Synchronization of n non-identical double-integrated plants

Synchronization of n non-identical double-integral plants with non-identical output initial conditions will be studied. Achievement of two objectives will furnish us with our synchronization goal: (i) elimination of steady-state errors between the n outputs and (ii) portraying each of the n identical steady-state outputs as a double integral (dt²) of a common input x(t).     

An extended model for pairwise conflict resolution in air traffic management

A conflict resolution model for aircraft traversing planar intersecting trajectories is developed and solved. The model incorporates the flight dynamics of each aircraft. Three types of optimal conflict avoidance manoeuvres are examined. The first is the minimum‐time safe deviation to a designated objective and the second and third are the minimum‐time safe deviation to and from a designated ground track. These objectives lead to singular optimal control problems where the control variable constraint is defined in terms of the maximum allowable turn rate ∣u(t)∣⩽u_M,0⩽t⩽t_f, for the aircraft executing the avoidance manoeuvre and the non‐autonomous state variable constraint is defined in terms of the radius r_p of the protected zone about the potentially conflicting aircraft. A fast, accurate procedure is derived for computing the optimal steering program which requires the solution of a coupled differential‐algebraic system of equations to determine the control law on any boundary arc of an extremal trajectory. An example pairwise trajectory conflict is analysed in detail. The incorporation of variable airspeed v(t) and an acceleration/deceleration control u₂(t) is also discussed. Copyright © 1999 John Wiley & Sons Ltd.     

A Newton-like approximation algorithm for the steady-state solution of the riccati equation for time-varying systems

An approximation technique is developed for the steady-state solution of the time-varying matrix Riccati equation. We show how the Newton-type algorithm of Kleinman, developed for computing the steady solution to the algebraic Riccati equation for time-invariant systems, can be extended for time-varying linear systems. The time-varying case is considerably more involved than the time-invariant one. Consider a linear time-varying system x (t) = F (t) x (t) + G (t) u (t). If ( F , G ) is uniformly completely controllable, we show how one can construct a recursive sequence of matrix functions (using linear techniques) which converge to the steady-state solution of the associated time-varying matrix Riccati equation (a non-linear object). At each successive state, the next approximation is in terms of the steady-state solution to a linear Lyapunov differential equation (which is the extension of the algebraic Lyapunov equations used by Kleinman) for which an explicit expression exists. This provides an approximation technique for obtaining infinite-time, linear-quadratic, optimal controllers and steady-state Kalman—Bucy filters for time-varying systems using purely linear techniques. Thus, we provide new types of suboptimal stabilizing feedback laws for linear time-varying systems.     

Effect of fixation of shoulder and elbow joint movement on the precision of laparoscopic instrument manipulations

Background Motion analysis of the upper limb and the surgical instruments is used for objective assessment of endoscopic manipulations. The aim of this study was to investigate the effect of fixation of shoulder and elbow joint movement on the precision of laparoscopic instrument manipulations.Methods Two experiments were conducted to correlate hand movement with instrument tip during free and restricted movement of the shoulder and elbow joints. A three-dimensional infrared optical tracking system has been used. Five subjects participated in the study, and each completed the range of movements twice. End points were velocity (m/s), angular velocity (r/s) and acceleration (m/s²).Results There was a weak correlation for all end points between the instrument tip and individual joint movement during free upper limb movement (r < 0.4). With restricted movement of the shoulder and elbow joints, the correlation between hand movement and instrument tip was found to be good for the velocity (r = 0.66 for flexion; r = 0.72 for abduction; r = 0.56 for supination) and angular velocity (r = -0.83 for flexion; r = -0.48 for abduction; r = -0.70 for supination), but weak for the acceleration (r < 0.4).Conclusions The characteristics of hand movements do not correlate with movement of the laparoscopic instrument tip when the upper limb is unsupported. The precision of laparoscopic surgical manipulations is increased if both joints (shoulder and elbow) are supported.     

