Changes In Left Ventricular Diameter Research Articles

An ultrasonic gauge for measurement of ventricular dimensions.

Abstract The paper describes a relatively simple and inexpensive ultrasonic instrument which is used for the continuous measurement of organ dimensions. A d.c. voltage is produced at the output by measuring the transit time of a burst of ultrasound to pass from one transducer to the other. The instrument is easily calibrated and a linear range of 100 mm length has been achieved. Digital technique is used throughout and it is small in size and self-contained, so that it can be easily converted to a portable instrument. This instrument has been used in studies concerned with left ventricular diameter changes on dogs under drug treatment.

Specificity of autonomic influences on cardiac responses during myocardial ischemia.

A possible role of the autonomic nervous system in the left ventricular response to acute regional myocardial ischemia was sought in conscious dogs instrumented for measurement of left ventricular pressure, internal diameter, and aortic flow. Ischemia produced by occluding the left circumflex coronary artery caused tachycardia and reduced contractility. Changes during control occlusions were compared with those during occlusion.s after beta-adrenergic blockade, parasympathetic blockade, and combined sympathetic and parasymphatetic blockade. Beta-blockade did reduce the tachycardia and slightly reduced left ventricular diameter changes in response to coronary occlusion. Results obtained in animals following surgical cardiac sympathectomy indicated reduced tachycardia and no effects on other parameters. The principal effect of parasympathetic blockade was to augment the increase in end diastolic diameter during occlusion Right atrial pacing indicated this change was due to higher initial heart rates. Combined parasympathetic and sympathetic blockade did not alter inotropic responses to coronary occlusion. Results indicated that inotropic support due to changes in activity in autonomic nerves is not increased during acute occlusion of the left circumflex coronary artery.

Left ventricular dimensions recorded by sonocardiometry.

A new technic for continuously recording the dimensions of internal organs in intact unanesthetized animals has been developed as a modification of sonar technics. A sound is emitted by a small barium titanate crystal mounted on one side of the left ventricle, and the time required for the sound waves to pass through the chamber to another crystal on the opposite side is monitored 1,000 to 2,500 times/sec. Such crystals have continued to function reliably for more than 3 months after installation in the animal. Changes in left ventricular diameter have been recorded during spontaneous cardiac responses to various conditions including physical exertion on a treadmill.

Continuous measurements of left ventricular dimensions in intact, unanesthetized dogs.

Left ventricular dimensions have been directly measured for extended periods of time in intact unanesthetized dogs under various conditions. The diameter of the left ventricle during diastole is very large in relation to the change in diameter during each cycle. Thus, considerable quantities of blood remain within the chamber at the end of systolic ejection. The stroke output can be increased by either more complete systolic ejection during exercise or by greater diastolic filling during a startle reaction. Accelerated heart rate occurs in both cases. Changes in left ventricular diameter occur very rapidly, often being manifest within the duration of a single cardiac cycle. Mechanisms by which changes in ventricular size can be directly affected by neural and hormonal influences are briefly considered.