induction of anesthesia, beagle dogs' tracheas were intubated with an endotracheal tube with a bronchial blocker (Univent System Corp, Tokyo, Japan) to apply one-lung ventilation. The proper position of the bronchial blocker during one-lung ventilation was confirmed with a fiberoptic bronchoscope. Measurements and Main Results: Lung elastance (E L) and resistance (R L) were calculated from measurements of airway pressure, esophageal pressure, and airway flow in five anesthetized, paralyzed dogs during sinusoidal forcing at a constant mean airway pressure of 10 cmH 2O in a wide range of breathing frequencies (0.2 to 1.0 Hz in intervals of 0.2) and tidal volumes (50, 100, 200, and to 300 mL). Measurements were made before and after the left mainstem bronchus was occluded with the bronchial blocker. During ventilation of both lungs, E L and R L depended relatively little on frequency, and both E L and R L were independent of tidal volume. During one-lung ventilation, E L doubled and, at most frequencies, R L increased; frequency dependences were not increased, and no dependence on tidal volume was observed. Conclusions: The lack of tidal volume dependence in E L and lack of large-frequency dependence in R L during one-lung ventilation are inconsistent with changes induced by severe pulmonary edema. Although decreases in ventilatable lung volume may contribute to increases in lung elastance, other characteristics of mechanical behavior during one-lung ventilation differ from those of pulmonary edema; therefore, other additional mechanisms must be involved in determining lung mechanical properties during severe pulmonary edema.

Delivery of Nebulized Budesonide Liposomes to the Respiratory Tract of Allergic Sheep

ABSTRACT Inhaled budesonide has been shown to be an effective therapy for asthma. In a previous study in a sheep model, acute treatment with budesonide delivered by pressurized metered dose inhaler (pMDI) modified the late bronchoconstrictor response to inhaled antigen. In the present study, we utilized the same sheep model to assess whether the delivery of budesonide in a liposome preparation would modify the late asthmatic response and the associated airway hyperresponsiveness that is detectable 24 hours after challenge. In a crossover trial, six conscious intubated sheep were pretreated with 1 mg of budesonide/dilauroyl phosphatidylcholine (DLPC), or DLPC alone, 16 hours and again 1 hour prior to the administration of aerosolized Ascaris suum antigen. Using esophageal and tracheal pressure measurements and plethysmography, specific lung resistance (sRL) was measured over an 8-hour period following administration of the antigen. In addition, airway responsiveness to carbachol (as assessed by potential d...

Changes in breathing and ventilatory muscle recruitment patterns induced by lung volume reduction surgery.

Patients with chronic obstructive pulmonary disease have abnormal breathing and ventilatory muscle recruitment patterns at rest and during exercise, and these alterations may contribute to the limited exercise capacity seen in this disease. Lung volume reduction surgery (LVRS), a recently described treatment for emphysema, is reported to improve exercise performance. We studied the breathing and ventilatory muscle recruitment (VMR) patterns in eight patients with severe chronic obstructive lung disease (median FEV1 = 0.79 L, range 0.46 to 1.13 L) by measuring esophageal and gastric pressure measurements as well as tidal volumes (VT), respiratory rates (f), inspiratory (TI) and expiratory (TE) times, and watts at rest and during maximal exercise, before and 3 mo after lung volume reduction surgery. Maximal exercise capacity increased a median of 49% (median increase 17 watts, range 6 to 44 watts, p < 0.05) and maximal minute ventilation (VEmax) increased by a median of 22% (median increase 6.5 L/min, range 3 to 25 L/min, p < 0.05). At isowatt exercise after surgery, VT increased 0.31 L (range 0.07 to 0.69 L) and f decreased four breaths/min (range +0.5 to -15 breaths/min). Dyspnea scores as measured by a visual analog scale (VAS) decreased significantly at rest and at peak exercise after surgery. End-expiratory esophageal (Pes) and gastric (Pga) pressures at rest and at isowatt exercise decreased. A rightward shift in the slope of the Pes versus Pga plot was also observed suggesting increased use of the diaphragm after surgery. Our data indicate that LVRS improves the mechanics of breathing both at rest and during exercise.

