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PubMed2003

Spinal stiffness changes throughout the respiratory cycle.

Posteroanterior stiffness of the lumbar spine is influenced by factors, including trunk muscle activity and intra-abdominal pressure (IAP). Because these factors vary with breathing, this study investigated whether stiffness is modulated in a cyclical manner with respiration. A further aim was to investigate the relationship between stiffness and IAP or abdominal and paraspinal muscle activity. Stiffness was measured from force-displacement responses of a posteroanterior force applied over the spinous process of L2 and L4. Recordings were made of IAP and electromyographic activity from L4/L2 erector spinae, abdominal muscles, and chest wall. Stiffness was measured with the lung volume held at the extremes of tidal volume and at greater and lesser volumes. Stiffness at L4 and L2 increased above base-level values at functional residual capacity (L2 14.9 N/mm and L4 15.3 N/mm) with both inspiratory and expiratory efforts. The increase was related to the respiratory effort and was greatest during maximum expiration (L2 24.9 N/mm and L4 23.9 N/mm). The results indicate that changes in trunk muscle activity and IAP with respiratory efforts modulate spinal stiffness. In addition, the diaphragm may augment spinal stiffness via attachment of its crural fibers to the lumbar vertebrae.

Abdomen↗
PubMed2000

Effects of lung volume on parasternal pressure-generating capacity in dogs.

Previous studies have suggested that the optimum length for force generation of the parasternal intercostal (PS) muscles is well above functional residual capacity (FRC). We further explored this issue by examining the pressure-generating capacity of the PS muscles as a function of lung volume in anaesthetized dogs. Upper thoracic spinal cord stimulation (SCS) was used to electrically activate the PS muscles. Changes in airway pressure and parasternal resting length (LR) during airway occlusion were monitored over a wide range of lung volumes during SCS. To assess the effects of parasternal contraction alone, SCS was performed following phrenicotomy and section of the external intercostal, levator costae and triangularis sterni muscles. With increasing lung volume, there were progressive decrements in the capacity of the PS muscles to produce changes in airway pressure. The relationship between PS pressure generation and lung volume was similar to a previous comparable assessment of the external intercostal muscles. The PS muscles shortened during passive inflation and also shortened further (by > 20 % of LR) during SCS. Total shortening (passive plus active) increased progressively with increasing lung volume. Our results indicate that the capacity of the PS muscles to produce changes in airway pressure (a) falls progressively with increasing lung volume and (b) is similar to that of the external intercostal muscles. We speculate that the fall in PS pressure-generating capacity is related, in part, to progressive reductions in end-inspiratory length.

Animals↗
PubMed1996

Mechanical significance of respiratory muscle activity in humans during halothane anesthesia.

BACKGROUND: Prior human studies have shown that halothane attenuates activity in the parasternal intercostal muscle and enhances phasic activity in respiratory muscles with expiratory actions. This expiratory muscle activity could contribute to reductions in the functional residual capacity produced by anesthesia. Termination of this activity could contribute to the maintenance of inspiratory rib cage expansion. The purpose of this study was to estimate in humans the mechanical significance of expiratory muscle activity during halothane anesthesia and to search for the presence of scalene muscle activity during halothane anesthesia that might contribute to inspiratory rib cage expansion. METHODS: Six subjects (3 males, 3 females) were studied while awake and during 1.2 MAC halothane anesthesia, both during quiet breathing and during carbon dioxide rebreathing. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration was determined using images of the thorax obtained by three-dimensional, fast computed tomography and respiratory impedance plethysmography. Functional residual capacity was measured by a nitrogen dilution technique. Measurements were obtained after paralysis with 0.1 mg/kg vecuronium and mechanical ventilation. RESULTS: Phasic inspiratory activity was present in the scalene muscle of four anesthetized subjects during quiet breathing and all anesthetized subjects during rebreathing. Phasic inspiratory activity was present in the parasternal intercostal muscle during halothane anesthesia in only the three female subjects and was enhanced by rebreathing; parasternal intercostal muscle activity was never present in anesthetized males. During anesthesia with quiet breathing, phasic expiratory activity was observed in the transversus abdominis muscles of only the three male subjects. Despite these differences in the pattern of respiratory muscle use, the pattern of chest wall responses to rebreathing was similar between males and females. When expiratory muscle activity was present, paralysis increased the end-expiratory thoracic volume by expanding the rib cage, demonstrating that this activity reduced thoracic volume in these subjects. Changes in thoracic blood volume were significant determinants of the change in functional residual capacity produced by paralysis. CONCLUSIONS: In humans anesthetized with 1.2 MAC end-tidal halothane, there are marked interindividual differences in respiratory muscle use during quiet breathing that may be related to sex; phasic inspiratory scalene muscle and parasternal intercostal muscle activity may contribute to inspiratory rib cage expansion in some subjects; and when present, expiratory muscle activity significantly constricts the rib cage and contributes to reductions in functional residual capacity caused by halothane anesthesia.

