Airway Pressure Measurements Research Articles

Arousals and Nocturnal Respiration in Symptomatic Snorers and NonSnorers

The purpose of the present investigation was to examine the relationship among upper airway resistance, snoring, and arousals, all measured simultaneously, in nonapneic snorers complaining of excessive daytime sleepiness (EDS). To accomplish this task, we selected a group of nine nonapneic snorers who presented because of snoring, EDS, tiredness, or fatigue. Ten healthy, alert, nonapneic, nonsnoring subjects recruited from among the hospital personnel acted as a comparison group. All subjects had nocturnal polysomnography, which included measurements of snoring, nasal and pharyngeal airway pressure, esophageal pressure, and total respiratory flow. Each polysomnogram was analyzed to identify all arousals and all respiratory events, i.e. apneas, hypopneas, and periods of increased upper airway resistance. Each arousal was examined to determine whether it was associated with a respiratory event, and each respiratory event was examined to determine whether it was associated with an arousal. The results were compared between snorers and nonsnorers. There was no significant difference between the two groups in the total sleep time (182+/-61 minutes in controls vs. 188+/-50 minutes in patients) or the total number of arousals per hour of sleep (24+/-12 in controls vs. 28+/-10 in snorers). However, the distribution of arousals, i.e. electroencephalogram (EEG) vs. respiratory, was different in snorers and nonsnorers. In snorers 55% of arousals were respiratory, whereas in nonsnorers only 17% of arousals were associated with respiratory events. Not unexpectedly, the snorers had significantly more respiratory events during the night (512) than controls (112). However, the relative proportion of these events that was accompanied by arousals was similar in both groups. We conclude that the difference in daytime function between symptomatic snorers and asymptomatic nonsnorers is unlikely to be due strictly to the number of arousals during the night; however, it is possible that respiratory and EEG arousals have different impacts on daytime performance, which may explain the difference in daytime function between our two groups.

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.

Partial liquid ventilation: a comparison using conventional and high-frequency techniques in an animal model of acute respiratory failure.

To test the hypothesis that high-frequency ventilation (HFV), when compared with conventional techniques, enhances respiratory gas exchange during partial liquid ventilation (PLV). A four-period crossover design. Animal research laboratory of Children's Health Care-St. Paul. Thirty-two newborn piglets, weighing 1.40 +/- 0.39 kg. Animals were divided into four groups of eight animals: a) PLV with high-frequency jet ventilation; b) PLV with jet ventilation using a background intermittent mandatory ventilation (IMV) rate; c) PLV with high-frequency oscillation; or d) PLV with high-frequency flow interruption using a background IMV rate. After anesthesia, paralysis, and tracheotomy, a normal saline wash procedure produced lung injury. Perfluorocarbon was then instilled via the endotracheal tube in an amount estimated to represent functional residual capacity. Animals received randomly either PLV using conventional techniques or PLV using the selected HFV technique as initial treatment. Then, animals were crossed over to the alternative treatment at equal mean airway pressure, as measured at the endotracheal tube tip. This sequence was repeated for a total of four crossover periods, such that all animals were treated twice with PLV using conventional techniques and twice with PLV using HFV. We measured airway pressures at the endotracheal tube tip, aortic and central venous blood pressures, arterial blood gases, and respiratory system mechanics at baseline, after induction of lung injury, and at specified intervals throughout the experiment. Measurements were made before and 15 mins after crossovers, then ventilators were adjusted to normalize gas exchange. Measurements were again made 30 mins later, at the end of the treatment period. All types of PLV provided adequate gas exchange. Only PLV using jet ventilation with IMV produced gas exchange equal to that seen during PLV using conventional techniques at equivalent mean airway pressure. By the end of the treatment periods, only PLV using high-frequency oscillation continued to require higher airway pressure than PLV using conventional techniques for equivalent gas exchange. Gas exchange was not enhanced during PLV-HFV. Application of HFV with PLV provides no clear acute physiologic advantages to PLV using more conventional techniques.

