Use of factor analysis to consolidate multiple outcome measures in chronic obstructive pulmonary disease.

Multiple outcome measures are often used in clinical research and practice. However, the use of multiple measures inflates the probability of a type I error. In this paper, we used factor analysis techniques to reduce multiple outcome measures to a lesser number of orthogonal dimensions. The data were obtained from 119 patients with chronic obstructive pulmonary disease. Each patient had measurements made of 28 variables, including multiple parameters of pulmonary function, exercise tolerance and gas exchange. Factor analysis using a maximum likelihood iterative solution was performed. The factors were then rotated to a varimax solution. The analysis yielded four meaningful factors: exercise tolerance, disease severity, lung volumes and flow rates. Exercise tolerance and disease severity were the most important factors accounting, respectively, for 44 and 13% of the common variance. For further analyses, these composite factors could be used or a representative clinical measure from each factor might be chosen. We conclude that many physiologic measures provide highly correlated information about chronic obstructive pulmonary disease patients. Factor analysis may help reduce these measures into a smaller number of reliable composites.

Comparison of isocapnic hyperventilation and walking exercise training at home in pulmonary rehabilitation.

Eighteen COPD patients enrolled in a comprehensive, multidisciplinary pulmonary rehabilitation program were randomly assigned to perform either: 1) walking, or 2) ventilatory muscle exercise training (VMT) using a prototype, portable device for isocapnic hyperventilation training. Both groups performed exercise training at home. Twelve patients completed the study and follow-up evaluation (five VMT, seven walkers). Pulmonary function did not change in either group. For the VMT patients, there were modest increases in ventilatory muscle endurance and exercise performance. VO2max and VEmax increased significantly. For the walkers, only walking endurance time increased significantly. These results indicate that isocapnic hyperventilation exercise training can be performed successfully by COPD patients in an unsupervised home setting and can lead to improvement in both ventilatory muscle endurance and exercise performance. Walking exercise training did not improve ventilatory muscle endurance.

Upper extremity exercise training in chronic obstructive pulmonary disease.

Many patients with chronic obstructive pulmonary disease (COPD) report greater limitation for activities involving the upper extremities than the lower extremities. Exercise training has generally emphasized lower-extremity exercise. We designed and evaluated two simple, practical, and widely applicable upper-extremity training programs in 45 patients with COPD participating concurrently in a comprehensive, multidisciplinary pulmonary rehabilitation program. Patients were randomly assigned to one of the following three groups: (1) gravity-resistance (GR) upper-extremity training; (2) modified proprioceptive neuromuscular facilitation (PNF) upper-extremity training; or (3) no upper-extremity training (control). Patients were evaluated before and after at least six weeks of uninterrupted training. Twenty-eight patients completed the study. Compared to controls, both GR and PNF patients demonstrated improved performance on tests specific to the training performed (upper-extremity performance test, maximal level and endurance on isokinetic arm cycle). There were no significant changes on isotonic arm cycle, ventilatory muscle endurance, or simulated activities of daily-living tests. Ratings of perceived breathlessness and fatigue decreased significantly in all groups for several tests. We conclude that specific upper-extremity training may be beneficial in the rehabilitation of patients with COPD and warrants further investigation.

Prediction of maximum exercise tolerance in patients with COPD.

Exercise tolerance in patients with COPD is difficult to predict from measurements of lung function. We examined multiple physiologic and psychosocial variables in an attempt to predict exercise performance in a group of patients with COPD enrolled in a clinical trial of pulmonary rehabilitation. A total of 119 patients (FEV1 = 1.41 +/- 0.64 L) were divided randomly into either a study group (group A, n = 58) or validation group (group B, n = 61). Stepwise multiple regression in group A revealed that peak oxygen uptake (peak VO2) was predicted best by the following equation: Peak VO2 (L/min) = (0.0327 x DCO) + (0.0040 x MVV)-(0.0156 x peak-exercise VD/VT) + (0.0259 x resting VE) + 0.848; r = 0.90; SE = 0.233 L/min. This equation was then cross-validated in group B. It demonstrated excellent validity: measured peak VO2 (L/min) = (1.13 x predicted peak VO2)-0.0891; r = 0.90; SE = 0.239 L/min. We conclude that exercise tolerance was predicted reasonably well from measurements of lung function and gas exchange in this group of patients with COPD. However, the variability of the prediction would limit its usefulness in individual patients.

