Pathogenesis of oedema in chronic severe anaemia: studies of body water and sodium, renal function, haemodynamic variables, and plasma hormones

BACKGROUND

Patients with chronic severe anaemia often retain salt and water. Fluid retention in these patients is not caused by heart failure and the exact mechanisms remain unclear. This study was designed to examine some of the possible mechanisms.

METHODS AND RESULTS

Haemodynamic variables, body fluid compartments, renal function, and plasma hormones were measured in four patients with oedema caused by chronic severe anaemia (mean (SE) haematocrit 13 (1.7)) who had never received any treatment. Cardiac output was increased (6.1 (0.6) l/min/m2) and right atrial (7.8 (1) mm Hg), mean pulmonary arterial (20.5 (2.0) mm Hg), and mean pulmonary arterial wedge (13 (2.7) mm Hg) pressures were slightly increased. The mean systemic arterial pressure (81 (1.3) mm Hg) and systemic vascular resistance (12.3 (1.1) mm Hg x min x m2/l were low. There were significant increases in total body water (+14%), extracellular volume (+32%), plasma volume (+70%), and total body exchangeable sodium (+30%). Renal blood flow was moderately decreased (-46%) and the glomerular filtration rate was slightly reduced (-24%). There were significant increases in plasma noradrenaline (2.1-fold), renin activity (15-fold), aldosterone (3.2-fold), growth hormone (6.3-fold), and atrial natriuretic peptide (12-fold).

CONCLUSION

In patients with oedema caused by chronic severe anaemia there is retention of salt and water, reduction of renal blood flow and glomerular filtration rate, and neurohormonal activation similar to that seen in patients with oedema caused by myocardial disease. However, unlike patients with myocardial disease, patients with anaemia have a high cardiac output and a low systemic vascular resistance and blood pressure. It is suggested that the low concentration of haemoglobin in patients with anaemia causes a reduced inhibition of basal endothelium-derived relaxing factor activity and leads to generalised vasodilatation. The consequent low blood pressure may be the stimulus for neurohormonal activation and salt and water retention.

Relation of pathophysiologic mechanisms to outcome in heart failure

Advances in the treatment of heart failure with angiotensin-converting enzyme inhibitors have been accompanied by an improved understanding of the pathophysiology of heart failure. The inability of the heart to act as a pump is determined in some patients by alterations to the architecture of the heart and changes in the extracellular space, particularly fibrosis. The degree to which the failure of the heart as a pump can be attributed to a reduced ability of the myocyte to contract is contentious. The origin of symptoms is still uncertain but does relate to identified changes in the lung, increased peripheral resistance and atrophy of skeletal muscle. The mechanisms of action of angiotensin-converting enzyme inhibitors are numerous and do not yet account easily for the clinical benefits. Further epidemiologic studies are needed to ascertain the proportion of patients who manifest progressive heart failure rather than deterioration due to further cardiac events. Understanding the pathophysiology of heart failure will allow therapy to be tailored to the requirements of the individual patient.

Reduced content of connexin43 gap junctions in ventricular myocardium from hypertrophied and ischemic human hearts

BACKGROUND

Gap junctions are a determinant of myocardial conduction. Disturbances of gap-junctional content may account for abnormalities of impulse propagation, contributing to the arrhythmic tendency and mechanical inefficiency of ischemic and hypertrophied myocardium. The aim of this study was to characterize gap junction organization in normal human ventricular myocardium and to establish whether abnormalities exist in myocardium of chronically ischemic and hypertrophied hearts.

METHODS AND RESULTS

Cardiac gap-junctional connexin43 antibodies and confocal microscopy were used in a quantitative immunohistochemical study of surgical myocardial samples to explore the structural basis of electromechanical ventricular dysfunction in chronic ischemic and hypertrophic heart diseases. Normal adult human left ventricular myocardium had a gap-junctional surface area of 0.0051 micron2/micron3 myocyte volume; gap junctions were confined to intercalated disks, of which there was a mean of 11.6 per cell. The right ventricle showed similar gap junction surface area. Left ventricular myocardium from ischemic hearts (distant from any fibrotic scarring), despite normal numbers of intercalated disks per cell, had a reduced gap junction surface area (0.0027 micron2/micron3; P = .02), as did hypertrophied myocardium (0.0031 micron2/micron3; P = .05). The cardiac myocytes in the pathological tissues were larger than normal, and estimated gap-junctional content per cell was reduced in ischemic ventricle (P = .02) compared with normal.

CONCLUSIONS

Gap junctions in normal adult human working ventricular myocardium occupy an area of 0.0051 micron2/micron3 myocyte volume. This surface area is reduced in ventricular myocardium from hearts subject to chronic hypertrophy and ischemia, despite a normal number of intercellular abutments, and this alteration may contribute to abnormal impulse propagation in these hearts.

Coexistence of functioning beta 1- and beta 2-adrenoceptors in single myocytes from human ventricle

BACKGROUND

Both beta 1- and beta 2-adrenoceptors (beta 1 AR and beta 2 AR) are present in human ventricle. This study was designed to determine whether the two subtypes contribute to contraction in single myocytes from human heart.

METHODS AND RESULTS

(-)-Epinephrine increased the contraction amplitude and velocity of single myocytes isolated from the ventricles of failing and nonfailing human hearts. Concentration-response curves to (-)-epinephrine were constructed in the presence and absence of selective antagonists for beta 1 AR (CGP 20712A) and beta 2 AR (ICI 118,551). Responses to (-)-epinephrine were antagonized to a variable degree by the blockers, suggesting heterogeneous contribution of beta 1AR and beta 2AR among cells. The most common response in single myocytes was that ICI 118,551 (50 nmol/L) shifted the concentration-response curve less than 10-fold: this was lower than the 100-fold shift expected for a pure beta 2AR effect. Inclusion of CGP 20712A (300 nmol/L) with ICI 118,551 shifted the (-)-epinephrine curve still further. These observations suggest that both beta 1AR and beta 2AR contribute to the increase in contraction amplitude with (-)-epinephrine in this group of myocytes. When 300 nmol/L CGP 20712A was present as the sole antagonist, only a marginal shift of the concentration-response curve for (-)-epinephrine was usually observed, indicating that beta 1AR were not mediating the effect of these low concentrations of (-)-epinephrine. Both beta 1AR and beta 2AR mediated a considerable abbreviation of the time to peak contraction and time to 50% relaxation in the single cells.

CONCLUSIONS

beta 1AR and beta 2AR coexist and function on human ventricular myocytes. At low (-)-epinephrine concentrations, contractile responses are predominantly mediated by beta 2AR rather than beta 1AR in myocytes from failing hearts.

