Spinal anesthesia in the percutaneous fixation of fragility fractures of the pelvis.

Introduction: The number of geriatric patients with a pelvic ring fracture is rising and minimal invasive fixation techniques are increasingly popular. The patient characteristics of these fragile patients are similar to those of patients with a proximal femur fracture. In the field of proximal femur fracture surgery spinal anesthesia is a very commonly used anesthetic technique in this more fragile patient population. Methods: All patients were treated between January 2022 and May 2022 in the Amsterdam UMC location AMC in The Netherlands. The operations were performed by a surgeon who specialized in pelvic and acetabular fracture surgery in a hybrid operating theatre. All patient in this case series received spinal anesthesia using 2-2.5 ml glucosated bupivacaine 5 mg/ml. Results: We describe, for the first time, four cases of percutaneous pelvic ring fracture fixation using spinal anesthesia. There were no perioperative or direct postoperative complications. Patients quickly regained the ability to mobilize, reported little pain complaints, and could be safely discharged to either a rehabilitation center or home. Conclusion: We believe spinal anesthesia could be a safe alternative to general anesthesia for the percutaneous fixation of pelvic ring injuries in a selected group of frail elderly patients. A proper assessment should determine whether or not spinal anesthesia is an option in pelvic fracture fixation, taking patient preference, the advice of the anesthetist, the choice of operative technique, and fracture pattern into consideration.

Two-stage treatment in patients with patients with high-energy femoral fractures does not lead to an increase in deep infectious complications: a propensity score analysis.

PURPOSE: In patients following severe trauma sometimes the physiological condition or soft tissue status may not allow definitive fixation of a femoral fracture. In these patients, an external fixator can be placed to temporarily stabilise the fracture, after which definitive fixation can be performed in a second procedure. The aim of this study was to compare the postoperative wound infection and union rates of patients treated with direct intramedullary nailing (IMN) and patients treated with the 'two-stage treatment'. METHODS: All patients with high-energy femoral fractures treated with IMN between 2000 and 2016 in a single Level 1 trauma centre were eligible. Electronic charts were reviewed for patient and surgical characteristics; furthermore, the development of complications was noted. A propensity score analysis was performed to assess the attributed risk of the external fixator on the development of postoperative wound infections. RESULTS: A total of 149 patients were included in this study; 93 underwent direct IMN and 56 underwent the two-stage treatment. Patients who underwent two-stage treatment were more severely injured, reflected by lower EMV and higher ISS on admission. Patients in the two-stage treatment group had a significant higher risk of postoperative wound infections (OR: 4.698, 95% CI: 1.203-18.339) but not a higher risk on deep postoperative wound infections (OR 2.345, 95% CI: 0.439-12.540). Union rate did not differ between the two groups (94% vs 94% NS). CONCLUSIONS: The two-stage treatment is a safe treatment option in patients with a high-energy femoral fracture in terms of postoperative wound infections. Union rates are also comparable between the two treatment groups.

Implementation of an acute surgical admission ward.

BACKGROUND: The aim of the study was to assess the impact of an acute surgical admission ward on admission and discharge processes. METHODS: This prospective cohort study was conducted in a university tertiary referral centre. All acute surgical patients were clustered in the acute surgical unit (ASU) in February and March 2012, and discharged or transferred to specialized departments within 48 h. The primary outcome was length of hospital stay (LOS). Secondary outcomes were impact on emergency department waiting times, discharge home within 48 h, incorrect ward admissions, readmissions and mortality. Outcomes of the study group were compared with those of a historical reference group admitted during the same interval the year before. RESULTS: Some 249 patients were admitted to the ASU during the study interval. The reference group consisted of 211 patients. The total LOS decreased significantly from a median of 4·0 to 2·0 days (P = 0·004). The percentage of patients who were discharged within 48 h increased from 30·3 to 43·4 per cent (P = 0·004). The rate of incorrect ward admission decreased from 9·5 to 0 per cent. Emergency department waiting time, readmission rate and 30-day mortality did not change. CONCLUSION: Introduction of an acute surgical unit-shortened length of hospital stay without comprising readmission and mortality rates.

Temporal decline in defibrillation thresholds with an active pectoral lead system.

