Corticosteroid-induced myopathy involving respiratory muscles in patients with chronic obstructive pulmonary disease or asthma

We made observations on two patients with asthma and one with COPD who developed steroid-induced myopathy during prolonged treatment with high doses of corticosteroids. On admission, quadriceps force was on the average reduced to 31% of predicted (range 16 to 46% of predicted, nondominant leg), and urinary excretion of creatine in 24 h averaged 687 mg (range 275 to 1,045 mg/24 hr). Respiratory muscle involvement was evidenced by reductions in PImax and PEmax, being 38% (range 36 to 39) and 48% of predicted (range 36 to 68), respectively. Tapering of treatment with corticosteroids resulted in important recovery of quadriceps force and respiratory muscle force. In all three patients, a correlation between muscle forces and steroid dose was present during reduction of the dose. After 6 months quadriceps force averaged 62% of predicted (range 31 to 85), and PImax and PEmax reached 74% (range 52 to 92) and 92% of predicted (range 80 to 106), respectively, after 3 months. Consequently, respiratory muscle force appeared to recover faster than quadriceps force. The implications of these observations for patients treated with the usual doses of corticosteroids for shorter periods require further investigation.

Steroid-induced myopathy and its significance to respiratory disease: a known disease rediscovered

Skeletal muscle myopathy is a well-known side-effect of systemically administered corticosteroids. In recent years renewed attention is being paid to the involvement of the respiratory muscles and its consequent significance in pulmonary patients. Two different clinical patterns of steroid-induced muscular changes are known. In acute myopathy and atrophy after short term treatment with high doses of steroids, generalized muscle atrophy and rhabdomyolysis occur, including the respiratory muscles. Chronic steroid myopathy, occurring after prolonged treatment with moderate doses, is characterized by the gradual onset of proximal limb muscle weakness and may be accompanied by reduced respiratory muscle force. Animal studies demonstrated diaphragmatic myopathy and atrophy similar to the alterations in peripheral skeletal muscles. Fluorinated steroids induced selective type IIb (fast-twitch glycolytic) fibre atrophy, resulting in changes in contractile properties of the diaphragm. Non-fluorinated steroids may also induce histological, biochemical and functional alterations in the diaphragm. Observations in patients with collagen vascular disorders and with asthma and chronic obstructive pulmonary disease (COPD) underline the potential hazards of treatment with corticosteroids to respiratory muscle structure and function.

Effects of Broxaterol and Theophylline on Fatigued Canine DiaphragmIn Vivo: A Randomized, Controlled Study

Since broxaterol, a new beta 2-agonist, has been shown to improve contractility of fatigued canine diaphragm in vitro, a controlled, randomized study was designed to assess its effects on fatigued canine diaphragm in vivo, and compare these to the expected inotropic effects of aminophylline. Diaphragm fatigue was induced in 21 dogs using electrophrenic stimulation at 20 Hz until transdiaphragmatic pressure (Pdi) at 20 Hz was reduced to about 50% of its original value. After stabilization of fatigue, animals were randomized in three groups. Aminophylline-treated animals received an intravenous bolus of 20 mg/kg, broxaterol-treated animals were given an initial bolus of 100 micrograms/kg, and control animals obtained an equal load of saline. After 3 h, aminophylline-treated animals and broxaterol-treated animals received a second dose of 20 mg/kg and 200 micrograms/kg, respectively, whereas control animals received a second dose of saline. Pdi was measured every 30 min for 6 h. At therapeutic serum levels, theophylline did not affect Pdi at any stimulation frequency compared with control conditions. In contrast, broxaterol administration resulted in a significant (p less than 0.05) and long-lasting increase in Pdi at low stimulation frequencies. Pdi at 20 Hz thus increased by 20 +/- 16% 90 min after the first bolus, and by 36 +/- 18% 90 min after the second dose. We conclude that (1) broxaterol promotes recovery of low-frequency fatigue in a dose-dependent way, and (2) theophylline does not improve the force output of fatigued canine diaphragm in vivo.