Subcellular mechanism of the species difference in the contractile response of ventricular myocytes to endothelin-1

The aim of the experiments was to compare the effects of endothelin and alpha-adrenoceptor stimulation on the contraction and inositol phosphate turnover of cardiomyocytes enzymatically isolated from rat and guinea-pig hearts. The effects of agonists on the contraction amplitude of warmed (32 degrees C), electrically stimulated (0.5 Hz) myocytes was recorded using a video-edge detection system. Phosphoinositide hydrolysis was measured in suspensions of myocytes prelabelled with myo-[2(-3)H]-inositol. A doubling of contraction amplitude was observed in rat ventricular myocytes in response to maximally effective concentrations of either endothelin-1 (10 nM) or phenylephrine (1 mM). In rat myocytes, prazosin prevented the effect of phenylephrine but not the effect of endothelin-1. Reversal of the maximal inotropic effect of endothelin was slow (halftime for reversal 11.5 +/- 4.5 min) compared with phenylephrine (3.4 +/- 1.1 min). Endothelin (10 nM) added at the peak effect of phenylephrine produced no further increase in contraction amplitude. The half-time for the reversal of the effect of phenylephrine plus endothelin in these experiments was not significantly different from that with endothelin alone (12.8 +/- 4.0 min). This indicates that phenylephrine did not interact with endothelin binding. Phosphoinositide hydrolysis was increased in rat myocytes by either endothelin or phenylephrine. In guinea-pig myocytes, endothelin-1 stimulated phosphoinositide hydrolysis but did not induce an inotropic response, whereas phenylephrine gave neither an increase in phosphoinositide hydrolysis nor an inotropic effect. We conclude that the observations in rat myocytes are consistent with different receptors for endothelin-1 and phenylephrine, but a common final pathway through the inositol phosphate system for the inotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Incomplete reversal of beta-adrenoceptor desensitization in human and guinea-pig cardiomyocytes by cyclic nucleotide phosphodiesterase inhibitors

1. The decreased response to beta-adrenoceptor stimulation seen in heart failure may be related to a defect in cyclic AMP production. The inotropic effects of the selective phosphodiesterase (PDE) III inhibitors, SK&F 94120 and SK&F94836, and the non-selective PDE inhibitor, 3-isobutyl-l-methylxanthine (IBMX), alone and when combined synergistically with isoprenaline, were studied in control and beta-adrenoceptor-desensitized ventricular myocytes. 2. Myocytes isolated from noradrenaline-treated guinea-pigs had a reduced maximum response to isoprenaline compared with control animals (60.0 +/- 2.5%, n = 42 vs 79.5 +/- 1.7% maximum calcium: n = 46, P < 0.001). Together with an approximately 20 fold increase in the isoprenaline EC50, this is indicative of beta-adrenoceptor desensitization as a result with chronic infusion with noradrenaline. 3. The maximum inotropic response of IBMX was depressed following noradrenaline treatment, from 74.9 +/- 4.6% (n = 7) in control, to 61.7 +/- 2.70% (n = 6), as a percentage of maximum calcium in noradrenaline-treated guinea-pig ventricular myocytes (P < 0.02). The pD2 value for IBMX was also reduced (P < 0.02). No significant differences in the inotropic effects of SK&F94120 and SK&F94836 were seen between control and beta-adrenoceptor desensitized myocytes. 4. Threshold inotropic concentrations of SK&F94120 and SK&F94836 caused a five fold decrease in the EC50 of control myocytes for isoprenaline, and an 11 fold decrease in the noradrenaline-treated guinea-pig ventricular myocytes. 5. The maximum response to isoprenaline in myocytes isolated from normal guinea-pigs was unaffected by PDE inhibition; either at threshold or maximum inotropic concentrations, or by CPT cyclic AMP, an analogue of cyclic AMP.6. A significant potentiation of the maximum isoprenaline response by threshold inotropic concentrations was observed with SK&F 94120 (P<0.05), but not with IBMX or SK&F 94836, in myocytes isolated from noradrenaline-treated guinea-pig hearts. This potentiation, however, did not completely restore the response to levels seen in control myocytes.7. The extent of potentiation of the maximum isoprenaline response by maximum inotropic concentrations of either IBMX or CPT cyclic AMP, was no greater than that by threshold concentrations of IBMX, in myocytes isolated from noradrenaline-treated guinea-pig hearts.8. In cardiac myocytes isolated from the explanted hearts of 16 patients with heart failure, threshold concentrations of IBMX and SK&F 94120 decreased the isoprenaline EC50 by a factor of four and six,respectively, but potentiation of the maximum isoprenaline response occurred only with SK&F 94120.The attenuated isoprenaline response was increased from 60.3 +/- 4.5% to 74.3 +/- 4.2% as a % maximum calcium (P<0.05, n = 6), but remained substantially lower than the 116 +/- 7% (P<0.001, n = 6) seen in myocytes isolated from non-failing hearts.9. We conclude that the reduced maximum contraction amplitude with isoprenaline in cardiac myocytes from either patients in end-stage failure, or noradrenaline-treated guinea-pigs, is partly but not solely due to insufficient cyclic AMP levels, since inhibition of cyclic AMP degradation does not result incomplete reversal of the beta-adrenoceptor desensitization.

Beneficial effect of oestrogen on exercise-induced myocardial ischaemia in women with coronary artery disease

Oestradiol-17 beta causes relaxation of isolated coronary arteries and increases blood flow in several vascular beds in human beings and animals. Oestrogen replacement therapy is associated with a lower incidence of cardiovascular disease, but the acute effects of oestradiol-17 beta on myocardial ischaemia are unknown. We have studied the acute effect of sublingual oestradiol-17 beta on exercise-induced myocardial ischaemia in eleven women (mean age 58 [SD 8] years) with coronary artery disease. The women did two treadmill exercise tests on separate days; 40 min before the test they took sublingual oestradiol-17 beta (1 mg) or placebo, in random order. Plasma oestradiol-17 beta concentrations were confirmed to be higher after sublingual oestradiol-17 beta than after placebo (2531 [1192] vs 155 [168] pmol/L, p < 0.001). Oestradiol-17 beta increased both time to 1 mm ST depression (456 [214] vs 579 [191] s, p < 0.004; difference of medians 92 [95% CI 46-254]) and total exercise time (569 [249] vs 658 [193] s, p < 0.01; difference 54 [10-212]). Acute administration of oestradiol-17 beta therefore has a beneficial effect on myocardial ischaemia in women with coronary artery disease. This effect may be due to a direct coronary-relaxing effect, to peripheral vasodilation, or to a combination of these mechanisms. Oestradiol-17 beta may prove to be a useful adjunct to the treatment of angina in postmenopausal women with coronary heart disease.

Endothelium dependent and independent responses in coronary artery disease measured at angioplasty

OBJECTIVE--To investigate the effects of substance P and papaverine, two drugs that increase coronary blood flow by different mechanisms, on vasomotion in stenotic coronary arteries at percutaneous transluminal coronary angioplasty (PTCA). DESIGN--Coronary blood flow responses to substance P and papaverine were measured in stenotic coronary arteries at the time of PTCA with quantitative angiography and a Doppler flow probe. SETTING--A cardiothoracic referral centre. PATIENTS--15 patients undergoing elective PTCA of a discrete epicardial coronary artery stenosis. INTERVENTIONS--Pharmacological coronary flow reserve was determined with papaverine 5-10 minutes before and after successful PTCA. Endothelium dependent responses to 2 minute infusions of substance P (10-15 pmol.min-1) were assessed immediately before PTCA. MAIN OUTCOME MEASURES--Coronary blood flow responses and changes in epicardial coronary artery area at stenotic, proximal, and distal sites with papaverine and substance P. RESULTS--Stenotic sites dilated with papaverine before PTCA (17.7%(6.9%) (mean (SEM)) area increase, p < 0.05 v baseline). Substance P dilated stenotic sites (16.8%(5.7%) area increase, p < 0.05) and proximal (14.3%(5.4%), p < 0.05) and distal sites (41.7%(9.3%), p < 0.005). Coronary flow reserve increased but did not reach normal values after PTCA (2.3(0.4) before PTCA v 3.0(0.4) after PTCA, p < 0.05) and was associated with an increase in peak flow with papaverine. Angioplasty did not alter baseline flow. After PTCA papaverine caused significant vasoconstriction at the stenotic site (-13.6%(4.3%) area decrease, p < 0.05). There was a negative correlation (r = -0.68, p < 0.05) between the dilator response with papaverine before PTCA and the constrictor response after PTCA. CONCLUSIONS--Substance P causes endothelium dependent dilatation in atheromatous coronary arteries, even at sites of overt atheroma. The cause of the paradoxical constrictor response to papaverine after PTCA is uncertain, but unopposed flow mediated vasoconstriction (the myogenic response) after balloon induced endothelial denudation may be one of several contributory factors.

