Coherence between electromyographic signals of anterior tibialis, soleus, and gastrocnemius during standing balance tasks.

Introduction: Knowledge about the mechanics and physiological features of balance for healthy individuals enhances understanding of impairments of balance related to neuropathology secondary to aging, diseases of the central nervous system (CNS), and traumatic brain injury, such as concussion. Methods: We examined the neural correlations during muscle activation related to quiet standing from the intermuscular coherence in different neural frequency bands. Electromyography (EMG) signals were recorded from six healthy participants (fs = 1,200 Hz for 30 s) from three different muscles bilaterally: anterior tibialis, medial gastrocnemius, and soleus. Data were collected for four different postural stability conditions. In decreasing order of stability these were feet together eyes open, feet together eyes closed, tandem eyes open, and tandem eyes closed. Wavelet decomposition was used to extract the neural frequency bands: gamma, beta, alpha, theta, and delta. Magnitude-squared-coherence (MSC) was computed between different muscle pairs for each of the stability conditions. Results and discussion: There was greater coherence between muscle pairs in the same leg. Coherence was greater in lower frequency bands. For all frequency bands, the standard deviation of coherence between different muscle pairs was always higher in the less stable positions. Time-frequency coherence spectrograms also showed higher intermuscular coherence for muscle pairs in the same leg and in less stable positions. Our data suggest that coherence between EMG signals may be used as an independent indicator of the neural correlates for stability.

Changes in Electroencephalography Activity in Response to Power Mobility Training: A Pilot Project.

Purpose: The purposes of this pilot project were to examine the impact of power mobility training on (1) electroencephalography (EEG) activity in children with severe cerebral palsy (CP) and (2) power mobility skill acquisition. Method: A single-subject A-B-A-B research design with a 5-week duration for each phase (20 wk total) was replicated across three participants with severe CP (Gross Motor Function Classification System Level V). Data related to the target behaviour, as represented by EEG activity, were collected each week. Power mobility skills were assessed using the Canadian Occupational Performance Measure (COPM), the Wheelchair Skills Checklist (WSC), and the Assessment of Learning Powered mobility use (ALP). Weekly power mobility training was provided during the intervention phases. EEG data were analyzed by means of three measurement metrics (power spectral density, mutual information, and transfer entropy). Results: All three participants demonstrated changes in activation in frontoparietal EEG recordings and clinically significant improvements in power mobility skill acquisition as measured by the COPM as well as by the ALP and WSC. Conclusions: Power mobility training appeared to affect both neuroplastic and skill acquisition. Combining the use of EEG with direct therapist-observation measurement tools may provide a more complete understanding of the impact of power mobility training on children with severe CP.

Objectif : le présent projet pilote vise à examiner les répercussions de l'entraînement à la mobilité motorisée sur 1) l'activité électroencéphalographique (ÉEG) chez les enfants atteints d'une paralysie cérébrale (PC) marquée et 2) l'acquisition d'habiletés à la mobilité motorisée. Méthodologie : les chercheurs ont répliqué une méthodologie de recherche A-B-A-B individuelle d'une durée de cinq semaines par phase (total de 20 semaines) chez trois participants ayant une PC marquée (niveau V du système de classification de la motricité brute). Chaque semaine, ils ont colligé les données relatives au comportement ciblé, représentées par l'activité ÉEG. Ils ont évalué l'habileté à la mobilité motorisée au moyen de la mesure canadienne du rendement occupationnel (MCRO), de la liste des habiletés en fauteuil roulant (LHFR) et de l'évaluation de l'apprentissage d'utilisation de la mobilité motorisée (ÉAUMM). Pendant les phases d'intervention, ils ont fourni un entraînement hebdomadaire à la mobilité motorisée. Ils ont analysé les données d'ÉEG à l'aide de trois mesures de rendement (densité du spectre de puissance, information mutuelle et entropie de transfert). Résultats : les trois participants ont démontré des changements à l'activation des enregistrements ÉEG frontopariétaux et des améliorations cliniquement significatives à l'acquisition des habiletés de mobilité motorisée mesurée par la MCRO, l'ÉAUMM et la LHFR. Conclusion : l'entraînement à la mobilité motorisée semble avoir des effets à la fois sur la plasticité neurale et sur l'acquisition d'habiletés. La combinaison de l'ÉEG avec des outils de mesure observés directement par le thérapeute pourrait permettre de mieux comprendre les répercussions de l'entraînement à la mobilité motorisée chez les enfants ayant une PC marquée.

Does power mobility training impact a child's mastery motivation and spectrum of EEG activity? An exploratory project.

