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PubMed1977

Interaction of lung volume and chemical drive on respiratory muscle EMG and respiratory timing.

The effect of increased FRC on the change in respiratory muscle electrical activity (EMG) and the duration of inspiration (Ti) and expiration (Te) produced by increases in chemical drive (i.e., progressive hypercapnia and isocapnic hypoxia) was assessed in 15 anesthetized, spontaneously breathing dogs. FRC was raised by applying continuous positive pressure (4 and 8 cmH2O) to the airway. Progressive hypercapnia and hypoxia were produced by rebreathing techniques. At any PCO2 or PO2, increases in FRC decreased diaphragm EMG (D); increased abdominal muscle EMG (AB); and prolonged Te without affecting Ti. The effect of increased FRC on D, AB, and Te diminished as PCO2 increased or PO2 decreased. The effect of sustained increases in lung volume in the absence of phasic changes was assessed by performing airway occlusion for a single inspiration during rebreathing at both control and increased FRC. The effects of increases in FRC were present during airway occlusion but were eliminated by vagotomy. We conclude, therefore, that tonic vagal stimulation produced by increases in FRC modified the change in respiratory muscle electrical activity and timing produced by increasing chemical drive.

Animals↗
PubMed1999

Immediate effect of respiratory muscle stretch gymnastics and diaphragmatic breathing on respiratory pattern. Respiratory Muscle Conditioning Group.

We investigated the immediate effect of respiratory muscle stretch gymnastics (RMSG) and diaphragmatic breathing (DB) on the respiratory pattern in patients with chronic obstructive pulmonary disease (COPD). Sixteen patients with COPD (age, 71.3 +/- 3.9 year) were entered in the study. DB was performed for 10 minutes in supine position. For RMSG, 5 patterns were repeated 10 times each. Respiratory variables were measured in sitting position before and after both RMSG and DB, performed in random order, patient to patient, with a 20-minute washout period in-between. After RMSG, but not after DB, there was a significant overall prolongation in expiratory time. After DB, but not after RMSG, there was an overall decrease in minute ventilation, carbon dioxide output, respiratory gas exchange ratio, end tidal O2 fraction, end tidal CO2 fraction and tidal diaphragmatic volume. The results suggest that RMSG may have a beneficial effect on the respiratory pattern. On the other hand, DB may provoke post-hyperventilation hypoxemia.

Aged↗
PubMed1984

[Fatigue of the respiratory muscles].

When respiratory muscle demands for energy exceed supplies, the energy stored within the muscles is depleted and the force of contraction diminishes. This state is called inspiratory muscle fatigue. When it occurs alveolar ventilation decreases, arterial carbon dioxide tension (Pa CO2), increases and hypercapnic respiratory failure ensues. It has also been suggested that such a dysfunction of the respiratory muscles contributes to the pathogenesis of dyspnoea. The purpose of this article is to review: those factors that predispose to respiratory muscle fatigue and determine energy demand and supply, and the principal means of investigation available, including the study of pressures created by muscular contraction, and electromyography.

Abdominal Muscles↗
PubMed2005

Skeletal muscle pump versus respiratory muscle pump: modulation of venous return from the locomotor limb in humans.