Bronchodilator properties of an inhaled leukotriene D4 antagonist (verlukast--MK-0679) in asthmatic patients

The safety, tolerability and bronchodilator properties of inhaled verlukast (MK-0679), a new potent and selective LTD4-receptor antagonist, were studied in 12 asthmatic subjects with more than 15% increase in FEV1 after salbutamol inhalation. On three separate study days the patients inhaled placebo, verlukast 2 mg and verlukast 8 mg from a metered dose inhaler according to a randomized, double-blind, cross-over allocation schedule. Pulmonary function and tolerability were assessed regularly and after 8 h a second dose of test drug was inhaled. Thirty minutes later a beta 2-agonist dose-response curve was performed by inhaling salbutamol in cumulative doses of 200, 400 and 800 micrograms. Verlukast (8 mg) caused significant improvement in mean FEV1 from 1.5 through 8 h after inhalation as compared to placebo (P less than 0.05). The maximum change in FEV1 occurred at 2 h after inhalation with mean percent increases above baseline of 3.5, 7.7, and 9.2% after placebo, verlukast 2 mg and 8 mg, respectively. The bronchodilator response to inhaled salbutamol was significantly larger after verlukast 8 mg than after placebo pretreatment (P less than 0.05), whereas verlukast 2 mg afforded no additive bronchodilator effect. We conclude that inhalation of the LTD4-antagonist verlukast induces modest but significant bronchodilatation and may be beneficial in the treatment of asthma.

High-frequency diaphragmatic flutter: symptoms and treatment by carbamazepine

Classic diaphragmatic flutter, a rare disorder associated with dyspnoea, thoracic or abdominal wall pain, and epigastric pulsations, is caused by involuntary contractions of the diaphragm with a frequency of 0.5-8.0 Hz. We have seen three patients with diaphragmatic flutter of higher frequency not associated with respiratory disease. The patients presented with longstanding oesophageal belching, hiccups, and retching, respectively. The diagnosis was established by the presence on electromyography of the diaphragm and scalene and parasternal intercostal muscles of repetitive discharges of 9-15 Hz. Spirographic tracings, especially those of volume or flow vs time, showed similar high-frequency oscillations superimposed on tidal respiratory movements. Treatment with carbamazepine 200-400 mg three times daily led to disappearance or great improvement of flutter and clinical symptoms in all three patients. The phenomenon was not seen in other patients with chronic hiccups or oesophageal belching or in patients without these symptoms who had undergone electromyography or spirography for other reasons. Thus, high-frequency diaphragmatic flutter seems to be a new disease entity. The response to carbamazepine, which suggests that the flutter causes the symptoms, requires further study.

Effects of theophylline on canine diaphragmatic contractility and fatigue

To distinguish the effects of theophylline on respiratory muscle contractility from alterations in respiratory muscle interaction or blood flow, we examined in vitro contractile properties and fatigue of canine diaphragm in two series of experiments. In the first series, a 40-mg/kg aminophylline infusion was given to dogs, and diaphragm strips were removed for in vitro study when stable tissue fixation of the drug was reached. Compared with control bundles examined before aminophylline infusion, no alterations in twitch tension, tetanic tension, or force-frequency characteristics were observed. Moreover, theophylline-treated strips fatigued faster than control strips, whether subjected to repetitive submaximal or maximal contractions (p less than 0.01). In the second series, diaphragm bundles were equilibrated with high theophylline doses (400 mg/L) in vitro, and inotropic effects compared with the results in the first series. Supratherapeutic theophylline concentrations increased force development at low stimulation frequencies (p less than 0.05 at 10 Hz) and significantly elevated twitch-tetanus ratio (p less than 0.01) but did not protect against development of in vitro muscle fatigue. Poor penetration of theophylline in diaphragm bundles in vitro was excluded, since drug concentrations in the muscle bundle and the muscle bath were virtually equal. We conclude that diaphragmatic tissue concentrations correlate well with therapeutic serum and supratherapeutic bath levels and that only high theophylline concentrations increase canine diaphragmatic contractility in vitro. None of the theophylline concentrations studied could protect diaphragm bundles against the development of low- or high-frequency fatigue in vitro.

