Postural changes in rib cage and abdominal volume-motion coefficients and their effect on the calibration of a respiratory inductance plethysmograph

Volume-motion coefficients were determined for the rib cage and abdomen in normal human subjects in upright, supine, and semirecumbent postures by the isovolume calibration technique of Konno and Mead (J Appl Physiol 1967; 22:407-422, using the respiratory inductive plethysmograph (RIP) to measure displacements of rib cage and abdominal walls. Volume motion coefficients changed systematically with posture; those for the rib cage were smallest in the upright posture, and for the abdomen, greatest in the upright posture. These volume motion coefficients were then used to estimate tidal volume during resting breathing in the different postures, and compared with estimates of tidal volume derived from calibration by the change in posture technique reported by Sackner and coworkers (American Review of Respiratory Disease 1980; 122:867-871). Estimates of tidal volume derived from RIP signals using both calibration techniques were compared with independently measured spirometric volume changes. Errors in tidal volume averaged 6% with the isovolume technique and 9 to 23% with the change in posture technique (depending upon whether the calibrating postures were upright, supine or semirecumbent supine). The larger errors with the change in posture calibration method are attributable to both the change in volume motion coefficients with posture and the change in distribution of tidal volume between rib cage and abdomen compartments with change in posture.     

Validation of respiratory inductive plethysmography in patients with pulmonary disease

The assumption that the respiratory system behaves with 2 df of motion in healthy persons allows calibration of respiratory inductive plethysmography (RIP) with spirometry (SP). To ascertain whether RIP could be calibrated by the same assumption in patients with lung disease, even though at least 3 df of motion are visualized (ie, upper and lower rib cage and upper and lower abdomen move out of phase), RIP was calibrated by a two-position calibration procedure and validated satisfactorily by simultaneous SP in the erect, semirecumbent, supine, and lateral decubitus positions. In lung disease, the contribution to tidal volume of regions moving independently of the combined rib cage and abdominal movements either is small or remains relatively constant with change of body posture. For clinical monitoring of the resting breathing pattern where patient movements cannot be restricted, respiratory inductive plethysmography can serve as a reliable semiquantitative, noninvasive ventilatory monitoring device.     

Diaphragm function after upper abdominal surgery in humans

Patients undergoing upper abdominal surgery characteristically develop changes in lung function and are liable to develop atelectasis in the lower lobes. We studied 15 patients to assess lung function and, in particular, diaphragm function in patients undergoing cholecystectomy. Postoperatively, forced expiratory volume in one second and vital capacity decreased in all patients. The alveolar-arterial oxygen difference widened in the 10 patients in whom it was measured. Chest roentgenograms demonstrated patchy atelectasis in 9 of the 10 patients in whom films were obtained. There was a significant reduction in tidal volume with no change in minute ventilation immediately postoperatively. Diaphragm function was assessed by: changes in transdiaphragmatic pressure swings during quiet tidal breathing, the ratio of changes in gastric to esophogeal pressure swings, and the ratio of changes in abdominal to rib cage diameters. The results showed a significant decrease in changes in transdiaphragmatic pressure and the ratio of changes in gastric to esophogeal pressure swings in the postoperative period. In the 4 patients studied with magnetometers, there was a reduction in the ratio of changes in abdominal to rib cage diameters in all patients. These data indicate reduced diaphragm activity in the postoperative period, with a shift from predominantly abdominal to rib cage breathing. There was a reversal toward normal function by 24 h. This reduction in diaphragm function may be responsible for the atelectasis, reduced vital capacity, and hypoxemia in postoperative patients.     