The effects of exercise testing on the prescription of oxygen therapy.

This study reviews the effects of using oxygen saturation measurements during exercise and the effects of the method of exercise testing on the prescription of oxygen therapy. Using cutaneous oximetry (designated A and B models) and co-oximetry, 25 of 41 patients (model A), 30 of 39 patients (model B), and 28 of 42 patients (co-oximetry) had an oxygen saturation measurement greater than 85 percent at maximal incremental exercise despite an arterial oxygen tension less than 55 mm Hg. Also, in a group of patients who underwent incremental followed by constant work rate testing, 9 of 28 exhibited a fall in arterial oxygen tension to 55 mm Hg or below only during the constant work rate testing. Oxygen saturation measurements cannot reliably be used as a substitute for arterial oxygen tension measurements for the prescription of oxygen therapy. The type of exercise study performed may influence the outcome of such oxygen prescription.

Rapid changes in arterial blood gas levels after exercise in pulmonary patients.

We evaluated arterial blood gas levels at rest, end-exercise, and 20, 40, 60, and 120 seconds after exercise in 24 pulmonary patients. Significant changes from end-exercise arterial PO2 (PaO2) were noted by 40 seconds postexercise. Changes in arterial PCO2 were less pronounced. Sampling delays as short as 20 seconds led to significant underestimation of the changes in PaO2 during exercise in a few patients. Longer delays led to a greater number of misleading studies. We conclude that, if blood gas analyses are used to detect abnormal changes in PaO2 or P(A-a)O2 during exercise, then blood must be sampled during exercise. The common practice of performing arterial punctures after exercise may provide misleading information in some patients.

Pulmonary function tests cannot predict exercise-induced hypoxemia in chronic obstructive pulmonary disease.

We studied 40 patients with chronic obstructive pulmonary disease (COPD) to determine whether measurements of pulmonary function could predict a fall in arterial oxygen pressure (PaO2) with exercise. The PaO2 fell more than 3 mm Hg in 21 patients (group 1), did not change (+/- 3 mm Hg) in nine patients (group 2), and increased more than 3 mm Hg in ten patients (group 3). Group 3 had significantly less severe expiratory obstruction than groups 1 and 2. The most significant variables in predicting a change in PaO2 with exercise were the ratio of the forced expiratory volume in one second over the forced vital capacity (FEV1/FVC) and the single-breath carbon monoxide diffusing capacity (Dsb). Measurements of FEV1/FVC of 0.50 or more and Dsb of 20 ml/min/mm Hg or more were 100 percent predictive in excluding a fall in PaO2 with exercise. Measurements below these thresholds could not be used reliably to predict which patients would develop worsening hypoxemia with exercise. Because of wide variability in reference values from eight different published studies for diffusing capacity, recommended criteria based on the percent predicted Dsb should be used with caution. We conclude that pulmonary function measurements cannot be used to predict exercise-induced hypoxemia in patients with COPD; however, the measurements may be useful in identifying patients whose condition is less severe who are unlikely to develop worsening hypoxemia with exercise.

The use of cutaneous oximetry in the prescription of long-term oxygen therapy.