Tracheal pressure triggering a demand-flow continuous positive airway pressure system decreases patient work of breathing

Triggering a ventilator "ON" at the carinal end of the endotracheal tube decreases imposed work of breathing by bypassing the resistance imposed by the breathing circuit and the endotracheal tube. We compared work of breathing during spontaneous ventilation between three methods of triggering the ventilator "ON": a) conventional pressure triggering from inside the ventilator; b) flow-by triggering; or c) tracheal pressure triggering at the carinal end of the endotracheal tube. We hypothesized that the work of breathing would be substantially decreased with tracheal pressure triggering compared with conventional pressure and flow-by methods in patients receiving continuous positive airway pressure. Clinical, prospective study. University teaching hospital. Fourteen adults diagnosed with acute respiratory failure. All patients were breathing spontaneously at an FIO2 of 0.30 to 0.40 and received 5 cm H2O of continuous positive airway pressure. Three different methods of triggering the ventilator while set in the continuous positive airway pressure mode were administered in random order. Real-time measurements of esophageal pressure and tidal volume were integrated with a respiratory monitor (CP-100, Bicore, Riverside, CA) that uses the Campbell diagram to calculate total work of breathing. Imposed work of breathing was calculated by integrating tidal volume with the pressure at the carinal end of the endotracheal tube. Physiologic work of breathing was calculated by subtracting imposed work of breathing from the total work of breathing. Breathing frequency, the index of rapid shallow breathing (breathing frequency/tidal volume), peak inspiratory flow rate demand, exhaled minute ventilation, and the duration of respiratory muscle contraction assessed by the ratio of inspiratory time to total cycle time were also measured. Data were analyzed by Friedman's repeated-measures analysis of variance on ranks. Alpha was set at .05 for statistical significance. Imposed work of breathing decreased to approximately zero during tracheal pressure triggering. As a result, total work of breathing decreased by approximately 40% compared with the flow-by and conventional methods. During tracheal pressure triggering only, airway pressure increased above baseline pressure to approximately 11 cm H2O, which resembled pressure-support ventilation. Also, during tracheal pressure triggering, tidal volume and peak inspiratory flow rate were significantly increased, while the pressure-time product and the index of rapid shallow breathing were significantly decreased. Hemodynamic status and oxygen saturation were not clinically affected. The tracheal pressure triggering of a demand-flow continuous positive airway pressure system creates an effect similar to pressure-support ventilation that significantly decreases imposed work of breathing and, thus, total work of breathing. We recommend moving the triggering site of the ventilator to the carinal end of the endotracheal tube.

A new microtransducer catheter for measuring esophageal pressure in infants

Measurement of esophageal pressure, as a reflection of pleural pressure, is essential for assessment of dynamic lung mechanics in neonates and infants. Conventionally, an esophageal balloon or a fluid-filled catheter is used, but considerable skill is required to obtain accurate results. Both devices have problems, and failure to achieve valid occlusion tests have been reported, particularly in small infants with lung disease. Recently, a flexible #3 French gauge (FG) microtransducer catheter (MTC®, Dräger Netherlands) has become available for medical monitoring. We have assessed the accuracy and feasibility of using this device for measuring lung mechanics in 51 spontaneously breathing infants and small children aged 1 day to 24 months (weight 1.35 to 12.0 kg), 9 of whom were healthy neonates, the remainder suffering from a variety of cardio-respiratory diseases, and in 18 sick ventilated infants (weight 0.6 to 4.0 kg). Positioning of the catheter was well tolerated by all infants. The ratio of esophageal to airway opening pressure changes (ΔPes:ΔPao) ranged from 0.94 to 1.09 [mean (SD) 1.013 (0.03)] for the spontaneously breathing infants and from 0.98 to 1.06 [mean (SD) 1.003 (0.02)] in the ventilated infants with no significant difference in this ratio between the two groups (p = 0.16). This new generation of catheter tip pressure transducers may provide a simpler and more reliable tool for assessing transpulmonary pressure changes in infants than has previously been available. Pediatr Pulmonol. 1996; 22:117–124. © 1996 Wiley-Liss, Inc.

Nocturnal polysomnography with and without continuous pharyngeal and esophageal pressure measurements.

