La rigidez cadavérica, el espasmo cadavérico y tipos de fibras musculares / The cadaveric rigidity, the cadaveric spasm and types of muscle fibers

La rigidez cadavérica (rigor mortis) es un proceso no muy bien comprendido por la mayoría de los médicos. El conocimiento de la intimidad del proceso de la rigidez cadavérica es de vital importancia ya que es una de las variables que junto con las livideces (livor mortis) y la temperatura (algor mortis) del cadáver ayudan a determinar el cronotanatodiagnóstico, tanatocronodiagnóstico o intervalo postmortal del período inmediato de la muerte. Para entender el mecanismo de la rigidez y el espasmo cadavérico es preciso hacer un repaso de la contracción muscular fisiológica en el vivo. Hay que tener presente que el tipo de fibra muscular predominante modificará las características de la contracción muscular fisiológica en el vivo, y también la rigidez y el espasmo cadavérico. (AU)

The cadaveric rigidity (rigor mortis) is a process which is not very well understood by the majority of the doctors. The knowledge of the intimacy of the cadaveric stiffness process is of vital importance since it is one of the variables that, as well as the postmortem lividity (livor mortis) and the body temperature post mortem (algor mortis) help determine the chronotanatodiagnostic, tanatochronodiagnostic or postmortal interval of the immediate period of death. In order to understand the mechanism of stiffness and cadaveric spasm, it is necessary to review the physiological muscle contraction in vivo. We should keep in mind that the predominant type of muscle fiber will modify the characteristics of physiological muscle contraction in vivo, as well as stiffness and cadaveric spasm. (AU)

Necromechanics: Death-induced changes in the mechanical properties of human tissues.

After the death phenomenon, the rigor mortis development, characterized by body stiffening, is one of the most evident changes that occur in the body. In this work, the development of rigor mortis was assessed using a skinfold caliper in human cadavers and in live people to measure the deformation in the biceps brachii muscle in response to the force applied by the device. Additionally, to simulate the measurements with the finite element method, a two-dimensional model of an arm section was used. As a result of the experimental procedure, a decrease in deformation with increasing postmortem time was observed, which corresponds to an increase in rigidity. As expected, the deformations for the live subjects were higher. The finite element method analysis showed a correlation between the c1 parameter of the neo-Hookean model in the 4- to 8-h postmortem interval. This was accomplished by adjusting the c1 material parameter in order to simulate the measured experimental displacement. Despite being a preliminary study, the obtained results show that combining the proposed experimental procedure with a numerical technique can be very useful in the study of the postmortem mechanical modifications of human tissues. Moreover, the use of data from living subjects allows us to estimate the time of death paving the way to establish this process as an alternative to the existing techniques. This solution constitutes a portable, non-invasive method of estimating the postmortem interval with direct quantitative measurements using a skinfold caliper. The tools and methods described can be used to investigate the subject and to gain epidemiologic knowledge on rigor mortis phenomenon.

Experimental characterization of post rigor mortis human muscle subjected to small tensile strains and application of a simple hyper-viscoelastic model.

In models developed for impact biomechanics, muscles are usually represented with one-dimensional elements having active and passive properties. The passive properties of muscles are most often obtained from experiments performed on animal muscles, because limited data on human muscle are available. The aim of this study is thus to characterize the passive response of a human muscle in tension. Tensile tests at different strain rates (0.0045, 0.045, and 0.45 s⁻¹) were performed on 10 extensor carpi ulnaris muscles. A model composed of a nonlinear element defined with an exponential law in parallel with one or two Maxwell elements and considering basic geometrical features was proposed. The experimental results were used to identify the parameters of the model. The results for the first- and second-order model were similar. For the first-order model, the mean parameters of the exponential law are as follows: Young's modulus E (6.8 MPa) and curvature parameter α (31.6). The Maxwell element mean values are as follows: viscosity parameter η (1.2 MPa s) and relaxation time τ (0.25 s). Our results provide new data on a human muscle tested in vitro and a simple model with basic geometrical features that represent its behavior in tension under three different strain rates. This approach could be used to assess the behavior of other human muscles.

Fluorescence lifetime of actin in the familial hypertrophic cardiomyopathy transgenic heart.

