Quantification of left ventricular diastolic pressure-volume relations during routine cardiac catheterization by two-dimensional digital echo quantification and left ventricular micromanometer

BACKGROUND

Currently there is no simple clinical method for quantifying the left ventricular (LV) diastolic pressure-volume relation. Echocardiographic-automated endocardial border detection, however, may be combined with LV micromanometer to construct LV pressure-volume loops. We investigated the feasibility of on-line display and sampling of LV pressure-volume loops by such an approach. For this purpose we used a new echocardiographic digital echo quantification (DEQ) method in combination with LV pressures on-line and in real-time.

METHODS

Eighteen patients were screened by conventional echocardiography and DEQ. Ten of the patients with high quality images were included in the study. Left ventricular pressures and volumes were recorded simultaneously and were displayed on-line as pressure-volume loops. Changes in LV volume were induced by intravenous saline. Left ventricular chamber compliance was estimated as change in volume divided by change in pressure from minimum diastolic pressure to end-diastolic pressure (average LV chamber compliance).

RESULTS

Left ventricular pressure-volume loops were displayed on-line during the examination. When compared with the Simpson's method, DEQ underestimated end-diastolic volume (EDV) by 35% and overestimated end-systolic volume (ESV) by 14%. Beat-to-beat variability for ESV and EDV were 7.4% +/- 0.8% and 7.2% +/- 0.7 %, respectively. Volume loading increased LV end-diastolic pressure (LVEDP) from 14.0 +/- 1.6 to 24.7 +/- 2.0 mm Hg (P <.05) and EDV from 79 +/- 10 to 85 +/- 11 mL (NS), and decreased LV chamber compliance from 4.0 +/- 0.7 to 2.0 +/- 0.3 mL/mm Hg (P <.05).

CONCLUSION

The current study demonstrates that LV pressure-volume loops can be displayed and evaluated in real-time during routine cardiac catheterization. This may represent a clinically useful method for identifying patients with reduced chamber compliance. The underestimation of the volumes by DEQ compared with the Simpson's method suggests that further refinements should be performed to improve the endocardial border detection algorithm.

Assessment of ventricular diastolic function

A large number of patients suspected of having congestive heart failure have normal left ventricular systolic function and may, therefore, have primary diastolic heart failure. This diagnosis, however, should not be made unless there is also objective evidence of diastolic dysfunction, ie, signs of abnormal left ventricular relaxation and/or diastolic distensibility. The most useful noninvasive diagnostic approaches are the measurement of transmitral and pulmonary venous flow velocities by pulsed wave Doppler, and mitral annulus velocities by tissue Doppler echocardiography. In some patients, the assessment of intraventricular flow propagation by colour M-mode Doppler echocardiography provides additional information. Diastolic heart failure is most often due to coronary artery disease and/or hypertension; therefore, other noninvasive or invasive tests are needed to define the etiology of myocardial dysfunction. However, in the few patients who have constrictive pericarditis, the Doppler echocardiographic assessment of diastolic filling provides the most important clues to the etiology of the disease. Doppler echocardiographic assessment of left ventricular filling may also be used to obtain semiquantitative estimates of left ventricular diastolic pressure. Furthermore, left ventricular filling patterns, in particular, the deceleration time of early transmitral filling, are powerful predictors of patient prognosis. It is probably not cost effective to perform a comprehensive assessment of diastolic filling in every patient undergoing an echocardiographic examination. However, in selected patients, the assessment of diastolic filling provides information that is important for patient management.

High frame rate Doppler echocardiography in the rat: an evaluation of the method

AIMS

In small animal models, two-dimensional (2D) and Doppler echocardiography should provide more information than M-mode, especially in animals with infarcted and distorted left ventricles, but has been limited by low frame rates and poor near field resolution. New, high frame rate echo-Doppler equipment with digital processing was tested for accuracy of measurements.

METHODS AND RESULTS

Fourteen normal Wistar rats (232-328 g) were examined under halothane anaesthesia. Pulsed Doppler recordings from both left ventricular outflow tract(LVOT) and right ventricular outflow tract (RVOT) cor-responded well with simultaneous ultrasound transit time measurements of aortic flow (LVOT: v=0.99x+4.8, min R=0.93. Standard error of estimate (SEE)=8.3 ml x min(-1), and RVOT: v=0.97x -4.3. R=0.93. SEE =8.4 ml x min(-1). No systematic differences were observed over a flow range of 20-90 ml x min(-1). Left ventricular (LV) dimensions assessed by 2D parasternal long-axis and short-axis views were equal to M-mode measurements with LV diameter 6.6 + 0.44 mm, anterior wall 1.8 +/- 0.18 mm, and posterior wall 1.5 + 0.56 mm. Mean absolute difference 4.4-8.5%. Intra- and interobserver variability was 4.6 +/- 4.1% and 6.7 +/- 7.0% for Doppler measurements, and 4.3 +/- 3.8% and 3.8 +/- 4.6% for dimensions, respectively.

CONCLUSION

High frame rate Doppler echocardiography provides accurate non-invasive measurements of cardiac structure and function in the rat.

Atrioventricular filling dynamics, diastolic function and dysfunction

Left ventricular diastolic dysfunction is associated with slowing of LV relaxation and a decrease in LV chamber compliance. This impairment of function leads to changes in filling velocities as measured by pulsed wave Doppler echocardiography in the pulmonary veins and across the mitral valve, and in intraventricular flow propagation velocity as measured by color M-mode Doppler. This paper explores some of the physiology of LV filling in a clinical context.

Acute regional myocardial ischemia identified by 2-dimensional multiregion tissue Doppler imaging technique

BACKGROUND AND OBJECTIVE

Tissue Doppler echocardiography (TDE) is a promising method for the assessment of regional myocardial function, but pulsed TDE does not provide quantitative data from multiple regions simultaneously. This feature is important for the objective assessment of regional differences in myocardial function. In the present study, we investigated a new off-line TDE method that provides quantitative pulsed velocity data from an unlimited number of regions selected within a 2-dimensional (2D) image. The goal of the study was to determine the ability of this new approach to quantify regional myocardial function during acute myocardial ischemia induced by balloon angioplasty.

METHODS

Twenty-two patients undergoing angioplasty of the left anterior descending coronary artery (LAD) were studied. Left ventricular longitudinal wall motion was assessed by 2D TDE from the apical 4-chamber view before, during, and after angioplasty. Images were sampled at a rate of 69 +/- 15 frames/s, and the off-line analysis allowed simultaneous measurement of velocities in multiple myocardial segments.

RESULTS

There were 3 major alterations in the systolic velocity pattern during LAD occlusion. Peak early systolic velocities along the apical septum were significantly reduced during LAD occlusion (2.8 +/- 1.2 cm/s to 0.6 +/- 1.7 cm/s, P <.001). Myocardial velocities in mid systole suggested paradoxical wall motion (1.0 +/- 1.2 cm/s to -0.8 +/- 0.9 cm/s, P <.001). When comparing the ischemic regions of the left ventricle with the nonischemic regions, each patient demonstrated lower myocardial systolic velocities in the ischemic region. Furthermore, during early diastole, the wall motion of the ischemic segments showed a postsystolic contraction pattern with velocities changing from -0.9 +/- 1.0 cm/s to 1.9 +/- 1.3 cm/s (P <.001).

CONCLUSION

This new 2D TDE approach is able to quantify detailed myocardial velocity profiles from multiple regions simultaneously. Single-beat comparisons of ischemic and nonischemic regions might enhance the sensitivity for diagnosing ischemic heart disease. Reversed systolic wall motion during midsystole and marked positive velocity during early diastole might be new and important markers of myocardial wall ischemia.

Methods for assessing hepatic distending pressure and changes in hepatic capacitance in pigs

The equilibrium pressure obtained during simultaneous occlusion of hepatic vascular inflow and outflow was taken as the reference estimate of hepatic vascular distending pressure (P(hd)). P(hd) at baseline was 1.1 +/- 0.2 (mean +/- SE) mmHg higher than hepatic vein pressure (P(hv)) and 0.7 +/- 0.3 mmHg lower than portal vein pressure (P(pv)). Norepinephrine (NE) infusion increased P(hd) by 1. 5 +/- 0.5 mmHg and P(pv) by 3.7 +/- 0.6 mmHg but did not significantly increase P(hv). Hepatic lobar vein pressure (P(hlv)) measured by a micromanometer tipped 2-Fr catheter closely resembled P(hd) both at baseline and during NE-infusion. Dynamic pressure-volume (PV) curves were constructed from continuous measurements of P(hv) and hepatic blood volume increases (estimated by sonomicrometry) during brief occlusions of hepatic vascular outflow and compared with static PV curves constructed from P(hd) determinations at five different hepatic volumes. Estimates of hepatic vascular compliance and changes in unstressed blood volume from the two methods were in close agreement with hepatic compliance averaging 32 +/- 2 ml. mmHg(-1). kg liver(-1). NE infusion reduced unstressed blood volume by 110 +/- 38 ml/kg liver but did not alter compliance. In conclusion, P(hlv) reflects hepatic distending pressure, and the construction of dynamic PV curves is a fast and valid method for assessing hepatic compliance and changes in unstressed blood volume.