OBJECTIVES: The objective of this study was to characterize temporal changes in defibrillation thresholds (DFTs) after implantation with an active pectoral, dual-coil transvenous lead system. BACKGROUND: Ventricular DFTs rise over time when monophasic waveforms are used with non-thoracotomy lead systems. This effect is attenuated when biphasic waveforms are used with transvenous lead systems; however, significant increases in DFT still occur in a minority of patients. The long-term stability of DFTs with contemporary active pectoral lead systems is unknown. METHODS: This study was a prospective assessment of temporal changes in DFT using a uniform testing algorithm, shock polarity and dual-coil active pectoral lead system. Thresholds were measured at implantation, before discharge and at long-term follow-up (70 +/- 40 weeks) in 50 patients. RESULTS: The DFTs were 9.2 +/- 5.4 J at implantation, 8.3 +/- 5.8 J before discharge and 6.9 +/- 3.6 J at long-term follow-up (p < 0.01 by analysis of variance; p < 0.05 for long-term follow-up vs. at implantation or before discharge). The effect was most marked in a prespecified subgroup with high implant DFTs (> or =15 J). No patient developed an inadequate safety margin (< 9 J) during follow-up. CONCLUSIONS: The DFTs declined significantly after implantation with an active pectoral, dual-coil transvenous lead system, and no clinically significant increases in DFT were observed. Therefore, routine defibrillation testing may not be required during the first two years after implantation with this lead system, in the absence of a change in the cardiac substrate or treatment with antiarrhythmic drugs.

The influence of external and internal noise on the detection of increments and decrements in the level of sinusoids.

This paper examines the influence of external and internal noise on the detection of increments and decrements in the level of sinusoidal pedestals. In experiment 1, the pedestals were presented either 18 dB above the masked threshold in broadband noise (condition 18-Masked) or 18 dB above the absolute threshold (condition 18-Abs). Pedestal frequencies were 250, 1000 or 4000 Hz, and increment/decrement durations ranged from 5 to 200 ms. For condition 18-Masked, thresholds decreased with increasing pedestal frequency, while for condition 18-Abs, thresholds did not change significantly with pedestal frequency. These results are consistent with the idea that, in condition 18-Masked, thresholds were influenced by the inherent fluctuations produced by the background noise at the output of the auditory filter centred at the pedestal frequency. These fluctuations would decrease in rate with decreasing centre frequency, and this might have a greater deleterious effect on performance. In contrast, the characteristics of the internal noise that presumably limited performance in condition 18-Abs do not appear to vary with pedestal frequency. In experiment 2, a 4000 Hz pedestal was used. It was presented either in quiet or in the presence of narrowband noise centred at 4000, or 7000 Hz, or both. The noise bandwidth ranged from 50 to 400 Hz. The increment/decrement duration ranged from 5 to 100 ms. The noise centred at 7000 Hz produced only a small deterioration in performance relative to that measured in quiet. The noise centred at 4000 Hz had a larger effect, and the effect increased with decreasing noise bandwidth. This is consistent with the idea that slow fluctuations at the output of the auditory filter impair increment and decrement detection more than rapid fluctuations. A model is proposed to account for the results, based on a simulated auditory filter, a compressive non-linearity, a sliding temporal integrator, a logarithmic transform and a template mechanism. Analysis using the model suggests that the effect of centre frequency observed in experiment 1, when background noise was present, cannot be explained entirely in terms of the fluctuations produced by the background noise at the output of the auditory filter centred at the pedestal frequency.

Clinical predictors and efficacy of antitachycardia pacing in patients with implantable cardioverter defibrillators: the importance of the patient's sex.

The ICD has become accepted as primary therapy for malignant ventricular arrhythmias. The incorporation of antitachycardia pacing into ICDs has provided a better tolerated alternative to shocks but has the potential disadvantage of delaying definitive therapy. Accordingly, we sought to delineate the characteristics of patients likely to experience unsuccessful termination of pacing and to identify ineffective pacing strategies. Of 519 patients who received ICDs, 11 clinical and tachycardia characteristics in the 162 who received antitachycardia pacing therapy for sustained ventricular arrhythmias were evaluated. Tachycardia episodes were grouped according to outcome of pacing (successful, unsuccessful, acceleration). Of 1,946 episodes, 1,502 (77.2%) were successfully reverted with pacing, 322 (16.5%) were unsuccessful, and 121 (6.2%) were accelerated. Antitachycardia pacing was less successful in women, patients with a history of myocardial infarction, those with more severe left ventricular dysfunction, those who received antiarrhythmic drugs, and those programmed to ramp pacing. Tachycardia acceleration was inversely related to tachycardia cycle length and was more frequent in patients programmed to more aggressive ramp pacing protocols. Women had an almost threefold incidence of tachycardia acceleration compared with men (14% vs 5%, P < 0.001). Antitachycardia pacing is generally successful in terminating ventricular tachycardia and has a low incidence of tachycardia acceleration. Caution should be used with rapid tachycardias and aggressive ramp pacing protocols because of an increased risk of acceleration. Antitachycardia pacing appears less successful and has a higher incidence of complications in women.

