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PubMedDate not supplied

Computer-aided characterization and optimization of the Thumper compression waveform in closed-chest CPR.

Optimization of blood flow and blood pressure is critical for a positive outcome of cardiopulmonary resuscitation (CPR). The use of models can facilitate the analysis of different methods of performing CPR. Programming with SPICE software, the authors modified a hardware model electrically equivalent to the human cardiovascular system into a software model to analyze and predict the hemodynamic output parameters of different compression waveform inputs used in thoracic pump CPR. Thumper waveforms produced with the computer model predicted the same decaying frequency response as those found in other studies with humans and a recording manikin in which the generated pressures decreased with increased compression rates from 60 to 140 cycles/min. Using a square-wave input having a flat frequency response, the model predicted a constant diastolic pressure and a steady increase in systolic pressure from 94 to 109 mmHg while increasing compression rate from 60 to 140 cycles/min at a constant 50% duty cycle. Blood flows predicted with the use of a square-wave compression input were greater than the flows predicted with the use of a Thumper waveform, and increased with an increase in compression rate. The model also predicted increased mean systolic pressure when the duty cycle increased from 20% to 80% while diastolic pressure decreased slightly. Although mean systolic pressure increased with increased duty cycle, the model predicted a decrease in coronary flow at the higher duty cycles of all compression waveforms. Increases of 75% to 100% in systolic pressure and blood flow were produced when increases in chest compression force and the rapidity of the rise time, termed "spike-impulse" CPR, were simulated.

Blood Pressure↗

PubMed1990

Nerve-roots of the cauda equina. The effect of hypotension and acute graded compression on function.

The influence of hypotension on the function of nerve-roots of the cauda equina under acute graded compression was studied with use of an established porcine model. In twenty adult miniature pigs, the nerve-roots of the cauda equina were compressed at pressures of zero (sham), fifty, 100, or 200 millimeters of mercury, and hypotension was induced with sodium nitroprusside. Compression was maintained for two hours, and a ninety-minute period of recovery followed. The nerve-roots were monitored electrophysiologically throughout the experiment. To assess the effect of compression and hypotension on the function of the nerve-roots, values of afferent and efferent amplitude and nerve-conduction velocity were compared with values in twenty adult miniature pigs that had similar graded compression without hypotension. Hypotension significantly affected efferent and afferent amplitudes at the end of the compression period; the effect remained significant at the end of the recovery period. The most profound effect of hypotension occurred during compression at fifty millimeters of mercury--a pressure that had no effect on the function of the nerves in normotensive animals.

Animals↗

PubMed1989

[The influence of mixing and heating on the compressive strength of investment materials].

In the present study, the compressive strength of four representative dental investment materials was compared. The whole investigation was divided in three experiments. In the first one the effect of different ways of mixing on the compressive strength of the investments was examined. In the second the compressive strength of investments mixed mechanically under vacuum was compared: a) two hours after mixing, b) at the highest heating temperature and c) at room temperature after the heating procedure. In the third experiment, a comparison was made between the compressive strength of investments at the highest heating temperature. The investments were mixed mechanically under vacuum but half of the specimens were placed in a pressure device during setting. From the results obtained the following conclusions were made: a) Mixing mechanically under vacuum increases the compressive strength of the investments, b) the compressive strength of phosphate-bonded investments increases at the highest temperature of the heating procedure and c) the use of a pressure device during the setting of the investments results also in an increased compressive strength.

Calcium Sulfate↗

PubMed1978

Clinical experiments with hearing aids with amplitude compression.

The model for audiological rehabilitation in Denmark is brief-described. Clinical experiments have not demonstrated a general superiority of the compression hearing aids compared to the conventional hearing aids. In situations with negligible background noise the compression hearing aid tends to provide the best comprehension of speech. However, in situations with background noise the conventional hearing aid is generally preferred by hearing impaired persons. The attitude with regard to compression hearing aids differs among Danish hearing clinics. One clinic with a very positive attitude delivers compression hearing aids to 27% of the total clientele. In several clinics it has been observed that patients with a perceptive impairment who are using the hearing aid for the first time may benefit from compression during the early stages of hearing aid adjustment. In many cases, however, these patients prefer less compression as they continue to use their hearing aids in daily life. It is pointed out, that in connection with compression hearing aids it is especially important to provide careful instruction about the possibilities and limitations of the hearing aid.

Acoustics↗

PubMed1986

Effects of intermittent pneumatic calf compression on postoperative thrombin and plasmin activity.

