Recipients with blood group A associated with longer survival rates in cardiac valvular bioprostheses

Background

Pigs/bovines share with humans some of the antigens present on cardiac valves. Two such antigens are: the major xenogenic Ag, “Gal” present in all pig/bovine very close to human B-antigen of ABO-blood-group system; the minor Ag, pig histo-blood-group AH-antigen identical to human AH-antigen and present by some animals. We hypothesize that these antigens may modify the immunogenicity of the bioprosthesis and also its longevity. ABO distribution may vary between patients with low (<6 years) and high (≥15 years) bioprostheses longevity.

Methods

Single-centre registry study (Paris, France) including all degenerative porcine bioprostheses (mostly Carpentier-Edwards 2nd/3rd generation heart valves) explanted between 1985 and 1998 and some bovine bioprostheses. For period 1998–2014, all porcine bioprostheses with longevity ≥13 years (follow-up ≥29 years). Important predictive factors for bioprosthesis longevity: number, site of implantation, age were collected. Blood group and other variables were entered into an ordinal logistic regression analysis model predicting valve longevity, categorized as low (<6 years), medium (6–14.9 years), and high (≥15 years).

Findings

Longevity and ABO-blood group were obtained for 483 explanted porcine bioprostheses. Mean longevity was 10.2 ± 3.9 years [0–28] and significantly higher for A-patients than others (P = 0.009). Using multivariate analysis, group A was a strong predictive factor of longevity (OR 2.09; P < 0.001). For the 64 explanted bovine bioprosthesis with low/medium longevity, the association, with A-group was even more significant.

Interpretation

Patients of A-group but not B have a higher longevity of their bioprostheses. Future graft-host phenotyping and matching may give rise to a new generation of long-lasting bioprosthesis for implantation in humans, especially for the younger population.

Fund

None.

Role of both actin-myosin cross bridges and NO-cGMP pathway modulators in the contraction and relaxation of human placental stem villi

INTRODUCTION

Human placental stem villi (PSV) present contractile properties. We studied the role of actin-myosin cross bridges (CBs) and the effects of NO-cGMP pathway modulators in the PSV contraction and relaxation.

METHODS

In vitro contractile properties were investigated in 71 PSV from term human placentas studied according to their long axis. Contraction was induced by both KCl and electrical tetanic stimulation. Relaxation was induced by inhibiting the CB cycle with either 2,3-butanedione monoxime (BDM) or blebbistatin (BLE) and by activating the NO-cGMP pathway with isosorbide dinitrate (ISDN), sildenafil (SIL) or ISDN + SIL.

RESULTS

PSV tension slowly increased by 140% of the basal tone after KCl exposure and by 85% after tetanus. The addition of BDM, BLE, ISDN, SIL and ISDN + SIL induced a relaxation of PSV, the overall time course of relaxation (in s) was respectively (means ± SD) 3412 ± 1904, 14,250 ± 3095*, 3813 ± 1383, 2883 ± 1188 and 2440 ± 477; significantly longer in BLE compared with BDM, ISDN, SIL and ISDN + SIL:*p < 0.001). the overall time course of relaxation (in s) was respectively (means ± SD) 3412 ± 1904, 14,250 ± 3095*, 3813 ± 1383, 2883 ± 1188 and 2440 ± 477; significantly longer in BLE compared with BDM, ISDN, SIL and ISDN + SIL:*p < 0.001). These relaxation kinetics were particularly slow. Other relaxation parametres, i.e., maximum lengthening, -peak dT/dt, and resting tension, did not differ between these 5 subgroups.

DISCUSSION AND CONCLUSION

Isolated human PSV were able to contract after both KCl exposure and tetanus. This increase in contractility was reversed by inhibiting the CB cycle with BDM or BLE and by stimulating the NO-cGMP pathway with ISDN or SIL. The association ISDN + SIL did not potentiate the relaxing processes.

Statistical mechanics of myosin molecular motors in skeletal muscles

Statistical mechanics provides the link between microscopic properties of matter and its bulk properties. The grand canonical ensemble formalism was applied to contracting rat skeletal muscles, the soleus (SOL, n = 30) and the extensor digitalis longus (EDL, n = 30). Huxley's equations were used to calculate force (pi) per single crossbridge (CB), probabilities of six steps of the CB cycle, and peak muscle efficiency (Eff(max)). SOL and EDL were shown to be in near-equilibrium (CB cycle affinity 2.5 kJ/mol) and stationary state (linearity between CB cycle affinity and myosin ATPase rate). The molecular partition function (z) was higher in EDL (1.126+/-0.005) than in SOL (1.050+/-0.003). Both pi and Eff(max) were lower in EDL (8.3+/-0.1 pN and 38.1+/-0.2%, respectively) than in SOL (9.2+/-0.1 pN and 42.3+/-0.2%, respectively). The most populated step of the CB cycle was the last detached state (D3) (probability P(D3): 0.890+/-0.004 in EDL and 0.953+/-0.002 in SOL). In each muscle group, both pi and Eff(max) linearly decreased with z and statistical entropy and increased with P(D3). We concluded that statistical mechanics and Huxley's formalism provided a powerful combination for establishing an analytical link between chemomechanical properties of CBs, molecular partition function and statistical entropy.

Mechanics and crossbridge kinetics of tracheal smooth muscle in two inbred rat strains

The aim of the study was to determine whether the nonspecific in vivo airway hyperresponsiveness of the inbred Fisher F-344 rat strain was associated with differences in the intrinsic contractile properties of tracheal smooth muscle (TSM) when compared with Lewis rats. Isotonic and isometric contractile properties of isolated TSM from Fisher and Lewis rats (each n=10) were investigated, and myosin crossbridge (CB) number, force and kinetics in both strains were calculated using Huxley's equations adapted to nonsarcomeric muscles. Maximum unloaded shortening velocity and maximum extent of muscle shortening were higher in Fisher than in Lewis rats (approximately 46% and approximately 42%, respectively), whereas peak isometric tension was similar. The curvature of the hyperbolic force/velocity relationship did not differ between strains. Myosin CB number and unitary force were similar in both strains. The duration of CB detachment and attachment was shorter in Fisher than in Lewis rats (approximately -46% and -34%, respectively). In Fisher rats, these results show that inherited, genetically determined factors of airway hyperresponsiveness are associated with changes in crossbridge kinetics, contributing to an increased tracheal smooth muscle shortening capacity and velocity.

Effects of halogenated anaesthetics on diaphragmatic actin-myosin cross-bridge kinetics

BACKGROUND

The effects of halogenated anaesthetics on cross-bridge (CB) kinetics are unclear. As halogenated anaesthetics do not markedly modify the intracellular calcium transient in the diaphragm, we used an isolated rat diaphragm preparation to assess the effects of halothane and isoflurane on CB kinetics.

METHODS

The effects of halothane and isoflurane (1 and 2 minimum alveolar concentration (MAC)) on rat diaphragm muscle strips were studied in vitro (Krebs-Henseleit solution, 29 degrees C, oxygen 95%/carbon dioxide 5%) in tetanus mode (50 Hz). From the force-velocity curve and using A. F. Huxley's equations, we determined the main mechanical and energetic variables and calculated CB kinetics.

RESULTS

At 1 and 2 MAC, isoflurane and halothane induced no significant inotropic effects. Whatever the concentrations tested, halothane and isoflurane did not significantly modify the CB number, the elementary force per CB, the attachment and detachment constants, the duration of the CB cycle and mean CB velocity.

