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PubMed2003

Effects of immobilization and dynamic compression on intervertebral disc cell gene expression in vivo.

STUDY DESIGN: An in vivo analysis of the intervertebral disc's cellular response to dynamic compression and immobilization was performed using a rat-tail model. OBJECTIVE: To assess the effects of immobilization and short-term dynamic compression on intervertebral disc cell expression of anabolic and catabolic genes. SUMMARY OF BACKGROUND DATA: Static compressive loads applied in vivo alter the composition of the disc matrix and cell viability in a dose-dependent manner. The effects of in vivo dynamic compression, which is a more physiologic load, and reported risk factor for low back pain have not been investigated. METHODS: An Ilizarov-type device was implanted on the rat tail and used to determine the effects from 72 hours of immobilization (n = 6), 2 hours of dynamic compression (1 MPa/0.2 Hz) (n = 8), and the coupled effect of immobilization followed by compression (n = 8). Real-time reverse transcription-polymerase chain reaction was used to measure changes in anabolic and catabolic gene levels relative to both internal control subjects and a sham-operated group (n = 7). RESULTS: Immobilization and dynamic compression affect anabolic and catabolic genes, with an overall downregulation of types 1 and 2 collagen and upregulation of aggrecanase, collagenase, and stromelysin in the anulus. The effects of immobilization and compression appear to be additive for collagen types 1 and 2 in the anulus, but not in the nucleus, and not for catabolic genes. CONCLUSIONS: Short-duration dynamic compression and immobilization alter gene expression in the rat disc. In studying the response of the disc to loading, it is necessary to look at both anabolic and catabolic pathways, and to consider strain history.

Aggrecans↗

PubMed2004

Extrinsic compression of the left innominate vein in hemodialysis patients.

PURPOSE: Central venous stenosis is a common problem in hemodialysis patients. The most well known cause is intrinsic stenosis, usually a result of subclavian vein catheterization. A lesser-known cause is extrinsic compression of the left innominate vein. This study investigates the prevalence of this phenomenon in a series of patients undergoing diagnostic fistulography. MATERIALS AND METHODS: One hundred six fistulograms of 48 patients were reviewed retrospectively. In reviewing the fistulograms, attention was paid to the central veins, which were graded for extrinsic compression of the left innominate vein. Presence of collaterals was noted, as well as the presence of any intrinsic stenosis of the left innominate or subclavian veins. Medical records were reviewed for a history of catheterization of the left-side venous system for hemodialysis or any other reason. The type of vascular access (native fistula, synthetic graft) and indication for the fistulogram were recorded. RESULTS: Some degree of extrinsic compression was observed in 21 of 48 of patients (44%). Twelve of 48 patients (25%) had mild, six of 48 patients (13%) had moderate and three of 48 patients had (6%) severe compression. Among patients with any degree of extrinsic compression only four of 21 patients (19%) had previous left subclavian or jugular catheterization. Intrinsic stenosis was observed in 11 of 48 patients (23%). All but two of them had undergone previous left subclavian or jugular catheterization and two had concomitant extrinsic compression. Collaterals were seen in 21 of 48 patients (44%). Eleven of 21 patients (52%) with extrinsic compression showed collateral veins. Ten of 11 patients (91%) with intrinsic stenosis had collateral veins. All three patients with severe extrinsic compression were symptomatic and were treated with stent placement after angioplasty failed because of elastic recoil. CONCLUSION: Extrinsic compression is a common finding on diagnostic hemodialysis fistulography and may be hemodynamically significant. Unlike intrinsic stenosis, it is unrelated to previous central catheterization. Angioplasty alone may not be adequate for treatment and stent placement may be required.

Arteriovenous Shunt, Surgical↗

PubMed1999

Nature of the energy transfer process in compressible turbulence.