Adult↗
PubMed1996

Pulmonary function changes during epidural anesthesia for cesarean delivery.

Although changes in pulmonary function in parturients are documented, little is known about effects of regional anesthesia on these changes. This study was undertaken to determine if two local anesthetics, often used for epidural anesthesia for cesarean delivery, have different effects on pulmonary function testing. Nineteen ASA physical status I parturients undergoing elective cesarean delivery with epidural anesthesia were randomly assigned in double-blind fashion to receive either 0.5% bupivacaine or 2% lidocaine with epinephrine (1/200,000). Pulmonary function tests were measured using a calibrated spirometer with computer-recorded flow volume loops. Peak inspiratory pressure and peak inspiratory flow rate, peak expiratory pressure (PEP) and peak expiratory flow rate, forced vital capacity (FVC), and forced expiratory volume in 1 s (FEV1) were measured. Measurements were taken prior to epidural placement and at T-10 and T-4 levels. Peak inspiratory pressure, FEV1/FVC, FEV1, FVC, peak expiratory flow rate, and peak inspiratory flow rate did not differ from baseline in either group. Patients receiving lidocaine showed a significantly greater decrease in PEP at both T-10 and T-4 levels. Pep is largely dependent on abdominal musculature. If a denser motor block is provided by 2% lidocaine with epinephrine than by 0.5% bupivacaine, these muscles would be more affected, resulting in a greater decrease in PEP. These results may have implications regarding choice of local anesthetic for epidural anesthesia in parturients with some degree of respiratory compromise undergoing cesarean delivery.

Adult↗
PubMed2000

Lung function study and diffusion capacity in anorexia nervosa.

STUDY OBJECTIVES: In humans, malnutrition alters the respiratory system in different ways. It impairs the ventilatory drive, decreases respiratory muscle strength and reduces immune competence. In addition, typical emphysema-like changes were demonstrated in starved animals. The presence of emphysema has never been demonstrated in starved humans. Our objective was to investigate whether pulmonary emphysema occurs in anorexia nervosa by means of a pulmonary function study. POPULATION AND METHOD: We examined 24 women aged between 14 and 38 years (nine smokers). We studied the lung function including lung volumes, ventilatory capacity, maximal respiratory pressures and transfer factor, as well as PaO2. RESULTS: All respiratory tests were within normal limits with the exception of decreased maximal inspiratory (59% of predicted values) and expiratory pressures (35%), and increased residual volume (162%). Diffusion capacity (98.1 +/- 16.2%) and transfer coefficient (98.4 +/- 16.2%) were also normal. The diffusion coefficient was lower in current smokers than in those who had never smoked (P < 0.01), a difference similar to that calculated from existing reference values for transfer factor for smokers and nonsmokers. CONCLUSION: In anorexia nervosa, pulmonary function tests are within normal limits with the exception of maximal pressures and residual volume. Diffusion capacity is not decreased. The present results within the limitations of the used method are not compatible with the hypothesis of starvation-induced pulmonary emphysema.

Adolescent↗
PubMed1998

Role of reaction resistance in limiting carbon monoxide uptake in rabbit lungs.