The role of calcium antagonists in the treatment of chronic heart failure

Calcium antagonists have been widely used for the treatment of angina and hypertension. Because of vasodilator and anti-ischaemic properties, calcium antagonists might be expected to bring benefit to patients with heart failure, particularly when the heart failure is due to coronary heart disease. Eight trials of calcium antagonists, fulfilling specific criteria, have been reviewed. The evidence at present does not support the use of calcium antagonists in established heart failure. Some benefit may accure from the use of the newer calcium antagonists but further trials are awaited. Calcium antagonists appear to improve diastolic fraction in patients with coronary heart disease, no overt heart failure but a reduced ejection fraction.

Nitric oxide attenuates cardiac myocyte contraction

Cardiac muscle fibers have microvessels in close proximity, the distance from the nearest capillary being no greater than 8 microns. We performed experiments on isolated, electrically stimulated, contracting guinea pig cardiac myocytes to test whether NO from endothelium or nitrovasodilators or directly superfused in solution might affect myocyte contractility. In endothelium-myocyte coculture experiments, 10(-7) M bradykinin reduced myocyte shortening by 11 +/- 3.5%. This effect was abolished in the presence of NG-nitro-L-arginine methyl ester and was unaffected by indomethacin. Sodium nitroprusside, but not organic nitrovasodilators, reduced myocyte contraction amplitude by 23% at 3 x 10(-5) M. This effect was reversed by methylene blue. Superfusion with NO solution had an effect similar to sodium nitroprusside, as did exposure to 8-bromoguanosine 3',5'-cyclic monophosphate. Thus the present study shows that cardiac myocyte contraction is attenuated by NO, which appears to act via production of guanosine 3',5'-cyclic monophosphate within the myocytes. Because cardiac myocytes in vivo are in such close proximity to endothelium, the effects of endothelial products on cardiac myocyte contractility may be important in myocardial function.

Skeletal muscle blood flow in heart failure measured by ultrafast computed tomography: validation by comparison with plethysmography

OBJECTIVES

Abnormalities of skeletal muscle perfusion and metabolism may be important in the symptomatic limitation of patients with chronic heart failure. A method for assessing both skeletal muscle blood flow and mass would be useful in clinical practice and research. Ultrafast computed tomography has the potential to make these measurements. The aim was to determine the accuracy with which skeletal muscle blood flow could be measured by ultrafast computed tomography in patients with chronic heart failure.

METHODS

Leg blood flow measured by venous occlusion plethysmography was compared with skeletal muscle blood flow by ultrafast computed tomography. Fourteen patients with chronic heart failure (aged 51 to 76 years) were investigated. Plethysmography and ultrafast computed tomography measurements were performed at rest and during hyperaemic flow induced by symptom limited bicycle exercise followed by five minutes of leg ischaemia. The ultrafast computed tomography measurements were made by analysing the opacification of the blood pool and of the muscle after an intravenous bolus of non-ionic radio-opaque contrast.

RESULTS

Flows assessed by plethysmography ranged from 1.5 to 38.1 ml x 100 ml-1 x min-1. The slope of the line relating the two methods was 1.1 (95% confidence interval 0.91 to 1.31), and the mean (95% limits of agreement) of the differences between the two methods was 2.5(10.6) ml x 100 ml-1 x min-1.

CONCLUSIONS

Ultrafast computed tomography is a useful tool in the measurement of both skeletal muscle mass and perfusion in humans.

Cardiovascular protection by oestrogen--a calcium antagonist effect?

During their premenopausal years, women have a lower risk than men of getting cardiovascular disease. This protection continues after the menopause if women receive oestrogen replacement. Based on new experimental evidence we propose that some of the cardiovascular benefits of oestrogen replacement therapy may be due to a long-term calcium antagonist effect of oestrogen.

Measurement accuracy of cardiac output in humans: indicator-dilution technique versus geometric analysis by ultrafast computed tomography

OBJECTIVES

The aim of this study was to evaluate measurement accuracy of cardiac output in humans by comparing the indicator-dilution technique with geometric analysis by ultrafast computed tomography.

BACKGROUND

Ultrafast computed tomography can be used to measure cardiac output by two methods. First, by scanning to obtain end-systolic and end-diastolic short-axis images of the ventricular cavities at sequential tomographic levels, the stroke volume and therefore the cardiac output can be calculated. Second, indicator-dilution theory (the Stewart-Hamilton equation) can be applied to measurements of the concentration of radiographic contrast in the blood pool after a bolus injection. The latter method has not been validated in humans.

METHODS

The accuracy of the geometric method itself was first established by comparing left and right ventricular stroke volumes in 29 patients without valvular regurgitation or an intracardiac shunt, whose left and right ventricular stroke volumes should have been identical (group A). In a subset of 17 patients, the geometric method was compared with the indicator-dilution method (group B).

RESULTS

Geometric analysis showed that the mean difference between left and right ventricular stroke volume was 1.8 +/- 7.3 ml, with a percentage SD of the differences of 9.3% (r = 0.9). Comparison wih indicator dilution-calculated cardiac output showed a mean difference of 0.079 +/- 1.22 liters/min, with a percent SD of the differences of 23.7% (r = 0.6). There was no improvement in this comparison with individual calibration of the scanner for each patient.

CONCLUSIONS

The disparity found between data obtained with the geometric and indicator-dilution methods may be a result of the hemodynamic effects of contrast medium or it may suggest the possibility that some assumptions of indicator-dilution theory are not valid.

Low frequency oscillations in pulmonary arterial pressure in chronic heart failure

Spontaneous, sustained low frequency oscillations of pulmonary arterial pressure were observed in 8 patients with moderate to severe chronic heart failure during recordings of pulmonary arterial pressure of 8.6 to 48 hours duration. The oscillations (frequency range 0.015 to 0.035 Hz) had a distinct peak from and lower frequency range than respiration (0.2 to 0.6 Hz) and heart rate (0.8 to 1.9 Hz). They were present from 42% to 82% of the recording time with an amplitude varying from undetectable to a maximum range from 5.3 mm Hg to 19.7 mm Hg. When detectable, the mean amplitude of the low frequency oscillations of pulmonary arterial pressure ranged from 1.2 +/- 1.2(SD) mm Hg to 4.3 +/- 3.3 mm Hg. These oscillations are lower in frequency than the low frequency component usually described in recordings of systemic arterial pressure and heart rate in normal subjects, and are closer to the very low frequency rhythms described in severe chronic heart failure and Cheyne Stokes respiration.

Nitric oxide production within cardiac myocytes reduces their contractility in endotoxemia

We investigated whether increased nitric oxide (NO) synthase activity within cardiac myocytes contributes to the depressed cardiac contractility observed in endotoxic shock. Isolated ventricular myocytes were studied to examine the effects of substrates and inhibitors of NO synthase on myocyte contractility. When stimulated electrically, the resting length of myocytes from control animals shortened by 5.3 +/- 0.3% (means +/- SE, n = 32). Baseline contraction of myocytes from endotoxin-treated animals was reduced to 3.0 +/- 0.3% (n = 17, P < 0.001). The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) had no effect on myocytes from control animals, but it increased the contraction of myocytes from endotoxin-treated animals by 40% (fractional shortening increased to 4.3 +/- 0.4%, P < 0.01). Similar results were obtained with NG-methyl-L-arginine. The effect of L-NAME could be reversed by excess L-arginine, but not D-arginine. The effect of endotoxin was abolished by dexamethasone pretreatment. Methylene blue also reversed the effects of endotoxin but had toxic effects on myocytes. Agents that either prevent synthesis or the effects of NO reverse the depression of myocyte contraction seen following endotoxin treatment.

Relation between ventilation and carbon dioxide production in patients with chronic heart failure

OBJECTIVES

The aim of this study was to analyze the relation between ventilation and carbon dioxide production and the control of ventilation in patients with chronic heart failure.

