Abdominal Recruitment Research Articles

Chest wall hyperinflation during acute bronchoconstriction in asthma.

The mechanics of the chest wall was studied in seven asthmatic patients before and during histamine-induced bronchoconstriction (B). The volume of the chest wall (VCW) was calculated by three-dimensional tracking of 89 chest wall markers. Pleural (Ppl) and gastric (Pga) pressures were simultaneously recorded. VCW was modeled as the sum of the volumes of the pulmonary-apposed rib cage (VRC,p), diaphragm-apposed rib cage (VRC,a), and abdomen (VAB). During B, hyperinflation was due to the increase in end-expiratory volume of the rib cage (0.63 +/- 0.09 L, p < 0.01), whereas change in VAB was inconsistent (0.09 +/- 0.07 L, NS) because of phasic recruitment of abdominal muscles during expiration. Changes in end-expiratory VRC,p and VRC,a were along the rib cage relaxation configuration, indicating that both compartments shared proportionally the hyperinflation. VRC,p-Ppl plot during B was displaced leftward of the relaxation curve, suggesting persistent activity of rib cage inspiratory muscles throughout expiration. Changes in end-expiratory VCW during B did not relate to changes in FEV(1) or time and volume components of the breathing cycle. We concluded that during B in asthmatic patients: (1) rib cage accounts largely for the volume of hyperinflation, whereas abdominal muscle recruitment during expiration limits the increase in VAB; (2) hyperinflation is influenced by sustained postinspiratory activity of the inspiratory muscles; (3) this pattern of respiratory muscle recruitment seems to minimize volume distortion of the rib cage at end-expiration and to preserve diaphragm length despite hyperinflation.

Respiratory response to exercise in postpolio patients with severe inspiratory muscle dysfunction

Objectives: To evaluate the limiting factors of exercise performance and to analyze the respiratory strategies adopted during exercise in postpolio patients with severe inspiratory muscle dysfunction. Patients: Five patients with prior poliomyelitis associated with scoliosis and with respiratory muscle dysfunction (mean vital capacity, 1.74L [range, 1.1 to 2.4]) were studied at rest and during leg or arm cycle exercise. Methods: Gas exchange was examined by arterial blood gases and mass spectrometry of expired air. Ventilatory mechanics were studied by measurement of esophageal and gastric pressures. Results: Blood gases at rest were normal, except for subnormal Po 2 levels in three patients. In all but one patient, ventilatory insufficiency was the limiting factor for exercise. A compensatory breathing pattern with abdominal muscle recruitment during expiration was present already at rest in three of the patients. The pressures generated by the diaphragm were below fatiguing margins, ie, levels that in healthy subjects can be sustained for at least 45 minutes. Conclusions: The extent of ventilatory dysfunction was not evident in blood gas values at rest; however, it was revealed by blood gas values during the exercise test. Diaphragm fatigue seems to be avoided at the cost of impaired blood gases.

Altered Abdominal Muscle Recruitment in Patients With Chronic Back Pain Following a Specific Exercise Intervention

The efficacy of specific exercise interventions that advocate training the co-contraction of the deep abdominal muscles with lumbar multifidus for treating chronic back pain conditions has not been tested. A randomized controlled trial involving 42 subjects with a specific chronic back pain condition investigated whether this form of intervention results in changes to the ratio of activation of the internal oblique relative to the rectus abdominis. Data were collected before and after the intervention, using surface electromyography, while subjects performed different abdominal maneuvers. Subjects were randomly allocated to either a specific exercise group or control group. Following intervention, the specific exercise group showed a significant (p < 0.05) increase in the ratio of activation of the internal oblique relative to the rectus abdominis. The control group showed no significant change. The study findings provide evidence that the conscious and automatic patterns of abdominal muscle activation can be altered by specific exercise interventions.

Abdominal muscle recruitment and PEEPi during bronchoconstriction in chronic obstructive pulmonary disease.

BACKGROUND: It has been recently shown that, when breathing at rest, many patients with severe chronic obstructive pulmonary disease (COPD) contract abdominal muscles during expiration, and that this contraction is...