Magnetic resonance imaging for the evaluation of rejection of a kindney allograft in the rat

Orthotopic DA (RT1^a) into Lewis (RT1¹) rat kidney allografts and control Lewis-into-Lewis grafts were assessed by magnetic resonance imaging (MRI) and perfusion measurement after intravenous injection of a superparamagnetic contrast agent. MRI anatomical scores (range 1–6) and perfusion rates were compared with graft histology (rank of rejection score 1–6). Not only acute rejection, but also chronic events were monitored after acute rejection was prevented by daily cyclosporine (Sandimmune) treatment during the first 2 weeks after transplantation. In acute allograft rejection (n=11), MRI scores reached the maximum value of 6 and perfusion rates were severely reduced within 5 days after transplantation; histology showed severe acute rejection (histologic score 5–6). In the chronic phase (100–130 days after transplantation), allografts (n=5) manifested rejection (in histology cellular rejection and vessel changes), accompanied by MRI scores of around 2–3 and reduced perfusion rates. Both in the acute and chronic phases, the MRI anatomical score correlated significantly with the histological score (Spearman rank correlation coefficient r _s 0.89, n=30, P<0.01), and perfusion rates correlated significantly with the MRI score or histological score (r _s values between-0.60 and -0.87, n=23, P<0.01). It is concluded that MRI represents an interesting tool for assessing the anatomical and hemodynamical status of a kidney allograft in the acute and chronic phases after transplantation.     

Pharmacokinetics,Urinary and Mammary Excretion of Ceftriaxone in Lactating Goats

The pharmacokinetic properties of ceftriaxone were investigated in 10 goats following a single intravenous (i.v.) and intramuscular (i.m.) administration of 20 mg kg⁻¹ body weight. After i.v. injection, ceftriaxone serum concentration–time curves were characteristic of a two‐compartment open model. The distribution and elimination half‐lives (t_1/2α, t_1/2β) were 0.12 and 1.44 h respectively. Following i.m. injection, peak serum concentration (C_max) of 23.6 μg ml⁻¹ was attained at 0.70 h. The absorption and elimination half‐lives (t_1/2ab, t_1/2el) were 0.138 and 1.65 h respectively. The systemic bioavailability of the i.m. administration (F %) was 85%. Following i.v. and i.m. administration, the drug was excreted in high concentrations in urine for 24 h post‐administration. The drug was detected at low concentrations in milk of lactating goats. A recommended dosage of 20 mg kg⁻¹ injected i.m. every 12 h could be expected to provide a therapeutic serum concentration exceeding the minimal inhibitory concentrations for different susceptible pathogens.     

Normal urinary calcium/creatinine ratios in African-American and Caucasian children

A random urine calcium/creatinine ratio (UCa/Cr) is of practical use in screening for hypercalciuria. However, due to worldwide variations, reference values for the pediatric population are not yet well established. Furthermore, no study has been conducted to establish normal UCa/Cr values in young African-American (AA) children. It has also been previously reported that an elevated UCa/Cr is related to a high urine Na/K ratio (UNa/K). The objectives of the present study were: (1) to set normal values of random UCa/Cr by age and race in the pediatric population of Metropolitan Kansas City, (2) to identify potential racial differences in UCa/Cr between Caucasian (CS) and AA children, and (3) to determine the relationship between UCa/Cr and UNa/K in healthy children.A total of 368 healthy children of both genders were enrolled in the study. They were divided into four age groups as follows: (1) <7 months, (2) 8–18 months, (3) 19 months to 6 years, and (4) 7–16 years. Each group was subdivided into AA and CS. A non-fasting random urine specimen from each subject was analyzed for Ca, Na, K and creatinine.The median UCa/Cr values for AA were: (1) 0.13, (2) 0.09, (3) 0.06, and (4) 0.04 and for CS they were (1) 0.26, (2) 0.11, (3) 0.10, and (4) 0.09. The data showed a strong inverse relationship between UCa/Cr and age, the youngest children demonstrating the highest UCa/Cr. In each age group, UCa/Cr in CS exceeded the corresponding value in AA. The age-dependent 95th percentiles of UCa/Cr values for CS were (1) 0.70, (2) 0.50, (3) 0.28, and (4) 0.20 and for AA they were (1) 0.38 and (3) 0.24. Due to outliers, the 95th percentile could not be established for the other two AA subgroups. The relationship between UCa/Cr and UNa/K was found to be extremely weak in both AA (r ² =0.00005) and CS (r ² =0.02). On the other hand, a strong linear correlation was observed between UNa/K and age (CS r ² =0.23, P<0.001, AA r ² =0.19, P<0.001), explaining in part the lack of correlation between UNa/K and UCa/Cr.We conclude that the child’s age, ethnicity and geographic location should be taken into consideration when assessing UCa/Cr ratio. Contrary to what has previously been reported in hypercalciuric children, no significant relationship was found between UCa/Cr and UNa/K in healthy children. Received: 7 June 2000 / Revised: 21 September 2000 / Accepted: 23 September 2000     