Using a two-point closure theory, the eddy-damped-quasinormal-Markovian approximation, we have investigated the energy transfer process and triadic interactions of compressible turbulence. In order to analyze the compressible mode directly, the Helmholtz decomposition is used. The following issues were addressed: (1) What is the mechanism of energy exchange between the solenoidal and compressible modes, and (2) is there an energy cascade in the compressible energy transfer process? It is concluded that the compressible energy is transferred locally from the solenoidal part to the compressible part. It is also found that there is an energy cascade of the compressible mode for high turbulent Mach number. Since we assume that the compressibility is weak, the magnitude of the compressible (radiative or cascade) transfer is much smaller than that of the solenoidal cascade. These results are further confirmed by studying the triadic energy transfer function, the most fundamental building block of the energy transfer.

Journal Article↗

PubMed2000

ECG signal compression using analysis by synthesis coding.

In this paper, an elecrocardiogram (ECG) compression algorithm, called analysis by synthesis ECG compressor (ASEC), is introduced. The ASEC algorithm is based on analysis by synthesis coding, and consists of a beat codebook, long and short-term predictors, and an adaptive residual quantizer. The compression algorithm uses a defined distortion measure in order to efficiently encode every heartbeat, with minimum bit rate, while maintaining a predetermined distortion level. The compression algorithm was implemented and tested with both the percentage rms difference (PRD) measure and the recently introduced weighted diagnostic distortion (WDD) measure. The compression algorithm has been evaluated with the MIT-BIH Arrhythmia Database. A mean compression rate of approximately 100 bits/s (compression ratio of about 30:1) has been achieved with a good reconstructed signal quality (WDD below 4% and PRD below 8%). The ASEC was compared with several well-known ECG compression algorithms and was found to be superior at all tested bit rates. A mean opinion score (MOS) test was also applied. The testers were three independent expert cardiologists. As in the quantitative test, the proposed compression algorithm was found to be superior to the other tested compression algorithms.

Algorithms↗

PubMed2001

Medical image compression by discrete cosine transform spectral similarity strategy.

Due to the bandwidth and storage limitations, medical images must be compressed before transmission and storage. However, the compression will reduce the image fidelity, especially when the images are compressed at lower bit rates. The reconstructed images suffer from blocking artifacts and the image quality will be severely degraded under the circumstance of high compression ratios. In this paper, we present a strategy to increase the compression ratio with simple computational burden and excellent decoded quality. We regard the discrete cosine transform as a bandpass filter to decompose a sub-block into equal-sized bands. After a band gathering operation, a high similarity property among bands is found. By the utilization of similarity property, the bit rate of compression can be greatly reduced. Meanwhile, the characteristics of the original image are not sacrificed. Thus, it can avoid the misdiagnosis of diseases for doctors. Simulations are carried to different kind of medical images to demonstrate that the proposed method achieves better performance when compared to other existing transform coding scheme as the JPEG in terms of bit rate and quality. For the case of angiogram image, its peak signal-to-noise-ratio gain is 13.5 dB at the same bit rate of 0.15 bits per pixel when comparing to the JPEG compression. As to the other kind of medical images, their benefits are not so obvious as an angiogram image; however, the gains for them are still from 4-8 dB at high compression ratios. Two doctors from the Department of Radiology, National Cheng Kung University Hospital, Tainan, Taiwan, R.O.C., and Chang Gung Medical Hospital, Kaoshuing, Taiwan, R.O.C., are invited to verify the decoded image quality; the diagnoses of all the test images are correct when the compression ratios are below 20.

Algorithms↗

PubMed1997

Compression in mammography and the perception of discomfort.

Breast compression in mammography is an uncomfortable experience for most women. The discomfort experienced has the potential to deter women from attending regular breast screening by mammography. The aim of the present study was to assess factors related to the degree of discomfort experienced by women attending for first-time mammography at the Central and Eastern Sydney BreastScreen Service. Prior to the mammogram, expectations of discomfort, menstrual status, existing breast pain, and other breast problems were recorded on a questionnaire. At the time of the mammogram, breast size and weight were estimated. During the mammogram one of the craniocaudal views of the breast was taken at a slightly lower level of compression and after the procedure the participants were asked if they perceived any difference in discomfort between the normally compressed view and the less compressed view. Radiologists were asked to comment on any differences in image quality between the same two cranio-caudal films. A total of 200 women, including non-English-speaking women, participated in the present study. A total of 29% of women reported moderate, considerable or severe discomfort, a much higher level than reported in previous studies. The source of expectations (P = 0.001) had a significant relationship to the expectation of discomfort. Prior expectations (P = 0.01) and breast weight (P = 0.001) were the only factors found to have a significant relationship to the experience of discomfort. The analysis of differences in level of compression and discomfort indicates that the relationship between mammography discomfort and level of compression is complex and not simply the result of the amount of compression applied. However, analysis of the relationship of varying compression and image quality suggests that a slight lowering in the level of compression is unlikely to significantly compromise perceived image quality. Directions for further research are suggested.