Using current Medicare guidelines for the prescription of long-term oxygen therapy, we studied the impact on decision-making of substituting cutaneous oxyhemoglobin saturation measurements (SaO2) for direct arterial oxygen tension measurements (PaO2). Fifty-five patients with chronic lung disease and resting hypoxemia were studied. More than 80 percent of patients with a resting PaO2 of 7.33 kPa (55 mm Hg) or less had a cutaneous oximetry SaO2 greater than 85 percent. These patients would not have met the guidelines for long-term oxygen therapy if the cutaneous oximetry measurements were used instead of direct PaO2 measurements. Substituting a threshold criterion of 88 percent instead of 85 percent resulted in fewer patients being denied oxygen therapy but also included patients with PaO2 values greater than 7.33 kPa (55 mm Hg). We conclude that cutaneous oximetry cannot be substituted equivalently for PaO2 measurements in prescribing long-term oxygen therapy.

Skin color and ear oximetry.

Measurements of arterial blood oxygen saturation from two ear oximeters were compared with 655 simultaneously drawn arterial blood samples in 187 patients grouped by skin color quantified by the Munsell color system. Technical problems including warning lights and messages with the two ear oximeters were recorded. There were significantly more technical problems in patients with the darkest skin color associated with inability to obtain a reading or warning message indicating poor tissue penetration of the signal (18 and 15 percent vs 1 percent). When readings could be obtained, the ear oximetry readings were found to be slightly less accurate in the darker patient groups. These findings suggest that dark skin color may affect the performance and accuracy of ear oximeters, including the newer type of pulse oximeters.

Laser resection of granulation tissue secondary to transtracheal oxygen catheter.

Oxygen therapy through a transtracheal catheter has been used increasingly for the long-term delivery of continuous oxygen. Compared to nasal cannula it results in significant reduction in oxygen flow requirements. This form of therapy has gained patient acceptance because of several advantages including improved convenience, aesthetics, compliance, and mobility. Reported complications generally have been minor, including subcutaneous emphysema, cough, "mucous ball" formation and mild hemoptysis. In this report, we describe a case of granulation tissue formation at the transtracheal catheter puncture site which was treated with Nd:YAG laser bronchoscopy to reestablish patency of the upper airway. No recurrence was noted after two years of follow-up.

Maximum intensity exercise training in patients with chronic obstructive pulmonary disease.

We studied high intensity, symptom-limited, endurance exercise training in 52 patients with COPD participating in a pulmonary rehabilitation program. The patients had moderate to severe airway obstruction and reduced exercise tolerance with ventilatory limitation. The target workload for endurance exercise testing was 95 percent of the baseline maximum treadmill work load. At training weeks 1, 4 and 8, they were training at 85, 84, and 86 percent respectively, of baseline maximum. After rehabilitation, there was an increase in maximal treadmill work load, VO2max, and endurance exercise time, and a decrease in perceived symptoms. Patients who did not reach anaerobic threshold (group 2) were able to train at a higher percentage of maximum exercise tolerance than patients who reached anaerobic threshold (group 1). The increase in exercise performance of both groups, however, was similar. We conclude that patients with moderate to severe COPD can perform exercise training successfully at intensity targets which represent higher percentages of maximum than typically recommended in normal individuals or other patients.

Treatment of dyspnea in COPD. A controlled clinical trial of dyspnea management strategies.

We conducted a randomized clinical trial to evaluate a limited pulmonary rehabilitation program focused on coping strategies for shortness of breath but without exercise training. Eighty-nine patients with COPD were randomly assigned to either 6-week treatment or general health education control groups. Treatment consisted of instruction and practice in techniques of progressive muscle relaxation, breathing retraining, pacing, self-talk, and panic control. Tests of 6-min walk distance, quality of well-being, and psychological function as well as six dyspnea measures were administered at baseline, posttreatment, and 6 months after the intervention. Baseline pulmonary function tests also were obtained. At the end of the 6-week treatment, there were no significant differences between the treatment and control groups on any outcome measure. At the 6-month follow-up, a significant group difference was seen on only one variable, Mahler's transition dyspnea index. The results of this evaluation suggest that a treatment program of dyspnea management strategies, without structured exercise training or other components of a comprehensive pulmonary rehabilitation program, is not sufficient to produce significant improvement in dyspnea, exercise tolerance, health-related quality of well-being, anxiety, or depression.