Clinical studies have revealed that the D166V mutation in the ventricular myosin regulatory light chain (RLC) can cause a malignant phenotype of familial hypertrophic cardiomyopathy (FHC). It has been proposed that RLC induced FHC in the heart originates at the level of the myosin cross-bridge due to alterations in the rates of cross-bridge cycling. In this report, we examine whether the environment of an active cross-bridge in cardiac myofibrils from transgenic (Tg) mice is altered by the D166V mutation in RLC. The cross-bridge environment was monitored by tracking the fluorescence lifetime (tau) of Alexa488-phalloidin-labeled actin. The fluorescence lifetime is the average rate of decay of a fluorescent species from the excited state, which strongly depends on various environmental factors. We observed that the lifetime was high when cross-bridges were bound to actin and low when they were dissociated from it. The lifetime was measured every 50 ms from the center half of the I-band during 60 s of rigor, relaxation and contraction of muscle. We found no differences between lifetimes of Tg-WT and Tg-D166V muscle during rigor, relaxation and contraction. The duty ratio expressed as a fraction of time that cross-bridges spend attached to the thin filaments during isometric contraction was similar in Tg-WT and Tg-D166V muscles. Since independent measurements showed a large decrease in the cross-bridge turnover rate in Tg-D166V muscle compared to Tg-WT, the fact that the duty cycle remains constant suggests that the D166V mutation of RLC causes a decrease in the rate of cross-bridge attachment to actin.

Atlantic salmon skin and fillet color changes effected by perimortem handling stress, rigor mortis, and ice storage.

The changes in skin and fillet color of anesthetized and exhausted Atlantic salmon were determined immediately after killing, during rigor mortis, and after ice storage for 7 d. Skin color (CIE L*, a*, b*, and related values) was determined by a Minolta Chroma Meter. Roche SalmoFan Lineal and Roche Color Card values were determined by a computer vision method and a sensory panel. Before color assessment, the stress levels of the 2 fish groups were characterized in terms of white muscle parameters (pH, rigor mortis, and core temperature). The results showed that perimortem handling stress initially significantly affected several color parameters of skin and fillets. Significant transient fillet color changes also occurred in the prerigor phase and during the development of rigor mortis. Our results suggested that fillet color was affected by postmortem glycolysis (pH drop, particularly in anesthetized fillets), then by onset and development of rigor mortis. The color change patterns during storage were different for the 2 groups of fish. The computer vision method was considered suitable for automated (online) quality control and grading of salmonid fillets according to color.

[Rigor mortis -- a definite sign of death?]. / Rigor mortis -- ein sicheres Todeszeichen?

In the past years an ongoing controversial debate exists in Germany, regarding quality of the coroner's inquest and declaration of death by physicians. We report the case of a 90-year old female, who was found after an unknown time following a suicide attempt with benzodiazepine. The examination of the patient showed livores (mortis?) on the left forearm and left lower leg. Moreover, rigor (mortis?) of the left arm was apparent which prevented arm flexion and extension. The hypothermic patient with insufficient respiration was intubated and mechanically ventilated. Chest compressions were not performed, because central pulses were (hardly) palpable and a sinus bradycardia 45/min (AV-block 2 degrees and sole premature ventricular complexes) was present. After placement of an intravenous line (17 G, external jugular vein) the hemodynamic situation was stabilized with intermittent boli of epinephrine and with sodium bicarbonate. With improved circulation livores and rigor disappeared. In the present case a minimal central circulation was noted, which could be stabilized, despite the presence of certain signs of death ( livores and rigor mortis). Considering the finding of an abrogated peripheral perfusion (livores), we postulate a centripetal collapse of glycogen and ATP supply in the patients left arm (rigor), which was restored after resuscitation and reperfusion. Thus, it appears that livores and rigor are not sensitive enough to exclude a vita minima, in particular in hypothermic patients with intoxications. Consequently a careful ABC-check should be performed even in the presence of apparently certain signs of death, to avoid underdiagnosing a vita minima. Additional ECG- monitoring is required to reduce the rate of false positive declarations of death. To what extent basic life support by paramedics should commence when rigor and livores are present until physician DNR order, deserves further discussion.

The conformation of myosin head domains in rigor muscle determined by X-ray interference.

