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. 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.

PREDISPOSING RISK FACTORS FOR ASTHMA EXACERBATIONS

Total immunoglobulin E (IgE) and sensitization to inhalant allergens are predisposing risk factors for asthma exacerbations among young children, according to findings reported by Wever-Hess et al. The results also showed that children living in damp houses are at increased risk for recurrences.

A total of 257 children younger than age 5 years were followed for two years. An asthma exacerbation was defined as an increase in cough, wheeze, and/or breathlessness; an increase in ß 2-agonist use; and a need for short-course oral corticosteroids.

During follow-up, at least one exacerbation occurred in 63% of children age 1 year and younger and in 40% of children age 2 to 4 years. Recurrent exacerbations were found in 18% and 15% of the respective subgroups. Among the children age 1 year and younger, damp housing and colds were predisposing risk factors for exacerbation (odds ratios [OR], 7.6 and 3.6, respectively) and sensitization to inhalant allergens and damp housing were predisposing risk factors for recurrent exacerbations (ORs, 8.1 and 3.8, respectively). Hospital admissions were significantly associated with the number of exacerbations.

Among children age 2 to 4 years, mean age at initial presentation and total IgE level were predisposing risk factors for exacerbation (ORs, 0.92 and 2.3, respectively). There were no predisposing risk factors for recurrent exacerbations in this group. Hospital admissions were significantly associated with damp housing.

Wever-Hess J, Kouwenberg JM, Duiverman EJ, et al. Risk factors for exacerbations and hospital admissions in asthma of early childhood. Pediatr Pulmonol. 2000;29:250-256.

WHICH CHF PATIENTS BENEFIT FROM CPAP?

Short-term application of continuous positive airway pressure (CPAP) causes greater reductions in cardiac volumes among patients with congestive heart failure and idiopathic dilated cardiomyopathy (IDC) than among those with congestive heart failure and 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.

Figure 1 Changes in Cardiac Volumes

Changes in cardiac volumes from baseline following CPAP application in chronic heart failure patients with idiopathic dilated cardiomyopathy (IDC) or ischemic cardiomyopathy (IsC). (LVEDV, left ventricular end-diastolic volume; LVESV, left ventricular end-systolic volume; RVEDV, right ventricular end-diastolic volume; RVESV, right ventricular end-systolic volume.)

PULMONARY DISEASE LINKED TO HOSPITALIZATION FOR RESPIRATORY INFECTION

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 of age had a chronic underlying condition--most commonly, a chronic pulmonary condition. 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% showed 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.

DIAGNOSING OBSTRUCTIVE AIRWAY DISEASE

The individual signs and symptoms of obstructive airway disease (OAD) have little diagnostic value, results from a recent study suggest. Instead, Straus et al found that a combination of four signs/symptoms--self-reported history of chronic OAD, a smoking history of greater than 40 pack-years, age 45 years or older, and maximum laryngeal height of 4 cm or less--are predictive of OAD.

The researchers noted that spirometry should always be included in the workup (if readily available) because it can definitively establish a diagnosis of airway obstruction and provide prognostic information. "However, in those settings in which spirometry is unavailable, our model provides useful diagnostic support for the clinician," they concluded.

Strauss et al evaluated the accuracy of the following elements of the clinical examination in diagnosing OAD: patient self-reported history of chronic OAD, smoking history, wheezing on auscultation, laryngeal height, and laryngeal descent. A total of 76 patients with known chronic OAD, 114 patients with suspected OAD, and 119 patients without known or suspected OAD underwent clinical examination and spirometry. The gold standard for the diagnosis of OAD was a forced expiratory volume in one second (FEV1) and a ratio of FEV1 to forced vital capacity both below the fifth percentile.

The only factors that were significantly associated with OAD diagnosis were a smoking history of more than 40 pack-years, a self-reported history of chronic OAD, maximum laryngeal height of at least 4 cm, and age 45 years or older. Patients with all four of these characteristics had a likelihood ratio for OAD of 220.5, whereas patients with none of them had a likelihood ratio of 0.13.

Straus SE, McAlister FA, Sackett DL, et al. The accuracy of patient history, wheezing, and laryngeal measurements in diagnosing obstructive airway disease. JAMA. 2000;283:1853-1857.

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 m 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.

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 TB 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.