Effects of aminophylline on respiratory muscle interaction

We studied the effects of aminophylline on respiratory muscle interaction during quiet breathing by measuring (1) changes in rib cage and abdominal cross-sectional area, (2) tidal volume, (3) abdominal and esophageal pressure, (4) diaphragm and parasternal intercostal electromyogram (EMG) and parasternal intercostal intramuscular pressure, and (5) triangularis sternl and transversus abdominis EMG, in 14 supine anesthetized dogs. Measurements were done before and 5 and 10 min after administration of progressively increasing doses of aminophylline, reaching a total dose of 5, 10, 20, 40, and 80 mg/kg. In 12 of 14 dogs after aminophylline administration, quiet inspiration became biphasic, or if inspiration was already biphasic under control conditions, the first phase was clearly enhanced after aminophylline administration. Biphasic inspiration was defined as an inspiratory pattern in which rib cage and abdominal expansion showed two distinct phases. First, the onset of inspiration was characterized by a sudden increase in rib cage cross-sectional area often associated with a decrease in abdominal dimensions. During this initial part the parasternals and the diaphragm were electrically silent, confirming that it was achieved by relaxation of expiratory muscles. Further inspiration occurred predominantly through expansion of the abdomen. In the first phase, a pressure drop in the parasternal intercostals was present, presumably due to passive shortening of these muscles caused by expiratory muscle relaxation. On the average, 42 +/- 28% of the rib cage expansion was due to expiratory muscle relaxation at a dose of 80 mg/kg versus 17 +/- 21% under control conditions (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Theophylline minimally alters contractile properties of canine diaphragm in vitro

We examined the effects of theophylline on contractile properties and high-frequency fatigue of canine diaphragm in vitro. Eighteen diaphragm muscle bundles were obtained from 10 anesthetized dogs and equilibrated in oxygenated Krebs solution to 100, 200, or 300 mg/l theophylline. These bundles were compared with 18 matched control bundles from the contralateral hemidiaphragm. No statistically significant differences in twitch tension, tetanic tension, twitch-to-tetanus ratio, time to peak tension, or half-relaxation time were observed. Concentrations of 300 mg/l theophylline, however, significantly (P less than 0.05) increased force production at 10 Hz by 32%. A similar tendency was present at lower concentrations and exhibited a clear dose-response behavior. High-frequency fatigue was similar in control and theophylline-treated bundles. We conclude that supratherapeutic in vitro concentrations of theophylline do not increase maximal tetanic tension and do not protect against muscle fatigue but potentiate relative force production at low stimulation frequencies. This relatively small effect cannot be explained by poor diffusion of the drug in the muscle bundle, because theophylline concentrations in the muscle bath and in the muscle bundle were virtually identical. Moreover, it remains unclear whether this potentially beneficial effect can be achieved at in vivo attainable serum concentrations.

Respiratory changes in parasternal intercostal intramuscular pressure

In an attempt to obtain insight in the forces developed by the parasternal intercostal muscles during breathing, changes in parasternal intramuscular pressure (PIP) were measured in 14 supine anesthetized dogs using a microtransducer method. In six animals, during bilateral parasternal stimulation a linear relationship between contractile force exerted on the rib and PIP was demonstrated (r greater than 0.95). In eight animals, during quiet active inspiration, substantial (55 +/- 11.5 cmH2O) PIP was developed. During inspiratory resistive loading and airway occlusion the inspiratory rise in PIP increased in proportion to the inspiratory fall in pleural pressure (r = 0.82). Phrenicotomy and vagotomy resulted in an increase in the inspiratory rise in PIP of 21% and 99%, respectively. During passive deflation, when the parasternal intercostals were passively lengthened, large rises (320 +/- 221 cmH2O) in intramuscular pressure were observed. During passive inflation intramuscular pressure remained constant or even decreased slightly (-8 +/- 25 cmH2O) as expected on the basis of the passive shortening of the muscles. PIP thus invariably increased when tension increased either actively or passively. From PIP it is clear that the parasternals exert significant forces on the ribs during respiratory maneuvers.