In the absence of adenosine triphosphate, the head domains of myosin cross-bridges in muscle bind to actin filaments in a rigor conformation that is expected to mimic that following the working stroke during active contraction. We used x-ray interference between the two head arrays in opposite halves of each myosin filament to determine the rigor head conformation in single fibers from frog skeletal muscle. During isometric contraction (force T(0)), the interference effect splits the M3 x-ray reflection from the axial repeat of the heads into two peaks with relative intensity (higher angle/lower angle peak) 0.76. In demembranated fibers in rigor at low force (<0.05 T(0)), the relative intensity was 4.0, showing that the center of mass of the heads had moved 4.5 nm closer to the midpoint of the myosin filament. When rigor fibers were stretched, increasing the force to 0.55 T(0), the heads' center of mass moved back by 1.1-1.6 nm. These motions can be explained by tilting of the light chain domain of the head so that the mean angle between the Cys(707)-Lys(843) vector and the filament axis increases by approximately 36 degrees between isometric contraction and low-force rigor, and decreases by 7-10 degrees when the rigor fiber is stretched to 0.55 T(0).

Tenderization of hot-boned broiler breast meat by clamping during chilling.

Hot-boned broiler breast fillets were tightly clamped between rigid aluminum plates during chilling to determine whether tenderness is increased if breast fillets are not allowed to shorten during rigor. In two experiments, 6-wk-old broilers were processed in a pilot plant. Approximately 5 min after evisceration, the breast fillets (pectoralis major) were deboned, and each fillet was subjected to one of two treatments while chilling for 2 h in ice slush. Fillets were placed in perforated plastic bags (hot-boned control) or clamped between rigid aluminum plates that compressed the meat to a uniform thickness of 7.2 mm during chilling. In Experiment 2, chilling time in ice slush was 1 h, and a third treatment was added to make an incomplete block design in which one breast half was left intact on the carcass and was deboned immediately after chilling. All breast fillets were sealed in plastic bags after the chilling period, held overnight at 4 C, and then cooked at 85 C for 30 min in a steam kettle. In Experiment 1, clamping for 2 h reduced Warner-Bratzler shear values of hot-boned fillets from 11.4 to 2.7 kg. In Experiment 2, shear values for the treatments were 13.0, 9.2, and 5.1 kg for the hot-boned, cold-boned, and hot-boned clamped treatments, respectively, with significantly lower shear values for the clamped fillets. Clamped fillets were significantly thinner than the control fillets in both experiments. Cooked yield as a percentage of postchill weight was significantly higher for the clamped compared to the hot-boned control pieces, 81.1 versus 77.3%, with cold-boned pieces being intermediate and not different from the other treatments. Shear values were reduced, and cooked yield was increased by clamping hot-boned fillets during chilling.

Development of rigor mortis is not affected by muscle volume.

There is a hypothesis suggesting that rigor mortis progresses more rapidly in small muscles than in large muscles. We measured rigor mortis as tension determined isometrically in rat musculus erector spinae that had been cut into muscle bundles of various volumes. The muscle volume did not influence either the progress or the resolution of rigor mortis, which contradicts the hypothesis. Differences in pre-rigor load on the muscles influenced the onset and resolution of rigor mortis in a few pairs of samples, but did not influence the time taken for rigor mortis to reach its full extent after death. Moreover, the progress of rigor mortis in this muscle was biphasic; this may reflect the early rigor of red muscle fibres and the late rigor of white muscle fibres.

Relationship between early post-mortem muscle pH and shortening-induced toughness in the Pectoralis major muscle of processed broilers air-chilled at 0 degrees C and -12 degrees C.