Altered patterns of abdominal muscle activation in patients with chronic low back pain

This study investigated patterns of abdominal muscle recruitment during the abdominal drawing in manoeuvre in subjects with chronic low back pain (CLBP) and radiological diagnosis of spondylolysis or spondylolisthesis. Data were collected using surface electromyography from 12 physically active subjects with CLBP and 10 controls. The control subjects displayed an ability to preferentially activate internal oblique with minimal activation of upper rectus abdominis during the action of drawing in the abdominal wall. The group with CLBP were unable to achieve this. This finding may reflect the presence of neuromuscular dysfunction in this group. Further study is required to investigate if these findings are linked to the ability of patients with CLBP to provide dynamic stability of their lumbar spine.

Effects of pursed-lips breathing and expiratory resistive loading in healthy subjects

To examine the effect of pursed-lips breathing (PLB) on breathing pattern and respiratory mechanics, we studied 11 healthy subjects breathing with and without PLB at rest and during steady-state bicycle exercise. Six of these subjects took part in a second study, which compared the effects of PLB to expiratory resistive loading (ERL). PLB was found to prolong expiratory and total breath durations and to promote a slower and deeper breathing pattern. During exercise, the compensatory increase that occurred in tidal volume was not sufficient to counter the reduction in breathing frequency, causing minute ventilation to be reduced. Although ERL similarly caused minute ventilation and breathing frequency to be decreased, unlike PLB, it produced no change in tidal volume and prolonged expiratory and total breath durations to a lesser extent. PLB and ERL increased the expiratory resistance to a comparable degree, also increasing the expiratory resistive work of breathing and promoting greater expiratory rib cage and abdominal muscle recruitment in response to the expiratory loads. End-expiratory lung volume, which was determined from inspiratory capacity maneuvers, was not altered by PLB; however, with ERL it was increased by 0.20 and 0.24 liter during rest and exercise, respectively. Inspiratory muscle recruitment patterns were not altered by PLB at rest, although small increases in the relative contribution of the rib cage/accessory muscles in conjunction with abdominal muscle relaxation occurred during exercise. Similar trends were observed with ERL. We conclude that, although ERL and PLB induce comparable respiratory muscle recruitment responses, they are not equivalent with respect to breathing pattern changes and effect on end-expiratory lung volume.

Some effects of vagal blockade on abdominal muscle activation and shortening in awake dogs.

1. The mechanisms of abdominal muscle activation are thought to be different during expiratory threshold loading (ETL) compared with hypercapnia. Our objectives in the present study were to determine the effects of removing excitatory vagal feedback on abdominal muscle activation, shortening and pattern of recruitment during ETL and hypercapnia. Six tracheotomized dogs were chronically implanted with sonomicrometer transducers and fine wire EMG electrodes in each of the four abdominal muscles. Muscle length changes and EMG activity were studied in the awake dog during ETL (6 dogs) and CO2 rebreathing (3 dogs), before and after vagal blockade. 2. Following vagal blockade, the change in volume (increase in functional residual capacity, FRC) during ETL was greater and active phasic shortening of all the abdominal muscles was reduced, when shortening was compared with a similar change in lung volume. Similarly, at comparable minute ventilation, abdominal muscle active shortening was also reduced during hypercapnia. The internal muscle layer was recruited preferentially in both control and vagally blocked dogs during both ETL and hypercapnia. 3. The degree of recruitment of the abdominal muscles during ETL and hypercapnia in awake dogs is influenced by vagal feedback, but less so than in anaesthetized dogs. These results illustrate the importance of the vagi and abdominal muscle activation in load compensation. However, vagal reflexes are apparently not contributing to the preferential recruitment of the internal muscle layer. In awake dogs during vagal blockade abdominal muscle recruitment still occurs by extravagal mechanisms.

Abdominal muscle activity during hypercapnia in awake dogs.