Effects of proportional assist ventilation on inspiratory muscle effort in patients with chronic obstructive pulmonary disease and acute respiratory failure.

Acute respiratory failure may develop in patients with chronic obstructive pulmonary disease because of intrinsic positive end-expiratory pressure (PEEPi) and increased resistive and elastic loads. Proportional assist ventilation is an experimental mode of partial ventilatory support in which the ventilator generates flow to unload the resistive burden (flow assistance: FA) and volume to unload the elastic burden (volume assistance: VA) proportionally to inspiratory muscle effort, and PEEPi can be counterbalanced by application of external PEEP. The authors assessed effects of proportional assist ventilation and optimal ventilatory settings in patients with chronic obstructive pulmonary disease and acute respiratory failure. Inspiratory muscles and diaphragmatic efforts were evaluated by measurements of esophageal, gastric, and transdiaphragmatic pressures. Minute ventilation and breathing patterns were evaluated by measuring airway pressure and flow. Measurements were performed during spontaneous breathing, continuous positive airway pressure, FA, FA+PEEP, VA, VA+PEEP, FA+VA, and FA+VA+PEEP. FA+PEEP provided the greatest improvement in minute ventilation (89 +/- 3%) and dyspnea (62 +/- 2%). The largest reduction in pressure time product per breath of the respiratory muscles and diaphragm (44 +/- 3% and 33 +/- 2%, respectively) also was observed during FA+PEEP condition. When VA was added to this setting, a reduction in respiratory rate (50 +/- 3%), an increase in inspiratory time (102 +/- 6%), and a further reduction in pressure time product per minute (65 +/- 2% and 64% for the respiratory muscles and diaphragm, respectively) was observed. However, values of pressure time product per liter of minute ventilation during FA+VA+PEEP did not differ with those observed during FA+PEEP condition. Worsening of patient-ventilator interaction and breathing asynchrony occurred when VA was implemented. Application of PEEP to counterbalance PEEPi and FA to unload the resistive burden provided the optimal conditions in such patients. Ventilator over-assistance and patient-ventilator asynchrony was observed when VA was added to this setting. The clinical use of proportional assist ventilation should be based on continuous measurements of respiratory mechanics.

Impact of pleurotomy, continuous positive airway pressure, and fluid balance during cardiopulmonary bypass on lung mechanics and oxygenation

To determine effects of surgical pleurotomy, continuous positive airway pressure, and fluid balance during cardiopulmonary bypass (CPB) on lung mechanical properties and indices of oxygenation. Prospective, descriptive, and interventional study. Cardiothoracic service at a major university referral center. Eighteen anesthetized-paralyzed patients undergoing elective coronary artery bypass grafting requiring CPB. During CPB, continuous positive airway pressure (CPAP) was applied to nine patients, in nine others, no CPAP was applied. From measurements of airway and esophageal pressures and flow, lung resistance and elastance were determined before sternotomy and after sternal reapproximation. Measurements were made during forced ventilation over a physiologic range of tidal volumes and frequencies, and frequency and volume dependences of lung resistance and elastance were additionally identified. In all patients, lung resistance and elastance increased after CPB, consistent with models of pulmonary edema. Multiple regression analysis showed that these increases were relatively less in patients with intact pleurae (p < 0.05) or net negative fluid balance (p < 0.05); however, no difference in these increases was noted between patients receiving CPAP and those receiving no CPAP. Increases in lung resistance were positively correlated to net fluid balance, and negatively correlated to frequency and tidal volume (p < 0.05). Increases in lung elastance were positively correlated to tidal volume (p < 0.05). Absolute change in alveolar-arterial oxygen gradient was negatively correlated with net fluid balance, whereas percentage change was positively correlated to changes in lung elastance (p < 0.05). These findings suggest that pleurotomy before CPB and positive fluid balance during CPB enhance postbypass pulmonary edema and/or atelectasis, as demonstrated by acute changes in respiratory mechanics and indices of oxygenation. Low levels of CPAP applied during CPB did not significantly change either mechanical properties or oxygenation.