Myocardial strain by Doppler echocardiography. Validation of a new method to quantify regional myocardial function

BACKGROUND

Myocardial strain is a measure of regional deformation, and by definition, negative strain means shortening and positive strain, elongation. This study investigates whether myocardial strain can be measured by Doppler echocardiography as the time integral of regional velocity gradients, using sonomicrometry as reference method.

METHODS AND RESULTS

In 13 anesthetized dogs, myocardial longitudinal strain was measured on apical images as the time integral of regional Doppler velocity gradients. Ultrasonic segment-length crystals were placed near the left ventricular (LV) apex and near the base. Apical ischemia was induced by occluding the left anterior descending coronary artery (LAD), and preload was increased by saline. Percentage systolic strain by Doppler correlated well with strain by sonomicrometry (y=0.82x-1.79, r=0.92, P<0.01). During LAD occlusion, apical myocardium became dyskinetic, as indicated by positive strain values and negative Doppler velocities. At the LV base, myocardial strain by Doppler, strain by sonomicrometry, and velocity of shortening by sonomicrometry (dL/dt) were unchanged during apical ischemia. However, myocardial Doppler velocities at the base decreased from 4.2+/-0.7 (+/-SEM) to 2.7+/-0. 4 cm/s (P<0.05), probably reflecting loss of motion caused by tethering to apical segments. Volume loading increased myocardial Doppler velocities from 2.2+/-0.3 to 4.1+/-0.8 cm/s (P<0.05) and Doppler-derived strain from -12+/-1% to -22+/-2% (P<0.05), whereas peak LV elastance remained unchanged.

CONCLUSIONS

Myocardial strain by Doppler echocardiography may represent a new, powerful method for quantifying regional myocardial function and is less influenced by tethering effects than Doppler tissue imaging. Like myocardial Doppler velocities, strain is markedly load-dependent.

Regulation of ET: pulmonary release of ET contributes to increased plasma ET levels and vasoconstriction in CHF

Endothelin (ET) contributes to the increased systemic vascular resistance and elevated cardiac filling pressures seen in congestive heart failure (CHF). We investigated to what extent ET-mediated vasoconstriction in CHF occurs through an endocrine action of elevated plasma ET or by an autocrine/paracrine mechanism related to induction of vascular ET gene expression. Three weeks of pacing (225 beats/min) induced a marked release of ET-1 from the pulmonary circulation with a sixfold elevation of arterial plasma ET in CHF pigs compared with sham-operated pigs. Arterial plasma ET was the strongest and only independent predictor of systemic vascular resistance. In contrast, vascular preproET-1 and ET-receptor mRNA expression were unaltered or decreased in CHF pigs and did not correlate with indexes of vascular tone. However, myocardial preproET-1 mRNA expression increased twofold in CHF pigs. PreproET-2 and preproET-3 mRNAs were not detectable in cardiovascular tissues. In conclusion, plasma ET was markedly increased because of an augmented release from the pulmonary circulation during CHF, and arterial plasma ET correlated with systemic vascular resistance. The absence of ET induction in the peripheral vasculature suggests that ET increases vascular tone during CHF by an endocrine, not an autocrine/paracrine, mechanism.

Mechanism of pulmonary venous pressure and flow waves

The pulmonary venous systolic flow wave has been attributed both to left heart phenomena, such as left atrial relaxation and descent of the mitral annulus, and to propagation of the pulmonary artery pressure pulse through the pulmonary bed from the right ventricle. In this study we hypothesized that all waves in the pulmonary veins originate in the left heart, and that the gross wave features observed in measurements can be explained simply by wave propagation and reflection. A mathematical model of the pulmonary vein was developed; the pulmonary vein was modeled as a lossless transmission line and the pulmonary bed by a three-element lumped parameter model accounting for viscous losses, compliance, and inertia. We assumed that all pulsations originate in the left atrium (LA), the pressure in the pulmonary bed being constant. The model was validated using pulmonary vein pressure and flow recorded 1 cm proximal to the junction of the vein with the left atrium during aortocoronary bypass surgery. For a pressure drop of 6 mmHg across the pulmonary bed, we found a transit time from the left atrium to the pulmonary bed of tau approximately 150ms, a compliance of the pulmonary bed of C approximately 0.4 ml/mmHg, and an inertance of the pulmonary bed of 1.1 mmHgs2/ml. The pulse wave velocity of the pulmonary vein was estimated to be c approximately 1m/s. Waves, however, travel both towards the left atrium and towards the pulmonary bed. Waves traveling towards the left atrium are attributed to the reflections caused by the mismatch of impedance of line (pulmonary vein) and load (pulmonary bed). Wave intensity analysis was used to identify a period in systole of net wave propagation towards the left atrium for both measurements and model. The linear separation technique was used to split the pressure into one component traveling from the left atrium to the pulmonary bed and a reflected component propagating from the pulmonary bed to the left atrium. The peak of the reflected pressure wave corresponded well with the positive peak in wave intensity in systole. We conclude that the gross features of the pressure and flow waves in the pulmonary vein can be explained in the following manner: the waves originate in the LA and travel towards the pulmonary bed, where reflections give rise to waves traveling back to the LA. Although the gross features of the measured pressure were captured well by the model predicted pressure, there was still some discrepancy between the two. Thus, other factors initiating or influencing waves traveling towards the LA cannot be excluded.

The pulmonary venous systolic flow pulse--its origin and relationship to left atrial pressure

OBJECTIVES

The purpose of this study was to determine the origin of the pulmonary venous systolic flow pulse using wave-intensity analysis to separate forward- and backward-going waves.

BACKGROUND

The mechanism of the pulmonary venous systolic flow pulse is unclear and could be a "suction effect" due to a fall in atrial pressure (backward-going wave) or a "pushing effect" due to forward-propagation of right ventricular (RV) pressure (forward-going wave).

METHODS

In eight patients during coronary surgery, pulmonary venous flow (flow probe), velocity (microsensor) and pressure (micromanometer) were recorded. We calculated wave intensity (dP x dU) as change in pulmonary venous pressure (dP) times change in velocity (dU) at 5 ms intervals. When dP x dU > 0 there is a net forward-going wave and when dP x dU < 0 there is a net backward-going wave.

RESULTS

Systolic pulmonary venous flow was biphasic. When flow accelerated in early systole (S1), pulmonary venous pressure was falling, and, therefore, dP x dU was negative, -0.6 +/- 0.2 (x +/- SE) W/m2, indicating a net backward-going wave. When flow accelerated in late systole (S2), pressure was rising, and, therefore, dP x dU was positive, 0.3 +/- 0.1 W/m2, indicating a net forward-going wave.

CONCLUSIONS

Pulmonary venous flow acceleration in S1 was attributed to a net backward-going wave secondary to a fall in atrial pressure. However, flow acceleration in S2 was attributed to a net forward-going wave, consistent with propagation of the RV systolic pressure pulse across the lungs. Pulmonary vein systolic flow pattern, therefore, appears to be determined by right- as well as left-sided cardiac events.

Diastolic flow pattern in the normal left ventricle

OBJECTIVES

This study sought to clarify the diastolic flow pattern in the normal left ventricle.

BACKGROUND

During left ventricular filling, basally directed (retrograde) velocities are seen in the outflow compartment. These velocities may represent blood returned from the apical region or a shortcut at a more basal level.

METHODS

Left ventricular flow patterns were identified in 18 healthy individuals (age 47 +/- 12 years) with the use of high frame-rate two-dimensional color Doppler and color M-mode Doppler echocardiography techniques. Intraventricular velocities were measured with single pulsed Doppler at 3 levels in both inflow and outflow compartments (posterolateral and anteroseptal parts of the left ventricle).

RESULTS

During early transmitral flow acceleration, all intraventricular velocities were directed towards the apex. However, after peak early and late inflow velocities and during diastasis, retrograde velocities were identified in the outflow compartment. These retrograde velocities occurred earlier, and were higher, at the level of the deflected anterior mitral leaflet tip compared with more apical levels (P <.001). A velocity pattern was established, consistent with early intraventricular vortex formation behind both mitral leaflets. The vortex adjacent to the anterior leaflet subsequently enlarged to include a major part of the left ventricle.

CONCLUSION

Uniform diastolic flow patterns were identified in the normal left ventricles. The findings suggest that both early and late diastolic filling start with an initial motion of a fluid column, succeeded by vortex formation, which explains retrograde flow in the outflow compartment.

Mechanisms of retarded apical filling in acute ischemic left ventricular failure

BACKGROUND

We examined the hypothesis that retardation of apical filling as measured by color M-mode Doppler echocardiography in the diseased left ventricle (LV) reflects a decrease in the intraventricular mitral-to-apical pressure gradient.

