WALK TEST PREDICTS MORTALITY IN PULMONARY HYPERTENSION

The distance achieved during a six-minute walk test is strongly associated with mortality in patients with primary pulmonary hypertension (PPH), according to findings from a recent study. The results suggest that this submaximal exercise test "may serve as a prognostic indicator of PPH, which may complement invasive standard prognostic markers, such as [right ventricular] hemodynamic variables," reported Miyamoto et al.

These investigators designed their study to assess the relationship between the distance walked in six minutes and exercise capacity (as determine by maximal cardiopulmonary exercise testing) and to evaluate the use of the walk test as a predictive tool. Forty-three patients (age 14 to 67 years) with PPH and 16 healthy controls were evaluated.

The distance walked during six minutes was significantly associated with each subject's New York Heart Association functional class. It was also significantly associated with baseline hemodynamic values for cardiac output, total pulmonary resistance, and mean right atrial pressure. Furthermore, the distance walked strongly correlated with maximal exercise measurements of peak oxygen consumption per unit of time, oxygen pulse, and the regression slope relating minute ventilation to carbon dioxide output.

Twelve patients died of cardiopulmonary causes during a mean follow-up of 21 months. Of the noninvasive variables assessed in this study, distance walked was the only independent predictor of mortality. Patients who walked less than 332 meters were significantly less likely to survive than were those patients who walked farther.

Miyamoto S, Nagaya N, Satoh T, et al. Clinical correlates and prognostic significance of six-minute walk test in patients with primary pulmonary hypertension. Comparison with cardiopulmonary exercise testing. Am J Respir Crit Care Med. 2000;161:487-492.

WHICH CHF PATIENTS ARE MOST LIKELY TO BENEFIT FROM CPAP

Short-term application of continuous positive airway pressure (CPAP) causes greater reductions in cardiac volumes among congestive heart failure patients with idiopathic dilated cardiomyopathy (IDC) than among those with ischemic cardiomyopathy (IsC), Mehta et al found in a recent study.

The researchers applied CPAP of 10 cm H₂O for 30 minutes to chronic heart failure patients with IDC (n = 9) or IsC (n = 13). The results are shown in Figure 1.

Among patients with IDC, CPAP significantly reduced right ventricular but not left ventricular end-diastolic and end-systolic volumes. The greatest decrease occurred among IDC patients with the largest cardiac volumes. In contrast, CPAP did not significantly alter cardiac volumes in the IsC group.

"The greater reductions in cardiac volumes in the IDC group compared with the IsC group are likely related to differences between the two disease processes. IDC is characterized by diffuse myocardial disease with far less focal scarring and greater myocardial compliance than in patients with IsC," Mehta et al concluded.

Mehta S, Liu PP, Fitzgerald FS, et al. Effects of continuous positive airway pressure on cardiac volumes in patients with ischemic and dilated cardiomyopathy. Am J Respir Crit Care Med. 2000;161:128-134.

RECURRENT PEDIATRIC PNEUMONIA

Most children with recurrent pneumonia have an underlying illness--often, oropharyngeal incoordination leading to aspiration, Owayed et al found in a recent retrospective review.

The researchers evaluated medical records from 238 children younger than age 18 years. Each child had had at least two pneumonia episodes within one year or at least three episodes in his or her lifetime.

Almost all of the patients (92%) had an underlying illness, including aspiration syndrome secondary to oropharyngeal muscle incoordination (48%), immune disorders (10%), congenital cardiac defects (9%), bronchial asthma (8%), pulmonary anomalies (8%), gastroesophageal reflux (5%), and sickle cell anemia (4%). Cerebral palsy accounted for almost half of the cases of aspiration disorders.

In 81% of cases, the underlying illness had been diagnosed before the first case of pneumonia occurred. Aspiration disorders, immune disorders, and congenital heart disease tended to be diagnosed before the first case of pneumonia, whereas asthma, respiratory tract anomalies, and gastroesophageal reflux were often not recognized until later. Of these, asthma was the most common undiagnosed illness.