Action of the inspiratory muscles of the rib cage during breathing in newborns

To determine whether the rib cage muscles actively contribute to tidal volume change in infancy, we measured tidal volume (VT), using a pneumotachograph, respiratory gastric pressure swings (Pga), using a liquid-filled gastric catheter, and rib cage and abdominal volume, using respiratory inductive plethysmography in 15 newborns, both before and during 2% CO2-induced hyperventilation. Active rib cage expansion produced by phasic contraction of the inspiratory muscles of the rib cage should reduce respiratory abdominal pressure fluctuations by moving the anterior abdominal wall outward and cephalad, thereby having an expanding influence on the abdominal cavity. During quiet sleep (n = 13), CO2-induced hyperventilation was associated with significant increases in VT, Pga, rib cage volume (Vrc), and abdominal volume (Vab). Increments in Pga were small relative to VT, as shown by an increase in the slope of the VT versus Pga respiratory loop (VT/Pga) in all subjects (p less than 0.001, paired t test). CO2 breathing was associated with an increase in the contribution of the rib cage compartment to total volume change (Vrc/Vrc + Vab) in all infants studied (p less than 0.001, paired t test), and the total volume response to hyperventilation was more strongly related to changes in rib cage volume (slope = 0.62, r = 0.90) than to abdominal volume (slope = 0.31, r = 0.60). During REM sleep (n = 6), mean VT/Pga did not change significantly, and the rib cage contribution to tidal breathing decreased in three of six infants.(ABSTRACT TRUNCATED AT 250 WORDS)     

Accuracy of respiratory inductive plethysmograph over wide range of rib cage and abdominal compartmental contributions to tidal volume in normal subjects and in patients with chronic obstructive pulmonary disease

We assessed the accuracy of the respiratory inductive plethysmograph in the supine position to spirometry by the two-body position, least squares calibration and single-body position, isovolume calibration procedures. The comparison was carried out simultaneously in normal subjects breathing naturally and with voluntarily controlled abdominal or thoracic breathing, and in patients with COPD breathing naturally and with voluntarily controlled abdominal breathing patterns. In both groups, there was no significant difference in estimation of tidal volume between the 2 calibration procedures for the various breathing patterns. There was greater deviation from spirometric tidal volume values for both calibration methods in patients with COPD during abdominal than during natural breathing. In the normal subjects, agreement between the rib cage and abdominal partitioning of tidal volume for both calibration methods was good, but in the patients with COPD there was greater variability. In normal subjects, over a wide range of rib cage and abdominal compartmental contributions to tidal volume, either calibration procedure appears satisfactory. For patients with COPD, if large changes occur in the distribution of rib cage and abdominal contributions to tidal volume, then validation of respiratory inductive plethysmography to spirometry must be rechecked.     

Assessment of asynchronous and paradoxic motion between rib cage and abdomen in normal subjects and in patients with chronic obstructive pulmonary disease

Both scalar tracings and XY plots of rib cage (RC) and abdominal (AB) excursions were analyzed to detect asynchronous and/or paradoxic motion of one compartment with respect to the other in an effort to distinguish differences between normal subjects and patients with chronic obstructive pulmonary disease (COPD). An inspiratory asynchrony index (IAI) was obtained by connecting a straight line from beginning inspiration to end inspiration of the RC-AB loop, and dividing the area enclosed by the inspiratory portion by the tidal volume. In like manner, an expiratory asynchrony index (EAI) was computed. Values of IAI and EAI in the supine posture were greater in patients with COPD than in normal subjects, and such differences were consistently demonstrated during natural and voluntarily controlled abdominal breathing. Paradoxic motion as percent of volume or time period of inspiratory and expiratory compartmental excursions was indicated when RC or AB compartments moved in an opposite direction to the sum of the two. During natural breathing, paradoxic motion was almost absent in normal subjects and variably present in patients with COPD. Voluntarily controlled breathing patterns produced increased IAI, EAI, and paradoxic motion. Passive tilting from supine to the upright posture did not affect indexes in normal subjects but reduced asynchronous and paradoxic motion of the RC in patients with COPD. Other indexes of loop analysis, such as phase angle and maximal compartment amplitude/tidal volume, were not as consistent in distinguishing between normal subjects and patients with COPD during natural and voluntarily controlled breathing patterns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrical and mechanical output of the expiratory muscles in anesthetized dogs

In anesthetized intact and vagotomized dogs chest wall diameters, expiratory muscles' (EM) electrical activity, work, mean pressure and volume displacement contributed by EM contraction were assessed in the supine and upright posture during rebreathing, and during continuous positive pressure breathing (CPAP) in the supine posture. Corresponding inspiratory mechanical output variables were related to diaphragm activity. During resting breathing triangularis sterni and internal interosseous were more easily recruited than transversus abdominis and external oblique. EM activity increased with tilting, CPAP and rebreathing. Vagotomy depressed or abolished abdominal EM activity, with lesser effects on rib cage EM. Expiratory mechanical output grossly paralleled EM activity: it markedly depended on rib cage and abdominal EM coactivation, besides lung inflation and chest wall shape. Upper rib cage configuration at end-expiration never departed from the relaxation one, suggesting trivial effects of the triangularis sterni contraction. Lower chest wall distortion occurred almost regularly, so that much of EM activity was not converted into external work. In contrast with expiratory electromechanical relations, those for the diaphragm were always highly significant and independent of EM activation.     