Implantable cardiac defibrillators.

The implantable cardioverter defibrillator (ICD) represents an important development in the effort to reduce the incidence of sudden cardiac death (almost 400,000 yearly in the United States). Early generation ICDs, which required epicardial lead systems and abdominal placement of the pulse generator, have been replaced by transvenous leads and pectoral implants. Other important refinements, which include biphasic waveforms, extensive memory capability, antitachycardia pacing, and enhanced sensing algorithms, have greatly improved patient tolerance. Ongoing trials and those in the planning stages will continue to expand the indications for ICDs and will focus on cost-effectiveness.

Transient sinus node dysfunction in acute myocardial infarction associated with the use of a coronary stent.

We describe a patient with acute inferior wall myocardial infarction who developed sinus node dysfunction following thrombosis of the sinus node artery during percutaneous transluminal coronary angioplasty and intracoronary stent implantation. Sinus node function normalized spontaneously over the next week, allowing beta blockers to be initiated. Our experience suggests that sinus node dysfunction in this setting may be transient and should be managed conservatively.

Acute hemodynamic effects of right ventricular pacing site and pacing mode in patients with congestive heart failure secondary to either ischemic or idiopathic dilated cardiomyopathy.

The hemodynamic effects of pacing in patients with congestive heart failure (CHF) remain controversial. Early studies reported that pacing from the right ventricular (RV) apex improved acute hemodynamic parameters in patients with left ventricular systolic dysfunction, but these findings were not confirmed in subsequent controlled studies. More recently, it has been proposed that pacing from the RV side of the ventricular septum improves hemodynamic function compared with intrinsic conduction or apical pacing. Either dual-chamber or ventricular pacing have been evaluated, again with inconsistent findings. To assess the effects of pacing site and mode on acute hemodynamic function, we evaluated 21 subjects with CHF and intrinsic conduction disease. Hemodynamics were compared in AAI, VVI, and DDD modes with pacing from the RV apex or high septum. The pacing rate was constant in each patient and the order of testing was randomized. In the absence of ventricular pacing (AAI mode), the mean systemic arterial pressure was 85 +/- 11 mm Hg, the right atrial pressure was 11 +/- 4 mm Hg, the pulmonary capillary wedge pressure was 18 +/- 8 mm Hg and the cardiac index was 2.4 +/- 0.7 L/min/m(2). Compared with AAI pacing, there were no improvements in any hemodynamic parameter with DDD pacing from either RV site. Hemodynamic function worsened with VVI pacing from both RV sites. Subgroup analyses of patients with dilated cardiomyopathy, with prolonged PR interval, or with significant mitral regurgitation also failed to demonstrate an improvement with pacing. We conclude that pacing mode but not RV pacing site affects acute hemodynamic function. Pacing in the DDD mode prevents the deleterious effects of VVI pacing in this patient population.

Comparison of the NAL(R) and Cambridge formulae for the fitting of linear hearing aids.

