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PubMed2004

Physiological assessment of contrast-enhancing frequency shaping and multiband compression in hearing aids.

Spectral enhancement is now being used in many hearing aids in an attempt to compensate for broadened cochlear filtering. However, spectral enhancement may be counteracted by multiband-compression algorithms designed to compensate for the reduced dynamic range of the impaired cochlea. An alternative scheme for spectral enhancement, contrast-enhancing frequency shaping (CEFS), has been proposed, which results in an improved neural representation of the first and second formants of voiced speech segments in the impaired ear. In this paper, models of the normal and impaired ear are used to assess the compatibility of CEFS with multiband compression. Model auditory nerve responses were assessed under four conditions: (1) unmodified speech presented to a normal ear; (2) amplified, unshaped speech presented to an impaired ear; (3) CEFS speech presented to an impaired ear; and (4) CEFS+multiband-compression speech presented to an impaired ear. The results show that multiband compression does not reduce the benefits of CEFS, and in some cases multiband compression assists in preventing distortion of the neural representation of formants. These results indicate that the combination of contrast-enhancing frequency shaping and multiband compression should lead to improved perception of voiced speech segments in hearing aid users.

Algorithms↗

PubMed2003

The effect of epidural compression on cerebral cortex: a rat model.

We developed a rat model of epidural plastic bead implantation to study the effect of physical compression on the cerebral cortex. Epidural implantation of a bead of appropriate size compressed the underlying sensorimotor cortex without apparent ischemia, since the capillary density of the cortex was increased. Although the thickness of all layers of the compressed cortex was significantly decreased, no apparent changes in the number of NADPH-diaphorase reactive neurons, reactive astrocytes, or microglial cells were observed, nor were apoptotic neurons observed. In fact, the densities of the neurons in most cortical layers apparently increased. To determine how epidural compression affects neuronal morphology, the dendritic arbors of layer III and V pyramidal neurons were evaluated using a fixed tissue intracellular dye injection technique. Neurons in both layers remained pyramidal in shape and their somatic sizes remained unaltered for at least a month after compression. On the other hand, their total dendritic length was significantly reduced beginning at 3 days post implantation. These analyses showed that apical dendrites were affected sooner than basal ones. The reduction of dendritic length was associated with a drop in the number of dendritic branches rather than dendritic trunks, suggesting the trimming of the peripheral part of the dendritic arbor. Detailed analysis showed that dendritic spines on all dendrites were reduced as early as 3 days following implantation. These results suggest that cortical neurons remodel their structures substantially within 3 days after being subjected to epidural compression.

Animals↗

PubMed1996

Oliguria during laparoscopic surgery: evidence for direct renal parenchymal compression as an etiologic factor.

Abdominal insufflation during laparoscopy has been associated with transient oliguria, which abates after desufflation. Direct renal compression evoking a Page kidney effect was proposed as a mechanism. In an effort to confirm this theory, the left kidney was subjected to 15 mm Hg compression in six anesthetized mongrel dogs. For this, a pressure cuff was placed around the kidney excluding the renal hilar structures. The contralateral kidney was left untouched to serve as a control. After a steady-state period, the pressure cuff was inflated to 15 mm Hg for 2 hours. Cuff desufflation was followed by a 1-hour recovery period. Urine output, glomerular filtration rate (GFR), and effective renal blood flow (ERBF) were measured for both kidneys during each clearance period. For the treated kidneys, the mean urine output decreased 63% (P < 0.05) during compression and increased 109% (P < 0.05) after cuff desufflation. The GFR decreased 21% (P < 0.01) during compression and increased 25% (P < 0.05) during recovery. The ERBF decreased 26% (P < 0.05) during compression, and during the 1-hour recovery period, ERBF did not recover to baseline values. For the control kidneys, there were no significant changes in urine output or GFR during the experimental and recovery periods. These data support the view that direct renal parenchymal compression is an important factor in the development of insufflation-induced oliguria. The clinical implications of insufflation-induced oliguria during laparoscopy deserve further investigation.

Animals↗

PubMed2004

Forearm compression by laparoscopic hand-assist devices.