The vast majority of quantitative data examining the effects of breathing on venous return have been derived from anaesthetized or reduced animal preparations, making an extrapolation to an upright exercising human problematic due to the lack of a hydrostatic column and an absence of muscular contraction. Thus, this study is the first to quantitatively examine the effects of different breathing mechanics on venous return from the locomotor limbs both at rest and during calf contraction exercise in the semirecumbent human. When subjects inspired using predominantly their ribcage/accessory inspiratory muscles at rest (change in gastric pressure (DeltaP(GA)) = <2 cmH(2)O, change in oesophageal pressure (DeltaP(ES)) = approximately -6 cmH(2)O; inspiratory time/total breath time (T(I)/T(TOT)) = 0.5), a slight facilitation of femoral venous return was observed during inspiration (65% of all flow occurred during inspiration), with a slight reduction in femoral venous return during the ensuing expiratory phase of the breath. However, when subjects inspired using a predominantly diaphragmatic breath at rest (DeltaP(GA) = > 5 cmH(2)O, DeltaP(ES) = approximately -6 cmH(2)O; T(I)/T(TOT) = 0.5), femoral venous return was markedly impeded (net retrograde flow of 11%) and significantly lower than that observed during ribcage breathing conditions (P < 0.01). During the ensuing expiratory phase of a diaphragmatic breath, there was a large resurgence of femoral venous blood flow. The pattern of modulation during ribcage and diaphragmatic breathing persisted during both mild (peak calf force = 7 kg) and moderate (peak calf force = 11 kg) levels of calf contraction. Despite the significant within-breath modulation of femoral venous return by breathing, net blood flow in the steady state was not altered by the breathing pattern followed by the subjects. Though popliteal blood flow appeared to be modulated by respiration at rest, this pattern was absent during mild calf contraction where popliteal outflow was phasic with the concentric phase of calf contraction. We conclude that respiratory muscle pressure production is the predominant factor modulating venous return from the locomotor limb both at rest and during calf contraction even when the veins of the lower limb are distended due to the presence of a physiologic hydrostatic column.

Adaptation, Physiological↗
PubMed1988

Tracheal occlusion pressure: a simple index to monitor respiratory muscle fatigue during acute respiratory failure in patients with chronic obstructive pulmonary disease.

STUDY OBJECTIVE: To assess respiratory muscle fatigue in acute respiratory failure in patients with chronic obstructive pulmonary disease and evaluate its influence on weaning patients from mechanical ventilation. DESIGN AND PATIENTS: We studied the time course of tracheal occlusion pressure (P0.1) and high-to-low ratio of the diaphragmatic electromyogram in 16 patients in acute respiratory failure with chronic obstructive pulmonary disease. METHODS: All patients were intubated and studied during a 15-minute weaning period from ventilation. Minute ventilation (VE), arterial blood gases, P0.1 and high-to-low ratio of the diaphragm were measured every day from the onset to the end of acute failure (before extubation) at 5 and 15 minutes into the weaning period. The diaphragmatic electromyogram was recorded with an esophageal electrode and the high-to-low ratio of the electrical signal analyzed to assess diaphragmatic fatigue. MEASUREMENTS AND MAIN RESULTS: In all patients P0.1 was markedly increased (7.1 +/- 2.4 cm H2O, mean +/- SE) on the first day of acute failure and did not change during weaning. In 11 patients, P0.1 had decreased to 4.7 +/- 1.8 cm H2O (P less than or equal to 0.002) before extubation (which was done after 5 to 9 days). In these patients, the high-to-low ratio of the diaphragm decreased rapidly-during the first minutes of weaning on the first day of acute failure and remained low throughout weaning, whereas before extubation no decrease in high-to-low ratio was seen during weaning. In 5 patients, P0.1 did not change significantly from the onset of acute failure and the high-to-low ratio remained low before extubation. These 5 patients had to be reintubated within 2 to 6 days. In both groups of patients, VE did not change significantly from the first to last day of acute failure (10.3 +/- 3 compared with 10.7 +/- 2.1 min-1), whereas blood gases during room air breathing improved significantly from the first to last day of acute failure, respectively, in each group (arterial oxygen pressure [PaO2], 33.5 +/- 1.5 compared with 44 +/- 9 mm Hg (P less than or equal to 0.05) and PaO2 56 +/- 2.3 compared with 49 +/- 2 mm Hg (P less than 0.005). CONCLUSIONS: Extubation should not be done in patients with respiratory muscle fatigue despite improvement in arterial blood gases and clinical status; and P0.1 provides a valid and simple index to assess the likelihood of respiratory muscle fatigue.

Acute Disease↗
PubMed1970

Activity patterns in respiratory muscles and in respiratory neurones of the rostral medulla of the cat.

