Abstract
The consequences of phrenic nerve paralysis vary from a considerable reduction in respiratory function to an apparently normal state. Acoustic analysis of lung sound intensity (LSI) could be an indirect non-invasive measurement of respiratory muscle function, comparing activity on the two sides of the thoracic cage. Lung sounds and airflow were recorded in ten males with unilateral phrenic paralysis and ten healthy subjects (5 men/5 women), during progressive increasing airflow maneuvers. Subjects were in sitting position and two acoustic sensors were placed on their back, on the left and right sides. LSI was determined from 1.2 to 2.4 L/s between 70 and 2000 Hz. LSI was significantly greater on the normal (19.3±4.0 dB) than the affected (5.7±3.5 dB) side in all patients (p = 0.0002), differences ranging from 9.9 to 21.3 dB (13.5±3.5 dB). In the healthy subjects, the LSI was similar on both left (15.1±6.3 dB) and right (17.4±5.7 dB) sides (p = 0.2730), differences ranging from 0.4 to 4.6 dB (2.3±1.6 dB). There was a positive linear relationship between the LSI and the airflow, with clear differences between the slope of patients (about 5 dB/L/s) and healthy subjects (about 10 dB/L/s). Furthermore, the LSI from the affected side of patients was close to the background noise level, at low airflows. As the airflow increases, the LSI from the affected side did also increase, but never reached the levels seen in healthy subjects. Moreover, the difference in LSI between healthy and paralyzed sides was higher in patients with lower FEV1 (%). The acoustic analysis of LSI is a relevant non-invasive technique to assess respiratory function. This method could reinforce the reliability of the diagnosis of unilateral phrenic paralysis, as well as the monitoring of these patients.
Highlights
There are several causes of diaphragmatic dysfunction that can affect one or both muscles
Lung sound intensity in unilateral phrenic paralysis Acoustic and spirometric parameters were analyzed in patients and healthy subjects
Our study shows that patients with unilateral phrenic nerve paralysis have a lower inspiratory sound intensity on the affected side than the healthy one
Summary
There are several causes of diaphragmatic dysfunction that can affect one or both muscles. The consequences of diaphragm dysfunction vary from the most serious cases of bilateral lesions that can require mechanical ventilation, to the mildest unilateral lesions that may to some extent impair breathing and in consequence exercise capacity [2,3]. Diaphragm dysfunction due to phrenic paralysis has been studied with various techniques including x-ray, fluoroscopy, ultrasonography, and external or internal stimuli of the diaphragm. These techniques provide information regarding the position and mobility of the diaphragm muscle [4,5,6,7], but do not predict the degree of respiratory dysfunction [8]. In cases of unilateral paralysis, spirometric function may be normal
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