BACKGROUND

Patients with chronic heart failure exhibit an increased ventilatory response to exercise. Ventilation is closely linked to carbon dioxide production, producing a high correlation between the two variables. This relation is nonlinear at high levels of exercise.

METHODS

The ventilation/carbon dioxide production ratio during exercise was examined in 29 patients with chronic heart failure and 9 normal volunteers.

RESULTS

In the patients with heart failure, there were three patterns: in the least severely affected patients, the pattern was similar to that of the normal subjects, with an initial decrease in the ventilation/carbon dioxide production ratio to a plateau maintained during exercise; in more severely affected patients, there was an increase in the ratio at the end of exercise, and in the most severely affected patients, the ratio increased from the outset of exercise. The ventilation/carbon dioxide relation is not adequately described by a straight line relation.

CONCLUSIONS

The ventilation/carbon dioxide ratio is not fixed, and the changes that occur in this ratio reflect either a noncarbon dioxide-driven ventilatory stimulus or an increase in ventilation-perfusion mismatch due to increased dead space ventilation. The different patterns of this ratio may provide clues to the pathophysiologic mechanisms of the excessive ventilation and breathlessness seen during exercise in chronic heart failure.

Reduced contractile responses to forskolin and a cyclic AMP analogue in myocytes from failing human ventricle

Myocytes were isolated from the right or left ventricles of failing and non-failing human hearts. Contractile responses to increasing concentrations of Ca2+, isoprenaline, forskolin and dibutyryl cyclic AMP (a lipophilic analogue of cyclic AMP) were determined. Responses were correlated with the age of the patient, and the severity of failure as defined by New York Heart Association class of symptoms (NYHA), left ventricular ejection fraction (LVEF), left ventricular end diastolic pressure (LVEDP) and dose of diuretics prescribed (diuretic class). The maximum contraction amplitude in high Ca2+ did not change with either age or severity of failure (n = 31-40 patients). Responses to isoprenaline (relative to Ca2+ in the same cell, isoprenaline/calcium ratio) decreased with increasing age (P < 0.001, n = 38), and increasing severity of disease (NYHA, P < 0.001, n = 38; LVEF, P < 0.001, n = 34; LVEDP, P < 0.001, n = 30; diuretic class, P < 0.01, n = 36). The decrease in forskolin/calcium ratio also correlated with age (n = 17, P < 0.005) and increasing severity (NYHA, P < 0.002, n = 17; LVEF, P < 0.05, n = 15; LVEDP, P < 0.02, n = 14; diuretic class, P < 0.05, n = 15). Multiple regression indicated that the contribution of age was greater than that of disease severity for both isoprenaline and forskolin responses. The dibutyryl cyclic AMP/calcium ratio did not change significantly with the age of the patient (P > 0.1, n = 13), or severity as defined by LVEDP (P = 0.05-0.1, n = 12) but did decrease with increasing NYHA class (P < 0.01, n = 13) or diuretics (P < 0.02, n = 12) or with low LVEF (P < 0.002, n = 12). Overall, neither forskolin nor dibutyryl cyclic AMP produced maximum responses greater than isoprenaline in myocytes from failing hearts. Where the response to isoprenaline was not limited by the appearance of arrhythmias, forskolin or dibutyryl cyclic AMP could give a significant (but small) increase in contraction over that with isoprenaline alone. These results provide evidence for a post-receptor defect in addition to beta-adrenoceptor desensitisation in myocytes from failing human heart.

Cardiac flow measurement by ultrafast CT: validation of continuous and pulsatile flow

To gauge the accuracy of ultrafast CT in measuring cardiac output and myocardial perfusion in humans, measurements of continuous and pulsatile flow were made in a large asymmetrical phantom. The variation in the relationship between Hounsfield number and contrast concentration was assessed in a human thorax phantom. Radiopaque contrast medium was injected during perfusion of the phantom at a range of flow rates between 1.5 and 8 L/min. The phantom was scanned in two modes (50 and 100 ms) during continuous and pulsatile flow and with the phantom surrounded by air and by water. Flow in the tubes was calculated using indicator dilution theory, and flow in the tissue-equivalent chamber was calculated by applying first-pass distribution principles. The standard deviation of the difference between calculated and measured flow varied from 0.2 to 0.6 L/min, giving 95% limits of agreement from 0.4 to 1.2 L/min. The constant (K) relating Hounsfield unit number to iodine concentration varied widely both in different locations within the phantom and under different scan conditions (17.2-27.6 HU/mg I). Within a human thorax phantom, K varied from 14.15 to 23.18 HU/mg I and was dependent on location within the thorax phantom, the scan mode, and the cross-sectional diameter of the phantom. These data suggest that though the ultrafast CT scanner can measure continuous and pulsatile flow accurately in tubes, precise measurements of cardiac output in humans will require K to be assessed for each subject. Measurements of flow in tissue should be possible.

Angina and normal coronary arteries in women: gynecologic findings

OBJECTIVES

Our aim was to evaluate the hypotheses that women with severe angina and normal coronary arteries (syndrome X) have an increased incidence of hysterectomy and show a positive cardiac response to 17 beta-estradiol replacement therapy.

STUDY DESIGN

The gynecologic histories of 30 women with syndrome X were determined. Anginal and 17 beta-estradiol insufficiency symptoms were recorded daily for 1 month. Subsequently, 20 of the women underwent hyperemic response testing before and after 2 months of estrogen replacement therapy. Hyperemic response results were compared with those of 12 asymptomatic post-menopausal women not receiving estrogen replacement therapy. Symptoms were recorded daily during estrogen replacement therapy.

RESULTS

A total of 18 women (60%) underwent hysterectomy. All were experiencing hot flushes. Hyperemic response was diminished in women with syndrome X compared with controls. Hyperemic response increased and anginal symptoms decreased during estrogen replacement therapy.

CONCLUSION

The incidence of hysterectomy was increased and estrogen replacement therapy alleviated cardiac symptoms and enhanced hyperemic response in a group of women with syndrome X.

Effect of 17 beta-oestradiol on contraction, Ca2+ current and intracellular free Ca2+ in guinea-pig isolated cardiac myocytes

1. The effect of 17 beta-oestradiol on cardiac cell contraction, inward Ca2+ current and intracellular free Ca2+ ([free Ca2+]i) was investigated in guinea-pig single, isolated ventricular myocytes. The changes of cell length were measured by use of a photodiode array, the voltage-clamp experiments were performed with a switch clamp system and [free Ca2+]i was measured with the Ca2+ indicator, Fura-2. 2. 17 beta-Oestradiol (10, 30 microM) caused a decrease in cell shortening at both 22 and 35 degrees C. This negative inotropic effect was accompanied by a decrease in action potential duration mainly brought about by a shortening of the plateau region of the action potential. 17 beta-Oestradiol (10, 30 microM) induced a similar decrease in cell shortening in voltage-clamped and current-clamped cells. 3. In Fura-2 loaded cells, 17 beta-oestradiol (10 and 30 microM) decreased systolic Fura-2 fluorescence to 72 +/- 7% and 47 +/- 4% (n = 6, P less than 0.001) of control respectively. 17 beta-Oestradiol (10 microM) had no significant effect on diastolic Fura-2 fluorescence, but at higher concentration (30 microM) induced a slight decrease in resting Fura-2 fluorescence. The effect of 17 beta-oestradiol was reversible after 1-2 min of washout of the steroid. 4. 17 beta-Oestradiol (10 and 30 microM) decreased the peak inward Ca2+ current (ICa), which was sensitive to [Ca2+]o, dihydropyridines and isoprenaline, to 59 +/- 3% and 39 +/- 5% (n = 7 approximately 9, P less than 0.01) respectively, without producing any significant change in the shape of the current-voltage relationship.5. The recovery time of ICa from inactivation was delayed by 17beta-oestradiol (10microM). The inhibitory effect of 17beta-oestradiol on ICa was less at a holding potential of -80 mV than at -40 mV.6. We conclude that 17beta-oestradiol has a negative inotropic effect on guinea-pig single ventricular myocytes by inhibiting ICa and so reducing systolic [Ca2+]i. 17beta-Oestradiol may therefore have a Ca2+ channel blocking property in guinea-pig isolated ventricular myocytes.

