Respiratory acoustic impedance in left ventricular failure

Assessment of respiratory mechanics by impulse oscillometry in orthopneic patients with acute left ventricular failure

BACKGROUND

This study investigated the respiratory function and mechanics of patients with orthopnea caused by acute left ventricular failure (ALVF).

METHODS

The study comprised 40 patients with ALVF and 15 control subjects. All patients underwent lung function tests and impulse oscillometry in both sitting and supine positions. In a subgroup of 22 patients, isosorbide dinitrate was administered and impulse oscillometry was performed 15 minutes later in the supine position.

RESULTS

No patient reported dyspnea while seated, and the orthopnea score was 2.9 ± 1.4. Left ventricular ejection fraction was 43% ± 10%. Patients demonstrated restrictive spirometric pattern in the sitting position, whereas functional residual capacity was comparable to that of the control group. In the supine position, all pulmonary volumes decreased, except inspiratory capacity which increased. Respiratory reactance (Xrs5) was higher in patients in both sitting (421.8 ± 630.6%pred vs 147.2 ± 72.8%pred, P = .01) and supine (699.8 ± 699.9%pred vs 251.2 ± 151.6%pred, P ≤ .001) positions. Respiratory resistance (Rrs5) (10.6% ± 17.8% mean decrease) and Xrs5 (17.2% ± 39.4% mean decrease) improved after nitrates administration. Orthopnea was better correlated with Xrs5%pred in the supine position (r = .42, P = .007). Ejection fraction was positively correlated with inspiratory capacity %pred (r = .42, P = .007) in the sitting position.

CONCLUSION

Patients with ALVF demonstrated increased respiratory reactance that correlated with orthopnea severity and improved after nitrates administration.

Diagostic value of respiratory impedance measurements in elderly subjects

Obstructive lung disease (OLD) is highly prevalent in elderly subjects but markedly under-diagnosed. Indeed, only 40-50% of hospitalized elderly patients are able to adequately perform spirometric tests. This study aimed to evaluate, in an acute-care geriatric hospital, the diagnostic value of measuring airway impedance (Zrs) by the forced oscillation technique (FOT) for: (1) identifying OLD and (2) identifying responders vs. non-responders to bronchodilators. Sixty-seven patients (aged 82+/-8 years) underwent consecutive measurement of Zrs and forced expiratory volumes before and after bronchodilators. Zrs was measured by FOT at frequencies of 4-30 Hz. Correlations, ROC curves and logistic regression models were established to determine the sensitivity (Se) and specificity (Sp) of Zrs in identifying OLD. Significant correlations were found between spirometric and Zrs measurements. The Zrs parameters yielding the best Se and Sp for detecting OLD were: Fn (resonant frequency; Se: 76%; Sp: 78%) and R0 (resistance extrapolated for a frequency of 0: Se: 76%; Sp: 74%). Using the logistic regression models, 76% of the patients were correctly classified as having OLD or not. Zrs was however not contributive in identifying responders to bronchodilators. Zrs measurements by FOT are contributive to the diagnosis of OLD in elderly hospitalized patients.