Abbreviated mycophenolic acid AUC from C0, C1, C2, and C4 is preferable in children after renal transplantation on mycophenolate mofetil and tacrolimus therapy

In order to allow a similar algorithm to be used for both adults and children on tacrolimus-based and mycophenolate mofetil [MMF, a pro-drug for mycophenolic acid (MPA)]-based immunosuppression, a limited sampling technique from the trough level (C0) and the levels 30 min (C0.5) and 2 h (C2) after intake was to be developed from MPA area under the time–concentration curves (AUC). We retrospectively analyzed 49 full ten-point pharmacokinetic (PK) profiles from 29 pediatric patients on MMF and tacrolimus. We used stepwise multiple regression analysis to calculate limited sampling approaches. Agreement with the AUC was tested by means of Bland and Altman analysis. The correlation between AUC and pre-dose trough concentration was r²=0.5188 (P<0.0001) and between AUC and post-dose trough concentration r²=0.6924 (P<0.0001). The next best correlations were with 2 h (C2, r²=0.6711, P<0.0001), 4 h (C4, r²=0.6411, P<0.0001), 1.5 h (C1.5, r²=0.6344, P<0.0001), and 6 h (C6, r²=0.6219, P<0.0001). Three-point estimates at C0, C0.5, and C2 resulted in an acceptable correlation between predicted AUC and AUC from the full profile when we used the formula AUC = 10.01391+3.94791×C0+3.24253×C0.5+1.0108×C2, Pearsons r=0.8996, 95% confidence interval 0.8277–0.9424. However, even better results could be obtained when we used AUC = 8.217+3.163×C0+0.994×C1+1.334×C2+4.183×C4, Pearsons r=0.9456, 95% confidence interval 0.9051–0.9691. Bland and Altman analysis revealed good agreement between AUC predicted from C0, C0.5, and C2 and AUC from the full profile, but was inferior to the four-point approach. Also, the previously reported formula derived for adults was not usable in these patients. A special formula must be used for children. The AUC of MPA can be predicted by limited sampling including C0, C0.5, and C2, while an approach using C0, C1, C2, and C4 is preferable.     

Two different doses of caudal neostigmine co-administered with levobupivacaine produces analgesia in children

Background: This study was aimed to evaluate the analgesic efficacy, duration of analgesia, and side effects of two different doses of caudal neostigmine used with levobupivacaine in children. Methods: Sixty boys, between 5 months and 5 years, undergoing genito‐urinary surgery were allocated randomly to one of three groups (n = 20 each). Group I patients received caudal 0.25% levobupivacaine (1 ml·kg^?1) alone. Groups II and III patients received neostigmine (2 and 4 μg·kg^?1 respectively) together with levobupivacaine used in the same dose as Group I. Pain scores were assessed using Children’s and Infant’s Postoperative Pain Scale (CHIPPS) at 15th (t₁) min after arrival to postanesthetic care unit, and 1st (t₂), 2nd (t₃), 3rd (t₄), 4th (t₅), 8th (t₆), 16th (t₇), and 24th (t₈) hour postoperatively. Duration of analgesia, amount of additional analgesic (paracetamol), score of motor blockade and complications were recorded for 24 h postoperatively, and compared between groups. Results: CHIPPS scores were higher during t₂, t₃, t₆, t₇ and t₈ periods, duration of analgesia was shorter, and total analgesic consumption was higher in Group I compare to neostigmine groups (P < 0.05). Duration of postoperative analgesia and total analgesic consumption were similar in Groups II and III (P > 0.05). Adverse effects were not different between three groups. Conclusions: Caudal neostigmine in doses of 2 and 4 μg·kg^?1 with levobupivacaine extends the duration of analgesia without increasing the incidence of adverse effects, and 2 μg·kg^?1 seems to be the optimal dose, as higher dose has no further advantages.     

