Evaluation of Breathing Pattern: Comparison of a Manual Assessment of Respiratory Motion (MARM) and Respiratory Induction Plethysmography

Altered breathing pattern is an aspect of dysfunctional breathing but few standardised techniques exist to evaluate it. This study investigates a technique for evaluating and quantifying breathing pattern, called the Manual Assessment of Respiratory Motion (MARM) and compares it to measures performed with Respiratory Induction Plethysmography (RIP). About 12 subjects altered their breathing and posture while 2 examiners assessed their breathing using the MARM. Simultaneous measurements with RIP were taken. Inter-examiner agreement and agreement between MARM and RIP were assessed. The ability of the measurement methods to differentiate between diverse breathing and postural patterns was compared. High levels of agreement between examiners were found with the MARM for measures of the upper rib cage relative to lower rib cage/abdomen motion during breathing but not for measures of volume. The measures of upper rib cage dominance during breathing correlated with similar measures obtained from RIP. Both RIP and MARM measures methods were able to differentiate between abdominal and thoracic breathing patterns, but only MARM was able to differentiate between breathing changes occurring as result of slumped versus erect sitting posture. This study suggests that the MARM is a reliable clinical tool for assessing breathing pattern.     

Estimates of ventilation from body surface measurements in unrestrained subjects

To make estimates of ventilation from measurements of body surface movements in unrestrained subjects, we measured changes in linear dimensions and cross-sectional areas of the rib cage (RC) and abdomen (AB) of six healthy unrestrained subjects during a variety of maneuvers. RC and AB anteroposterior diameters and abdominal length in the cephalocaudal axis (axial displacement) were measured with magnetometers, and RC and AB cross-sectional areas were measured with a respiratory inductance plethysmograph. Flow was measured at the mouth with a pneumotachograph and integrated electrically to give volume. Volume and body surface measurements were analyzed by multiple linear regression. Addition of the axial measurements to either the anteroposterior dimensions or cross-sectional areas of RC and AB improved estimates of tidal volume in all subjects (P less than 0.01). With measurements of axial displacement and cross-sectional area of the RC and AB, tidal volume could be reliably estimated to within 20% of actual ventilation. We conclude that measurement of axial displacements improves estimates of ventilation in unrestrained subjects.     

Chest wall mechanics during artificial ventilation.

Chest wall mechanics were studied in six healthy volunteers before and during anesthesia prior to surgery. The intratracheal, esophageal, and intragastric pressures were measured concurrently. Gas flow was measured by pneumotachography and gas volume was obtained from it by electrical integration. Rib cage and abdomen movements were registered with magnetometers, these being calibrated by "isovolume" maneuvers. During spontaneous breathing in the conscious state, rib cage volume displacement corresponded to 40% of the tidal volume. During anesthesia and artificial ventilation, this rose to 72% of the tidal volume. The relative contributions of rib cage and abdomen displacements were not influenced by a change in tidal volume. Compliance was higher with a larger tidal volume, a finding which could be due to a curved pressure-volume relationship of the overall chest wall.     

Effect of intravenous midazolam on breathing pattern and chest wall mechanics in human

Breathing pattern, thoracoabdominal motion, and separate end-expiratory positions of the rib cage and abdomen were measured noninvasively in eight healthy subjects before and after intravenous administration of either placebo or midazolam, a short-acting benzodiazepine. Compared with placebo, midazolam produced a significant (P less than 0.01) decrease in mean inspiratory flow of 29% from preinjection values, resulting in a 39% reduction in tidal volume (VT). This ventilatory depression was partly compensated by a 35% decrease in expiratory time producing an increase in respiratory rate (+39%). The fall in VT was almost entirely (91%) mediated by a reduction of the abdominal contribution to tidal breathing while sparing rib cage motion. This fact contrasts with the effects of inhalational anesthetics or morphine, which preferentially depress rib cage expansion, indicating that thoracoabdominal motion may selectively be depressed by different pharmacological agents. In addition, continuous recording of end-expiratory levels showed a significant transient fall in the rib cage's end-tidal position 2 min after midazolam administration associated with the occurrence of central apneas.     