METHODS AND RESULTS

In 9 open-chest anesthetized dogs, micromanometers were placed near the mitral tip and in the apical region. From the color M-mode Doppler images, the time delay (TD) between peak velocity at the mitral tip and the apical region was determined as an index of LV flow propagation. Acute ischemic LV failure was induced by coronary microembolization. Induction of ischemia caused a marked increase in LV end-diastolic pressure and a decrease in LV ejection fraction. The time constant of LV isovolumic apical pressure decay (tau) increased from 31+/-8 to 49+/-16 ms (P<0.001). The peak early diastolic mitral-to-apical pressure gradient (DeltaPLVmitral-apex) decreased from 1.9+/-0.9 to 0.7+/-0.5 mm Hg (P<0.01), and TD increased from 5+/-3 to 57+/-26 ms (P<0.001). The slowing of flow propagation was limited to the apical portion of the LV cavity. The TD correlated with DeltaPLVmitral-apex (r=-0.94, P<0.01) and with tau (r=0.92, P<0.01). Before ischemia, the mitral-to-apical flow propagation velocity far exceeded the velocity of the individual blood cells, whereas during ischemia, flow propagation velocity approximated the blood velocity.

CONCLUSIONS

Retardation of apical filling in acute ischemic failure was attributed to a decrease in the mitral-to-apical driving pressure, reflecting slowing of LV relaxation. The slowing of flow propagation appeared to represent a shift in apical filling from a pattern of column motion to a pattern dominated by convection.

Hepatic oxygen metabolism in porcine endotoxemia: the effect of nitric oxide synthase inhibition

The role of endotoxin (lipopolysaccharide, LPS) and nitric oxide in hepatic oxygen metabolism was investigated in 36 pigs receiving 1) LPS (1.7 microgram. kg-1. h-1) for 7 h and NG-nitro-L-arginine methyl ester (L-NAME; 25 mg/kg) after 3 h, 2) LPS, 3) NaCl and L-NAME, and 4) NaCl. Infusion of LPS reduced hepatic oxygen delivery (DO2H) from 60 +/- 4 to 30 +/- 5 ml/min (P < 0.05) and increased the oxygen extraction ratio from 0.29 +/- 0.07 to 0.68 +/- 0.04 after 3 h (P < 0.05). Hepatic oxygen consumption (VO2H) was maintained (18 +/- 4 and 21 +/- 4 ml/min, change not significant), but acidosis developed. Administration of L-NAME during endotoxemia caused further reduction of DO2H from 30 +/- 3 to 13 +/- 2 ml/min (P < 0.05) and increased hepatic oxygen extraction ratio from 0.46 +/- 0.04 to 0.80 +/- 0.03 (P < 0.05). There was a decrease in VO2H from 13 +/- 2 to 9 +/- 2 ml/min that did not reach statistical significance, probably representing a type II error. Acidosis was aggravated. Administration of L-NAME in the absence of endotoxin also increased the hepatic oxygen extraction ratio, but no acidosis developed. In a different experiment, liver blood flow was mechanically reduced in the presence and absence of endotoxin, comparable to the flow reductions caused by L-NAME. The increase in hepatic oxygen extraction ratio (0.34) and maximum hepatic oxygen extraction ratio (approximately 0.90) was similar whether DO2H was reduced by occlusion or by L-NAME. We concluded that L-NAME has detrimental circulatory effects in this model. However, neither endotoxin nor L-NAME seemed to prevent the ability of the still circulated parts of the liver to increase hepatic oxygen extraction ratio to almost maximum when oxygen delivery was reduced. The effect of L-NAME on oxygen transport thus seems to be caused by a reduction in DO2H rather than by alterations in oxygen extraction capabilities.

Mechanics of intraventricular filling: study of LV early diastolic pressure gradients and flow velocities

This study investigates mechanisms of left ventricular (LV) intracavitary flow during early, rapid filling. In eight coronary artery disease patients with normal LV ejection fraction we recorded simultaneous LV apical and outflow tract pressures and intraventricular flow velocities by color M-mode Doppler echocardiography. In five anesthetized dogs we also recorded left atrial pressure and LV volume by sonomicrometry. In patients, as the early diastolic mitral-to-apical filling wave arrived at the apex, we observed an apex-outflow tract pressure gradient of 3.5 +/- 0.3 mmHg (mean +/- SE). This pressure gradient correlated with peak early apex-to-outflow tract flow velocity (r = 0.75, P < 0.05). The gradient was reproduced in the dog model and decreased from 3.1 +/- 0.3 to 1.7 +/- 0.5 mmHg (P < 0.05) with caval constriction and increased to 4.2 +/- 0.5 mmHg (P < 0.001) with volume loading. The pressure gradient correlated with peak early transmitral flow (expressed as time derivative of LV volume; r = 0.95) and stroke volume (r = 0.97). In conclusion, arrival of the early LV filling wave at the apex was associated with a substantial pressure gradient between apex and outflow tract. The pressure gradient was sensitive to changes in preload and correlated strongly with peak early transmitral flow. The significance of this gradient for intraventricular flow propagation in the normal and the diseased heart remains to be determined.

ET-receptor antagonism, myocardial gene expression, and ventricular remodeling during CHF in rats

Both myocardial and plasma endothelin-1 (ET-1) are elevated in congestive heart failure (CHF). However, the role played by endogenous ET-1 in the progression of CHF remains unknown. The aim of the present study was to investigate and correlate myocardial gene expression programs and left ventricular (LV) remodeling during chronic ET-receptor antagonism in CHF rats. After ligation of the left coronary artery, rats were randomized to oral treatment with a nonselective ET-receptor antagonist (bosentan, 100 mg . kg-1 . day-1, n = 11) or vehicle (saline, n = 13) for 15 days, starting 24 h after induction of myocardial infarction. Bosentan substantially attenuated LV dilatation during postinfarction failure as evaluated by echocardiography. Furthermore, bosentan decreased LV systolic and end-diastolic pressures and increased fractional shortening. Myocardial expression of preproET-1 mRNA and a fetal gene program characteristic of myocardial hypertrophy were increased in the CHF rats and were not affected by bosentan. Consistently, right ventricular-to-body weight ratios, diameters of cardiomyocytes, and echocardiographic analysis demonstrated a sustained hypertrophic response and a normalized relative wall thickness after intervention with bosentan. Thus the modest reduction of preload and afterload provided by bosentan substantially attenuates LV dilatation, causing improved pressure-volume relationships. However, the compensatory hypertrophic response was not altered by ET-receptor antagonism. Therefore, ET-1 does not appear to play a crucial role in the mechanisms of myocardial hypertrophy during the early phase of postinfarction failure.

Early diastolic intraventricular filling pattern in acute myocardial infarction by color M-mode Doppler echocardiography

The aim of the present study was to investigate whether slowing of mitral-to-apical filling is present in patients with acute myocardial infarction (AMI). Twenty-eight patients with their first AMI were examined by color M-mode Doppler echocardiography. Twenty-eight age- and sex-matched healthy individuals served as control subjects. From the color M-mode Doppler images, we measured the time difference (TD) between occurrence of peak flow velocity at the mitral tip and in the apical region by a blinded analysis. The TD was increased in the AMI group compared with the control subjects (70 +/- 60 versus 40 +/- 30 msec, p = 0.02) and correlated with peak SGOT (r = 0.46, p = 0.02) and age (r = 0.57, p < 0.01). In the 15 patients with anterior AMI, the correlation between TD and SGOT was better (r = 0.68, p < 0.01). This study demonstrated slowing of early diastolic mitral-to-apical flow propagation in patients with AMI. Infarction size and age appear to be of importance for the retardation of mitral-to-apical flow propagation.

Regulation of hepatic vascular volume: contributions from active and passive mechanisms during catecholamine and sodium nitroprusside infusion

BACKGROUND

It is unclear how the liver contributes to regulation of cardiac filling. The aims of this study were to establish an animal model to quantify hepatic vascular capacitance and to determine the mechanisms whereby catecholamines and sodium nitroprusside modify hepatic blood volume.

METHODS AND RESULTS

In 8 anesthetized pigs we measured hepatic and systemic pressures and flows. Liver vascular volume was measured by sonomicrometry calibrated against integrated hepatic inflow during outflow occlusion. Pressure-volume (P-V) curves were constructed during outflow occlusion. Sonomicrometry accurately reflected hepatic blood volume (r=.99+/-.001), and hepatic P-V curves were highly reproducible. Norepinephrine (0.3 and 0.7 microg x kg body weight (bwt)(-1) min(-1) intraportally) significantly reduced hepatic blood volume by 3.3+/-1 and 4.3+/-1 mL x kg bwt(-1), respectively. Nitroprusside (8 and 18 microg x kg bwt(-1) x min(-1) intraportally) increased hepatic blood volume by 1.1+/-0.2 and 1.9+/-0.3 mL x kg bwt(-1), respectively. Norepinephrine and nitroprusside parallel shifted the hepatic P-V curves, indicating reduced and increased unstressed blood volume, respectively. These curve shifts accounted for more than 90% of the respective blood volume changes. Compliance was unchanged. Phenylephrine but not isoprenaline yielded similar results as norepinephrine.