Adult↗

PubMed2001

The effects of compression ratio, signal-to-noise ratio, and level on speech recognition in normal-hearing listeners.

Previous research has demonstrated reduced speech recognition when speech is presented at higher-than-normal levels (e.g., above conversational speech levels), particularly in the presence of speech-shaped background noise. Persons with hearing loss frequently listen to speech-in-noise at these levels through hearing aids, which incorporate multiple-channel, wide dynamic range compression. This study examined the interactive effects of signal-to-noise ratio (SNR), speech presentation level, and compression ratio on consonant recognition in noise. Nine subjects with normal hearing identified CV and VC nonsense syllables in a speech-shaped noise at two SNRs (0 and +6 dB), three presentation levels (65, 80, and 95 dB SPL) and four compression ratios (1:1, 2:1, 4:1, and 6:1). Stimuli were processed through a simulated three-channel, fast-acting, wide dynamic range compression hearing aid. Consonant recognition performance decreased as compression ratio increased and presentation level increased. Interaction effects were noted between SNR and compression ratio, as well as between presentation level and compression ratio. Performance decrements due to increases in compression ratio were larger at the better (+6 dB) SNR and at the lowest (65 dB SPL) presentation level. At higher levels (95 dB SPL), such as those experienced by persons with hearing loss, increasing compression ratio did not significantly affect speech intelligibility.

Adult↗

PubMed1999

Comparison of different forms of compression using wearable digital hearing aids.

Four different compression algorithms were implemented in wearable digital hearing aids: (1) The slow-acting dual-front-end automatic gain control (AGC) system [B. C. J. Moore, B. R. Glasberg, and M. A. Stone, Br. J. Audiol. 25, 171-182 (1991)], combined with appropriate frequency response equalization, with a compression threshold of 63 dB sound pressure level (SPL) and with a compression ratio of 30 (DUAL-HI); (2) The dual-front-end AGC system combined with appropriate frequency response equalization, with a compression threshold of 55 dB SPL and with a compression ratio of 3 (DUAL-LO). This was intended to give some impression of the levels of sounds in the environment; (3) Fast-acting full dynamic range compression in four channels (FULL-4). The compression was designed to minimize envelope distortion due to overshoots and undershoots; (4) A combination of (2) and (3) above, where each applied less compression than when used alone (DUAL-4). Initial fitting was partly based on the concept of giving a flat specific-loudness pattern for a 65-dB SPL speech-shaped noise input, and this was followed by fine tuning using an adaptive procedure with speech stimuli. Eight subjects with moderate to severe cochlear hearing loss were tested in a counter-balanced design. Subjects had at least 2 weeks experience with each system in everyday life before evaluation using the Abbreviated Profile of Hearing Aid Benefit (APHAB) test and measures of speech intelligibility in quiet (AB word lists at 50 and 80 dB SPL) and noise (adoptive sentence lists in speech-shaped noise, or that same noise amplitude modulated with the envelope of speech from a single talker). The APHAB scores did not indicate clear differences between the four systems. Scores for the AB words in quiet were high for all four systems at both 50 and 80 dB SPL. The speech-to-noise ratios required for 50% intelligibility were low (indicating good performance) and similar for all the systems, but there was a slight trend for better performance in modulated noise with the DUAL-4 system than with the other systems. A subsequent trial where three subjects directly compared each of the four systems in their everyday lives indicated a slight preference for the DUAL-LO system. Overall, the results suggest that it is not necessary to compress fast modulations of the input signal.

Acoustic Stimulation↗

PubMed1996

Compression of digital chest radiographs with a mixture of principal components neural network: evaluation of performance.