The contribution of reaction resistance to overall resistance to pulmonary carbon monoxide (CO) uptake [DLCO/(ThetaCO . Vc), where DLCO is lung CO diffusing capacity, ThetaCO is CO uptake conductance of erythrocytes, and Vc is pulmonary capillary blood volume] was determined in 10 anesthetized, paralyzed, and artificially ventilated rabbits. On the basis of the classical double-reciprocal equation of F. G. W. Roughton and R. E. Forster (J. Appl. Physiol. 11: 290-302, 1957), DLCO/(ThetaCO . Vc) was obtained by solving the relation DLCO/(ThetaCO . Vc) = 1 - 2/(DLNO/DLCO), where DLNO/DLCO represents the ratio between the respective single-breath diffusing capacities (DL) of nitric oxide (NO) and CO pulmonary capillary blood. The lungs of eight rabbits were inflated, starting from residual volume, by using 55 ml of indicator gas mixture (0.2% CO and 0.05% NO in nitrogen). DL values were calculated by taking the end-tidal partial pressures of CO and NO as analyzed by using a respiratory mass spectrometer. The overall value was DLCO/(ThetaCO . Vc) = 0.4 +/- 0.025 (mean +/- SD). Because of the use of O2-free indicator gas mixtures, the end-tidal O2 partial pressures were approximately 21 Torr. In one other rabbit, the application of 0.2% CO and 0.001% NO yielded DLCO/(ThetaCO . Vc) = 0.39; in the tenth rabbit, however, inspiratory volume was varied, and an identical value was found at functional residual capacity. We conclude that the contribution of reaction resistance to overall resistance to pulmonary CO uptake is independent of the inspiratory NO concentration used, including, with respect to the pertinent literature, the conclusion that in rabbits, dogs, and humans this contribution amounts to 40% when determined at functional residual capacity.

Animals↗
PubMed1978

Respiratory cycle time duration during exercise in patients with chronic obstructive lung disease.

Respiratory cycle time components during rest and graded exercise were measured in 18 patients with chronic obstructive lung disease, and compared with controls matched for sex and age. For a given exercise level (50 W) increased minute ventilation was present in the patients. This was due to shorter cycle time. Both inspiratory and expiratory time shortened to the same degree rendering the ratio inspiratory time/total respiratory cycle time similar in the two groups. At maximal exercise total respiratory cycle time and inspiratory time was shorter in the patients than in the control group, but the ratio between them was still similar. However, for a given total cycle time during maximal exercise inspiratory time was shorter. Inspiratory time and the ratio inspiratory time/total cycle time as measured during 50 W exercise, were positively correlated with the patient's exercise capacity, but not of sufficient accuracy for useful prediction of the latter. The difference in concomitant variation of tidal volume and inspiratory time during exercise ventilation between the patients and the control subjects seemed satisfactorily explained by the different lung volumes at which the two groups were breathing.

Adult↗
PubMed2001

Characterisation of the Hering-Breuer deflation reflex in the human neonate.

Human infants have been observed making inspiratory efforts in response to chest compression. These may be a manifestation of the Hering-Breuer deflation reflex. We sought to stimulate the reflex in 33 term infants by rapidly reducing lung volume using an inflatable jacket. The effect of altering the timing, magnitude or rate of application of the lung deflation on the strength of the inspiratory response was investigated. Inspiratory effort was quantified by measuring (1) the rate of fall in oesophageal pressure on inspiration; and (2) the mean inspiratory flow (MIF) in response to lung deflation. Variables which significantly affected (1) and resulted in increased inspiratory effort were, in order of importance: larger rises in oesophageal pressure on chest compression (38%) (percentage of variance explained), greater reductions in lung volume below functional residual capacity (FRC) (26%), faster rates of lung deflation (19%) and slower respiratory rates (11%). Increased inspiratory efforts, as assessed by response (2), were generated by greater reductions in FRC (23%), larger rises in oesophageal pressure (11%) and faster rates of lung deflation (10%). Increasing deflation pressures eventually resulted in a plateau in both measures of inspiratory response. These results were consistent with the Hering-Breuer deflation reflex being activated which could have a role in protecting the FRC of the newborn infant.

