Out-of-hospital cardiac arrest: the prospect of E-CPR in the Maastricht region.

AIM: The current outcome of out-of-hospital cardiac arrest (OHCA) patients in the Maastricht region was analysed with the prospect of implementing extracorporeal cardiopulmonary resuscitation (E-CPR). METHODS: A retrospective analysis of adult patients who were resuscitated for OHCA during a 24-month period was performed. RESULTS: 195 patients (age 66 [57-75] years, 82 % male) were resuscitated for OHCA by the emergency medical services and survived to admission at the emergency department. Survival to hospital discharge was 46.2 %. Notable differences between non-survivors and survivors were observed and included: age (70 [58-79] years) vs. (63 [55-72] years, p = 0.01), chronic heart failure (18 vs. 7 %, p = 0.02), shockable rhythm (67 vs. 99 %, p < 0.01), and return of spontaneous circulation (ROSC) at departure from the site of the arrest (46 vs. 99 %, p < 0.01) and on arrival to the emergency department (43 vs. 98 %, p < 0.01), respectively. Acute coronary syndrome was diagnosed in 32 % of non-survivors vs. 59 % among survivors, p < 0.01. Therapeutic hypothermia was provided in non-survivors (20 %) vs. survivors (43 %), p < 0.01. Percutaneous coronary intervention (PCI) was performed in 14 % of non-survivors while 52 % of survivors received PCI (p < 0.01). No statistical significance was observed in terms of gender, witnessed arrest, bystander CPR, or automated external defibrillator deployed among the cohort. At hospital discharge, moderately severe neurological disability was present in six survivors. CONCLUSION: These observations are compatible with the notion that a shockable rhythm, ROSC, and post-arrest care improve survival outcome. Potentially, initiating E-CPR in the resuscitation phase in patients with a shockable rhythm and no ROSC might serve as a bridge to definite treatment and improve survival outcome.

Variation of the mineral density in cortical bone may serve to keep strain amplitudes within a physiological range.

Within-bone variation in mineral density could be functional. A heterogeneous mineral-density distribution might serve to maintain habitual amplitudes of bone strain within a non-harmful, i.e., physiological range. Regions of a bone that would be strained the most on the basis of architecture alone might have a higher mineral density to make them more stiff and resistant to strain. We hypothesised that the cortical bone of the rabbit mandible contains such a functional distribution of mineral density. We thereby expected similar mineral-density patterns in the mandibles of different individuals due to the shared masticatory function. Secondly, we hypothesised that the highest mineral densities occur in mandibular regions predicted to be exposed to the largest amplitudes of strain-when taking into account bone architecture only. Mineral-density maps of the cortical bone of rabbit mandibles were obtained using micro-computed tomography (µCT). The µCT scans of two rabbits were converted into finite-element models (FEMs). To predict mandibular deformation during biting, these models were loaded by muscle forces and reaction forces. The forces acted on the condyles and on either the incisal or molar bite point. The FEMs were assigned a homogeneous material stiffness to calculate the strain amplitudes that would occur when only the architecture of the mandibular bone would be of influence. We found the cortical bone-mineral density patterns to be similar in all six mandibles. The mineral density of the corpus was higher than that of the ramus. A second consistent feature of the mandibular mineral-density distribution was that the medial ridge of the temporal-muscle insertion groove contained more mineral than its surrounding regions. The strain amplitudes calculated with the FEMs were variable and did not feature clear corpo-ramal differences. However, specific mandibular bone sites calculated to be exposed to the largest amplitudes of strain, including the medial ridge of the temporal-muscle insertion groove, did correspond with high-mineral-density regions. We conclude that, in the rabbit mandible, the heterogeneous mineral-density distribution might serve to suppress bone-strain amplitudes in regions architecturally susceptible to the largest deformations during loading.

The role of masticatory muscles in the continuous loading of the mandible.

Muscles are considered to play an important role in the ongoing daily loading of bone, especially in the masticatory apparatus. Currently, there are no measurements describing this role over longer periods of time. We made simultaneous and wireless in vivo recordings of habitual strains of the rabbit mandible and masseter muscle and digastric muscle activity up to ∼25 h. The extent to which habitually occurring bone strains were related to muscle-activity bursts in time and in amplitude is described. The data reveal the masseter muscle to load the mandible almost continuously throughout the day, either within cyclic activity bouts or with thousands of isolated muscle bursts. Mandibular strain events rarely took place without simultaneous masseter activity, whereas the digastric muscle only played a small role in loading the mandible. The average intensity of masseter-muscle activity bouts was strongly linked to the average amplitude of the concomitant bone-strain events. However, individual pairs of muscle bursts and strain events showed no relation in amplitude within cyclic loading bouts. Larger bone-strain events, presumably related to larger muscle-activity levels, had more constant principal-strain directions. Finally, muscle-to-bone force transmissions were detected to take place at frequencies up to 15 Hz. We conclude that in the ongoing habitual loading of the rabbit mandible, the masseter muscle plays an almost non-stop role. In addition, our results support the possibility that muscle activity is a source of low-amplitude, high-frequency bone loading.

