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Image: Graph showing respiratory sound intensity in both sides of a patient with unilateral paralysis, with the paralysed side on the left.
Diaphragmatic paralysis consists of the total or partial stopping of diaphragm motor activity. The main cause of this malfunction is a phrenic nerve lesion, normally due to tumours oppressing the nerve or as a consequence of thoracic surgery (in about 20% of operations). The effects of diaphragmatic paralysis are variable, depending on whether the ceasing of motor activity is total or partial and if it affects one or two hemidiaphragms. In any case, all patients suffer a limited respiratory capacity.
Among the traditional techniques used to diagnose diaphragmatic paralysis are thoracic radiography, phrenic nerve stimulation, fluoroscopy and ultrasonography, but these techniques are subjective and some of them are invasive. Moreover, none of these techniques show the information about patients’ pulmonary function which sound respiratory analysis does.
Respiratory air flow is positively correlated with lung sound intensity, which means that the more air flow we have, the more sound intensity we obtain. This is the case not only is for healthy people but also for patients with unilateral diaphragmatic paralysis. However, in healthy people the sound difference between the left and right hemithorax is minimal. In unilateral diaphragmatic paralysis the difference is bigger, due to the reduction of ventilation on the affected side. This respiratory sound intensity difference is measured by contact microphones located on the patient’s back.
“Traditionally, researchers look for abnormal sound presence in obstructive pathologies, such as asthma or COPD. This new method proposes an alternative scenario: to evaluate normal respiratory sounds to, indirectly, assess pulmonary function,” explains Raimon Jané, group leader of IBEC’s Biomedical Signal Processing and Interpretation group. “If the diaphragm is not correctly activated, the normal respiratory sound intensity will decrease.”
This method, in combination with conventional spirometry, shows complementary and relevant information for unilateral diaphragmatic paralysis, because the lower the spirometric parameters are, the higher the respiratory sound intensity difference is.
“The acoustic analysis of the respiratory sound intensity provides a non-invasive alternative to diagnose patients more precisely,” says Raimon. “This analysis is quantifiable in dB, which allow the assessment of these patients in an objective way. Moreover, among the main applications of this method is long-term patient monitoring to evaluate pulmonary function improvement after rehabilitation.”
Reference: Fiz, J.A., Jané, R., Lozano, M., Gómez, R., Ruiz, J. (2014). Detecting Unilateral Phrenic Paralysis by Acoustic Respiratory Analysis. PLoS ONE 9(4): e93595