1. An experiment was conducted to investigate the development of shortening-induced toughness in the Pectoralis major (PM) muscles of commercially processed broilers, air-chilled at 0 degrees C and -12 degrees C, as a function of muscle pH early post-mortem. Electrical stimulation was used immediately after stunning and neck cutting to provide carcases with pH values 15 min post-mortem (pH15 min) ranging between 6.79 and 5.85. 2. The deep PM muscle temperatures of carcases chilled at -12 degrees C were lower (cooler) after primary chilling and at 215 min post-mortem than those chilled at 0 degrees C, although chilling regimen had no major effect on pH values over the 24 h post-mortem period. However, carcases chilled at -12 degrees C had longer sarcomeres, lower cooking losses and lower shear force values than those chilled at 0 degrees C. 3. Correlation analysis of the results for both chilling regimens clearly demonstrated that over the pH15min range 6.79 to 5.85, carcases with the lowest pH15min values had the shortest sarcomeres, the highest cooking losses and the toughest meat. In addition, there was no evidence to support the occurrence of cold shortening within this population. This suggests that an early onset of rigor at higher temperatures in broiler carcases, as well as inducing rigor shortening and toughness, might also induce greater protein denaturation and subsequent loss of water holding capacity as manifested in increased cooking losses. 4. Quadratic regression curves showed that over the pH15min range 6.80 to 6.30, only the fast chilling regimen at -12 degrees C could inhibit rigor shortening and minimise changes in cooking loss and shear force values. However, neither chilling regimen was effective in preventing severe rigor shortening, increased cooking losses and adverse toughness in carcases with pH15min values below 6.30. 5. The benefits of fast chilling carcases with pH15min values above 6.3 can also be quantified in terms of carcases exceeding a 4.00 kg/cm2 toughness threshold. Only 1.9% of these carcases chilled at -12 degrees C exceeded this limit (maximum shear force value of 4.72 kg/cm2) compared to 34.9% of the carcases chilled at 0 degrees C (maximum shear force value of 8.46 kg/cm2), further emphasising the considerable reduction in textural variability and improvement in tenderness gained by fast air-chilling at -12 degrees C.

Estimating time of death of deer in Missouri; a comparison of three indicators.

Estimation of time of death (TOD) of white-tailed deer is important to wildlife law enforcement officers. The purpose of this study was to develop and test a model for estimating TOD of white-tailed deer in Missouri. We compare the utility of carcass temperature, pupil diameter, and rigor mortis as TOD indicators. The effects of body size, ambient temperature, and various carcass handling methods on the estimate were also examined. Data were collected from 1484 deer during the 1995-96 and 1996-97 hunting seasons. Stepwise regression indicated that all three indicators were significant and that body size and ambient temperature could influence the model. Predictive equations were developed for various combinations of the indicators based on practicality and statistical probabilities. TOD was estimated for 28 animals where the exact TOD was known. There was no significant difference between the estimated and known TOD (p = 0.759) and the average of the absolute differences in 1 h and 28 min.

A comparison of texture and quality of breast fillets from broilers stunned by electricity and carbon dioxide on a shackle line or killed with carbon dioxide.

To compare the broiler breast muscle quality resulting from three different slaughter methods, 36 broilers in each of two replicates were randomly divided into three groups receiving CO2 stunning, electrical stunning (ES), or CO2 killing. Carbon dioxide stunning was accomplished in a tunnel with a gradient from 40 to 60% CO2 by allowing the broilers on shackles to pass through the tunnel for 25 s. Electrical stunning was done by passing the bird's head through a charged 1% brine solution (35 mA, 7 s). For CO2 killing, the birds were killed by asphyxiation in an atmosphere of less than 2% oxygen (air displaced by CO2) for 2.5 min. Following slaughter, all breast fillets were harvested at 1.25 h postmortem and analyzed for pH, R value, shear value (SV), expressible moisture, and color (lightness and redness at 1.25 and 24 h postmortem). There were no differences (P<0.05) between treatments in pH, R value, SV, 1.25-h color values, or expressible moisture. There was an increase (P<0.05) in lightness between 1.25 and 24 h postmortem in all treatments, with the CO2 stun exhibiting the greatest increase and resulting in a significantly greater L* value at 24 h postmortem than the CO2 killing treatment. These results suggest that the postmortem metabolism or characteristics of the meat from animals processed with these stunning or killing methods does not differ to a large extent.

The effect of seasonal heat stress on rigor development and the incidence of pale, exudative turkey meat.