Influence of hypercapnia on rabbit intrapulmonary neuroepithelial bodies: microfluorimetric and morphometric study

The present investigation was undertaken to investigate the influence of hypercapnia on intrapulmonary neuroepithelial bodies (NEB). Rabbits were mechanically ventilated with a hypercapnic gas mixture (7% carbon dioxide, 20% oxygen, 73% nitrogen). Lung samples were examined by a microspectrographical analysis of the NEB formaldehyde-induced fluorescence to quantify the cytoplasmic 5-hydroxy-tryptamine (5HT) content and by electron microscopy to determine morphometrically the extent of the secretory exocytosis at the basal poles of the NEB epithelial cells. In contrast to our earlier studies on the effects of hypoxia and/or vagal stimulation, hypercapnia did not alter significantly the NEB cytoplasmic fluorescence nor did it affect the corpuscular epithelial exocytosis. NEB appear not to be influenced by hypercapnia to discharge their contents of 5HT and peptides. This investigation appears to support a high selectivity of the intrapulmonary NEB to local hypoxia and changes in vagal efferent output.

Influence of hypercapnia on rabbit intrapulmonary neuroepithelial bodies: microfluorimetric and morphometric study

The present investigation was undertaken to investigate the influence of hypercapnia on intrapulmonary neuroepithelial bodies (NEB). Rabbits were mechanically ventilated with a hypercapnic gas mixture (7% carbon dioxide, 20% oxygen, 73% nitrogen). Lung samples were examined by a microspectrographical analysis of the NEB formaldehyde-induced fluorescence to quantify the cytoplasmic 5-hydroxy-tryptamine (5HT) content and by electron microscopy to determine morphometrically the extent of the secretory exocytosis at the basal poles of the NEB epithelial cells. In contrast to our earlier studies on the effects of hypoxia and/or vagal stimulation, hypercapnia did not alter significantly the NEB cytoplasmic fluorescence nor did it affect the corpuscular epithelial exocytosis. NEB appear not to be influenced by hypercapnia to discharge their contents of 5HT and peptides. This investigation appears to support a high selectivity of the intrapulmonary NEB to local hypoxia and changes in vagal efferent output.

Respiratory changes in diaphragmatic intramuscular pressure

We attempted to measure diaphragmatic tension by measuring changes in diaphragmatic intramuscular pressure (Pim) in the costal and crural parts of the diaphragm in 10 supine anesthetized dogs with Gaeltec 12 CT minitransducers. During phrenic nerve stimulation or direct stimulation of the costal and crural parts of the diaphragm in an animal with the chest and abdomen open, Pim invariably increased and a linear relationship between Pim and the force exerted on the central tendon was found (r greater than or equal to 0.93). During quiet inspiration Pim in general decreased in the costal part (-3.9 +/- 3.3 cmH2O), whereas it either increased or slightly decreased in the crural part (+3.3 +/- 9.4 cmH2O, P less than 0.05). Similar differences were obtained during loaded and occluded inspiration. After bilateral phrenicotomy Pim invariably decreased during inspiration in both parts (costal -4.3 +/- 6.4 cmH2O, crural -3.1 +/- 0.6 cmH2O). Contrary to the expected changes in tension in the muscle, but in conformity with the pressure applied to the muscle, Pim invariably increased during passive inflation from functional residual capacity to total lung capacity (costal +30 +/- 23 cmH2O, crural +18 +/- 18 cmH2O). Similarly, during passive deflation from functional residual capacity to residual volume, Pim invariably decreased (costal -12 +/- 19 cmH2O, crural -12 +/- 14 cmH2O). In two experiments similar observations were made with saline-filled catheters. We conclude that although Pim increases during contraction as in other muscles, Pim during respiratory maneuvers is primarily determined by the pleural and abdominal pressures applied to the muscle rather than by the tension developed by it.