The performance of a new, neural network-based image compression method was evaluated on digital radiographs for use in an educational environment. The network uses a mixture of principal components (MPC) representation to effect optimally adaptive transform coding of an image and has significant computational advantages over other techniques. Nine representative digital chest radiographs were compressed 10:1, 20:1, 30:1, and 40:1 with the MPC method. The five versions of each image, including the original, were shown simultaneously, in random order, to each of seven radiologists, who rated each one on a five-point scale for image quality and visibility of pathologic conditions. One radiologist also ranked four versions of each of the nine images in terms of the severity of distortion: The four versions represented 30:1 and 40:1 compression with the MPC method and with the classic Karhunen-Loève transform (KLT). Only for the images compressed 40:1 with the MPC method were there any unacceptable ratings. Nevertheless, the images compressed 40:1 received a top score in 26%-33% of the evaluations. Images compressed with the MPC method were rated better than or as good as images compressed with the KLT technique 17 of 18 times. Four of nine times, images compressed 40:1 with the MPC method were rated as good as or better than images compressed 30:1 with the KLT technique.

Neural Networks, Computer↗

PubMed2000

Assessment of visually lossless irreversible image compression: comparison of three methods by using an image-comparison workstation.

PURPOSE: To determine the degree of irreversible image compression detectable in conservative viewing conditions. MATERIALS AND METHODS: An image-comparison workstation, which alternately displayed two registered and magnified versions of an image, was used to study observer detection of image degradation introduced by irreversible compression. Five observers evaluated 20 16-bit posteroanterior digital chest radiographs compressed with Joint Photographic Experts Group (JPEG) or wavelet-based trellis-coded quantization (WTCQ) algorithms at compression ratios of 8:1-128:1 and x2 magnification by using (a) traditional two-alternative forced choice; (b) original-revealed two-alternative forced choice, in which the noncompressed image is identified to the observer; and (c) a resolution-metric method of matching test images to degraded reference images. RESULTS: The visually lossless threshold was between 8:1 and 16:1 for four observers. JPEG compression resulted in performance as good as that with WTCQ compression at these ratios. The original-revealed forced-choice method was faster and as sensitive as the two-alternative forced-choice method. The resolution-metric results were robust and provided information on performance above visually lossless levels. CONCLUSION: The image-comparison workstation is a versatile tool for comparative assessment of image quality. At x2 magnification, images compressed with either JPEG or WTCQ algorithms were indistinguishable from unaltered original images for most observers at compression ratios between 8:1 and 16:1, indicating that 10:1 compression is acceptable for primary image interpretation.

Algorithms↗

PubMedDate not supplied

Discrimination of metastatic from acute osteoporotic compression spinal fractures with MR imaging.

A study was performed to determine which magnetic resonance (MR) imaging findings are useful in discrimination between metastatic compression fractures and acute osteoporotic compression fractures of the spine. The MR imaging findings in 27 patients with metastatic compression fractures and 55 patients with acute osteoporotic compression fractures were compared by using the chi(2) test. MR imaging findings suggestive of metastatic compression fractures were as follows: a convex posterior border of the vertebral body, abnormal signal intensity of the pedicle or posterior element, an epidural mass, an encasing epidural mass, a focal paraspinal mass, and other spinal metastases. MR imaging findings suggestive of acute osteoporotic compression fractures were as follows: a low-signal-intensity band on T1- and T2-weighted images, spared normal bone marrow signal intensity of the vertebral body, retropulsion of a posterior bone fragment, and multiple compression fractures. The signal intensity on fast spin-echo T2-weighted images obtained without fat suppression played little role in distinguishing between metastatic compression fractures and acute osteoporotic compression fractures.

Acute Disease↗

PubMed1997

Pulsatile compression of the rostral ventrolateral medulla in hypertension.

