Objective: To develop and validate a new non-invasive method for the estimation of pulmonary arterial pressure (PAP) based on advanced signal processing of the second heart sound.
Design: Prospective comparative study.
Setting: Referral cardiology centre.
Patients: This method was first tested in 16 pigs with experimentally induced pulmonary hypertension and then in 23 patients undergoing pulmonary artery catheterisation.
Methods: The heart sounds were recorded at the surface of the thorax using a microphone connected to a personal computer. The splitting time interval between the aortic and the pulmonary components of the second heart sound was measured using a computer assisted spectral dechirping method and was normalised for heart rate.
Results: The systolic PAP varied between 14-73 mm Hg in pigs and between 20-70 mm Hg in patients. The normalised splitting interval was measurable in 97% of the recordings made in pigs and 91% of the recordings made in patients. There was a strong relation between the normalised splitting interval and the systolic PAP (pigs: r = 0.94, standard error of the estimate (SEE) = 5.3 mm Hg; patients: r = 0.84, SEE = 7.8 mm Hg) or the mean pulmonary pressure (pigs: r = 0.94, SEE = 4.1 mm Hg; patients: r= 0.85, SEE = 5.8 mm Hg).
Conclusion: This study shows that this new non-invasive method based on advanced signal processing of the second heart sound provides an accurate estimation of the PAP.
Pulmonary arterial hypertension is a frequent and serious complication of several cardiovascular or respiratory diseases that is difficult to assess non-invasively. As the options for treatment of pulmonary hypertension have expanded, the requirement for accurate and non-invasive methods to allow regular and safe estimation of pulmonary arterial pressure (PAP) has increased. Measurement of PAP by Doppler echocardiography provides a high degree of correlation (0.89 [less than or equal to] r 0.97) in comparison with pulmonary artery catheterisation. (1-3) However, PAP cannot be estimated by Doppler echocardiography in approximately 50% of patients with normal PAP, 10-20% of patients with increased PAP, and 34-76% of patients with chronic obstructive pulmonary disease because of the absence of tricuspid regurgitation, a weak Doppler signal, or a poor signal to noise ratio (SNR). (1-4) Moreover, Doppler echocardiography cannot be used to monitor PAP continuously. Consequently, it would be useful to develop other non-invasive methods to allow frequent and accurate measurement of PAP.
It is well known that the time interval between the aortic (A2) and the pulmonary (P2) components of the second heart sound (S2), as well as the dominant frequency of P2, are increased in the presence of pulmonary hypertension. (5-7) It has therefore been suggested that the A2-P2 splitting interval (SI) may be useful to estimate the PAP. However, the basic relation between the SI and the PAP is not well known. Moreover, the applicability of this acoustic approach is limited because the SI is relatively short (generally 100 ms) and is difficult to measure, especially in patients for whom A2 and P2 are overlapping. (7,8) Recently, we have proposed a new approach based on advanced signal processing that can successfully identify and extract overlapping A2 and P2 components from S2 recordings and that can be used to measure the A2-P2 SI accurately. (9,10) The objective of this work was to study the relation between the SI measured using this new acoustic method and the PAP measured by catheterisation. This relati on was first studied in an animal model designed to vary the PAP over a wide range and then in patients undergoing pulmonary artery catheterisation.
Animal care and experiments were conducted in accordance with the guidelines of the Canadian Council for Animal Care. The protocol was approved by the institutional animal care committee of Laval University, Ste-Foy, Canada. Sixteen pigs weighing between 27-35 kg were anaesthetised and ventilated as previously described. …