BACKGROUND AND PURPOSE: Laparoscopic hand-assist devices have facilitated the broad application and acceptance of laparoscopy in urology and other surgical fields. This study evaluated forearm compression by these devices. MATERIALS AND METHODS: Five commercially available hand-assist devices were tested (Gelport, Intromit, PneumoSleeve, Handport, LapDisc). In three surgeons using a porcine model, compressive forces were measured along the paths of the median and ulnar nerves at the point of maximum proximal forearm circumference using FlexiForce A101 sensors. Glove size for all three surgeons was 7 1/2; however, the maximum forearm circumference ranged from 26 to 33 cm. The hand-assist devices were placed in pigs after skin and fascial incision (9 cm), and the insufflation pressure was set at 18 mm Hg. Surgeons subjectively rated the ease of device insertion and hand insertion, degree of forearm compression, and the development of paresthesias. RESULTS: The LapDisc was rated superior with regard to insertion. The Gelport was rated superior for hand insertion and removal; however, moderate to severe forearm compression and paresthesias were reported. The maximum forearm compression forces were highest with the LapDisc (97 mm Hg) and the Gelport (78 mm Hg) and lowest with the Handport (33 mm Hg). CONCLUSION: The choice of hand-assist device is dependent on its ease of use, efficacy at maintaining insufflation, and effect on the surgeon's performance and fatigue. The impact of forearm compression should be considered in the selection of the hand-assist device and in the development of new devices.

Animals↗

PubMed1996

Telephone transmission of 20-channel digital electroencephalogram using lossless data compression.

BACKGROUND: The use of telecommunications for computer-assisted transmission of neurophysiological signals is a relatively new practice. With the development of digital technology, it is now possible to record electroencephalograms (EEGs) in digital form. Previous reports have demonstrated the possibility of real-time telephone transmission of a limited number of EEG channels. OBJECTIVES: To assess the effectiveness of specific data-compression software to improve the transmission of digital 20-channel EEG records over ordinary public telephone lines. METHODS: A prototype system was built to transmit digital EEG signals from one computer to another using two 14.4-kbps modems and proprietary lossless data-compression software. RESULTS: Forty compressed digital EEG records of 20 channels each were sent from different locations at variable distances using "plain old telephone service" (POTS). The mean compression ratio was 2.2 to 2.8:1 using a sampling frequency of 128 Hz and 2.8:1 at a sampling rate of 256 Hz. Transmission time was reduced proportionately. CONCLUSION: Although this study used a store-and-forward approach, the results suggest that it may be possible to transmit a large number of compressed EEG channels in real time using data compression.

Electroencephalography↗

PubMed1995

A compression mechanism for sequence databases to improve the efficiency of conventional tools.

This paper describes a method to compress molecular biology databases that are characterized by an increasing proportion of data derived from genome projects. The performance of our tool has been tested on various data files of the EMBL nucleotide sequence database. The best compression ratios were achieved on EST (Expressed Sequence Tags) data, typically derived from large-scale sequence projects. The compression of sequence database updates was tested in combination with the common Unix compression program 'compress'. Our tool improved the efficiency of 'compress' on average by 16%.

Base Sequence↗

PubMed1986

Optimisation of indices of external pneumatic compression for prophylaxis against deep vein thrombosis: radionuclide gated imaging studies.

The amount and rate of blood expelled with different modes of intermittent external pneumatic compression applied to the lower leg were studied on a regional basis in a series of experiments on healthy human volunteers. Radionuclide imaging of the labelled blood pool, with acquisition of counts synchronised to the pressurisation cycle, provided data on regional blood volumes in the leg in relation to time. To determine the changes in blood volume of the lower leg resulting from external pneumatic compression labelled red blood cell counts were determined during 10 different types of compression cycle. Since venous stasis is considered to be a major cause of venous thrombosis the red blood cell counts were used to calculate regional values of the fraction of blood ejected as well as comparative indices proportional to regional flow rate, regional velocity, and regional wall shear stress. All these indices should be maximised for optimal prophylaxis against deep vein thrombosis. The four compartment cuff in each compression mode applied a mean pressure of 45 mm Hg, but different combinations of values were used for intercompartmental pressure gradation (delta p) and for intercompartmental time sequencing to the onset of compression (delta t). Uniform compression (delta p = 0; delta t = 0) was substantially inferior to cycles with gradation and sequencing. The optimal values of delta p were in the range 5-10 mm Hg and of delta t in the range 0-0.5 seconds.