CONCLUSION

In the rat diaphragm at therapeutic concentrations, halogenated anaesthetics do not significantly modify CB mechanical and kinetic properties.

Haemodynamic evaluation of pulmonary hypertension

Pulmonary hypertension is characterised by the chronic elevation of pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) leading to right ventricular enlargement and hypertrophy. Pulmonary hypertension may result from respiratory and cardiac diseases, the most severe forms occurring in thromboembolic and primary pulmonary hypertension. Pulmonary hypertension is most often defined as a mean PAP >25 mmHg at rest or >30 mmHg during exercise, the pressure being measured invasively with a pulmonary artery catheter. Doppler echocardiography allows serial, noninvasive follow-up of PAPs and right heart function. When the adaptive mechanisms of right ventricular dilatation and hypertrophy cannot compensate for the haemodynamic burden, right heart failure occurs and is associated with poor prognosis. The haemodynamic profile is the major determinant of prognosis. In both primary and secondary pulmonary hypertension, special attention must be paid to the assessment of pulmonary vascular resistance index (PVRI), right heart function and pulmonary vasodilatory reserve. Recent studies have stressed the prognostic values of exercise capacity (6-min walk test), right atrial pressure, stroke index and vasodilator challenge responses, as well as an interest in new imaging techniques and natriuretic peptide determinations. Overall, careful haemodynamic evaluation may optimise new diagnostic and therapeutic strategies in pulmonary hypertension.

Myosin cross-bridge kinetics in airway smooth muscle: a comparative study of humans, rats, and rabbits

To analyze the kinetics and unitary force of cross bridges (CBs) in airway smooth muscle (ASM), we proposed a new formalism of Huxley's equations adapted to nonsarcomeric muscles (Huxley AF. Prog Biophys Biophys Chem 7: 255-318, 1957). These equations were applied to ASM from rabbits, rats, and humans (n = 12/group). We tested the hypothesis that species differences in whole ASM mechanics were related to differences in CB mechanics. We calculated the total CB number per square millimeter at peak isometric tension (Psi x10(9)), CB unitary force (Pi), and the rate constants for CB attachment (f(1)) and detachment (g(1) and g(2)). Total tension, Psi, and Pi were significantly higher in rabbits than in humans and rats. Values of Pi were 8.6 +/- 0.1 pN in rabbits, 7.6 +/- 0.3 pN in humans, and 7.7 +/- 0.2 pN in rats. Values of Psi were 4.0 +/- 0.5 in rabbits, 1.2 +/- 0.1 in humans, and 1.9 +/- 0.2 in rats; f(1) was lower in humans than in rabbits and rats; g(2) was higher in rabbits than in rats and in rats than in humans. In conclusion, ASM mechanical behavior of different species was characterized by specific CB kinetics and CB unitary force.

Myosin cross bridges in skeletal muscles: "rower" molecular motors

Different classes of molecular motors, "rowers" and "porters," have been proposed to describe the chemomechanical transduction of energy. Rowers work in large assemblies and spend a large percentage of time detached from their lattice substrate. Porters behave in the opposite way. We calculated the number of myosin II cross bridges (CB) and the probabilities of attached and detached states in a minimal four-state model in slow (soleus) and fast (diaphragm) mouse skeletal muscles. In both muscles, we found that the probability of CB being detached was approximately 98% and the number of working CB was higher than 10(9)/mm(2). We concluded that muscular myosin II motors were classified in the category of rowers. Moreover, attachment time was higher than time stroke and time for ADP release. The duration of the transition from detached to attached states represented the rate-limiting step of the overall attached time. Thus diaphragm and soleus myosins belong to subtype 1 rowers.

Interaction of protamine with alpha- and beta-adrenoceptor stimulations in rat myocardium

BACKGROUND

Protamine alters the inotropic responses to beta-adrenoceptor stimulation, but its mechanism of action is not well-understood. Moreover, its interaction with alpha-adrenoceptor stimulation and the lusitropic (relaxation) response to beta-adrenoceptor stimulation remain unknown.

METHODS

The effects of protamine (10 or 100 microg/ml) on the responses induced by phenylephrine and isoproterenol were studied in rat left ventricular papillary muscles. Inotropic and lusitropic effects were studied under low and high loads. The authors also studied the interaction of protamine with forskolin (50 microm) and dibutyryl 3',5'-cAMP (0.5 mm). Data are mean percentage of baseline active force +/- SD.

RESULTS

In control groups, phenylephrine (135 +/- 17%, P < 0.05) and isoproterenol (185 +/- 44%, P < 0.05) induced a positive inotropic effect. Isoproterenol induced positive lusitropic effects under low and high loads. Protamine abolished the inotropic responses to alpha- (102 +/- 23%, not significant) and beta-adrenoceptor stimulations (99 +/- 17%, not significant) but did not modify the lusitropic responses to isoproterenol. Protamine abolished the inotropic responses to forskolin (89 +/- 6 vs. 154 +/- 20%, P < 0.05) and markedly decreased that of dibutyryl 3',5'-cAMP (132 +/- 31 vs. 167 +/- 30%, P < 0.05) but did not modify their lusitropic responses.

CONCLUSIONS

Protamine abolished the inotropic responses to alpha- and beta-adrenoceptor stimulations but preserved the lusitropic responses to beta-adrenoceptor stimulation. Although protamine may act at several sites on the adrenoceptor stimulation cascade, one of its main sites of action is situated downstream from cAMP-mediated phosphorylation.

Angiotensin-converting enzyme inhibitor therapy improves respiratory muscle strength in patients with heart failure

STUDY OBJECTIVES

Respiratory muscle strength has been shown to be reduced in patients with chronic heart failure. The purpose of this prospective study was to determine whether long-term therapy with the angiotensin-converting enzyme (ACE) inhibitor perindopril improves respiratory muscle strength in patients with chronic heart failure.

PATIENTS AND METHODS

Eighteen patients with stable chronic heart failure were administered perindopril, 4 mg/d, in addition to their standard therapy for a period of 6 months. Fourteen patients completed the study. Maximum inspiratory pressure (PImax) and maximum expiratory pressure (PEmax) expressed in percentage of predicted values, left ventricular ejection fraction (LVEF) determined by means of two-dimensional echocardiography, and pulmonary volumes were obtained before and after therapy.

MEASUREMENTS AND RESULTS

As compared to baseline, there was a significant increase in both PImax and PEmax after therapy (57 +/- 27% predicted vs 78 +/- 36% predicted and 62 +/- 20% predicted vs 73 +/- 15% predicted, respectively; each p < 0.05). LVEF increased (34 +/- 5% vs 41 +/- 10%; p < 0.05); functional class improved by > or = 1 New York Heart Association (NYHA) class in five patients. There were no changes in pulmonary volumes. No correlation was found between changes in PImax and PEmax and changes in either LVEF or NYHA functional class.

CONCLUSIONS

In patients with chronic heart failure, long-term therapy with the ACE inhibitor perindopril improved respiratory muscle strength, as indicated by significant increases in PImax and PEmax.