PURPOSE: The purposes of this exploratory project were: (1) to evaluate the impact of power mobility training with a child who has multiple, severe impairments and (2) to determine if the child's spectrum of electroencephalography (EEG) activity changed during power mobility training. STUDY DESIGN: A single-subject A-B-A-B research design was conducted with a four-week duration for each phase. Two target behaviours were explored: (1) mastery motivation assessed via the dimensions of mastery questionnaire (DMQ) and (2) EEG data collected under various conditions. Power mobility skills were also assessed. METHODS: The participant was a three-year, two-month-old girl with spastic quadriplegic cerebral palsy, gross motor function classification system level V. Each target behaviour was measured weekly. During intervention phases, power mobility training was provided. RESULTS: Improvements were noted in subscale scores of the DMQ. Short-term and long-term EEG changes were also noted. Improvements were noted in power mobility skills. CONCLUSIONS: The participant in this exploratory project demonstrated improvements in power mobility skill and function. EEG data collection procedures and variability in an individual's EEG activity make it difficult to determine if the participant's spectrum of EEG activity actually changed in response to power mobility training. Additional studies are needed to investigate the impact of power mobility training on the spectrum of EEG activity in children who have multiple, severe impairments. Implications for Rehabilitation Power mobility training appeared to be beneficial for a child with multiple, severe impairments though the child may never become an independent, community-based power wheelchair user. Electroencephalography may be a valuable addition to the study of power mobility use in children with multiple, severe impairments. Power mobility training appeared to impact mastery motivation (the internal drive to solve complex problems and master new skills) in a child who has multiple, severe impairments.

Stretch-induced increase in cardiac contractility is independent of myocyte Ca2+ while block of stretch channels by streptomycin improves contractility after ischemic stunning.

Stretching the cardiac left ventricle (LV) enhances contractility but its effect on myoplasmic [Ca(2+)] is controversial. We measured LV pressure (LVP) and [Ca(2+)] as a function of intra-LV stretch in guinea pig intact hearts before and after 15 min global stunning ± perfusion with streptomycin (STM), a stretch-activated channel blocker. LV wall [Ca(2+)] was measured by indo-1 fluorescence and LVP by a saline-filled latex balloon inflated in 50 µL steps to stretch the LV. We implemented a mathematical model to interpret cross-bridge dynamics and myofilament Ca(2+) responsiveness from the instantaneous relationship between [Ca(2+)] and LVP ± stretching. We found that: (1) stretch enhanced LVP but not [Ca(2+)] before and after stunning in either control (CON) and STM groups, (2) after stunning [Ca(2+)] increased in both groups although higher in STM versus CON (56% vs. 39%), (3) STM-enhanced LVP after stunning compared to CON (98% vs. 76% of prestunning values), and (4) stretch-induced effects on LVP were independent of [Ca(2+)] before or after stunning in both groups. Mathematical modeling suggested: (1) cooperativity in cross-bridge kinetics and myofilament Ca(2+) handling is reduced after stunning in the unstretched heart, (2) stunning results in depressed myofilament Ca(2+) sensitivity in the presence of attached cross-bridges regardless of stretch, and (3) the initial mechanism responsible for increased contractility during stretch may be enhanced formation of cross-bridges. Thus stretch-induced enhancement of contractility is not due to increased [Ca(2+)], whereas enhanced contractility after stunning in STM versus CON hearts results from improved Ca(2+) handling and/or enhanced actinomyosin cross-bridge cycling.

Low-cost EEG-based sleep detection.

A real-time stage 1 sleep detection system using a low-cost single dry-sensor EEG headset is described. This device issues an auditory warning at the onset of stage 1 sleep using the "NeuroSky Mindset," an inexpensive commercial entertainment-based headset. The EEG signal is filtered into low/high alpha and low/high beta frequency bands which are analyzed to indicate the onset of sleep. Preliminary results indicate an 81% effective rate of detecting sleep with all failures being false positives of sleep onset. This device was able to predict and respond to the onset of drowsiness preceding stage 1 sleep allowing for earlier warnings with the result of fewer sleep-related accidents.

Reduced mitochondrial Ca2+ loading and improved functional recovery after ischemia-reperfusion injury in old vs. young guinea pig hearts.

