Ventilatory dysfunction resulting from bilateral anterolateral high cervical cordotomy. Dual beneficial effect of aminophylline

Recovery of respiratory activity after C2 hemisection (C2HS): involvement of adenosinergic mechanisms

Consequences of spinal cord injury (SCI) depend on the level and extent of injury. Cervical SCI often results in a compromised respiratory system. Primary treatment of SCI patients with respiratory insufficiency continues to be with mechanical ventilatory support. In an animal model of SCI, an upper cervical spinal cord hemisection paralyzes the hemidiaphragm ipsilateral to the side of injury. However, a latent respiratory motor pathway can be activated to restore respiratory function after injury. In this review, restoration of respiratory activity following systemic administration of theophylline, a respiratory stimulant will be discussed. Pharmacologically, theophylline is a non-specific adenosine receptor antagonist, a phosphodiesterase inhibitor and a bronchodilator. It has been used in the treatment of asthma and other respiratory-related diseases such as chronic obstructive pulmonary disease (COPD) and in treatment of apnea in premature infants. However, the clinical use of theophylline to improve respiration in SCI patients with respiratory deficits is a more recent approach. This review will focus on the use of theophylline to restore respiratory activity in an animal model of SCI. In this model, a C2 hemisection (C2HS) interrupts the major descending respiratory pathways and paralyzes the ipsilateral hemidiaphragm. The review also highlights involvement of central and peripheral adenosine receptors in functional restitution. Biochemical binding assays that highlight changes in adenosine receptors after chronic theophylline administration are discussed as they pertain to understanding adenosine receptor-mediation in functional recovery. Finally, the clinical application of theophylline in SCI patients with respiratory deficits in particular is discussed.

Diaphragm pacing during prolonged mechanical ventilation of the lungs could prevent from respiratory muscle fatigue

Respiratory muscle fatigue after prolonged mechanical ventilation of the lungs is a common occurrence. This is probably due to disuse atrophy. The standard technique used to overcome this problem is to gradually wean the patient from the respirator over the course of several days or weeks.

HYPOTHESIS

based on experience with the rehabilitation of skeletal muscles during long-term immobilisation of the extremities following trauma or surgery and on experience with diaphragm pacing in quadriplegics, intermittent electrical or magenetic stimulation of the diaphragm while the lungs are still being mechanically ventilated may be beneficial. The result of such stimulation would be to preserve the dysfunctioning diaphragm from atrophy.

CONSEQUENCES

dependence on the respirator, length of intubation time, risk of complications and length of stay in the ICU would be considerably reduced.

Theophylline improves measurements of respiratory muscle efficiency

To determine the effect of theophylline on respiratory muscle efficiency (RME), 12 normal subjects were given theophylline vs placebo in a double-blind, randomized crossover protocol. Spirometry, resting energy expenditure, minute ventilation, RME and oxygen cost of breathing were measured at baseline, after taking theophylline, and after placebo. RME was calculated by dividing the added work required to breathe through a threshold load by the added energy consumed during loaded breathing. Oxygen cost of breathing was calculated by dividing the increase in oxygen consumption induced by breathing an air/carbon dioxide mixture by the associated increase in minute ventilation. RME increased from 3.3 +/- 1.6% at baseline to 7.9 +/- 3.2% after theophylline (p < 0.01) but did not change significantly after placebo (4.8 +/- 2.4%). Oxygen cost of breathing decreased from 3.9 +/- 2.4 mL O2 per liter at baseline to 1.7 +/- 0.7 mL O2 per liter after theophylline (p < 0.05) but did not change significantly after placebo (2.8 +/- 1.3 mL O2 per liter). Theophylline use was also associated with an 18% increase in minute ventilation (p < 0.01) and a 15.7% increase in resting energy expenditure (p < 0.01). Theophylline improves measured RME and reduces oxygen cost of breathing in normal subjects. These effects are offset by increases in resting energy expenditure and minute ventilation.

Pulmonary Manifestations of Neurological Disease

Breathing is a complicated act that requires sophisticated control mechanisms. The nervous system coordinates 3 fundamentally important components of respiration. The central nervous system has a central pattern generator that, along with appropriate feedback mechanisms, establishes both the resiratory rate and the depth of respirations. The peripheral nervous system facilitates transmission of these respiratory commands to the ventilatory muscles. The nervous system also contributes to the control of airway size. Laryngeal function is coordinated with inspiration, and local nerves in the lung have a major role in determining bronchial patency. Finally, the nervous system acts in incompletely understood ways to regulate perfusion of the lungs and to match local pulmonary blood flow with ventilation. Failure of the nervous system to adequately control these 3 different aspects of respiration may result in lifethreatening illness. Understanding how the nervous system affects control of ventilation, airway patency, and pulmonary perfusion therefore will enable intensivists to recognize and manage the pulmonary complications of neurological disease.

A randomized, controlled trial of theophylline in patients with severe chronic obstructive pulmonary disease

To assess the effects of theophylline in chronic obstructive pulmonary disease, we conducted a randomized, placebo-controlled, double-blind, crossover trial in 60 patients with severe but stable disease. The patients (mean age, 61 years) were studied before and after two months of placebo and two months of treatment with a sustained-release preparation of theophylline (10 mg per kilogram of body weight per day), administered orally. The two treatments were administered in a random order and separated by an eight-day washout period. After taking theophylline for two months (mean plasma concentration, 14.8 mg per liter), as compared with the two months of placebo, the patients had significant improvements in dyspnea, pulmonary gas exchange (partial pressure of arterial oxygen, 66 vs. 61 mm Hg [P less than 0.0001]; partial pressure of arterial carbon dioxide, 44 vs. 49 mm Hg [P less than 0.0001]), vital capacity (63 percent vs. 58 percent of the predicted value [P less than 0.0001]), and forced expiratory volume in one second (36 percent vs. 32 percent of the predicted value [P less than 0.0001]), with no significant change in airway resistance or functional residual capacity. Minute ventilation increased by a mean of 18 percent (P less than 0.0001) in the patients taking theophylline because of increased tidal volume, with no change in respiratory frequency. The respiratory-muscle performance of the patients taking theophylline improved by approximately 29 percent (P less than 0.0001), as indicated by a decline in the ratio of inspiratory pleural pressure during quiet breathing to maximal pleural pressure. We conclude that theophylline improves respiratory function and dyspnea in patients with severe chronic obstructive pulmonary disease and that these improvements are probably due to better respiratory-muscle performance.

Effect of theophylline on respiratory muscle function

Theophylline improves diaphragmatic contractility of the respiratory muscles both in isolated muscle preparations, as well as in animals and normal human beings. Furthermore, theophylline restores diaphragmatic fatigue and prevents fatigue of the diaphragm when given prophylactically. Finally, it was recently shown that theophylline improves diaphragmatic function in COPD patients, all of whom were CO2 retainers (PaCO2 53 +/- 3 mm Hg) and hypoxemic (PaO2 57 +/- 8 mm Hg). Patients improved transdiaphragmatic pressure and were less susceptible to fatigue. Presently the mechanisms of action of theophylline regarding its effects on diaphragmatic function are not fully elucidated. Experimental evidence, however, suggests that theophylline may have an effect on transmembrane calcium movements by blocking adenosine receptors.