Chest wall motion in paraplegic subjects

To assess the isolated effect of an abnormal increase in abdominal compliance on the pattern of chest wall motion during breathing, we have studied seven patients with complete transection of the midthoracic cord (Th4-Th7). Measurements of chest wall motion were obtained with magnetometers, and concentric needle electrodes were used to record the electromyograms of various respiratory muscles. When breathing quietly in the seated posture, all patients had phasic inspiratory activity in both the scalenes and the parasternal intercostals in the cranial interspaces, and the upper and lower rib cage anteroposterior (AP) diameters increased proportionately and in phase. This confirms that the scalenes and the cranial parasternal intercostals are important determinants of the inspiratory expansion of the rib cage in humans. In six of the seven patients, however, the inspiratory increase in abdomen AP diameter was disproportionately larger than the increase in lower rib cage AP diameter. As a result, the tidal breathing loop was displaced to the right of the relaxed thoracoabdominal configuration. Binding the abdomen reduced or suppressed this deformation. These observations thus indicate that an isolated increase in abdominal compliance may cause the chest wall to depart from its relaxed configuration during breathing. This departure probably results from a combination of two factors: (1) a reduction in the rib cage expanding action of the diaphragm, and (2) a decrease in the activation of the rib cage inspiratory muscles relative to the diaphragm.     

Bilateral diaphragmatic paralysis with hypercapnic respiratory failure: A physiologic assessment

Bilateral diaphragmatic paralysis was suspected in a patient presenting with hypercapnic respiratory failure who exhibited paradoxic (i.e., inward) abdominal movement on inspiration during tidal breathing in the supine posture; no paradoxic abdominal motion was observed at the bedside with the patient upright. Transdiaphragmatic pressure measurements established the diagnosis of diaphragmatic paralysis, although 20 cm H₂O pressure developed across the diaphragm during the latter part of a forced expiration, presumably due to the development of passive tension in the diaphragm as it was stretched near residual volume. Analysis of the relative motion of the rib cage and abdomen during breathing by the use of magnetometers confirmed the presence of abdominal paradox throughout the breathing cycle when the patient was supine, and established that paradoxic motion of the abdomen also occurred when the patient was in the erect posture but only in the latter half of inspiration. Our findings confirm that the use of transdiaphragmatic pressure measurements and magnetometry will help to quantify diaphragmatic function, that passive tension develops in the paralyzed diaphragm near residual volume and should not be confused with active contraction, and that paradoxic motion of the abdomen may be masked from the clinician when the patient is erect.     

Rib cage and abdominal volume displacements during breathing in pregnancy

To examine the effect of abdominal distension upon the actions of both rib cage and abdomen, we made serial determinations of tidal volume with a chest wall volume-displacement method in 8 pregnant women. Enhancement of tidal volume, long recognized in pregnancy, was achieved usually by augmentation of rib cage volume displacement. By contrast, abdominal volume displacement during quiet breathing is not altered in a predictable fashion by the gravid state. Given these findings, we hypothesize that the increased diaphragmatic contraction of pregnancy is accompanied by the transmission of that force to the lower rib cage via the area of apposition and that diaphragmatic contraction accounts for enhancement of the tidal breath. Diminished abdominal compliance might contribute to the augmentation of rib cage volume displacement as well. Konno-Mead diagrams suggest that this hypothesis is true in some, but not all, subjects.     

Inspiratory muscle strength in asthma

Augmentation of inspiratory muscle strength (Pimax) represents an adaptive response to airway obstruction. We explore the possibility that respiratory muscle weakness may herald hospital admission during acute bronchospasm. The Pimax measured 81 +/- 25 percent of a predicted value in 20 patients with acute bronchospasm (forced expiratory volume in one second, 36 +/- 17 percent predicted). Pimax was related to both hyperinflation (functional residual capacity, as percent predicted) and body weight (subjects were 122 +/- 29 percent ideal body weight), but not to the degree of airway obstruction per se. Furthermore, measurements of axial (craniocaudal) motion of the rib cage and asynchrony of rib cage and abdominal motions during tidal breathing did not correlate with either the degree of air flow obstruction or Pimax. We conclude that little if any respiratory muscle weakness occurs with bronchospasm. Furthermore, Pimax does not correlate with the degree of airway obstruction and does not explain abnormalities of rib cage and abdominal motion associated with asthma.     