Validation of a new dyspnea measure: the UCSD Shortness of Breath Questionnaire. University of California, San Diego.

OBJECTIVE: Evaluate the reliability and validity of a new version of the University of California, San Diego Shortness of Breath Questionnaire (SOBQ), a 24-item measure that assesses self-reported shortness of breath while performing a variety of activities of daily living. DESIGN: PATIENTS enrolled in a pulmonary rehabilitation program were asked to complete the SOBQ, the Quality of Well-Being Scale, the Center for Epidemiologic Studies Depression Scale, and a 6-min walk with modified Borg scale ratings of perceived breathlessness following the walk. SETTING: University medical center pulmonary rehabilitation program. PATIENTS: Thirty-two male subjects and 22 female subjects with a variety of pulmonary diagnoses: COPD (n=28), cystic fibrosis (n=9), and postlung transplant (n=17). MEASUREMENTS AND RESULTS: The current version of the SOBQ was compared with the previous version, the format of which often resulted in a significant number of "not applicable" answers. The results demonstrated that the SOBQ had excellent internal consistency (alpha=0.96). The SOBQ was also significantly correlated with all validity criteria. CONCLUSIONS: The SOBQ is a valuable assessment tool in both clinical practice and research in patients with moderate-to-severe lung disease.

Restricted pulmonary function in cystic fibrosis.

Some patients with cystic fibrosis have reduced pulmonary volumes, indicating a restrictive pattern of pulmonary disease. We identified ten patients with pulmonary functional evidence of restriction among 158 patients with cystic fibrosis followed at the University of California San Diego Medical Center in 1984 and 1985. We characterized the radiographic, pulmonary functional, and clinical characteristics of these restricted patients compared to matched nonrestricted patients. Pulmonary volumes were measured by three different techniques: plethysmography; nitrogen washout; and radiography. Except for plethysmographic pulmonary volumes, there were no significant differences between the matched restricted and nonrestricted patients. Radiographic pulmonary volume tended to overestimate gas volume measured by the other techniques. Differences among these techniques (thought to represent air-space filling) correlated best with radiographic evidence of air trapping and bronchial markings and not with parenchymal lesions. Serial pulmonary function tests demonstrated changes in pulmonary volume in several patients and a trend toward improvement in pulmonary volume in the restricted patients over time. We conclude that restricted pulmonary function does not necessarily indicate more severe disease in patients with cystic fibrosis and may be reversible in some. The mechanism of restriction may be related more to radiographic evidence of airway disease than to parenchymal abnormalities.

Cardiovascular risk factor assessment of medical students as an educational tool.

For three consecutive years, beginning in 1986, we evaluated cardiovascular disease (CVD) risk factors of medical students as part of the teaching program in a Preventive Cardiology Academic Award. Entering students in three consecutive classes were screened on the first day of orientation to medical school. The first year, we evaluated 108 students (71 men and 37 women), the second year, 99 students (75 men, 24 women), and the third year 108 students (67 men and 41 women). During the single four-hour period, we obtained data on personal and family history of CVD risk factors, type A behavior, knowledge of CVD, attitudes toward CVD prevention, measures of depression and anger, blood pressure, blood pressure reactivity, physical activity, and diet. Blood was drawn for lipid analysis. Height and weight were measured, and a physical fitness step test was administered. Pulmonary function was measured during the third year. We used a four-tiered approach to preventive cardiology education. During the assessment session, abnormalities, such as elevated blood pressure or abnormal pulse, were discussed with the student. In the second tier, the data were analyzed and returned to all students during teaching sessions, enabling them to compare their levels with the class and the national averages. For the third tier, students with high-risk values, defined as low-density lipoprotein cholesterol level > or = 150 mg/dL, a total cholesterol or triglyceride level > or = 200 mg/dL, or blood pressure > or = 140/90 mmHg, were seen by faculty physicians who suggested remedial interventions in separate sessions.(ABSTRACT TRUNCATED AT 250 WORDS)

Self-efficacy expectations predict survival for patients with chronic obstructive pulmonary disease.