CONCLUSIONS

The pig model used in this study, accurately quantified hepatic capacitance. Alpha-adrenergic stimulation decreased and nitroprusside increased capacitance by changing unstressed blood volume. These changes in capacitance correspond to expulsion of 300 mL and pooling of 130 mL of blood, respectively, in a 70-kg individual, reflecting that the liver is not only a passive blood reservoir but can respond actively and vigorously to pharmacological interventions.

Transient, isopeptide-specific induction of myocardial endothelin-1 mRNA in congestive heart failure in rats

Increased myocardial expression of preproendothelin-1 (ppET-1) mRNA has been associated with congestive heart failure (CHF) in rats. However, the time course and isoform pattern of ppET mRNA induction and the cellular localization of ET in failing hearts are unknown. Thus our aim was to investigate myocardial ppET mRNA expression in CHF rats during the first 6 wk after induction of myocardial infarction. Furthermore, performing immunohistochemical analysis, we also investigated the origin and localization of immunoreactive endothelin (ET) in different regions of the failing heart. Ribonuclease protection assays revealed a marked increase in ppET-1 mRNA levels in rat myocardial tissues during CHF. The induction of ppET-1 mRNA was isopeptide specific and transient. The most substantial upregulation was observed in the infarcted area, where maximal expression of ppET-1 mRNA was observed after 7 days (25-fold increase, P < 0.05). However, a marked and statistically significant induction of ppET-1 mRNA was also observed in the nonischemic myocardium. Immunohistochemical analysis revealed ET-1-like immunoreactivity in cardiomyocytes, vascular endothelial cells, macrophages, and proliferating fibroblasts. Thus immunohistochemistry revealed the structural basis for the dramatic upregulation of the myocardial ET system in the infarcted region, suggesting a role for ET in the healing process after myocardial infarction. However, the global upregulation of ppET-1 mRNA in the heart also suggests an autocrine/paracrine regulatory mechanism in the nonischemic myocardium during CHF.

Increased cardiac expression of endothelin-1 mRNA in ischemic heart failure in rats

OBJECTIVES

Plasma endothelin (ET) concentrations are increased in heart failure. The aims of the present study were to investigate to what extent cardiac ET mRNA expression is induced in ischemic heart failure and whether there may be compensatory downregulation of myocardial mRNA levels for the ETA and ETB receptor subtypes.

METHODS

In rats with ischemic heart failure (left ventricular end-diastolic pressure > 15 mmHg) due to left coronary artery ligation. Northern blot analyses were performed on mRNA isolated from cardiac tissues.

RESULTS

A substantial upregulation was revealed in all chambers of the failing hearts. Up to 27-fold upregulation (mean 10.6 +/- 4.0, P = 0.002) of left ventricular ET-1 mRNA levels was measured 1 week after myocardial infarction, whereas only a modest upregulation was detected after 6 weeks (mean 2.7 +/- 0.5, P < 0.05). Ribonuclease protection assay revealed 2.8 +/- 0.4-fold higher levels of ET-1 mRNA in the left ventricular area subjected to myocardial infarction compared to the non-infarcted tissue after 1 week. Left ventricular ET-1 mRNA correlated significantly with left ventricular end-diastolic pressure after 1 week (r2 = 0.86, P = 0.007). The ETA and ETB receptor mRNA levels tended to increase 1 week after myocardial infarction although these changes were not statistically significant.

CONCLUSIONS

Cardiac ET-1 mRNA levels are increased in ischemic heart failure and correlate significantly with left ventricular end-diastolic pressure 1 week after myocardial infarction. The increase in cardiac ET-1 mRNA is not accompanied by a decrease in ET receptor mRNA.

Nitric oxide synthase inhibition reduces venous return in porcine endotoxemia

Mechanisms of circulatory effects induced by nitric oxide synthase inhibition in endotoxemia were investigated in 36 pigs randomized to 1) endotoxin infusion (1.7 micrograms.kg-1.h-1 iv) for 7 h and bolus NG-nitro-L-arginine methyl ester (L-NAME; 25 mg/kg iv) after 3 h; 2) endotoxin infusion for 7 h; 3) saline infusion for 7 h and L-NAME after 3 h; and 4) saline infusion for 7 h. Fifteen minutes after L-NAME injection during endotoxemia, reductions in cardiac output (41%, P < 0.05), portal venous flow (51%, P < 0.05), and hepatic artery flow (50%, P < 0.05) were observed. Systemic vascular resistance increased by 82% (P < 0.05), and the portocaval vascular resistance increased by 101% (P < 0.05). Despite marked vasoconstriction after L-NAME, left ventricular intracavitary filling pressure, central venous pressure, and arterial pressure remained unchanged. During endotoxemia, hematocrit increased from 38.4 +/- 1.4 to 41.9 +/- 1.2 after L-NAME, and blood volume (n = 3) was reduced by an average of 8.3 ml/kg body wt. These changes probably reflect transcapillary fluid loss as urine output was unchanged. In conclusion, L-NAME decreased intravascular blood volume and increased splanchnic venous resistance. These effects will tend to reduce venous return. Combined with a marked increase in left ventricular after-load, L-NAME may thus compromise cardiovascular function in endotoxemia.

[Physicians' view on drug therapy for hypertension. A questionnaire in the county of Hordaland]

A questionnaire survey was conducted in Hordaland county to discover opinions on drug therapy for uncomplicated hypertensives with no other risk factors. The response rate was 66%; 179 general practitioners and 31 hospital doctors. The doctors were well informed about the documentation of the clinical benefit of various drugs. As regards the minimum blood pressure that was considered as warranting drug treatment, the majority of the doctors followed the recently issued national guidelines. For young patients the first choice drugs were beta-blockers (27%), ACE-inhibitors (25%) or calcium-blockers (20%). For older patients 65% of the doctors preferred diuretics or beta-blockers. The majority (80%) based their choice of drug primarily on documentation of clinical value or absence of side effects. The doctors underestimated the cost of the newer antihypertensive drugs.

[Cardiology education in Norway--does it keep up with the needs?]

Despite an increase in the number of education positions for cardiologists in Norway in the late 1980s, there is felt to be a marked lack of sub-specialists in cardiology in most types of hospitals. A working group under the Norwegian Society of Cardiology has used a questionnaire in 1993, membership data from the Norwegian Society of Cardiology in 1994, a telephone query to all hospitals in the country, and data from the Norwegian Medical Association in 1995 to examine this apparent lack of specialists and the potentials for educating them. We were able to confirm a current lack of approximately 60 cardiologists. In addition, the capacity for education has been reduced and will not compensate for the predicted retirement of specialists from approximately year 2000. The capacity for educating cardiologists must be increased.

A potential clinical method for calculating transmural left ventricular filling pressure during positive end-expiratory pressure ventilation: an intraoperative study in humans

OBJECTIVES

This study sought to investigate whether right atrial pressure could be used to estimate pericardial pressure during positive end-expiratory pressure (PEEP).

BACKGROUND

Because of elevated intrathoracic pressure during PEEP, pulmonary capillary wedge pressure may not accurately reflect left ventricular preload. An estimate of pericardial pressure during PEEP would allow assessment of transmural filling pressure.

METHODS

In eight patients, at the start of cardiac surgery, pericardial and pleural pressures were recorded by balloon transducers placed over the anterolateral left ventricular wall. We also recorded intravascular pressures and left ventricular short-axis area by transesophageal echocardiography.

RESULTS

A stepwise increase in PEEP from 0 to 15 cm H2O caused a linear increase in pleural pressure from 0.3 +/- 0.6 (mean +/- SEM) to 6.1 +/- 0.8 mm Hg (p < 0.01). Pericardial pressure increased from 2.3 +/- 0.5 to 5.9 +/- 0.6 mm Hg (p < 0.01). The correlation between right atrial (Pra) and pericardial pressure (Pperic) was good: Pra = 0.85 x Pperic + 1.8, r = 0.77. The correlation between changes in right atrial pressure and in pericardial pressure was better: delta Pra = 0.96 x delta Pperic -0.2, r = 0.97. Pulmonary capillary wedge pressure increased with PEEP (p < 0.05), whereas left ventricular area decreased (p < 0.05). However, there was a progressive reduction in transmural pressure, calculated as wedge pressure minus pericardial pressure (p < 0.05), and in transmural pressure, estimated as wedge pressure minus right atrial pressure (p < 0.05). The estimated transmural filling pressure correlated (r = 0.86) with end-diastolic area.

