Investigation of the theory and mechanism of the origin of the second heart sound

Beat-to-beat alterations of acoustic intensity and frequency at the maximum power of heart sounds are associated with NT-proBNP levels

Background

Auscultatory features of heart sounds (HS) in patients with heart failure (HF) have been studied intensively. Recent developments in digital and electrical devices for auscultation provided easy listening chances to recognize peculiar sounds related to diastolic HS such as S3 or S4. This study aimed to quantitatively assess HS by acoustic measures of intensity (dB) and audio frequency (Hz).

Methods

Forty consecutive patients aged between 46 and 87 years (mean age, 74 years) with chronic cardiovascular disease (CVD) were enrolled in the present study after providing written informed consent during their visits to the Kitasato University Outpatient Clinic. HS were recorded at the fourth intercostal space along the left sternal border using a highly sensitive digital device. Two consecutive heartbeats were quantified on sound intensity (dB) and audio frequency (Hz) at the peak power of each spectrogram of S1-S4 using audio editing and recording application software. The participants were classified into three groups, namely, the absence of HF (n = 27), HF (n = 8), and high-risk HF (n = 5), based on the levels of NT-proBNP < 300, ≥300, and ≥900 pg/ml, respectively, and also the levels of ejection fraction (EF), such as preserved EF (n = 22), mildly reduced EF (n = 12), and reduced EF (n = 6).

Results

The intensities of four components of HS (S1-S4) decreased linearly (p < 0.02-0.001) with levels of body mass index (BMI) (range, 16.2-33.0 kg/m2). Differences in S1 intensity (ΔS1) and its frequency (ΔfS1) between two consecutive beats were non-audible level and were larger in patients with HF than those in patients without HF (ΔS1, r = 0.356, p = 0.024; ΔfS1, r = 0.356, p = 0.024). The cutoff values of ΔS1 and ΔfS1 for discriminating the presence of high-risk HF were 4.0 dB and 5.0 Hz, respectively.

Conclusions

Despite significant attenuations of all four components of HS by BMI, beat-to-beat alterations of both intensity and frequency of S1 were associated with the severity of HF. Acoustic quantification of HS enabled analyses of sounds below the audible level, suggesting that sound analysis might provide an early sign of HF.

Heart Sound Analysis in Individuals Supported With Left Ventricular Assist Devices

OBJECTIVE

LVADs are surgically implanted mechanical pumps that improve survival rates of individuals with advanced heart failure. LVAD therapy is associated with high morbidity, which can be partially attributed to challenges with detecting LVAD complications before adverse events occur. Current methods used to monitor for complications with LVAD support require frequent clinical assessments at specialized LVAD centers. Analysis of recorded precordial sounds may enable real-time, remote monitoring of device and cardiac function for early detection of LVAD complications. The dominance of LVAD sounds in the precordium limits the utility of routine cardiac auscultation of LVAD recipients. In this work, we develop a signal processing pipeline to mitigate sounds generated by the LVAD.

METHODS

We collected in vivo precordial sounds from 17 LVAD recipients, and contemporaneous echocardiograms from 12 of these individuals, to validate heart valve closure timings.

RESULTS

We characterized various acoustic signatures of heart sounds extracted from in vivo recordings, and report preliminary findings linking fundamental heart sound characteristics and level of LVAD support.

CONCLUSION

Mitigation of LVAD sounds from precordial sound recordings of LVAD recipients enables analysis of intrinsic heart sounds.

SIGNIFICANCE

These findings provide proof-of-concept evidence of the clinical utility of heart sound analysis for bedside and remote monitoring of LVAD recipients.

Intelligent Diagnosis of Heart Murmurs in Children with Congenital Heart Disease

Heart auscultation is a convenient tool for early diagnosis of heart diseases and is being developed to be an intelligent tool used in online medicine. Currently, there are few studies on intelligent diagnosis of pediatric murmurs due to congenital heart disease (CHD). The purpose of the study was to develop a method of intelligent diagnosis of pediatric CHD murmurs. Phonocardiogram (PCG) signals of 86 children were recorded with 24 children having normal heart sounds and 62 children having CHD murmurs. A segmentation method based on the discrete wavelet transform combined with Hadamard product was implemented to locate the first and the second heart sounds from the PCG signal. Ten features specific to CHD murmurs were extracted as the input of classifier after segmentation. Eighty-six artificial neural network classifiers were composed into a classification system to identify CHD murmurs. The accuracy, sensitivity, and specificity of diagnosis for heart murmurs were 93%, 93.5%, and 91.7%, respectively. In conclusion, a method of intelligent diagnosis of pediatric CHD murmurs is developed successfully and can be used for online screening of CHD in children.