Obstruction Due to Retained Carbon Dioxide Absorber Canister Wrapping

Obstruction Due to Retained Carbon Dioxide Absorber Canister Wrapping

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.

Carbon dioxide absorption during laparoscopic cholecystectomy and inguinal hernia repair

Laparoscopic surgical procedures require CO2 insufflation. The extent of CO2 absorption may differ with regard to the surgical technique used. The aim of this study was to quantify the CO2 absorption following intra- and extraperitoneal insufflation. The study was approved by the Ethics Committee and informed consent was obtained. Two groups of 25 ASA I and II patients each were prospectively studied: laparoscopic cholecystectomy (group A) and inguinal hernia repair (group B). All patients had no medical history of pulmonary or cardiac disease. All patients underwent the same standardized general anaesthesia. Following tracheal intubation, all patients were mechanically ventilated (RR=12 min−1; VT=8 ml kg−1). After 20 min (T1), baseline measurements of HB, BP, CVP, airway pressure, PET CO2 and oxygen saturation were performed and an arterial blood was sampled for gas analysis. Then, CO2 insufflation was started and the VT was adjusted to maintain PET CO2 at baseline level. After 20 min of insufflation (T2), all measurements and arterial blood gas sampling were repeated. The paired and unpaired Student's t-test was used to compare within and between groups respectively. Differences were considered significant at the P<0.01 level. Age in group A and B was 53 ± 13 and 60 ± 12 years respectively. Weight was 69 ± 9 (group A) and 72 ± 9.5 kg (group B). The comparison within groups at T1 and T2 revealed no significant differences for PET CO2, Pa CO2, HR and BP. In both groups, a statistically significant increase in peak airway pressure, CVP and VT was found. The increase in VT required to maintain normocapnia in group A was 30.9 ± 8.4% (from 556 ± 79 to 724 ± 84 mL), the required increase in group B was 55.4 ± 19.5% (from 592 ± 92 to 909 ± 104 mL). Statistical differences between groups were found for the increase in VT, CVP and airway pressure. This study provides evidence that extraperitoneal CO2 insufflation induces a greater CO2 absorption compared with intraperitoneal insufflation.

Changes in Lung and Chest Wall Properties with Abdominal Insufflation of Carbon Dioxide Are Immediately Reversible

Previously we have reported that large increases in lung and chest wall elastances as well as lung resistance occur with abdominal insufflation of carbon dioxide during laparoscopic surgery. To examine whether these effects were reversible with abdominal deflation, we calculated lung and chest wall elastances and resistances from measurement of airway flow and pressure and esophageal pressure in 17 anesthetized/paralyzed patients undergoing laparoscopic surgery. Measurements were made immediately prior to abdominal insufflation and after deflation. Lung and chest wall elastances and resistances were not changed from baseline (P > 0.05), although total respiratory elastance remained slightly increased compared to baseline (P < 0.05). The change in total respiratory elastance did not correlate with abdominal insufflation time, surgical site, smoking history, or physical characteristics of the patients. There were no differences in frequency and tidal volume dependences of the elastances and resistances before and after abdominal insufflation (P > 0.5). We conclude that residual changes in respiratory mechanics caused by carbon dioxide insufflation during laparoscopic surgery are minor, and that the reported compromise of respiratory function indicated by pulmonary function tests after laparoscopy does not appear to be due to changes in passive mechanical properties of the lungs or chest wall.