Acute effect of 17 beta-estradiol on rabbit coronary artery contractile responses to endothelin-1

We assessed the acute effect of 17 beta-estradiol on coronary artery constrictor responses to endothelin-1. 17 beta-Estradiol significantly shifted endothelin-1, calcium, or BAY K 8644 concentration-dependent contraction curves to the right in endothelium-denuded coronary arteries isolated from nonpregnant female rabbits. The -log 50% effective dose (ED50) of calcium in high KCl medium (100 mM) was 3.8 +/- 0.11 in control and 3.2 +/- 0.1 and 2.8 +/- 0.12 after incubation with 17 beta-estradiol (1 and 10 microM, respectively). The -log ED50 of BAY K 8644 (KCl 15 mM) was 7.8 +/- 0.1 in control and 7.4 +/- 0.08 and 7.2 +/- 0.05 in the presence of 17 beta-estradiol (1 and 10 microM, respectively). The -log ED50 of endothelin-1 was 9.2 +/- 0.08 in control and 8.8 +/- 0.1, 8.4 +/- 0.07, and 8.1 +/- 0.12 after incubation with 17 beta-estradiol (3, 10, and 30 microM, respectively). Similar results were obtained from coronary arteries of male rabbits. These increases of -log ED50 values were significant (P less than 0.05 or 0.01). 17 beta-Estradiol and verapamil induced dose-dependent relaxation in both endothelium-intact or -denuded coronary arteries submaximally precontracted by endothelin-1. NG-monomethyl-L-arginine had no effect on relaxation induced by 17 beta-estradiol, whereas it eliminated relaxation induced by acetylcholine in rings with an intact endothelium. These data suggest that 17 beta-estradiol attenuates the rabbit coronary artery contraction induced by endothelin-1 via an endothelium-independent mechanism, possibly by affecting calcium influx.

Impairment of endothelium dependent responses in a rat model of chronic heart failure: effects of an exercise training protocol

OBJECTIVE

The aim was to document the response of aortic rings from a rat model of heart failure to endothelium dependent and endothelium independent vasodilating agents. The effects of an exercise training schedule upon these responses was studied.

METHODS

Heart failure was produced in one group of female Wistar rats by coronary artery occlusion, and sham operations were performed in a matched group. The rats were allowed to recover for six weeks, following which half the rats with heart failure were started on a treadmill exercise schedule for a further six weeks. After this time the rats were killed, and rings of aorta were studied in an organ bath to measure the response to both endothelium dependent and endothelium independent vasoactive agents.

RESULTS

The presence of heart failure was confirmed in both the non-trained (NT, n = 5) and trained rats (TR, n = 5), but not in the sham operated animals (SH, n = 6). The constrictor response to prostaglandin F2 alpha was similar in aortic rings from all the animals. The relaxation response to the endothelium dependent vasodilator acetylcholine (10(-7) and 10(-6) M) was impaired in the rats with heart failure compared to the sham operated animals (10% v 33% with 10(-7) M acetylcholine, p < 0.005). The dilator response in the trained rats was not significantly greater than in the non-trained rats (TR 35% v NT 24% with 10(-6) M acetylcholine). There was no difference in the response to sodium nitroprusside (10(-7) and 10(-6) M) between the three groups.

CONCLUSIONS

Chronic heart failure impairs the response of aortic rings to the endothelium dependent vasodilator acetylcholine in a rat model of heart failure. The response to sodium nitroprusside, an endothelium independent relaxing agent, is not impaired by heart failure. These findings may help to explain the raised systemic vascular resistance and the failure of vasodilatation in skeletal muscle vasculature which limits exercise capacity in subjects with heart failure.

Prevalence of heart failure in three general practices in north west London

There is little recent information on the prevalence of heart failure in the United Kingdom. Assuming that patients with heart failure would be taking diuretic drugs all such patients were identified in three general practices in north west London. The practice records of these patients were examined to determine which patients had heart failure. Of the 30,204 patients served by the practices, 117 had heart failure, a prevalence of 3.9 per 1000 patients. The mean age of these patients was 74 years. The prevalence of heart failure among patients under 65 years of age was 0.6 per 1000 patients rising to 27.7 per 1000 among those aged 65 years and over. The aetiology of heart failure was considered to be coronary heart disease for 32% of patients, valve disease for 19%, hypertension for 6%, cor pulmonale for 4% and congenital heart disease for 2%. The aetiology for the remaining 37% of patients was unknown. Most patients were referred to hospital and only 20% had been treated solely by the general practitioner. An electrocardiogram and chest radiograph had been obtained for over 80% of patients but only 28% had an echocardiogram. Heart failure occurs primarily in elderly patients, and coronary heart disease is the dominant aetiological factor.

Pathogenesis of congestive state in chronic obstructive pulmonary disease. Studies of body water and sodium, renal function, hemodynamics, and plasma hormones during edema and after recovery

BACKGROUND

The pathogenesis of salt and water accumulation in patients with chronic obstructive pulmonary disease is unclear and may differ from that in patients with congestive heart failure due to myocardial disease. This study was undertaken to investigate some of the mechanisms involved.

METHODS AND RESULTS

Hemodynamics, water and electrolyte spaces, renal function, and plasma hormone concentrations were measured in nine patients with edema due to chronic obstructive pulmonary disease and in six patients after recovery. Mean cardiac output (3.8 +/- 0.26 l/min.m2) was normal, but right atrial (11 +/- 1 mm Hg) and mean pulmonary arterial (41 +/- 3 mm Hg) pressures were increased. Mean pulmonary arterial wedge pressure (11 +/- 1 mm Hg) was normal. Pulmonary vascular resistance (8.6 +/- 1.3 mm Hg.min.m2/l) was increased, but systemic vascular resistance (19.3 +/- 1.3 mm Hg.min.m2/l) and mean arterial pressure (83 +/- 4 mm Hg) were low. All patients were hypoxemic (PaO2, 40 +/- 2 mm Hg) and hypercapnic (PaCO2, 60 +/- 2 mm Hg). There was a significant increase in total body water (+21%), extracellular volume (+45%), plasma volume (+45%), blood volume (+88%), and exchangeable sodium (+38.2%). Renal plasma flow was severely reduced (-63.2%), but glomerular filtration rate was only mildly decreased (-32%). Significant increases were seen in plasma norepinephrine (3.5-fold normal), renin activity (7.6-fold normal), vasopressin (twice normal), atrial natriuretic peptide (9.4-fold normal), growth hormone (10.7-fold normal), and cortisol (1.9-fold normal). After recovery, the PaO2 increased (50 +/- 3 mm Hg) and PaCO2 fell (45 +/- 4 mm Hg), and the patients became free from edema. All the body compartments returned toward normal, although they did not entirely reach normal values. Renal plasma flow increased significantly, and glomerular filtration became normal. Right atrial and pulmonary arterial pressures and pulmonary vascular resistance decreased (p less than 0.01). Cardiac output decreased but not significantly. Blood pressure increased but not significantly. However, systemic vascular resistance increased significantly to a normal value.

CONCLUSIONS

We conclude that patients with edema due to chronic obstructive pulmonary disease have severe retention of salt and water, reduction in renal blood flow and glomerular filtration, and neurohormonal activation similar to that seen in patients with edema due to myocardial disease. However, unlike the latter, in chronic obstructive pulmonary disease cardiac output is normal, and systemic vascular resistance and arterial blood pressure are low. This probably is due to the vasodilator properties of hypercapnia. The consequent low arterial blood pressure may be the stimulus for the neurohormonal activation and retention of salt and water.