Extracellular calcium modulates the effects of protamine on rat myocardium

We studied the effects of protamine (10-300 microg. mL(-1)) as well as its interaction with heparin in rat left ventricular papillary muscles in vitro at calcium concentrations of 0.5 and 1 mM under low (isotony) and high (isometry) loads. Protamine induced a negative inotropic effect that was less pronounced at calcium 0.5 mM (active force at protamine 300 microg/mL, 84 +/- 20 vs 57 +/- 15% of baseline, P: < 0.05); whereas at calcium 1 mM there was a marked contracture of the muscle. For the smallest concentrations of protamine and at calcium 0.5 mM, we observed a moderate positive inotropic effect that was suppressed by nifedipine. Protamine induced a negative lusitropic effect under low load and decreased postrest potentiation, suggesting an impairment in the functions of the sarcoplasmic reticulum. Heparin was able to inhibit and reverse the negative inotropic effect of protamine. The negative inotropic effect of protamine is enhanced by an increase in extracellular calcium concentration. This negative inotropic effect is probably related to calcium overload and impairment in sarcoplasmic reticulum functions, and heparin can block these effects.

IMPLICATIONS

The negative inotropic effect of protamine is enhanced by an increase in extracellular calcium concentration. This negative inotropic effect is probably related to calcium overload and impairment in sarcoplasmic reticulum functions, and heparin can block these effects.

Pulmonary artery pulse pressure and wave reflection in chronic pulmonary thromboembolism and primary pulmonary hypertension

OBJECTIVES

The purpose of this time-domain study was to compare pulmonary artery (PA) pulse pressure and wave reflection in chronic pulmonary thromboembolism (CPTE) and primary pulmonary hypertension (PPH).

BACKGROUND

Pulmonary artery pressure waveform analysis provides a simple and accurate estimation of right ventricular afterload in the time-domain. Chronic pulmonary thromboembolism and PPH are both responsible for severe pulmonary hypertension. Chronic pulmonary thromboembolism and PPH predominantly involve proximal and distal arteries, respectively, and may lead to differences in PA pressure waveform.

METHODS

High-fidelity PA pressure was recorded in 14 patients (7 men/7 women, 46 +/- 14 years) with CPTE (n = 7) and PPH (n = 7). We measured thermodilution cardiac output, mean PA pressure (MPAP), PA pulse pressure (PAPP = systolic - diastolic PAP) and normalized PAPP (nPAPP = PPAP/MPAP). Wave reflection was quantified by measuring Ti, that is, the time between pressure upstroke and the systolic inflection point (Pi), deltaP, that is, the systolic PAP minus Pi difference, and the augmentation index (deltaP/PPAP).

RESULTS

At baseline, CPTE and PPH had similar cardiac index (2.4 +/- 0.4 vs. 2.5 +/- 0.5 l/min/m2), mean PAP (59 +/- 9 vs. 59 +/- 10 mm Hg), PPAP (57 +/- 13 vs. 53 +/- 13 mm Hg) and nPPAP (0.97 +/- 0.16 vs. 0.89 +/- 0.13). Chronic pulmonary thromboembolism had shorter Ti (90 +/- 17 vs. 126 +/- 16 ms, p < 0.01) and higher deltaP/PPAP (0.26 +/- 0.01 vs. 0.09 +/- 0.07, p < 0.01).

CONCLUSIONS

Our study indicated that: 1) CPTE and PPH with severe pulmonary hypertension had similar PA pulse pressure, and 2) wave reflection is elevated in both groups, and CPTE had increased and anticipated wave reflection as compared with PPH, thus suggesting differences in the pulsatile component of right ventricular afterload.

Mechanical and electrophysiological effects of thiopental on rat cardiac left ventricular papillary muscle

Thiopental induces a negative inotropic effect on mammalian heart muscle, where it decreases Ca2+ current and Ca2+ release from the sarcoplasmic reticulum and reduces K+ currents. We analysed the effects of thiopental on the mechanical and electrical activities of rat myocardium, which differ markedly from those of other mammals. The effects of thiopental on mechanical parameters and on the transmembrane resting (RP) and action (AP) potentials of rat left ventricular papillary muscle were investigated. These effects were also studied in the presence of atenolol, a beta-blocking agent, and 4-aminopyridine (4-AP), a blocker of the transient outward K+ current. Thiopental (3.8 x 10(-6), 3.8 x 10(-5) and 1.1 x 10(-4) M) induced a dose-dependent positive inotropic effect. This positive inotropic effect persisted in the presence of atenolol (1 x 10(-6) M) but did not develop in the presence of 1 mM 4-AP; 4-AP had a positive inotropic effect but not in the presence of thiopental. Moreover, thiopental (3.8 x 10(-5) M) lengthened the plateau and the slow repolarizing phase of the AP, while 1 mM 4-AP only prolonged the plateau duration. In rat myocardium, the positive inotropic effect of thiopental in part mimics that of 4-AP, and in part may be explained by the lengthening of the slow repolarizing phase of the AP.

Species-dependent changes in mechano-energetics of isolated cardiac muscle during hypoxia

The present study investigates the mechanical and energetic changes induced by hypoxia in isolated cardiac muscles of different species characterized by different myosin isoforms. Classic mechanical parameters of contraction and energetic parameters derived from the tension-velocity relationship were studied in rat and guinea pig left ventricular papillary muscles and in frog ventricular strips before and after 15 min hypoxia (n = 8 in each group). The isomyosin pattern is predominantly V1 with high ATPase activity in rat and V3 with low ATPase activity in guinea pig and frog heart ventricles. At baseline, cardiac mechanical performance was greater in rat than in guinea pig and frog muscle, but the economy of tension generation did not differ significantly between the three species. Hypoxia significantly decreased myocardial mechanical performance in all three groups. Mechanical impairment was more marked in rat than in the other two species and was intermediate in guinea pig. The energetic consequences of hypoxia differed according to species and in a different manner from the mechanical parameters. Hypoxia decreased the economy of tension generation in rat heart, in contrast to no change in guinea pig and frog muscle. These results suggest that in terms of mechano-energetic properties, cardiac muscles with V1 isomyosin were more sensitive to hypoxia than those containing V3 isomyosin.

Severe mechanical dysfunction in pharyngeal muscle from adult mdx mice

The mdx mouse is a widely used animal model of human muscular dystrophy. Although diaphragm muscle exhibits severe muscle weakness throughout the life of the animal, the limb muscle function of mdx mice spontaneously recovers by 6 mo of age. Pharyngeal dilator muscles such as sternohyoid (SH) contribute to upper airway patency during breathing. We hypothesized that SH muscle function was impaired in 6-mo-old mdx mice. Mechanical properties and myosin heavy chain (MHC) composition were investigated in isolated SH from 6-mo-old control (C, n = 10) and mdx (n = 10) mice. As compared with C, peak tetanic tension (Pmax) and maximum shortening velocity were 50% and 16% lower in mdx mice (p < 0.001 and p < 0.05, respectively). Peak mechanical power was lower in mdx than in C (19.0 +/- 3.2 versus 57.4 +/- 5.1 mW g(-)(1), p < 0.001). Both C and mdx SH were composed exclusively of fast myosin isoforms. As compared with C, mdx SH presented a higher proportion of IIX-MHC and a reduction in IIB-MHC (each p < 0.001). In conclusion, our results demonstrated severe SH muscle dysfunction in 6-mo-old mdx mice, that is, at a time when limb muscle function has recovered. Thus, SH muscle of the mdx mouse may be an excellent muscle for studying Duchenne muscular dystrophy.