Measurement of radiometric surface temperature and integrated backscattered light intensity during feedback-controlled laser-assisted cartilage reshaping

Cartilage undergoes characteristic mechanical stress relaxation following laser irradiation below the ablation threshold. Porcine auricular cartilage (1–2 mm thickness) was irradiated with a Nd:YAG laser (=1.32 m) at two power levels (W/cm²). Surface temperature (S _c (t) (°C)) (monitored using a single element HgCdTe infrared detector, 10-14 m spectral range), and integrated back scattered light intensityI(t) were measured during laser irradiation. A HeNe laser beam (=632.8 nm) was incident on the back surface of the cartilage specimen and fractional integrated backscattered light intensity was measured using an integrating sphere anda silicon photodiode. Laser irradiation (5.83 W/cm², 50 Hz pulse repetition rate (PRR)) continued until surface temperature reached approximately 70°C, during which cartilage mechanical stress relaxation was observed. Integrated back scattered light intensity reached a plateau at about 70°C). At higher laser power (39.45 W/cm², 50 Hz PRR), a feedback-controlled cryogen spray was used to maintain surface temperature below 50°C. A similar plateau response was noted in integrated backscattered light intensity. This signal may be used to optimise the process of stress relaxation in laser cartilage reshaping. Several clinical applications involving reconstructive surgery are proposed.     

Elimination Half-Lives of Sulphadimethoxine and its N4-acetyl Metabolite in Tissues of Laying Hens

The depletion rates of sulphadimethoxine (SDM) and its metabolite N⁴-acetylsulphadimethoxine (N⁴-AcSDM) were estimated in blood and various tissues of laying hens. The tissue contents (ppm) of SDM and N⁴-AcSDM after the withdrawal of SDM, which was fed to hens at 400 ppm diet for 5 successive days, were determined by HPLC. The elimination half-life (t_1/2) of N⁴-AcSDM in the liver, ovary and muscle was estimated to be 4.3 h with a 95 % confidence interval from 3.6 to 5.3 h. No significant difference between t_1/2 of N⁴-AcSDM in the tissues and that of SDM (4.4 h) in the blood, kidney, muscle, ovary and adipose tissue was observed. On the other hand, the t_1/2 of N⁴-AcSDM in the kidney (8.1 h) was significantly longer than that in the above 3 tissues.     

Pharmacokinetic profile of propofol after a single-dose injection during general anesthesia in Japanese adults

Purpose. To determine the pharmacokinetic parameters of propofol after a single-dose injection in Japanese adults. Methods. This study was carried out in adult patients who underwent minor surgery under general anesthesia with sevoflurane. We injected 1.0, 1.5, or 2.0 mg·kg⁻¹ of propofol at a constant rate using a syringe pump. Arterial blood samples were taken for 480 min after the administration of propofol. The whole-blood concentration of propofol was determined with gas chromatography, and a time–blood concentration curve was analyzed by a two-compartment open-model analysis and a model-independent analysis. Results. The half-lives of the central and peripheral compartment (t _1/2α and t _1/2β) were 2.26 ± 0.69 and 47.9 ± 22.1 min, respectively. The volume of the central compartment (V_c) was 0.582 ± 0.170 l·kg⁻¹, and the apparent volume of distribution at a steady state (V_dss) was 2.62 ± 1.06 l·kg⁻¹. The total body clearance (Cl) and mean residence time (MRT) were 53.7 ± 11.9 ml·min⁻¹·kg⁻¹ and 98.1 ± 16.4 min, respectively. Conclusions. Among the pharmacokinetic parameters determined in Japanese adults, t _1/2α, t _1/2β, and Vc were similar, V_dss was smaller, and Cl was larger, as compared with values in Caucasians. These findings suggest that propofol could be eliminated well during minor surgery in Japanese adults. Received: January 27, 1999 / Accepted: March 31, 2000     

Changes in free water fraction and aquaporin function with dwell time during continuous ambulatory peritoneal dialysis

Diffusive (K_BD, A₀/Δx(t)) transport parameters and sieving coefficients (S) for small solutes and free water fraction (FWF), that is, the fraction of total water flow that is transported through aquaporins, were assessed as functions of dwell time t for 35 continuous ambulatory peritoneal dialysis patients using glucose 3.86% dialysis fluid. The individual values of the unrestricted pore area over diffusion distance, A₀/Δx(t), were estimated using the mixed effects nonlinear regression and applied for evaluation of S(t) for sodium and FWF(t). FWF decreased on average from the initial 51% of the total transcapillary water flow to 36% at 120 min, whereas the small pore water fraction and sodium sieving coefficient increased. Our results were consistent with the three‐pore model if the contribution of the transcellular pores (α_TP) at the beginning of dwell study was doubled and later decreased to the standard value of 0.02. We conclude that transport characteristics of fluid and small solutes should be considered as time‐dependent variables during the peritoneal dialysis.     