The ST segment--the herald of ischaemia, the siren of misdiagnosis, or syndrome X?

Syndrome X is the term applied to patients with anginal-type chest pain who, despite a positive exercise stress test, have angiographically normal coronary arteries. Such patients probably belong to a heterogeneous group, and in a proportion the exercise test is falsely positive. With the availability of more accurate techniques for the detection of myocardial ischaemia, it is apparent that some patients can be shown to develop transient myocardial ischaemia with stress. The paradox of normal coronary arteries and a positive exercise test may be resolved by improved understanding of the regulatory control of regional myocardial blood flow, particularly at the level of the microvasculature, and of the metabolic expression of myocardial ischaemia.

Abnormal diastolic filling patterns in chronic heart failure--relationship to exercise capacity

Abnormal patterns of diastolic ventricular filling are well recognized in chronic heart failure, but their relationship to the severity of heart failure is not known. The present study evaluates the relationship of diastolic filling indices to the severity of heart failure and to exercise capacity. In 40 patients with chronic heart failure secondary to ischaemic left ventricular impairment, exercise capacity was measured as peak oxygen consumption (VO2max) by progressive treadmill exercise. Left ventricular function was assessed by M-mode and Doppler echocardiographic indices. Peak aortic velocity correlated weakly with VO2max (R = +0.38, P less than 0.05). VO2max did not correlate with other systolic indices, including mean aortic acceleration, time to peak velocity, or isovolumic contraction time. VO2max correlated with the mitral inflow E/A ratio (R = -0.57, P less than 0.005) and with the Doppler estimate of isovolumic relaxation time (R = -0.48, P less than 0.01). Two distinct patterns of diastolic filling were observed: subjects with mild-to-moderate heart failure (NYHA grade II, VO2max 15-20 ml.kg-1.min-1) had abnormally low E/A ratios and long isovolumic relaxation times, whereas those with severe heart failure (NYHA grade III-IV, VO2max less than 12 ml.kg-1.min-1) had abnormally high E/A ratios and short isovolumic relaxation times. Different patterns of abnormal diastolic filling with different degrees of severity of heart failure may explain some of the previous controversy as to the prevalence of abnormal diastolic function in chronic heart failure. Exercise capacity in chronic heart failure appears more closely related to abnormalities of diastolic filling pattern than to indices of systolic function.

Blood flow and skeletal muscle in patients with heart failure

The factors that contribute to the symptoms of breathlessness and fatigue, and that limit exercise capacity in patients with chronic heart failure are poorly understood. Recent evidence suggests that the major mechanism is not related to central hemodynamics but to a reduction of skeletal muscle mass and diminished blood flow to skeletal muscle on exercise.

Isolated ventricular myocytes from failing and non-failing human heart; the relation of age and clinical status of patients to isoproterenol response

Single cardiac myocytes were isolated from the ventricles of failing and non-failing human hearts. The contraction amplitude, time-to-peak shortening and time to 50% and 90% relaxation were measured in cells stimulated at 0.2 Hz at 32 degrees C. The effects of increasing extracellular calcium and isoproterenol were investigated using cumulative concentration/response curves. Maximum contraction amplitude in high calcium or velocities of contraction or relaxation were not impaired in cells from failing hearts. Beta-adrenoceptor function in a single cell was assessed by the maximum contraction amplitude in the presence of isoproterenol relative to that with high calcium in the same cell (isoproterenol/calcium ratio). A decrease in the isoproterenol/calcium ratio correlated positively with an increase in the isoproterenol EC50 (concentration for half-maximal effect) for a cell (P less than 0.02, n = 39). The isoproterenol/calcium ratio in left ventricular myocytes decreased with increasing severity of disease, correlating with failure as defined by New York Heart Association class (P less than 0.001, n = 26 patients), left ventricular ejection fraction (P less than 0.001, n = 24), left ventricular end diastolic pressure (P less than 0.05, n = 21) and amount of diuretics prescribed (P less than 0.001, n = 26). In right ventricular myocytes, only increasing NYHA class correlated with decreasing isoproterenol/calcium ratios. There was a correlation of the isoproterenol/calcium ratio between right and left ventricular cells from patients with ischemic heart disease (P less than 0.05), n = 11). Beta-adrenoceptor subsensitivity occurred in mitral valve disease, ischemic heart disease, congenital abnormalities and congestive cardiomyopathy, but not in the right ventricle of patients with myocarditis. The isoproterenol/calcium ratio correlated negatively with the age of the patient (P less than 0.001, n = 26, left ventricle). Multiple regression indicated that the maximum contraction amplitudes in either high isoproterenol or high calcium declined significantly with age only, but that both age and severity of disease contributed to the decrease in isoproterenol/calcium ratio. Time-to-peak tension in isoproterenol, as well as relaxation times in high calcium also decreased with the age of the patient. Analysis of variance showed that between-patient variation was significantly greater than between-cell for most of the parameters measured. Beta-adrenoceptor desensitisation may be detected in individual myocytes from failing hearts, and this relates more to the severity of disease and the age of the patient rather than the etiology of heart failure. A decline in absolute contractility of muscle cells with age was detected.

Heart failure in a district general hospital

The frequency, clinical characteristics, and outcome of patients admitted with heart failure to a district general hospital in North-West London serving a population of approximately 155,000 was assessed over a six-month period. The number of patients with heart failure was determined by both a prospective ward survey and a retrospective study of all patient records with diagnostic codes for heart failure or pulmonary oedema. During those six months, 2,877 patients were admitted to the medical and geriatric services of whom 140 (4.9%) had heart failure. Only 29 patients in heart failure were under the age of 65 years. In 86 patients the mode of presentation was acute pulmonary oedema. Fifty-two (37%) patients had an arrhythmia at the time of admission of whom 48 had atrial fibrillation. An electrocardiogram, a chest X-ray, and an echocardiogram were performed in 137, 136, and 81 patients respectively. The aetiology of heart failure was considered to be coronary artery disease (41%), valve disease (9%), hypertension (6%), cor pulmonale (4%), a dilated cardiomyopathy (1%), congenital heart disease (1%), thyrotoxicosis (1%), and unknown (36%). During the period of hospital stay 42 patients (30%) died; a further 20 patients (14%) died in a one-year follow-up. In a district general hospital heart failure is a common reason for admission and patients remain in hospital for a considerable time. Arrhythmias are commonly associated with heart failure. The prognosis is poor and the hospital mortality high. The management of heart failure is an important consideration in allocating hospital resources in a district general hospital.

Progesterone induces endothelium-independent relaxation of rabbit coronary artery in vitro

The effect of progesterone on isolated rabbit coronary arteries and its possible mechanism was investigated by measuring changes of isometric tension. Progesterone (1, 3, 10 and 30 microM) induced significant coronary relaxation in K+ (30 mM)-, prostaglandin F2 alpha (3 microM)- or Bay K 8644 (1 microM plus 15 mM K+)- precontracted arteries. There was no difference between endothelium-intact and -denuded coronary arteries from both male and female rabbits, precontracted with these three agents. Haemoglobin, indomethacin, methylene blue, glibenclamide or barium chloride did not affect the relaxation. In endothelium-denuded rabbit coronary arteries, progesterone shifted calcium concentration-dependent constrictor-response curves to the right, the maximal contraction was also reduced. The -log ED50s were 3.6 in control, and 3.3 and 2.9 after incubation with progesterone (3 and 30 microM), respectively. Similar results were obtained in rat aorta. We conclude that progesterone induces significant endothelium-independent relaxation in rabbit coronary arteries in vitro, possibly by affecting calcium influx.

