Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-09-08
2002-04-09
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S586000, C600S528000
Reexamination Certificate
active
06368283
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for estimating systolic and mean pulmonary artery pressures of a patient. More specifically, the invention relates to converting the second heart sound signal contained in the phonocardiagram (PCG) into a pulmonary artery pressure estimate.
Pulmonary hypertension is a disease characterized by a progressive and sustained elevation of pulmonary artery pressure (PAP). Pulmonary hypertension is a common and serious complication of multiple cardiovascular and respiratory diseases. Acquired heart diseases lead to pulmonary hypertension by increasing pulmonary blood flow or by increasing pulmonary venous pressure, which is the most common cause of pulmonary hypertension. Congenital heart diseases associated with left-to-right shunts or abnormal communication between the great vessels are commonly associated with pulmonary hypertension and intrinsic pulmonary diseases, respiratory disorders, can also lead to pulmonary hypertension. Among the respiratory disorders are the syndrome of alveolar hypoventilation and sleep apnea. Among the intrinsic lung diseases are chronic obstructive pulmonary disease, chronic obstruction of upper airways, diseases limiting pulmonary expansion and respiratory distress syndrome.
The major consequence of pulmonary hypertension is right ventricular failure. Pulmonary hypertension is an important risk factor for morbidity and mortality in patients with cardiovascular or respiratory diseases. In patients with primary pulmonary hypertension, the median survival time is 2.8 years. With the onset of right ventricular failure, patient survival is generally limited to approximately 6 months. Early detection and regular monitoring of pulmonary hypertension in patients is therefore essential to adjust the medical treatment and determine optimal timing for surgery. As the options available for treating pulmonary hypertension have increased, the requirement for accurate and noninvasive methods allowing regular and safe estimation of PAP has also increased.
BACKGROUND OF THE INVENTION
Pulmonary hypertension is a serious cardiovascular dysfunction that is difficult to assess noninvasively. The PAP is usually measured using a pulmonary arterial catheter, Swan-Ganz catheter, in patients necessitating continuous monitoring of PAP. However, this method can cause several complications including lesions of the tricuspid valve, pulmonary valve, right ventricle, or pulmonary arteries, cardiac arrhythmia, dislodgment of a thrombus and infectious complications. This method is not recommended for repeated measurements, one time every week or month or 6 months depending of the evolution of the disease, because of the potential risks for the patient. Since regular evaluation of the PAP is very important for the follow up of the evolution of the disease and for the assessment of the efficacy of the treatment, noninvasive methods have been developed to allow frequent and accurate measurement of PAP.
Doppler echocardiography has been used for non-invasive estimation of the systolic PAP when tricuspid regurgitation can be detected as described by Nishimura, R. A. and Tajik, A. J., “Quantitative hemodynamics by Doppler echocardiography: A noninvasive alternative to cardiac catheterization,”
Prog Cardiovasc Dis
, vol. 36, no. 4, pp. 309-342, 1994. The right ventricular systolic pressure can be calculated by adding the systolic pressure gradient across the tricuspid valve, measured by using continuous-wave Doppler to the estimated right atrial pressure. The atrial pressure is set to 14 mm Hg when the jugular venous pressure is normal or mildly elevated and 20 mm Hg when the jugular pressure is markedly elevated. When the jugular venous pressure is not available, it is recommend to use 5, 10, or 20 mm Hg to estimate the right atrial pressure depending on the degree of collapse of the inferior vena cava during inspiration. Recently, it was demonstrated that the right atrial pressure may be estimated with reasonable accuracy, r=0.75, using the tricuspid E/Ea ratio, where E is the tricuspid inflow velocity of the E wave measured by pulsed Doppler and Ea is the tricuspid annulus velocity measured by tissue Doppler at early diastole. Furthermore, the systolic pressure gradient across the pulmonary valve must be either negligible or estimated by Doppler and added to the tricuspid gradient and right atrial pressure. This noninvasive method can provide a high degree of correlation, 0.89≦r≦0.97, and a standard error (SEE) varying from 7 to 12 mmHg in comparison with pulmonary artery catheterization, systolic PAP range: 20-160 mmHg.
However, the estimation of PAP by Doppler echocardiography has several important limitations. Firstly, the PAP cannot be estimated by Doppler in approximately 50% of patients with normal PAP, 10% to 20% of patients with elevated PAP, and 34% to 76% of patients with chronic obstructive pulmonary disease because of the absence of tricuspid regurgitation, a weak Doppler signal or poor signal-to-noise ratio. To improve the feasibility of the method in patients with a weak Doppler signal or poor signal-to-noise ratio, it is necessary to use contrast agent enhancement. Secondly, Doppler echocardiography tends to overestimate PAP in patients with normal PAP and significantly underestimates the PAP in patients with severe pulmonary arterial hypertension. One surprising limitation of the method is the relatively important standard error in contrast to the above mentioned high levels of correlation. This is due to various error contributions associated with the non zero angle of the Doppler beam with the flow, the approximate estimation of the right atrial pressure, the presence of obstruction and pressure loss in the right ventricular outflow tract or in the pulmonary valve in some patients, the non simultaneous measurement of Doppler and catheter measurements in some studies, the non simultaneous recording of peak atrial, peak ventricular and peak pulmonary arterial pressures in patients, the use of the modified Bernoulli equation, and other factors. Furthermore, Doppler echocardiography requires an expensive ultrasound system and a highly qualified technician. This method is thus not applicable for daily measurements of PAP in small clinics or at home.
Acoustic methods based on signal processing of the second heart sound, s
2
(t), have been studied for the estimation of PAP. The onset of the aortic, A
2
(t), and the pulmonary, P
2
(t), components of S
2
(t) marks the end of left and right ventricular systole and the beginning of left and right ventricular diastole, respectively. In patients with pulmonary hypertension, the intensity of P
2
(t) is accentuated and the delay of P
2
(t) in relation to A
2
(t) is increased due to the prolongation of right ventricular systole. Furthermore, the A
2
(t)−P
2
(t) splitting time interval, SI, is indirectly proportional to the heart rate. Hence Leung et al. have underlined in “Analysis of the second heart sound for diagnosis of paediatric heart disease,”
IEEE Proceedings Sci Meas Technol
, vol. 145, no. 6, pp. 285-290, 1998, the importance of normalizing the SI with respect to the duration of the cardiac cycle to obtain valuable diagnostic information. The normalized SI (NSI) has been found to be 3.3±1.8% in normal subjects whereas it was 5.2±1.1% in patients with pulmonary stenosis, a condition resulting in pressure overload of the right ventricle and 5.9±0.7% in patients with atrial septal defect, a condition resulting in volume overload of the right ventricle and the pulmonary circulation. However, the relationship between NSI and the pulmonary artery pressure has not been studied.
Several studies have been done on the relationship between the resonant frequency, Fp, and the quality factor, Q, of the spectrum of P
2
(t) and the systolic PAP measured by pulmonary artery catheterization. In the study of Aggio et al. “Noninvasive estimation of the pulmonary systolic pressure from the spectral analysis of the second heart
Durand Louis-Gilles
Pibarot Philippe
Xu Jingping
Institut de Recherches Cliniques de Montreal
Myers Bigel Sibley & Sajovec P.A.
Nasser Robert L.
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