This paper describes a laboratory-based comparison of the effectiveness of two formulae for fitting linear hearing aids, the NAL(R) formula and the Cambridge formula. The formulae prescribe the desired insertion gain as a function of frequency, based on the audiometric threshold. The two formulae have a similar rationale; both are based on the goal that, for speech with a moderate level, all frequency bands should be equally loud (equal loudness per critical band) over the frequency range important for speech (400-5000 Hz), and the overall loudness should be comfortable. However, the formulae differ; generally the Cambridge formula leads to slightly more high-frequency gain (above 2 kHz) and slightly less mid-frequency gain (between 500 Hz and 2000 Hz) than the NAL(R) formula. The two formulae were implemented using an experimental digital hearing aid whose frequency-gain characteristic could be controlled very precisely. A loudness model (Moore and Glasberg, 1997) was used to adjust the overall gains for each subject and each formula so that a speech-shaped noise with an overall level of 65 dB SPL would give the same loudness as for a normally hearing person (according to the model). The adjustments were, on average, smaller for the Cambridge than for the NAL(R) formula. A condition was also used with all insertion gains set to zero, simulating unaided listening. Evaluation was based on: (1) subjective ratings of the loudness, intelligibility and quality of continuous discourse presented in quiet at levels of 45, 55, 65 and 75 dB SPL and in babble at an 0-dB speech-to-babble ratio, using speech levels of 55, 65 and 75 dB SPL; (2) measures of the speech reception threshold (SRT) in background noise for two noise levels (65 and 75 dB SPL) and four types of background noise. Neither the subjective ratings nor the measures of the SRTs revealed any consistent difference between the results obtained using the two formulae, although both formulae led to lower (better) SRTs than for simulated unaided listening. It is concluded that the differences between the NAL(R) formula and the Cambridge formula are too small to have measurable effects, at least in a laboratory setting.

Sensing lead failure in implantable defibrillators: a comparison of two commonly used leads.

INTRODUCTION: Despite major technological advances, structural problems in implantable cardioverter defibrillator (ICD) endocardial sensing leads remain a significant problem. There are two types of ICD sensing leads: (1) dedicated bipolar leads and (2) integrated lead systems that include defibrillation coils. The long-term performance of these two lead systems has not been directly compared. METHODS AND RESULTS: We prospectively examined the incidence of lead failure manifested by inappropriate arrhythmia detection in 247 consecutive patients undergoing abdominal ICD implant at a single center between 1991 and 1995. A total of 107 patients received BT-10 (dedicated bipolar) leads and 140 patients received Endotak (integrated bipolar) leads. Over a mean follow-up of 860 +/- 442 days, there were 19 (17.8%) lead failures with the BT-10 lead (261 to 1,505 days postimplant) compared with only 6 (4.3%; P < 0.01) with the Endotak lead (410 to 1,211 days postimplant). Lead failure was due to an insulation defect in all cases, with the problem occurring in the proximal lead (within the pulse generator pocket) in all but one case. Lead survival was significantly better with the Endotak lead (P = 0.015, risk ratio = 3.0, 95% confidence intervals 1.2 to 7.6). CONCLUSION: Late lead failure due to insulation defects in BT-10 sensing leads (causing inappropriate ICD activation) is a relatively common and progressive phenomenon, with difficulties becoming apparent as long as 4 years after implant. This problem is a likely cause of inappropriate shocks in patients with BT-10 leads. Implantation of a new sensing lead should be considered at the time of elective pulse generator replacement, even in the absence of demonstrable oversensing.

Short term escape rhythm characteristics after radiofrequency ablation of the atrioventricular junction.

Radiofrequency ablation of the atrioventricular (AV) node has become an established method of treating drug-resistant supraventricular arrhythmias, especially atrial fibrillation. Although it is routine to implant a permanent pacemaker following ablation, one of the potential adverse effects of the procedure is that many patients become pacemaker-dependent and are at risk of an adverse outcome in the event of pacemaker malfunction. Obtaining information about the characteristics of the escape rhythm would be helpful in risk-stratifying these patients and might facilitate modifications of the procedure that would reduce the incidence of this problem. We prospectively studied the clinical parameters and escape rhythm characteristics in 24 patients undergoing radiofrequency ablation of the AV node. Initially, 2 patients had no detectable escape beats and 4 had escape rates <30 beats/min. At 12 hours, 3 of these 4 had adequate (>30 beats/min) escape rates (there were no 12-hour data in 2). The escape rhythm was stable in 17 of the other 18 while 1 had no escape beats at 12 hours. Patients developing right bundle branch block had a greater chance of having an inadequate escape rhythm at 12 hours but this difference was not seen at 24 hours. We conclude that an adequate escape rhythm is usually present immediately after radiofrequency ablation of the AV node and tends to remain stable up to 24 hours. The absence of an escape rhythm immediately after ablation is of limited prognostic value since reliable escape rhythms may emerge subsequently.

Pacing for patients with congestive heart failure and dilated cardiomyopathy.