Effect of mechanical loading on displacements of chest wall during breathing in humans

Using a respiratory inductive plethysmograph (Respitrace) we studied thoracoabdominal movements in eight normal subjects during inspiratory resistive (Res) and elastic (El) loading. The magnitude of loads was chosen so as to produce a fall in inspiratory mouth pressure of 20 cmH2O. The contribution of rib cage (RC) to tidal volume (VT) increased significantly from 68% during quiet breathing (QB) to 74% during El and 78% during Res. VT and breathing frequency did not change significantly. During loading a phase lag was present on inspiration so that the abdomen led the rib cage. However, outward movement of the abdomen ceased in the latter part of inspiration, and the RC became the sole contributor to VT. These observations suggest greater recruitment of the inspiratory musculature of the RC than the diaphragm during loading, although changes in the mechanical properties of the chest wall may also have contributed. Indeed, an increase in abdominal end-expiratory and end-inspiratory pressures was observed in five out of six subjects, indicating abdominal muscle recruitment which may account for part of the reduction in abdominal excursion. Both Res and El increased the rate of emptying of the respiratory system during the ensuing unloaded expiration as a result of a reduction in rib cage expiratory-braking mechanisms. The time course of abdominal displacements during expiration was unaffected by loading.     

Does rib cage-abdominal paradox signify respiratory muscle fatigue?

Studies suggesting that abnormal motion of the rib cage (RC) and abdomen (Ab) may indicate respiratory muscle fatigue have not separated the influence of respiratory load from that of fatigue in its pathogenesis. We hypothesized that abnormalities on RC-Ab motion are primarily related to increased load rather than fatigue. We tested this hypothesis in subjects breathing against resistive loads while maintaining 30 and 60% of maximum mouth pressure (Pmmax). RC-Ab asynchrony and paradox and the degree of variation in compartmental contribution to tidal volume were measured by inductive plethysmography and quantitated by the Konno-Mead method of analysis. Comparing measurements of base line and 30 and 60% of Pmmax indicated that the degree of asynchrony, paradox, and variation in compartmental contribution were significantly related to the level of the load; significant abnormalities were observed at even 30% of Pmmax, a target pressure that can be sustained indefinitely. In another group of subjects, fatigue was induced by sustaining 60% of Pmmax to the limits of tolerance. Indexes of abnormal RC-Ab motion increased from base line during the 1st min of loaded breathing but displayed no progression from the beginning to the end of the fatigue run. Immediately on discontinuation of the load, the indexes returned to levels similar to base line despite persistence of the fatigue state. These results in healthy subjects breathing against severe resistances indicate that RC-Ab asynchrony and paradox and variation in compartmental contribution to tidal volume are predominantly due to increases in respiratory load rather than muscle fatigue.     

Rib cage distortion during voluntary and involuntary breathing acts

We examined chest wall and rib cage configuration in seven normal subjects during a variety of breathing maneuvers. Magnetometers were used to measure lower rib cage anteroposterior, lower rib cage transverse, upper rib cage anteroposterior, and abdomen anteroposterior diameters. Changes of these diameters were recorded during voluntary maneuvers, rebreathing, reading, and "natural" breathing. Relative motion of the rib cage and abdomen was displayed with the rib cage represented by the product of its lower anteroposterior and transverse diameters. During spontaneous breathing the rib cage and chest wall are near their relaxation configuration. During chemically driven ventilation the chest wall and rib cage progressively depart from this configuration. Much greater distortions of the chest wall and rib cage occurred during some voluntary maneuvers. Additionally, esophageal pressure and gastric pressure were measured during voluntary distortion of the rib cage. Substantial changes in lower rib cage shape occurred during voluntary maneuvers when compared with spontaneous breaths at the same transmural pressure. We conclude that the unitary behavior of the rib cage in normal subjects requires muscle coordination.     