The Distribution of Survival Times after Injury

Introduction

The distribution of survival times after injury has been described as “trimodal,” but several studies have not confirmed this. The purpose of this study was to clarify the distribution of survival times after injury.

Methods

We defined survival time (t_s) as the interval between injury time and declared death time. We constructed histograms for t_s?≤?150?min from the 2004–2007 Fatality Analysis Reporting System (FARS, for traffic crashes) and National Violent Death Reporting System (NVDRS, for homicides). We estimated statistical models in which death times known only within intervals were treated as interval-censored. For confirmation, we also obtained EMS response times (t_r), prehospital times (t_p), and hospital times (t_h) for decedents in the 2008 National Trauma Data Bank (NTDB) with t_s?=?t_p?+?t_h?≤?150. We approximated times until circulatory arrest (t_x) as t_r for patients pulseless at the injury scene, t_p for other patients pulseless at hospital admission, and t_s for the rest; for any declared t_s, we calculated mean t_x/t_s. We used this ratio to estimate t_x for hospital deaths in FARS or NVDRS and provide independent support for using interval-censored methods.

Results

FARS and NVDRS deaths were most frequent in the first few minutes. Both showed a second peak at 35–40?min after injury, corresponding to peaks in hospital deaths. Third peaks were not present. Estimated t_x in FARS and NVDRS did not show second peaks and were similar to estimates treating some death times as interval-censored.

Conclusions

Increases in frequency of survival times at 35–40?min are primarily artifacts created because declaration of death in hospitals is delayed until completing resuscitative attempts. By avoiding these artifacts, interval censoring methods are useful for analysis of injury survival times.     

Gas exchange, metabolic rate and fluid requirements during anaesthesia of acyanotic and cyanotic infants and children with congenital heart malformations

In order to study gas exchange and metabolic rate in anaesthetized children scheduled for corrective cardiac surgery and to find out if chronic hypoxaemia influenced gas exchange and energy expenditure, oxygen consumption (V?O₂) and carbon dioxide elimination (Vdot;co₂) were measured and energy expenditure (E) was calculated. Infants and children whose haematocrit (Hct) was less than 44% and arterial oxygen saturation (Sao₂) on room-air was greater than 93% were classified as acyanotic (group AC, n= 11, weight range 3.7 to 20 kg), and those whose Hct was higher than 44% and Sao₂ less than 93% as cyanotic (group C, n= 14, weight range 3.4 to 24.3 kg). The majority of children in both groups weighed less than the 50th percentile for normal children. There was no difference in V?o₂, V?co₂ and E between the groups. These variables were related to weight according to the following expressions: V?o₂ (ml min^?1) = 6.1 × kg + 21.6, r= 0.95; V?co₂ (ml min^?1) = 5.7 × kg + 2.9, r= 0.96, and E (kcal h^?1) 1.8 × kg + 5.3; E (J h^?1) = 7.6 × kg + 22.3, r= 0.96. Fluid volumes (FV) could be calculated according to the expression: FV (ml h^?1) = 3.0 × kg + 8.7; r= 0.96. Oxygen consumption was 15 to 20% higher in anaesthetized infants and children with congenital heart malformations than in anaesthetized infants and children with normal cardiopulmonary function. Accordingly, energy expenditure and fluid requirements were also higher. This difference was most probably due to an undernutrition in children with congenital heart malformations which resulted in a compensatory hypermetabolism.     

Numerical method for the solution of the singular riccati matrix

A computational scheme is presented for the solution of the Riccati matrix associated with time-varying quadratic regulation. It is shown that the local truncation error of the algorithm is at most O(Δt³) where Δt is the interval of computation. The main contribution of this short communication is to demonstrate that the scheme yields the solution even in the face of singularities. Higher-order formulae are useful when the sensitivity of the Riccati matrix to error is large.     