Predictors of prognosis in severe chronic heart failure

A total of 127 patients with chronic heart failure referred to our exercise laboratory were studied retrospectively to identify parameters predictive of prognosis. Patients were followed for a mean of 14.6 months. The group as a whole had severe ventricular dysfunction with a median ejection fraction of 17% and a median peak rate of oxygen consumption of 13.7 ml/kg/min. During the follow-up period 23 patients (18%) died and 18 (14%) underwent cardiac transplantation. The effect of the following variables on outcome (death or transplantation) were examined: age, cause of heart failure, cardiothoracic ratio on chest radiography, left ventricular end-systolic dimension on echocardiography, left ventricular ejection fraction on radionuclide ventriculography, mean dose of diuretic, plasma sodium and urea concentrations, and peak oxygen consumption during exercise. Although all variables except cause of heart failure affected outcome on univariate analysis, multivariate analysis identified three variables that were statistically significant and independent predictors of outcome. In order of importance these were plasma sodium level, left ventricular ejection fraction and peak oxygen consumption. Even in this group of patients with severe heart failure, these variables were predictive of outcome.

Endothelium-independent relaxation of rabbit coronary artery by 17 beta-oestradiol in vitro

1. We assessed the relaxant effect of 17 beta-oestradiol (10(-7), 10(-6) and 10(-5) M) on rabbit isolated coronary arteries precontracted with prostaglandin F2 alpha (3 x 10(-6) M), high extracellular potassium (30 mM) and Bay K 8644 (10(-6) M) plus high extracellular potassium (15 mM) by measuring isometric tension. 17 beta-Oestradiol (10(-6) and 10(-5) M) induced significant relaxation in coronary arteries from male and female rabbits. No differences were seen between arteries with or without endothelium. There were also no differences between coronary arteries isolated from male and female rabbits. 2. Inhibitors of endothelium-derived relaxing factor and vasodilator prostanoids, namely, reduced haemoglobin, N omega-nitro-L-arginine methyl ester and indomethacin, did not affect the relaxation induced by 17 beta-oestradiol in endothelium-intact coronary arteries. 3. Methylene blue, an inhibitor of guanylate cyclase, did not affect the coronary artery relaxation induced by 17 beta-oestradiol. 4. The calcium concentration-dependent contraction curve in potassium-depolarization medium was shifted to the right by 17 beta-oestradiol (10(-6) and 10(-5) M) in the rabbit coronary artery and rat aorta. The -log EC50s of calcium in control and after incubation with 17 beta-oestradiol (10(-6) and 10(-5) M) were 3.7 +/- 0.09, 3.1 +/- 0.10 and 2.8 +/- 0.08 respectively in rabbit coronary arteries and 3.8 +/- 0.11, 3.3 +/- 0.14 and 2.9 +/- 0.15 in rat aorta. 5. The results indicate that 17 beta-oestradiol induces rabbit coronary artery relaxation by an endothelium-independent mechanism in vitro. A calcium antagonistic property may be involved in the mechanism of rabbit coronary arterial relaxation by 17beta-oestradiol.

Diuretics as initial and sole treatment in chronic cardiac failure

Six patients with chronic congestive cardiac failure, who had never received any drug treatment, were studied before and after one month of therapy with frusemide alone at a dose of 40 mg a day. Measurements were made at rest of plasma epinephrine, norepinephrine, renin activity, aldosterone, atrial natriuretic peptide, cortisol, growth hormone and prolactin, together with central hemodynamics, body fluid volumes and renal function. The initial measurements of hemodynamics, body fluid compartments and renal function confirmed the presence of the physiopathology typical of congestive cardiac failure. Plasma concentrations of norepinephrine, atrial natriuretic peptide, aldosterone and growth hormone were significantly increased. The mean value of plasma renin activity, although high, was not significantly different from normal. After one month of treatment, body weight, body fluid volumes and exchangeable sodium were reduced. Hemodynamics and renal plasma flow and glomerular filtration were not significantly affected. Plasma norepinephrine fell to within normal limits; atrial natriuretic peptide increased significantly; plasma renin activity and cortisol increased to levels which were abnormally high; growth hormone increased to levels similar to those associated with acromegaly. Increased circulating concentrations of atrial natriuretic peptide during treatment by frusemide may have an important influence on the kidney, blood vessels and neuro-endocrine response.

A possible molecular mechanism for 'stunning' of the myocardium

Stunning of the myocardium is mechanical dysfunction that persists after the re-establishment of coronary flow despite the absence of damage and the lack of any evidence for continuing ischaemia. Many mechanisms have been put forward and largely disproved. The most probable mechanism is abnormal function of the sarcoplasmic reticulum due to the generation of oxygen radicals within the myocardium. An hypothesis is proposed based on evidence indicating that the function of the calcium release channel of the sarcoplasmic reticulum is modified by reactive oxygen species before the channel is rendered non-functional.

The influence of right heart catheterisation on pulmonary arterial pressure in chronic heart failure: relationship to neuroendocrinal changes

Continuous ambulatory measurement of pulmonary arterial pressure was used to investigate changes following right heart catheterisation in patients with chronic heart failure. Ten males, mean age 56 years, with chronic heart failure, underwent 24 hour pressure recording using a micromanometer tipped catheter with in vivo calibration and frequency modulated recording. Eight patients were taking diuretics and 3 vasodilators. Blood was drawn for catecholamines, plasma renin activity and atrial natriuretic peptide 1 hour before catheterisation (-1 h), at the time of catheterisation (0 h) and 1, 2, 3, 4 and 6 hours later and aldosterone, cortisol and growth hormone at -1, 0 and 6 hours. Analysis of variance was used to determine changes in pulmonary arterial pressure, heart rate and hormones from the time of catheterisation in lying, sitting and standing postures. There was no significant change in pulmonary arterial pressure or heart rate over the 12 hours following or 24 hours after catheterisation in any posture. In the majority of patients plasma noradrenaline, plasma renin activity, atrial natriuretic peptide, aldosterone and cortisol were elevated. There was no significant change in hormone levels during the 6 hours following catheterisation. These findings suggest that the effect of invasive haemodynamic monitoring and chronic medical therapy on central haemodynamics is minor, and that a delay between insertion of catheters and measurement of pressure is unnecessary.

Comparison of rabbit coronary arterial relaxation induced by acetylcholine and lemakalim: activation of ATP sensitive potassium channels

STUDY OBJECTIVE

The purpose was to assess the role of ATP sensitive potassium channels (KATP) in endothelium dependent vasodilatation induced by acetylcholine, or endothelium independent vasodilatation induced by lemakalim in rabbit coronary arteries.

DESIGN

The effect of glibenclamide, a specific inhibitor of KATP, on coronary artery relaxation induced by acetylcholine or lemakalim was investigated. The relaxing effectiveness of acetylcholine and lemakalim on coronary arteries precontracted with KCl (K+) or prostaglandin F2 alpha (PGF2 alpha) was compared.

EXPERIMENTAL MATERIALS

Left epicardial coronary arteries from male New Zealand white rabbits (2.5-3.0 kg), killed by an overdose of pentobarbitone, were dissected free of connective tissue. Rings suspended in organ baths for the measurement of isometric tension.

MEASUREMENTS AND MAIN RESULTS

K+ (30 mmol.litre-1) and PGF2 alpha (3 mumols.litre-1) caused comparable contraction (p greater than 0.05) in endothelium intact or endothelium denuded coronary arterial rings. Acetylcholine induced relaxation was greater in endothelium intact rings precontracted with PGF2 alpha than with K+ and was abolished by the removal of endothelium. Relaxations induced by acetylcholine (0.1 and 0.3 mumol.litre-1) were reduced from 82(SEM 2.7)% and 93(2.8)% to 71(2.4)% and 82(2.7)% (p less than 0.05), and to 63(3.2)% and 79(4.5)% (p less than 0.05 or less than 0.01) by glibenclamide (3 and 10 mumols.litre-1) respectively in PGF2 alpha precontracted rings; and also attenuated (p less than 0.05 or less than 0.01) in K+ precontracted rings. Lemakalim induced relaxation was greater in endothelium denuded rings precontracted with PGF2 alpha than with K+, and was markedly reduced by glibenclamide (p less than 0.01).