Oxidative damage and impaired cytosolic Ca(2+) concentration ([Ca(2+)](cyto)) handling are associated with mitochondrial [Ca(2+)] ([Ca(2+)](mito)) overload and depressed functional recovery after cardiac ischemia-reperfusion (I/R) injury. We hypothesized that hearts from old guinea pigs would demonstrate impaired [Ca(2+)](mito) handling, poor functional recovery, and a more oxidized state after I/R injury compared with hearts from young guinea pigs. Hearts from young (∼4 wk) and old (>52 wk) guinea pigs were isolated and perfused with Krebs-Ringer solution (2.1 mM Ca(2+) concentration at 37°C). Left ventricular pressure (LVP, mmHg) was measured with a balloon, and NADH, [Ca(2+)](mito) (nM), and [Ca(2+)](cyto) (nM) were measured by fluorescence with a fiber optic probe placed against the left ventricular free wall. After baseline (BL) measurements, hearts were subjected to 30 min global ischemia and 120 min reperfusion (REP). In old vs. young hearts we found: 1) percent infarct size was lower (27 ± 9 vs. 57 ± 2); 2) developed LVP (systolic-diastolic) was higher at 10 min (57 ± 11 vs. 29 ± 2) and 60 min (55 ± 10 vs. 32 ± 2) REP; 3) diastolic LVP was lower at 10 and 60 min REP (6 ± 3 vs. 29 ± 4 and 3 ± 3 vs. 21 ± 4 mmHg); 4) mean [Ca(2+)](cyto) was higher during ischemia (837 ± 39 vs. 541 ± 39), but [Ca(2+)](mito) was lower (545 ± 62 vs. 975 ± 38); 5) [Ca(2+)](mito) was lower at 10 and 60 min REP (129 ± 2 vs. 293 ± 23 and 122 ± 2 vs. 234 ± 15); 6) reduced inotropic responses to dopamine and digoxin; and 7) NADH was elevated during ischemia in both groups and lower than BL during REP. Contrary to our stated hypotheses, old hearts showed reduced [Ca(2+)](mito), decreased infarction, and improved basal mechanical function after I/R injury compared with young hearts; no differences were noted in redox state due to age. In this model, aging-associated protection may be linked to limited [Ca(2+)](mito) loading after I/R injury despite higher [Ca(2+)](cyto) load during ischemia in old vs. young hearts.

Comparison of cumulative planimetry versus manual dissection to assess experimental infarct size in isolated hearts.

INTRODUCTION: Infarct size (IS) is an important variable to estimate cardiac ischemia/reperfusion injury in animal models. Triphenyltetrazolium chloride (TTC) stains viable cells red while leaving infarcted cells unstained. To quantify IS, infarcted and non-infarcted tissue is often manually dissected and weighed (IS-DW). An alternative is to measure infarcted areas by cumulative planimetry (IS-CP). METHODS: We prospectively compared these two methods in 141 Langendorff-prepared guinea pig hearts (1.44+/-0.02 g) that were part of different studies on mechanisms of cardioprotection. Hearts were perfused with Krebs-Ringer's and subjected to 30 min global ischemia after various cardioprotective treatments. Two hours after reperfusion hearts were cut into 6-7 transverse sections (3mm) and stained for 5 min in 1% TTC and 0.1M KH2PO4 buffer (pH 7.4, 38 degrees C). Each slice was first scanned and its infarcted area measured with Image 1.62 software (NIH). Infarctions in individual slices of each heart were averaged (IS-CP) on the basis of their weight. After scanning, IS-DW was determined by careful manual dissection of infarcted from non-infarcted tissue and measuring their respective total weight. RESULTS: We found limited tissue permeation of TTC in relation to the slice thickness leaving tissue in the center unstained, as well as significant cross-contamination of stained vs. unstained tissue after manual dissection. IS-CP and IS-DW ranged from 6.0 to 73.1% and 19.4 to 70.5%, respectively, and correlated as follows: IS-DW=(27.6+/-1.4)+(0.518+/-0.038) * IS-CP; r=0.75 (Pearson), p<0.001. In addition, IS-CP correlated better with return of function after reperfusion like developed left ventricular pressure, contractility and relaxation, and myocardial oxygen consumption. DISCUSSION: Despite a good correlation between both methods, limited tissue permeation by TTC diffusion and limited precision in the ability to manually dissect stained from unstained tissue leads to an overestimation of infarct size by dissection and weighing compared to cumulative planimetry.

Reverse electron flow-induced ROS production is attenuated by activation of mitochondrial Ca2+-sensitive K+ channels.

Mitochondria generate reactive oxygen species (ROS) dependent on substrate conditions, O(2) concentration, redox state, and activity of the mitochondrial complexes. It is well known that the FADH(2)-linked substrate succinate induces reverse electron flow to complex I of the electron transport chain and that this process generates superoxide (O(2)(*-)); these effects are blocked by the complex I blocker rotenone. We demonstrated recently that succinate + rotenone-dependent H(2)O(2) production in isolated mitochondria increased mildly on activation of the putative big mitochondrial Ca(2+)-sensitive K(+) channel (mtBK(Ca)) by low concentrations of 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619). In the present study we examined effects of NS-1619 on mitochondrial O(2) consumption, membrane potential (DeltaPsi(m)), H(2)O(2) release rates, and redox state in isolated guinea pig heart mitochondria respiring on succinate but without rotenone. NS-1619 (30 microM) increased state 2 and state 4 respiration by 26 +/- 4% and 14 +/- 4%, respectively; this increase was abolished by the BK(Ca) channel blocker paxilline (5 microM). Paxilline alone had no effect on respiration. NS-1619 did not alter DeltaPsi(m) or redox state but decreased H(2)O(2) production by 73% vs. control; this effect was incompletely inhibited by paxilline. We conclude that under substrate conditions that allow reverse electron flow, matrix K(+) influx through mtBK(Ca) channels reduces mitochondrial H(2)O(2) production by accelerating forward electron flow. Our prior study showed that NS-1619 induced an increase in H(2)O(2) production with blocked reverse electron flow. The present results suggest that NS-1619-induced matrix K(+) influx increases forward electron flow despite the high reverse electron flow, and emphasize the importance of substrate conditions on interpretation of effects on mitochondrial bioenergetics.