Pulmonary function and maximal transrespiratory pressures in ankylosing spondylitis

Clinical measurements and pulmonary functions, including maximal transrespiratory pressures, were studied in 30 patients (age 43 (SD 10) years) with ankylosing spondylitis. Vital capacity (VC) was slightly reduced to 79 (16)% and forced expiratory volume in one second (FEV1) was similarly reduced to 82 (20)% such that the average FEV1/VC ratio was 77.8 (6.65). Total lung capacity was slightly reduced to 85 (13)%. Transfer factor of the lung for carbon monoxide (TLCO) averaged 88 (17)% and TLCO per unit lung volume was 114 (26)%. Reductions in lung volumes correlated well with clinical measurements. Both maximal expiratory pressures (PEmax) and inspiratory pressures (PImax) were clearly reduced to 56 (17)% and 76 (28)% respectively. This suggests that spirometrically determined volumes were better preserved than respiratory muscle strength in ankylosing spondylitis. It is speculated that the reduction in respiratory muscle strength may be due to intercostal muscle atrophy.

Corticosteroid-induced myopathy and the respiratory muscles. Report of two cases

Two women with connective tissue disease developed a characteristic steroid-induced myopathy. Reduced maximal transrespiratory pressures indicated reduced respiratory muscle strength. Gradual steroid dosage tapering resulted in prompt clinical improvement and marked increases in respiratory muscle strength, maximal inspiratory pressure increasing by 33 percent in one patient and by 70 percent in the other. This reversible steroid-induced respiratory muscle weakness may be of great significance in reconsidering long-term steroid therapy in patients with underlying lung disease.

Effects of acute hyperinflation on the mechanical effectiveness of the parasternal intercostals

We studied the mechanical effectiveness of the parasternal intercostals at FRC and near TLC in 14 supine, vagotomized, and anesthetized dogs. First, we determined the relationship between parasternal intramuscular pressure (Pps), measured with Gaeltec 12 CT-mini-transducers, and parasternal EMG activity (Eps) during breathing at FRC and near TLC. Second, we examined the changes in Pps and the changes in parasternal force (Fps) generated during bilateral parasternal stimulation at FRC and near TLC with a given supramaximal stimulus. Before phrenicotomy, the inspiratory increases in Pps remained relatively constant near TLC (FRC, 50.4 +/- 16.5 versus TLC, 48.7 +/- 13.3 cm H2O, NS), whereas the Eps clearly decreased (82.9 +/- 5.5% FRC, p less than 0.01). This indicates that the gain converting electrical activity into pressure for the parasternals is greater near TLC than at FRC. A similar pattern of changes in Pps and in Eps was observed during quiet inspiration at FRC and near TLC after phrenicotomy. During bilateral parasternal stimulation the increases in Pps near TLC tended to be greater than those at FRC (140.7 +/- 28.6 versus 100 +/- 28.3 cm H2O, NS), whereas the increases in Fps were significantly greater near TLC than at FRC (277.4 +/- 60.6 versus 214.2 +/- 47.1 g, p less than 0.05). Therefore, we conclude that the mechanical effectiveness of the parasternal contraction near TLC remains relatively unchanged and is even greater in relation to that at FRC.

A subtractive method for decomposing muscle tension into individual twitches

When an isolated strip of skeletal muscle tissue is held at fixed length and stimulated electrically with a very brief pulse of electricity it responds with a transient increase in tension known as a twitch. If the same strip is stimulated repetitively with short pulses it produces a tension that can be considered to be composed of individual twitches arising from each stimulus. We present a subtractive method for decomposing a muscle tension curve into individual twitches of various heights. The locations of the twitches are known a priori from the times at which each stimulus was applied to the muscle. The shape of each twitch is assumed the same as that of a single twitch obtained just prior to the repetitive stimulation tension signal. We therefore find the heights of the individual twitches composing a tension curve. We find that most of a tension signal from isolated dog diaphragm strips can be accounted for as the sum of twitches of the same shape but different heights. We also derive a refractory factor, for stimulation at a given frequency, that describes how the heights of the twitches in a tension curve are attenuated as a function of stimulation frequency.

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.