PSG with simultaneous pharyngeal and esophageal pressure measurements of the upper airway may interfere with sleep architecture and cause a bias. The aim of this study was to evaluate the degree of disturbance to sleep caused by inclusion of pressure measurements of the airway, and whether this would reduce the validity of the PSG. Thirty-two consecutive patients referred for PSG for possible obstructive sleep apnea syndrome (OSAS) were included. For pressure recordings, a 6-F silicone tube, 1.9 mm in diameter, containing six pressure transducers, was introduced through one nostril into the pharynx and esophagus. Each patient had two nocturnal PSGs, one of which included airway pressure measurements. There were no statistically significant differences between PSGs performed with and without simultaneous pressure recordings for the following sleep quality parameters: total sleep time, number of sleep-stage shifts, sleep efficiency, arousal during sleep (= intrasleep wakefulness), percent REM sleep, and number of microarousals. We did not find any statistically significant differences for respiratory parameters such as type, duration, and index of different respiratory events and snoring. However, there was a slight tendency for reduced sleep quality and oxygen saturation when pressure measurements were included. The only significant change seen was in the duration of non-REM sleep with oxygen saturation below 90%. The multisensor airway pressure probe demonstrated that proximal obstructions were more common than distal obstructions, and obstruction in one or two segments was far more frequent than obstruction in more than two.

Respiratory mechanics in the open chest: effects of parietal pleurae

To understand how the parietal pleurae affect the mechanical behavior of the human respiratory system after the chest wall is opened by median sternotomy, we studied 18 anesthetized / paralyzed patients immediately before coronary artery bypass grafting surgery. Elastances and resistances of the total respiratory system (E rs, R rs) were calculated from measurements of airway pressure and flow during mechanical ventilation in the frequency and tidal volume ranges of normal breathing. Elastances and resistances of the lungs ( El, Rl), chest wall (E cw, R cw) were also estimated from measurements of esophageal pressure. Data were collected in the closed chest, after median sternotomy with the parietal pleurae intact and after the left parietal pleura was opened for internal mammary artery harvest. After sternotomy with pleurae intact ( n = 14), E rs did not change but R rs decreased ( p < 0.05). E cw (including the contribution of the pleurae) was higher than in the closed chest ( p < 0.05) while El and Rl were lower ( p < 0.05); R cw did not change. Opening the left pleura ( n = 10) decreased E rs ( p < 0.05), but R rs did not change. We conclude that the chest wall / pleurae compartment offers significant impedance to lung expansion after sternotomy and rib retraction, unless one pleura is opened.

睡眠時無呼吸症候群―最近の進歩 閉塞性睡眠時無呼吸の治療前後における循環動態の比較

Forty habitual snorers with symptoms related to the obstructive sleep apnea syndrome (OSAS) agreed to have polysomnography with measurement of esophageal pressure (Pes) and simultaneous blood pressure monitoring. Fifteen OSAS patients underwent not only the baseline investigation but also a nocturnal evaluation with echocardiography. All subjects underwent continuous nasal positive airway pressure (nCPAP) treatment and post-treatment evaluation. We found that two thirds of our subjects had pulsus paradoxus. We also demonstrated by continuous nocturnal echocardiographic monitoring that a leftward shift of the interventricular septum (LSIVS) occurred in young OSAS patients, and that pulsus paradoxus was simultaneously associated with a significantly negative Pes nadir and LSIVS during obstructed breathing. Furthermore, nCPAP treatment led to normal unobstructed breathing, a significant decrease in the Pes nadir, and the disappearance of LSIVS and pulsus paradoxus. These findings suggest that the presence of pulsus paradoxus in OSAS patients indicates a marked increase in the Pes nadir, and that its disappearance during nCPAP may be evidence for an effective treatment of OSAS.