Changes in Lung and Chest Wall Properties with Abdominal Insufflation of Carbon Dioxide Are Immediately Reversible

Previously we have reported that large increases in lung and chest wall elastances as well as lung resistance occur with abdominal insufflation of carbon dioxide during laparoscopic surgery.To examine whether these effects were reversible with abdominal deflation, we calculated lung and chest wall elastances and resistances from measurement of airway flow and pressure and esophageal pressure in 17 anesthetized/paralyzed patients undergoing laparoscopic surgery. Measurements were made immediately prior to abdominal insufflation and after deflation. Lung and chest wall elastances and resistances were not changed from baseline (P > 0.05), although total respiratory elastance remained slightly increased compared to baseline (P < 0.05). The change in total respiratory elastance did not correlate with abdominal insufflation time, surgical site, smoking history, or physical characteristics of the patients. There were no differences in frequency and tidal volume dependences of the elastances and resistances before and after abdominal insufflation (P > 0.5). We conclude that residual changes in respiratory mechanics caused by carbon dioxide insufflation during laparoscopic surgery are minor, and that the reported compromise of respiratory function indicated by pulmonary function tests after laparoscopy does not appear to be due to changes in passive mechanical properties of the lungs or chest wall. (Anesth Analg 1996;82:501-5)

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.

Accuracy of Breath-by-Breath Analysis of Flow-Volume Loop in Identifying Sleep-Induced Flow-Limited Breathing Cycles in Sleep Apnoea-Hypopnoea Syndrome

1. Inspiratory flow limitation is involved in the pathophysiology of sleep-related breathing disorders. Since the definition of flow-limited cycle is based on a dissociation between flow and respiratory efforts, identification of inspiratory flow limitation requires upper airway or intrathoracic pressure measurements. We examined the accuracy of the analysis of the flow-volume loop of a tidal breath in identifying inspiratory flow limitation during sleep in ten patients with a sleep apnoea-hypopnoea syndrome. 2. Measurements were taken during continuous positive airway pressure trials. After data acquisition, the presence of inspiratory flow limitation was identified by the presence of an inspiratory plateau or decrease in inspiratory flow independently of the increase in inspiratory efforts. The flow-volume loop was reconstructed for each breathing cycle by plotting the instantaneous flow and the tidal volume. The instantaneous inspiratory and expiratory flows were measured at 50% of the respective portion of the tidal volume, and a breath-by-breath analysis of the mid-tidal volume-flow ratio (inspiratory/expiratory ratio) was obtained. The analysis of the flow-volume loop was compared with standard inspiratory flow limitation criteria using different values of the inspiratory/expiratory ratio threshold, below which breathing cycles were classified as flow-limited. With a lower limit of the normal inspiratory/expiratory ratio threshold of 0.97, the sensitivity and specificity of the method were both 76%. In each subject, the proportion of breathing cycles identified as flow-progressively decreased with an increasing positive pressure level.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung tissue and airway impedances during pulmonary edema in normal range of breathing.

How pulmonary edema affects lung tissue and airway properties is not clear. From measurements of airway pressure and flow, we measured lung elastance (EL) and resistance (RL) in 5 anesthetized-paralyzed open-chested dogs during sinusoidal forcing in the frequency (f) and tidal volume (VT) ranges of normal breathing. RL was divided into its tissue (Rti) and airway (Raw) components from measurements of alveolar pressure through capsules glued to the lung surface. After induction of severe pulmonary edema by injection of oleic acid into the right atrium, forcing was repeated at the same mean airway pressure (Paw) as in control animals (11 cmH2O) and at a higher Paw (14 cmH2O), as would occur in closed-chested dogs during edema (G. M. Barnas, D. Stamenovic, and K. R. Lutchen. J. Appl. Physiol. 73: 1040-1046, 1992). Edema increased EL, and this increase was greater at Paw = 14 cmH2O (P < 0.05). The f dependences of EL and Rti were increased by edema (P < 0.05), and there was a large negative dependence of EL on VT at Paw = 14 cmH2O. Edema increased RL (P < 0.05), but this increase depended on f, VT, and Paw. The increase in RL was due largely to increases in Rti at Paw = 14 cmH2O and to increases in Raw at Paw = 11 cmH2O. We conclude that the functional effects of oleic acid-induced pulmonary edema on RL are due mostly to changes in lung tissue.