HEART SOUND MODEL BASED ON CASCADED AND LOSSLESS ACOUSTIC TUBES

In order to further understand the generation mechanism of Heart Sound, we introduce a new method for simulating Heart Sound by using cascaded and lossless acoustic tubes. Based on the theory of acoustics, we abstract the ventricles and arteries inside of the heart as multistage tubes with equal length and different radii. By controlling the radii of tubes, we simulate the process of relaxation and constriction of the ventricles and arteries. Then, we calculate the transfer function of the tubes based on the theory of reflective transmission line. To gain the tubes’ radii, we use formant frequency as the model target parameters and put forward an approximation method. Finally, the experimental results show that compared with traditional model, the model based on cascaded and lossless acoustic tubes could better reflect the state of the ventricles and arteries. Meanwhile, by comparing the model tube radius of normal Heart Sound and pathological Heart Sound, we can give a better explanation to the cause of pathological Heart Sound.

Multi-Sense CardioPatch: A Wearable Patch for Remote Monitoring of Electro-Mechanical Cardiac Activity

This study describes the conceptual design and the first prototype implementation of the Multi-Sense CardioPatch, a wearable multi-sensor patch for remote heart monitoring aimed at providing a more detailed and comprehensive heart status diagnostics. The system integrates multiple sensors in a single patch for detection of both electrical (electrocardiogram, ECG) and mechanical (heart sounds, HS) cardiac activity, in addition to physical activity (PA). The prototypal system also comprises a microcontroller board with a radio communication unit and it is powered by a Li-Ion rechargeable battery. Results from preliminary evaluations on healthy subjects have shown that the prototype can successfully measure electro-mechanical cardiac activity, providing useful cardiac indexes. The system has potential to improve remote monitoring of cardiac function in chronically diseased patients undergoing home-based cardiac rehabilitation programs.

Usefulness of the second heart sound for predicting pulmonary hypertension in patients with interstitial lung disease

CONTEXT AND OBJECTIVE

P2 hyperphonesis is considered to be a valuable finding in semiological diagnoses of pulmonary hypertension (PH). The aim here was to evaluate the accuracy of the pulmonary component of second heart sounds for predicting PH in patients with interstitial lung disease.

DESIGN AND SETTING

Cross-sectional study at the University of Brasilia and Hospital de Base do Distrito Federal.

METHODS

Heart sounds were acquired using an electronic stethoscope and were analyzed using phonocardiography. Clinical signs suggestive of PH, such as second heart sound (S2) in pulmonary area louder than in aortic area; P2 > A2 in pulmonary area and P2 present in mitral area, were compared with Doppler echocardiographic parameters suggestive of PH. Sensitivity (S), specificity (Sp) and positive (LR+) and negative (LR-) likelihood ratios were evaluated.

RESULTS

There was no significant correlation between S2 or P2 amplitude and PASP (pulmonary artery systolic pressure) (P = 0.185 and 0.115; P= 0.13 and 0.34, respectively). Higher S2 in pulmonary area than in aortic area, compared with all the criteria suggestive of PH, showed S = 60%, Sp= 22%; LR+ = 0.7; LR- = 1.7; while P2> A2 showed S= 57%, Sp = 39%; LR+ = 0.9; LR- = 1.1; and P2 in mitral area showed: S= 68%, Sp = 41%; LR+ = 1.1; LR- = 0.7. All these signals together showed: S= 50%, Sp = 56%.

CONCLUSIONS

The semiological signs indicative of PH presented low sensitivity and specificity levels for clinically diagnosing this comorbidity.

