Changes In Cardiac Size Research Articles

Cardiac function in acute hypothyroidism.

It has been established that chronic hypothyroidism may affect cardiac function by several mechanisms. It is not known how long the patient has to be hypothyroid for cardiac involvement to develop. This study was undertaken to assess the effect of a short period of hypothyroidism (10 days) on cardiac function. Nine patients who had had total thyroidectomy, had received ablative radioiodine for thyroid cancer and were euthyroid on replacement therapy were studied while both euthyroid and hypothyroid. Cardiac assessment was performed by X-ray, ECG, echocardiography and gated blood-pool scans. After 10 days of hypothyroidism, the left-ventricular ejection fraction failed to rise after exercise in 4 of the 9 patients studied, which was significant (P less than 0.002). No significant changes in cardiac size or function at rest were detected. This functional abnormality in the absence of any demonstrable change in cardiac size and the absence of pericardial effusion with normal basal function suggest that short periods of hypothyroidism may reduce cardiac reserve, mostly because of alterations in metabolic function.

Diagnostic Radiology and Nuclear Cardiology: Their Use in Assessment of Equine Cardiovascular Disease

Survey thoracic radiography, although limited by physical considerations in the adult horse, can supply clinically useful information about changes in cardiac size and function. The radiographic features of cardiomegaly, altered pulmonary circulation, pulmonary edema, and pleural effusion as manifested in the horse are discussed. Nuclear cardiology can be performed in the standing horse. The initial transit of a radioactive tracer through the central circulation provides information about cardiac chamber size, efficiency of ventricular contraction, valvular competence, and presence of intracardiac or extracardiac shunts. Computer analysis of similar studies allows quantitation of several useful cardiac parameters including ventricular ejection fraction and shunt size (QP/QS). Gated blood pool nuclear studies are better suited to evaluate cardiac response to stress but are difficult to perform in the conscious horse with standard imaging equipment.

Function of the pericardium and pericardioperitoneal canal in elasmobranch fishes.

Previous studies of cardiac function in elasmobranch fishes have not included the influence of the pericardioperitoneal canal on pericardial pressure and volume and thus on cardiac function. Accordingly, we studied the function of the pericardium and pericardioperitoneal canal in sharks and rays. We found negative pericardial pressure that rose to a plateau of approximately 0 mmHg when fluid was infused into the pericardium with the canal undisturbed. However, this pericardial pressure elevation caused severe cardiac tamponade. After the canal was occluded, the pressure plateau was substituted with an exponential rise. We injected radioisotopes into the pericardial cavity and obtained scintigrams several hours later. The scans and counts of body fluids and tissues indicated absorption, disputing the suggestion that the primary function of the canal may be inadequate absorption of pericardial fluid. We conclude that the pericardioperitoneal canal maintains negative pericardial pressure, which is a prerequisite in elasmobranch fishes and may serve to regulate pericardial pressure level to optimize cardiac function in relation to changes in cardiac size.

Respiratory system compliance as seen from the cardiac fossa.

Changes in cardiac size and shape should impose stresses on the surrounding lung and chest wall. To examine pressure-volume relationships of the cardiac fossa we measured pressures required to increase the pericardial volume of freshly killed dogs at different levels of lung inflation, first by expanding the pericardium uniformly and then by expanding only the left ventricle. In both cases we obtained linear pressure-volume relationships, the slopes of which expressed an apparent compliance. Compliance decreased as lung volumes were increased by raising end-expiratory pressure, and compliance with symmetrical pericardial filling exceeded that with asymmetrical (left ventricular) distension. These compliances were compared with the total respiratory system compliance measured during tidal ventilation, and we found that the compliance of the cardiac fossa was significantly less than would be predicted from lung and chest wall compliances as classically measured. We concluded that the respiratory system imposes a finite compliance load on cardiac filling that raises local epicardial pressure above ambient pleural pressure. This respiratory system load depends upon lung volume and the cardiac shape change.

Videodensitometric system for measurement of vessel blood flow, particularly in the coronary arteries, in man

A system that allows the objective determination of blood flow in individual blood vessels (that is, coronary arteries) in intact man is described. Roentgenographic images (produced at a rate of 60/sec) are recorded on video tape before and during a single injection of radiopaque contrast material into the circulation and replayed any number of times. The dilution and dispersal of this contrast material can then be quantitatively determined from simultaneous indicatordilution (roentgen density) curves obtained from any site within the X-ray field by multiple roentgen videodensitometric analyses of the video tape record. Cyclic nonspecific changes in roentgen density due to motion of the vessel or catheter and changes in cardiac size and position are compensated for in real time measurements by digital computer. By obtaining the difference in mean transit times from indicator-dilution curves a measured distance apart along a coronary vessel, mean blood velocity can be determined and blood flow can then be calculated as the product of velocity and the vessel cross-sectional area obtained from biplane orthogonal roentgenograms. The effects of persisting contrast medium in the myocardium and cardiac chambers superposed in the videodensitometric sampling system are minimized by computer dynamic background cancellation techniques. Simultaneous determination of flow values in a canine "coronary" artery by roentgen videodensitometry and electromagnetic flowmeter show a good correlation (<i>r</i> = 0.95) among flow values of less than 150 ml/min. Similar coronary artery-roentgen density curves suitable for videodensitometric determination of flow have been obtained from clinical catheterization studies in man.

The size of the heart during the course of essential hypertension.

Changes in cardiac size, as measured by teleroentgenogram, in the course of essential hypertension were studied in 45 patients. Although the majority showed progressive cardiac enlargement from the discovery of hypertension, a goodly number revealed a stationary cardiac size for 10 or more years. Congestive heart failure was found to occur with normal heart measurements. Weight loss did not affect a reduction in cardiac size. Normal cardiac measurements for a decade or more were not unusual. Marked cardiac enlargement was present in several patients for 10 years with little functional limitation. Prognosis on the basis of cardiac size alone was unwarranted.