A previous study of neurosurgical patients demonstrated an imbalance between thrombin and plasmin action following surgery. The present study was designed to determine the effect of intermittent pneumatic calf compression on postoperative enzyme activity. Fibrinopeptide A (FPA) and B beta 1-42 levels, reflecting thrombin and plasmin action respectively, were measured daily in patients undergoing elective craniotomy. Two of 9 patients not receiving calf compression developed positive fibrinogen leg scans, while none of 5 patients receiving prophylaxis had positive scans. Calf compression was associated with a markedly altered pattern of changes in the fibrinopeptide values following surgery. Without compression, there was perturbation of the balance between thrombin and plasmin action on the day after surgery as reflected by an increase in the FPA/B beta 1-42 ratio. In contrast, in those receiving prophylaxis there was no change in this ratio on the first postoperative day. Calf compression both blunted the mean postoperative increase in the FPA level (1.8 nM vs 4.7 nM; p less than .05) and augmented the mean B beta 1-42 value (3.0 nM vs 0.2 nM; p less than .05) so that the mean increase in the FPA/B beta 1-42 ratio was only 0.1 with calf compression as compared to 2.2 without it (p less than .05). Systemic modulation of both the coagulation and fibrinolytic pathways thus occurred in association with calf compression.

Adult↗

PubMedDate not supplied

Radiologic diagnosis of gastro-oesophageal reflux by means of graded abdominal compression.

The aim of the study was to ascertain whether abdominal compression by a standardized technique increases the reliability of the radiologic diagnosis of gastro-oesophageal reflux. Eighty-eight patients were examined by means of a manometric reflux test, 24-hour measurements of pH and endoscopy. The radiologic examination was performed with and without graded abdominal compression, the patient at the same time turning from side to side. When abdominal compression was included the result of the radiologic examination was positive in 31 patients. In the absence of abdominal compression reflux was detected in 11 of these patients. In one patient reflux was detected only without compression. All these 31 patients had one more test positive and in 27 at least 2 more tests were positive. Another 21 patients had reflux disease as indicated by at least 2 of the 3 other tests. The compression technique seems to yield no false positive responses, and proved to be significantly more reliable than examinations without compression.

Abdomen↗

PubMed1988

HPNS effects among 18 divers during compression to 360 msw on heliox.

Heliox compression deeper than 16 ATA can lead to EEG changes associated with confusion and somnolence. In man the symptoms termed the high pressure neurologic syndrome (HPNS) can also include increased tremor, memory problems, dizziness, nausea, and vomiting. In a series of 3 dives at NUTEC, a compression profile developed for operational use down to 360 msw was evaluated. In each dive 6 different divers were compressed to 360 msw on heliox. Neuropsychologic and neurophysiologic testing were performed repeatedly. The HPNS testing revealed only mild effects of the compression. Only 3 divers had impairments of more than 2 SD in peripheral motor function compared to their predive average. Memory was impaired periodically in 2 divers. The same was found for perceptual speed and reasoning. Fifty percent of the divers had an increase of more than 2 SD in postural tremor, but that had minimal effect on their motor performance. Six of the 18 divers had an EEG power spectrum with both alpha band inhibition and theta increase. While the performance impairment was most marked around 240 msw, the EEG changes occurred mainly deeper than 300 msw. In only 1 of the 18 divers marked EEG changes, marked tremor increase, and marked cognitive performance impairment were observed at the same time. Although mild HPNS was observed, the divers were little impaired during the compression to 360 msw. The results confirm that using a compression profile with rates decreasing progressively with increasing depth, and with several intermediate stops, provides fit divers at depth. By using standard batteries of HPNS testing we were able to obtain evidence for the acceptability of this compression profile.

Central Nervous System Diseases↗

PubMed1986

Compression systems for hearing aids and cochlear prostheses.

Audio and speech compression systems have suffered several characteristic deficiencies. Single-channel compression systems cannot compress wideband signals without suffering from either spectral distortion or the inability to respond quickly to fast transients. When the input signal contains noise in addition to the desired speech signal, single-channel systems unnecessarily attenuate speech information. Single-channel compressors cannot compress the input signal differentially as a function of frequency. Multichannel compressors are capable of different levels of compression as a function of frequency. However, standard multichannel compressors unnecessarily attenuate important information about the shape of the short-term speech spectrum. This has resulted in poorer speech perception when using standard multichannel systems as compared with single-channel compression systems. A more general form of multichannel compression can emphasize information about the shape of the short-term speech spectrum. Susceptibility to many forms of noise is also reduced with such multichannel systems. Spectral distortion and undesired rapid overshoots and undershoots of signal level, characteristic of many single- and multi-channel systems, can be substantially reduced with such systems.

