Influence of the pericardium on left ventricular diastolic pressure-volume curves in dogs with sustained volume overload

The pericardium is largely responsible for displacement of the left ventricular diastolic pressure-volume curve observed after acute volume loading in dogs. Likewise the pericardium has been considered likely to play a role in displacement of the curve in patients with acute cardiac failure and in shifts following manipulation of afterload. This study was designed to examine the influence of the pericardium on the diastolic pressure-volume relation of the left ventricle when volume load is more sustained, a setting relevant to observations made in patients with heart failure. We measured left ventricular pressure and volume in six conscious dogs with sustained volume overload (mean left ventricular end-diastolic pressure 21 mm Hg, left ventricular end-diastolic volume 149% of the upper limit of normal for our laboratory) produced by aortocaval shunt created 7 to 29 days earlier. Simultaneous left ventriculograms and pressures were obtained before and during nitroprusside infusion with the pericardium intact and in four dogs the studies were repeated 7 to 15 days after pericardiectomy. In all six dogs with intact pericardium, nitroprusside displaced the entire pressure-volume curve downward whereas after pericardiectomy, the pressure-volume data points obtained before and during nitroprusside infusion fell on a single curve. These results were similar to those previously reported for acute volume overload. Nitroprusside did not alter the time course of left ventricular pressure fall during the isovolumic period of diastole either before pericardiectomy (28.8 +/- 10.2 sec,-1, 28.4 +/- 11.9 sec-1) or after (28.8 +/- 6.7 sec-1, 26.1 +/- 7.2 sec-1). These data indicate that in dogs subjected to volume overload sustained for periods of up to 29 days, the pericardium affects the left ventricular diastolic pressure-volume curve and contributes to the elevation of left ventricular filling pressure through upward displacement of this curve.

Effects of oxygen breathing on pulmonary vascular input impedance in patients with pulmonary hypertension

The effect of oxygen breathing on the stiffness of the large pulmonary artery has not been elucidated. We analyzed the proximal pulmonary arterial impedance with a multisensor catheter in ten patients with pulmonary arterial hypertension (PAH), eight patients with pulmonary venous hypertension, and six control subjects. The stiffness of the vessel was quantified by the characteristic impedance (Zo) and compared with the plasma norepinephrine level. Ten minutes of high-oxygen breathing decreased the Zo (from 78 +/- 18 to 57 +/- 14 dynes.sec.cm-5, p less than 0.01) and pulmonary arterial resistance in all the cases with PAH. In this group, norepinephrine also decreased (from 381 +/- 89 to 319 +/- 77 pg/ml, p less than 0.01) following the correction of hypoxemia. Yet, those parameters did not change in the other two groups. These results indicate that in patients with PAH, oxygen breathing can reduce the stiffness of the main pulmonary artery because of the sympatholytic effect.

Assessment of the magnitude of aortic regurgitation by dye injection into the descending aorta

A technique simpler than the angiographic method for estimating aortic regurgitant volume was tried with 31 patients with aortic insufficiency. During cardiac catheterization, we injected dye into the descending aorta while recording the dye dilution curve in the left ear. The distance between the aortic arch and the tip of the catheter at the lowest point from which the injected dye could be detected in the left ear was rated in terms of the number of corresponding vertebral bodies. This "distance score" closely correlated with the regurgitant stroke volume and with the fraction to total stroke volume, which were measured by angiocardiography (r = 0.927, p less than 0.001; and r = 0.900, p less than 0.001, respectively). The correlation coefficients of the aortographic grade to those parameters were not as high as they were in the relationship of the score to the same parameters. Therefore, these results indicate that the "distance score" is a practical method for assessing the magnitude of aortic regurgitant volume.

The effect of pericardium on the diastolic properties of the heart--experimental studies on volume load and on acute ischemia in open chest dogs

