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The act of breathing depends on coordinated activity of the respiratory muscles to generate subatmospheric pressure. This action is compromised by disease states affecting anatomical sites ranging from the cerebral cortex to the alveolar sac. Weakness of the respiratory muscles can dominate the clinical manifestations in the later stages of several primary neurologic and neuromuscular disorders in a manner unique to each disease state. Structural abnormalities of the thoracic cage, such as scoliosis or flail chest, interfere with the action of the respiratory muscles-again in a manner unique to each disease state. The hyperinflation that accompanies diseases of the airways interferes with the ability of the respiratory muscles to generate subatmospheric pressure and it increases the load on the respiratory muscles. Impaired respiratory muscle function is the most severe consequence of several newly described syndromes affecting critically ill patients. Research on the respiratory muscles embraces techniques of molecular biology, integrative physiology, and controlled clinical trials. A detailed understanding of disease states affecting the respiratory muscles is necessary for every physician who practices pulmonary medicine or critical care medicine. [ABSTRACT FROM AUTHOR]

Because patients who fail a trial of weaning from mechanical ventilation experience a marked increase in respiratory load, we hypothesized that these patients develop diaphragmatic fatigue. Accordingly, we measured twitch transdiaphragmatic pressure using phrenic nerve stimulation in 11 weaning failure and 8 weaning success patients. Measurements were made before and 30 minutes after spontaneous breathing trials that lasted up to 60 minutes. Twitch transdiaphragmatic pressure was 8.9 +/- 2.2 cm H2O before the trials and 9.4 +/- 2.4 cm H2O after their completion in the weaning failure patients (p = 0.17); the corresponding values in the weaning success patients were 10.3 +/- 1.5 and 11.2 +/- 1.8 cm H2O (p = 0.18). Despite greater load (p = 0.04) and diaphragmatic effort (p = 0.01), the weaning failure patients did not develop low-frequency fatigue probably because of greater recruitment of rib cage and expiratory muscles (p = 0.004) and because clinical signs of distress mandating the reinstitution of mechanical ventilation arose before the development of fatigue. Twitch pressure revealed considerable diaphragmatic weakness in many weaning failure patients. In conclusion, in contrast to our hypothesis, weaning failure was not accompanied by low-frequency fatigue of the diaphragm, although many weaning failure patients displayed diaphragmatic weakness. [ABSTRACT FROM AUTHOR]

RATIONALE: Exercise-induced dynamic hyperinflation contributes to decreased exercise tolerance in chronic obstructive pulmonary disease (COPD). It is unknown whether respiratory retraining (ventilation-feedback [VF] training) can affect exercise-induced dynamic hyperinflation and increase exercise tolerance. Objectives: To determine whether patients with COPD would achieve longer exercise duration if randomized to a combination of exercise training plus VF training than either form of training on its own. METHODS: A total of 64 patients randomized to 1 of 3 groups: VF plus exercise (n = 22), exercise alone (n = 20), and VF alone (n = 22). MEASUREMENTS AND MAIN RESULTS: Exercise duration before and after 36 training sessions and exercise-induced dynamic hyperinflation and respiratory pattern before and after training were measured. In the 49 patients who completed training, duration of constant work-rate exercise was 40.0 (+/- 20.4) minutes (mean +/- SD) with VF plus exercise, 31.5 (+/- 17.3) minutes with exercise alone, and 16.1 (+/- 19.3) minutes with VF alone. Exercise duration was longer in VF plus exercise than in VF alone (P < 0.0001), but did not reach predetermined statistical significance when VF plus exercise was compared with exercise alone (P = 0.022) (because of multiple comparisons, P

OBJECTIVE: Because the results of a meta-analysis are used to formulate the highest level recommendation in clinical practice guidelines, clinicians should be mindful of problems inherent in this technique. Rather than reviewing meta-analysis in abstract, general terms, we believe readers can gain a more concrete understanding of the problems through a detailed examination of one meta-analysis. The meta-analysis on which we focus is that conducted by an American College of Chest Physicians/American Association for Respiratory Care/American College of Critical Care Medicine Task Force on ventilator weaning. DATA SOURCE: Two authors extracted data from all studies included in the Task Force's meta-analysis. DATA SYNTHESIS AND OVERVIEW: The major obstacle to reliable internal validity and, thus, reliable external validity (generalizability) in biological research is systematic error, not random error. If systematic errors are present, averaging (as with a meta-analysis) does not decrease them--instead, it reinforces them, producing artifact. The Task Force's meta-analysis commits several examples of the three main types of systematic error: selection bias (test-referral bias, spectrum bias), misclassification bias (categorizing reintubation as weaning failure, etc.), and confounding (pressure support treated as unassisted breathing). Several additional interpretative errors are present. CONCLUSIONS: An increase in study size, as achieved through the pooling of data in a meta-analysis, is mistakenly thought to increase external validity. On the contrary, combining heterogeneous studies poses considerable risk of systematic error, which impairs internal validity and, thus, external validity. The strength of recommendations in clinical practice guidelines is based on a misperception of the relative importance of systematic vs. random error in science. [ABSTRACT FROM AUTHOR]

