The diaphragm: contractile properties and fatigue

Induction of diaphragmatic nitric oxide synthase after endotoxin administration in rats: role on diaphragmatic contractile dysfunction

Nitric oxide (NO), a free radical that is negatively inotropic in the heart and skeletal muscle, is produced in large amounts during sepsis by an NO synthase inducible (iNOS) by LPS and/or cytokines. The aim of this study was to examine iNOS induction in the rat diaphragm after Escherichia Coli LPS inoculation (1.6 mg/kg i.p.), and its involvement in diaphragmatic contractile dysfunction. Inducible NOS protein and activity could be detected in the diaphragm as early as 6 h after LPS inoculation. 6 and 12 h after LPS, iNOS was expressed in inflammatory cells infiltrating the perivascular spaces of the diaphragm, whereas 12 and 24 h after LPS it was expressed in skeletal muscle fibers. Inducible NOS was also expressed in the left ventricular myocardium, whereas no expression was observed in the abdominal, intercostal, and peripheral skeletal muscles. Diaphragmatic force was significantly decreased 12 and 24 h after LPS. This decrease was prevented by inhibition of iNOS induction by dexamethasone or by inhibition of iNOS activity by N(G)-methyl-L-arginine. We conclude that iNOS was induced in the diaphragm after E. Coli LPS inoculation in rats, being involved in the decreased muscular force.

Current thoughts regarding treatment of chronic obstructive pulmonary disease

The available evidence indicates that pulmonary rehabilitation benefits patients with symptomatic COPD. The effect of pulmonary rehabilitation programs on health care use is promising but requires further investigation. In contrast, aerobic lower extremity training is of benefit in several areas of importance to patients with COPD. These areas include exercise endurance, perception of dyspnea, quality of life, and self-efficacy. The exact role of upper extremity exercise training programs requires further studies but should be used in patients who develop symptoms with arm activities. Psychological support improves the awareness of the patient and increases his or her understanding of the disease, but when used alone it is of limited value. Pulmonary rehabilitation when coupled with smoking cessation, optimization of blood gases, and medications offers the best treatment option for patients with symptomatic airflow obstruction.

Reduction pneumoplasty for giant bullous emphysema. Implications for surgical treatment of nonbullous emphysema

A review of the literature on reduction pneumoplasty for giant bullous emphysema was undertaken to identify current criteria for this surgical treatment and in the hope of obtaining insights into evaluating reduction pneumoplasty for nonbullous emphysema. Twenty-two retrospective case series, published since 1950, were retrieved by a computer search of the literature and a search of the Index Medicus prior to 1966. Reduction pneumoplasty is most effective when bullae are larger than one third of a hemithorax with evidence of compression of adjacent lung tissue and an FEV1 of less than 50% predicted; the presence of emphysema in nonbullous lung and the amount of compression are best judged by CT. The rationale for reduction pneumoplasty for nonbullous emphysema is supported by the similar early functional changes after reduction pneumoplasty for bullous and nonbullous-improvement of blood gas values and lung mechanics. A single study showing that decline of lung function after surgery for bullous emphysema was less in those who stopped smoking than in those who continued to smoke supports the need for preoperative and maintained smoking cessation in patients receiving reduction pneumoplasty. After 4 decades, the duration of improvement in lung function, whether worsening of emphysema occurs in remaining lung, and late morbidity and mortality after reduction pneumoplasty for bullous emphysema are not well defined. A registry with an unoperated-on comparison group could more rapidly accumulate such data after reduction pneumoplasty for nonbullous emphysema.

Mammalian locomotor-respiratory integration: implications for diaphragmatic and pulmonary design

Diaphragmatic function and intrapulmonary respiratory flow in running mammals were found to differ substantially from the corresponding conditions known in resting mammals. In trotting dogs, orbital oscillations of the diaphragm were driven by inertial displacements of the viscera induced by locomotion. In turn, oscillations of the visceral mass drove pulmonary ventilation independent of diaphragmatic contractions, which primarily served to modulate visceral kinetics. Visceral displacements and loading of the anterior chest wall by the forelimbs are among the factors that contribute to an asynchronous ventilation of the lungs and interlobar gas recycling. Basic features of mammalian respiratory design, including the structure of the diaphragm and lobation of the lungs, appear to reflect the mechanical requirements of locomotor-respiratory integration.