Heat stress is one of the prominent ante-mortem stressors that elicits pale, soft, and exudative meat characteristics in stress-susceptible pigs. Industry reports of exudative turkey meat increase in the early summer with the onset of prolonged high temperatures. To study the effect of seasonal heat exposure on turkeys, 122 17-wk-old Nicholas tom turkeys were subjected in January either to growth temperatures of 16/24 C (night/day) (control) or to elevated temperatures of 32/38 C (night/day) (heat-stressed, HS). Turkeys were processed at 21 wk of age in a manner simulating commercial conditions. Pectoralis muscle samples were taken at 15 min (prechill), 2 h (postchill), and 24 h and analyzed for R-value, pH, and color. At 2 h, the remaining intact Pectoralis muscle was harvested, aged on ice for 23 h, and analyzed for drip loss and cook loss. Percentage mortality and carcass weights were not significantly different between treatments. By 15 min post-mortem, the HS birds exhibited a faster pH decline and had higher R-values that persisted through 24 h. The HS birds were also paler in color and exhibited increased drip loss and cook loss when compared to controls; however, expressible moisture was not different between treatments. In addition, the HS birds had a higher frequency of abnormal birds than controls when birds were grouped as normal (L* < 53) or abnormal (L* > 53).

Effect of rapid rigor mortis processes on protein functionality in pectoralis major muscle of domestic turkeys.

The pale, soft, exudative (PSE) phenomenon in turkey pectoralis major (breast) muscle was studied using a combination of biochemical, meat quality, microscopic, and gel electrophoresis techniques. Breast muscle samples were collected from turkeys characterized by slow vs fast postmortem glycolysis assessed by muscle pH at 20 min after death. The PSE group was characterized by lower muscle ATP (P < .05) and higher lactate levels (P < .05) compared with the normal group. Excess water-holding capacity and cooking yield were significantly lower (P < .05) in the PSE group than in normal turkeys. Breast muscle of the PSE group was also lighter (P < .05) than that in the normal group as determined by Minolta L* values. The SDS-PAGE, Western blotting, and immunofluorescence microscopy revealed that phosphorylase, a soluble enzyme, became tightly associated with the myofibrils in muscle from the PSE group. Also, less myosin could be solubilized from PSE vs normal myofibril samples. The results indicate that irreversible myosin insolubility due to low pH and high-temperature conditions is decisive in the development of PSE turkey breast muscle.

Muscle metabolism and meat quality of Pectoralis from turkeys treated with postmortem electrical stimulation.

This experiment was conducted to evaluate the effects of electrical stimulation (ES) on muscle metabolism and breast meat quality in turkeys. Thirty-six turkey hens were either ES at the neck in a saline bath (570 V, 450 mA, AC, 60 Hz, 2 s on 1 s off for 10 pulses) or used as unstimulated controls. One breast fillet from all carcasses was harvested at 2 h postmortem. The opposite fillet was harvested from the ES carcasses at 8 h postmortem and from the unstimulated controls at either 8 or 24 h postmortem. All fillets were sampled at time of deboning for expressible moisture, pH, R-value, gravimetric fragmentation index (GFI), and sarcomere length. The remainder of the fillet and the samples for GFI and sarcomere length were aged on ice until 24 h postmortem. After aging, fillets were analyzed for cook loss and shear value. Color was measured at time of deboning and at 24 h postmortem. Electrical stimulation accelerated rigor mortis development as indicated by significantly lower pH values and higher R-values at 2 h postmortem when compared to control fillets. The pH and R-values of the 2-h ES treatment were not significantly different from the 8-h ES, 8-h controls, or the 24-h controls. Fillets from carcasses that were ES and deboned at 2 h had significantly longer sarcomeres than the 2-h controls; however, there were no significant differences between the 2-h ES and the 8-h ES treatments, 8-h controls, or the 24-h controls. Although ES accelerated muscle metabolism at 2 h postmortem, it had no effect on shear value, expressible moisture, cook loss, GFI, L*, or a* color values. These results suggest that this postmortem ES system would not benefit turkey processors.

Effect of muscle opposition during rigor on development of broiler breast meat tenderness.