Constriction↗
PubMed1999

Is the correct use of a dry powder inhaler (Turbohaler) age dependent?

BACKGROUND: The metered-dose inhalers are the most commonly used devices in the treatment of asthma, but dry powder inhalers (eg, Turbohaler) are being increasingly used. Studies evaluating how well children can use a Turbohaler are lacking. OBJECTIVE: We assessed whether the correct use of a Turbohaler could be easily taught to unselected stable asthmatic children. METHODS: One hundred sixty-one asthmatic children aged 5 to 17 years (mean, 9.8 years) consecutively attending the outpatient clinic were included in study. After a demonstration and 10 minutes of training, the inhalation technique was checked in a standardized way (yes/no response). Keeping the device upright, proper preparation of the drug dose and inspiratory flow on inhalation were measured by the Turbohaler trainer. RESULTS: One hundred thirty-three children (83%) performed every step correctly (ie, 96% of children older than 8 years but only 55% of children between 5 and 8 years; P <.001). Of 28 children incorrectly using the Turbuhaler-trainer, 20 generated insufficient inspiratory flow through the device. There was no significant difference in airway obstruction (expressed as percent of predicted forced vital capacity, FEV1, and Tiffeneau index) between correct and incorrect users, but when measured through the pneumotachograph, mean peak inspiratory flow (expressed as percent predicted) was significantly lower in those children incorrectly using the device. Turbohaler use was reevaluated after 4.7 +/- 2.0 months in a subset of 64 patients. Fifty-three of 64 (83%) children again used the device correctly. Only 3 of 13 who used the device incorrectly at the first evaluation used it correctly at the second evaluation. CONCLUSIONS: We conclude that the correct use of the Turbohaler can be easily taught to asthmatic children older than 8 years. Those who use the device correctly after initial instructions continue to do so afterwards.

Asthma↗
PubMed1996

Respiratory function after cardiac surgery.

STUDY OBJECTIVE: Cardiac surgery is complicated by decreased postoperative respiratory muscle strength and spirometry with accompanying increased atelectasis. The specific respiratory symptoms attributable to these physiologic changes are unknown, and this study looked at the symptoms and underlying physiology. DESIGN: Convenience sampling of observational cohort. SETTING: Tertiary care university hospital. PATIENTS: One hundred thirty-eight patients undergoing elective surgery were enrolled. INTERVENTIONS: Changes from admission to 8-week postoperative values in atelectasis, pleural effusions, spirometry (forced vital capacity and forced expiratory volume in one second), and respiratory muscle strength (negative inspiratory pressure) were measured. These physiologic changes were compared with changes in respiratory symptoms of cough, wheeze, phlegm, and dyspnea on walking up a slight hill noted from admission to 8-week follow-up by stepward logistic regression. MEASUREMENTS AND RESULTS: Spirometry and negative inspiratory pressure decreased and atelectasis increased from admission to discharge. These disturbances had only incompletely resolved at 8-week follow-up. Some patients reported fewer symptoms of cough (11%), phlegm (9%), wheeze (35%), and dyspnea (46%) at 8 weeks follow-up. Other patients reported increased symptoms of cough (15%), phlegm (10%), wheeze (6%), and dyspnea (4%) at 8 weeks follow-up. Residual atelectasis at 8 weeks was predictive of fewer symptoms of dyspnea (odds ratio [OR] 0.335, p = 0.199; 95% confidence interval [CI] 0.188, 0.597), increased symptoms of dyspnea (OR 855, p = 0.006; 95% CI 6.6, 11052), and increased symptoms of cough (OR 260, p = 0.023; 95% CI 2.13, 31829). Negative inspiratory pressure at 8 weeks was predictive of fewer symptoms of dyspnea (OR 1.05, p = 0.032; 95% CI 1.02, 1.09) and increased symptoms of wheeze (OR 0.7, p = 0.45; 95% CI 0.533, 0999). Forced vital capacity at 8 weeks was predictive of increased symptoms of wheeze (OR 0.005; p = 0.015; 95% CI 0.0060, 0.775). CONCLUSIONS: Postoperative changes in respiratory muscle strength and spirometry can persist up to at least 8 weeks postoperatively. Many patients report a change in respiratory symptoms of cough, phlegm, dyspnea, or wheeze. The change in respiratory symptoms at 8 weeks is correlated with residual respiratory muscle weakness, decrease in spirometry, and residual atelectasis.