CONCLUSIONS

The present observations suggest that right atrial pressure may be used to estimate changes in pericardial pressure with PEEP and that pulmonary capillary wedge pressure minus right atrial pressure is a potentially clinically useful approximation of transmural filling pressure.

The NO donor sodium nitroprusside reverses the negative effects on hepatic arterial flow induced by endotoxin and the NO synthase inhibitor L-NAME

In previous studies we have observed that the nitric oxide synthase inhibitor L-NAME induces a profound deterioration of liver circulation in experimental endotoxemia. Using the same porcine model we now have evaluated the possibility of modulating these effects with the nitric oxide donor sodium nitroprusside. Infusion of endotoxin led to a gradual deterioration of hemodynamic parameters, including liver blood flow. The decreases in portal blood flow paralleled and matched the decreases in cardiac output, and no compensatory increase in hepatic arterial flow occurred. L-NAME had detrimental effects on hemodynamics, including the liver circulation. The latter effects could, however, partially be reversed by sodium nitroprusside. Hepatic arterial flow increased from 1.9 to 7.2 ml/kg/min, with a concomitant decrease in hepatic arterial resistance from 5,364 to 1,746 dyn s/cm5 kg. A control group exhibited no significant change in either flow or resistance. The response to sodium nitroprusside was rapid and vigorous, and probably largely due to relaxation of the hepatic arterioles, and not to abatement of intrahepatic edema or plugging of the sinusoids. Furthermore, we conclude that the endotoxin-induced dysfunction of the hepatic arterial buffer response may be due to a selective inhibition of vascular endothelial function.

Intraventricular early diastolic velocity profile during acute myocardial ischemia: a color M-mode Doppler echocardiographic study

The aim of the study was to investigate the effect of acute myocardial ischemia on the early diastolic mitral-to-apical velocity profile. Intraventricular filling velocities were measured by color M-mode Doppler echocardiography, which allows simultaneous measurements of velocities at multiple sites. Twenty patients were examined during angioplasty and eight dogs during transient coronary artery occlusion. Velocities at each 0.46 cm level from the mitral tip toward the apex were determined at the time of peak early transmitral velocity. Before angioplasty, early diastolic flow velocities decreased progressively from the mitral tip toward the apex. During angioplasty, intraventricular velocities showed a more abrupt decrease from the middle region toward the apex (p < 0.05). A similar change in the mitral-to-apical profile was found during myocardial ischemia in dogs (p < 0.05). Also, there was a decrease in peak early transmitral velocity (p < 0.01) and peak early transmitral pressure gradient (p = 0.06). Volume loading and constriction of the caval veins performed in the nonischemic ventricle did not appear to change the mitral-to-apical velocity profile. Regional myocardial ischemia was associated with a change in the mitral-to-apical velocity profile as measured by color M-mode Doppler echocardiography. The altered filling pattern could not be explained by changes in loading conditions and may reflect impaired relaxation of the ischemic ventricle.

Splanchnic venous pressure-volume relation during experimental acute ischemic heart failure. Differential effects of hydralazine, enalaprilat, and nitroglycerin

BACKGROUND

Vasodilator drugs have variable effects on veins and arteries. However, direct measurements of their effects on the splanchnic veins, perhaps the most important volume reservoir, have not been reported. We assessed the effect of acute heart failure and the subsequent administration of hydralazine, enalaprilat, and nitroglycerin on the splanchnic venous pressure-volume relation in intact dogs.

METHODS AND RESULTS

Experimental acute ischemic heart failure was induced in 19 splenectomized dogs by microsphere embolization of the left main coronary artery. Embolization was repeated until left ventricular end-diastolic pressure (LVEDP) reached 20 mm Hg and cardiac output decreased by 50%. The splanchnic vascular pressure-volume relation was determined by radionuclide plethysmography during the control stage, after acute heart failure had been established, and after administration of a vasodilator (hydralazine, enalaprilat, or nitroglycerin) at a dose sufficient to reduce mean aortic pressure by approximately 20%. Induction of acute heart failure was associated with a decrease in the splanchnic vascular volume from 100% to 86 +/- 2% and an increase in LVEDP from 6 +/- 1 to 21 +/- 1 mm Hg (P < .001). There was a parallel leftward shift of the splanchnic vascular pressure-volume curve. After the administration of hydralazine, enalaprilat, and nitroglycerin, the splanchnic vascular volumes increased from 86% to 88 +/- 3%, 96 +/- 3%, and 113 +/- 3%, respectively (P = NS, P < .01, and P < .001, respectively, versus heart failure). After drug administration, the LVEDPs were 18 +/- 2, 16 +/- 1, and 13 +/- 1 mm Hg (P = NS, P < .05, and P < .001, respectively, versus heart failure).

CONCLUSIONS

Acute heart failure was associated with a parallel leftward shift of the splanchnic venous pressure-volume relation (venoconstriction). Splanchnic (systemic) venoconstriction may in part explain the increased LVEDP during acute heart failure by displacement of blood to the central compartment. Subsequently administered enalaprilat and, to a greater degree, nitroglycerin produced splanchnic venodilation, thereby lowering LVEDP. Hydralazine had no significant effect on the splanchnic veins and only a modest effect on LVEDP. In this model, splanchnic capacitance changes appear to modulate change in left ventricular preload.

Measurement of intestinal vascular capacitance in dogs: an application of blood pool scintigraphy

To define relative changes in intestinal vascular capacitance, we developed a model that allowed us to construct intestinal vascular pressure-volume relationships (PVR). Thirteen alpha-chloralose-anesthetized and splenectomized dogs were studied using a pneumatic constrictor and a small catheter to change and measure portal venous pressure. A small lead sheet was placed beneath the abdominal wall. Relative changes in intestinal blood volume (IBV) were determined by in vivo blood pool scintigraphy with 99mTc-labeled erythrocytes and were expressed as percentages corrected for specific activity and abdominal wall radioactivity. PVRs were constructed using data recorded during graded inflations of the portal venous constrictor. The abdominal wall contributed 32.4 +/- 7.7% (SD) of the total counts. During a 4-h control period, PVRs varied by no more than 6% (of IBV). In the isolated intestinal circulation, the change in IBV was precisely proportional to the volume of blood added, indicating that this method can detect very small changes in volume (< or = 5 ml). Nitroglycerin (25 micrograms.kg-1.min-1) increased capacitance by 20%. Although it measures only relative changes, the model is stable and sensitive, provides reproducible measurement of intestinal PVRs, and, with adaptation, may prove useful in patient studies.

Visual assessment of intra ventricular flow from colour M-mode Doppler images

Left intra ventricular filling was studied by colour M-mode Doppler ultrasound to determine whether the flow pattern can be assessed visually, and explore its relation to left ventricular (LV) function. Patients with coronary artery disease (CAD) or dilated cardiomyopathy (DCM) were divided into three groups according to angiographically evaluated LV function. The groups were compared with a control group of 54 healthy volunteers. The mitral to apical delay of early diastolic flow was qualitatively assessed from printed colour M-mode images, twice by four independent observers blinded to the subject's status. The repeatability of the assessments as determined by the kappa statistic was good intra observer (kappa = 0.75) and moderate inter observer (kappa = 0.53). The CAD-group with angiographically normal LV function (n = 25) had flow patterns resembling those observed in the control group. The group with ejection fraction (EF) < 50% (n = 19) had flow patterns clearly different from the control group. Patients with regional wall motion abnormality (RWMA) but EF > 50% (n = 16) exhibited flow patterns intermediate between the control and the low EF group. Among the 50 CAD patients there was a negative correlation between EF and the presence of delay of apical peak velocity (Spearman's rs = -0.62, p < 0.0001). A visible delay of apical peak velocity had a sensitivity towards DCM of 83% and specificity of 75%. The sensitivity towards CAD with either RWMA or low EF was 55% and the specificity 75%. In conclusion, visual assessment of intra ventricular flow patterns was feasible and allowed discrimination between normal and diseased ventricles.

Intracavitary filling pattern in the failing left ventricle assessed by color M-mode Doppler echocardiography

OBJECTIVES

The present study aimed to investigate the mechanism of intracavitary changes in filling pattern during acute ischemic left ventricular failure and during beta-adrenergic blockade.

BACKGROUND

Recent clinical studies with color M-mode Doppler imaging have shown abnormal intracavitary filling patterns in the diseased ventricle.

METHODS

In open chest anesthetized dogs with intracardiac micromanometers and myocardial segment-length crystals, global ischemic left ventricular failure was induced (n = 8) by coronary microembolization. In nonischemic ventricles inotropy was decreased (n = 6) by intravenous propranolol and increased (n = 6) by intravenous isoproterenol. From color M-mode Doppler images we calculated the time difference between peak early diastolic filling velocity at the mitral tip and apex using computer analysis. The time difference of peak velocity was used as an index of the timing of apical filling.