Comparison of calibration methods for respiratory inductive plethysmography in infants

In infants under the age of 6 mo respiratory inductive plethysmograph (RIP)-calculated tidal volumes (VT) were compared with simultaneously measured volumes using a pneumotachograph (PNT) to 1) assess whether using multiple points (MP) along the inspiratory profile of a breath is superior to using only VT when calculating volume-motion (VM) coefficients, 2) verify the assumption of independent contributions of the abdomen and rib cage to VT, which was accomplished by extending the normal RIP model to include a term representing interaction between these two compartments, and 3) investigate whether VM coefficients are sleep-state dependent. Neither use of multiple points nor inclusion of the interacting term improved the performance of the RIP over that observed using a simple two-compartment model with VT measurements. However, VM coefficients obtained during quiet sleep (QS) were not reliable when used during rapid-eye-movement (REM) sleep, suggesting that coefficients obtained during one sleep state may not be applicable to another state where there is a substantial change in the relative abdominal/rib cage contributions to VT.     

Effect of position on the mechanical interaction between the rib cage and abdomen in preterm infants.

To determine the influence of body position on chest wall and pulmonary function, we studied the ventilatory, pulmonary mechanics, and thoracoabdominal motion profiles in 20 preterm infants recovering from respiratory disease who were positioned in both the supine and prone position. Thoracoabdominal motion was assessed from measurements of relative rib cage and abdominal movement and the calculated phase angle (an index of thoracoabdominal synchrony) of the rib and abdomen Lissajous figures. The ventilatory and pulmonary function profiles were assessed from simultaneous measurements of transpulmonary pressure, airflow, and tidal volume. The infants were studied in quiet sleep, and the order of positioning was randomized across patients. The results demonstrated no significant difference in ventilatory and pulmonary function measurements as a function of position. In contrast, there was a significant reduction (-49%) in the phase angle of the Lissajous figures and an increase (+66%) in rib cage motion in prone compared with the supine position. In addition, the degree of improvement in phase angle in the prone position was correlated to the severity of asynchrony in the supine position. We speculate that the improvement in thoracoabdominal synchrony in the prone position is related to alterations of chest wall mechanics and respiratory muscle tone mediated by a posturally related shift in the area of apposition of the diaphragm to the anterior inner rib cage wall and increase in passive tension of the muscles of the rib cage. This study suggests that the mechanical advantage associated with prone positioning may confer a useful alternative breathing pattern to the preterm infant in whom elevated respiratory work loads and respiratory musculoskeletal immaturity may predispose to respiratory failure.     

Accuracy of the respiratory inductive plethysmograph during loaded breathing

Indirect methods of measuring ventilation, such as the respiratory inductive plethysmograph (RIP), operate on the assumption that the respiratory system possesses two degrees of freedom of motion: the rib cage and abdomen. Accurate measurements have been obtained in many patients with pulmonary disease who possess additional degrees of freedom. Since calibration and validation of the RIP was carried out during quiet breathing in these patients, the amount of asynchronous or paradoxic breathing was presumably similar during the calibration and validation runs. Conversely, accuracy might be lost if following the initial calibration procedure the magnitude of chest wall distortion increased during subsequent validation runs. We calibrated the RIP during quiet breathing and examined its accuracy while subsequently breathing against resistive loads that required the generation of 20-80% of the subject's maximum inspiratory mouth pressure (Pmmax). We compared the relative accuracy of three commonly employed calibration methods: isovolume technique, least-squares technique, and single position loop-area technique. Up to 60% of Pmmax, 89% of the RIP values with the least-squares technique were within +/- 10% of simultaneous spirometric (SP) measurements and 100% were within +/- 20% of SP, compared with 63 and 91%, respectively, for the loop-area technique and 19 and 54%, respectively, for the isovolume technique. At 70 and 80% of Pmmax accuracy deteriorated. Accuracy of respiratory timing was judged in terms of fractional inspiratory time (TI/TT).(ABSTRACT TRUNCATED AT 250 WORDS)     