We previously found the internal abdominal muscle layer to be preferentially recruited during expiratory threshold loading in anesthetized and awake dogs. Expiratory threshold loading increases end-expiratory lung volume and hence can activate reflex pathways such as tonic vagal reflexes, which could influence abdominal muscle recruitment. Our objectives in the present study were to determine the effects of hypercapnia on abdominal muscle activation and the pattern of recruitment in awake dogs. Five tracheotomized dogs were chronically implanted with sonomicrometer transducers and fine-wire electromyogram (EMG) electrodes in each of the four abdominal muscles: transversus abdominis, internal oblique, external oblique, and rectus abdominis. Muscle length changes and EMG activity were studied in the awake dog at rest and during CO2 rebreathing. CO2 rebreathing produced a tripling of tidal volume and activation of the abdominal muscles. Despite the increase in tidal volume, there was no significant change in abdominal muscle end-inspiratory length. Both tonic and phasic expiratory shortening were greater in the internal muscle layer (transversus abdominis and internal oblique) than in the external muscle layer (external oblique and rectus abdominis). We conclude that the internal abdominal muscles are preferentially recruited by hypercapnia and vagal reflexes probably do not contribute to this differential recruitment but that segmental reflexes may be involved. The mechanical consequences of this recruitment are discussed.

Control of breathing patterns and abdominal muscles during graded loads and tilt.

Tilting from supine to upright purportedly enhances both segmental and pulmonary proprioceptive feedback, whereas an expiratory threshold load (ETL) preferentially enhances pulmonary feedback. To test this we studied 13 adults when supine and 60 degrees and 90 degrees head up. We measured tidal volume, inspiratory duration (TI), and expiratory duration (TE) from flow; estimated end-expiratory lung volume from inspiratory capacity; and determined burst amplitudes and durations from abdominal electromyograms (EMGs). ETLs were incremented from 0 (control) to 25 cmH2O in 5-cmH2O steps. Tidal volume was significantly increased by ETL but was unaffected by body position. Every load prolonged TE, whereas TI remained unchanged. When subjects were supine, abdominal EMGs were silent but became tonically active when subjects were upright. During ETL, abdominal activity became rhythmical and phase locked to expiration. Bursts amplitudes were enhanced with each increment in ETL, but burst durations did not change even though TE was prolonged. The altered breathing pattern and active expiration augmented inspiratory flow and decreased end-tidal PCO2. Responses were greatest when subjects were 90 degrees head up. The load-related increments in abdominal recruitment, with no change in burst durations, fit the concept of two central pattern generators: one controlling pattern and the other controlling rhythm of the central respiratory drive.

Expiratory muscle activity in the awake and sleeping human during lung inflation and hypercapnia.

Expiratory muscle activity has been shown to occur in awake humans during lung inflation; however, whether this activity is dependent on consciousness is unclear. Therefore we measured abdominal muscle electromyograms (intramuscular electrodes) in 13 subjects studied in the supine position during wakefulness and non-rapid-eye-movement sleep. Lung inflation was produced by nasal continuous positive airway pressure (CPAP). CPAP at 10-15 cmH2O produced phasic expiratory activity in two subjects during wakefulness but produced no activity in any subject during sleep. During sleep, CPAP to 15 cmH2O increased lung volume by 1,260 +/- 215 (SE) ml, but there was no change in minute ventilation. The ventilatory threshold at which phasic abdominal muscle activity was first recorded during hypercapnia was 10.3 +/- 1.1 l/min while awake and 13.8 +/- 1 l/min while asleep (P less than 0.05). Higher lung volumes reduced the threshold for abdominal muscle recruitment during hypercapnia. We conclude that lung inflation alone over the range that we studied does not alter ventilation or produce recruitment of the abdominal muscles in sleeping humans. The internal oblique and transversus abdominis are activated at a lower ventilatory threshold during hypercapnia, and this activation is influenced by state and lung volume.

The Pattern of Respiratory Muscle Recruitment during Pursed-Lip Breathing

Data from the present study indicate a change in the pattern of chest wall muscle recruitment and improved ventilation with pursed-lip breathing (PLB) in COPD. Pursed lip breathing led to increased rib cage and accessory muscle recruitment during inspiration and expiration, increased abdominal muscle recruitment during expiration, decreased duty cycle of the inspiratory muscles and respiratory rate, and improved SaO2. In addition, PLB resulted in no change in pressure across the diaphragm and a less fatiguing breathing pattern of the diaphragm. Changes in chest wall muscle recruitment and respiratory temporal parameters concomitant with the increased SaO2 indicate a mechanism of improving ventilation with PLB while protecting the diaphragm from fatigue in COPD. Alterations in the pattern of respiratory muscle recruitment with PLB may be associated also with the amelioration of dyspnea. Further investigation is necessary to explore the relationship between the pattern of respiratory muscle recruitment during PLB and dyspnea.

