Heart disease

Despite progressively falling cardiac output, increased peripheral resistance supports arterial BP until relatively late, partly by an a-adrenergic mechanism. Thus, increased peripheral resistance is not affected by |3-blockade, but is opposed by a-block-ade. Ultimately BP tends to decline precipitously—the “last drop” phenomenon. (In experimental animals that are anesthetized or not recovered from surgery, BP falls […]

The progressively increasing diastolic chamber pressures ultimately equilibrate (averaged over the respiratory cycle) throughout the heart. The typical range of 15 to 30 mm Hg applies mainly to euv-olemic patients and animals. All physiologic phenomena in tamponade occur earlier and at lower pressures in hypovolemic patients and later and at higher pressures in hypervolemic than […]

Tamponading pericardial fluids compress the heart throughout systole and diastole. Although the atria fill continuously, blood mainly enters the heart when blood is leaving it during the right and left ventricular ejection periods, since ventricular ejection expels blood, reducing ventricular volumes. Ejection thus transiently reduces pericardial pressure, transiently increasing transmural pressure. Ejection simultaneously aids atrial […]

Since the systemic and pulmonary venous beds must generate sufficient pressure to fill both sides of the heart, cardiac filling is supported by a parallel rise in systemic and pulmonary venous pressures which, in tamponade, are determined primarily by pericardial rather than myocardial compliance. Secondarily, of course, cardiac chamber compliance is reduced by pericardial compression […]

For each cardiac chamber, its transmural pressure—intracardiac pressure minus pericardial pressure—is a principal determinant of its filling. (Transmural pressure is a true filling [distending] pressure that contributes to ventricular preload.) Normal pericardial pressure is lower than the right atrial mean and right ventricular diastolic pressures so that right atrial transmural pressure (right atrial pressure minus […]

Figure 2 schematizes the major hemodynamic events and compensatory mechanisms in uncomplicated cardiac tamponade. When increasing pericardial contents put the in-trapericardial pressure on the steep portion of its J-shaped pressure-volume curve (Fig 1), the cardiac chambers must operate on parallel steep pressure-volume curves, a form of diastolic dysfunction where, at any diastolic volume, there is […]

Clinically significant cardiac compression by pericardial fluids depends on three interrelated conditions. The pericardial contents must do the following: (1) fill the relatively small pericardial reserve volume (Fig 1)—the volume which, added to the normal 15 to 35 mL of pericardial fluid, will just distend the parietal pericardium by filling its numerous recesses and sinuses; […]

Cardiac tamponade is always life threatening and nearly always requires urgent and precise therapeutic intervention. It is perhaps unique in that appreciation of its pathophysiologic state is essential to precise diagnosis and rational treatment. Since the 19th centuiy, investigations in experimental animals provided a basic understanding that has been continually refined by recent investigators to […]

Reagents Dibutyryl cAMP ((Bu)2cAMP), U73122, 22(R)-hydroxycholesterol, H8Q, PMA, hCG, and Waymouth MB 752/1 medium were obtained from Sigma (St. Louis, MO). Fetal bovine serum (FBS), gentamicin, and horse serum were purchased from Invitrogen Life Technologies (Carlsbad, CA). GF-10Q203X (Bisindolylmaleimide I) and Go6983 were purchased from Calbiochem (San Diego, CA). Cell Culture and Animals R2C cells […]

The nerve content of the conduction system varies in mammals. There are three types. In ruminants (sheep, cattle), the atrioventricular node, bundle, and bundle branches all contain ganglion cells and nerve fibers. In the hog and horses, nerve cells are lacking in the bundle and bundle branches. However, nerve fibers are copiously present throughout the […]