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Biomedical subjects

Amal Jubran

Publications and source records attributed to Amal Jubran.

11 recordsLinked to original sources
PubMed2006

Variable performance of weaning-predictor tests: role of Bayes' theorem and spectrum and test-referral bias.

OBJECTIVE: We examined whether variation in reported reliability of the frequency-to-tidal volume ratio (f/V(T)) in predicting weaning success is explained by spectrum and test-referral bias, as reflected by variation in pretest probability of success. DESIGN: Two authors extracted data from all studies on reliability of f/V(T) as a weaning predictor. RESULTS: Prevalence of successful weaning in studies of f/V(T) revealed significant heterogeneity; mean success rate was 0.75. The heterogeneity and high success rate reflects occurrence of spectrum bias, suggested by the lower value of f/V(T) in subsequent studies than in the original report (77.4 vs. 89.1) and test-referral bias, suggested by lower specificity of f/V(T) in subsequent studies than in the original report (0.52 vs. 0.64). When data from studies in the ACCP Task Force's meta-analysis of studies on f/V(T) were entered into a Bayesian model with pretest probability (prevalence of success) as the operating point, observed posttest probabilities were closely correlated with values predicted by the original report on f/V(T): positive-predictive value r = 0.86 and negative-predictive value r = 0.82. Average sensitivity, the most precise measure of screening-test reliability, was 0.87 +/- 0.14 and average specificity 0.52 +/- 0.26. CONCLUSIONS: Much of the heterogeneity in performance of f/V(T) can be explained by variation in pretest probability of successful outcome, which may be secondary to spectrum and test-referral bias. The average sensitivity of 0.87 indicates that f/V(T) is a reliable screening test for successful weaning.

Bayes Theorem↗
PubMed2006

Critical illness and mechanical ventilation: effects on the diaphragm.

Although life-saving, mechanical ventilation is associated with numerous complications. These include pneumonia, cardiovascular compromise, barotrauma, and ventilator-induced lung injury. Recent data from animal studies suggest that controlled mechanical ventilation can cause dysfunction of the diaphragm, decreasing its force-generating capacity--a condition referred to as ventilator-induced diaphragmatic dysfunction (VIDD). The decrease in diaphragmatic contractility is time-dependent and worsens as mechanical ventilation is prolonged. Evidence supporting the occurrence of comparable diaphragmatic dysfunction in critically ill patients is scarce, although most patients receiving mechanical ventilation display profound diaphragmatic weakness. Atrophy, fibers remodeling, oxidative stress, and structural injury have been implicated as potential mechanisms of VIDD. The decrease in diaphragmatic force that occurs during controlled mechanical ventilation is attenuated during assisted modes of ventilation. Whether the decrease in diaphragmatic contractility observed during controlled ventilation contributes to failure to wean from the ventilator is difficult to ascertain. Weaning-failure patients have reasons other than VIDD for respiratory-muscle weakness. Until we have further data, it seems prudent to avoid the use of controlled mechanical ventilation in patients with acute respiratory failure.

Critical Illness↗
PubMed2005

Fluctuations in end-expiratory lung volume during Cheyne-Stokes respiration.

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.

Aged↗
PubMed2005

Weaning prediction: esophageal pressure monitoring complements readiness testing.

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.

Aged↗
PubMed2005

Hypogonadism in men with chronic obstructive pulmonary disease: prevalence and quality of life.

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 (FEV1 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.

Age Factors↗
PubMed2004

Respiratory and skeletal muscles in hypogonadal men with chronic obstructive pulmonary disease.

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 H(2)O, 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 H(2)O, 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.

Aged↗
PubMed2004

Pulse oximetry.

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Humans↗
PubMed2004

Effect of lung volume reduction surgery on diaphragmatic neuromechanical coupling at 2 years.

STUDY OBJECTIVES: We previously reported that patients with emphysema show an increase in diaphragmatic neuromechanical coupling at 3 months after lung volume reduction surgery. Diaphragmatic neuromechanical coupling was quantified as the quotient of tidal volume (normalized to total lung capacity) to tidal change in transdiaphragmatic pressure (normalized to maximal transdiaphragmatic pressure). As such, neuromechanical coupling estimates the fraction of diaphragmatic capacity used to generate tidal breathing. The present investigation was conducted to determine whether benefit is maintained at 2 years. SUBJECTS: Fifteen patients with severe COPD, 8 of whom completed the 2-year study. METHODS: Lung volumes, exercise capacity (6-min walking distance), diaphragmatic function (maximal transdiaphragmatic pressure and twitch transdiaphragmatic pressure elicited by phrenic nerve stimulation), and diaphragmatic neuromechanical coupling were recorded before surgery, and at 3 months and 2 years after surgery. RESULTS: Two years after surgery, lung volumes deteriorated to preoperative values, but patients showed persistent improvements in 6-min walking distance (p < 0.05). Three months after surgery, maximal transdiaphragmatic pressure (p < 0.05), twitch transdiaphragmatic pressure (p < 0.01), and diaphragmatic neuromechanical coupling (p < 0.01) had increased over preoperative values. The improvements in neuromechanical coupling resulted from improvements in diaphragmatic strength and, to a lesser extent, from a decrease in transdiaphragmatic pressure required to maintain tidal breathing. The change in respiratory muscle function at 2 years varied among patients: diaphragmatic contractility was > 10% of preoperative value in half of the patients who concluded our study, and neuromechanical coupling was > 10% of preoperative value in three fourths of the patients who concluded our study. Patients who maintained their gains in neuromechanical coupling also maintained their gains in 6-min walking distance. CONCLUSION: Patients undergoing lung volume reduction surgery can maintain early gains in neuromechanical coupling and exercise capacity 2 years later.

Aged↗
PubMed2002

Is weaning failure caused by low-frequency fatigue of the diaphragm?

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.

Adult↗
PubMed2002

Dyspnea and decreased variability of breathing in patients with restrictive lung disease.

Patients with restrictive lung disease are typically dyspneic and have an increase in overall respiratory center drive, as a result of increased lung elasticity. When we subjected healthy volunteers to external elastic loads, their variability of breathing was lessened. Accordingly, we hypothesized that patients with restrictive lung disease display decreased variability of breathing and, also, that decreased variability of breathing is related to dyspnea. Breathing pattern was measured nonobtrusively over 1 hour in 10 patients with restrictive lung disease and in 7 healthy subjects. On a separate occasion, dyspnea was measured while all subjects copied different tidal volumes and frequencies. Compared with healthy subjects, the random fraction of breath variability was reduced in patients with restrictive lung disease: 27 times for expiratory time, 12 times for tidal volume, and 6 times for inspiratory time (p < 0.01 in each instance). Conversely, the nonrandom, correlated fraction for tidal volume was increased almost 3-fold in the patients (p < 0.01). Small variations from average resting tidal volume caused marked increases in dyspnea in patients, and the relationship was parabolic (r2 = 0.97; p < 0.001). In conclusion, patients with restrictive lung disease adopt a tightly constrained breathing pattern, probably as a strategy for avoiding dyspnea.

Analysis of Variance↗