Monitoring of the permeability of the inferior esophageal sphincter using sound signals

An original method is described for graphic display of sounds arising from the cardia during the swallowing of saliva or water. Two dynamic microphones were placed on the skin of epigastric xyphoid area and simultaneously on the latero-cervical position. The following conditions must be filled: position of the subject (upright or lying), correct application of microphone with pressure (2 kPa), specially for the xyphoid situation. For graphic restitutions from magnetic signal, a time-recording paper was used, on line or off line, with an analogical device including Butterworth band active filter (optimal frequency range 0.8-1.2 kHz), amplifier and integrator (tau = 2 s). Occurrence of typical cardia sounds were 86-97 % for saliva and 95-100 % for water in two normal subjects for the evaluation of reproducibility (one man and one woman 35 and 47 years old respectively, n = 234 sequences, interval 20 s). Using the distance between the upper and lower microphones, the esophageal time transit can be measured. The signal was more unconstantly recorded for saliva 40 +/- 44 % in adults (n = 10) and 76 +/- 17 % in children (n = 7), than for 80 et 87 % for water respectively. The optimal interval between two swallows appeared to be 15-25 s. In patients with presumption of achalasia (n = 8), the two phonic signals were recorded during esophageal pressure measurement. The presence of esophageal sounds seems to be the sign of absence of achalasia.

Automated system for detailed measurement of respiratory mechanics.

The mechanical properties of the respiratory system (i.e., elastance and resistance) depend on the frequency, tidal volume, and shape of the flow waveform used for forcing. We developed a system to facilitate accurate measurements of elastance and resistance in laboratory and clinical settings at the frequencies and tidal volumes in the physiologic range of breathing. A personal computer (PC) is used to drive a common clinically used ventilator while simultaneously collecting measurements of airway flow, airway pressure, and esophageal pressure from the experimental subject or animal at different frequencies and tidal volumes. Analysis analogous to discrete Fourier transform at the fundamental frequency (i.e., ventilator setting) is used to calculate elastances and resistances of the total respiratory system and its components, the lungs and the chest wall. We have shown that this analysis is independent of the high-frequency harmonics that are present in the waveform from clinical ventilators. The system has been used successfully to make measurements in anesthetized/paralyzed dogs and awake or anesthetized human volunteers in the laboratory, and in anesthetized human volunteers in the laboratory, and in anesthetized humans in the operating room and intensive care unit. Elastances and resistances obtained with this approach are the same as those obtained during more controlled conditions, e.g., sinusoidal forcing. Accurate, standardized measurements of lung and chest wall properties can be obtained in many settings with relative ease with the system described. These properties, and their frequency and tidal volume dependences in the physiologic range, provide important information to aid in the understanding of changes in respiratory function caused by day-to-day conditions, clinical intervention and pathologies.

Correlation of high-frequency esophageal ultrasonography and manometry in the study of esophageal motility

Background & Aims : No studies correlate manometric measurements with morphological changes during the esophageal peristaltic sequence. The aim of this study was to develop and use a system for sonographically imaging the esophageal wall while simultaneously recording esophageal pressure changes. Methods : An ultrasonography transducer attached to a manometric probe was used to evaluate the esophagus. Results : Four sonographic phases of an esophageal peristaltic sequence were identified. The esophageal lumen was not open at rest in phase 1 (resting), increased to a maximum mean circumference of 4.90 ± 0.57 cm in phase 2 (passive distention), and returned to a closed position in phases 3 (contraction) and 4 (relaxation). The muscle layers of the esophageal wall were at baseline resting width in phase 1, decreased in width during phase 2, increased and reached maximum mean widths during phase 3, and returned to baseline widths during phase 4. The measurement of esophageal intraluminal pressure remained at a baseline resting level during phases 1 and 2, increased to a maximum mean peak of 67.95 ± 9.18 mm Hg during phase 3, and returned to baseline during phase 4. Conclusions : A combined ultrasonography transducer/manometry probe was used to dynamically and simultaneously evaluate esophageal wall motion, muscle thickness, and esophageal pressure changes during peristalsis.