Short-term variability of pulse pressure and systolic and diastolic time in heart transplant recipients

In heart transplant recipients (HTR), short-term systolic blood pressure variability is preserved, whereas heart rate variability is almost abolished. Heart period is the sum of left ventricular ejection time (LVET) and diastolic time (DT). In the present time-domain prospective study, we tested the hypothesis that short-term fluctuations in aortic pulse pressure (PP) in HTR were related to fluctuations in LVET. Seventeen male HTR (age 48 +/- 6 yr) were studied 16 +/- 11 mo after transplantation. Aortic root pressure was obtained over a 15-s period using a micromanometer both at rest (n = 17) and following the cold pressor test (CPT, n = 14). There was a strong positive linear relationship between beat-to-beat LVET and beat-to-beat PP in all patients at rest and in 13 of 14 patients following CPT (each P < 0.01). The slope of this relationship showed little scatter both at rest (0.34 +/- 0.07 mmHg/ms) and following CPT (0.35 +/- 0.09 mmHg/ms, P = not significant). Given the essentially fixed heart period, DT varied inversely with LVET. As a result, in 13 of 17 HTR at rest and in 12 of 14 HTR following CPT, there was a negative linear relationship between beat-to-beat PP and DT. In conclusion, our short-term time-domain study demonstrated a strong positive linear relationship between LVET and blood pressure variability in male HTR. We also identified a subgroup of HTR in whom there was a mismatch between PP and DT.

Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure

In mechanically ventilated patients with acute circulatory failure related to sepsis, we investigated whether the respiratory changes in arterial pressure could be related to the effects of volume expansion (VE) on cardiac index (CI). Forty patients instrumented with indwelling systemic and pulmonary artery catheters were studied before and after VE. Maximal and minimal values of pulse pressure (Pp(max) and Pp(min)) and systolic pressure (Ps(max) and Ps(min)) were determined over one respiratory cycle. The respiratory changes in pulse pressure (DeltaPp) were calculated as the difference between Pp(max) and Pp(min) divided by the mean of the two values and were expressed as a percentage. The respiratory changes in systolic pressure (DeltaPs) were calculated using a similar formula. The VE-induced increase in CI was >/= 15% in 16 patients (responders) and < 15% in 24 patients (nonresponders). Before VE, DeltaPp (24 +/- 9 versus 7 +/- 3%, p < 0.001) and DeltaPs (15 +/- 5 versus 6 +/- 3%, p < 0.001) were higher in responders than in nonresponders. Receiver operating characteristic (ROC) curves analysis showed that DeltaPp was a more accurate indicator of fluid responsiveness than DeltaPs. Before VE, a DeltaPp value of 13% allowed discrimination between responders and nonresponders with a sensitivity of 94% and a specificity of 96%. VE-induced changes in CI closely correlated with DeltaPp before volume expansion (r(2) = 0. 85, p < 0.001). VE decreased DeltaPp from 14 +/- 10 to 7 +/- 5% (p < 0.001) and VE-induced changes in DeltaPp correlated with VE-induced changes in CI (r(2) = 0.72, p < 0.001). It was concluded that in mechanically ventilated patients with acute circulatory failure related to sepsis, analysis of DeltaPp is a simple method for predicting and assessing the hemodynamic effects of VE, and that DeltaPp is a more reliable indicator of fluid responsiveness than DeltaPs.

[Biomechanics and bio-energetics of smooth muscle contraction. Relation to bronchial hyperreactivity]

Mechanical studies of isolated muscle and analysis of molecular actomyosin interactions have improved our understanding of the pathophysiology of airway smooth muscle. Mechanical properties of airway smooth muscle are similar to those of other smooth muscles. Airway smooth muscle exhibits spontaneous intrinsic tone and its maximum shortening velocity (Vmax) is 10-30 fold lower than in striated muscle. Smooth muscle myosin generates step size and elementary force per crossbridge interaction approximately similar to those of skeletal muscle myosin. Special slow cycling crossbridges, termed latch-bridges, have been attributed to myosin light chain dephosphorylation. From a mechanical point of view, it has been shown that airway hyperresponsiveness is characterized by an increased Vmax and an increased shortening capacity, with no significant change in the force-generating capacity.

Isotonic mechanics of a pharyngeal dilator muscle and diaphragm in the rat before and after fatigue

Pharyngeal and diaphragm muscles contract and relax in synergy, which is why it was decided to compare their mechanical performance throughout the overall load continuum. The effects of fatigue were also studied. The isotonic mechanics of rat sternohyoid (SH; n=10) and diaphragm (D; n=10) were investigated in vitro. Force and length were measured in muscles contracting from zero load up to isometry. Maximum isometric tension (Pmax), peak mechanical work (Wmax), maximum unloaded shortening velocity (vzL) and mechanical efficiency (eff(max)) were recorded. Data were obtained both at baseline and after fatigue. SH muscles had a lower Pmax (96.0+/-13.7 versus 119.5+/-22.7 mN x mm(-2); p<0.05), a lower Wmax (5.5+/-1.2 versus 8.0+/-2.1 mJ x g(-1); p<0.01), a lower eff(max) (56.0+/-6.9 versus 62.6+/-5.8%; p<0.05) and a higher vzL (4.8+/-0.4 versus 3.4+/-0.4 initial length (L0) x s(-1); p<0.001) than D muscles. Wmax occurred at a higher relative load in SH (40% Pmax) than in D (30% Pmax). Fatigue did not modify eff(max) in SH muscles, whereas it significantly improved eff(max) in D muscles. These findings suggest that under control conditions, economy of force generation was less efficient in sternohyoid than in diaphragm muscles. Fatigue in sternohyoid muscles induced unfavourable mechanical behaviour. This may partly explain pharyngeal dilator muscle failure in the presence of increased loads. Whether these findings are relevant to human sleep apnoea syndrome has yet to be determined.

The effects of gadolinium, a stretch-sensitive channel blocker, on diaphragm muscle

Stretch-activated channels (SAC) have been identified in many cell types including striated muscles. In diaphragm muscle, the influence of SAC on the length-active tension relationship remains unknown. Patch clamp experiments were performed on single fibres (n = 10). In isolated diaphragm muscle from adult hamsters, the effects of gadolinium (Gd3+), the most potent inhibitor of SAC blocker, on tension response to stretch at baseline were studied (n = 10), after pretreatment of the muscle with 1 nmol isoproterenol (n = 10), 0.5 micromol forskolin (n = 6), or 0.1 mmol dibutyryl cyclic adenosine monophosphate (cAMP) (n = 10). Results were compared to those obtained in low [Na+]e (n = 10), Ca2+-free medium (n = 6) or after 5 micromol nifedipine (n = 8). Gd3+ reduced active tension measured over a range of initial muscle lengths in a concentration-dependent manner (10 and 50 micromol). In isolated fibres, mechanical stretch generated a membrane current that was sensitive to Gd3+. In muscles, lowering [Na+]e mimicked the effects of Gd3+, while no change in the length-tension relationship was observed in Ca2+-free medium or after nifedipine. Drugs which increase cAMP prevented the effects of Gd3+ on active tension. In the diaphragm, gadolinium-sensitive channels are activated during physiological changes in length and influence tension development. Moreover, cyclic adenosine monophosphate content modulates the effects of gadolinium on stretch-activated channels.