Cochlear Implants↗

PubMedDate not supplied

A radiological and histological analysis of fracture healing using prebending of compression plates.

The use of an exactly contoured compression plate to the surface of a bone will lead to asymmetrical loading of that fracture line with possible gapping of bone opposite the plate. The stability of fixation can be increased through the use of compression combined with prebending. The present study in 19 sheep demonstrates the biological effects of 3 modes of plating fixation: (1) no compression; (2) compression; and (3) compression after prebending using 2 types of compression plates with different stiffness evaluated radiographically and histologically. Compression together with prebending, especially when using plates of adequate stiffness, can prevent bone resorption at the fragment surfaces even under immediate weight-bearing conditions in the sheep tibia. Prevention of interfragmentary bone resorption lowers the risk of non-union and/or implant failure secondary to motion at the fracture site.

Animals↗

PubMed1983

Regeneration of the retinotectal projection following compression onto a half tectum in goldfish.

This study tested whether regeneration of the optic nerve following half-tectal compression in goldfish leads to the immediate reestablishment of the compressed projection or to an initial half map followed by the gradual compression. Half of the tectum was removed and the optic nerve crushed in large 12-18 cm goldfish which were kept at 20 degrees C and later mapped either in air or in water. At 35 to 41 days, the maps showed the presence of the nasal field projection and only the first 27 degrees of the temporal field. Most of the temporal field was represented after 200 days or more. After 253 to 343 days when the compression was largely complete, the optic nerve was recrushed. The projections mapped 35 to 41 days later were always compressed with up to 99% of the temporal field represented, as were projections regenerated at 28 degrees C and mapped at 23-25 days. Regeneration after compression restores the compressed projection, consistent with the concept of altered tectal markers.

Animals↗

PubMed1978

Limitations of bandwidth compression hearing aids applied to the voiced portion of speech.

Numerous speech processing techniques have been applied to assist hearing-impaired subjects with extreme high-frequency hearing losses who can be helped only to a limited degree with conventional hearing aids. The results of providing this class of deaf subjects with a speech encoding hearing aid, which is able to reproduce intelligible speech for their particular needs, have generally been disappointing. There are at least four problems related to bandwidth compression applied to the voiced portion of speech: (1) the problem of pitch extraction in real time; (2) pitch extraction under realistic listening conditions, i.e. when competing speech and noise sources are present; (3) an insufficient data base for successful compression of voiced speech; and (4) the introduction of undesirable spectral energies in the bandwidth-compressed signal, due to the compression process itself. Experiments seem to indicate that voiced speech segments bandwidth limited to f = 1000 Hz, even at a loss of higher formant frequencies, is in most instances superior in intelligibility compared to bandwidth-compressed voiced speech segments of the same bandwidth, even if pitch can be extracted with no error. With the added complexity of real-time pitch extraction which has to function in actual listening conditions, it is doubtful that a speech encoding hearing aid, based on bandwidth compression on the voiced portion of speech, could be successfully implemented. However, if bandwidth compression is applied to the unvoiced portions of speech only, the above limitations can be overcome (1).

Auditory Perception↗

PubMed1982

Effect of compression rate on use of trimix to ameliorate HPNS in man to 686 m (2250 ft).

Previous man dives, in a series designed to evaluate the physiological effects of helium, nitrogen, and oxygen (trimix), investigated the comparative effects of 5% vs. 10% nitrogen with fast compression (12 h 20 min) to 460 m (1509 ft) and subsequent compression over 2.5 d to 650 m (2132 ft). In 1981 three divers were compressed twice as slowly as for these earlier dives to 650 m over a period of 6 d 8 h using 10% N2 in heliox. An extensive series of studies were made over 4 d 15 h at 650 m before further compression to 686 m (2250 ft) for a stay of 24 h with extensive tests of psychological and neurophysiological performance, pulmonary function, reflex, Doppler, and other studies. High pressure nervous syndrome (HPNS) tremors and EEG theta activity increases were effectively controlled with no nausea, vomiting, or somnolence (microsleep). Some euphoria was present. At 686 m there was a 20% to 30% impairment of concentration and attention; otherwise the physical condition of the divers was fine and they completed all tasks without difficulty. Slow compression prevented the initial large performance decrement of 40% to 50% on Day 1 as found in previous fast-compression dives. Otherwise the performance tests showed much the same decrement of 15% to 20% seen in earlier dives; deeper than 570 m (1870 ft), however, the addition test was worse, with a decrement of 35%. The results are discussed with respect to the previous two dives with faster compression, and the possible nonlinearity of nitrogen antagonism of HPNS is considered.