ROS scavenging before 27 degrees C ischemia protects hearts and reduces mitochondrial ROS, Ca2+ overload, and changes in redox state.

We have shown that cold perfusion of hearts generates reactive oxygen and nitrogen species (ROS/RNS). In this study, we determined 1) whether ROS scavenging only during cold perfusion before global ischemia improves mitochondrial and myocardial function, and 2) which ROS leads to compromised cardiac function during ischemia and reperfusion (I/R) injury. Using fluorescence spectrophotometry, we monitored redox balance (NADH and FAD), O(2)(*-) levels and mitochondrial Ca(2+) (m[Ca(2+)]) at the left ventricular wall in 120 guinea pig isolated hearts divided into control (Con), MnTBAP (a superoxide dismutase 2 mimetic), MnTBAP (M) + catalase (C) + glutathione (G) (MCG), C+G (CG), and N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) groups. After an initial period of warm perfusion, hearts were treated with drugs before and after at 27 degrees C. Drugs were washed out before 2 h at 27 degrees C ischemia and 2 h at 37 degrees C reperfusion. We found that on reperfusion the MnTBAP group had the worst functional recovery and largest infarction with the highest m[Ca(2+)], most oxidized redox state and increased ROS levels. The MCG group had the best recovery, the smallest infarction, the lowest ROS level, the lowest m[Ca(2+)], and the most reduced redox state. CG and L-NAME groups gave results intermediate to those of the MnTBAP and MCG groups. Our results indicate that the scavenging of cold-induced O(2)(*-) species to less toxic downstream products additionally protects during and after cold I/R by preserving mitochondrial function. Because MnTBAP treatment showed the worst functional return along with poor preservation of mitochondrial bioenergetics, accumulation of H(2)O(2) and/or hydroxyl radicals during cold perfusion may be involved in compromised function during subsequent cold I/R injury.

Mitochondrial Ca2+-induced K+ influx increases respiration and enhances ROS production while maintaining membrane potential.

We recently demonstrated a role for altered mitochondrial bioenergetics and reactive oxygen species (ROS) production in mitochondrial Ca(2+)-sensitive K(+) (mtK(Ca)) channel opening-induced preconditioning in isolated hearts. However, the underlying mitochondrial mechanism by which mtK(Ca) channel opening causes ROS production to trigger preconditioning is unknown. We hypothesized that submaximal mitochondrial K(+) influx causes ROS production as a result of enhanced electron flow at a fully charged membrane potential (DeltaPsi(m)). To test this hypothesis, we measured effects of NS-1619, a putative mtK(Ca) channel opener, and valinomycin, a K(+) ionophore, on mitochondrial respiration, DeltaPsi(m), and ROS generation in guinea pig heart mitochondria. NS-1619 (30 microM) increased state 2 and 4 respiration by 5.2 +/- 0.9 and 7.3 +/- 0.9 nmol O(2).min(-1).mg protein(-1), respectively, with the NADH-linked substrate pyruvate and by 7.5 +/- 1.4 and 11.6 +/- 2.9 nmol O(2).min(-1).mg protein(-1), respectively, with the FADH(2)-linked substrate succinate (+ rotenone); these effects were abolished by the mtK(Ca) channel blocker paxilline. DeltaPsi(m) was not decreased by 10-30 microM NS-1619 with either substrate, but H(2)O(2) release was increased by 44.8% (65.9 +/- 2.7% by 30 muM NS-1619 vs. 21.1 +/- 3.8% for time controls) with succinate + rotenone. In contrast, NS-1619 did not increase H(2)O(2) release with pyruvate. Similar results were found for lower concentrations of valinomycin. The increase in ROS production in succinate + rotenone-supported mitochondria resulted from a fully maintained DeltaPsi(m), despite increased respiration, a condition that is capable of allowing increased electron leak. We propose that mild matrix K(+) influx during states 2 and 4 increases mitochondrial respiration while maintaining DeltaPsi(m); this allows singlet electron uptake by O(2) and ROS generation.