Adult↗
PubMed1976

Pulmonary function in premature lambs during the first few hours of life.

This study establishes the mean values, variations, and trend of pulmonary function during the first few hours of life in premature lambs. Measurements of intraesophaheal and tracheal pressure, air flow, tidal volume, and functional residual capacity enabled calculations of lung compliance, specific lung compliance, and inspiratory and expiratory resistance of the lungs. Arterial carbon dioxide tension and pH were maintained within a physiologic range. Mean arterial oxygen tension (PO2) at elevated inspired oxygen tension, varied in the individual animals from 51 to 185 mm Hg at an inspired oxygen concentration of 46 to 71%. It was found that the lungs of premature lambs delivered by cesarean section were mechanically unstable; the lambs were all ineffectual at breathing and required some form of mechanical ventilation. During the first 6 hours of postnatal life the lungs of premature lambs are characterized by a wide range of mechanical values and blood gas tensions.

Animals↗
PubMed2000

Impact of different inspiratory flow patterns on arterial C02-tension.

Ventilation with decelerating inspiratory flow is known to reduce the dead space fraction and to decrease PaCO2. Constant inspiratory flow with an end-inspiratory pause (EIP) is also known to increase the removal of CO2. The aim of the study was to elucidate the effect of the pause/no-flow period while both the pattern and rate of inspiratory flow was unchanged, and when the lung was ventilated with sufficient PEEP to prevent end-expiratory collapse. Surfactant depleted piglets were assigned to decelerating or constant inspiratory flow with 24 breaths per minute (bpm) or 12 bpm, or to constant flow, without and with an end-inspiratory pause of 25%. By adding an EIP the total time without active inspiratory flow of the respiratory cycle was kept unchanged. Gas exchange, airway pressures, functional residual capacity (using sulfurhexafluoride) and haemodynamics (thermo-dye indicator dilution technique) were measured. Irrespective of ventilatory frequency, PaCO2 was lower and serial dead space reduced with decelerating flow, compared with constant inspiratory flow. With an end-inspiratory pause added to constant inspiratory flow, serial dead space was reduced but did not decrease PaCO2. The results of this study corroborate the assumption that total time without active inspiratory flow is important for arterial CO2-tension.

Animals↗
PubMed1988

Comparison of two different mouthpieces for the measurement of Pimax and Pemax in normal and weak subjects.

We investigated the effect of mouthpiece design on maximum static expiratory (PEmax) and inspiratory (PImax) mouth pressures. We measured PEmax from total lung capacity (TLC) and PImax from residual volume (RV) in 21 healthy volunteers, and in 40 patients referred for respiratory muscle testing. We compared two different mouthpieces, a semi-rigid plastic flanged type fitting inside the lips, and a 4 cm diameter rubber tube held against the lips. The tube mouthpiece gave significantly higher values for PEmax (p less than 0.02) in all subjects. PImax was also significantly higher (p less than 0.005) with the tube mouthpiece in subjects who recorded normal pressures. We conclude that maximum pressures are obtained in all normal subjects with the rubber tube mouthpiece, and that differences in quoted normal ranges of maximum static respiratory pressures reflect in part the design of the mouthpiece and the way in which it was used.

Equipment Design↗
PubMed1991

The effects of varying inflation and deflation pressures on the maximal expiratory deflation flow-volume relationship in anesthetized rhesus monkeys.