Patterns of chest wall kinematics during volitional pursed-lip breathing in COPD at rest

BACKGROUND: Analysis of chest wall kinematics can contribute to identifying the reasons why some patients benefit from pursed-lip breathing (PLB). MATERIAL AND METHODS: We evaluated the displacement of the chest wall and its compartments, the rib cage and abdomen, by optoelectronic plethysmography (OEP), during supervised PLB maneuver in 30 patients with mild to severe chronic obstructive pulmonary disease (COPD). RESULTS: OEP showed two different patterns. A first pattern characterized the 19 most severely obstructed and hyperinflated patients in whom PLB decreased end-expiratory volumes of the chest wall and abdomen, and increased end-inspiratory volumes of the chest wall and rib cage. Deflation of the abdomen and inflation of the rib cage contributed to increasing tidal volume of the chest wall. The second pattern characterized 11 patients in whom, compared to the former group, PLB resulted in the following: (i) increased end-expiratory volume of the rib cage and chest wall, (ii) greater increase in end-inspiratory volume of the rib cage and abdomen, and (iii) lower tidal volume of the chest wall. In the patients as a whole changes in end-expiratory chest wall volume were related to change in Borg score (r(2)=0.5, p<0.00002). CONCLUSIONS: OEP helps identifying the reason why patients with COPD may benefit from PLB at rest.     

Chest wall configurational changes before and during acute obstructive episodes in asthma

We induced bronchial obstruction in 7 otherwise healthy asthmatic subjects and then measured the degree of airway obstruction and the dimensions of the chest wall including the anteroposterior (AP) diameters of the upper and lower rib cage and the abdomen and the transverse diameter of the lower rib cage. Airway obstruction was accompanied by a pronounced increase in the end-expiratory AP diameter of the upper rib cage in all 7 subjects and of the low lateral rib cage in 3 of the 4 subjects in whom this was measured. Other end-expiratory dimensions showed variable changes. In 6 of 7 subjects, obstruction caused the lower rib cage to become more elliptical in cross section during inspiration; transient inward motion of the lower anterior rib cage during early inspiration was noted. This latter motion coupled with the continuous outward motion of the upper anterior rib cage produced a pronounced rocking motion of the sternum during inspiration. These distortions of the chest cage were maximal when obstruction was most severe and gradually diminished as obstruction resolved. These inspiratory changes in chest cage cross-sectional configuration are similar to those seen in normal subjects who attempt to overcome external resistive loading by the increased use of inspiratory muscles; the end-expiratory configuration in asthma indicates an increase in functional residual capacity, which is actively maintained. Multiple degrees of freedom of motion of the chest cage exist during obstructive episodes. Estimates of volume change from measurements of rib cage cross-sectional area and abdominal diameter should be made with caution.     

Relationship between respiratory muscle electromyogram and rib cage motion in tetraplegia

In an attempt to understand the intersubject variation in rib cage motion in tetraplegia, and to assess the isolated action of the diaphragm on the human rib cage, we studied the pattern of rib cage motion in relation to the pattern of nondiaphragmatic respiratory muscle electromyogram (EMG) in 20 tetraplegic patients breathing at rest in the seated posture. The general pattern included a greater expansion of the lower than of the upper rib cage, and a greater and earlier expansion of the lower rib cage in its transverse than in its anteroposterior (AP) diameter. However, whereas the upper rib cage moved paradoxically inward with inspiration in 11 patients, it did not move or slightly expanded in 9 patients; in 1 of these, all rib cage diameters increased in the same proportion during inspiration as during relaxation. This intersubject variation was not related to the duration of tetraplegia, the pattern of the abdominal muscle EMG, or the presence of continuous spastic EMG activity in the parasternal intercostals. By contrast, it was related in part to the pattern of scalene EMG activity: upper rib cage AP paradox was present in 7 of 8 patients with spastic or silent scalenes but only in 4 of 12 patients with phasic inspiratory scalene EMG activity. When studied during quiet breathing in the supine posture, the 8 subjects with denervated scalene, intercostal, and abdominal muscles still showed inspiratory increase in the rib cage transverse diameter, but in 7 patients the lower rib cage AP diameter decreased in concert with the upper rib cage AP diameter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Absence of a hemidiaphragm: Mechanical implications