Adolescent↗

PubMed1996

Identification of sequence motifs causing band compressions on human cDNA sequencing.

In order to characterize DNA sequences leading to band compressions in an automated dideoxy-DNA sequencing system which uses fluorescent dye primers, we compiled DNA sequences at compression sites from accumulated sequence data of human cDNAs (about 205 kb in total length). The results clearly showed that almost all the 3'-end regions at the compression sites (> 98%) carried two types of common sequence motifs. The predominant one (about 68%) contained a sequence of 5'-Y'GN1-2AR'-3' (Y' and R': pyrimidine and purine residues capable of base pairing). The remainder (about 32%) carried a hairpin motif with a relatively stable GC-rich stem (> or = 3 bp) connected by a loop consisting of 3 or 4 nucleotides. The occurrence of compressions at these motif sites was further confirmed by using synthetic DNAs with random sequences (about 58 kb in total length). Since DNA sequences at compression sites analyzed so far shared either of the type of motifs in the sequencing system employed here, it was possible to predict the nucleotide residue to be located at a compression site by carefully checking the sequence preceding the site.

Artifacts↗

PubMed1999

Cardiopulmonary resuscitation: effect of CPAP on gas exchange during chest compressions.

BACKGROUND: Conventional cardiopulmonary resuscitation (CPR) includes 80-100/min precordial compressions with intermittent positive pressure ventilation (IPPV) after every fifth compression. To prevent gastric insufflation, chest compressions are held during IPPV if the patient is not intubated. Elimination of IPPV would simplify CPR and might offer physiologic advantages, but compression-induced ventilation without IPPV has been shown to result in hypercapnia. The authors hypothesized that application of continuous positive airway pressure (CPAP) might increase CO2 elimination during chest compressions. METHODS: After appropriate instrumentation and measurement of baseline data, ventricular fibrillation was induced in 18 pigs. Conventional CPR was performed as a control (CPR(C)) for 5 min. Pauses were then discontinued, and animals were assigned randomly to receive alternate trials of uninterrupted chest compressions at a rate of 80/min without IPPV, either at atmospheric airway pressure (CPR(ATM)) or with CPAP (CPR(CPAP)). CPAP was adjusted to produce a minute ventilation of 75% of the animal's baseline ventilation. Data were summarized as mean +/- SD and compared with Student t test for paired observations. RESULTS: During CPR without IPPV, CPAP decreased PaCO2 (55+/-28 vs. 100+/-16 mmHg) and increased SaO2 (0.86+/-0.19 vs. 0.50+/-0.18%; P < 0.001). CPAP also increased arteriovenous oxygen content difference (10.7+/-3.1 vs. 5.5+/-2.3 ml/dl blood) and CO2 elimination (120+/-20 vs. 12+/-20 ml/min; P < 0.01). Differences between CPR(CPAP) and CPR(ATM) in aortic blood pressure, cardiac output, and stroke volume were not significant. CONCLUSIONS: Mechanical ventilation may not be necessary during CPR as long as CPAP is applied. Discontinuation of IPPV will simplify CPR and may offer physiologic advantage.

Animals↗

PubMed2001

Effects of lithotomy position and external compression on lower leg muscle compartment pressure.