Anesthetic preconditioning enhances Ca2+ handling and mechanical and metabolic function elicited by Na+-Ca2+ exchange inhibition in isolated hearts.

BACKGROUND: Anesthetic preconditioning (APC) is well known to protect against myocardial ischemia-reperfusion injury. Studies also show the benefit of Na+-Ca2+ exchange inhibition on ischemia-reperfusion injury. The authors tested whether APC plus Na+-Ca2+ exchange inhibitors given just on reperfusion affords additive protection in intact hearts. METHODS: Cytosolic [Ca2+] was measured by fluorescence at the left ventricular wall of guinea pig isolated hearts using indo-1 dye. Sarcoplasmic reticular Ca2+-cycling proteins, i.e., Ca2+ release channel (ryanodine receptor [RyR2]), sarcoplasmic reticular Ca2+-pump adenosine triphosphatase (SERCA2a), and phospholamban were measured by Western blots. Hearts were assigned to seven groups (n = 8 each): (1) time control; (2) ischemia; (3, 4) 10 microM Na+-Ca2+ exchange inhibitor KB-R7943 (KBR) or 1 microM SEA0400 (SEA), given during the first 10 min of reperfusion; (5) APC initiated by sevoflurane (2.2%, 0.41 +/- 0.03 mm) given for 15 min and washed out for 15 min before ischemia-reperfusion; (6, 7) APC plus KBR or SEA. RESULTS: The authors found that APC reduced the increase in systolic [Ca2+], whereas KBR and SEA both reduced the increase in diastolic [Ca2+] on reperfusion. Each intervention improved recovery of left ventricular function. Moreover, APC plus KBR or SEA afforded better functional recovery than APC, KBR, or SEA alone (P < 0.05). Ischemia-reperfusion-induced degradation of major sarcoplasmic reticular Ca2+-cycling proteins was attenuated by APC, but not by KBR or SEA. CONCLUSIONS: APC plus Na+-Ca2+ exchange inhibition exerts additive protection in part by reducing systolic and diastolic Ca2+ overload, respectively, during ischemia-reperfusion. Less degradation of sarcoplasmic reticular Ca2+-cycling proteins may also contribute to cardiac protection.

Ischemia reperfusion dysfunction changes model-estimated kinetics of myofilament interaction due to inotropic drugs in isolated hearts.

BACKGROUND: The phase-space relationship between simultaneously measured myoplasmic [Ca2+] and isovolumetric left ventricular pressure (LVP) in guinea pig intact hearts is altered by ischemic and inotropic interventions. Our objective was to mathematically model this phase-space relationship between [Ca2+] and LVP with a focus on the changes in cross-bridge kinetics and myofilament Ca2+ sensitivity responsible for alterations in Ca2+-contraction coupling due to inotropic drugs in the presence and absence of ischemia reperfusion (IR) injury. METHODS: We used a four state computational model to predict LVP using experimentally measured, averaged myoplasmic [Ca2+] transients from unpaced, isolated guinea pig hearts as the model input. Values of model parameters were estimated by minimizing the error between experimentally measured LVP and model-predicted LVP. RESULTS: We found that IR injury resulted in reduced myofilament Ca2+ sensitivity, and decreased cross-bridge association and dissociation rates. Dopamine (8 microM) reduced myofilament Ca2+ sensitivity before, but enhanced it after ischemia while improving cross-bridge kinetics before and after IR injury. Dobutamine (4 microM) reduced myofilament Ca2+ sensitivity while improving cross-bridge kinetics before and after ischemia. Digoxin (1 microM) increased myofilament Ca2+ sensitivity and cross-bridge kinetics after but not before ischemia. Levosimendan (1 microM) enhanced myofilament Ca2+ affinity and cross-bridge kinetics only after ischemia. CONCLUSION: Estimated model parameters reveal mechanistic changes in Ca2+-contraction coupling due to IR injury, specifically the inefficient utilization of Ca2+ for contractile function with diastolic contracture (increase in resting diastolic LVP). The model parameters also reveal drug-induced improvements in Ca2+-contraction coupling before and after IR injury.

Ischemia-reperfusion injury changes the dynamics of Ca2+-contraction coupling due to inotropic drugs in isolated hearts.