RESULTS

There was marked retardation of apical filling with microembolization and propranolol. Time difference of peak velocity increased from 20 +/- 6 (mean +/- SEM) to 101 +/- 17 ms (p < 0.05) and from 21 +/- 8 to 80 +/- 18 ms (p < 0.05), respectively. Time constant of isovolumic relaxation increased from 34 +/- 3 to 43 +/- 5 ms (p < 0.05) and from 31 +/- 1 to 39 +/- 3 ms (p < 0.05) during microembolization and beta-blockade, respectively. Isoproterenol tended to cause the opposite changes. Time difference of peak velocity showed a positive correlation with time constant of isovolumic relaxation (r = 0.89, p < 0.01) and a negative correlation with peak early transmitral pressure gradient (r = 0.88, p < 0.01). In the intact left ventricle, peak apical filling velocity coincided with peak early transmitral pressure gradient. During ischemic failure however, peak apical filling velocity occurred 53 +/- 14 ms after peak early transmitral pressure gradient had decreased to zero and at a time when transmitral flow had ceased, suggesting a change in intraventricular flow distribution.

CONCLUSIONS

Color M-mode Doppler imaging revealed retarded apical filling during depression of myocardial function by global myocardial ischemia or beta-blockade. The abnormal filling pattern may be a sign of impaired left ventricular relaxation.

Influence of heart rate and left atrial pressure on pulmonary venous flow pattern in dogs

In six open-chest anesthetized dogs we investigated the effect of heart rate (HR) on the relationship between left atrial pressure (LAP) and pulmonary venous flow (QPV). QPV was measured by ultrasonic transit time during volume loading and right atrial pacing. Consistent with previous studies, we found a negative correlation between LAP and mean flow rate during atrial systole divided by mean flow rate in the R-R interval. However, this relationship was shifted upward by tachycardia. The QPV maximum amplitude divided by mean flow rate in the R-R interval increased with loading but decreased with tachycardia. mean flow rate during ventricular systole divided by mean flow rate during the R-R interval increased with both loading and tachycardia. Regression coefficients for HR and LAP as predictors of these indexes were all significantly different from zero (P = 0.0001). We conclude that HR significantly influences the relationship between the QPV pattern and LAP. This could be a limitation of the pulmonary venous flow pattern as an indicator of left ventricular diastolic function.

Effect of enalaprilat on splanchnic vascular capacitance during acute ischemic heart failure in dogs

This study investigates the effect of angiotensin-converting-enzyme inhibition by intravenous enalaprilat (100 micrograms/kg) on splanchnic vascular capacitance during acute left ventricular failure induced by coronary microembolization in alpha-chloralose/urethan anesthetized dogs. Changes in hepatic and splenic vascular volumes were determined from organ diameters (sonomicrometry) at 15, 30, and 45 min after enalaprilat injection. Changes in vascular capacitance were assessed from organ pressure-diameter curves obtained during transient hepatic outflow occlusion. Thirty minutes after enalaprilat, hepatic volume was increased by 52 +/- 14 ml (P < 0.01), and portal and hepatic vein pressures were decreased from 10.2 +/- 0.9 to 8.7 +/- 0.8 mmHg (P < 0.01) and from 3.9 +/- 1.6 to 3.1 +/- 0.7 mmHg (P < 0.05), respectively. Splenic volume did not change. Enalaprilat shifted the hepatic pressure-diameter curve upward, resulting in a larger hepatic volume at any given pressure. Curve intercept was increased, suggesting an increase in unstressed vascular volume. Curve slope was unchanged. In conclusion, enalaprilat increased hepatic vascular volume during acute left ventricular failure in dogs. The pressure-diameter curve shift suggests a reduction in the smooth muscle tone of hepatic capacitance vessels.

Effect of carotid sinus baroreceptor reflex on hepatic and splenic vascular capacitance in vagotomized dogs

Mechanisms of how baroreflex activation changes splanchnic vascular volumes were studied in eight vagotomized dogs, anesthetized by chloralose/urethan. Hepatic and splenic vascular volume changes were determined from organ dimensions by sonomicrometry. Pulsatile carotid sinus pressure (CSP) in isolated and separately perfused carotid sinuses was changed among 200, 120, and 40 mmHg. Lowering CSP from 120 to 40 mmHg significantly decreased both hepatic and splenic vascular volume (at similar portal pressure) by 1.9 +/- 0.5 and 1.8 +/- 0.6 ml/kg body wt, respectively. Increasing CSP from 120 to 200 mmHg tended to increase regional vascular volumes (P = NS). The combined volume change of liver and spleen between CSP 40 and 200 mmHg was 4.2 +/- 0.6 ml/kg body wt (P < 0.001). Pressure-volume (dimension) curves at high, low, and baseline CSP were determined to separate active and passive mechanisms of vascular volume changes. Changes in CSP did not change regional vascular compliance. Low CSP significantly decreased unstressed liver and unstressed splenic volume by 3.3 +/- 0.9 and 1.9 +/- 0.5 ml/kg body wt, respectively. These results indicate that liver and spleen both contribute to blood volume mobilization by vasoconstriction during low CSP and that the carotid sinus baroreceptor reflex modulates hepatic and splenic vascular capacitance by changing unstressed volume rather than by changing vascular compliance.

Juxtacardiac pleural pressure during positive end-expiratory pressure ventilation: an intraoperative study in patients with open pericardium

OBJECTIVES

This study was conducted to measure the cardiac constraining effect of the lungs during positive end-expiratory pressure and relate extracardiac pleural pressure (radial stress) to airway pressure, right atrial pressure and left ventricular filling.

BACKGROUND

During positive end-expiratory pressure ventilation, the extracardiac pressure is elevated, and therefore intracavitary filling pressure does not reflect ventricular preload. Estimates of this pressure might be useful clinically to assess left ventricular preload.

METHODS

In eight patients who had undergone coronary or valvular surgery and whose pericardium was left widely open, a flat pleural balloon transducer was placed over the anterolateral left ventricular wall. We recorded pulmonary capillary wedge pressure, right atrial pressure and left ventricular short-axis end-diastolic area by transesophageal echocardiography. Incremental positive end-expiratory pressure was applied.

RESULTS

Extracardiac pleural pressure increased (p < 0.01) from 0.6 +/- 1.8 (+/- SD) to 2.4 +/- 1.8, 5.3 +/- 1.5 and 8.2 +/- 1.5 mm Hg at a positive end-expiratory pressure of 5, 10 and 15 cm H2O, respectively. The slope relating extracardiac pleural pressure to positive end-expiratory pressure (in mm Hg) was 0.70 +/- 0.10, and the intercept was zero. Increasing extracardiac pleural pressure was associated with a progressive increase in pulmonary capillary wedge pressure and a decrease in left ventricular end-diastolic area. Consequently, although pulmonary capillary wedge pressure and left ventricular area changed in opposite directions, the value of pulmonary capillary wedge pressure minus extracardiac pleural pressure correlated positively with left ventricular area (r = 0.95, p < 0.001). Changes in right atrial pressure (Pra) correlated with changes in extracardiac pleural pressure (Ppleural): delta Pra = -0.3 + 0.56. delta Ppleural (r = 0.89, p < 0.001).

CONCLUSIONS

In postoperative patients with open pericardium, pulmonary capillary wedge pressure minus extracardiac pleural pressure predicts left ventricular end-diastolic area during positive end-expiratory pressure. Further studies should be done to determine whether the observed relations between airway pressure and extracardiac pleural pressure and between right atrial pressure and extracardiac pleural pressure may give clinically useful estimates of left ventricular preload during positive end-expiratory pressure.

Selective positive end-expiratory pressure and right ventricular function in dogs

Differential ventilation with selective positive end-expiratory pressure (PEEP) has been shown to reduce cardiac output less than general PEEP. In previous studies we have demonstrated that during selective PEEP left ventricular preload is better maintained than during general PEEP. The present study was designed to determine whether the different haemodynamic responses to selective and general PEEP also might be due to different effects on RV preload. The study was performed on nine acutely instrumented dogs, in which extraventricular pressure was measured by pericardial balloon transducers. Measures of RV preload were obtained by the use of ultrasonic segment length transducers as well as end-diastolic transmural pressure (RVEDP). The study showed reductions in RVEDP during general and selective right (R) PEEP, accompanied by moderate reductions in RV inflow tract segment lengths. These changes were most marked with general PEEP. Selective LPEEP did not change RV preload significantly. Therefore, better maintained cardiac output with selective PEEP than with general PEEP is partly due to less impairment of right ventricular filling.