The rostral ventrolateral medulla (RVLM) has been known to be a major regulating center of sympathetic and cardiovascular activities. An association between essential hypertension and neurovascular compression of the RVLM has been reported in clinical observations, including magnetic resonance imaging (MRI) studies. To reconfirm this relationship, we performed MRI using a high-resolution 512 x 512 matrix in patients with essential and secondary hypertension and in normotensive subjects. The duration of hypertension and the degree of organ damage by hypertension were not significantly different between the two hypertension groups. Neurovascular compression of the RVLM was observed in 74% of the essential hypertension group, and the incidence of compression was significantly higher than in the secondary hypertension group (11%) or in the normotensive group (13%) (P < .01). These results from the clinical studies suggest that neurovascular compression of the RVLM is, at least in part, causally related to essential hypertension. Although blood pressure elevation by pulsatile compression of the RVLM in an experimental baboon model has already been reported, its underlying mechanism is not well known. Accordingly, we performed experiments to investigate whether pulsatile compression of the RVLM would increase arterial pressure and to elucidate the mechanism of the pressor response in rats. Sympathetic nerve activity, arterial pressure, heart rate, and plasma levels of epinephrine and norepinephrine were increased by pulsatile compression of the RVLM. The pressor response was abolished by intravenous treatment with hexamethonium or RVLM injection of kainic acid. In summary, the results from the MRI studies suggest that neurovascular compression of the RVLM is, at least in part, causally related to essential hypertension. This was supported by the results from experimental studies using rats indicating that pulsatile compression of the RVLM increases arterial pressure by enhancing sympathetic outflow.

Animals↗

PubMed2002

Importance of continuous chest compressions during cardiopulmonary resuscitation: improved outcome during a simulated single lay-rescuer scenario.

BACKGROUND: Interruptions to chest compression-generated blood flow during cardiopulmonary resuscitation (CPR) are detrimental. Data show that such interruptions for mouth-to-mouth ventilation require a period of "rebuilding" of coronary perfusion pressure to obtain the level achieved before the interruption. Whether such hemodynamic compromise from pausing to ventilate is enough to affect outcome is unknown. METHODS AND RESULTS: Thirty swine (weight 35 +/- 2 kg) underwent 3 minutes of untreated ventricular fibrillation before 12 minutes of basic life support CPR. Animals were randomized to receive either standard airway (A), breathing (B), and compression (C) CPR with expired-gas ventilation in a 15:2 compression-to-ventilation ratio or continuous chest compression CPR. Those randomized to the standard 15:2 group had no chest compressions for a period of 16 seconds each time the 2 ventilations were delivered. Defibrillation was attempted at 15 minutes of cardiac arrest. All resuscitated animals were supported in an intensive care environment for 1 hour, then in a maintenance facility for 24 hours. The primary end point of neurologically normal 24-hour survival was significantly better in the experimental group receiving continuous chest compression CPR (12 of 15 versus 2 of 15; P<0.0001). CONCLUSIONS: Mouth-to-mouth ventilation performed by single layperson rescuers produces substantial interruptions in chest compression-supported circulation. Continuous chest compression CPR produces greater neurologically normal 24-hour survival than standard ABC CPR when performed in a clinically realistic fashion. Any technique that minimizes lengthy interruptions of chest compressions during the first 10 to 15 minutes of basic life support should be given serious consideration in future efforts to improve outcome results from cardiac arrest.

Animals↗

PubMed1992

Respiratory responses to chest compression in human subjects.

To test the hypothesis that respiratory compensation for chest compression in the conscious state is different from that in the unconscious state, a range of chest compression was applied to eight conscious and eight anesthetized subjects. Chest compression was carried out by inflating a pneumatic cuff inserted under a chest corset and placed over the anterior chest wall for 5 min. Cuff inflation pressures were 25, 50, and 100 mm Hg: light, moderate, and heavy chest compression, respectively. In both conscious and anesthetized subjects, chest compression immediately caused a decrease in tidal volume (VT) and a concomitant increase in respiratory frequency (f). These changes stabilized within 2 min and remained nearly steady for the rest of the sustained chest compression. The decrease in VT was more prominent the greater the loads, and the change in f was in reverse proportion to the change in VT. In conscious subjects the increase in f was due to shortening of both inspiratory time (T1) and expiratory time (TE), whereas in anesthetized subjects the increase in f was due solely to shortening of TE. In conscious subjects, the values of minute ventilation (VI) and end-tidal PCO2 (PETCO2) during light and moderate chest compression were not different from the control values, whereas VI increased and PETCO2 decreased during heavy chest compression. In anesthetized subjects, the values of VI and PETCO2 were not different from the control values at any different magnitudes of chest compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2007

Effects of initial graft tension on the tibiofemoral compressive forces and joint position after anterior cruciate ligament reconstruction.