Respiratory system mechanics were evaluated in a 22-year-old asymptomatic man with absence of the left hemidiaphragm. We described changes in esophageal pressure (Pes), gastric pressure (Pga), chest wall configuration, and mediastinal motion during tidal breathing, breaths to total lung capacity (TLC), and Mueller maneuvers in the upright and supine position. We predicted that contraction of the single hemidiaphragm would drive the abdominal contents caudal on the side with the intact hemidiaphragm and displace the abdominal contents cephalad on the other side. This would drive the mediastinum toward the side with the intact diaphragm, thereby reducing its effectiveness in expanding the lung on that side. When upright, this effect would be minimized to the extent that the rib cage muscles lower pleural pressure in the thorax without the diaphragm. We found that (vital capacity) VC and TLC were greater upright than supine and that Pga deflections were almost as strongly negative as Pes deflections during upright quiet breathing and breaths to TLC. Thus the rib cage muscles enhanced the inspiratory action of the right hemidiaphragm in the upright position. In the supine position, Pes became negative without change of Pga during breaths to TLC and quiet inspirations. Here, contraction of the hemidiaphragm was the dominant mechanism generating the inspiratory pressure. During maximal Mueller efforts, the mediastinum shifted toward the side with the intact diaphragm in both positions and the maximum inspiratory pressures were low. These pressures were likely to have been limited by both the finite impedance to rotation of the thoracoabdominal contents or mediastinum and a mechanical disadvantage of the remaining hemidiaphragm. We conclude that the effectiveness of the single hemidiaphragm as an inspiratory pump requires passive impedance of the abdominal viscera and mediastinum and is enhanced in the upright position by the action of the rib cage muscles.     

Absence of a hemidiaphragm: mechanical implications

Respiratory system mechanics were evaluated in a 22-year-old asymptomatic man with absence of the left hemidiaphragm. We described changes in esophageal pressure (Pes), gastric pressure (Pga), chest wall configuration, and mediastinal motion during tidal breathing, breaths to total lung capacity (TLC), and Mueller maneuvers in the upright and supine position. We predicted that contraction of the single hemidiaphragm would drive the abdominal contents caudal on the side with the intact hemidiaphragm and displace the abdominal contents cephalad on the other side. This would drive the mediastinum toward the side with the intact diaphragm, thereby reducing its effectiveness in expanding the lung on that side. When upright, this effect would be minimized to the extent that the rib cage muscles lower pleural pressure in the thorax without the diaphragm. We found that (vital capacity) VC and TLC were greater upright than supine and that Pga deflections were almost as strongly negative as Pes deflections during upright quiet breathing and breaths to TLC. Thus the rib cage muscles enhanced the inspiratory action of the right hemidiaphragm in the upright position. In the supine position, Pes became negative without change of Pga during breaths to TLC and quiet inspirations. Here, contraction of the hemidiaphragm was the dominant mechanism generating the inspiratory pressure. During maximal Mueller efforts, the mediastinum shifted toward the side with the intact diaphragm in both positions and the maximum inspiratory pressures were low. These pressures were likely to have been limited by both the finite impedance to rotation of the thoracoabdominal contents or mediastinum and a mechanical disadvantage of the remaining hemidiaphragm. We conclude that the effectiveness of the single hemidiaphragm as an inspiratory pump requires passive impedance of the abdominal viscera and mediastinum and is enhanced in the upright position by the action of the rib cage muscles.     

The contributions of rib cage and abdominal displacements to the hyperinflation of acute bronchospasm