We studied the effect of the pericardium on the end-diastolic pressure-segment length (P-L) relation in volume loading (Experiment I) and in acute ischemia (Experiment II). Experiment I: In 6 open chest dogs, segment length of left and right ventricles were measured using ultrasonic crystals during blood infusion. Drawing end-diastolic pressure (P, on ordinate) against segment length (L, on abscissa), the P-L curve with pericardium positioned upward compared to that without pericardium. The slopes (b) of the exponential curve (P = aebL) with pericardium were steeper than those without pericardium in both ventricles. The difference between the slopes with and without pericardium was significantly larger in the right ventricle (RV, 0.30 +/- 0.10, mean +/- SEM) than in the left ventricle (LV, 0.05 +/- 0.02, p less than 0.05). These results show that the pericardium inhibits the distensibility of the free wall more in RV than in LV, and enhances a mechanical coupling of both ventricles during volume over-load. Experiment II: In 8 open chest dogs, segment lengths of ischemic and non-ischemic regions in LV were measured after left circumflex coronary occlusion. When the segment lengths and LV pressure became stable, a pericardiectomy was performed. After the pericardiectomy, whereas heart rate and LV systolic pressure did not change, end-diastolic segment length in the ischemic region further lengthened (12.0 +/- 0.2 to 12.5 +/- 0.2 mm, p less than 0.01) and that in the non-ischemic region did not change despite the concomitant fall in LV end-diastolic pressure (EDP, 11.9 +/- 0.6 to 9.8 +/- 0.6 mmHg, p less than 0.01). These results suggest that the pericardium alters the LV end-diastolic pressure-volume relation and is one of the factors contributing to an increase in LVEDP during acute ischemia.

Cineventriculographic analysis of the ventricular septal motion during stimulation of various pacemaker sites

By means of cineventriculography, contraction pattern of the ventricular septum was studied during electrical stimulation of the right atrium (RA), outflow tract (RVO) and apex (RVA) of the right ventricle and apex (LVA) and lateral wall (LVL) of the left ventricle. RA pacing produced a monophasic shortening of the septal hemiaxes after initial lengthening for about 40 msec from R wave of ECG. In contrast, ventricular stimulation near the septum (i.e. RVO, RVA and LVA) resulted in a biphasic and decreased contraction of the septal wall, in which an early preejection shortening was followed by a brief lengthening and second shortening. LVL pacing showed a monophasic and increased contraction of the septal wall. The biphasic motion of the septal wall was likely to be related to the abnormal mechanical contraction caused by the abnormal conduction sequence of ventricular depolarization. On the other hand, the lateral wall demonstrated a biphasic and decreased contraction during LVL pacing, and a monophasic and increased contraction during RVO, RVA and LVA pacing. Thus, the biphasic and diminished contraction at the site of electrical stimulation was compensated by the monophasic and forceful contraction of the contralateral wall. It is considered that the ventricular septum plays an important functional role in regulation of cardiac performance.

Alteration of the left ventricular diastolic pressure-segment length relation produced by the pericardium. Effects of cardiac distension and afterload reduction in conscious dogs

Left ventricular pressure and segment length were measured in seven conscious chronically instrumented dogs with the pericardium intact and 3-9 days after pericardiectomy. Diastolic pressure-length plots were obtained under control conditions and after acute volume loading followed by sodium nitroprusside infusion. In all dogs with intact pericardium, volume loading displaced the entire diastolic pressure-length curve upwards and sodium nitroprusside shifted it toward control. After pericardiectomy the pressure-segment length data during control, volume loading and sodium nitroprusside fell on a single curve (intercepts and slopes not statistically different); After dextran infusion, intrapericardial pressure rose from control 1.5 +/- 0.7 mm Hg to 8.2 +/- 0.5 mm Hg, and it fell to 4.8 +/- 0.1 mm Hg after nitroprusside. Therefore, in acute cardiac dilatation the pericardium contributed significantly to the increased left ventricular diastolic pressure and to the fall during sodium nitroprusside infusion and appeared responsible for shifts in the diastolic pressure-segment length relation.

Pulmonary arterial pressure-flow characteristics in atrial septal defect: comparative study with ventricular septal defect and patent ductus arteriosus

Pulmonary arterial pressure-flow relation was studied in 142 patients with artrial septal defect (ASD) and was compared with that of 139 patients with ventricular septal defect (VSD) and was compared with that of ductus arteriosus (PDA). The incidence of pulmonary arterial mean pressure (PAm) over 25 mmHg was 21 percent in ASD, 36 percent in VSD and 43 percent in PDA, and that over 40 mmHg was 3 percent, 23 percent and 19 percent, respectively. Large left to right shunt over 50 percent was found more frequently in ASD (58 percent) than in VSD (22 percent) and PDA (30 percent). When patients were separated into 2 groups at a PAm of 40 mmHg, lower pressure group showed a positive correlation between PAm and left-to-right shunt in each disease, although the correlation was poor in ASD (r equals 0.23) as compared with VSD (r equals 0.49) and PDA (r equals 0.47). The slope of the regression line was less steep in ASD (0.08) than in VSD (0.17) and PDA (0.14). It is considered that pulmonary hypertension in ASD develops on the basis of pulmonary vascular changes caused by prolonged hyperkinetic circulation.