Deflation flow-volume curve analysis is a pulmonary function test sensitive to small airways dysfunction that is suitable for use in infants and children who are intubated. This test relies upon deflation flow-volume (DFV) curve analysis, which is a technique to obtain maximal expiratory flow-volume curves (MEFV) by forced deflation of the lungs in infants who are intubated. The method mimics the voluntary forced flow-volume curves that adults and older children undertake. We studied 10 anesthetized male Rhesus monkeys of the same weight as human infants but developmentally equivalent to older children. We reviewed the effects on forced deflation vital capacity (DVC) and flows at various subdivisions of vital capacity (PEF, MEF50, MEF25, MEF10) of systematically varying the required inspiratory and deflation pressure during the course of 56 consecutive deflation maneuvers. Inflation pressures of +40 and +50 cm H2O caused a marked but transient bradycardia along with a (probably spurious) short-lasting fall to 89% mean arterial oxygen saturation (SaO2). Increasing positive and negative pressures increased DVC and expiratory flows. The highest mean DVC was 75.6 +/- 1.3 ml/kg, PEF was 128.0 +/- 3.5, MEF50 was 85.9 +/- 2.2, MEF25 was 74.3 +/- 1.9, and MEF10 was 38.5 +/- 2.9 ml/kg/s, all obtained at the pressure gradient of 90 cm H2O (+50/-40 cm H2O) at the start of the deflation maneuver. At this gradient, the intraindividual coefficients of variation were: DVC = 0.8%, PEF = 3.1%, MEF50 = 2.2%, MEF25 = 2.1%, MEF10 = 5.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Activation of human respiratory muscles during different voluntary manoeuvres.

1. This study used three techniques (bilateral phrenic nerve stimulation, motor cortex stimulation and quantitative electromyography) to assess the degree of activation of the diaphragm, intercostal-accessory muscles and abdominal muscles during postural tasks and respiratory manoeuvres. They included maximal inspiratory and expulsive efforts. 2. Bilateral phrenic nerve stimuli at supramaximal levels produced an average change in transdiaphragmatic pressure (Pdi) of 28 cmH2O during relaxation. During maximal inspiratory or expulsive efforts, all subjects were able to activate the diaphragm fully at functional residual capacity as judged by the failure of stimuli delivered during the voluntary efforts to increase Pdi. Peak voluntary Pdi was about 30% less for inspiratory than expulsive manoeuvres. 3. By contrast, transcranial activation of motor cortical output to the diaphragm and abdominal muscles produced an increment in abdominal pressure of 25 +/- 7 cmH2O during maximal voluntary expulsive efforts. Given the lack of response to phrenic nerve stimulation at similar voluntary pressures, this suggests that abdominal muscles, and not the diaphragm, fail to generate their full contractile force during maximal voluntary expulsive manoeuvres. 4. Motor cortical stimulation during weak inspiratory efforts produced a small reduction in oesophageal pressure (i.e. increase in net inspiratory force) of 7-14 cmH2O. This response could not be extinguished during maximal voluntary inspiratory efforts in two of three subjects. This occurred despite the cortical co-activation of 'antagonist' muscles in the chest wall and abdomen, and passive transmission of pressure from the abdominal to thoracic compartments. 5. Integrated electromyographic activity (EMG) recorded from abdominal muscles (rectus abdominis, external oblique) was greater during trunk flexion than during maximal expulsive efforts. Similarly, integrated EMG of the intercostal-accessory muscles (sternomastoid, scalenes, parasternal intercostals) was greater during tasks requiring head and/or neck flexion than during the maximal inspiratory efforts. 6. These data show that the diaphragm can be fully activated by the central nervous system during voluntary respiratory tasks but that other agonist 'respiratory' muscles need not be activated fully. Given the complex actions of 'inseries' respiratory muscles revealed here, it is argued that differences in the transdiaphragmatic pressure during various postural and respiratory tasks do not necessarily imply variation in the level of diaphragmatic neural drive.

Diaphragm↗
PubMed2000

Thoracic epidural analgesia as an adjunct to general anaesthesia for cardiac surgery. Effects on pulmonary mechanics.