Repeatability of colour M-mode Doppler measurements of left ventricular filling

We investigated the repeatability of two recently reported colour M-mode Doppler measures of left ventricular diastolic function. 'Delay of peak velocity' is the time interval from peak velocity of early filling at the mitral tip level to peak velocity in the apical region. The 'velocity of flow propagation' is the speed of the mitral to apical spread of the early diastolic filling. Two examiners independently and blindly made measurements by both methods on 32 digital recordings twice, using custom software. Inter- and intra-observer repeatability were given in terms of limits of agreement, where 1 denotes perfect agreement. Limits of intra-observer agreement were 0.72-1.43 for measurements of 'delay of peak velocity', and 0.39-2.28 for 'velocity of flow propagation'. Limits of inter-observer agreement were 0.68-1.42 and 0.19-2.04 respectively. The correlation between the methods was weak (r = 0.45), suggesting that they may detect different properties of early diastole. We suggest that the reliability of the methods may be improved by replicate measurements performed blindly. There are reasons to express the velocity of flow propagation on a logarithmic scale.

Intraventricular early diastolic filling during acute myocardial ischemia, assessment by multigated color m-mode Doppler echocardiography

BACKGROUND

Color M-mode Doppler echocardiography has been suggested as a new noninvasive technique for assessing left ventricular diastolic function. The present study investigated intraventricular filling pattern by color M-mode Doppler in patients during percutaneous transluminal coronary angioplasty (PTCA). In a dog model of myocardial ischemia, the color M-mode flow pattern was related to indices of global and regional myocardial function.

METHODS AND RESULTS

From color M-mode images, the time difference (TD) between occurrence of peak velocity in the apical region and at the mitral tip was determined in 20 patients and eight anesthetized dogs during coronary occlusions. During PTCA, the timing of peak velocity was progressively delayed from mitral valve to apex. Consistent with this, the dog model showed delayed apical filling during coronary occlusion; TD increased from 18 +/- 4 to 71 +/- 9 milliseconds (P < .01). In the ischemic region, systolic shortening (sonomicrometry) decreased from 20 +/- 3% to -5 +/- 2% (p < .01). The one-third filling fraction decreased from 59 +/- 5% to 31 +/- 6% (P < .01) and correlated with TD (r = .85, P < .01). The time constant of isovolumic relaxation (tau) increased slightly and correlated with TD (r = .81, P < .01). Pacing tachycardia, caval constriction, and volume loading were performed to mimic the ischemia-induced changes in heart rate, stroke volume, and intracavitary filling pressure, respectively. There were no significant changes in TD or tau during these interventions.

CONCLUSIONS

Color M-mode Doppler echocardiography showed a marked delay of apical peak filling velocity during PTCA. The experimental data suggest that this reflects retarded filling of the ischemic ventricle. Thus, color M-mode Doppler may provide a useful method for assessing diastolic dysfunction.

[Lipid-lowering medication--indications and possible hazards. Report from a hearing]

Drug treatment of hyperlipidaemia should be founded on scientific evidence. A hearing was arranged to arrive at practical measures based on reported clinical trials. Several studies during recent years have shown regression of coronary atheromatosis, and some people would say the effect is striking. Studies using clinical endpoints, like morbidity and mortality, have not yielded equally convincing results, but it should be noted that the results of studies with more than 10% reduction in total serum cholesterol levels are not yet available. So far, the trials have been too small to judge effects on total mortality. It is uncertain whether the treatment actually has untoward effects on the incidence of violent deaths and neoplasms. An upper limit for drug treatment of about 8 mmol/l was proposed during the hearing. The limit can be lowered to 7 if established coronary disease is present. For women without coronary disease the limit should be higher than that for men. All in all, this implies an increase in the total number of individuals treated compared with present practice. It was agreed that at present, high risk individuals are undertreated. The new levels have been set partly on the basis of economic considerations.

Effect of nifedipine on splanchnic and pulmonary vascular capacitance

This study examines the hypothesis that nifedipine may increase splanchnic vascular capacitance and thus change the distribution of blood between the splanchnic and pulmonary circulation in heart failure patients. Relative regional blood volumes were determined by equilibrium blood pool scintigraphy during a 10 min baseline period and for 30 min after nifedipine 20 mg sublingually, with simultaneous recordings of systemic and pulmonary arterial pressures, hepatic venous wedge pressure, and cardiac output. Eight patients with ischaemic heart failure received nifedipine. Four patients served as controls. Nifedipine reduced mean arterial pressure and systemic vascular resistance in every patient. There were no significant changes in the relative blood volumes of the intestinal, hepatic, or splenic regions or in hepatic venous wedge pressure (reflecting portal venous pressure), suggesting unchanged splanchnic vascular pressure-volume relationship. Nifedipine caused a 6.3 +/- 1.0% increase in relative pulmonary blood volume and a slight increase in pulmonary vascular distending pressure from 16.1 +/- 2.9 mmHg to 17.5 +/- 2.8 mmHg (P < 0.05), suggesting that the increase in pulmonary blood volume was passively mediated. In conclusion, nifedipine did not change splanchnic vascular capacitance, but caused a small increase in pulmonary blood volume, which probably was a passive response to increased distending pressure.

Changes in pulmonary vein flow pattern during volume loading

OBJECTIVE

The aim was to investigate the effect of increased left ventricular filling pressure on the pulmonary vein flow (PVQ) pattern.

METHODS

Pulmonary vein flow was recorded using an ultrasonic transit time flow meter in six anaesthetised dogs. Mean left atrial pressure was increased by stepwise volume loading from 7.8(SEM 1.3) to 18.9(1.9) mm Hg (p < 0.01).

RESULTS

With loading the PVQ signal developed several characteristic positive and negative waves which corresponded to directionally opposite pressure waves in the left atrium. There was a marked increase in the amplitude of the PVQ signal: peak flow increased from 165(50) to 310(38) ml.min-1 (p < 0.01), while minimum flow decreased from 49(37) to -61(23) ml.min-1 (p < 0.01). The minimum value of PVQ occurred during early ventricular systole, corresponding to the left atrial C wave. With progressive loading there was an increasing deceleration of flow during atrial contraction. To quantify the effect of atrial contraction and the C wave on the flow pattern a ratio was calculated between the integrated flow from the start of atrial contraction to the nadir of the x descent and the integrated flow during the rest of the cardiac cycle. This ratio decreased from 0.40(0.06) to 0.11(0.07) with loading (p < 0.01). In each experiment this flow ratio varied inversely with mean left atrial pressure (regression coefficients between 0.66 and 0.97).

CONCLUSIONS

Volume loading caused marked changes in the pulmonary vein flow pattern. The PVQ waves reflected the pressure waves in the left atrium. The relative flow during atrial contraction varied inversely with mean left atrial pressure. Further studies should be done to determine whether this index reflects left ventricular filling pressure under different conditions.

Selective positive end-expiratory pressure and intracardiac dimensions in dogs

Effects of differential ventilation with general vs. selective right (R) and left (L) positive end-expiratory pressure (PEEP) on left (LV) and right ventricular (RV) end-diastolic dimensions were compared in seven pentobarbital-anesthetized dogs. All three modes of PEEP reduced LV cross-sectional area: general PEEP more than RPEEP and RPEEP more than LPEEP. General PEEP and, to a lesser degree, RPEEP decreased both the LV anteroposterior diameter and LV septum-free wall diameter, whereas LPEEP reduced the LV septum-free wall diameter only. Cardiac output was unaffected by LPEEP, whereas general PEEP (20 cmH2O) reduced cardiac output by 48%, and RPEEP (20 cmH2O) reduced it by 23%. RV septum-free wall diameter was not changed by any mode of PEEP. In conclusion, cardiac output was better maintained with selective PEEP than with general PEEP because LV filling was less impeded with selective PEEP. During LPEEP LV assumed a different configuration than during RPEEP and general PEEP, probably reflecting a different pattern of heart-lung interaction.

Effect of the pericardium on atrial systolic function

The effect of pericardial constraint on atrial systolic function was investigated in nine acutely instrumented anesthetized dogs. Left and right atrial pressures were recorded by high-fidelity catheters; auricular diameters and free wall segment lengths were measured by sonomicrometry. Atrial function curves were constructed by relating atrial systolic dimensional shortening to atrial end-diastolic pressure during progressive volume loading. With the pericardium closed, the function curves were shifted markedly downward and rightward, such that atrial systolic shortening was reduced at any given pressure. There was a concomitant leftward and upward shift of the atrial end-diastolic pressure-dimension relationship. The relationship between atrial systolic shortening and atrial end-diastolic dimension was not shifted. These results suggest that the apparent depression of atrial systolic function with the pericardium closed is due to a restrictive effect of the pericardium on atrial filling. In conclusion, in the acutely dilated heart, the pericardium restricts atrial filling and thus causes a reduction in atrial systolic contribution to ventricular filling.