Owayed et al noted that the following can be considered clinical clues to diagnosis in children with pneumonia:

• Immune disorders: Recurrent infections at other locations and failure to thrive.
• Underlying pulmonary pathology: Recurrences involving the same location.
• Gastroesophageal reflux: The association of respiratory symptoms with feeding.
• Asthma: Recurrent wheezing.

Owayed AF, Campbell DM, Wang EEL. Underlying causes of recurrent pneumonia in children. Arch Pediatr Adolesc Med. 2000;154:190-194.

RESPIRATORY INFECTIONS TRIGGER HOSPITALIZATIONS

Many patients hospitalized for serious acute respiratory conditions have viral infections complicated by chronic underlying conditions, Glezen et al found in a recent study. They believe that vaccines for respiratory syncytial virus and parainfluenza viruses should be added to the currently available influenza vaccine.

The study included 1,029 patients who were hospitalized for pneumonia, tracheobronchitis, bronchiolitis, croup, exacerbations of asthma or chronic obstructive pulmonary disease (COPD), and/or congestive heart failure. Almost all (93%) of the patients who were older than 5 years had a chronic underlying condition--most commonly, a chronic pulmonary condition, such as asthma or COPD. Among the patients with chronic pulmonary disease, those from low-income populations were about eight times more likely to be hospitalized than were those from middle-income populations.

Of the 403 patients who submitted serum specimens for antibody testing, 45% had evidence of viral infection. Together, influenza, parainfluenza, and respiratory syncytial virus accounted for about 75% of the viral infections that were detected.

Glezen et al speculated that vaccines effective against influenza, parainfluenza, and respiratory syncytial viruses could reduce the number of hospitalizations among high-risk patients by about 50%. Given that hospitalization rates for lower respiratory tract infections have skyrocketed in the past two decades, the use of such vaccines could have important implications for public health.

Glezen WP, Greenberg SB, Atmar RL, et al. Impact of respiratory virus infections on persons with chronic underlying conditions. JAMA. 2000;283:499-505.

A SHORTER TB PROPHYLAXIS FOR HIV-POSITIVE PATIENTS

Two months' administration of rifampin and pyrazinamide was similar to a 12-month isoniazid regimen in terms of safety and efficacy in the prevention of tuberculosis (TB) among patients infected with human immunodeficiency virus (HIV) who had a positive TB skin test result. Furthermore, the shorter regimen had a higher completion rate than the longer regimen.

Gordin et al studied 1,583 HIV-infected patients age 13 years and older with a positive TB skin test. The subjects were randomized to standard treatment with 300 mg/d isoniazid with 50 mg/d pyridoxine hydrochloride for 12 months or to 600 mg/d rifampin (or 450 mg/d for those who weighed less than 50 kg) plus 20 mg/kg/d pyrazinamide for two months. Mean follow-up was about 37 months in both groups.

Patients given the shorter regimen had a significantly higher completion rate (80%) than did patients given standard treatment (69%). The rate of confirmed tuberculosis was 28% lower in the two-month treatment group than in the standard treatment group (0.8 vs 1.1 per 100 person-years); however, this difference was not statistically significant.

The two groups also had similar rates of HIV progression and/or death and overall adverse events. In addition, neither regimen appeared to lead to drug-resistant TB.

Gordin F, Chaisson RE, Matts JP, et al. Rifampin and pyrazinamide vs isoniazid for prevention of tuberculosis in HIV-infected persons: an international randomized trial. JAMA. 2000;283:1445-1450.

REHABILITATION PROGRAM FOR CHRONIC LUNG DISEASE

A six-week multidisciplinary pulmonary rehabilitation program showed long-term benefits for patients with disabling chronic lung disease. In a recent randomized controlled trial, rehabilitated patients showed greater improvements in walking ability and health status than did patients who received standard treatment. These benefits, which persisted for at least one year, translated into a decreased use of health services.