BACKGROUND: Case reports have suggested that externally applied pressure from antithrombosis devices may contribute to the development of compartment syndromes during extended surgery in the lithotomy position. The purpose of this study was to assess the effects of a pneumatic compression device on directly measured intracompartment pressure in the lower leg with the leg positioned in the lithotomy position. METHODS: In 25 conscious, healthy men and women, the authors measured pressure within the tibialis anterior muscle compartment with the leg supine and in the lithotomy position with and without intermittent compression. Three different devices were used to keep the leg in the lithotomy position, supporting the leg either behind the knee, under the calf, or at the ankle. RESULTS: The lithotomy position with support behind the calf or knee increased intracompartment pressure to 16.5+/-3.4 versus 10.7+/-5.8 mmHg supine (mean +/- SD; P < 0.05). The addition of intermittent compression decreased pressure to 13.4+/-5.1 mmHg during lithotomy (P < 0.05) and to 9.1+/-7.0 mmHg in the supine position (P < 0.05). In contrast, the lithotomy position with support near the ankle decreased intracompartment pressure to 8.7+/-5.6 versus 13.3+/-5.1 mmHg supine (P < 0.05). The addition of intermittent compression decreased pressure to 6.5+/-5.4 mmHg during lithotomy (P < 0.05) and to 10.3+/-4.7 mmHg in the supine position (P < 0.05). CONCLUSIONS: These results show that the lithotomy position is associated with changes in intracompartment pressure that are dependent on the method of leg support used. Furthermore, they indicate that intermittent external compression can reduce intracompartment pressure in the lower leg. Therefore, increases in intracompartment pressure during surgery in the lithotomy position with the calf or knee supported may be one of the factors that contribute to the development of compartment syndrome. Further, use of intermittent external compression may significantly reduce this pressure increase.

Adult↗

PubMed2002

Tourniquet compression: a non-invasive method to enhance nerve regeneration in nerve grafts.

One hindlimb of a rat was subjected to tourniquet compression (150, 200 and 300 mmHg; 2 h). After 6 days a 10 mm sciatic or tibial nerve graft from the compressed limb was sutured to bridge a 3-4 mm gap in the sciatic nerve of the non-compressed limb. The distances of regenerating sensory axons were measured 6 days post surgery (tibial grafts, 8 days). Compression at 200 and 300 mmHg led to significantly longer regeneration distances than those seen in controls. Incorporation of BrdU and expression of p75 receptor by non-neuronal cells (Schwann cells) in sciatic nerves 6 days after compression (150 and 300 mmHg; 2 h) was also increased as a sign of Schwann cell activation. Tourniquet compression may be used as a non-invasive method to enhance nerve regeneration in nerve grafts.

Animals↗

PubMed2001

Static wrist position associated with least median nerve compression: sonographic evaluation.

OBJECTIVE: To determine the wrist angle that produces the least compression to the median nerve and to evaluate the usefulness of sonography in determining the optimal position. DESIGN: Seventeen wrists of 17 healthy volunteers received dynamic, high-frequency (8 MHz), high-resolution sonography with the wrist splinted at various positions: 15 degrees of flexion, neutral position, and 15 degrees and 30 degrees of extension. The morphologic changes of the median nerve were evaluated with the wrist positioned at various angles. RESULTS: The neutral position caused significantly lower compression of the median nerve than it did in the other positions. However, in some cases, the lowest pressure was found when the wrist was fixed in 15 degrees of flexion or 15 degrees of extension. Because median nerve compression may decrease the anteroposterior diameter, increase the transverse diameter, and decrease the cross-sectional area, greater anteroposterior diameter, lower flattening ratio (transverse diameter/anteroposterior diameter), and greater cross-sectional area were considered to indicate lower median nerve compression. CONCLUSIONS: Neutral position of the wrist is the best position with the least median nerve compression in most individuals. However, the optimal position may vary from person to person. Sonographic examination can help to determine the splint position that results in the lowest median nerve compression.

Adult↗

PubMed1985

Compression volume during mechanical ventilation: comparison of ventilators and tubing circuits.

Four ventilators (Puritan-Bennett MA-1 and MA-2, Emerson, and Bear I) and four commercially available disposable and nondisposable tubing circuits (Bennett nondisposable, Becton-Dickinson, Inspiron, and Life-line) were tested on a lung analog for differences in inspiratory-circuit compression volume. The compression ratio (Rc), equal to the gas volume compressed per cm H2O peak airway pressure, was calculated for each combination of ventilator and circuit at each of four compliance settings (0.15, 0.10, 0.05, 0.01 L/cm H2O) on the analog. Rc values ranged from 0.3 to 4.5 ml/cm H2O at the highest and lowest compliance settings, respectively, accounting for a reduction in delivered tidal volume of up to 20%. The Emerson ventilator with all tubing systems and the Bennett nondisposable circuit with each ventilator demonstrated slightly smaller compression volumes. Application of an inspiratory pause on the Bear I ventilator did not affect its compression characteristics. The clinical importance of compression volume and data from other ventilation systems are reviewed.