Effect of resistive loads on pattern of respiratory muscle recruitment during exercise

In healthy subjects, we compared the effects of an expiratory (ERL) and an inspiratory (IRL) resistive load (6 cmH2O.l-1.s) with no added resistive load on the pattern of respiratory muscle recruitment during exercise. Fifteen male subjects performed three exercise tests at 40% of maximum O2 uptake: 1) with no-added-resistive load (control), 2) with ERL, and 3) with IRL. In all subjects, we measured breathing pattern and mouth occlusion pressure (P0.1) from the 3rd min of exercise, in 10 subjects O2 uptake (VO2), CO2 output (VCO2), and respiratory exchange ratio (R), and in 5 subjects we measured gastric (Pga), pleural (Ppl), and transdiaphragmatic (Pdi) pressures. Both ERL and IRL induced a high increase of P0.1 and a decrease of minute ventilation. ERL induced a prolongation of expiratory time with a reduction of inspiratory time (TI), mean expiratory flow, and ratio of inspiratory to total time of the respiratory cycle (TI/TT). IRL induced a prolongation of TI with a decrease of mean inspiratory flow and an increase of tidal volume and TI/TT. With ERL, in two subjects, Pga increased and Ppl decreased more during inspiration than during control suggesting that the diaphragm was the most active muscle. In one subject, the increases of Ppl and Pga were weak; thus Pdi increased very little. In the two other subjects, Ppl decreased more during inspiration but Pga also decreased, leading to a decrease of Pdi. This suggests a recruitment of abdominal muscles during expiration and of accessory and intercostal muscles during inspiration. With IRL, in all subjects, Ppl again decreased more, Pga began to decrease until 40% of TI and then increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal muscle activity during CO2 rebreathing in sleeping neonates

Comparison of the abdominal muscle response to CO2 rebreathing in rapid-eye-movement (REM) and non-REM (NREM) sleep was performed in healthy premature infants near full term. Eight subjects were studied at a postconceptional age of 40 +/- 1.6 (SD) wk (range 38-43 wk) during spontaneous sleep. Sleep stages were defined on the basis of electrophysiological and behavioral criteria, and diaphragmatic and abdominal muscle electromyographic activity was recorded by cutaneous electrodes. The responses to CO2 were measured by a modified Read rebreathing technique. The minute ventilation and diaphragmatic and abdominal muscle electromyographic activities were calculated and plotted against end-tidal CO2 partial pressure. Both the ventilatory and diaphragmatic muscle responses to CO2 decreased from NREM to REM sleep (P less than 0.05). Abdominal muscles were forcefully recruited in response to CO2 rebreathing during NREM sleep. In REM sleep, abdominal muscle response to CO2 was virtually absent or decreased compared with NREM sleep (P less than 0.05). We conclude that 1) the abdominal muscles are recruited during NREM sleep in response to CO2 rebreathing in healthy premature infants near full term and 2) the abdominal muscle recruitment is inhibited during REM sleep compared with NREM sleep, and this REM sleep-related inhibition probably contributes to the decrease in the ventilatory response to CO2 rebreathing in REM sleep.

Mechanical role of expiratory muscles during breathing in prone anesthetized dogs

The purpose of the present study was to assess the mechanical role of the expiratory muscles during spontaneous breathing in prone animals. The electromyographic (EMG) activity of the triangularis sterni, the rectus abdominis, the external oblique, and the transversus abdominis was studied in 10 dogs light anesthetized with pentobarbital sodium. EMGs were recorded during spontaneous steady-state breathing in supine and prone suspended animals both before and after cervical vagotomy. We also measured the end-expiratory lung volume [functional residual capacity (FRC)] in supine and prone positions to assess the mechanical role of expiratory muscle activation in prone dogs. Spontaneous breathing in the prone posture elicited a significant recruitment of the triangularis sterni, the external oblique, and the transversus abdominis (P less than 0.05). Bilateral cervical vagotomy eliminated the postural activation of the external oblique and the transversus abdominis but not the triangularis sterni. Changes in posture during control and after cervical vagotomy were associated with an increase in FRC. However, changes in FRC, on average, were 132.3 +/- 33.8 (SE) ml larger (P less than 0.01) postvagotomy. We conclude that spontaneous breathing in prone anesthetized dogs is associated with a marked phasic expiratory recruitment of rib cage and abdominal muscles. The present data also indicate that by relaxing at end expiration the expiratory muscles of the abdominal region are directly responsible for generating roughly 40% of the tidal volume.