CONCLUSIONS

These results suggest that activation of KATP may partially be involved in endothelium dependent relaxation induced by acetylcholine in rabbit coronary arteries. Lemakalim-induced endothelium independent relaxation results mainly from activation of KATP.

Contractile responses of myocytes isolated from patients with cardiomyopathy

Single cardiac myocytes isolated from failing and non-failing human ventricles were superfused at 32 degrees C and electrically stimulated at 0.2 Hz. Their contraction amplitude and velocities of contraction and relaxation were continuously during challenge with isoprenaline or high extracellular calcium. Action potentials were monitored with intracellular microelectrodes, and calcium transients followed using the fluorescent dye fura-2. Changes in contractility were correlated with severity of disease, as defined by New York Heart Association class, dose of diuretics, left ventricular ejection fraction and left ventricular end-diastolic pressure. Beta-adrenoceptor desensitization was detected in these cells as a decreased response to isoprenaline relative to that of calcium in the same cell. Significant correlations were obtained between reduction of beta-adrenoceptor sensitivity and all four indicators of disease severity. No correlation between the maximum contraction amplitude in high extracellular calcium and severity of disease was observed, the same was true for contraction and relaxation velocity in high calcium. Some significant decline in contractility with age of the patient was noted. Analysis with respect to aetiology of disease showed a subpopulation with dilated or hypertrophic cardiomyopathy where relaxation of the single cells was impaired. This was related to a prolonged calcium transient and action potential. Isoprenaline accentuated the lengthened second phase of relaxation, whereas high extracellular calcium reduced it. These interventions had similar effects on action potential duration. The actions of isoprenaline and calcium were similar on cells from failing and non-failing human hearts and on normal guinea-pig myocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of contractile function between papillary muscles and isolated myocytes from the same human hearts

The contractile function in response to increasing extracellular calcium and isoprenaline has been investigated using papillary muscles from seven human hearts (failing and non-failing) obtained at the time of transplant. Myocytes have been enzymatically isolated from adjacent myocardium, and their contractile characteristics measured in parallel to those of the intact papillary muscle. Similar experiments were performed on rabbit hearts, but in this case separate animals were used for the papillary muscles and cells. For human myocardium, the EC50 (concentration for half-maximal effect) for calcium, and the percentage increase in amplitude between basal (1.3mM) and maximally activating calcium, was similar between papillary muscle and cells. Variability of absolute responses was 4-5 times greater for papillary muscle than for myocytes. Isoprenaline accelerated the time to peak tension, time to 50% relaxation and time to 90% relaxation in papillary muscle; a similar effect on shortening was seen for time to peak tension and time to 50% relaxation in cells. Time to peak tension and time to 50% relaxation were not significantly different between the human preparations with isoprenaline, but the time to 50% relaxation with high calcium was faster for myocytes than for papillary muscle (p less than 0.05). Isoprenaline induced after-contractions in some cells, prolonging the time to 90% relaxation. This was not observed in papillary muscle preparations. Papillary muscles were less sensitive to the stimulatory effects of isoprenaline than cells taken from the same hearts. EC50 values were higher (p less than 0.05) and increases in contraction were lower (p less than 0.05) in whole tissue. This difference between cells and papillary muscle was not seen in rabbit hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of edema in constrictive pericarditis. Studies of body water and sodium, renal function, hemodynamics, and plasma hormones before and after pericardiectomy

BACKGROUND

The pathogenesis of sodium and water accumulation in chronic constrictive pericarditis is not well understood and may differ from that in patients with chronic congestive heart failure due to myocardial disease. This study was undertaken to investigate some of the mechanisms.

METHODS AND RESULTS

Using standard techniques, the hemodynamics, water and electrolyte spaces, renal function, and plasma concentrations of hormones were measured in 16 patients with untreated constrictive pericarditis and were measured again in eight patients after pericardiectomy. The average hemodynamic measurements were as follows: cardiac output, 1.98 l/min/m2; right atrial pressure, 22.9 mm Hg; pulmonary wedge pressure, 24.2 mm Hg; and mean pulmonary artery pressure 30.2 mm Hg. The systemic and pulmonary vascular resistances (36.3 +/- 2.5 and 3.2 +/- 0.3 mm Hg.min.m2/l, respectively) were increased. Significant increases occurred in total body water (36%), extracellular volume (81%), plasma volume (53%), and exchangeable sodium (63%). The renal plasma flow was only moderately decreased (49%), and the glomerular filtration rate was normal. Significant increases also occurred in plasma concentrations of norepinephrine (3.6 times normal), renin activity (7.2 time normal), aldosterone (3.4 times normal), cortisol (1.4 times normal), growth hormone (21.8 times normal), and atrial natriuretic peptide (5 times normal). The ratio of left atrial to aortic diameter measured by echocardiography was only minimally increased (1.29 +/- 0.04), indicating that in constrictive pericarditis the atria are prevented from expanding. The studies repeated after pericardiectomy in the eight patients showed that all measurements returned toward normal.

CONCLUSIONS

The restricted distensibility of the atria, in constrictive pericarditis, limits the secretion of atrial natriuretic factor and, thus, reduces its natriuretic and diuretic effects. This results in retention of water and sodium greater than that occurring in patients with edema from myocardial disease. The arterial pressure is maintained more by the expansion of the blood volume than by an increase in the peripheral vascular resistance.

Inhibition by barium and glibenclamide of the net loss of 86Rb+ from rabbit myocardium during hypoxia

STUDY OBJECTIVE

The aim was to determine the effects of barium ions and glibenclamide on the hypoxia induced K+ efflux from rabbit myocardium.

DESIGN

Experiments were performed on the isolated interventricular septum of the rabbit perfused with a physiological solution through the septal artery. The stimulation rate was 90 beats.min-1 and the temperature 32 degrees C. The flux of 86Rb+ was used as a surrogate of K+ fluxes.

EXPERIMENTAL MATERIAL

Septa were obtained from adult male New Zealand white rabbits.

MEASUREMENTS AND MAIN RESULTS

The uptake of 86Rb+ by the septum could be fitted to a single exponential curve with a rate constant of 0.024(SEM 0.001) min-1 (n = 14). Washout experiments were performed in which septa were labelled with 86Rb+ and then perfused with unlabelled solution for 60 min. The rate constants for the efflux of 86Rb+ were similar and were 0.022(0.001) min-1 (n = 13) for radioactivity in the tissue and 0.029(0.001) min-1 (n = 13) for radioactivity in the effluent. These rate constants were similar to those reported previously for 42K+. Septa were labelled for 150 to 180 min with 86Rb+ and then perfused with a hypoxic substrate free solution for 15 min followed by reoxygenation. The net loss of 86Rb+ was calculated to be equivalent to 4.00(0.20) mmol.kg-1 wet tissue of K+ (n = 8) and in washout experiments (n = 6) this loss was shown to be due to increased efflux. Ba2+, 0.1 mM and 1.0 mM, added at the onset of hypoxia decreased net tissue loss of 86Rb+ by 64(6)% (n = 5) and 97(1)% (n = 6) respectively (both p less than 0.01). Glibenclamide (0.1 mM) decreased tissue net loss by 52(3)% (n = 6, p less than 0.01).

CONCLUSIONS

Part of hypoxia induced net K+ loss in this preparation can be attributed to activation of ATP sensitive K+ channels but other mechanisms are also involved.