Preoperative cardiorespiratory trends in infants with congenital diaphragmatic hernia

The objective of this study was to determine the cardiovascular and pulmonary adaptations of infants with congenital diaphragmatic hernia (CDH) from birth until delayed surgery through the use of continuous monitoring. Continuous cardiovascular (HR, heart rate variability [HR-SD], BP, blood pressure variability [BP-SD], and oxygen saturation) and ventilatory (minute volume, airway pressure, and effective compliance) measurements were made on-line, using a computerized whole-body plethysmograph-incubator (Vital-trends, VT1000), in nine ventilated infants with CDH. Data collection commenced at birth and continued until surgery. Minute mean values for each variable were recorded. Hourly means were computed from the minute means, averaged across infants each hour over the first 50 hours of life, and regressed against postnatal age. Results showed a significant increase in BP ( P < .01), BP-SD ( P < .05), HR-SD ( P < .04), and pH ( P < .02) versus postnatal age, and a decrease in PaCO 2 ( P < .04), FiO 2 ( P < .001), Alveolar-arterial oxygen gradient ( P < .003), and oxygenation index ( P < .002). Infants with CDH show cardiopulmonary trends over the first 2 days of life that are qualitatively similar to those of normal newborn infants. Deviation from these idealized patterns may identify an infant who is not responding satisfactorily to the given therapy and who may require alternative treatment modalities.

Respiratory muscle function in infants.

In newborns and infants a variety of respiratory disorders lead to ventilatory failure. In early life the ventilatory response to loaded breathing is limited. The risk factors of ventilatory failure are related to the developing respiratory pump because of the immaturity of the chest wall, respiratory muscles and coupling between thoracic and abdominal movements. Assessment of respiratory muscle function in infants is limited, due to the objections to using invasive techniques. However, measurement of airway pressures during crying may provide an index of respiratory muscle strength in infants. Real-time ultrasonography allows investigation of diaphragmatic movements. Pattern of thoracoabdominal motion can be assessed using uncalibrated respiratory inductive plethysmography. Finally, electromyographic recording of respiratory muscles by surface electrodes is of clinical usefulness during sleep studies.

Respiratory and haemodynamic effects of conventional volume controlled PEEP ventilation, pressure regulated volume controlled ventilation and low frequency positive pressure ventilation with extracorporeal carbon dioxide removal in pigs with acute ARDS.

The purpose of this study was to evaluate whether any benefit of low frequency positive pressure ventilation with extracorporeal carbon dioxide removal (LFPPV-ECCO2R) existed over either volume controlled ventilation (VCV) with measured best-PEEP or pressure regulated volume controlled ventilation (PRVCV) with an inspiration/expiration (I/E) ratio of 4:1, with respect to arterial oxygenation, lung mechanics and haemodynamics, in acute respiratory failure. Fifteen adult pigs were used for the study. Respiratory failure was induced by surfactant depletion by repeated lung lavage. The different therapeutic approaches were applied randomly to each pig for 1 h. Measurements of gas exchange, airway pressures and haemodynamics were performed during ventilatory and haemodynamic steady state. Paco2 was kept constant in all modes. At almost similar total-PEEP, Pao2 values were significantly higher with LFPPV-ECCO2R compared to VCV with best-PEEP. Peak inspiratory pressure (PIP) and intrapulmonary pressure amplitude defined as the difference between PIP and total-PEEP were significantly lower with PRVCV and LFPPV-ECCO2R compared to VCV with best-PEEP. There was no significant difference between the modes concerning cardiocirculatory parameters. PRVCV with I/E ratio of 4:1 and LFPPV-ECCO2R proved to be better modes to achieve better gas exchange and lower PIP at lower intrapulmonary pressure amplitudes. It is concluded that PRVCV is an adequate form of treatment under these experimental conditions imitating acute respiratory failure, without necessitating other invasive measures.