Respiratory Muscle Function during Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is characterized by recurrent upper airway obstruction during sleep. Inspiratory muscles may be subjected to potentially fatiguing loads during an obstructive apnea and this may be related to the termination of obstructive apnea. We have measured transdiaphragmatic pressure (Pdi) and breathing patterns in six male patients with OSA during sleep to characterize respiratory muscle function in OSA and determine whether apnea termination is consistently related to a pressure time index of the diaphragm (PTI) associated with respiratory muscle fatigue. There was a large intersubject variability in Pdi generation during apnea. No consistent level of PTI was associated with apnea termination. During prolonged apneas, the respiratory duty cycle plateaued, which is suggestive of an inhibitory reflex possibly mediated by chest wall afferents. There were intersubject differences in both inspiratory and expiratory muscle recruitment during apnea. In the majority of patients, the diaphragm appeared to be the primary inspiratory muscle during apnea, but in some it appeared to be the intercostal/accessory muscles. The majority of patients demonstrated an increase in gastric pressure and inward abdominal movement during the expiratory phases of an apnea, consistent with abdominal muscle recruitment stimulated by increased ventilatory drive.

Effect of CPAP on respiratory effort and dyspnea during exercise in severe COPD

Recent work has demonstrated the ability of continuous positive airway pressure (CPAP) to relieve dyspnea during exercise in patients with severe chronic obstructive pulmonary disease (COPD). The present study examined the effects of CPAP (7.5-10 cmH2O) on the pattern of respiratory muscle activation and its relationship to dyspnea during constant work load submaximal bicycle exercise [20 +/- 4.8 (SE) W] in eight COPD patients (forced expiratory volume in 1 s = 25 +/- 3% predicted). Tidal volume, respiratory rate, minute ventilation, and end-expiratory lung volume increased with exercise as expected. There was no change in breathing pattern, end-expiratory lung volume, or pulmonary compliance and resistance with the addition of CPAP. CPAP reduced inspiratory muscle effort, as indicated by the pressure-time integral of transdiaphragmatic (integral of Pdi.dt) and esophageal pressure (integral of Pes.dt, P less than 0.01 and P less than 0.05, respectively). In contrast, the pressure-time integral of gastric pressure (integral of Pga.dt), used as an index of abdominal muscle recruitment during expiration, increased (P less than 0.01). Dyspnea improved with CPAP in five of the eight patients. The amelioration of dyspnea was directly related to reductions in integral of Pes.dt (P less than 0.001) but inversely related to increases in integral of Pga.dt (P less than 0.01). In conclusion, CPAP reduces inspiratory muscle effort during exercise in COPD patients. However, the expected improvement in dyspnea is not seen in all patients and may be explained by more marked increases in expiratory muscle effort in some individuals.

Transversus abdominis muscle function in humans

We used a high-resolution ultrasound to make electrical recordings from the transversus abdominis muscle in humans. The behavior of this muscle was then compared with that of the external oblique and rectus abdominis in six normal subjects in the seated posture. During voluntary efforts such as expiration from functional residual capacity, speaking, expulsive maneuvers, and isovolume "belly-in" maneuvers, the transversus in general contracted together with the external oblique and the rectus abdominis. In contrast, during hyperoxic hypercapnia, all subjects had phasic expiratory activity in the transversus at ventilations between 10 and 18 l/min, well before activity could be recorded from either the external oblique or the rectus abdominis. Similarly, inspiratory elastic loading evoked transversus expiratory activity in all subjects but external oblique activity in only one subject and rectus abdominis activity in only two subjects. We thus conclude that in humans 1) the transversus abdominis is recruited preferentially to the superficial muscle layer of the abdominal wall during breathing and 2) the threshold for abdominal muscle recruitment during expiration is substantially lower than conventionally thought.