Griffiths et al randomized 200 patients to a multidisciplinary rehabilitation program or to standard medical care for six weeks and followed these patients for a year. The patients had chronic obstructive bronchitis, emphysema, or chronic poorly reversible asthma or bronchiectasis.

The rehabilitation program consisted of two-hour sessions devoted to educational activities, an exercise program aimed at achieving 30 minutes of exercise, and a teaching portion that looked at psychological issues relating to chronic disability. These sessions were conducted three times a week.

During the one-year follow-up, the number of patients admitted to the hospital in each of the two groups was similar (about 40), but the mean number of days these patients spent in the hospital was significantly shorter in the rehabilitation group (10.4 days vs 21 days in the control group). The rehabilitation group also had significantly greater improvements in walking ability and health status both at the end of the six-week period and after one year, compared with the control group.

Griffiths TL, Burr ML, Campbell IA, et al. Results at 1 year of outpatient multidisciplinary pulmonary rehabilitation: a randomised controlled trial. Lancet. 2000; 355:362-368.

IDIOPATHIC ENVIRONMENTAL INTOLERANCE LINKED TO PANIC

Patients with idiopathic environmental intolerance (IEI)--formerly known as multiple chemical sensitivity--display high anxiety sensitivity like that of patients with panic disorder, according to findings by Poonai et al. Both conditions include symptoms of chest tightness, breathlessness, palpitations, apprehension, and avoidance of situations in which the symptoms occur.

Thirty-six patients with IEI and 37 healthy control subjects inhaled carbon dioxide, which is known to reproduce panic symptoms in patients with panic disorders. Their vital signs were then measured, and they were asked to rate sensations of panic and fear on a questionnaire.

A significantly greater proportion of the IEI group (71%) experienced panic symptoms after carbon dioxide inhalation, compared with the control group (26%). However, the two groups were similar in terms of changes in breathing rate, heart rate, and other physical measures. The rate of panic in the IEI group was similar to that found among patients with panic disorders, Poonai et al noted.

Patients with IEI scored significantly higher than control subjects on the Anxiety Sensitivity Index (ASI), which is a self-reported measure of panic-related anxiety. Furthermore, the IEI patients who panicked after the carbon dioxide inhalation had a mean ASI score consistent with social phobia.

"The response to carbon dioxide suggests a tendency to overreport and possibly catastrophically misinterpret physical symptoms among IEI patients," Poonai et al noted, adding that this is also a consistent finding among patients with panic disorder. Furthermore, given that 67% of the IEI group fulfilled the criteria for a mood or anxiety disorder, the researchers suggested that a psychological assessment may be warranted for all patients with IEI.

Poonai N, Antony MM, Binkley KE, et al. Carbon dioxide inhalation challenges in idiopathic environmental intolerance. J Allergy Clin Immunol. 2000;105:358-363.

OBSTRUCTIVE SLEEP APNEA AND HYPERTENSION RISK

A clear independent association between obstructive sleep apnea and hypertension was documented in a recent study of almost 2,700 patients. The findings suggest that "sleep apnea syndrome should be taken into account in the differential diagnosis of essential hypertension," Lavie et al reported.

The researchers prospectively examined 2,677 adults (age 20 to 85 years) who were referred to a sleep clinic for suspected sleep apnea. Overall, 40% of this population had hypertension.

The severity of sleep apnea was linearly associated with increased blood pressure and increased incidence of hypertension. In fact, sleep apnea was a significant predictor of systolic and diastolic blood pressure even after other important confounding factors were taken into account.

Furthermore, the risk for hypertension increased by 1% with each additional apneic episode per hour of sleep and by 13% with each 10% decrease in nocturnal oxygen saturation nadir.

Lavie P, Herer P, Hoffstein V. Obstructive sleep apnoea syndrome as a risk factor for hypertension: population study. BMJ. 2000;320:479-482.

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