In each of 10 mongrel dogs anesthetized with alpha chloralose, strain-gauge arches were sutured to five epicardial and three endocardial locations. Comparisons of contractile force responses during stimulation of the left and right roots of the same segmental level revealed several differences dependent upon the particular myocardial area observed. Of the three left ventricular endocardial areas studied, the interventricular septum was the most responsive, particularly during stimulation of the right roots. The basal free wall and posterior papillary muscle were more responsive to left-root than to right-root stimulations. Epicardial responses were consistent with those previously reported. Generally, all areas responded to the greatest degree during stimulation of the second roots with the third and first next in order of effectiveness. Although stimulation of each level of preganglionic outflow activated all epicardial and endocardial segments of the myocardium, the magnitude of the changes in contractile force were highly variable dependent upon the specific level of preganglionic outflow and the location of the strain-gauge arch.
Structure-function studies were performed upon the canine in situ interventricular septum. In response to both neural and chemical stimulation, the left septal apex generated greater percent change in contractile force, and contracted earlier than did the basal portion. Under positive inotropic stimulation the left septum contracted earlier and more forcefully than the right. Coarctation of the pulmonary artery elicited moderate augmentation in right septal contraction with no change in the left, whereas partial occlusion of the aorta resulted in increased contractile force in both septa with predominance on the left. Stimulation of the peripheral end of the cervical vagosympathetic trunk induced comparable suppression in contractile force of all surfaces of the septum as well as in both right and left epicardial muscle segments. Based upon careful anatomical dissection of fresh specimens, the interventricular septum was found to be comprised of thin right and relatively thick left muscle masses. The septum may be divided into three different structural zones. The cranial portion is small and consists of a very thin membranous region. The muscular septum is divisible into cranial and caudal portions, each demonstrating characteristic contractile behaviors which are exaggerated under neurally and chemically augmented states and which play an important role in regulation of cardiac output.
The structure-functional dynamics of the right ventricle differ importantly from the left ventricle. By cauterizing the right ventricular free wall, Kagan concluded that the right ventricular pressure generation was a function primarily of the septum (1). This view is compatible with the concept that the right ventricle is primarily a volume pump. Recently however, significant pressure gradients have been demonstrated from inflow to outflow tracts (from sinus to conus) (2) and these differences have been related to the regional dynamic behavior (3) as determined by architectural differences between the sinus and conus (4). However, the close dynamic relationships between the free wall and septum have been completely neglected when considering right ventricular function. Recent measurements of intramyocardial pressures within the interventricular septum demonstrate significant regional contractile changes under neural and humoral control. This report describes the behavior of both the free wall and the septal components of the right ventricle, and the analysis of the relative independence of this behavior with respect to left ventricular function.Methods. Sixteen open-chest dogs, weighing 18-24 kg, under phencyclidine hydrochloride (2 mg/kg im) and a-chloralose (80 mg/ kg iv) anesthesia were studied during positive pressure respiration. A standard limb lead electrocardiogram was utilized and two button catheters (2) placed in the lateral wall of the right ventricular sinus and conus connected to P23Db Statham transducers. Two Model SA-SA-M-7BW Scientific Advances subminiature pressure transducers were placed halfway through the right ventricular myocardium, one in mid-sinus and
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