Altered exercise gas exchange and cardiac function in patients with mild chronic obstructive pulmonary disease

Patients with advanced COPD have significantly reduced gas exchange and pulmonary function; however, little is known regarding physical work capacity and exercise gas exchange in patients with mild COPD. A total of 39 individuals (20 men and 19 women) without evidence of COPD (controls) and 51 individuals (29 men and 22 women) with mild COPD (FEV1 > or = 60 percent of predicted; and ratio of FEV1 over forced vital capacity of 60 to 70 percent) were tested to determine resting pulmonary function and resting and peak exercise gas exchange in response to progressive maximal cycle ergometer testing. In general, those with mild COPD had similar smoking histories and essentially equivalent resting gas exchange studies as compared to the controls. Measured maximal oxygen consumption was less in both the male (p < 0.003) and the female patients (p < 0.001). This was due, in part, to a lower maximal ventilation in the men with obstruction (p < 0.04), resulting from a significant reduction in tidal volume (p < 0.05). Women presented with similar decreases in maximal ventilation (p < 0.04) and maximal tidal volume (p < 0.01), while no difference in maximal respiratory rate was noted in either group (p > 0.05). Breathing reserve was 32 percent and 53 percent less for the male and female patients with obstruction than for controls. Maximal heart rates were less in the individuals with obstruction, where they reached 93 percent (p < 0.02) and 96 percent (p < 0.003) of the age- and sex-specific maximal heart rates for men and women as compared to 101 percent and 99 percent obtained in the controls. Achieved absolute work loads for men and women (in kilogram.meters per minute) were lower in the groups with obstruction (p < 0.002 and 0.0003) as well. These results demonstrate that work capacity and gas exchange are significantly decreased in individuals with even mild COPD. The reduction in functional work capacity is secondary to a loss of pulmonary function, as well as chronic deconditioning. Increased dyspnea may be responsible for the premature cessation of exercise observed in patients with mild COPD. Thus, early intervention with exercise training may be warranted to counter the deleterious effects of deconditioning and declining pulmonary function in patients with mild COPD.

Maximal inspiratory pressure is not a reliable test of inspiratory muscle strength in mechanically ventilated patients

Maximal Inspiratory pressure (MIP) is an important clinical method used to assess respiratory muscle strength. The reliability and reproducibility of this measurement in mechanically ventilated patients is not certain. In 14 stable, mechanically ventilated patients, capable of spontaneous inspiratory efforts, we assessed maximal inspiratory efforts using the technique originally described by Marini and associates. MIP was measured in triplicate, by one to five experienced investigators, on one to seven successive days, for a total of 396 determinations on 54 patient days. The coefficients of variation among the triplicate efforts averaged 12 +/- 1%, indicating the test to be highly reproducible. There was significant variation among the MIP reported by different investigators studying the same patient on the same day (32 +/- 4%). The differences between best MIP by different investigators averaged 12.6 +/- 1.3cm H2O (40 +/- 4%). In 17 of 44 cases, one investigator placed MIP above -30cm H2O, whereas another placed it below. ANOVA showed that MIP was significantly affected by investigator (p less than 0.0001) as well as by patient (p less than 0.0001). Because "true" MIP must be equal to or greater than the best measured MIP, these data indicate that the MIP is commonly underestimated in patients receiving mechanical ventilation, even when standardized technique is used. Furthermore, our data show that reproducibility of triplicate MIP determination by a single observer does not indicate that the test is reliable.

Hypophosphatemia in course of chronic obstructive pulmonary disease. Prevalence, mechanisms, and relationships with skeletal muscle phosphorus content

Serum phosphorus levels (Ps), dietary intake of phosphorus, and renal phosphate handling indexes were evaluated in 158 patients with chronic obstructive pulmonary disease (COPD) of varying degrees of severity; moreover, skeletal muscle phosphorus content (Pm) was measured in muscle samples obtained by quadriceps femoris needle biopsy in 14 of the same patients. Hypophosphatemia (Ps less than or equal to 2.5 mg/dl) was found in 34 (21.5 percent) of 158 patients without differences between groups of COPD patients presenting increasing severity of respiratory illness. No relationship was found between serum levels and dietary intake of phosphorus; hypophosphatemia was associated with low renal phosphate threshold (TmPO4/GFR) values in 31 (91 percent) of 34 patients. The prevalence of hypophosphatemia was significantly higher among COPD patients taking one or more drugs commonly used in COPD and known as negatively influencing renal phosphate handling: xanthine derivatives, corticosteroids, loop diuretics, and beta 2-adrenergic bronchodilators. Short-term administration of therapeutic doses of these drugs in COPD patients previously not taking any drug reduced TmPO4/GFR values; phosphaturic effect of short-term theophylline administration on renal phosphate handling was additive to that of long-term assumption of the drug. Muscle phosphorus content was both reduced in COPD patients as compared with control subjects and significantly correlated to serum phosphorus levels and to TmPO4/GFR values. The present investigation revealed a high prevalence of hypophosphatemia among COPD patients as well as a defect in renal phosphate reabsorption secondary, at least in part, to pharmacologic therapy. Moreover, it also suggests that in COPD patients muscle phosphorus content is likely to be reduced in presence of hypophosphatemia.