Two experiments were conducted to determine the effect of mutual opposition of breast muscles during rigor development on ultimate tenderness of the cooked meat. In each experiment, 32 broilers were conventionally processed. Immediately after evisceration, the supracoracoideus tendon was cut at the humeral insertion on one wing (treatment) and the opposite wing was sham-operated with the tendon exposed but not cut (control). The tendon of insertion for the Pectoralis minor muscle was cut to prevent the opposition of breast muscles during rigor, while avoiding confounding effects caused by making cuts on the muscles, as would occur during typical deboning. Cutting the tendon significantly (P < 0.05) increased Warner-Bratzler shear values after cooking for both the Pectoralis major and P. minor. Deboning at 2 h post-mortem resulted in shear values for the P. major of 7.22 kg for controls and 9.08 kg for treated carcasses; P. minor shear values were 2.98 kg for controls and 4.04 kg for treated carcasses. Deboning at 24 h post-mortem produced P. major shear values of 4.68 kg for controls and 5.68 kg for treated carcasses. On whole carcasses, breast muscle opposition during rigor contributes to the tenderness of the cooked meat.

Observations on rheological, electrical, and optical changes during rigor development in pork and beef.

Electrical and optical changes were measured in bovine sternomandibularis and porcine sternocephalicus strips tested sinusoidally in a rigorometer up to 3 h postmortem. Rigor development was detected by decreased muscle elongation, decreased stress-strain hysteresis area, and increased elastic modulus. Elastic modulus was affected by loading rate (r = .98, P < .005) from loading rates of 3.6 to 13.3 kPa/s. Capacitance decreased and resistance increased at 120 Hz, 1 kHz, and 10 kHz as rigor developed. Sometimes changes were irregular at one frequency but steady at another. The most consistent electrical predictors of rigor development were capacitance at 120 Hz and resistance at 10 kHz. Electrical impedance changed as muscle strips were stretched in the rigorometer, so that dimensional effects could be a source of error if testing causes muscle contraction. The dominant fiber-optic reflectance changes during rigor development were increases toward 400 nm and decreases toward 700 nm, although transient increases were sometimes detected toward 700 nm. Optical changes generally were later than electrical changes. All these complex changes are an obstacle to the early prediction of pH-dependent aspects of meat quality from electrical and optical measurements.

Meat toughening does not occur when rigor shortening is prevented.

The objective of this experiment was to test the hypothesis that meat toughening during the first 24 h postmortem results from sarcomere shortening during rigor mortis development. Eleven market-weight lambs were used to measure changes in shear force of clamped longissimus during rigor development. Within 15 min of exsanguination, while attached at both ends, each longissimus was separated from the vertebrae body and clamped between three sets of metal plates to prevent muscle shortening (six clamped sections per lamb). Five of the clamped sections were placed at -1.1 degrees C for 0, 3, 6, 12, or 24 h. After storage at their respective times at -1.1 degrees C, the samples were placed at -30 degrees C for 90 min and then at -5 degrees C for 8 d. The sixth section (168-h section) was stored at -1.1 degrees C for the first 24 h, at 4 degrees C for 144 h, and then treated the same as other sampling times. Sections were sampled for pH, sarcomere length, shear force, and Western blot analyses before and after storage at -5 degrees C. Shear force values were the same (P > .05) from 0 to 24 h (4.5 kg at 0 h to 4.9 kg at 24 h) then declined (P < .05) to 3.3 kg at 168 h postmortem. As evident by lack of statistical difference in the sarcomere lengths, we were successful in holding the muscle length constant. Western blot analyses of nebulin, vinculin, and troponin-T indicated that minimum degradation occurred through 12 h, was slightly increased by 24 h, and was relatively extensive by 168 h postmortem. Although limited proteolysis occurred during storage at -5 degrees C for 8 d, this by itself had no effect on shear force. Results indicate that shear force values do not increase during rigor development when muscle is prevented from shortening; thus, the toughening that occurs during the first 24 h of slaughter is most likely due to sarcomere shortening.

Estimation of the breaking of rigor mortis by myotonometry.

Myotonometry was used to detect breaking of rigor mortis. The myotonometer is a new instrument which measures the decaying oscillations of a muscle after a brief mechanical impact. The method gives two numerical parameters for rigor mortis, namely the period and decrement of the oscillations, both of which depend on the time period elapsed after death. In the case of breaking the rigor mortis by muscle lengthening, both the oscillation period and decrement decreased, whereas, shortening the muscle caused the opposite changes. Fourteen h after breaking the stiffness characteristics of the right and left m. biceps brachii, or oscillation periods, were assimilated. However, the values for decrement of the muscle, reflecting the dissipation of mechanical energy, maintained their differences.