BACKGROUND: A lasting impairment of pulmonary function is common after cardiac surgery. Pain from the sternotomy may contribute to the impairment. Thoracic epidural analgesia (TEA) can efficiently relieve pain in the postoperative phase, but may also affect respiratory muscle function if local anaesthetics are used. We examined the effects of TEA on pulmonary function and ventilation at rest, before and after coronary artery bypass graft surgery (CABG). METHODS: Thirty patients scheduled for CABG were randomized to receive either general anaesthesia alone or general anaesthesia with TEA. Before and after the operation the patients were examined by respiratory inductive plethysmography and spirometric tests. RESULTS: Before the operation, TEA caused significant reductions in forced vital capacity (FVC), forced expired volume in 1 s (FEV1), maximal inspiratory (PImax) and expiratory (PEmax) pressure. The rib cage contribution to tidal volume decreased significantly but the co-ordination of the thoracic and abdominal movements remained essentially unaffected. Minute volume and respiratory frequency did not change significantly. On the first postoperative day a decrease in maximal breathing efforts was found in both groups. No differences between the groups in FVC, FEV1 and PImax were found, but PEmax was significantly greater in the TEA group. Despite the impairment, breathing at rest was largely normal in both groups. CONCLUSIONS: A better pain-relief from TEA after CABG may improve the ability to cough by a greater expiratory muscle strength. FVC, FEV1, PImax and breathing at rest are not affected by TEA after cardiac surgery.

Aged↗
PubMed2002

Airway closure in anesthetized infants and children: influence of inspiratory pressures and volumes.

BACKGROUND: Cyclic opening and closing of lung units during tidal breathing may be an important cause of iatrogenic lung injury. We hypothesized that airway closure is uncommon in children with healthy lungs when inspiratory pressures are kept low, but paradoxically may occur when inspiratory pressures are increased. METHODS: Elastic equilibrium volume (EEV) and closing capacity (CC) were measured with a tracer gas (SF(6)) technique in 11 anesthetized, muscle-relaxed, endotracheally intubated and artificially ventilated healthy children, aged 0.6-13 years. Airway closing was studied in a randomized order at two inflation pressures, +20 or +30 cmH(2)O, and CC and CC/EEV were calculated from the plots obtained when the lungs were exsufflated to -20 cmH(2)O. (CC/EEV >1 indicates that airway closure might occur during tidal breathing). Furthermore, a measure of uneven ventilation, multiple breath alveolar mixing efficiency (MBAME), was obtained. RESULTS: Airway closure within the tidal volume (CC/EEV >1) was observed in four and eight children (not significant, NS) after 20 and 30 cmH(2)O inflation, respectively. However, CC(30)/EEV was >CC(20)/EEV in all children (P< or = 0.001). The MBAME was 75+/-7% (normal) and did not correlate with CC/EEV. CONCLUSION: Airway closure within tidal volumes may occur in artificially ventilated healthy children during ventilation with low inspiratory pressure. However, the risk of airway closure and thus opening within the tidal volume increases when the inspiratory pressures are increased.

Adolescent↗
PubMed1995

Pulmonary function and head lift during spontaneous recovery from pipecuronium neuromuscular block.

We have studied in seven healthy conscious volunteers the correlation between the electromyographic (EMG) and clinical criteria used to identify adequate recovery from sub-paralysing doses of pipecuronium. Pipecuronium (mean dose 1.88 (range 0.92-3.16) mg) was administered to reach a T4/T1 ratio of 0.5; full recovery to 1.0 was produced in a mean time of 25.3 (14-39) min. During recovery from neuromuscular block, we measured tidal volume, forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1) negative inspiratory pressure (NIP), peak expiratory flow rate (PEFR), mid-expiratory flow rate (MEFR) and 5-s head lift. The assessments were started when the train-of-four (TOF) ratio reached 0.5 +/- 0.001 and repeated at each 0.1 +/- 0.001 increase up to a ratio of 1.0. All volunteers showed ptosis and diplopia after the first dose and difficulty in swallowing with subsequent doses. They also experienced a pleasant, relaxing sedative sensation. All could sustain head lift for 5 s at a TOF ratio of 0.5 and higher, except for one subject who could not lift his head only at a ratio of 0.5. There was a statistically significant decrease in FVC, FEV1 and PEFR with a nonsignificant decrease in other pulmonary measurements, except for NIP which only decreased significantly at a ratio of 0.5. These changes are probably of no clinical importance. All the measured respiratory variables returned to control values at a TOF ratio of 0.9.

Adult↗