Adult↗

PubMed1995

Essential hypertension and neurovascular compression at the ventrolateral medulla oblongata: MR evaluation.

PURPOSE: To investigate, using MR imaging, neurovascular compression at the ventrolateral medulla oblongata in patients with essential hypertension. METHODS: Thirty-two patients with essential hypertension (57.6 +/- 7 years of age), 6 patients with secondary hypertension (56.7 +/- 10.3 years of age), and 18 control subjects (50.5 +/- 11 years of age) were evaluated. Transaxial three-dimensional fast low angle shot images were obtained (38/6/1 [repetition time/echo time/excitations]). The center of a 40-mm-thick slab (16 partitions) was placed at the pontomedullary junction. We evaluated the relationships between the upper ventrolateral medulla and the vertebral arteries and branches identified by their flow-related hyperintensities in each group. RESULTS: In the essential hypertension group, 29 (90.6%) of 32 cases showed neurovascular compression. Of those, 22 demonstrated neurovascular compression on the left side, 3 on both sides, and 4 on the right side. In the control group, 4 cases of 18 showed neurovascular compression. In the secondary hypertension group, 1 of 6 cases showed neurovascular compression. The rates of observed neurovascular compression between controls and essential hypertension group were statistically significant. CONCLUSION: We found a close correlation between essential hypertension and neurovascular compression at the ventrolateral medulla oblongata on the left side. MR with a 3-D fast low-angle shot sequence has acceptable spatial resolution and depicts blood vessels simultaneously by flow-related phenomena.

Adult↗

PubMed1994

[The compression of numerical radiological images].

A digital radiological image is made by a number of pixels, each of them characterized by a definite numerical value obtained by quantization which represents the luminance in that specific image unit. Spatial resolution and dynamic range are the main factors in determining the quality of a digital radiological image. The product of the two above factors defines the global dimensions of the image and is expressed in bits. In conventional radiographic images the global dimension of the image is expressed in MBytes, because of its high spatial and contrast resolution. To reduce the visualization and storage requirements as well as the transmission time of large image data sets, compression algorithms have been recently introduced. These algorithms are based on the fact that often in a digital image parts of the binary data are "redundant", that is they are not necessary for correct image representation. Therefore, compression methods are aimed at reducing both statistical and perceptive redundancy. Statistical redundancy is reduced by means of lossless coding which does not allow to compress images with a ratio higher than 4-5:1 and that--by definition--allows to recover the original image quality. On the other hand "lossy" compression algorithms, which eliminate the perceptive redundancy, are based on the reduction of spatial resolution and dynamic range and on transform-based methods. In particular, the latter have usually been more successful in terms of efficient compression, even when applied to conventional radiographic images. The basic transform procedure can be modified at various levels. JPEG is one of these methods, originally developed for photographic images, which can be usefully applied to radiological images as well. Lossy procedures allow to reach higher compression ratios than lossless methods, but the decrease in information content must be prevented from reducing diagnostic accuracy. In order to assess the diagnostic efficiency of the images compressed with lossy methods, semi-objective analyses are usually performed and ROC curves are produced and evaluated. A model ROC analysis is presented.

Algorithms↗

PubMed1993

The role of cold compression dressings in the postoperative treatment of total knee arthroplasty.

A prospective randomized study was performed to evaluate the role of cold compressive dressings in the postoperative treatment of total knee arthroplasty (TKA). Eighty consecutive unilateral and ten bilateral primary total knee replacements were evaluated in terms of blood loss, pain relief, and range of motion. Patients in the cold compression group demonstrated an average of 548 ml in suction drainage, whereas those in the control group averaged 807 ml. This resulted in an average 3.1 mg hemoglobin drop in the cold compression group and 4.7 mg in the control group. When body habitus and weight were taken into account in the cold compression group, an average total blood loss of 1298 cc was calculated, with 744 ml arising from soft tissue extravasation. The corresponding total blood loss calculated average was 1908 ml in the control group, with 1101 ml attributed to soft tissue extravasation. Total injectable morphine per kilogram per initial 48 hours averaged 0.53 mg in the cold compression patients and 0.69 mg in the control patients. In the cold compression knees, range of motion averaged 86 degrees before operation, 53 degrees on postoperative day (POD) 7, and 77 degrees on POD 14. In the control knees, range of motion averaged 88 degrees before operation, 44 degrees on POD 7, and 65 degrees on POD 14. The use of cold compression in the postoperative period of TKA results in a dramatic decrease in blood loss. In addition, mild improvements are seen in early return of motion and injectable narcotic pain needs in the postoperative period.