BACKGROUND: The initial tension applied to an anterior cruciate ligament graft at the time of fixation modulates knee motion and the tibiofemoral compressive loads. PURPOSE: To establish the relationships between initial graft tension, tibiofemoral compressive force, and the neutral tibiofemoral position in the cadaveric knee. STUDY DESIGN: Controlled laboratory study. METHODS: The tibiofemoral compressive forces and joint positions were determined in the anterior cruciate ligament-intact knee at 0 degrees , 20 degrees , and 90 degrees of knee flexion. The anterior cruciate ligament was excised and reconstructed with a patellar tendon graft using graft tensions of 1, 15, 30, 60, and 90 N applied at 0 degrees , 20 degrees , and 90 degrees of knee flexion. The compressive forces and neutral positions were compared between initial tension conditions and the anterior cruciate ligament-intact knee. RESULTS: Increasing initial graft tension increased the tibiofemoral compressive forces. The forces in the medial compartment were 1.8 times those in the lateral compartment. The compressive forces were dependent on the knee angle at which the tension was applied. The greatest compressive forces occurred when the graft was tensioned with the knee in extension. An increase in initial graft tension caused the tibia to rotate externally compared with the anterior cruciate ligament-intact knee (1.5 degrees and 7.7 degrees of external rotation when tensioned to 90 N at 0 degrees and 90 degrees of knee flexion, respectively). Increases in initial graft tension also caused a significant posterior translation of the tibia relative to the femur (0.9 and 5.3 mm of posterior translation when tensioned to 90 N at 0 degrees and 90 degrees of knee flexion, respectively). CONCLUSION: Different initial graft tension protocols produced predictable changes in the tibiofemoral compressive forces and joint positions. CLINICAL RELEVANCE: The tibiofemoral compressive force and neutral joint position were best replicated with a low graft tension (1-15 N) when using a patellar tendon graft.

Anterior Cruciate Ligament↗

PubMed2006

Biomechanical evaluation of primary stiffness of tibiotalar arthrodesis with an intramedullary compression nail and four other fixation devices.

BACKGROUND: Many techniques of tibiotalar arthrodesis have been described. Screw fixation is widely used. At our center, intramedullary compression nailing has been successfully used for over 10 years. The question to be answered by this study was whether tibiotalar arthrodesis with a compressed intramedullary nail was superior, in terms of primary stiffness and fusion-site compression, to selected other techniques. METHODS: Plane fusion surfaces were machined in third-generation synthetic composite tibiae and the bodies of anatomically correct tali; fixation was with a compressed external fixator (cEF), an uncompressed interlocking nail (uIN), a compressed interlocking nail (cIN), and two different three-screw techniques (ST1 and ST2); three specimens per construct were tested. The compressed contact surface of each construct was measured with pressure-sensitive film and expressed as a percent of the available fusion-site area. Construct stiffness was tested in dorsiflexion/plantar flexion (D/P), varus/valgus (V/V), and internal rotation/external rotation (I/E), analyzing 20 cycles per loading mode. RESULTS: Compressed surface area: cIN 80% +/- 10.7; cEF 60% +/- 8.6; ST2 59% +/- 4.4; ST1 55% +/- 6.1; uIN no discernible compression. The greatest primary stiffness in D/P was obtained with the cIN (p < 0.001), followed by ST1. In V/V, ST1 and the cIN had the greatest primary stiffness; the two techniques did not differ significantly. Stabilization with the cEF was significantly better (p < 0.001) than with ST2. In I/E, the cIN produced the greatest primary stiffness (p < 0.001), followed by the two screw techniques, which did not differ significantly between themselves. The uIN had the least primary stiffness in all directions tested. CONCLUSIONS: In this biomechanical study, the cIN and ST1 were superior, in terms of primary stiffness in tibiotalar arthrodesis, to the other techniques tested. In D/P and I/E, the cIN construct was significantly stiffer than the ST1 construct, whose I/E rigidity might, however, be enhanced by a fourth, horizontal screw. CLINICAL RELEVANCE: Intramedullary compression nailing offers stable tibiotalar arthrodesis fixation with a large bony contact area and may enhance the likelihood of successful tibiotalar arthrodesis.