Noninvasive Evaluation of Instantaneous Total Mechanical Activity of the Respiratory Muscles During Pressure Support Ventilation

The measurement of esophageal pressure (Pes) is the conventional method for the evaluation of the forces applied to the respiratory system by the respiratory muscles. As an alternative to Pes measurement, we propose the calculation of the instantaneous net pressure applied by the respiratory muscles [Pmusc(t)]. Prospective, randomized study. A general ICU of a university hospital. Eight intubated patients submitted to pressure support ventilation for acute respiratory failure. Four different levels of pressure support were used to unload progressively the respiratory muscles. Pmusc(t) was calculated at all levels of pressure support and compared with Pes corrected for chest wall load as a reference. Pmusc(t) was further used to calculate inspiratory work of breathing, which in turn was compared with data obtained with the conventional method. Airway pressure, airflow, and Pes were measured. Both for amplitude and for timing, Pmusc(t) showed good agreement with reference measurements. Work of breathing as calculated from Pmusc(t) agreed well with the measurement obtained with the conventional method (mean difference, 0.057 +/- 0.157 J). Noninvasive evaluation of Pmusc(t) allows extended monitoring of mechanical ventilation, which is particularly interesting for pressure preset ventilation modes.

Respiratory mechanics by least squares fitting in mechanically ventilated patients: Applications during paralysis and during pressure support ventilation

To evaluate a least squares fitting technique for the purpose of measuring total respiratory compliance (Crs) and resistance (Rrs) in patients submitted to partial ventilatory support, without the need for esophageal pressure measurement. Prospective, randomized study. A general ICU of a University Hospital. 11 patients in acute respiratory failure, intubated and assisted by pressure support ventilation (PSV). Patients were ventilated at 4 different levels of pressure support. At the end of the study, they were paralyzed for diagnostic reasons and submitted to volume controlled ventilation (CMV). A least squares fitting (LSF) method was applied to measure Crs and Rrs at different levels of pressure support as well as in CMV. Crs and Rrs calculated by the LSF method were compared to reference values which were obtained in PSV by measurement of esophageal pressure, and in CMV by the application of the constant flow, end-inspiratory occlusion method. Inspiratory activity was measured by P0.1. In CMV, Crs and Rrs measured by the LSF method are close to quasistatic compliance (-1.5 +/- 1.5 ml/cmH2O) and to the mean value of minimum and maximum end-inspiratory resistance (+0.9 +/- 2.5 cmH2O/(l/s)). Applied during PSV, the LSF method leads to gross underestimation of Rrs (-10.4 +/- 2.3 cmH2O/(l/s)) and overestimation of Crs (+35.2 +/- 33 ml/cmH2O) whenever the set pressure support level is low and the activity of the respiratory muscles is high (P0.1 was 4.6 +/- 3.1 cmH2O). However, satisfactory estimations of Crs and Rrs by the LSF method were obtained at increased pressure support levels, resulting in a mean error of -0.4 +/- 6 ml/cmH2O and -2.8 +/- 1.5 cmH2O/(l/s), respectively. This condition was coincident with a P0.1 of 1.6 +/- 0.7 cmH2O. The LSF method allows non-invasive evaluation of respiratory mechanics during PSV, provided that a near-relaxation condition is obtained by means of an adequately increased pressure support level. The measurement of P0.1 may be helpful for titrating the pressure support in order to obtain the condition of near-relaxation.

Pleural pressure changes during exercise do not affect measurement of mean pulmonary vascular pressures

SummaryThis study was designed to evaluate the influence of pleural pressure on mean pulmonary vascular pressures in exercising horses. Pulmonary artery (Pa), pulmonary wedge (Pw) and oesophageal pressures (Pes) were measured with transducer tip catheters in 6 Standardbred horses at rest and during treadmill exercise at 75, 90 and 100% of maximal heart rate. Oesophageal pressure (Pes) measurements were used to estimate pleural pressure. Vascular pressures were determined in 4 ways: 1) mean transmural vascular pressure (Ptm) at Pesequal to resting end expiratory pressure; 2) mean Ptmat Pesequal to mean Pesfor the data collection period; 3) mean Ptmwithout selection of specific data points and 4) mean pulmonary vascular pressure relative to atmospheric pressure (conventional method). Despite large fluctuations associated with breathing, mean Pesduring exercise remained close to zero, suggesting that pleural pressure fluctuates equally about zero. The swings in Peswere associated with approximately equal swings in vascular pressure so that, despite the marked fluctuations, mean Paand Pwdetermined with the 4 methods were not significantly different. The results indicate that during exercise it is valid to report mean pulmonary vascular pressures without accounting for the fluctuations in pleural pressure.