Positive inotropic drugs may attenuate or exacerbate the deleterious effects of ischemia and reperfusion (IR) injury on excitation-contraction coupling in hearts. We 1) quantified the phase-space relationship between simultaneously measured myoplasmic Ca2+ concentration ([Ca2+]) and isovolumetric left ventricular pressure (LVP) using indexes of loop area, orientation, and position; and 2) quantified cooperativity by linearly modeling the phase-space relationship between [Ca2+] and rate of LVP development in intact hearts during administration of positive inotropic drugs before and after global IR injury. Unpaced, isolated guinea pig hearts were perfused at a constant pressure with Krebs-Ringer solution (37 degrees C, 1.25 mM CaCl2). [Ca2+] was measured ratiometrically by indo 1 fluorescence by using a fiber-optic probe placed at the left ventricular free wall. LVP was measured by using a saline-filled latex balloon and transducer. Drugs were infused for 2 min, 30 min before, and for 2 min, 30 min after 30-min global ischemia. IR injury worsened Ca2+-contraction coupling, as seen from decreased orientation and repositioning of the loop rightward and downward and reduced cooperativity of contraction and relaxation with or without drugs. Dobutamine (4 microM) worsened, whereas dopamine (8 microM) improved Ca2+-contraction coupling before and after IR injury. Dobutamine and dopamine improved cooperativity of contraction and relaxation after IR injury, whereas only dopamine increased cooperativity of relaxation before IR injury. Digoxin (1 microM) improved Ca2+-contraction coupling and cooperativity of contraction after but not before ischemia. Levosimendan (1 microM) did not alter Ca2+-contraction coupling or cooperativity, despite producing concomitant increases in contractility, relaxation, and Ca2+ flux before and after ischemia. Dynamic indexes based on LVP-[Ca2+] diagrams (area, shape, position) can be used to identify and measure alterations in Ca2+-contraction coupling during administration of positive inotropic drugs in isolated hearts before and after IR injury.

Increasing heart size and age attenuate anesthetic preconditioning in guinea pig isolated hearts.

Anesthetic preconditioning (APC) reduces myocardial ischemia/reperfusion injury. Recent investigations have reported that older hearts are not susceptible to APC. We investigated if increasing heart size with age determines the susceptibility to APC in young guinea pigs. Langendorff-prepared guinea pig hearts of different weights (1.1-2.2 g) and ages (2-7 wks) were exposed to 1.3 mM sevoflurane for 15 min followed by 30 min washout (APC; n = 20) before 30 min global ischemia and 120 min reperfusion. Control hearts (n = 20) were not subject to APC. Left ventricular pressure was measured isovolumetrically and infarct size was determined by triphenyltetrazolium staining. Functional data were not different between groups at the beginning of the experiments nor did they correlate with heart weight or age. At 120 min reperfusion, left ventricular pressure, coronary flow, and tissue viability showed significant negative correlations with increasing heart weight and age in APC but not in control hearts; i.e., APC improved function and attenuated infarct size better in smaller/younger hearts than in larger/older hearts. Thus, increasing age and heart size attenuate the susceptibility for APC even in younger guinea pigs. This may have important implications for further basic science research and the possible clinical applicability of APC in humans.

Improved mitochondrial bioenergetics by anesthetic preconditioning during and after 2 hours of 27 degrees C ischemia in isolated hearts.

We examined if sevoflurane given before cold ischemia of intact hearts (anesthetic preconditioning, APC) affords additional protection by further improving mitochondrial energy balance and if this is abolished by a mitochondrial KATP blocker. NADH and FAD fluorescence was measured within the left ventricular wall of 5 groups of isolated guinea pig hearts: (1) hypothermia alone; (2) hypothermia+ischemia; (3) APC (4.1% sevoflurane)+cold ischemia; (4) 5-HD+cold ischemia, and (5) APC+5-HD+cold ischemia. Hearts were exposed to sevoflurane for 15 minutes followed by 15 minutes of washout at 37 degrees C before cooling, 2 hours of 27 degrees C ischemia, and 2 hours of 37 degrees C reperfusion. The KATP channel inhibitor 5-HD was perfused before and after sevoflurane. Ischemia caused a rapid increase in NADH and a decrease in FAD that waned over 2 hours. Warm reperfusion led to a decrease in NADH and an increase in FAD. APC attenuated the changes in NADH and FAD and further improved postischemic function and reduced infarct size. 5-HD blocked the cardioprotective effects of APC but not APC-induced alterations of NADH and FAD. Thus, APC improves redox balance and has additive cardioprotective effects with mild hypothermic ischemia. 5-HD blocks APC-induced cardioprotective effects but not improvements in mitochondrial bioenergetics. This suggests that mediation of protection by KATP channel opening during cold ischemia and reperfusion is downstream from the APC-induced improvement in redox state or that these changes in redox state are not attenuated by KATP channel antagonism.

Warm ischemic preconditioning improves mitochondrial redox balance during and after mild hypothermic ischemia in guinea pig isolated hearts.