Myosin molecular motor dysfunction in dystrophic mouse diaphragm

Cross-bridge properties and myosin heavy chain (MHC) composition were investigated in isolated diaphragm from 6-mo-old control (n = 12) and mdx (n = 12) mice. Compared with control, peak tetanic tension fell by 50% in mdx mice (P < 0.001). The total number of cross bridges per square millimeter (x10(9)), the elementary force per cross bridge, and the peak mechanical efficiency were lower in mdx than in control mice (each P < 0.001). The duration of the cycle and the rate constant for cross-bridge detachment were significantly lower in mdx than in control mice. In the overall population, there was a linear relationship between peak tetanic tension and either total number of cross bridges per square millimeter or elementary force per cross bridge (r = 0.996 and r = 0.667, respectively, each P < 0.001). The mdx mice presented a higher proportion of type IIA MHC (P < 0.001) than control mice and a reduction in type IIX MHC (P < 0.001) and slow myosin isoforms (P < 0.01) compared with control mice. We concluded that, in mdx mice, impaired diaphragm strength was associated with qualitative and quantitative changes in myosin molecular motors. It is proposed that reduced force generated per cross bridge contributed to diaphragm weakness in mdx mice.

Detection of the fluorescence of GI vessels in rats using a CCD camera or a near-infrared video endoscope

BACKGROUND

Choroidal near-infrared fluorescent angiography can detect vessels in the eye with high resolution. Observation of fluorescent gastrointestinal (GI) vessels by endoscopy may be useful in portal hypertension and bleeding ulcer. We here describe a technique for the detection of fluorescent GI vessels with a CCD camera or a near-infrared video endoscope.

METHODS

Laparotomy was performed on rats. A tissue target was excited by means of a laser diode. We took pictures of tissue under both white and near-infrared light, both before and after intravenous injection of indocyanine green. Fluorescent light was selected by means of filters placed in front of the lens of a CCD camera or a near-infrared video endoscope.

RESULTS

Under near-infrared light and after dye injection, we observed fluorescent vessels in real time and distinguished arterial from venous fluorescence.

CONCLUSIONS

This device permits visualization of GI vessels, which could be useful for diagnosis of vascular abnormalities during endoscopy and surgery.

Relaxation of diaphragm muscle

Relaxation is the process by which, after contraction, the muscle actively returns to its initial conditions of length and load. In rhythmically active muscles such as diaphragm, relaxation is of physiological importance because diaphragm must return to a relatively constant resting position at the end of each contraction-relaxation cycle. Rapid and complete relaxation of the diaphragm is likely to play an important role in adaptation to changes in respiratory load and breathing frequency. Regulation of diaphragm relaxation at the molecular and cellular levels involves Ca(2+) removal from the myofilaments, active Ca(2+) pumping by the sarcoplasmic reticulum (SR), and decrease in the number of working cross bridges. The relative contribution of these mechanisms mainly depends on sarcomere length, muscle tension, and the intrinsic contractile function. Increased capacity of SR to take up Ca(2+) can arise from increased density of active SR pumping sites or in slow-twitch fibers from phosphorylation of phospholamban, whereas impaired coupling between ATP hydrolysis and Ca(2+) transport into the SR or intracellular acidosis reduces SR Ca(2+) pump activity. In experimental conditions of decreased contractile performance, slowed, enhanced, or unchanged relaxation rates have been reported in vitro. In vivo, a slowing in the rate of decline of the respiratory pressure is generally considered an early reliable index of respiratory muscle fatigue. Impaired relaxation rate may, in turn, favor mismatch between blood flow and metabolic demand, especially at high breathing frequencies.

Impaired load dependence of diaphragm relaxation during congestive heart failure in the rabbit

The load dependence (LD) of relaxation was studied in the diaphragm of rabbits with congestive heart failure (CHF). CHF (n = 15) was induced by combined chronic volume and pressure overload. Aortic insufficiency was induced by forcing a catheter through the aortic sigmoid valves, followed 3 wk later by abdominal aortic stenosis. Six weeks after the first intervention, animals developed CHF. Sham-operated animals served as controls (C; n = 12). Diaphragm mechanics were studied in vitro on isolated strips, at 22 degrees C, in isotonic and isometric loading conditions. Contractility was lower in the CHF group, as reflected by lower total tension: 1.11 +/- 0.10 in CHF vs. 2.38 +/- 0.15 N/cm(2) in C in twitch (P < 0.001) and 2.46 +/- 0.22 in CHF vs. 4.90 +/- 0.25 N. cm(-2) in C in tetanus (P < 0.001). The index LD was used to quantify the load dependence of relaxation: LD is <1 in load-dependent muscles and tends toward 1 in load-independent muscles. LD was significantly higher in CHF than in C rabbits, in both twitch (0.99 +/- 0.01 vs. 0.75 +/- 0.03; P < 0. 001) and tetanus (0.95 +/- 0.02 vs. 0.84 +/- 0.02; P < 0.001). In the CHF rabbits' diaphragm, the fall in total tension was linearly related to the fall in load dependence of relaxation. The decrease in load dependence of relaxation in CHF animals suggests sarcoplasmic reticulum abnormalities. Impairment of the sarcoplasmic reticulum may also partly account for the decrease in contractile performance of diaphragm in CHF animals.

Impaired skeletal muscle performance in the early stage of cardiac pressure overload in rabbits: beneficial effects of angiotensin-converting enzyme inhibition

Abnormalities of skeletal muscles are frequently observed in patients with congestive heart failure. In these patients, angiotensin-converting enzyme (ACE) inhibitors improve exercise performance. The present study was designed to assess whether skeletal muscle dysfunction develops in the early stage of cardiac overload and if so, whether such functional alterations can be prevented by ACE inhibition. Mechanical performance, cross-bridge (CB) properties, and myosin heavy chain composition were investigated in respiratory and limb skeletal muscles of rabbits with moderate cardiac hypertrophy, and after single therapy with the ACE inhibitor perindopril (PE). After constriction of the aorta, the rabbits were treated during a 10-week period with either PE (1 mg/kg/day; n = 9) or a placebo (PL; n = 15). A third group of sham-operated animals received PL (n = 10). Analyses were performed on isolated diaphragm and soleus strips. Compared with sham-operated animals (shams), peak tetanic tension in PL fell by 40% in diaphragm and 34% in soleus. There were no significant differences in peak tetanic tension and the maximum shortening velocity between PE and shams. In both muscles, the total number of CBs was significantly lower in PL than in shams, but did not differ between shams and PE. The elementary force per CB did not differ between groups. In both muscles, the myosin heavy chain composition did not differ between groups. The study demonstrated that intrinsic performance of diaphragm and soleus muscles was affected early in the development of chronic pressure overload. Single therapy with PE tended to preserve muscle strength, essentially by limiting the loss of CBs.

Interaction of halogenated anesthetics with dobutamine in rat myocardium

BACKGROUND

Halogenated anesthetics potentiate the positive inotropic effects of alpha- and beta-adrenoceptor stimulations, but their interactions with dobutamine remain unknown.

METHODS

The effects of halothane, isoflurane, sevoflurane, and desflurane (1 and 2 minimum alveolar concentration) on the inotropic responses induced by dobutamine (10(-8)-10(-4) M) were studied in rat left ventricular papillary muscles in vitro. Inotropic effects were studied under low (isotony) and high (isometry) loads. The authors also studied the lusitropic effects in isotonic (R1) and isometric (R2) conditions. Data are the mean percentage of baseline +/- SD.