1. In the rostral medulla the activity patterns of respiratory neurones are of two main types: inspiratory and expiratory (Fig. 1). Some expiratory neurones begin activity early enough to fit Cohen & Wang's (1959) category of ;inspiratory-expiratory'. However, in the rostral medulla, ;inspiratory-expiratory' neurones do not constitute a distinct category within the expiratory group, since all intermediate activity patterns are observed. Similarly, no distinct categories of activity patterns can be distinguished within the inspiratory group.2. Expiratory neurones are rare in the extreme medial and lateral portions of the respiratory regions on each side of the rostral medulla (Fig. 3). Respiratory neurones are not bunched in anatomical clusters within each region, though a medio-dorsal group of neurones on each side is somewhat anatomically separated from the rest.3. At any one time there are at the very least 1000 respiratory neurones on each side of the rostral medulla.4. Many of the patterns of single unit activity recorded in respiratory muscles of the nose, throat and pharynx are different from the patterns of activity typical of respiratory neurones in the medulla near the cranial motor nuclei (Figs. 1 and 4). This suggests that many of the medullary recordings are from cells other than the motor neurones innervating these muscles.

Animals↗
PubMed1989

Respiratory muscle pharmacotherapy.

Respiratory muscle failure may be due to excessive respiratory load, electrolyte disturbances, acidosis and loss of muscle mass or failure. Acidosis and electrolyte disorders need recognition and correction. Pharmacotherapy with theophylline, sympathomimetic amines and perhaps digitalis have potential for improving respiratory muscle performance.

Digitalis Glycosides↗
PubMed1988

Respiratory muscle weakness during upper respiratory tract infections.

Global respiratory muscle strength was studied in 22 normal healthy volunteers during a 4-month winter period. Twelve subjects developed naturally acquired upper respiratory tract infections. Maximal static expiratory and inspiratory mouth pressures fell significantly during these infections. The greatest falls were documented between the third and seventh days of clinical illness. Full recovery occurred by the fourteenth day. We conclude that significant abnormalities of respiratory muscle function can occur during upper respiratory tract infections in otherwise healthy young adults.

Adult↗
PubMed1988

Respiratory muscle blood flow.

Respiratory muscle fatigue appears to be the cause of hypercapnic respiratory failure in many patients with lung disease. Recent studies have suggested that the rate of development of respiratory muscle fatigue largely depends on the balance between the level of respiratory muscle blood flow and the metabolic demands of these muscles. Physiological factors that alter muscle blood flow (for example, cardiogenic or septic shock, alterations in muscle length) or respiratory muscle metabolic demands (for example, increases in the work of breathing) may influence this balance, affecting the rate of development of respiratory muscle fatigue in these patients. Therapeutic measures that augment respiratory muscle blood flow (restoration of normal arterial pressure in patients in shock) or reduce the work of breathing (for example, mechanical ventilation) may prevent or reverse respiratory muscle fatigue.

Humans↗
PubMed2003

Integrated approach for in vivo evaluation of respiratory muscles mechanics.

The respiratory muscles constitute the respiratory pump, which determines the efficacy of ventilation. Any functional disorder in their performance may cause insufficient ventilation. This study was designed to quantitatively explore the relative contribution of major groups of respiratory muscles to global lung ventilation throughout a range of maneuvers in healthy subjects. A computerized experimental system was developed for simultaneous noninvasive measurement of inspired/expired airflow, mouth pressure and up to 8 channels of EMG surface signals from major respiratory muscles which are located near the skin (e.g., sternomastoid, external intercostal, rectus abdominis and external oblique) during various respiratory maneuvers. Lung volumes values were calculated by integration of airflow data. Hill's muscle model was utilized to calculate the forces generated by the muscles from the acquired EMG data. Analysis of EMG measurements and respiratory muscles forces revealed the following characteristics: (a) muscle activity increased with increased breathing effort, (b) inspiratory muscles contributed to inspiration even at relatively low flow rates, while expiratory muscles are recruited at higher flow rates, (c) the forces generated by the muscle depended on the muscle properties as well as on their EMG performance and (d) the pattern of the muscle's force curves varied between subjects, but were generally consistent for the same subject regardless of breathing effort.