Ischemic preconditioning (IPC) induces distinctive changes in mitochondrial bioenergetics during warm (37 degrees C) ischemia and improves function and tissue viability on reperfusion. We examined whether IPC before 2 h of hypothermic (27 degrees C) ischemia affords additive cardioprotection and improves mitochondrial redox balance assessed by mitochondrial NADH and flavin adenine dinucleotide (FAD) autofluorescence in intact hearts. A mediating role of ATP-sensitive K(+) (K(ATP)) channel opening was investigated. NADH and FAD fluorescence was measured in the left ventricular wall of guinea pig isolated hearts assigned to five groups of eight animals each: hypothermia alone, hypothermia with ischemia, IPC with cold ischemia, 5-hydroxydecanoic acid (5-HD) alone, and 5-HD with IPC and cold ischemia. IPC consisted of two 5-min periods of warm global ischemia spaced 5 min apart and 15 min of reperfusion before 2 h of ischemia at 27 degrees C and 2 h of warm reperfusion. The K(ATP) channel inhibitor 5-HD was perfused from 5 min before until 5 min after IPC. IPC before 2 h of ischemia at 27 degrees C led to better recovery of function and less tissue damage on reperfusion than did 27 degrees C ischemia alone. These improvements were preceded by attenuated increases in NADH and decreases in FAD during cold ischemia and the reverse changes during warm reperfusion. 5-HD blocked each of these changes induced by IPC. This study indicates that IPC induces additive cardioprotection with mild hypothermic ischemia by improving mitochondrial bioenergetics during and after ischemia. Because effects of IPC on subsequent changes in NADH and FAD were inhibited by 5-HD, this suggests that mitochondrial K(ATP) channel opening plays a substantial role in improving mitochondrial bioenergetics throughout mild hypothermic ischemia and reperfusion.

Anesthetic preconditioning: the role of free radicals in sevoflurane-induced attenuation of mitochondrial electron transport in Guinea pig isolated hearts.

Cardioprotection by anesthetic preconditioning (APC) can be abolished by nitric oxide (NO*) synthase inhibitors or by reactive oxygen species (ROS) scavengers. We previously reported attenuated mitochondrial electron transport (ET) and increased ROS generation during preconditioning sevoflurane exposure as part of the triggering mechanism of APC. We hypothesized that NO* and other ROS mediate anesthetic-induced ET attenuation. Cardiac function and reduced nicotinamide adenine dinucleotide (NADH) fluorescence, an index of mitochondrial ET, were measured online in 68 Langendorff-prepared guinea pig hearts. Hearts underwent 30 min of global ischemia and 120 min of reperfusion. Before ischemia, hearts were temporarily perfused with superoxide dismutase, catalase, and glutathione to scavenge ROS or N(G)-nitro-L-arginine-methyl-ester (L-NAME) to inhibit NO* synthase in the presence or absence of 1.3 mM sevoflurane (APC). APC temporarily increased NADH before ischemia, i.e., it attenuated mitochondrial ET. Both this NADH increase and the cardioprotection by APC on reperfusion were prevented by superoxide dismutase, catalase, and glutathione and by N(G)-nitro-L-arginine-methyl-ester. Thus, ROS and NO*, or reaction products including peroxynitrite, mediate sevoflurane-induced ET attenuation. This may lead to a positive feedback mechanism with augmented ROS generation to trigger APC secondary to altered mitochondrial function.

Negative inotropic drugs alter indexes of cytosolic [Ca(2+)]-left ventricular pressure relationships after ischemia.

Negative inotropic agents may differentially modulate indexes of cytosolic [Ca(2+)]-left ventricular (LV) pressure (LVP) relationships when given before and after ischemia. We measured and calculated [Ca(2+)], LVP, velocity ratios [[(d[Ca(2+)]/dt(max))/(dLVP/dt(max)); VR(max)] and [(d[Ca(2+)]/dt(min))/(dLVP/dt(min)); VR(min)]], and area ratio (AR; area [Ca(2+)]/area LVP per beat) before and after global ischemia in guinea pig isolated hearts. Ca(2+) transients were recorded by indo 1-AM fluorescence via a fiberoptic probe placed at the LV free wall. [Ca(2+)]-LVP loops were acquired by plotting LVP as a function of [Ca(2+)] at multiple time points during the cardiac cycle. Hearts were perfused with bimakalim, 2,3-butanedione monoxime (BDM), nifedipine, or lidocaine before and after 30 min of ischemia. Before ischemia, each drug depressed LVP, but only nifedipine decreased both LVP and [Ca(2+)] with a downward and leftward shift of the [Ca(2+)]-LVP loop. After ischemia, each drug depressed LVP and [Ca(2+)] with a downward and leftward shift of the [Ca(2+)]-LVP loop. Each drug except BDM decreased d[Ca(2+)]/dt(max); nifedipine decreased d[Ca(2+)]/dt(min), whereas lidocaine increased it, and bimakalim and BDM had no effect on d[Ca(2+)]/dt(min). Each drug except bimakalim increased VR(max) and VR(min) before ischemia; after ischemia, only BDM and nifedipine increased VR(max) and VR(min). Before and after ischemia, BDM and nifedipine increased AR, whereas lidocaine and bimakalim had no effect. At 30 min of reperfusion, control hearts exhibited marked Ca(2+) overload and depressed LVP. In each drug-pretreated group Ca(2+) overload was reduced on reperfusion, but only the group pretreated with nifedipine exhibited both higher LVP and lower [Ca(2+)]. These results show that negative inotropic drugs are less capable of reducing [Ca(2+)] after ischemia so that there is a relatively larger Ca(2+) expenditure for contraction/relaxation after ischemia than before ischemia. Moreover, the differential effects of pretreatment with negative inotropic drugs on [Ca(2+)]-LVP relationships after ischemia suggest that these drugs, especially nifedipine, can elicit cardiac preconditioning.