Considerable evidence has now accumulated that permanent pacing may provide symptomatic benefit for at least some patients with CHF. Recently, the most promising results with left ventricular or biventricular pacing have been obtained. The data for improvement in survival with pacing is less compelling. The mortality of CHF associated with systolic dysfunction of the left ventricle remains high and arrhythmic deaths are frequent. Clinical trials such as the Sudden Cardiac Death Heart Failure Trial (SCD-HeFT) are currently underway to investigate the role of the implantable defibrillator in patients with heart failure. The development and general availability of ICDs with biventricular pacing capability may play an increasingly important role in the overall therapeutic plan for this group of patients to allow for optimization of functional status with pacing and protection from sudden cardiac death with defibrillation.

Interaction of septadian and circadian rhythms in life-threatening ventricular arrhythmias in patients with implantable cardioverter-defibrillators.

Previous studies have shown that life-threatening ventricular arrhythmias display both circadian and septadian (day of the week) periodicity. We hypothesized that assessing the relation between these circadian and septadian rhythms may provide important pathophysiologic information about the mechanism of sudden cardiac death. Using the database from a population of 683 consecutive patients with a third-generation implantable cardioverter-defibrillator (ICD), we examined the time pattern of ICD activations for rapid (prospectively defined as cycle length <280 ms) tachycardias for each day of the week. A total of 5,270 arrhythmic episodes were analyzed. Despite the fact that event distribution was significantly nonuniform (p <0.001) for both circadian and septadian analyses, the circadian pattern was strikingly similar for each day of the week with a relatively broad peak between 9 A.M. and 6 P.M. and a long nadir between 9 P.M. and 6 A.M. We conclude that the trigger factors responsible for the daily circadian distribution of life-threatening ventricular arrhythmias in a population with ICDs are similar throughout the week and may thus be unrelated to the standard work week. These data suggest that the physiologic modulators of circadian and septadian rhythms may be different.

Comparison of bipolar and integrated sensing for redetection of ventricular fibrillation.

BACKGROUND: Implantable cardioverter-defibrillator function is critically dependent on reliable sensing of intracardiac signals. Lead systems that use integrated sensing, in which the distal shocking coil is part of both the sensing and shocking pathways, may be prone to undersensing of ventricular fibrillation, especially during redetection after a failed first shock. To assess the effect of endocardial lead system on redetection, we compared a dedicated rate-sensing lead and 2 generations of integrated sensing defibrillator leads with a uniform testing algorithm and pulse generator. METHODS: The study group consisted of 72 patients after implantable cardioverter-defibrillator implantation. Three transvenous rate-sensing leads were evaluated: a standard pacing lead, incorporating true bipolar sensing without ventricular coils, or an integrated shocking and sensing lead (Endotak C) with either 6-mm (60 series) or 12-mm (70 series) spacing between the sensing tip and shocking coil. Redetection was assessed from a failed first shock just below defibrillation threshold. RESULTS: Compared with the dedicated bipolar lead, redetection was prolonged with the 60 series lead (8.3 +/- 3.6 vs 6.6 +/- 2.3 seconds, P =.04). Moreover, prolonged redetection (>8 seconds) was observed in 41% of patients with 60 series leads compared with only 11% with dedicated bipolar leads (P <.01). No significant effects on redetection were noted with an integrated lead with greater spacing between the tip and coil (70 series). CONCLUSIONS: Delayed redetection is frequently noted with an integrated lead with close spacing between the tip and coil. Detailed evaluation of detection and redetection of these leads should be performed at the time of pulse generator replacement.

Chelant extraction of heavy metals from contaminated soils.