We hypothesized that patients with Cheyne-Stokes respiration exhibit periodic increases in end-expiratory lung volume, mediated by changes in breath components, postinspiratory inspiratory muscle activity, or both. Calibrated inductive plethysmography revealed that 12 of 12 patients with Cheyne-Stokes respiration experienced increases in end-expiratory volume during hyperpnea: maximum 412 +/- 112 (SE) ml (range 75-1,543 ml). Compared with quiet breathing, the breath with largest increase in end-expiratory volume had larger tidal volume (867 +/- 107 vs. 567 +/- 38 ml, p < 0.01) and shorter expiratory time (1.25 +/- 0.11 vs. 1.66 +/- 0.15 seconds, p < 0.05). During decrescendo, the breath with largest decrease in end-expiratory volume had smaller tidal volume (p < 0.01) and longer expiratory time (p < 0.01). Cross-correlation of time series revealed that end-expiratory volume was related to both breath components (p < 0.0001). Bipolar needle electrodes revealed that scalene muscle activity at end-expiration was 50.7 +/- 14.0% higher at highest increase in lung volume than during preceding apnea (p < 0.05). Time series for scalene activity and end-expiratory volume were cross-correlated (p < 0.008). Increase in tonic scalene activity at end-expiration, however, was equivalent during crescendo and decrescendo phases: 50.6 +/- 22.1 versus 42.0 +/- 12.9% (p = 0.48). In conclusion, patients with Cheyne-Stokes respiration exhibit fluctuations in end-expiratory lung volume, primarily because of alterations in tidal volume and expiratory time rather than postinspiratory inspiratory muscle activity. [ABSTRACT FROM AUTHOR]

Several variables are recommended for identifying if a patient is ready for a trial of weaning from mechanical ventilation, but there is no agreement as to whether monitoring any variable during the trial enhances patient management. To determine whether repeated measurements of esophageal pressure throughout a trial are more reliable than measurements of esophageal pressure or frequency-to-VT ratio during the first minute of the trial, we studied 60 patients. A trend index that quantified esophageal pressure swings over time was more reliable than the first-minute measurements: sensitivity, 0.91, and specificity, 0.89. Area under receiver operating characteristic curve for trend index (0.94) was greater than for first-minute measurement of esophageal pressure (0.44, p < 0.05) and tended to be greater than that for frequency-to-VT ratio (0.78, p = 0.13). The likelihood ratio was highest for the trend index (8.2, p < 0.05). The advantage of the trend index may be related to the progressive increase in esophageal pressure throughout a failed weaning trial, whereas breathing pattern changed little after 2 minutes of spontaneous breathing. In conclusion, continuous monitoring of esophageal pressure swings during a spontaneous breathing trial provides additional guidance in patient management over tests used for deciding when to initiate weaning. [ABSTRACT FROM AUTHOR]

We recently reported that hypogonadism does not affect respiratory muscle performance and exercise capacity in men with chronic obstructive pulmonary disease (COPD). In COPD, however, the relationship between exercise capacity and quality of life is controversial, making it unreliable to extrapolate about quality of life from exercise data. Accordingly, we determined prevalence and impact of hypogonadism on health-related quality of life in men with COPD. We enrolled 101 stable outpatient men (FEV[1] 1.34 +/- 0.04 L) older than 54 years; 38 patients were hypogonadal--a prevalence similar to that reported in the general population. The degree of airflow limitation did not predict levels of free testosterone. Quality of life, as quantified by a disease-specific instrument (St. George's Respiratory Questionnaire) and a general-health instrument (Veterans Short Form-36) were equivalent in the hypogonadal and eugonadal groups. Both groups demonstrated large decrements in perceived physical health and smaller decrements in perceived emotional and mental health. No relationship was found between free testosterone level and physical activity, respiratory symptoms, or quality of life. In conclusion, hypogonadism, although common among men older than 54 years with COPD, does not worsen the severity of respiratory symptoms or quality of life. [ABSTRACT FROM AUTHOR]

Hypogonadism, found in about one-third of patients with chronic obstructive pulmonary disease (COPD), has potential for decreasing muscle mass and muscle performance. Compared with eugonadal patients, we hypothesized that hypogonadal patients with COPD have decreased respiratory and skeletal muscle performance. Nineteen hypogonadal and 20 eugonadal men with COPD (FEV[1] 1.14 +/- 0.08 and 1.17 +/- 0.11 L [standard error], respectively) were studied. Diaphragmatic contractility, assessed as transdiaphragmatic twitch pressure generated by phrenic nerve stimulation, was similar in hypogonadal and eugonadal patients: 20.6 +/- 2.2 and 19.8 +/- 2.5 cm H2O, respectively. During progressive inspiratory threshold loading, hypogonadal and eugonadal patients had similar respiratory muscle endurance times (302 +/- 29 and 313 +/- 48 seconds, respectively) and airway pressure sustained during the last minute of loading (38.2 +/- 3.0 and 40.5 +/- 4.7 cm H2O, respectively) (similar to predicted values in healthy subjects). Hypogonadal and eugonadal patients had equivalent limb muscle strength and endurance. During cycle exercise to exhaustion, exercise performance, gas exchange, and respiratory muscle recruitment (estimated by esophageal and gastric pressure swings during tidal breathing) were similar in both groups. In conclusion, hypogonadism does not decrease respiratory or limb muscle performance and exercise capacity in men with moderate-to-severe COPD who, for the most part, are not underweight. [ABSTRACT FROM AUTHOR]