Effects of aortic irregularities on blood flow

Anatomic aortic anomalies are seen in many medical conditions and are known to cause disturbances in blood flow. Turner syndrome (TS) is a genetic disorder occurring only in females where cardiovascular anomalies, particularly of the aorta, are frequently encountered. In this study, numerical simulations are applied to investigate the flow characteristics in four TS patient- related aortic arches (a normal geometry, dilatation, coarctation and elongation of the transverse aorta). The Quemada viscosity model was applied to account for the non-Newtonian behavior of blood. The blood is treated as a mixture consisting of water and red blood cells (RBC) where the RBCs are modeled as a convected scalar. The results show clear geometry effects where the flow structures and RBC distribution are significantly different between the aortas. Transitional flow is observed as a jet is formed due to a constriction in the descending aorta for the coarctation case. RBC dilution is found to vary between the aortas, influencing the WSS. Moreover, the local variations in RBC volume fraction may induce large viscosity variations, stressing the importance of accounting for the non-Newtonian effects.

Arterial pressure changes monitoring with a new precordial noninvasive sensor

Background

Recently, a cutaneous force-frequency relation recording system based on first heart sound amplitude vibrations has been validated. A further application is the assessment of Second Heart Sound (S2) amplitude variations at increasing heart rates. The aim of this study was to assess the relationship between second heart sound amplitude variations at increasing heart rates and hemodynamic changes.

Methods

The transcutaneous force sensor was positioned in the precordial region in 146 consecutive patients referred for exercise (n = 99), dipyridamole (n = 41), or pacing stress (n = 6). The curve of S2 peak amplitude variation as a function of heart rate was computed as the increment with respect to the resting value.

Results

A consistent S2 signal was obtained in all patients. Baseline S2 was 7.2 ± 3.3 mg, increasing to 12.7 ± 7.7 mg at peak stress. S2 percentage increase was + 133 ± 104% in the 99 exercise, + 2 ± 22% in the 41 dipyridamole, and + 31 ± 27% in the 6 pacing patients (p < 0.05). Significant determinants of S2 amplitude were blood pressure, heart rate, and cardiac index with best correlation (R = .57) for mean pressure.

Conclusion

S2 recording quantitatively documents systemic pressure changes.

Diastolic time - frequency relation in the stress echo lab: filling timing and flow at different heart rates

A cutaneous force-frequency relation recording system based on first heart sound amplitude vibrations has been recently validated. Second heart sound can be simultaneously recorded in order to quantify both systole and diastole duration.

AIMS

1- To assess the feasibility and extra-value of operator-independent, force sensor-based, diastolic time recording during stress.

METHODS

We enrolled 161 patients referred for stress echocardiography (exercise 115, dipyridamole 40, pacing 6 patients).The sensor was fastened in the precordial region by a standard ECG electrode. The acceleration signal was converted into digital and recorded together with ECG signal. Both systolic and diastolic times were acquired continuously during stress and were displayed by plotting times vs. heart rate. Diastolic filling rate was calculated as echo-measured mitral filling volume/sensor-monitored diastolic time.

RESULTS

Diastolic time decreased during stress more markedly than systolic time. At peak stress 62 of the 161 pts showed reversal of the systolic/diastolic ratio with the duration of systole longer than diastole. In the exercise group, at 100 bpm HR, systolic/diastolic time ratio was lower in the 17 controls (0.74 +/- 0.12) than in patients (0.86 +/- 0.10, p < 0.05 vs. controls). Diastolic filling rate increased from 101 +/- 36 (rest) to 219 +/- 92 ml/m2* s-1 at peak stress (p < 0.5 vs. rest).

CONCLUSION

Cardiological systolic and diastolic duration can be monitored during stress by using an acceleration force sensor. Simultaneous calculation of stroke volume allows monitoring diastolic filling rate.Stress-induced "systolic-diastolic mismatch" can be easily quantified and is associated to several cardiac diseases, possibly expanding the spectrum of information obtainable during stress.

Model-based analysis of effects of systolic blood pressure on frequency characteristics of the second heart sound

Previous studies have shown that it is possible to estimate pulmonary and systemic blood pressure using the spectral information of the second heart sound. A mathematical model for the vibration of the closed aortic valve is proposed in the paper with the introduction of the nonlinear elasticity of the aortic wall tissue. Based on the parametric analysis, the effect of the aortic blood pressure at the moment of valve closure on vibration of aortic valve and produced sound is examined. The simulation results show that the increasing aortic pressure results in an increase in frequency and amplitude of produced sound. The results of this study also suggest that it is the increasing resonant frequency of the blood column induced by elevated distending pressure that plays significant role in the process. The application of the modeling study could be extended to interpret the relations of the second heart sound to pulmonary blood pressure.