The effects of locomotion on respiratory muscle activity in the awake dog

Using 6 chronically-instrumented awake dogs, we characterized the response of the respiratory muscles to mild and moderate treadmill exercise in terms of (1) the magnitude and timing of the EMGs of the costal and crural diaphragm, triangulars sterni and transverse abdominal muscles, and (2) the concomitant changes in esophageal ( Pe) and gastric ( Pg) pressures during treadmill exercise. Dogs wore a bivalved breathing mask which constrained breathing frequency and prevented some of the exercise-induced hypocapnia. Inspiratory and chest expiratory muscle EMGs increased linearly with a 1.5-fold tidal volume ( Vt) change during exercise. Abdominal muscle recruitment occured during most exercise levels and exhibited (1) phasic activity coincident with footplant and (2) tonic activation evidenced by a baseline shift in Pg and EMG activities. During control, inspiratory and expiratory flow preceded the onset of respiratory muscle EMG activity, but during exercise, electrical activation of these muscles coincided with the onset of mechanical flow. We conclude that phasic and tonic activation of expiratory muscles during exercise in the dog is significantly influenced by both respiratory and locomotory requirements. These patterns of expiratory muscle recruitment may assits inspiration by lengthening inspiratiry muscles through decrement in end-expiratory lung volume and by passive recoil of the rib cage and abdominal compartments.

Changes in neural drive (EMGd) and neuromuscular coupling during histamine-induced bronchoconstriction in patients with asthma

This study was undertaken in order to assess the neural drive to the respiratory muscles and the inspiratory neuromuscular coupling in patients with bronchial asthma during histamine-induced bronchoconstriction. Bronchoconstriction was produced in a graded fashion, with histamine phosphate aerosol of increasing dose, in twelve asymptomatic asthmatic patients and was measured by FEV1. Inspiratory drive was measured by electromyographic activity of the diaphragm (EMGd) and the coupling of the neural drive to the respiratory muscles was assessed by the relationship of mouth occlusion pressure (P0.1) to EMGd. During the test we also measured electromyographic activity of the inspiratory intercostal (EMGint), sternomastoid (EMGsm) and expiratory abdominal (EMGab) muscles. Histamine caused a significant decrease in FEV1, a significant increase in P0.1, EMGd, EMGint, and a relevant increase in EMGsm, with no substantial increase in EMGab. An inverse significant relationship between the change in FEV1 and changes in P0.1, EMGd and EMGint and a significant correlation between the change in FEV1 and in the P0.1/EMGd ratio were observed. We conclude that a progressive increase in bronchospasm is accompanied by a progressive increase in respiratory neural drive and decrease in neuromuscular coupling. This could be caused both by an increase in lung volume and a lack of abdominal expiratory muscle recruitment.

FATIGUE OF THE INSPIRATORY MUSCLES OF THE RIB CAGE IN HUMANS

Studies on respiratory muscle fatigue have focused on the diaphragm (DIA). We have found, however, that maximal static inspiratory pleural pressure (Pi max) is limited by the strength of the inspiratory muscles of the rib cage (RC). Failure to maintain Pi max during inspiratory endurance tasks might therefore result from fatigue of the RC muscles rather than DIA. To test this hypothesis, 5 trained subjects repeated maximal inspiratory efforts (duty cycle, 0.5) until Pi max could not be maintained. Subjects performed such efforts with a minimum of abdominal muscle recruitment. Before and after inspiratory efforts, DIA muscle strength was evaluated by measuring the transdiaphragmatic pressure generated during maximal expulsive efforts with an open glottis (Pdi max). (During expulsive efforts the DIA is maximally activated; thus, the Pdi obtained is a true index of DIA strength). Results (x±SD, *p<.01, paired t): We conclude that (1) Pi max is not limited by DIA strength, and (2) because DIA strength was unchanged, failure to maintain Pi max in these subjects appeared to be due to fatigue of the inspiratory muscles of the RC. RC muscle fatigue may be important in the pathogenesis of respiratory muscle failure. Supported by HL 07633.