Context: The outcome of patients receiving mechanical ventilation for particular indications has been studied, but the outcome in a large number of unselected, heterogeneous patients has not been reported.Objective: To determine the survival of patients receiving mechanical ventilation and the relative importance of factors influencing survival.Design, Setting, and Subjects: Prospective cohort of consecutive adult patients admitted to 361 intensive care units who received mechanical ventilation for more than 12 hours between March 1, 1998, and March 31, 1998. Data were collected on each patient at initiation of mechanical ventilation and daily throughout the course of mechanical ventilation for up to 28 days.Main Outcome Measure: All-cause mortality during intensive care unit stay.Results: Of the 15 757 patients admitted, a total of 5183 (33%) received mechanical ventilation for a mean (SD) duration of 5.9 (7.2) days. The mean (SD) length of stay in the intensive care unit was 11.2 (13.7) days. Overall mortality rate in the intensive care unit was 30.7% (1590 patients) for the entire population, 52% (120) in patients who received ventilation because of acute respiratory distress syndrome, and 22% (115) in patients who received ventilation for an exacerbation of chronic obstructive pulmonary disease. Survival of unselected patients receiving mechanical ventilation for more than 12 hours was 69%. The main conditions independently associated with increased mortality were (1) factors present at the start of mechanical ventilation (odds ratio [OR], 2.98; 95% confidence interval [CI], 2.44-3.63; P<.001 for coma), (2) factors related to patient management (OR, 3.67; 95% CI, 2.02-6.66; P<.001 for plateau airway pressure >35 cm H(2)O), and (3) developments occurring over the course of mechanical ventilation (OR, 8.71; 95% CI, 5.44-13.94; P<.001 for ratio of PaO(2) to fraction of inspired oxygen <100).Conclusion: Survival among mechanically ventilated patients depends not only on the factors present at the start of mechanical ventilation, but also on the development of complications and patient management in the intensive care unit. [ABSTRACT FROM AUTHOR]

This article reviews research and other work that suggests that congenital total blindness during infancy retards motor functions, most notably reaching for sound-making stimuli. Since there is a correlation between when infants who are blind begin to reach for rattles, bells, and the like and when sighted infants search for hidden toys in Piagetian experiments, it has been argued that for sound cues alone to elicit reaching, infants must first develop an object concept. Problems with this formulation are highlighted, and an alternative explanation is proposed that suggests possible interventions to redress the effects of congenital blindness on development. [ABSTRACT FROM AUTHOR]

It is claimed that blindness may predispose individuals to disturbed sleep because light is an important mechanism for entraining circadian rhythms. One in five respondents in a survey described the quality of their sleep as either poor or very poor. Exercise was associated with better sleep, and depression with poorer sleep. That visual acuity did not predict the quality of sleep casts doubt on the notion that restricted visual (photic) input is a widespread cause of sleep disturbance among persons who are visually impaired. As with sighted persons, depression appears to be a highly significant risk factor for disturbed sleep in persons who are visually impaired. [ABSTRACT FROM AUTHOR]

Sea-ice microalgae are a key source of energy and nutrient supply to polar marine food webs, particularly during spring, prior to open-water phytoplankton blooms. The nutritional quality of microalgae as a food source depends on their biomolecular (lipid:protein:carbohydrate) composition. In this study, we used synchrotron-based Fourier transform infra-red microspectroscopy (s-FTIR) to measure the biomolecular content of a dominant sea-ice taxa, Nitzschia frigida, from natural land-fast ice communities throughout the Arctic spring season. Repeated sampling over six weeks from an inner (relatively stable) and an outer (relatively dynamic) fjord site revealed high intra-specific variability in biomolecular content, elucidating the plasticity of N. frigida to adjust to the dynamic sea ice and water conditions. Environmental triggers indicating the end of productivity in the ice and onset of ice melt, including nitrogen limitation and increased water temperature, drove an increase in lipid and fatty acids stores, and a decline in protein and carbohydrate content. In the context of climate change and the predicted Atlantification of the Arctic, dynamic mixing and abrupt warmer water advection could truncate these important end-of-season environmental shifts, causing the algae to be released from the ice prior to adequate lipid storage, influencing carbon transfer through the polar marine system., (© 2024. The Author(s).)