Regional contraction patterns of the left ventricle during ventricular pacing

Ten mongrel dogs were used to assess regional myocardial function in response to electrical pacing form the inflow (RVI), outflow tracts (RVO), and apex (RVA) of the right ventricle and apex (LVA) and lateral wall (LVL) of the left ventricle. Strainguauge arches were sutured to the epicardial segments of the apical and lateral walls of the left ventricle and their mechanical shortening was measured during right artial (RA) and during ventricular pacing. The onset of shortening of two segment did not differ significantly in RA and RVI pacing, while the stimulation of RVA and LVA caused the initial contraction of the apical segment, and RVO and LVL pacing caused that of the lateral segment; i.e. RVA and RVO pacing resulted in left ventricular asynchrony of contraction similar to LVA and LVL pacing, respectively. Asynchrony of contraction was not accompanied by a uniform change in peak tension of regional myocardial segments, but prejection tension rose and ejection tension fell at the pacing site. The reduction in mean aortic pressure inversely correlated with the prolongation of the time interval between the onset of shortening of two segments during left ventricular pacing. The decrease in cardiac performance observed during ventricular pacing was related to the severity of asynchrony rather than the direction of the ventricular depolarization or change in regional myocardial tension.

Effects of isometric handgrip exercise on coronary sinus blood flow in idiopathic cardiomyopathy

Coronary sinus blood flow (CSBF) was measured by the dye dilution method in 18 patients with idiopathic cardiomyopathy including 13 with hypertrophic type and 5 with congestive type, and the capacity for increasing CSBF in response to handgrip exercise was studied in 14 patients. CSBF at rest ranged from 41 to 236 ml/min/M2. Average CSBF of 114 +/- 12 ml/min/M2 (112 +/- 14 in hypertrophic type and 119 +/- 25 in congestive type) was significantly larger than control value of 77 +/- 6 presented previously (p less than 0.01). Handgrip exercise at 30% maximal effort for 3 min resulted in the increase in CSBF, averaging 23 +/- 8 ml/min/M2 (22 +/- 8%). However, in about one-half of cases, the percent increase in CSBF was much smaller than the percent increase in effort index which represents myocardial oxygen demand. The change of CSBF was not correlated with the changes of left ventricular systolic pressure, cardiac output, and stroke work. The diminished response of CSBF to isometric handgrip exercise was ascribed to the decreased coronary vascular reserve in this disorder.

Effects of pacing location on coronary circulation in dogs

In 13 open chest dogs, the right atrium and various ventricular sites (i.e. the inflow and outflow tracts and apex of the right ventricle, apex and lateral wall of the left ventricle) were stimulated electrically at a given rate, ranging from 140 to 210 per min. Coronary circulation and cardiodynamics in response to ventricular pacing were compared with those to right atrial pacing at equivalent heart rate. Stimulation of the ventricle except lateral wall of the left ventricle produced no significant changes in coronary sinus blood flow and myocardial oxygen consumption despite decreased blood pressure and cardiac output. The minor change of coronary sinus blood flow was related to the decrease in coronary vascular resistance. Oxygen content of coronary sinus blood decreased during ventricular pacing, while arterial oxygen saturation remained constant. The response of coronary circulation to ventricular pacing did not differ essentially at faster and slower heart rates. It was considered that when stimuli were applied to the ventricular surface, the relatively constant myocardial oxygen consumption in the presence of lowered cardiac performance was attributed to the asynchrony of fractionate contractions of the ventricular muscle.