RESULTS

Dobutamine induced a positive inotropic effect (active isometric force: 185+/-36%, P < 0.001) and a positive lusitropic effect under low load (R1: 78+/-9%, P < 0.001), but not under high load (R2: 95+/-21%, not significant). Halothane, isoflurane, and sevoflurane did not modify the positive inotropic effect of dobutamine. Even in the presence of alpha-adrenoceptor blockade, isoflurane did not potentiate the positive inotropic effect of dobutamine. Desflurane significantly enhanced the positive inotropic effect of dobutamine (active isometric force: 239+/-35%, P < 0.001), but this potentiation was abolished by pretreatment with reserpine. In contrast to halothane, isoflurane, sevoflurane, and desflurane did not significantly modify the lusitropic effects of dobutamine.

CONCLUSIONS

Halogenated anesthetics, except desflurane, did not modify the positive inotropic effects of dobutamine. Desflurane enhanced the positive inotropic effect of dobutamine, but this effect was related to the desflurane-induced release in intramyocardial catecholamine stores.

Diaphragm strength and cross-bridge properties during chronic growth hormone hypersecretion

The aim of the study was to determine diaphragm performance and cross-bridge properties in rats bearing a growth hormone (GH)-secreting tumour. The tumour was induced by subcutaneous injection of GH-hypersecreting cells (GC cells) into the flank. Eighteen weeks after GC cell injection, rats developed a GH-secreting tumour (45.4+/-5.1 g) and the GH plasma level reached 5,408+/-648 microg x L(-1) in GH rats versus 7.2+/-2.2 microg x L(-1) in control rats (p<0.001). Diaphragm mechanics and cross-bridge properties were studied by applying the equations of A. Huxley in isolated diaphragm strips (control rats: n=12; GH rats n=20). In comparison to control rats, the total tension and total number of cross-bridges x mm(-2) in GH rats were lower in both twitch and tetanus (p<0.001). A linear relationship was observed between total tension and total cross-bridge number (r=0.94; p<0.001). Conversely, the cross-bridge single force and peak mechanical efficiency did not differ between control and GH rats, in either twitch or tetanus modes. In conclusion, the diaphragm strength was significantly lower in rats bearing growth hormone secreting tumours, and this was essentially determined by the lower cross-bridge number x mm(-2) without change in cross-bridge single force.

Cross-bridge kinetics in fatigued mouse diaphragm

The aim of this study was to determine cross-bridge number and kinetics in the diaphragm during fatigue and early recovery. Experiments were conducted in isolated mouse diaphragm (n=10). The force of a single cross-bridge (pi), the number of cross-bridges (m x 10(9) x mm2), the time cycle (tc) and the rate constants for cross-bridge attachment (f1) and detachment (g2) were calculated from the equations of A.F. Huxley. Following the fatigue protocol, peak isometric tension (Po) and maximum unloaded shortening velocity fell by 40+/-1% and 17+/-2%, respectively. In fatigued diaphragm, m fell by approximately 40% and returned to baseline after 10 min. When compared to baseline, g2 fell in fatigued diaphragm and remained significantly lower during the 15-min recovery period. In contrast, fatigue did not significantly modify pi, f1, or tc. There was a strong linear relationship between Po and m (p<0.001, r=0.988). No relationship was observed between tc and g2. These results indicate that changes in tension during fatigue and recovery run parallel to changes in the number of active cross-bridges, with no change in the force generated per cross-bridge. It is conceivable that fatigue durably impairs adenosine diphosphate release from the actomyosin complex without modifying the total duration of the cross-bridge cycle.

Arrhythmogenic right ventricular dysplasia

Arrhythmogenic right ventricular dysplasia (ARVD) is a new form of cardiomyopathy probably more frequent than commonly reported. It is a rare but important cause of sudden arrhythmic death in young, otherwise healthy persons, as well as a subtle cause of congestive heart failure. It may lead to temporary incapacitation with catastrophic consequences. Proper electrocardiographic criteria, echocardiography, nuclear medicine, or magnetic resonance imaging could identify most of these individuals. With the exception of full-thickness histological examination of the right ventricular free wall, contrast ventriculography remains the most definitive standard for a positive diagnosis. The wide clinical spectrum of arrhythmogenic right ventricular cardiomyopathies/dysplasia appears to be the result of one or possibly two factors: (a) replacement of most of the right ventricular myocardium by fat and (b) genetic susceptibility to environmental agents (myocarditis). Current treatment modalities include drug therapy, catheter or surgical ablative techniques, and modern treatments of congestive heart failure. Heart transplant is exceptional. Implantable defibrillators, used alone or in combination with drug therapy, will probably play an increasing role in ARVD and related cardiomyopathies.

Clinical use of respiratory changes in arterial pulse pressure to monitor the hemodynamic effects of PEEP

In ventilated patients with acute lung injury (ALI) we investigated whether respiratory changes in arterial pulse pressure (DeltaPP) could be related to the effects of PEEP and fluid loading (FL) on cardiac index (CI). Measurements were performed before and after application of a PEEP (10 cm H2O) in 14 patients. When the PEEP-induced decrease in CI was > 10% (six patients), measurements were also performed after FL. Maximal (PPmax) and minimal (PPmin) values of pulse pressure were determined over one respiratory cycle and DeltaPP was calculated: DeltaPP (%) = 100 x ((PPmax - PPmin)/ ([PPmax + PPmin]/2)). PEEP decreased CI from 4.2 +/- 1.1 to 3.8 +/- 1.3 L/min/m2 (p < 0.01) and increased DeltaPP from 9 +/- 7 to 16 +/- 13% (p < 0.01). The PEEP-induced changes in CI correlated with DeltaPP on ZEEP (r = -0.91, p < 0.001) and with the PEEP-induced increase in DeltaPP (r = -0.79, p < 0.001). FL increased CI from 3.5 +/- 1.1 to 4.2 +/- 0.9 L/min/m2 (p < 0.05) and decreased DeltaPP from 27 +/- 13 to 14 +/- 9% (p < 0.05). The FL-induced changes in CI correlated with DeltaPP before FL (r = 0.97, p < 0.01) and with the FL-induced decrease in DeltaPP (r = -0.85, p < 0.05). In ventilated patients with ALI, DeltaPP may be useful in predicting and assessing the hemodynamic effects of PEEP and FL.

Effects of load and tone on the mechanics of isolated human bronchial smooth muscle

Isotonic and isometric properties of nine human bronchial smooth muscles were studied under various loading and tone conditions. Freshly dissected bronchial strips were electrically stimulated successively at baseline, after precontraction with 10(-7) M methacholine (MCh), and after relaxation with 10(-5) M albuterol (Alb). Resting tension, i.e., preload determining optimal initial length (Lo) at baseline, was held constant. Compared with baseline, MCh decreased muscle length to 93 +/- 1% Lo (P < 0.001) before any electrical stimulation, whereas Alb increased it to 111 +/- 3% Lo (P < 0.01). MCh significantly decreased maximum unloaded shortening velocity (0.045 +/- 0.007 vs. 0.059 +/- 0.007 Lo/s), maximal extent of muscle shortening (8.4 +/- 1.2 vs. 13.9 +/- 2.4% Lo), and peak isometric tension (6.1 +/- 0.8 vs. 7.2 +/- 1.0 mN/mm2). Alb restored all these contractile indexes to baseline values. These findings suggest that MCh reversibly increased the number of active actomyosin cross bridges under resting conditions, limiting further muscle shortening and active tension development. After the electrically induced contraction, muscles showed a transient phase of decrease in tension below preload. This decrease in tension was unaffected by afterload levels but was significantly increased by MCh and reduced by Alb. These findings suggest that the cross bridges activated before, but not during, the electrically elicited contraction may modulate the phase of decrease in tension below preload, reflecting the active part of resting tension.