Controlled trial of external negative pressure ventilation in patients with severe chronic airflow obstruction

The effect of intermittent external negative pressure ventilation (ENPV) with the Emerson Pulmowrap ventilator upon leg cycle endurance time (ET), maximal transdiaphragmatic pressure (Pdimax), breathing pattern as expressed by the tension time index (TTdi), and sense of well being was studied in 16 patients with severe chronic airflow obstruction (CAO). The patients were randomized to 3 wk of in-hospital pulmonary rehabilitation (Group I, seven patients) or the same program plus ENPV (Group II, nine patients). Both groups were similar in terms of age (65 +/- 8 versus 61 +/- 13 yr), severity of CAO (FEV1 of 0.64 +/- 0.14 versus 0.59 +/- 0.18 L), and PaCO2 (44 +/- 9 versus 45 +/- 7 mm Hg). Blood theophylline levels and nutritional status were also similar in both groups. Baseline ET (2.9 +/- 0.6 versus 3.8 +/- 1.6 min) and Pdimax (45 +/- 15 versus 56 +/- 18 cm H2O) were decreased in both groups. Baseline TTdi was high but similar in both groups; at rest the values were 0.15 +/- 0.05 versus 0.16 +/- 0.04, and at end-exercise they were 0.17 +/- 0.06 versus 0.21 +/- 0.12. After treatment FEV1 and Pdimax remained unchanged, but the patients in both groups manifested clinical improvement and had a significant increase in mean ET (Group I from 2.9 to 6.9 and Group II from 3.8 to 6 min, p less than 0.01). TTdi decreased both at rest (0.14 +/- 0.07 versus 0.13 +/- 0.04) and at end-exercise (0.14 +/- 0.06 versus 0.15 +/- 0.09) with no difference between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Is diaphragmatic elevation a serious complication of open-heart surgery?

Diaphragmatic elevation or paralysis after open-heart surgery was retrospectively analyzed in 370 consecutive operations performed on 365 adult patients. The incidence of the complication was 7.2%. It was significantly correlated with ipsilateral pleural effusion and lower-lobe atelectasis, but no predisposing or causal factors could be identified. Diaphragmatic elevation did not prolong the hospital stay. Actuarial analysis of data from follow-up chest radiograms showed normalization of the diaphragmatic position within 6 months in 44% and within a year in 90% of the patients.

Double antibody radioimmunoassay for monitoring metastatic breast cancer

We previously reported the production of a panel of murine monoclonal antibodies which recognize glycoproteins abnormally expressed in human breast tumours. Using two of these antibodies, a double antibody radioimmunoassay was designed to quantify levels of these breast tumour marker glycoproteins in serum. Marker levels greater than 28 units were considered abnormal. Using this criterion, 63% and 75% of patients with breast cancer stages I and II, respectively, and 88% of those with metastatic disease were found to have elevated marker levels. Thirteen percent of patients with non-malignant breast disease also had elevated marker levels. Elevated marker levels were also detected in patients with non breast neoplasms. One hundred and eleven women with metastatic disease were followed. Eighty-two percent of those with progressive disease and 73% of those where disease regressed had 20% changes in marker levels. These changes in marker levels preceded by up to 6 months changes in disease state. From these results we conclude that this assay may be useful for monitoring the course of disease in breast cancer patients.

Hypophosphatemia-associated respiratory muscle weakness in a general inpatient population

Although hypophosphatemia has been implicated as a cause of respiratory failure, its impact on respiratory muscle function in patients hospitalized for other reasons remains to be determined. Maximal inspiratory pressures (MIP) and maximal expiratory pressures (MEP) were measured at the bedside in 23 hospitalized patients with serum phosphate levels less than 2.5 mg/dl, and these measurements were repeated daily during phosphate repletion until serum phosphate levels reached the normal range. A control group consisted of 11 normophosphatemic inpatients. Sixteen of 23 hypophosphatemic patients, but none of the control patients (p less than 0.001), exhibited respiratory muscle weakness, defined as a MIP less than 40 cm H2O or a MEP less than 70 cm H2O. The mean initial MIP and MEP values were also significantly lower for the hypophosphatemic group. A significant correlation existed between initial phosphate level and initial MIP value (r = 0.50, p less than 0.02). With phosphate repletion, mean +/- SD MIP increased from -37 +/- 26 cm H2O to -49 +/- 24 cm H2O (p less than 0.003) and MEP from 60 +/- 20 cm H2O to 69 +/- 19 cm H2O (p less than 0.02). It is concluded that respiratory muscle weakness is common among hypophosphatemic patients and improves with phosphate repletion.

