Estimation of respiratory rate and heart rate during treadmill tests using acoustic sensor

The objective was to test the robustness of an acoustic method to estimate respiratory rates (RR) during treadmill test. The accuracy was assessed by the comparison with simultaneous estimates from a capnograph, using as a common reference a pneumotachometer. Eight subjects without any pulmonary disease were enrolled. Tracheal sounds were acquired using a contact piezoelectric sensor placed on the subject's throat and analyzed using a combined investigation of the sound envelope and frequency content. The capnograph and pneumotachometer were coupled to a face mask worn by the subjects. There was a strong linear correlation between all three methods (r²ranged from 0.8 to 0.87), and the SEE ranged from 1.97 to 2.36. As a conclusion, the accuracy of the respiratory rate estimated from tracheal sounds on adult subjects during treadmill stress test was comparable to the accuracy of a commercial capnograph. The heart rate (HR) estimates can also be derived from carotid pulse using the same single sensor placed on the subject's throat. Compared to the pulse oximeter the results show an agreement of acoustic method with r²=0.76 and SEE = 3.51.

Comparison of respiratory rate estimation based on tracheal sounds versus a capnograph

The objective was to compare the accuracy of estimations of respiratory rate (RR), based on tracheal sounds, with simultaneous estimations from a capnograph, using as a common reference a pneumotachometer. Five subjects without pulmonary diseases were enrolled. Tracheal sounds were acquired using a contact piezoelectric sensor placed on the subject's throat and analyzed using a combined investigation of the sound envelope and frequency content. The capnograph and pneumotachometer were coupled to a face mask worn by the subjects. There was a strong linear correlation (r2= 0.98) between the acoustic method and the pneumotachometer and also between the capnograph and the pneumotachometer (r2 = 0.98). The SEE obtained by the acoustic method was 1.11 and the SEE obtained by the capnograph was 1.23. As a conclusion, the accuracy of the respiratory rate estimated from tracheal sounds on adult subjects was comparable to the accuracy of a commercial capnograph, using as a common reference a pneumotachometer.

Monitoring respiratory rate based on tracheal sounds. First experiences

The objective was to develop a non-invasive method for continuously monitoring respiratory rate (RR) based on tracheal sounds. 25 volunteers and 36 patients with chronic pulmonary diseases were enrolled in a clinical study. Tracheal sounds were acquired using a contact piezoelectric sensor placed on the examinee's throat and analyzed using a combined investigation of the sound envelope and frequency content. RR estimates were compared to reference measurements taken from a pneumotachometer coupled to a face mask worn by the examinee. RR was also manually counted by a respiratory technician. Two types of breathing (mouth and nose) and three different positions were studied (fowler, semi-fowler and supine). RR estimated in volunteers had a success rate (SR) of 96%, a correlation coefficient (r) of 0.99 and a standard error of the estimate (SEE) of 0.56. The RR estimated in patients was comparable or slightly better (SR = 85%, r = 0.93 and SEE = 1.49) than those obtained by manual count (SR = 82%, r = 0.91, SEE = 1.58), which is the method widely used in clinical settings. No significant difference in the capacity to estimate RR was found related to posture and breathing type, making this method useful for continuous monitoring.