Effects of varying pacemaker sites on left ventricular performance

The hemodynamic effects of the site of the artificial cardiac stimulation were studied in 17 open chest dogs. The right atrium and five ventricular sites (the inflow and outflow tracts and apex of the right ventricle, apex and lateral wall of the left ventricle) were stimulated electronically at a given rate, ranging from 130 to 190 per min. When cardiac performance during ventricular pacing was compared with those during right atrial pacing, the former uniformly caused a diminution of cardiac output and systemic blood pressure, without reduction of left ventricular end-diastolic pressure. Ventricular function curves, in which left ventricular stroke work was related to left ventricular end-diastolic pressure, shifted downwards and to the right during ventricular pacing. Stimulation frequency did not alter these variables. It was considered that the left ventricular dysfunction in ventricular pacing resulted from the absence of atrial contribution to ventricular filling, mitral regurgitation present and asynchronous ventricular contraction. No significant difference of cardiac performance was demonstrated by changing the site of ventricular pacing, suggesting that the mode of ventricular depolarization itself was not relevant to a decrease in cardiac performance.

Coronary blood flow and lactate metabolism during isometric handgrip exercise in heart disease

Twenty-one patients with various heart diseases undergoing the coronary sinus catheterization had myocardial blood flow studies before and during isometric handgrip exercise. At 30% of the maximal voluntary contraction (MVC), handgrip increased both coronary sinus blood flow by 19.8% and myocardial O2 consumption by 21.0% on the average as compared to those at rest. At 20% of MVC, the increase of the both was slight except for 1 case. The increase in coronary sinus blood flow significantly correlated to the increase of myocardial O2 consumption. Lactate extraction ratio decreased to less than 10% during handgrip in 4 of 19 cases studied despite of normal values at rest. Lactate extraction ratio had significantly positive correlations with coronary sinus blood flow and myocardial O2 consumption during handgrip, while there were not significant ones at rest. It is suggested that isometric handgrip exercise is useful as a stress test for detection of myocardial ischemia in the heart of coronary artery disease.

Plasma catecholamine levels in the coronary sinus, aorta and femoral vein of subjects undergoing cardiac catheterization at rest and during exercise

Plasma catecholamine (CA) levels in the coronary sinus (CS), aorta (Ao) and femoral vein (fv) were simultaneously measured in 22 patients with various heart diseases at rest and during handgrip exercise (IHG). The mean resting levels of plasma norepinephine (NE) in CS, Ao and FV were 359 +/- 49 (SEM) pg/ml, 290 +/- 27 and 234 +/- 24, respectively. The corresponding values of epinephrine (E) were 127 +/- 18 pg/ml, 186+/- 30 and 97 +/- 11, respectively. The E values in Ao were significantly greater than those in CS and in FV (p less than 0.05). IHG exercise induced an obvious elevation of plasma CA levels in every portion of the circulation studied. The mean increments of NE concentration were 81%, 54% and 67% of the resting levels at CS, Ao and FV, respectively, while IHG induced elevation of E were 70% of the resting values at each portion studied. Significant correlations were observed between individual CA concentrations in CS and in Ao, and also between those in Ao and in FV at rest. Under raised sympathoadrenal conditions, however, individual values of NE in CS failed to correlate signficantly to those in Ao and in FV, respectively. The NE output from CS was limited to only 3% and 5% of those in Ao at rest and during IHG, respectively. An actual mean increment of NE on its passing through the coronary circulation was only 2% or less of NE output in ao at both stages. It appears, thus, to be untenable that the cardiac tissue is one of the major source of circulating CA at physiological condition. From these reasons, the direct measurement of NE levels in CS may be mandatory, when plasma CA assay is designed for the purpose of studying the role of the sympathetic nerve activity in the regulation of cardiac function.

Reduced response of cardiac norepinephrine release to isometric handgrip exercise in heart failure

In order to evaluate the relation of cardiac norepinephrine (NE) release to left ventricular function, blood was taken simultaneously from the coronary sinus (CS) and the aorta (A) in 19 patients with heart diseases, at rest and during isometric handgrip exercise (IHG) at 30% of their maximal contraction. Plasma NE was analyzed by Renzini's THI method. The concentrations of plasma NE at rest were 397 +/- 66 (S.E.M.) ng/liter in CS and 292 +/- 50 in A. IHG significantly increased NE to 578 +/- 88 in CS and to 462 +/- 85 in A (p less than 0.001). Estimated NE release from the heart (deltaNE = NECS - NEA) correlated inversely to left ventricular end-diastolic pressure at rest (r = -0.520, p less than 0.05) and during IHG (r= -0.689, p less than 0.01). The changes in deltaNE induced by IHG correlated to the slope of the left ventricular function curve (r=0.618, p less than 0.01). It is concluded that the response of cardiac NE release to exercise is reduced in patients with depressed cardiac function.