Aged↗

PubMed1994

The effects of dynamic cardiac compression on ventricular mechanics and energetics. Role of ventricular size and contractility.

The purpose of this study was to determine the role of ventricular size or contractility in the effectiveness of dynamic cardiac compression in terms of the pressure-volume relationship and myocardial oxygen consumption. In 10 isolated cross-circulated dog hearts, the ventricle was directly compressed during systole. For the volume run, measurements for slope of the end-systolic pressure-volume relation, pressure-volume area, external work, coronary blood flow, and myocardial oxygen consumption were achieved before and during a fixed amount of dynamic cardiac compression. Left ventricular volume was then increased while stroke volume was kept constant, and measurements were repeated. For the contractility run, after the control measurements were taken, left ventricular contractility was significantly increased or decreased by infusion of either dobutamine or propranolol into the coronary circulation. Measurements were repeated before and during dynamic cardiac compression at the control level of end-diastolic and stroke volumes. Dynamic cardiac compression significantly increased slope of the end-systolic pressure-volume relation, pressure-volume area, and external work (p < 0.01), whereas coronary blood flow and myocardial oxygen consumption were not affected. The increase in pressure-volume area caused by dynamic cardiac compression was greater with the larger volume. Despite the significant differences in the native left ventricular contractility, the increases in slope of the end-systolic pressure-volume relation, pressure-volume area, and external work did not differ among the three groups. We conclude that dynamic cardiac compression enhances left ventricular systolic function independent of ventricular contractility and without affecting coronary blood flow or myocardial oxygen consumption. Mechanical enhancement is more effective in the dilated heart.

Animals↗

PubMed1993

Data compression of the exercise ECG using a Kohonen neural network.

The goal for any data compression scheme is to maximize compression while minimizing distortion. This is particularly true for measurement sensitive electrocardiographic data. Many different approaches have been taken to achieve this goal. One common technique used in image and speech data compression, vector quantization, was selected for this study. Central to vector quantization is the creation of a codebook of vectors. Creating the best possible codebook will enable the best possible data compression. A neural network was used to create a codebook of vectors that attempt to span the low-frequency data space. Since these vectors are potentially the less critical areas of the electrocardiographic signal, less important information will be subjected to increases in distortion. The Kohonen paradigm used in this study is an unsupervised neural network that adapts the codebook vectors based on distance measurements and controls the scope of the changes based on time. This network has been shown to work well with image and speech data, but to the author's knowledge has not been used on electrocardiographic data. The compression of the signal comes from inserting the address of the codebook vector that best represents the original vector in place of the vector. A test is first performed to determine if the distortion between the original and the replacement vector is within a present limit. If it is, the address is inserted. If the distortion is too large the original vector will be retained. Typically, the QRS segment and possibly the T segment will be preserved. The new compressed file can be further reduced by lossless techniques to increase the compression ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis, Computer-Assisted↗

PubMedDate not supplied

The intramedullary compression rod.

The Kaessmann compression device was employed in 26 patients with fractures of the long bones. In 15 fractures of the tibia, prompt healing occurred, even in fractures in the distal one-fourth of the tibia. Most of these cases were treated without external plaster support, and were permitted early ambulation, with partial weight-bearing. The technique for immobilizing these fractures involves a sliding a Kuntscher nail over a tension rod, and then fixing the clevis of the tension rod to the distal bone fragments by a transverse screw. The Kuntscher nail is fixed to the proximal bone fragment by a metal lip, and after compression is achieved, a locking sleeve fixed by a screw to the tension rod, prevents loss of compression. In 11 cases of pseudarthrosis of the tibia, the medullary canal was enlarged by passing graduated drills down the bony canal, over a guide wire. The compression rod was then inserted across the pseudarthrosis, and seventy to 80 kg/cm2 pressure was applied to the bone ends. No bone grafting procedure was performed. In all 11 cases, prompt union occurred. Postoperative management was similar to that employed in the treatment of fresh fractures. Three success fusions of the ankle also attest to the effectiveness of this immobilization. Although controversy exists regarding the role of compression in the healing of fractures, the axial compression rod does overcome distraction, compresses the bony surfaces, immobilizing them securely to produce union with an economy of callus.

Ankle Joint↗