Variations in habitual bone strains in vivo: long bone versus mandible.

Little is known about the similarities and dissimilarities between daily in vivo strain histories of different bones, other than the generally accepted view that most bones need daily loading to maintain their mass. Similarities in daily strain histories might uncover a common basic mechanical stimulus for homeostatic bone maintenance, whereas dissimilarities might explain why bones respond differently to changes in their environment. We compared the daily strain histories of two different bones from the rabbit: the tibiofibula and the mandible. Bone strain was recorded wirelessly in freely moving animals up to 57 h. Habitual strain amplitudes, rates, and frequencies were compared. The exponential decrease in occurrence of greater strain amplitudes was similar in long and mandibular bone. Also similar was the exponentially decreasing incidence of higher strain rates. Mandibular-bone strains distinguished themselves from long-bone strains, however, through the presence of a plateau in the occurrence of compressive strains with amplitudes between 200 and 450 microstrain (µÎµ) and in the occurrence of compressive-strain rates between 5000 and 10,000 µÎµ/s. The frequency spectrum of the mandibular-bone strain history contained peaks at 4.4 Hz and 8.9 Hz, which were absent in the long-bone strain spectrum. We hypothesise that the exponentially decreasing incidence of larger strain amplitudes and rates might outline the minimum amount of mechanical stimuli needed for bone maintenance. Furthermore, the strong presence of rhythmicity in mandibular strains might provide an important clue in confirming or improving the anabolic character of cyclic-loading regimes employed in clinical settings.

The daily habitual in vivo strain history of a non-weight-bearing bone.

Daily mechanical loading strongly influences the architecture and composition of bone tissue. Throughout the day, the amplitudes, rates, frequencies, and the dispersion over time of these loads vary. Nevertheless, most experimental and descriptive studies on the aforementioned relationship consider only cyclic loading and, in addition, focus on weight-bearing bones. A more complete assessment of the daily loading of bone might lead to a better understanding of the natural everyday stimulus for bone maintenance or adaptive responses. In the present study, we measured the daily habitual strain history of the non-weight-bearing mandible bone in the rabbit. Long-term continuous strain recordings were made using an implantable telemetry device able to read out bone-bonded strain gauges. The lateral surface of the rabbit mandibular corpus was chosen as the bone surface of interest. During the recordings, which lasted up to 33 h, the rabbits (N=7) were able to move unrestrictedly in their cages, performing their habitual behaviours. Analysis of the recordings revealed that the measured bone surface was subjected to 2.9 (+/-1.4)x10(3) strain events per hour of which 1.8 (+/-1.0)x10(3) had amplitudes < or =10 microstrains (muvarepsilon). Larger strain amplitudes occurred less often and principal strains fell within the range of -517 (+/-118) muvarepsilon to 298 (+/-81) muvarepsilon. Strain rates never exceeded 10,000 muvarepsilon/s and only 8.9% (+/-7.2%) of the habitual strain rates were higher than 1000 muvarepsilon/s. Strain frequency spectra displayed clear peaks at 4-5 and 9 Hz. The wirelessly recorded daily strain history of the rabbit mandible featured peak strain amplitudes resembling those of other mammalian mandibles, but much smaller than those found in many long-bone strain measurements.

A fully implantable telemetry system for the long-term measurement of habitual bone strain.

Long-term in-vivo recordings of habitual bone strain in freely moving animals are needed to better understand the everyday mechanical loading environment responsible for bone-tissue maintenance. However, wireless methods to make such recordings are scarce. We report on the successful customisation of a commercially available voltage transmitter hooked-up to a strain-gauge rosette, its subcutaneous implantation in rabbits, and the quality of the implant's strain-gauge recordings. Continuous wireless recordings of a completely operational strain-gauge rosette glued to the mandibular surface of a freely moving rabbit could be made up to 33h. The resolution of the system was 1.5 microstrains/bit. The noise in the signal was 4.5 microstrains. To facilitate the automatic counting of bone-strain events in the retrieved data, and to calculate their peak amplitude, a novel approach is presented. The described technique enables the quantification of the daily bone-strain history defining the architecture and composition of bone tissue, and can help to further elucidate the strain parameters which influence bone tissue.