Activity of respiratory muscles in upright and recumbent humans

It is established that during tidal breathing the rib cage expands more than the abdomen in the upright posture, whereas the reverse is usually true in the supine posture. To explore the reasons for this, we studied nine normal subjects in the supine, standing, and sitting postures, measuring thoracoabdominal movement with magnetometers and respiratory muscle activity via integrated electromyograms. In eight of the subjects, gastric and esophageal pressures and diaphragmatic electromyograms via esophageal electrodes were also measured. In the upright postures, there was generally more phasic and tonic activity in the scalene, sternocleidomastoid, and parasternal intercostal muscles. The diaphragm showed more phasic (but not more tonic) activity in the upright postures, and the abdominal oblique muscle showed more tonic (but not phasic) activity in the standing posture. Relative to the esophageal pressure change with inspiration, the inspiratory gastric pressure change was greater in the upright than in the supine posture. We conclude that the increased rib cage motion characteristic of the upright posture owes to a combination of increased activation of rib cage inspiratory muscles plus greater activation of the diaphragm that, together with a stiffened abdomen, acts to move the rib cage more effectively.     

Calibration of respiratory inductive plethysmograph during natural breathing

We describe a single-posture method for deriving the proportionality constant (K) between rib cage (RC) and abdominal (AB) amplifiers of the respiratory inductive plethysmograph (RIP). Qualitative diagnostic calibration (QDC) is based on equations of the isovolume maneuver calibration (ISOCAL) and is carried out during a 5-min period of natural breathing without using mouthpiece or mask. In this situation, K approximates the ratio of standard deviations (SD) of the uncalibrated changes of AB-to-RC volume deflections. Validity of calibration was evaluated by 1) analyzing RIP waveforms during an isovolume maneuver and 2) comparing changes of tidal volume (VT) amplitude and functional residual capacity (FRC) level measured by spirometry (SP) with RIP values. Comparisons of VT(RIP) to VT(SP) were also obtained in a variety of postures during natural (uninstructed) preferential RC and AB breathing and with voluntary changes of VT amplitude and FRC level. VT(RIP)-to-VT(SP) comparisons were equal to or closer than published reports for single posture, ISOCAL, multiple- and linear-regression procedures. QDC of RIP in supine posture with comparisons to SP in that posture and others showed better accuracy in horizontal than upright postures.     

Chest wall motion during epidural anesthesia in dogs

To determine the relative contribution of rib cage and abdominal muscles to expiratory muscle activity during quiet breathing, we used lumbar epidural anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to paralyze the abdominal muscles while leaving rib cage muscle motor function substantially intact. A high-speed X-ray scanner (Dynamic Spatial Reconstructor) provided three-dimensional images of the thorax. The contribution of expiratory muscle activity to tidal breathing was assessed by a comparison of chest wall configuration during relaxed apnea with that at end expiration. We found that expiratory muscle activity was responsible for approximately half of the changes in thoracic volume during inspiration. Paralysis of the abdominal muscles had little effect on the pattern of breathing, including the contribution of expiratory muscle activity to tidal breathing, in most dogs. We conclude that, although there is consistent phasic expiratory electrical activity in both the rib cage and the abdominal muscles of pentobarbital-anesthetized dogs lying supine, the muscles of the rib cage are mechanically the most important expiratory muscles during quiet breathing.     