Haemodynamic effects of selective positive end-expiratory pressure after unilateral pulmonary hydrochloric acid-aspiration in dogs

We investigated 1) the effects of HCl-mediated acute left lung injury on regional juxtacardiac pressures and 2) the haemodynamic effects of different modes of ventilation before and after induction of left lung injury. The study was done in 7 mechanically ventilated, anaesthetized dogs. Juxtacardiac pressures and haemodynamic variables were recorded during 1) differential ventilation (DV) with zero positive end-expiratory pressure (PEEP = 0) and 2) DV with general (G) PEEP and selective right (R) and left (L) lung PEEP. Left lung injury increased left, but not right pleural pressure of pericardial pressure. Pulmonary vascular resistance (PVR) and pulmonary artery pressure (PAP) were increased moderately. Cardiac output (CO) did not change. GPEEP reduced LV filling and cardiac output markedly and by approximately the same degree before and after lung injury. The haemodynamic effects of LPEEP were minor before as well as after the induction of lung injury. RPEEP, which had only moderate haemodynamic effects during control, caused a marked reduction in cardiac function after the induction of left lung injury. The transmission of airway pressure to the pleura was reduced in the diseased lung. These results suggest that serious haemodynamic side effects may be avoided by applying PEEP selectively to the diseased lung.

Nitroprusside and regional vascular capacitance in patients with severe congestive heart failure

BACKGROUND

This study investigates the effects of sodium nitroprusside on regional vascular capacitance in eight patients with severe congestive heart failure (New York Heart Association class IV) and pulmonary hypertension.

METHODS AND RESULTS

Regional relative blood volumes in the splanchnic and pulmonary region were determined by equilibrium blood pool scintigraphy. Hepatic venous wedge pressure and the mean of pulmonary artery and pulmonary capillary wedge pressure were used to represent the distending pressures of the splanchnic and pulmonary capacitance vessels, respectively. The dose of sodium nitroprusside was increased stepwise until systolic pulmonary artery pressure decreased below 50 mm Hg. This caused reductions in mean aortic pressure from 89 +/- 5 to 66 +/- 3 mm Hg (p less than 0.005), in pulmonary capillary wedge pressure from 31 +/- 1 to 16 +/- 2 mm Hg (p less than 0.001), and in hepatic venous wedge pressure from 10.0 +/- 1.0 to 5.9 +/- 0.6 mm Hg (p less than 0.005). Intestinal blood volume increased by 26 +/- 7% (p less than 0.005), whereas hepatic blood volume decreased by 9 +/- 3% (p less than 0.02). Pulmonary blood volume was unchanged. Analysis of intestinal and pulmonary vascular pressure-volume relations showed larger or equal blood volumes contained at lower distending pressures, indicating that sodium nitroprusside reduced smooth muscle tone of the capacitance vessels in these regions. The reduction of hepatic blood volume was compatible with passive expulsion of blood subsequent to reduced venous pressure. There was no change in the count rate from the spleen.

CONCLUSIONS

Nitroprusside reduced venous pressure in patients with congestive heart failure by active relaxation of intestinal and pulmonary capacitance vessels. Hepatic vascular volume was probably reduced by a passive mechanism.

Blood volume changes in liver and spleen during cardiogenic shock in dogs

Changes in vascular capacitance of the liver and spleen were studied in seven anesthetized dogs during cardiogenic shock induced by coronary microembolization. Left ventricular end-diastolic pressure increased from 2 +/- 2 to 28 +/- 4 mmHg (P less than 0.001), and mean aortic pressure decreased from 111 +/- 7 to 56 +/- 9 mmHg (P less than 0.001). Hepatic venous pressure increased from 1.8 +/- 0.6 to 5.0 +/- 1.0 mmHg (P less than 0.05). Portal venous pressure did not change. Blood volume changes were assessed from sonomicrometric measurements of organ diameters. Hepatic diameter increased after embolization, corresponding to an estimated 54 +/- 14 ml increase of hepatic blood volume (P less than 0.01). Splenic diameter gradually decreased during shock until an estimated 33 +/- 12 ml of blood had been released (P less than 0.05). Occlusion of hepatic venous outflow by a balloon catheter was used to cause ramp changes in hepatic volume and hepatic venous pressure so that a pressure-volume curve could be estimated. Analysis of the hepatic curves showed an increase in unstressed volume with no change in vascular compliance during shock. The blood volume increase could in part be attributed to increased outflow pressure, but active dilation of hepatic capacitance vessels probably contributed. Splenic curves were shifted downward, suggesting expulsion of blood by active contraction.

The relationship between atrial pressure, atrial dimensions and atrial natriuretic factor during pacing tachycardia in dogs

Acute supraventricular tachycardia is known to increase the plasma level of atrial natriuretic factor (ANF). The purpose of these experiments was to investigate if such an increase in plasma-ANF could be ascribed to changes in atrial pressure and atrial dimensions. Eight anaesthetized dogs were instrumented with atrial pressure catheters and sonomicrometers to measure left and right auricular and atrial free wall dimensions. An acute increase in atrial rate from 150 to 200 min-1 for 10 min did not change plasma-ANF or atrial haemodynamic variables. A further increase in atrial rate to 250 or 300 min-1 increased right and left atrial intracavitary pressures (P less than 0.01), both auricular diameters and right atrial free wall segment length (P less than 0.05). Left atrial free wall segment length remained unchanged. Plasma-ANF increased in all dogs (P less than 0.01). The change in plasma-ANF correlated well with changes in atrial pressures as well as with changes in atrial dimensions. These results support the hypothesis that release of ANF during acute atrial tachycardia may in part be attributed to atrial dilatation.

The effect of positive end-expiratory pressure ventilation on atrial filling

As a measure of atrial filling, left and right auricular diameter and free wall segment length were recorded by sonomicrometry during incremental positive end-expiratory pressure (PEEP) in eight acutely instrumented closed chest dogs. The effect of PEEP was assessed with the pericardium open (n = 6) and closed (n = 8). On both occasions, PEEP decreased left auricular diameter (P less than 0.05). PEEP also caused a reduction in right auricular diameter with the pericardium open (P less than 0.05), while the variable was unchanged with the pericardium closed. PEEP did not cause any changes in either left or right free wall segment lengths. Both left and right auricular pressure-diameter relationships were progressively shifted leftwards with incremental PEEP. These observations suggest that PEEP may reduce left ventricular output not only by interfering with passive ventricular filling, but also by reducing atrial dimensions.

Rate-induced increase in plasma atrial natriuretic factor can occur independently of changes in atrial wall stretch

Tachycardia is known to increase the plasma level of atrial natriuretic factor (ANF). The aim of the study was to determine whether such release of ANF can occur independently of increased atrial wall stretch. Seven anesthetized dogs were instrumented with pressure catheters and sonomicrometer crystals to measure left and right auricular and atrial free wall dimensions. During atrial pacing, the measured atrial dimensions were kept constant by adjusting vascular constrictors placed around the great vessel trunks. When atrial rate was increased progressively by pacing at 150, 200, and 250 min-1, plasma ANF increased from 40.8 +/- 5.4 to 43.0 +/- 6.0 (P = NS) and 103.1 +/- 17.6 (SE) pmol/l (P less than 0.05), respectively. Repeating the pacing sequence at two different levels of elevated left atrial pressure caused at each level a similar increase in plasma ANF at 250 min-1. The relationship between plasma ANF and atrial dimensions was shifted upward by pacing, such that ANF was higher for any given atrial dimension. In conclusion, pacing tachycardia elevates plasma ANF in the presence of constant atrial dimensions. These results support the hypothesis that chronotropic stimulation can cause release of ANF by a mechanism that is independent of atrial stretch.

The effect of nitroglycerin on pulmonary vascular capacitance in dogs

In this study we investigated the hypothesis that the decrease in pulmonary vascular pressures observed after administration of nitroglycerin is in part due to a shift in the pulmonary vascular pressure-volume relationship. The experiments were done in six closed-chest dogs anesthetized with pentobarbital, in which pulmonary, cardiac, and intestinal relative blood volumes were determined by equilibrium blood pool scintigraphy. Nitroglycerin (30 micrograms/kg/min) caused 7% (p less than 0.02) and 12% (p less than 0.02) reductions in pulmonary and total cardiac blood volume, respectively, and a 7% (p less than 0.01) increase in intestinal blood volume. This shift of blood from the heart and the pulmonary circulation to the systemic (intestinal) circulation was accompanied by reductions in mean pulmonary artery pressure from 16 +/- 2 mm Hg to 12 +/- 1 mm Hg (p less than 0.01), in mean pulmonary capillary wedge pressure from 11 +/- 2 mm Hg to 6 +/- 1 mm Hg (p less than 0.01), and in mean portal pressure from 9 +/- 1 mm Hg to 8 +/- 1 mm Hg (p less than 0.01). The position of the pulmonary vascular pressure-blood volume relationship was unaffected by nitroglycerin, whereas the portal pressure-intestinal blood volume relationship was shifted to the left and upward. These changes suggest that pulmonary vascular tone remained unchanged, whereas intestinal vascular tone decreased during administration of nitroglycerin. In conclusion, nitroglycerin decreased pulmonary vascular pressures through a passive emptying of the pulmonary circulation as a result of increased systemic (intestinal) vascular capacitance.