Heart sounds and murmurs: changes related to severity of chronic valvular disease in the Cavalier King Charles spaniel

Auscultatory, phonocardiographic (PCG), radiographic, and echocardiographic evidence of chronic valvular disease (CVD) were studied in 79 Cavalier King Charles Spaniels with a mean age of 7.6 years (SD 2.6). Cardiac murmurs were present in 59 of the dogs and the intensity of the systolic cardiac murmur, assessed by auscultation (grade 1-6), was correlated (P < .001) to the severity of CVD (heart failure class) and to the echocardiographic dimensions of the heart (left atrial ratio, La/Ao-d, and left ventricular end diastolic diameter, LVEDD) (both P < .001). The heart sounds and duration of electromechanical systole (Q-S2) were investigated in all dogs using measurements obtained from PCG recordings. Normal regression equations describing the relation between heart rate and systolic intervals (Q-S1, Q-S2 and S1-S2) were established based on observations in 11 normal control Cavalier King Charles Spaniels. The total electromechanical systole (Q-S2), Q-S1, and S1-S2 intervals in the 59 dogs were related to the corresponding normal regression equation. A shortening of Q-S2 and S1-S2 intervals were found in dogs belonging to heart failure class I (Q-S2; P < .01 and S1-S2; P < .05), class II, and classes III and IV (both P < .001). The ratio of the amplitudes of the first (S1) and second heart sounds (S2) measured on the PCG recordings was found to be increased in dogs belonging to class I (P < .01), class II, and classes III and IV (both P < .001). The relationship between cardiac dimensions (LVEDD and La/Ao-d) and S1a/S2a ratio was described by quadratic regression and found to be significant for both parameters (LVEDD; P < .001, R2 = .54 and La/Ao-d; P < .001, R2 = .63). The presence of a third heart sound (S3) was detected, using PCG, in 21 of the 68 dogs. The proportion of dogs exhibiting S3 increased with heart failure class (and increasing cardiac dimensions) (P < .001). These findings were confirmed by observations in 13 Cavalier King Charles Spaniels with cardiac failure progressing from heart failure class I to class II (Mean LVEDD from 30.2 to 35.2 mm and mean La/Ao-d from 1.09 to 1.43). An increase in intensity of the heart murmur, assessed by auscultation, increase in the ratio of the amplitudes of S1 and S2, as well as a shortening in Q-S2 and S1-S2 intervals (all P < .01) were found in these dogs.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical assessment of ventricular ejection dynamics with and without outflow obstruction

With the advent of multisensor micromanometric/velocimetric catheterization, digital angiography and Doppler and color echocardiography, extensive fluid dynamic quantitation is now possible in cardiology. Such high fidelity instantaneous measurements offer the clinician the prospect of identifying phasic changes in ventricular ejection dynamics that may disclose contraction abnormalities before overt muscle or pump failure is manifested. Accordingly, this review provides a basis for interpreting these measurements and a conceptual framework for understanding ventricular ejection dynamics with and without outflow obstruction. Necessary terminology and fluid dynamic background, including properties of flows generated by large transient forces, Euler and unsteady Bernoulli equations and local and convective acceleration gradients, are reviewed first. Physiologic aspects of ejection dynamics and transvalvular and intraventricular gradients without obstruction are discussed. Maximal outflow acceleration, rather than ejection velocity, coincides with the attainment of the early peak of the nonobstructive pressure gradients. These gradients are characteristically even more asymmetric than are the associated ejection velocity signals. Clinical correlations are introduced, beginning with obstructive transvalvular and subvalvular gradients in aortic stenosis and the phenomenon of recovery of pressure loss in the poststenotic dilation. The large obstructive gradients tend to be distinctively symmetric, as are the ejection waveforms, whose configuration they track more or less closely, depending on the degree of stenosis and relative preponderance of convective effects throughout ejection. Pitfalls in some unwarranted applications of the "simplified Bernoulli equation" are pointed out. Polymorphic gradients of hypertrophic cardiomyopathy, reflecting dynamically dissimilar intraventricular flow regimes in early, mid and late systole, are examined. Enormous late systolic gradients can be associated with progressive shrinkage of flow passage area and sharp increases in linear velocity while volumetric outflow is diminutive. The concept of ventriculoannular disproportion in dilated ventricles is defined and discussed. The implications of ejection fluid dynamics for systolic ventricular and myocardial loading are examined, and the concept of complementarity and competitiveness between intrinsic and extrinsic load components is introduced. Finally, critical research issues are identified and addressed. The primary emphasis is on using the basic principles of fluid dynamics to better understand ejection in the normal or abnormal human left ventricle and aortic root.(ABSTRACT TRUNCATED AT 400 WORDS)

