Respiratory muscles fatigue

Smooth muscle relaxation, central nervous system (CNS) excitation, and cardiac stimulation are the principal pharmacological effects observed in patients treated with theophylline. The action of theophylline on the respiratory system is easily seen in the asthmatic by the resolution of obstruction and improvement in pulmonary function. Other mechanisms that may contribute to the action of theophylline in asthma include antagonism of adenosine, inhibition of mediator release, increased sympathetic activity, alteration in immune cell function, and reduction in respiratory muscle fatigue. Theophylline also may exert an antiinflammatory effect through its ability to modulate inflammatory mediator release and immune cell function. 

Acute respiratory failure Slow weaning from ventilator Respiratory muscle fatigue Renal... 

Although the reversibility of airways obstruction is an important characteristic of asthma, those asthmatics with chronic symptoms do not reverse completely. The chronic airways obstruction is probably related to mucus plugging of bronchi and hypertrophy of the bronchial smooth muscle. These changes are not reversible by bronchodilators, and it is not clear that they can be reversed with any specific therapy. Both types of obstruction contribute to an imbalance of the ventilation to perfusion ratio in the lung and can result in hypoxemia and hypocarbia. The decreased carbon dioxide content of the blood is the result of the asthmatic s hyperventilation and will persist until the respiratory muscles fatigue and hypoventilation becomes prominent. Asthmatics can die quite quickly when this occurs. 

The mechanical efficiency of the respiratory muscles is limited by the force-velocity and force-length relationships which may be modeled as linear active resistance and elastance, respectively [Mihc-Emih and Zin, 1986]. Neuromechanical efficiency may be impaired in respiratory muscle fatigue or muscle weakness, resulting in diminished Pmus for any given neural drive. 

FIGURE 11.4 (a) Optimal waveforms for respiratory muscle driving pressure, P(t) respiratory airflow, V and respired volume, R, during normal breathing (NL) or under various types of ventilatory loads IRL and ERL, inspiratory and expiratory resistive load lEL and CEL, inspiratory and continuous elastic load, (b) Optimal waveforms for P(t) under increasing respiratory muscle fatigue (amplitude limited upper panel) and muscle weakness (rate limited lower panel). (From Poon and coworkers [1992]. With permission.)... 

Respiratory muscle weakness and respiratory muscle fatigue can decrease the capacity of these muscles to generate and sustain tension. As direct quantification of respiratory muscle tension is clinically impossible, measurements of pressure elicited by respiratory muscle contractions are used to indirectly determine their contribution to ventilator dependence. 

Only a small proportion of patients fail to wean from mechanical ventilation, but they require a disproportionate amount of resources. Weaning failure has been extensively studied in the clinical literature and several factors are likely to contribute to it. These factors include inadequate ventilatory drive, respiratory muscle weakness, respiratory muscle fatigue, increased work of breathing, or cardiac failure. There is accumulating... 

Pavlovic D, Wendt M. Diaphragm pacing during prolonged mechanical ventilation of the lungs could prevent from respiratory muscle fatigue. Med Hypotheses 2003 60 398-403. 

A large number of conditions can result in chronic ventilatory failure and patients with these conditions may benefit from home ventilation. Typically, patients with restrictive disorders have decreased compliance of the chest wall, resulting from a thoracic cage deformity or from respiratory muscle involvement (1). In patients with severe obstructive pulmonary disorders, respiratory muscle fatigue and alveolar hypoventilation, especially during sleep, are thought to contribute to respiratory failure (2,3) (Table 1). 

Individuals with asbestosis initially present with shortness of breath on exertion, which becomes progressively more severe and eventually present at rest when the disease is advanced. Dyspnoea is commonly the most disabling symptom, although a dry cough is also a feature of more advanced disease and may become more distressing than breathlessness (Parkes 1994). Dyspnoeic individuals may also experience thoracic pain due to respiratory muscle fatigue. 

Poon et al. (1992) have shown that the dynamic optimization model predicts closely the Pnius(0 trajectories under various conditions of ventilatory loading as well as respiratory muscle fatigue and weakness (Figure 20.4). In addition, the model also accurately predicts the ventilatory and breathing pattern... 

Fatigue of muscles is found post-exercise and in some patients with disorders of limb or respiratory muscles. Peripheral muscle fatigue is generally characterized by the changes in force frequency relationships that occur. The process is traditionally divided into a failure of force production at either low or high frequencies of electrical stimulation. 

Poisoning by pesticides that contain organophosphate compounds produces a variety of symptoms, including nausea, blurred vision, fatigue, muscle weakness and, potentially, death caused by paralysis of respiratory muscles. 

The most prominent and often limiting feature of dantrolene administration is dose-dependent muscle weakness. Other side effects are drowsiness, dizziness, malaise, fatigue, and diarrhea. Symptomatic hepatitis is reported in 0.5% of patients receiving it and fatal hepatitis in up to 0.2%. Contraindications include respiratory muscle weakness and liver disease. It is suggested that patients on dantrolene therapy be given regular liver function tests. 

Articaine has been implicated in an episode of weakness of the limb muscles, fatigue, and anorexia in a patient with a rare respiratory chain disorder due to a genetic defect in mitochondrial DNA (Kearn-Sayre Syndrome). 

Botulinum toxin A is a simple protein comprising a single polypeptide chain, readily detoxified by heat, mechanical stress, and oxygen (Stevenson et al., 1947 Lamanna, 1959). In contaminated water, it remains highly toxic for several days but decays rapidly in open air. This toxin inhibits the release of acetylcholine at sites needed to transmit nerve impulse to muscles. Botulinum toxin by ingestion produces nausea and diarrhea, followed by headache, dizziness, fatigue, weakness, vertigo, extreme constipation, convulsions, and death due to paralysis of respiratory muscles. 

The primary physiologic change is often a worsening of arterial blood gas results owing to poor gas exchange and increased muscle fatigue. In a patient experiencing a severe exacerbation, profound hypoxemia and hypercapnia can be accompanied by respiratory acidosis and respiratory failure. 

GA GB GD GF VX Frequent micturition, urinary incontinence. Apprehension, giddiness, insomnia, headache, drowsiness, difficulty concentrating, poor memory, confusion, slurred speech, ataxia, weakness, coma and areflexia, Cheyne-Stokes respiration, convulsions. Fasciculations, easy fatigue, cramps, weakness (including respiratory muscles), paralysis. 

In addition to cardiac and respiratory efforts, muscle activity is the next important parameter in terms of understanding how the body performs during training. Such information enables the wearer or coach to understand how the body is performing. Imbalances in the use of body muscles can be detected. Muscle fatigue can be estimated. Muscle performance capacity and efficiency can be analysed. 

Roussos C, Fixley D, Gross D, et al. Fatigue of the respiratory muscles and their synergistic behavior. J Appl Physiol 1979 46 897-904. 

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