Adult↗
PubMed2002

Respiratory muscle stretch gymnastics in patients with post coronary artery bypass grafting pain: impact on respiratory muscle function, activity, mood and exercise capacity.

A new rehabilitation (New-RH) program including respiratory muscle stretch gymnastics (RMSG) was developed to alleviate post-coronary artery bypass grafting pain (PCP). Effects on respiratory muscle function, pain, activities of daily living (ADL), mood and exercise capacity were investigated. Subjects were 16 consecutive patients undergoing median full sternotomy coronary artery bypass grafting (CABG), and were randomly divided into equal New-RH (S-group) and conventional therapy (C-group) groups. Rib cage dominant breathing was observed postoperatively in both groups. With preoperative tan deltaVrc/deltaVab, increases at 1-week postoperatively and decreases at discharge for S-group tended to exceed those of C-group (p > .05). Decreased maximum inspiratory and expiratory pressure status for functional residual capacity and percent forced expiratory volume in one second at discharge again only tended to be smaller for S-group (p > .05). S-group displayed significantly reduced pain around both scapulas at discharge (p = .049), and increased mean overall ADL and profile of mood states (POMS)/Vigor scores (p = .031 and p = .018, respectively). POMS/Tension-Anxiety scores at discharge for S-group were significantly smaller than those preoperatively (p = .025), and S-group displayed significantly increased distance walked over 6-minutes at discharge than C-group (p = .029). New-RH improves patient participation in exercise therapy and increases exercise capacity by reducing PCP, relieving anxiety and tension, and improving ADL.

Activities of Daily Living↗
PubMed1999

A second locus for autosomal dominant myopathy with proximal muscle weakness and early respiratory muscle involvement: a likely chromosomal locus on 2q21.

We recently mapped a locus for a new variant of autosomal dominant myopathy (Swedish families) with proximal muscle weakness, early respiratory muscle involvement, and unique muscle biopsy findings to chromosomal region 2q24-31. In this study, a French family with a similar clinical phenotype and pathology (muscle biopsy) was investigated to see whether the disease gene associated with the myopathy is mapped to the same region as the one in the Swedish families; however, chromosomal region 2q24-q31 was completely excluded. In order to localise the disease gene for the French family, a genome-wide scan was performed using polymorphic microsatellite markers. A maximum two-point lod score of 2.11 (the highest lod score that can be achieved in this family) was obtained for the markers in the region between D2S1272 and D2S1260, spanning 4 cM. This result suggests that the gene responsible for the French form is likely to be located on chromosome 2q21.

Chromosome Mapping↗
PubMed1992

[The appearance of "central core of respiratory muscle" in patients with respiratory failure].

We report the histological and histochemical features of core fibers present in respiratory muscles obtained from autopsy since 1980. Fifty autopsy cases of adults without neuromuscular disease were examined. "Central core" structure was present in 38 cases and absent in 12 cases. The duration of D.O.E. was greater than 1 month in 81.8% of core positive cases. In core negative cases, the duration of D.O.E. was less than 3 months. "Central core" structure were present in 80.0% of chronic respiratory failure cases and 41.7% of non-chronic cases. It is suggested that central core in respiratory muscles develops less than 3 months after the onset of D.O.E.

Adult↗
PubMed1989

Respiratory muscle rest.