Musical murmur and cardiac shudder

When echocardiographic studies show several structures vibrating at a similar frequency to an associated musical cardiac murmur, the structure vibrating most strongly may localize the origin of the murmur.

Influence of the aortic component of the second heart sound on left ventricular maximal negative dP/dt in the dog

Maximal negative left ventricular dP/dt is widely used as a measure of isovolumic muscular relaxation of the left ventricle. In the course of canine experiments designed to elucidate the hemodynamic events responsible for the aortic component of the second heart sound, high-fidelity left ventricular pressure and dP/dt signals were recorded and accelerations detected on the root of the aorta and epicardium at the cardiac apex. The second heart sound was coincident with maximal negative dP/dt and affected its magnitude to a variable and unpredictable extent. This may account for some of the unexpected variations in magnitude of maximal negative dP/dt that have been described in various disease states and in laboratory experiments where the effects of physiologic and pharmacologic interventions have been studied.

Frequency spectra of the first heart sound and of the aortic component of the second heart sound in patients with degenerated porcine bioprosthetic valves

To determine the usefulness of the frequency of heart sounds in the assessment of porcine bioprosthetic valve degeneration, frequency spectra of phonocardiograms of the first heart sound and the aortic component of the second sound were analyzed in 31 patients with degenerated porcine bioprosthetic valves. Comparisons were made with 35 control patients whose valves were inserted 1 month or less. Among 23 patients with degenerated porcine bioprosthetic valves in the mitral position, the dominant frequency of the first heart sound was 95 +/- 11 Hz, which exceeded the first sound in 18 controls (51 +/- 3 Hz) (p less than 0.01). The degenerated mitral porcine bioprosthetic valves of 14 patients showed calcification or fibrosis and the first heart sound in these patients was 115 +/- 16 Hz, which exceeded that of control subjects (p less than 0.001). The degenerated mitral porcine bioprosthetic valves of 9 patients showed torn leaflets only, and the first heart sound in these patients was 64 +/- 9 Hz, which did not differ from that of control subjects. In the aortic position, 8 valves were degenerated and the aortic component of the second sound was 109 +/- 12 Hz, which was higher than that in 17 control subjects (63 +/- 4 Hz) (p less than 0.001). Only 2 of these degenerated valves showed tears unaccompanied by calcific deposits or fibrosis, and the frequencies were comparable to that of control subjects. These observations indicate that the frequency of heart sounds in patients with degenerated porcine bioprosthetic valves becomes abnormally elevated when degeneration is accompanied by calcification or fibrosis, which causes the cusps to stiffen.

A mathematical model of aortic valve vibration

It has been shown experimentally that the second heart sound is produced by diastolic vibrations of the closed aortic valve. In the present paper a mathematical model of this vibration is developed from first principles. The model assumes a one dimensional but non-linear fluid behavior. The problem is coupled through a non-linear, planar valve. A solution is obtained using the method of characteristics developed in finite difference form. The resulting valve frequency and amplitude are in good agreement with patient data. The model predicts a strong dependency of response on the valve forcing function and valve stiffness; and a weaker dependency of response on valve mass.

Aortic valve closure and cardiac vibrations in the genesis of the second heart sound

Simultaneous M-mode echocardiograms and external phonocardiograms were recorded in 15 healthy subjects to evaluate the genesis of the second heart sound. The onset of the second sound was found synchronous with the coaptation of the aortic valve cusps and a sharp vibration on the aortic wall. The closed valve was oscillating for 30 to 45 ms after the coaptation of the cusps. Magnified echocardiographic studies of the interventricular septum revealed a consistent, momentary quiver across the septal myocardium a mean of 4 ms after the onset of the second sound. In most subjects, a transient myocardial vibration was observed in temporal association with the first heart sound as well. The present observations suggest that the aortic valve closure initiates the production of the second heart sound, the main audible component resulting, however, from vibrations in the cardiac structures after the valve closure.