Arthrodesis↗

PubMed2006

Optimal strategy for cardiopulmonary resuscitation with continuous chest compression.

OBJECTIVES: To apply the mathematical techniques of optimal control theory (OCT) to a validated model of the human circulation during cardiopulmonary resuscitation (CPR), so as to discover improved waveforms for chest compression and decompression that maximize the coronary perfusion pressure (CPP). METHODS: The human circulatory system is represented by seven difference equations that describe the pressure changes in systemic vascular compartments that are caused by chest compression. The forcing term is the intrathoracic pressure that is generated by the external chest compression, which is taken as the control variable for the system. The optimum waveform of this forcing pressure as a function of time, determined from OCT, is that which maximizes the calculated CPP between the thoracic aorta and the superior vena cava over a period of 13.3 seconds of continuous chest compression. RESULTS: The optimal waveform included both compression and decompression of the chest to the maximum allowable extent. Compression-decompression waveforms were rectangular in shape. The frequency of optimal compression-decompression that was found by OCT was 90 per minute. The optimal duty cycle (compression duration per cycle time) was 40%. The CPP for the optimum control waveform was 36 mm Hg vs. 25 mm Hg for standard CPR. CONCLUSIONS: Optimal control theory suggests that both compression and decompression of the chest are needed for best hemodynamics during CPR.

Cardiopulmonary Resuscitation↗

PubMed2004

Effects of angiotensin II type 1 receptor antagonist on pressor responses to pulsatile compression of the rostral ventrolateral medulla in rats.

The rostral ventrolateral medulla (RVLM) is known to be a major center regulating sympathetic and cardiovascular activities. A possible association between neurovascular compression of the RVLM and essential hypertension has been indicated. The present study was performed to determine the role of angiotensin II (AngII) in the pressor and sympathetic responses to pulsatile compression of the RVLM. To determine the role of glutamate and AngII in the RVLM, L-glutamate (Glu) 2 nmol or AngII 100 pmol was injected into the RVLM with or without RVLM pretreatment of kynurenate (Glu receptor antagonist) 3nmol, candesartan (AngII type 1 (AT1) receptor antagonist) 2 nmol, or PD123319 (AngII type 2 (AT2) receptor antagonist) 1 nmol in anesthetized Wistar rats. In addition, to determine the role of glutamate and AngII in the pressor and sympathetic effects to the RVLM compression, kynurenate, candesartan, or PD123319 was locally injected before pulsatile compression of the RVLM. Finally, to determine the effects of peripherally administered AngII antagonists in these pressor and sympathetic excitatory responses, candesartan 0.25 micromol or PD123319 0.05 micromol was intravenously injected before pulsatile compression of the RVLM. Glu injected into the RVLM significantly increased mean arterial pressure (MAP) and splanchnic sympathetic nerve activity (SNA), and these effects were reduced by RVLM pretreatment with kynurenate, but were unaffected by candesartan or PD123319. AngII injected into the RVLM and pulsatile compression of the RVLM also increased MAP and SNA. However, in contrast with Glu injections, these effects were reduced by RVLM pretreatment with candesartan or kynurenate, but were unaffected by PD123319. Pressor and sympathetic excitatory responses to RVLM compression were reduced by intravenous pretreatment with candesartan but not with PD123319. These results indicate that, upon pulsatile compression of the RVLM, AngII may activate RVLM neurons via AT1 receptors and stimulate Glu release to thereby elicit sympathetic activation and pressor effects. Candesartan may exert its hypotensive effect at least in part by affecting the RVLM neurons to reduce sympathetic outflow induced by pulsatile compression of the RVLM.

Angiotensin II↗