Cardiotonic drugs differentially alter cytosolic [Ca2+] to left ventricular relationships before and after ischemia in isolated guinea pig hearts.

OBJECTIVE: Cardiotonic agents may differentially alter indices of the cytosolic [Ca2+]/left ventricular pressure (LVP) relationship when given before and after ischemia. We measured and calculated systolic-diastolic [Ca2+], systolic-diastolic LVP, velocity ratios (VRs) d[Ca2+]/dtmax to dLVP/dtmax (VRmax), d[Ca2+]/dtmin to dLVP/dtmin (VRmin), and area ratio (AR, area Ca2+]/area LVP per beat) before and after 30 min global ischemia in guinea pig hearts. METHODS: Hearts were perfused with levosimendan, dobutamine, dopamine, or digoxin. Ca2+ transients were recorded by indo-1 fluorescence via a fiber optic probe placed on the LV free wall. [Ca2+]/LVP loops were acquired by plotting LVP time as a function of [Ca2+] at multiple time points during the cardiac cycle. RESULTS: Ischemia reperfusion increased [Ca2+] and decreased contractility and relaxation and produced a flatter and broader [Ca2+]/LVP loop. All drugs shifted the [Ca2+]/LVP loop rightward and upward when given before and after ischemia. Dobutamine increased [Ca2+] and contractility more than other drugs. Digoxin increased [Ca2+] the least but increased contractility similar to dopamine and levosimendan. Before ischemia dopamine and digoxin both decreased VRmax and VRmin, whereas dobutamine increased VRmin, but not VRmax, and levosimendan had no effect on VR. VRmax and VRmin were markedly elevated after ischemia, but again decreased with dopamine and digoxin; dobutamine again increased VRmin, but not VRmax, and levosimendan decreased both VRmax and VRmin. Before ischemia dopamine and digoxin both decreased AR, dobutamine increased AR, and levosimendan had no effect; after ischemia AR was markedly elevated but dopamine and digoxin decreased AR, dobutamine increased AR, and levosimendan decreased AR. CONCLUSION: Although each drug enhanced contractility and relaxation both before and after ischemia by increasing cytosolic [Ca2+] and Ca2+ flux, dopamine and digoxin improved, and dobutamine worsened responsiveness to Ca2+, i.e., velocity ratio and area ratio, whereas levosimendan had no net effect before ischemia but improved responsiveness after ischemia.

How inotropic drugs alter dynamic and static indices of cyclic myoplasmic [Ca2+] to contractility relationships in intact hearts.

The authors examined effects of positive (dopamine and digoxin) and negative (nifedipine and lidocaine) inotropic interventions on the instantaneous cyclic relationship between myoplasmic [Ca2+] and simultaneously developed left ventricular pressure (LVP) in intact guinea pig hearts. Novel indices were developed to quantify this relationship based on (1) transient [Ca2+] and LVP signal morphology, ie, maxima and minima, peak derivatives, beat areas, durations, and ratios of indices of LVP to [Ca2+]; (2) temporal delay; and (3) LVP versus [Ca2+] loop morphology, ie, orientation, size, hysteresis, position, shape, and duration. These analyses were used to assess the cost of phasic [Ca2+] for contraction and relaxation over one beat after inotropic intervention. It was found that dopamine and digoxin increased contractile and relaxation responsiveness to phasic [Ca2+], cumulative Ca2+, and net Ca2+ flux. Unlike dopamine, digoxin did not decrease relaxation response time. Nifedipine and lidocaine decreased contractile and relaxation responsiveness to phasic [Ca2+], cumulative Ca2+, and net Ca2+ flux. Unlike lidocaine, nifedipine decreased net available Ca2+ and Ca2+ influx. Positive inotropic agents increased [Ca2+]-LVP loop area and hysteresis and resulted in a more vertically oriented loop. Nifedipine and lidocaine decreased these loop indices and lidocaine exhibited greater loop hysteresis than did nifedipine. These novel indices provide a quantitative assessment of myoplasmic [Ca2+] handling for cardiac contractile function.