Humans↗

PubMed1991

Improvement in oxygen tensions and pulmonary blood flow with intermittent distal aortic compression during normoxia, hypoxic hypoxia, and hyperoxia in neonatal piglets.

BACKGROUND AND METHODS: We investigated the hypothesis that, in a newborn piglet during normoxia, hypoxia, and hyperoxia, increasing aortic pressure transiently by intermittent short-duration aortic compression would affect left-to-right shunting of blood and thus increase pulmonary artery blood flow, pulmonary arterial PO2, and aortic PO2 proximal to the point of compression. We also investigated whether a balloon atrial septostomy, by providing an open channel for communication between the right- and left-sided circulations, would further improve pulmonary blood flow and aortic PO2. Studies were performed in eight 7- to 10-day-old newborn piglets in three phases (FIO2 of 0.21, 0.12, and 1.0) before and after balloon arterial septostomy in each piglet. Blood gas measurements and hemodynamic variables were recorded before and at the end of a 30-sec period of aortic compression. RESULTS: During aortic compression, all the animals demonstrated a 50 to 70 mm Hg increase in aortic pressure proximal to the compression. Before balloon septostomy, there were 21%, 41%, and 8% increases in aortic PO2 in the room air, hypoxic, and hyperoxic phases of the experiment, respectively. There were also statistically significant increments in pulmonary blood flow and arterial pressures. After balloon septostomy, there were 35%, 25%, and 21% increments in aortic PO2 during the room air, hypoxic, and hyperoxic phases of the experiment, respectively. However, there was no statistically significant further improvement in the effects of aortic compression on PO2 with septostomy compared with those effects before septostomy. CONCLUSIONS: Our results suggest that increasing systemic arterial pressures in order to forcibly affect left-to-right shunting of blood may be potentially beneficial in the management of hypoxia in situations where low pulmonary artery blood flow may be contributing to hypoxia, e.g., in persistent pulmonary hypertension of the newborn.

Animals↗

PubMed1999

Influence of lower limb pneumatic compression on pulmonary artery temperature: effect on cardiac output measurements.

OBJECTIVES: To characterize the decreases in pulmonary artery temperature that coincide with the inflation cycle of pneumatic calf compression stockings and to examine their effects on the thermodilution measurement of cardiac output. DESIGN: Three-part observational study. SETTING: University hospital surgical intensive care unit. PATIENTS: Postoperative patients with indwelling pulmonary artery catheters. INTERVENTION: Thermodilution cardiac output measurements with and without pneumatic calf compression. MEASUREMENTS AND MAIN RESULTS: Phase 1 (n = 18) examined the effects of pneumatic compression on pulmonary artery temperature. There was no effect on pulmonary artery temperature (device off, 37.468+/-0.008 degrees C; device on, 37.458+/-0.014 degrees C), but the difference between the maximum and minimum pulmonary artery temperatures was increased (off, 0.031+/-0.006 degrees C; on, 0.055+/-0.012 degrees C [p < .001]). Phase 2 (n = 12) found that the mean thermodilution cardiac output with 10 mL of cold (0-5 degrees C) injectate was unchanged by pneumatic compression (off, 7.00+/-2.28 L/min; on, 6.89+/-2.22 L/min). However, when the compression devices were operating, the variability between the individual measurements was increased, as reflected by larger coefficients of variation (off, 3.19+/-1.96; on, 8.72+/-6.56 [p < .02]). Similar results were obtained during phase 3 (n = 5), when cardiac output was measured with room temperature Injectate. CONCLUSIONS: Intermittent pneumatic calf compression increased lower limb venous return, causing acute but transient decreases in pulmonary artery blood temperature. This did not affect the accuracy of thermodilution cardiac output measurements that were made using 10 mL of either cold or room temperature injectate.

Bandages↗

PubMed1994

The effects of syllabic compression and frequency shaping on speech intelligibility in hearing impaired people.