To quantitate the relative contributions of rib cage and abdomen to the hyperinflation of asthma, we examined chest wall movements during histamine-induced bronchospasm in 7 male asthmatic subjects. A reduction in FEV1 of 28.1 +/- 4.5% (mean +/- 1 SE) was associated with an increase in functional residual capacity (FRC) of 0.99 +/- 0.19 L, as measured by spirometer. Similar increases in FRC (0.91 +/- 0.18 L) were obtained using a DC respiratory inductive plethysmograph (RIP). The absolute error of measurement of delta FRC by RIP, compared with that by the spirometer, was 23.0 +/- 1.9%. The delta FRC by RIP was slightly less than by spirometer, as indicated by a net positive error of 7.2 +/- 7.3%. Increase in the volume of the rib cage, measured by RIP, usually accounted for the major change in FRC (75%). Even though the contribution of rib cage displacement to delta FRC ranged from as little as 30% to as much as 100% of the change in individual subjects, it was correlated with the rib cage contribution to the tidal breath prior to bronchoconstriction. We conclude that the relative contributions of rib cage and abdominal displacements to the volume of hyperinflation during mild to moderate acute induced bronchoconstriction are quite variable, but they can be predicted from the relative contributions of these compartments to tidal breathing prior to bronchoconstriction.     

Energy expenditure and rib cage-abdominal motion in chronic obstructive pulmonary disease

The resting energy expenditure (REE) was measured by indirect calorimetry in 10 patients with chronic obstructive pulmonary disease (COPD) in stable clinical state and in 10 normal subjects. In order to avoid artefactually increased values, REE was obtained from prolonged measurements in steady state using a ventilated hood, without facial apparatus. The REE of COPD patients was significantly increased to 117% of predicted basal metabolic rate and to 125% of the control group values. Rib cage and abdominal movements were measured in COPD patients by inductance plethysmography and expressed with three indices: rib cage contribution to tidal volume (RC/VT), variability in compartmental contribution to tidal volume (SD RC/VT), and maximal compartmental amplitude/tidal volume ratio (MCA/VT). No correlation was found between REE and any of the indices of rib cage and abdominal motion. We conclude that the REE is increased in patients with COPD in stable clinical state, but is not related to the degree of abnormal rib cage-abdominal motion.     

Influence of lung volume and rib cage configuration on transdiaphragmatic pressure during phrenic nerve stimulation in man

Transdiaphragmatic pressure was recorded during bilateral supramaximal percutaneous phrenic nerve stimulation at 1 Hz (twitch Pdi) to investigate the effect of lung volume and rib cage configuration on diaphragm contractility in man. Stimulations were performed in 5 normal supine subjects at resting end expiration (FRC) and at lung volumes above and below FRC, during relaxation against a closed airway and during isovolume manoeuvres. Twitch Pdi at FRC was 24.4 cm H2O. At lung volumes above FRC, twitch Pdi decreased by 7.04 +/- 3.2 cm H2O per litre of volume change. At lung volumes below FRC, twitch Pdi increased by 12.4 +/- 8.6 cm H2O per litre of volume change. When the diaphragm was lengthened during an isovolume manoeuvre at FRC, twitch Pdi increased. A similar relationship between lung volume and twitch Pdi was obtained during stimulations performed with abdominal binding. These results demonstrate that the pressure developed by the diaphragm during phrenic nerve stimulation is significantly affected both by increases and decreases in lung volume and by the rib cage configuration at which stimulation is performed.     

Rib cage mechanics in simulated diaphragmatic paralysis

To determine the action of the parasternal intercostals on the human rib cage, we studied the pattern of rib cage motion in relation to the pattern of respiratory muscle contraction in 4 normal subjects during attempts to perform tidal volume breathing with the parasternal intercostals alone. The dimensions of the chest wall, including the anteroposterior (AP) diameters of the lower rib cage and the abdomen, the transverse diameter of the lower rib cage, and the xiphipubic distance, were measured with linearized magnetometers. The electromyogram (EMG) of the diaphragm was obtained with an esophageal lead, while the EMGs of the intercostal, neck, and abdominal muscles were recorded using concentric needle electrodes. Minimizing diaphragmatic use during inspiration (transdiaphragmatic pressure = 0.08 to 1.54 cm H2O) was accompanied by a recruitment of the parasternals that was substantially greater than that of the scalenes; in 2 of the subjects, the activation of the scalenes at the beginning of inspiration was even delayed relative to the parasternals. The lateral intercostals showed variable changes during the maneuver, but the sternocleidomastoids, pectoralis major, rectus abdominis, and abdominal external oblique muscles were always silent. This pattern of EMG activity was associated with profound deformations of the rib cage. In all 4 subjects, the rib cage expanded considerably more along its transverse than its AP dimension relative to its relaxed configuration, and in 3 subjects, the xiphi-pubic distance decreased rather than increased in early inspiration.(ABSTRACT TRUNCATED AT 250 WORDS)