Frequency analysis approach to the origin of the first and second heart sounds

Catheter-tipped micromanometers were used to simultaneously record left ventricular and aortic pressures, and left ventricular and aortic internal phonocardiograms in order to determine if they had a common mode of origin and propagation. Spectrographic analysis showed that even with high-pass filtration the phonocardiogram obtained with a commonly used system (Millar) contained large amounts of energy in the subaudible frequency range (below 40 Hz). It was possible to derive close facsimiles of the phonocardiograms by double differentiation of the corresponding pressure pulse and conversely to derive the pressure pulse by double integration of the phonocardiograms. The propagation velocities of the first heart sound, second heart sound, and the foot of the aortic pressure pulse were found to be similar and were respectively, 4.3 +/- 0.2, 4.6 +/- 0.3, and 4.2 +/- 0.2 m/sec (+/- SE). These data support the concept that the low frequency pressure variations produced by the heart, which predominate in the left ventricular and aortic pressure pulse waveforms, are generated and propagated in the same manner as the high frequency pressure variations, which are the first and second heart sounds.

What is new in the clinical evaluation of patients with ischemic heart disease?

New information related to the mechanism of heart sound and murmurs, and a more detailed understanding of some aspects of cardiac function, permit a more complete and accurate interpretation of auscultatory signs in patients with ischemic heart disease. The diminished second sound in such patients is now recognized to reflect isovolumic relaxation, and the diminished first sound probably reflects impaired isovolumic contraction. Ejection murmurs can be interpreted in light of their relation to turbulent flow. The variability of regurgitant murmurs in the papillary muscle dysfunction syndrome seems to be explained by new observations related to the function of the papillary muscle.

Invasive and noninvasive phonocardiography and orifice-view aortography in the diagnosis of left ventricular outflow obstruction

Phonocardiography and orifice-view aortography for the detection of valvular and subvalvular stenosis is reviewed. Intracardiac phonocardiography may be useful in detecting a left ventricular outflow tract obstruction, and in distinguishing it from other conditions that can produce an apparent pressure gradient during cardiac catheterization. The frequency analysis of heart sounds on noninvasive phonocardiograms may be useful in identifying subclinical aortic stenosis. Orifice-view aortography can show the anatomy of deformed aortic valves and is useful in measuring the orifice area. In patients with heavily calcified valves, plain orifice-view roentgenograms may enable one to assess the valve area. Therefore the use of these techniques in selected patients may help establish a definitive diagnosis.

Analysis of mitral and aortic valve vibrations and their role in the production of the first and second heart sounds

Using a theoretical approach and stress and vibration analysis, formulae have been derived for the frequencies that would be generated by considering the mitral and aortic valve leaflets as vibrating membranes. In the analysis the physical characteristics of the valves, such as loading, valve geometry and valve tissue mechanical properties, were taken into consideration. The analysis showed that the fundamental frequencies for both the vibrating valves increase with the pressure difference across the valve membranes. This suggests that for a better understanding of the role played by the vibrating heart valves in the production of heart sounds, data are needed on the relation between these frequencies and the pressure difference across the valves. Unfortunately such data do not seem to be available.

Phonocardiography in the horse: 2. The relationship of the external phonocardiogram to intracardiac pressure and sound

The paper describes observations during individual cardiac cycles on the changing pressures and sounds recorded from the various chambers of the heart and aorta, related to phonocardiograms from an external microphone hand-held over the cardiac area. The majority of the first sound appears to arise from the left side of the heart after the AV valves have closed and the second sound is a consequence of sudden deceleration of blood against already closed semilunar valves. Systolic murmurs at the aortic root may be benign from increased flow and turbulence at the peak of ejection but these may not be recorded externally.