The current state of the art regarding the use of chelating agents to extract heavy metal contaminants has been addressed. Results are presented for treatability studies conducted as worst-case and representative soils from Aberdeen Proving Ground's J-Field for extraction of copper (Cu), lead (Pb), and zinc (Zn). The particle size distribution characteristics of the soils determined from hydrometer tests are approximately 60% sand, 30% silt, and 10% clay. Sequential extractions were performed on the 'as-received' soils (worst case and representative) to determine the speciation of the metal forms. The technique speciates the heavy metal distribution into an easily extractable (exchangeable) form, carbonates, reducible oxides, organically-bound, and residual forms. The results indicated that most of the metals are in forms that are amenable to soil washing (i.e. exchangeable+carbonate+reducible oxides). The metals Cu, Pb, Zn, and Cr have greater than 70% of their distribution in forms amenable to soil washing techniques, while Cd, Mn, and Fe are somewhat less amenable to soil washing using chelant extraction. However, the concentrations of Cd and Mn are low in the contaminated soil. From the batch chelant extraction studies, ethylenediaminetetraacetic acid (EDTA), citric acid, and nitrilotriacetic acid (NTA) were all effective in removing copper, lead, and zinc from the J-Field soils. Due to NTA being a Class II carcinogen, it is not recommended for use in remediating contaminated soils. EDTA and citric acid appear to offer the greatest potential as chelating agents to use in soil washing the Aberdeen Proving Ground soils. The other chelating agents studied (gluconate, oxalate, Citranox, ammonium acetate, and phosphoric acid, along with pH-adjusted water) were generally ineffective in mobilizing the heavy metals from the soils. The chelant solution removes the heavy metals (Cd, Cu, Pb, Zn, Fe, Cr, As, and Hg) simultaneously. Using a multiple-stage batch extraction, the soil was successfully treated passing both the Toxicity Characteristics Leaching Procedure (TCLP) and EPA Total Extractable Metal Limit. The final residual Pb concentration was about 300 mg/kg, with a corresponding TCLP of 1.5 mg/l. Removal of the exchangeable and carbonate fractions for Cu and Zn was achieved during the first extraction stage, whereas it required two extraction stages for the same fractions for Pb. Removal of Pb, Cu, and Zn present as exchangeable, carbonates, and reducible oxides occurred between the fourth- and fifth-stage extractions. The overall removal of copper, lead, and zinc from the multiple-stage washing were 98.9%, 98.9%, and 97.2%, respectively. The concentration and operating conditions for the soil washing extractions were not necessarily optimized. If the conditions had been optimized and using a more representative Pb concentration (approximately 12000 mg/kg), it is likely that the TCLP and residual heavy metal soil concentrations could be achieved within two to three extractions. The results indicate that the J-Field contaminated soils can be successfully treated using a soil washing technique.

Intravenous amiodarone suppression of electrical storm refractory to chronic oral amiodarone.

We report the case of an electrical storm in a cardiac arrest survivor with an ICD, in whom chronic oral amiodarone failed to suppress ventricular arrhythmias, and in whom intravenous amiodarone resulted in stability for 6 weeks prior to successful cardiac transplantation. Intravenous amiodarone can be successful in suppressing life-threatening ventricular arrhythmias, even when chronic oral amiodarone is unsuccessful.

Benefits of linear amplification and multichannel compression for speech comprehension in backgrounds with spectral and temporal dips.

People with cochlear hearing loss have markedly higher speech-receptions thresholds (SRTs) than normal for speech presented in background sounds with spectral and/or temporal dips. This article examines the extent to which SRTs can be improved by linear amplification with appropriate frequency-response shaping, and by fast-acting wide-dynamic-range compression amplification with one, two, four, or eight channels. Eighteen elderly subjects with moderate to severe hearing loss were tested. SRTs for sentences were measured for four background sounds, presented at a nominal level (prior to amplification) of 65 dB SPL: (1) A single female talker, digitally filtered so that the long-term average spectrum matched that of the target speech; (2) a noise with the same average spectrum as the target speech, but with the temporal envelope of the single talker; (3) a noise with the same overall spectral shape as the target speech, but filtered so as to have 4 equivalent-rectangular-bandwidth (ERB) wide spectral notches at several frequencies; (4) a noise with both spectral and temporal dips obtained by applying the temporal envelope of a single talker to speech-shaped noise [as in (2)] and then filtering that noise [as in (3)]. Mean SRTs were 5-6 dB lower (better) in all of the conditions with amplification than for unaided listening. SRTs were significantly lower for the systems with one-, four-, and eight-channel compression than for linear amplification, although the benefit, averaged across subjects, was typically only 0.5 to 0.9 dB. The lowest mean SRT (-9.9 dB, expressed as a speech-to-background ratio) was obtained for noise (4) and the system with eight-channel compression. This is about 6 dB worse than for elderly subjects with near-normal hearing, when tested without amplification. It is concluded that amplification, and especially fast-acting compression amplification, can improve the ability to understand speech in background sounds with spectral and temporal dips, but it does not restore performance to normal.