Albuterol has no effect on diaphragmatic fatigue in humans

Diaphragmatic fatigue may play an important role in precipitating acute respiratory failure. Pharmacologically, theophylline and beta-2 agonists have been used to improve diaphragmatic contractility. We designed experiments to study the effects of albuterol, a beta-2 agonist, on diaphragmatic fatigue in humans. In 5 normal subjects, fatigue was induced by breathing through an inspiratory resistance. Studies were done at 2 levels of diaphragmatic tension-time index (TTdi) of 0.25 and 0.30. At each TTdi, either placebo or albuterol (4 mg three times daily) was taken for 3 days. All subjects experienced side effects of sympathetic stimulation. Albuterol did not significantly increase the strength of the fresh diaphragm. With a TTdi of 0.25, values for mean endurance time were 649 +/- 250 (mean +/- SE) and 552 +/- 161 s, respectively, in placebo and albuterol runs. Respective values for TTdi of 0.30 were 109 +/- 14 and 143 +/- 27 s. During recovery, the mean values for the time needed for maximal transdiaphragmatic pressure (Pdimax) to reach 90% of the prefatigue Pdimax were 891 +/- 370 and 1043 +/- 394 s, respectively, for placebo and albuterol runs (TTdi = 0.25). Respective values for TTdi of 0.30 were 219 +/- 57 and 231 +/- 108 s. We conclude that, in humans, albuterol has no significant effect on the strength of the fresh or fatigued diaphragm, diaphragm endurance time, or the recovery of Pdimax from fatigue.

Ventilatory muscle dysfunction in patients with bilateral idiopathic diaphragmatic paralysis: reversal by intermittent external negative pressure ventilation

Bilateral idiopathic diaphragmatic paralysis (BIDP) may result in progressive ventilatory failure. To test the hypothesis that this is in part due to dysfunction of overtaxed inspiratory muscles, we studied 3 patients with BIDP before and after 2, 5, and 18 wk of daily intermittent external surface negative pressure ventilation (ENPV). The patients were evaluated using a zero to 10 functional score (FS) that graded dyspnea, orthopnea, capacity to perform activities of daily living, and ability to work. Pleural (Ppl), abdominal (Pab), and transdiaphragmatic (Pdi) pressures were used as an index of respiratory muscle function. All patients improved their functional score (FS increased 2, 6, and 6, respectively) and their pressure generating ability (Pplmax increased -18, -37, and -46 cm H2O, respectively). Forced vital capacity and functional residual capacity increased in the 2 patients ventilated for longer than 2 wk. These results indicate that ventilatory muscle dysfunction may result from chronic increased work of the inspiratory muscles and that it may improve after periods of intermittent ENPV. This may occur as early as 2 wk after initiation of therapy.

A non-invasive method for measuring inspiratory muscle fatigue during progressive isocapnic hyperventilation in man

Eleven normal adults each performed a ten minute progressive isocapnic hyperventilation (PIHV) test in which ventilatory levels were increased every two minutes. All subjects exhibited mechanical fatigue by failing to maintain the target of 80% of maximum voluntary ventilation (MVV). The mean ventilation at this level was 67.5 +/- 1.4% MVV. This fatigue was accompanied by a fall in transdiaphragmatic pressure. During the test the EMG of the sternomastoid (SM) was monitored by surface electrodes and was analyzed using fast-fourier transform. The centroid frequency (Fc) fell as ventilation increased, and correlated negatively with the inability to achieve target ventilation(r = -0.99, p less than 0.015). Five subjects performed the test while the diaphragmatic EMG was recorded from an oesophageal electrode (DIes) and from surface electrodes (DIs). The Fc of DIes fell with increasing ventilation levels (r = -0.95, p less than 0.05) and there was a correlation between the Fc changes of both DIes and the SM (r = -0.92, p less than 0.001). The Fc of DIs did not correlate with either mechanical performance or the Fc of DIes, because of contamination of surface signals by signals from expiratory muscles. It is concluded that the PIHV along with surface monitoring of EMG activity from the sternomastoid can serve as a non-invasive method for evaluating inspiratory muscle fatigue.