Effects of initial length on intrinsic tone in guinea pig tracheal smooth muscle

In the guinea pig, tracheal smooth muscle (TSM) exhibits intrinsic tone (IT). The active nature of IT suggests that it could be influenced by muscle length and load. In the guinea pig, IT is entirely suppressed by the cyclooxygenase inhibitor indomethacin. IT could be measured as the difference between resting tone before and after indomethacin addition. We examined, in electrically stimulated TSM strips (n = 9), the influence of initial muscle length (Li) on IT, the relationship between IT and the maximum extent of relaxation (DeltaF1), and the influence of indomethacin on active isometric force. When Li decreased from 100 to 75% of optimal Li, there was a significant decrease in IT (from 12.0 +/- 0.2 to 5.3 +/- 0.1 mN; P < 0.001). Over the range of Li studied, DeltaF1 underestimated the amount of IT, but there was a close linear relationship between DeltaF1 and IT (r = 0.9). Compared with the basal state, indomethacin increased active isometric force (from 9.5 +/- 1.0 to 19.7 +/- 2.0 mN at optimal Li; P < 0.001) and induced its length dependency. In guinea pig TSM, Li was an important determinant of IT.

Decreased regional blood flow in patients with acromegaly

BACKGROUND AND AIMS

One-third of acromegalic patients have hypertension. Acromegaly is also associated with intrinsic cardiac abnormalities known collectively as a hyperkinetic heart syndrome, which is characterized by an increased cardiac index and decreased systemic vascular resistance. As a result, blood flow should be increased in the regional vascular beds of acromegalic patients. The aim of the study was to measure, using direct methods, blood flow and vascular resistance at the level of the brachial artery in acromegalic patients with a confirmed hyperkinetic heart syndrome.

PATIENTS AND CONTROLS

Twelve patients with active acromegaly (five females, seven males; mean (+/- SD) age, 43 +/- 10 years) were studied. Twelve age- and sex-matched normal subjects served as controls.

METHODS

Right heart catheterization was used to measure the cardiac index and stroke volume and to calculate systemic vascular resistance in the acromegalic patients. Brachial haemodynamics were evaluated with a two-dimensional pulsed Doppler system (double transducer probe and range-gated time system of reception). The mean diameter of the brachial artery and mean blood velocity were measured and used to calculate mean blood flow. Vascular resistance was calculated in the brachial artery as the mean arterial pressure/blood flow ratio.

RESULTS

Age, body weight, height, body surface area and heart rate were similar in the acromegalic patients and controls, while mean arterial pressure was higher in patients. The cardiac index and stroke volume were increased in the acromegalic patients, at 4.08 +/- 0.47 (mean +/- SD) l/min/m2 body surface area and 116.7 +/- 19.4 ml, respectively, while systemic vascular resistance was low (12.5 +/- 2.1 U). Brachial artery diameter was similar in the patients and controls. Brachial artery mean blood velocity (P < 0.01) and mean blood flow (P < 0.05) were lower in the patients than in the controls (3.35 +/- 1.26 vs. 5.12 +/- 1.74 cm/s, and 16.4 +/- 9.4 vs. 25.6 +/- 11.6 ml/min/m2, respectively). The higher mean arterial pressure and lower mean blood flow resulted in higher forearm vascular resistance in the patients than in the controls (132 +/- 61 vs. 83.8 +/- 47 mmHg/ml/s/m2, respectively, P < 0.01).

CONCLUSION

While cardiac output is increased and systemic vascular resistance is decreased in active acromegaly, direct measurement of brachial artery haemodynamics showed lower regional blood flow and increased local resistance relative to healthy controls. These results suggest a heterogeneous distribution of cardiac output in acromegaly.

Increased compliance in diaphragm muscle of the cardiomyopathic Syrian hamster

We investigated the hypothesis that diaphragm compliance was abnormal in cardiomyopathic Syrian hamsters (CSH), an experimental model of myopathy. The passive elastic properties of isolated diaphragm muscles were analyzed at both the muscle and sarcomere levels. We used the following passive exponential relationship between stress (sigma) and strain (epsilon): sigma = (Eo/beta) (ebetaepsilon - 1), where Eo is the initial elastic modulus and beta is the stiffness constant. Immunocytochemistry procedures were used to analyze the distribution of two key elastic components of muscle, extracellular collagen and intracellular titin elastic components, as well as the extracellular matrix glycoprotein laminin. Muscle and sarcomere values of beta were nearly twofold lower in CSH (8.7 +/- 1.9 and 8.3 +/- 1.4, respectively) than in control animals (19.7 +/- 1.7 and 16.8 +/- 2.1, respectively) (P < 0.01 for each). Compared with controls, Eo was higher in CSH. Sarcomere slack length was significantly longer in CSH than in control animals (2.1 +/- 0.1 vs. 1.9 +/- 0.1 micrometer, P < 0.05). The surface area of collagen I was significantly larger in CSH (17.4 +/- 1.8%) than in control animals (12.4 +/- 0.7%, P < 0.05). There was no change in the distribution of titin or laminin labelings between the groups. These results demonstrate increased diaphragm compliance in cardiomyopathic hamsters. The increase in CSH diaphragm compliance was observed despite an increase in the surface area of collagen and was not associated with an abnormal distribution of titin or laminin.

Myocardial effects of desflurane in hamsters with hypertrophic cardiomyopathy

BACKGROUND

The effects of desflurane on myocardial contraction and relaxation in diseased myocardium have not been completely understood.

METHODS

The effects of desflurane (1.8 to 9.4 vol%) in left ventricular papillary muscles of healthy hamsters and those with genetically induced cardiomyopathy (strain BIO 14.6) were investigated in vitro (29 degrees C, pH 7.40, Ca2+ 2.5 mM; stimulation frequency, 3/min) under low (isotony) and high (isometry) load. Data are mean percentages of baseline +/- SD.

RESULTS

Desflurane induced no significant inotropic effect in healthy muscles (maximum unloaded shortening velocity and isometric active force at 9.4 vol%: 97 +/- 9% and 92 +/- 20%, respectively). In contrast, in cardiomyopathic muscles, desflurane induced a moderate negative inotropic effect (maximum unloaded shortening velocity and active force at 9.4 vol%: 84 +/- 19% and 75 +/- 25%, respectively). The negative inotropic effect was more pronounced than that in healthy muscles under low (P < 0.05) but not high load, and even when concentrations were corrected for minimum alveolar concentrations in each strain. Adrenoceptor blockade or pretreatment with reserpine did not modify the inotropic effect of desflurane, suggesting the absence of intramyocardial catecholamine release. However, tyramine also did not induce any significant catecholamine release in hamster myocardium. In both strains, desflurane induced no significant lusitropic effect under low or high load.