Volume quantification of chest wall motion in dogs

We employed high-speed multisliced X-ray-computed tomography to determine the relative volume contributions of rib cage (delta Vrc) and diaphragmatic motion (delta Vdi) to tidal volume (VT) during spontaneous breathing in 6 anesthetized dogs lying supine. Mean values were 40 +/- 6% (SE) for delta Vrc and 62 +/- 8% of VT for delta Vdi. The difference between VT and changes in thoracic cavity volume was taken to represent a change in thoracic blood volume (2 +/- 3% of VT). To estimate how much of delta Vrc was caused by diaphragmatic contraction and how much of delta Vdi was caused by rib cage motion, delta Vrc and delta Vdi were determined during bilateral stimulation of the C5-C6 phrenic nerve roots in the apneic dog and again during spontaneous breathing after phrenicotomy. Thoracic cavity volume (Vth) measured during hypocapnic apnea was consistently larger than Vth at end expiration, suggesting that relaxation of expiratory muscles contributed significantly to both delta Vrc and delta Vdi during spontaneous inspiration. Phrenic nerve stimulation did not contribute to delta Vrc, suggesting that diaphragmatic contraction had no net expanding action on the rib cage above the zone of apposition. Spontaneous breathing after phrenicotomy resulted in small and inconsistent diaphragmatic displacement (8 +/- 4% of VT). We conclude that the diaphragm does not drive the rib cage to inflate the lungs and that rib cage motion does not significantly affect diaphragmatic position during spontaneous breathing in anesthetized dogs lying supine.     

Respiratory load compensation in infants.

We have studied the respiratory compensation for elastic loads in 15 term and preterm infants. Elastic loads, approximately equal to the infant's effective elastance, were applied to the airway for five breaths while tidal volume and mask pressure were monitored. Motion of the rib cage and abdomen were monitored simultaneously with magnetometers. The studies were done both in active or REM sleep and in quiet or non-REM sleep. During quiet sleep the load immediately reduced the tidal volume by about 50% but a progressive increase in tidal volume occurred over the next four loaded breaths. During active sleep load compensation was disorganized with respect to both tidal volume and frequency, and compensation was significantly less. Active sleep was also characterized by marked rib cage distortion. We suggest that during active sleep there is tonic inhibition of the intercostal muscles, allowing the diaphragm to distort the rib cage. This distortion impairs load compensation by a direct mechanical effect and indirectly by initiating an intercostal-phrenic reflex.     

Diaphragmatic displacement measured by fluoroscopy and derived by Respitrace

In eight healthy volunteers we simultaneously measured the axial diaphragmatic motion by fluoroscopy and the cross-sectional area changes of the rib cage (RC) and abdomen (ABD) by Respitrace (RIP) during semistatic vital capacities (VC). We found that, if the fluoroscopic axial displacement of the posterior part of the diaphragm between residual volume (RV) and total lung capacity (TLC) is considered equal to 100%, the movement of the middle part is 90%, whereas that of the anterior part is only approximately 60%; the ratio of the axial displacements to mouth volume, furthermore, decreases at high lung volumes, especially for the anterior part. The RIP signal is nearly linearly related to mouth volume, but the contribution of the RC (delta RC) progressively increases (and is approximately 80% RIP at TLC), whereas the volume contribution of the ABD (delta ABD) levels off (to 20% RIP at TLC). The diaphragmatic volume displacement calculated from the theoretical analysis described by Mead and Loring also levels off at high volumes similarly as the ABD but is approximately 50% RIP at TLC. Finally, the axial movements of the three parts of the diaphragm are linearly related to the RC and ABD cross-sectional-area changes (r 0.91-0.97) and are even significantly better correlated with the "calculated" diaphragmatic volume displacement.     