Lumbar epidural block reduces cough strength in healthy young subjects

Effects of lumbar epidural block on maximum expiratory strength were studied in 12 healthy volunteers. Subjects performed maximum expiratory effort against occluded airway at functional residual capacity (FRC) and total lung capacity (TLC) while measuring airway pressure and electromyogram of the abdominal muscles (EMGab). Cough strength was assessed by maximum expiratory pressure (PEmax) and peak EMGab (peak-EMGab). Following injection of 2% lidocaine 17.8±1.1 ml into the lumbar epidural space (L2.3±0.4), upper levels of analgesia ranged from T11 to T4 (T7.8±1.3). Peak-EMGab and PEmax were significantly reduced by lumbar epidural block at both lung volumes. Compared with severe reduction in peak-EMGab, PEmax was well maintained at TLC, but changes in PEmax were identical to those in peak-EMGab at FRC. When analgesia spread to higher than T6, PEmax at TLC decreased considerably. We conclude that lumbar epidural block producing analgesia above T6 paralyzes the abdominal muscles and severely impairs the ability of effective cough in healthy young men.

Airway pressure measurements during high-frequency positive pressure ventilation in extremely low birth weight neonates.

Evaluation of a modified, computer-controlled, shutter method to determine the complete intrapulmonary pressure course and to ascertain the expiratory time constant for the respiratory system during high-frequency positive pressure ventilation. Prospective clinical study. Neonatal intensive care unit in a university hospital. Sixteen premature newborns (mean gestational age 26 +/- 2 [SD] wks, birth weight 741 +/- 138 g) were studied at various times during their clinical course. Installation of the shutter and air flow interruption did not result in any impairment of clinical and respiratory conditions. Time constants were between 58 and 190 msecs. In six patients, an inadvertent positive end-expiratory pressure (1 to 4.5 cm H2O) was found; in these patients only, expiratory time set at the respirator was < 4 time constants. In 13 measurements of nine patients, measured intrapulmonary peak inspiratory pressure was considerably lower (1 to 5 cm H2O) than that value set at the respirator. The computer-controlled shutter method is noninvasive and applicable without impairment, even in preterm neonates with birth weights of < 1000 g. This method provides important information to optimize respiratory therapy, particularly knowledge of the individual time constant. To avoid inadvertent positive end-expiratory pressure and gas trapping, expiratory time should be > 4 time constants.

Evaluation of a fiberoptic system for airway pressure monitoring.

Our objective was to evaluate the accuracy of a novel fiberoptic system for airway pressure measurement at the carinal end of the endotracheal tube in an in vitro pediatric lung model. A fiberoptic pressure measuring system was compared to the conventional method of measuring airway pressure with a pneumatic transducer using a test lung model. Pressure measurements were obtained using four endotracheal tubes of various internal diameters (ID) (3 to 6 mm) during simulated spontaneous and mechanical ventilation. Airway pressure was measured using both methods simultaneously and the results were compared by statistical analysis. Airway pressure measured by the fiberoptic system was not significantly different from measurements obtained by the pneumatic transducer except when using the 3-mm and 4-mm ID endotracheal tubes during mechanical ventilation. We conclude that the fiberoptic system provides accurate and precise measurement of airway pressure during spontaneous and mechanical ventilation. Additionally, the statistically significant differences obtained for 3- and 4-mm tubes are not large enough to be clinically significant. The fiberoptic system offers advantages over the pneumatic system for measuring the airway pressure. These advantages include decreased chance of false pressure measurement secondary to occlusion with water or mucous, less chance of kinking, and possibly, more rapid response to pressure changes due to the mechanical ventilator.