Analysis of Cleveland Clinic continuous-flow total artificial heart performance using the Virtual Mock Loop: Comparison with an in vivo study

The Virtual Mock Loop (VML) is a mathematical model designed to simulate mechanism of the human cardiovascular system interacting with mechanical circulatory support devices. Here, we aimed to mimic the hemodynamic performance of Cleveland Clinic’s self-regulating continuous-flow total artificial heart (CFTAH) via VML and evaluate the accuracy of the VML compared with an in vivo acute animal study. The VML reproduced 124 hemodynamic conditions from three acute in vivo experiments in calves. Systemic/pulmonary vascular resistances, pump rotational speed, pulsatility, and pulse rate were set for the VML from in vivo data. We compared outputs (pump flow, left and right pump pressure rises, and atrial pressure difference) between the two systems. The pump performance curves all fell in the designed range. There was a strong correlation between the VML and the in vivo study in the left pump flow (r² = 0.84) and pressure rise (r² = 0.80), and a moderate correlation in right pressure rise (r² = 0.52) and atrial pressure difference (r² = 0.59). Although there is room for improvement in simulating right-sided pump performance of self-regulating CFTAH, the VML acceptably simulated the hemodynamics observed in an in vivo study. These results indicate that pump flow and pressure rise can be estimated from vascular resistances and pump settings.     

Gentamicin interval in newborn infants as determined by renal function and postconceptional age

We evaluated the relationship between gentamicin pharmacokinetics and glomerular filtration rate in newborn infants to estimate the appropriate interval of administration in neonates with renal insufficiency. Gentamicin half-life (Gt 1/2) could be predicted from plasma creatinine concentration (Pcr) (r=0.78); the prediction was minimally but significantly increased (r=0.81) by adding postconceptional age to a multiple regression analysis. Infants with a postconceptional age of 29 weeks or more and a Pcr of 1 mg/dl or more had significantly greater trough and peak gentamicin levels than those with a Pcr less than 1 mg/dl. If gentamicin is indicated in a patient with renal insufficiency, the interval of administration should be 2–3 G_t 1/2, which can be estimated from Pcr (Gt 1/2=2.0+7.7 Pcr). The interval can then be adjusted according to peak and trough gentamicin levels.     

Glomerular function and microalbuminuria in children with insulin-dependent diabetes

Renal function has been evaluated in 45 diabetic children (age 12.5±4 years) with a mean diabetes duration of 4.9±3.5 years. Glomerular filtration rate (GFR; inulin and creatinine clearances), renal plasma flow (RPF; PAH clearance), resting urinary albumin excretion (UAE) were measured and compared with indexes of metabolic control: Hb A₁C and blood glucose values (mean, post-prandial and maximal excursion) on the same day. GFR (inulin clearance) and RPF were significantly increased in the diabetic group (171±31 and 778±172 ml/min per 1.73 m²) compared with controls (124±18 and 631±128 ml/min per 1.73 m²). Both parameters were strongly correlated (r=0.73;P<0.001). Creatinine clearance was not correlated to inulin clearance. Hyperfiltration (inulin clearance above 160 ml/min per 1.73 m²) was noted in 61% of the patients and was independent of diabetes duration. Five diabetic children had a UAE level above 15 g/min. No relationship could be established between UAE and any of the metabolic indexes; GFR was weakly correlated to HbA₁C (r=0.35;P<0.05), to mean (r=0.35;P<0.05) and post-prandial blood glucose (r=0.37;P<0.05). In contrast, there was a strong correlation between GFR and the maximal blood excursion (r=0.62;P<0.001). The study shows that renal abnormalities can be detected with a high frequency in diabetic subjects characterized by both an early onset and a short duration of diabetes and suggests the need for a more systematic evaluation of renal parameters in this population.     

Mechanical restitution curves reflect post-ischemic stunning in pigs

Objectives The time constant of mechanical restitution (T_(MRC)), proposed to reflect changes in calcium release and uptake, has been shown to increase in left ventriculariz (LV) failure. In this study, we tested the hypothesis that T_(MRC) also can identify post-ischemic, reversible LV dysfunction (stunning).

Design Stunning was induced by a series of left main coronary artery occlusions in eight anesthetized open chest pigs. Left ventricular pressure–volume relations were assessed using a pressure–volume catheter during right atrial pacing. Mechanical restitution curves (MRCs) were constructed using two different measures of contractile response: maximal first derivative of pressure (CR_(dP/dtmax)) and stroke work (CR_(SW)).

Results Mean arterial pressure, stroke volume and dP/dt_max were decreased 30 min after stunning. Slopes of end-systolic pressure volume relation and preload recruitable stroke work, however, showed no significant changes after stunning. For MRCs based on CR_(dP/dtmax), T_(MRC) increased in all eight animals. Using CR_(SW), T_(MRC) increased in seven out of eight pigs.

Conclusions Ischemia–reperfusion induce changes in MRCs based on CR_(dP/dtmax) and CR_(SW). The MRC concept may have potential as a clinical left ventricular performance index.