The respiratory muscles have great reserves, and under normal circumstances, in a fit person, it is probably impossible to fatigue them by activity. However, respiratory muscle fatigue can be induced experimentally, and with the stress of pulmonary disability, or with impairment of muscle function due to neuromuscular disease or skeletal deformity. Respiratory muscle fatigue contributes to respiratory failure and clinical deterioration. Resting the respiratory muscles can allow time for recovery but requires complete or partial artificial ventilation. Whilst positive pressure ventilation has been carried out for many years in Intensive Care Units, this technique is difficult in the long-term. Recently there has been renewed interest in non-invasive ventilatory support. Nocturnal ventilation in an iron lung can cause long-term improvement in acute and chronic respiratory failure of patients with neuromuscular or skeletal abnormalities. Such patients may be maintained with devices at home, such as a pneumosuit, a cuirass, or positive pressure ventilation via the nose. In patients with chronic pulmonary disease respiratory muscle rest may be helpful during acute exacerbations. However, the value of rest in chronic respiratory failure of end-stage pulmonary patients is as yet unproven.

Humans↗
PubMed1978

Myelinated nerve fiber supply and muscle spindles in the respiratory muscles of cat: quantitative study.

The present study was undertaken to provide quantitative data on the myelinated fibers of the phrenic and intercostal nerves and the number of spindles in the main respiratory muscles of the cat. The myelinated component of the phrenic and intercostal nerves was studied in the cat. Histograms of sequency distributions as a function of nerve fiber diameter were established for normal nerves. Certain nerves were then examined 35 to 40 days after excision of the dorsal spinal ganglia. The muscle spindles of the corresponding muscles were counted and localized, and, on the basis of several morphological criteria, were classified with those usually described in the interosseous muscles. The study of the nerves, as that of the spindles, demonstrates clear differences of proprioceptive innervation among the respirator muscles. The lateral part of the diaphragm and the Triangularis sterni have practically no spindles. The external muscles of the first thoracic spaces are very rich in spindles. Respiratory muscles can be ranged in an almost continuous manner between these two extremes.

Animals↗
PubMed1989

Respiratory muscle fatigue.

When respiratory muscle demands for energy exceed supplies, the energy stored within the muscles is depleted and the force of contraction diminishes. This state is called inspiratory muscle fatigue. When it occurs alveolar ventilation decreases, arterial carbon dioxide tension (PaCO2) increases and hypercapnic respiratory failure ensues. It has also been suggested that such a dysfunction of the respiratory muscles contributes to the pathogenesis of acute respiratory failure. The purpose of this article is to review those factors that predispose to respiratory muscle fatigue and determine energy demand and supply and the principal means of investigation available to detect respiratory muscle fatigue in the clinical setting.

Energy Metabolism↗
PubMed1992

[Relationship of respiratory muscle fatigue and respiratory effort sensation: mechanisms and treatment].

We investigated whether fatigue of the expiratory muscle may account for a change in the respiratory effort sensation in normal subjects. We also examined the effects of inspiratory muscle training (IMT) and a beta 2-agonist, fenoterol, on respiratory effort sensation during loaded breathing. Experiment 1: Expiratory threshold loading was performed until exhaustion or 30 min, to induce expiratory muscle fatigue. The respiratory effort sensation was scored using a modified Borg scale. The maximum static expiratory pressure during loading (PEmaxload) decreased with time, and the Borg score rose with time. The relationship between the sensory score and PEmaxload was virtually linear. Experiment 2: Twice daily, IMT was performed using a pressure threshold device for 15 min in each session. The inspiratory threshold was set to 30% of each subject's maximum inspiratory pressure (Plmax) and IMT was continued for 4 weeks. Respiratory sensation (Borg score) was evaluated during a progressive exercise test. IMT increased inspiratory muscle pressure by 30%. However, there was no change in Borg score during the exercise test. Experiment 3: Fenoterol (5 mg) was given 2 hours before the inspiratory threshold loading, and then threshold loaded breathing was continued until exhaustion or 60 min. Endurance time increased by 50% in fenoterol group compared to placebo group. The increase in Borg score with time was less in fenoterol group than in placebo group. The decrease in respiratory muscle strength after loading was comparable in both groups. We conclude that the increased respiratory effort sensation during expiratory threshold loading is closely related to expiratory muscle fatigue as indicated by the decrease in expiratory muscle force.(ABSTRACT TRUNCATED AT 250 WORDS)

Dyspnea↗