CONCLUSIONS

Desflurane had no inotropic effect in healthy muscles and a moderate negative inotropic effect in cardiomyopathic muscles. The absence of desflurane-induced intramyocardial catecholamine release was related to hamster myocardium characteristics.

Pulse pressure response to the strain of the valsalva maneuver in humans with preserved systolic function

Arterial pulse pressure response during the strain phase of the Valsalva maneuver has been proposed as a clinical tool for the diagnosis of left heart failure, whereas responses of subjects with preserved systolic function have been poorly documented. We studied the relationship between the aortic pulse amplitude ratio (i.e., minimum/maximum pulse pressure) during the strain phase of the Valsalva maneuver and cardiac hemodynamics at baseline in 20 adults (42 +/- 14 yr) undergoing routine right and left heart catheterization. They were normal subjects (n = 5) and patients with various forms of cardiac diseases (n = 15), and all had a left ventricular ejection fraction >/=40%. High-fidelity pressures were recorded in the right atrium and the left ventricle at baseline and at the aortic root throughout the Valsalva maneuver. Aortic pulse amplitude ratio 1) did not correlate with baseline left ventricular end-diastolic pressure, cardiac index (thermodilution), or left ventricular ejection fraction (cineangiography) and 2) was positively related to total arterial compliance (area method) (r = 0.59) and to basal mean right atrial pressure (r = 0.57) (each P < 0.01). Aortic pulse pressure responses to the strain were not related to heart rate responses during the maneuver. In subjects with preserved systolic function, the aortic pulse amplitude ratio during the strain phase of the Valsalva maneuver relates to baseline total arterial compliance and right heart filling pressures but not to left ventricular function.

Modifications of the inotropic responses to alpha- and beta-adrenoceptor stimulation by propofol in rat myocardium

Propofol induces cardiovascular depression but without significant effect on intrinsic myocardial contractility in many species. However, its interactions with adrenoceptor stimulation are unknown. We studied the effects of propofol (1 and 10 microg/mL) and its solvent on the inotropic response induced by phenylephrine (10(-8)-10(-4) M) or isoproterenol (10(-8)-10(-4) M) in rat left ventricular papillary muscles in vitro (Krebs-Henseleit solution, 29 degrees C, pH 7.40, calcium 0.5 mM, stimulation frequency 12 pulses/min). We also studied the lusitropic effects in isotonic and isometric conditions. In control groups, phenylephrine (127% +/- 3% of baseline; P < 0.05) and isoproterenol (169% +/- 11% of baseline; P < 0.05) induced a positive inotropic effect. Propofol (10 microg/mL) completely abolished the positive inotropic effect of phenylephrine (100% +/- 3% of baseline; P = not significant). In contrast, at the lowest concentration (1 microg/mL), propofol did not modify the positive inotropic effect of phenylephrine. Propofol did not modify the inotropic effect of isoproterenol. Propofol (10 microg/mL) enhanced the positive lusitropic effect of isoproterenol under low-load (P < 0.05) but not under high-load conditions.

IMPLICATIONS

A high concentration of propofol abolished the positive inotropic effect of alpha- but not beta-adrenoceptor stimulation and enhanced the positive lusitropic effect of beta-adrenoceptor stimulation.

Mechanics, energetics, and crossbridge kinetics of rabbit diaphragm during congestive heart failure

Crossbridge (CB) properties were investigated in isolated diaphragm of rabbits during congestive heart failure (CHF, n=9) induced by chronic volume and pressure overload. This model induced cardiac hypertrophy and heart failure. Controls (C) were prepared (n=14). Compared to C, peak tension in CHF fell by 57% in twitch and by 40% in tetanus; Vmax declined by 47% in twitch and by 48% in tetanus. Our study provided an analytical means of calculating from A. F. Huxley's equations the rate constants for CB attachment and detachment, CB single force (II), CB number per mm3 (m'), peak mechanical efficiency (Effmax), and turnover rate of myosin ATPase (kcat); m', II, and Effmax were lower in CHF than in C in both twitch and tetanus. The marked decline in m' and II accounted for the fall in diaphragm strength. In the overall population of C and CHF, Effmax was linearly related to II. Conversely, there was no relationship between Vmax and kcat. Dissociation between Vmax and kcat might be explained by the crucial role attributed to two apparently nonconserved surface 'loops' on the motor domain of myosin head.

A comparison between systolic aortic root pressure and finger blood pressure

BACKGROUND

Digital photoplethysmography is used to assess hemodynamic variability and baroreflex sensitivity. Numerous studies have critically evaluated the accuracy of the photoplethysmographic device against peripheral pressure. The aim of our study was to compare finger blood and aortic root pressure.

METHODS

We prospectively compared simultaneous recordings of systolic pressure at the aortic root and finger level over three consecutive respiratory cycles in 15 patients (56+/-11 years) undergoing routine cardiac catheterization. Data were obtained at baseline, during deep breathing maneuver (0.1 Hz), and after left ventricular cineangiography.

RESULTS

At baseline, systolic finger pressure overestimated systolic aortic pressure (145.2+/-22.5 vs 115.0+/-20.1 mm Hg; p<0.001). The pressure difference (30.2+/-17.0 mm Hg) was not influenced by systolic aortic pressure. There was no relationship between pressure difference and the main determinants of the pulse wave amplification phenomenon. There was a beat-to-beat relationship between finger and aortic pressure in 14 of 15 subjects (slope ranging from 0.37 to 1.70; ordinate: from -56 to +98 mm Hg). During the deep breathing maneuver and after left ventricular cineangiography, finger pressure still overestimated aortic pressure by 32.3+/-15.0 mm Hg and 38.3 13.9 mm Hg, respectively (each p<0.001). There was a beat-to-beat relationship between systolic aortic root pressure (IAoBP) and systolic finger (FBP) in 13 of 15 patients, with major scattering of both slopes and ordinates. Throughout the study, there was no predictable relationship between the level of IAoBP and pressure bias.

CONCLUSIONS

As expected, FBP was almost always higher than IAoBP. Importantly, the differences in systolic pressure did not correlate with known determinants of the pulse wave amplification phenomenon. The device must be used cautiously if one wants to noninvasively track spontaneous or induced changes in IAoBP.

Comparison of the effects of sevoflurane, isoflurane and halothane on rat myocardium

The effects of sevoflurane on myocardial contraction and relaxation are poorly understood. Therefore, we studied the effects of equianaesthetic concentrations (0.5, 1, 1.5, 2 and 2.5 MAC) of sevoflurane, isoflurane and halothane on inotropic and lusitropic (myocardial relaxation) variables, and post-rest potentiation in rat left ventricular papillary muscles in vitro. Sevoflurane and isoflurane caused comparable concentration-dependent negative inotropic effects which were significantly lower than those induced by halothane (P < 0.05). Sevoflurane and isoflurane did not modify lusitropic variables under low or high load, whereas halothane showed a negative lusitropic effect at high concentrations. Halothane suppressed post-rest potentiation, whereas isoflurane and sevoflurane did not. Post-rest recovery was unaffected by halothane, isoflurane or sevoflurane at any concentration. Thus in rat myocardium, sevoflurane and isoflurane caused comparable negative inotropic effects, had no significant lusitropic effects and did not alter post-rest potentiation, suggesting that they did not significantly modify the functions of the sarcoplasmic reticulum.