The effect of syllabic compression on speech intelligibility is rarely positive and in those cases that positive effects have been found, the same positive results could in general be obtained by frequency shaping of the frequency response curve. We programmed a syllabic compressor on a digital processor; the compressor differed from a conventional syllabic compressor by incorporating a delay in the signal path to suppress overshoots and thus minimize transient distortion. Furthermore, the time constants were short: attack time of 5 msec and release time of 15 msec. The compressor was only active in the high-frequency band. An essentially linear signal was added to deliver the low-frequency speech components. The processing resulted in a frequency response that mirrored the hearing loss near threshold and became much flatter for higher level input signals. Speech intelligibility scores for nonsense consonant-vowel-consonant words embedded in carrier phrases were determined for hearing-impaired persons with sloping audiograms and discrimination losses for speech. Results showed little additional effect of frequency shaping to the existing improved speech score for compressed speech. Optimum results were found for a compression ratio 2 with lower speech scores for linear amplification and for compression ratio 8. We next determined the effect of providing high-frequency emphasis to the speech signal and/or to the compression control signal to compensate for the upward spread of masking. The frequency response at the root-mean-square level was adjusted according to the half-gain rule. The positive effects of moderate compression could be found again; the high-frequency emphasis, however, was positive for the vowels but made consonant recognition poorer.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMed1996

Compression and its effect on the speech signal.

Compression systems are often used in hearing aids to increase the wearing comfort. A patient has to readjust frequently the gain of a linear hearing aid because of the limited dynamic hearing range and the changing acoustical conditions. A great deal of attention has been given to the static parameters but very little to the dynamic parameters. We present a general method to describe the dynamic behavior of a compression system by comparing modulations at the output with modulations at the input. The use of this method resulted in a single parameter describing the temporal characteristics of a compressor, the cut-off modulation frequency. In this paper its value is compared with known properties of running speech. A limitation of this method is the use of only small modulation depths, and the consequence of this limitation is tested. The use of this method is described for an experimental digital compressor developed by the authors, and the effects of some temporal parameters such as attack and release time are studied. This method shows the rather large effects of some of the parameters on the effectiveness of a compressor on speech. This method is also used to analyze two generally accepted compression systems in hearing aids. The theoretical method is next compared to the effects of compression on the distribution of the amplitude envelope of running speech, and it could be shown that single-channel compression systems do not reduce the distribution width of speech filtered in frequency bands. This finding questions the use of compression systems for fitting the speech banana in the dynamic hearing range of impaired listeners.

Correction of Hearing Impairment↗

PubMed2001

The preferred number of channels (one, two, or four) in NAL-NL1 prescribed wide dynamic range compression (WDRC) devices.

OBJECTIVE: The recently introduced NAL-NL1 rationale for fitting WDRC devices prescribes a relatively high compression threshold and prescribes compression ratios lower than those prescribed by loudness normalization rationales. The aim of this study was to investigate whether the compression characteristic prescribed by NAL-NL1 is most effective in a single-channel scheme or in a multi-channel scheme. DESIGN: Twenty-four subjects with flat or steeply sloping hearing loss participated in the study. One, two, and four channels were implemented digitally in the laboratory and evaluated on the basis of a paired-comparison test and a speech recognition test. The test stimuli consisted of speech and noise presented at average input levels, and speech and noise alternating every 3 sec among different input levels. The single-channel and 2-channel NAL-NL1 prescriptions were also evaluated in individually selected everyday situations in the field using a digital 2-memory device. RESULTS: The three compression schemes produced no significant difference in speech recognition scores. Most subjects showed no preference for either scheme in the paired-comparison test. Those who did mainly selected the single-channel scheme. These preferences can be explained on the basis on audibility and quality. In the field all subjects with a steeply sloping loss, but one, preferred the 2-channel scheme. Among the subjects with a flat loss more preferred the single-channel scheme than preferred the 2-channel scheme. Statistical analyses showed that those who preferred the 2-channel scheme were fitted with significantly greater differences in the compression ratio in the high frequencies, and those who preferred the single-channel scheme were fitted with significantly greater differences in the high-frequency gain for a 65 dB input. CONCLUSIONS: Multi-channel compression prescribed according to NAL-NL1 in up to four channels showed no adverse effects on speech recognition relative to a single-channel scheme. The paired-comparison test showed a small, but explainable preference for the single-channel scheme. The field test revealed a preference for the 2-channel scheme by subjects with steeply sloping loss. When using the NAL-NL1 rationale it is recommended to use at

Acoustic Stimulation↗