The validity of self-efficacy expectations as predictors of mortality was evaluated for 119 patients with chronic obstructive pulmonary disease (COPD). Patients completed 4 physiological measures that represent common clinical indicators of disease severity: (a) forced expiratory volume in 1 s (FEV1.0), (b) arterial blood gas measurement of resting partial pressure of oxygen (PaO2), (c) single-breath diffusing capacity (DLCO), and (d) maximum oxygen uptake (VO2max) during exercise. In addition, self-reported self-efficacy expectation for walking on a treadmill was measured. Self-efficacy was a significant univariate predictor of 5-year survival. However, when controlling for FEV1.0 in multivariate survival analysis, self-efficacy had only a marginal effect. We concluded that simple self-report scales could provide significant information about health status.

Experimental evaluation of rehabilitation in chronic obstructive pulmonary disease: short-term effects on exercise endurance and health status.

Randomly assigned 119 adults with chronic obstructive pulmonary disease to an 8-week comprehensive rehabilitation program or to an 8-week education control program. Comprehensive pulmonary rehabilitation included education, physical and respiratory therapy instruction, psychosocial support, and supervised exercise training; education control included biweekly classroom instruction and discussions on respiratory therapy, medical aspects of lung disease, clinical pharmacology, and diet, but no exercise training. Both groups received extensive physiological and psychosocial evaluation before and after the intervention. Six months after enrollment, patients randomly assigned to the rehabilitation program showed significant increases in exercise endurance, whereas patients randomly assigned to control program showed nonsignificant increases. Improvement in self-efficacy was correlated with improvements in exercise endurance.

The importance of exercise in pulmonary rehabilitation.

Exercise has been shown to be an important component of pulmonary rehabilitation and may be associated with both physiologic and psychological benefits for patients with chronic lung disease. In evaluating patients for pulmonary rehabilitation, exercise testing can be useful in measuring exercise tolerance, assessing causes of exercise limitation, developing a prescription for training, evaluating often unexpected changes in arterial blood gases, and screening for exercise-induced bronchospasm. A variety of testing procedures and measurements are available in pulmonary laboratories. The appropriate test depends on several variables, including patient and program goals, questions identified in the initial patient evaluation, the specific exercise training program, available laboratory expertise, and cost.

The role of exercise testing in pulmonary diagnosis.

Exercise stresses the body's functional reserves that allow for the increased metabolic work and gas transport necessary for the efficient production of energy with physical activity or stress. Disease that reduces reserve in the gas transport organs will produce exertional symptoms not present at rest. Exercise testing has been well established in the evaluation of healthy persons and cardiac patients who are limited by cardiac or peripheral muscle function. For patients with lung disease, however, whose exercise performance is limited by reduced ventilatory capacity and disordered gas exchange, principles of exercise testing (and training) are different. In the evaluation of pulmonary patients, exercise testing can be used to measure exercise tolerance, assess the limitation to exercise in patients with unexplained dyspnea, evaluate patients for respiratory disability, assess blood gas changes with exercise, and detect exercise-induced asthma. Nevertheless, our understanding of the role of exercise in pulmonary diagnosis is at an early stage of development and much needs to be learned about the practical applications of exercise testing in the diagnosis, staging, and serial evaluation of pulmonary diseases.

Measurement of lung volumes.

Measurements of lung volume play an integral role in the laboratory evaluation of patients with known or suspected lung disease. Several techniques are available to measure absolute lung volumes (containing residual volume). It should be noted that these techniques measure different theoretical volumes and may produce different results in patients with lung disease. Lung volume measurements are typically elevated in obstructive diseases and reduced in restrictive diseases, making them useful tests in diagnosing and distinguishing these two general classes of disease.