A mechanical flow controller manipulates the valve to maintain the downstream flow rate in spite of the leakage. The size of the valve opening at time t is V(t). The flowrate is measured by the vertical position of the float F(t). The gain of the controller is A/B. This arrangement would be entirely impractical for a modern flow control application, but a similar principle was actually used in ...

Echocardiography (M-mode and cross-sectional) disclosed premature opening of the pulmonary valve (very deep "a" wave) in a young man who underwent tricuspid valvulectomy without valve replacement 32 months before for refractory bacterial endocarditis. Cardiac catheterisation showed a prominent atrial wave on the pulmonary artery pressure curve. Thus, part of the right ventricular ejection appea...

JOHN WRIGHT This has been evolved with a modified pulse duplicator and the use of a hot film probe for measuring velocity, direction, and turbulence. Many of the commercially available mitral valve prostheses are being investigated for their flow characteristics. In addition, efficiency is being examined and some unusual findings point to the possibility of a hydraulic ram effect in the normal ...

Systolic pressure in the pulmonary artery was estimated from the interval between pulmonary valve closure and tricuspid valve opening, and the heart rate using a nomogram previously described. The timing of valve movements was recorded by Doppler ultrasound. The estimated pressure correlated well with that obtained at catheterisation in 45 of 48 patients with pulmonary hypertension. Instantaneo...

The anterior commissure defect of tricuspid valve may leave remnant regurgitation with inadequate leaflet coaptation after simple patch closure of the defect. A 19-year-old man underwent commissuroplasty for the anterior commissure defect caused by tricuspid valve endocarditis. Significant remnant regurgitation after patch closure of the anterior commissure defect was successfully solved by mod...

Background. Percutaneous retrograde nontransseptal balloon mitral valvuloplasty is a new technique developed in our institution for opening a stenotic mitral valve. This technique is based on a new, externally steerable cardiac catheter that enters the left atrium retrogradely via the left ventricle. Methods and Results. The technique was used in 86 consecutive patients (18 men and 68 women; me...

Of a total of 30 autologous fascia lata aortic, mitral, and tricuspid valve replacements in 25 patients, opening sounds were heard or recorded in association with 24 valves. Murmurs were heard during forward flow across 26 of the valves. In no patients did the sounds or murmurs develop or progress during the period offollow-up but were present immediately after operation. It is felt that these ...

Factors affecting the capacity of continuous centrifugals handling "C" massecuite are examined after the completion of several test runs on various machines at different factories. Feed pipe sizing, water addition and positioning, feed distribution, scaling of screens, etc., are discussed and recommendations made. Introduction For several years continuous centrifugals (typically BMA K850) opera...

Real-time, cross-sectional echocardiograms of the pulmonary valve were recorded in 22 patients with valvular pulmonary stenosis (VPS) (14 mild, eight moderate or severe) and 25 normal subjects. Normally during systole the pulmonary leaflet echoes moved rapidly apart and in the fully opened position lay parallel and in close apposition to the margins of the pulmonary artery. In 20 of 22 patients...

The aortic valve operates in a complex haemodynamic environment, opening and closing over 100,000 times a day. When complications arise, such as aortic stenosis, prognosis can be very poor, leading to death within the first few years. Surgical valve replacement is currently the standard treatment for aortic stenosis. A thorough understanding of the anatomy and function of the native valve is im...