Phonocardiography in the horse: 1. The intracardiac phonocardiogram

Using microtransducers, the intracardiac phonocardiogram was recorded in 8 horses from the right heart and in 6 of them also on the left side. All 4 heart sounds were recorded but not in all sites. Their timing was related to pressure events. Systolic ejection murmurs were recorded in both the pulmonary artery and the aorta. Diastolic murmurs were recorded in 2 horses with aortic regurgitation, with maximum amplitude in the left ventricle. The findings were similar to those reported in man and agree with some of the recent concepts on heart sound production.

Valve origin of the aortic incisura

The occurrence and magnitude of the incisura of the central aortic pressure were shown in 66 patients to depend on the functional state of the aortic valve. In normal subjects and children with congenital aortic stenosis (with thin flexible leaflets), the incisura ranged between 6 and 14 mm Hg. With aortic regurgitation, the incisura diminished as the severity of regurgitation increased. With calcific aortic stenosis, the incisura was smaller or absent. These observations imply a valve mechanism productive of the incisura. In vitro studies of human aortic valves confirmed these observations. Additional in vitro studies with high speed cinematography (2,000 frames/sec) of a stented normal porcine valve also showed that early diastolic stretch and recoil of the leaflets occurs. These results indicate that in the presence of a normal or diseased aortic valve the aortic incisura is produced primarily by valve distension or recoil, respectively. Distension and rebound of the aortic walls do not appear to contribute significantly in the presence of a normal or a diseased valve. Because acquired aortic valve disease affects the magnitude of the central aortic incisura, inspection of the incisura may be of ancillary valve in evaluating the pathologic state of the aortic valve.

Significance of momentary pressure changes during isovolumic relaxation

Sudden momentary fluctuations of left ventricular, aortic, right ventricular, and pulmonary arterial pressure were noted during isovolumic relaxation of the respective ventricles. The presence of such transients raised questions related to their meaning and significance. The purpose of this report is to emphasize the nonartifactural nature of these pressure transients and to describe their origin and significance in the cardiac cycle. Pressure transients were observed in 31 of 32 patients with normal aortic valves, and in 17 patients with normal pulmonary valves in whom right-sided measurements were made. Such transients, however, were absent on the left ventricular and aortic pressure recordings of three patients with calcific aortic stenosis. These sudden changes in pressure are indicative of momentary compressions and rarefactions of the blood that occur within the ventricles and their respective arterial chambers. Whenever present, pressure transients were noted to occur coincident with the major aortic or pulmonary components of the second sound. Since intraaterial sound pressure is derived from the pressure signal by litering the low frequencies and amplifying the high frequencies, one can deduce that intraarterial sound pressure is in fact a representation of these pressure changes. The recognition of these pressure transients on an otherwise smooth ventricular, aortic, or pulmonary arterial pressure places in proper perspective their role in the production of the second heart sound.

Artifact production with micromanometers used to record intracardiac pressure and sound

In horses experimental right and left heart catheterization using a catheter with two microtransducers 9 cm apart, usually in a transvalval position produced pressure and sound artifacts that confounded the diagnosis. Most were probably due to malpositioning resulting in movement through a valve during recording or impingement on the valve cusps or the chordae tendineae or lodgement in the apex of the heart. The recognition of these artifacts is particularly important in studies of large animals in which catheter siting cannot be monitored by radiography.

The aortic closure sound in pure aortic insufficiency

The second sound in aortic insufficiency has been described as accentuated, normal, or moderately diminished. A study of intracardiac phonocardiograms was performed to evaluate its intensity and to eliminate extracardiac factors. Pressure and intracardiac sound measurements were made in 28 patients undergoing diagnostic cardiac catheterization. Recordings were obtained above the aortic valve and within the left ventricle in 14 patients with normal aortic valves and 11 patients with aortic insufficiency uncomplicated by aortic stenosis. The amplitude of the aortic closure sound in the patients with pure aortic insufficiency, 1000 +/- 100 dynes/cm2, was significantly lower than in those patients with normal aortic valves, 3100 +/- 200 dynes/cm2 (P less than 0.001). The results indicate, therefore, that the presence of aortic insufficiency causes a diminished amplitude of the aortic closure sound. These results are supportive of the theory that the second heart sound is caused by diastolic vibrations of the closed aortic cusps. Diminished valvular vibrations and sound would occur in pure aortic insufficiency if the valve is unable to properly tense during diastole, or if the rate of development of the driving pressure is diminished.