Reflex compensation of spontaneous breathing when immersion changes diaphragm length

We measured tidal volume (VT), chest wall dimensions, end-tidal PCO2, and respiratory muscle electromyograms as seated subjects were immersed in water. We studied nine spontaneously breathing subjects; five were uninformed. Raising the water to xiphoid level pushed the abdomen in and expanded the rib cage at end expiration. This increased the diaphragm's operating length, giving it a contractile advantage, and shortened the inspiratory intercostals, giving them a contractile disadvantage. Peak inspiratory activities of both muscle groups decreased; inspiratory time (TI), respiratory frequency (f), and VT were unchanged. The experiments thus demonstrated operational length compensation during immersion and further showed that inspiratory muscle activation is not adjusted locally, according to changes in each muscle's length, but rather that the response is global. Xiphoid-to-shoulder immersion was less easily interpreted, since both rib cage and abdomen were compressed, lengthening both inspiratory muscles. Our subjects continued to maintain VT, f, and TI. Peak inspiratory activities of both muscles were further reduced. We do not attribute the change in inspiratory muscle activation to altered chemical drive or to voluntary response. Rather, the response appears to be a mechanoreceptive reflex that employs afferent information from the lungs or diaphragm to adjust all inspiratory muscle activities.     

Dependence of diaphragmatic length on lung volume and thoracoabdominal configuration

Changes in lung volume can be partitioned into volume displacements of the rib cage and abdomen. Abdominal displacements are often used as estimates of diaphragmatic displacements and changes in lengthening of diaphragmatic muscle. We used X-rays, ultrasound, and linear measurements of thoracic and abdominal diameters to estimate relationships among lung volume, thoracoabdominal configuration and diaphragmatic length, and we found that diaphragmatic length was strongly dependent on rib cage as well as abdominal displacement. In three subjects, the diaphragm shortened 57-85% as much during a breath made without abdominal displacement as during a normal breath in which the abdominal wall moved outward with the rib cage. We conclude that changes in diaphragmatic length can be estimated from surface measurements without radiation and that the length of the diaphragm cannot be estimated from displacements of the abdominal wall alone.     

Relative contributions of rib cage and abdomen to breathing in normal subjects.

By use of the method of Konno and Mead and the respiratory magnetometer, the partition of respired gas volumes into rib cage and diaphragm-abdomen components was accomplished in 81 normal subjects including 32 young and middle-aged men, 29 young and middle-aged women, and 20 elderly men. Studied were isovolume maneuvers and the relaxation configuration over the inspiratory capacity range, quiet tidal breathing, increased amplitudes of slow breathing, rapid inspirations and expirations, and both quiet and forceful phonation. No major differences were noted between men and women or between the young and the elderly during any respiratory acts. During quiet breathing most normal subjects are abdominal breathers when supine and thoracic breathers when upright. Rapid respiratory maneuvers were accomplished mostly through rib cage displacement suggesting that rib cage muscles are capable of more rapid action than diaphragm and abdominal muscles. Data from deep breathing and rapid maneuvers supported the view that abdominal and rib cage muscles often act to optimize the mechanical (length-tension) advantage of the diaphragm.     

Inhibition of breathing associated with gallbladder stimulation in dogs

The effect of mechanical stimulation of the gallbladder on breathing was studied in anesthetized spontaneously breathing dogs. Measurements of tidal volume, breathing frequency, rib cage and abdominal diameter, transdiaphragmatic pressure, and electrical activity of the diaphragm were made while traction or compression was applied to the gallbladder for periods of 30 s. Both forms of mechanical stimulation produced similar changes, including large decreases in tidal volume, respiratory rate, electrical activity of the diaphragm, and transdiaphragmatic pressure swings. Inspiratory rib cage expansion was little affected, but abdominal expansion was greatly reduced, and swings in gastric pressure were reduced more than swings in pleural pressure, indicating a selective decrease in diaphragmatic activity. Recovery of all measured parameters returned toward control values, despite continued traction or compression. Some inhibition persisted after the stimulus was withdrawn. The very brief interval between stimulus and response suggested that the mechanism was a neural reflex. The afferents involved are unknown but are not purely vagal in nature, since qualitatively similar results were seen in animals after vagotomy. The alteration in breathing frequency indicates that at least part of the reflex is supraspinally mediated. The change in pattern of breathing closely resembles that seen in subjects after abdominal surgery and supports the theory that reflex inhibition of breathing contributes to postoperative pulmonary complications seen in those subjects.