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PubMed1985

Evolution of transposable elements: an IS10 insertion increases fitness in Escherichia coli.

Strains of Escherichia coli carrying Tn10, a transposon consisting of two IS10 insertion sequences flanking a segment encoding for a tetracycline-resistance determinant, gain a competitive advantage in chemostat cultures. All Tn10-bearing strains that increase in frequency during competition have a new IS10 insertion that is found in the same location in the genome of those strains. We mapped, by a gradient of transmission, the position of the new IS10 insertion. We examined 11 isolates whose IS10 insertion was deleted by recombinational crossing-over, and in all cases the competitive fitness of the isolates was decreased. These results show that the IS10-generated insertion increases fitness in chemostat cultures. We named the insertion fit::IS10 and suggest that transposable elements may speed the rate of evolution by promoting nonhomologous recombination between preexisting variations within a genome and thereby generating adaptive variation.

Biological Evolution↗
PubMed1988

Evaluation of biofeedback seat insert for improving active sitting posture in children with cerebral palsy. A clinical report.

Biofeedback devices have been used successfully to improve head control and symmetrical standing in children with cerebral palsy. This clinical report describes a biofeedback seat insert developed to improve erect sitting posture in children with cerebral palsy who have inadequate trunk control. The seat insert is easily placed against the back of any seating device. A momentary-contact pressure switch on the seat insert is activated when the child exerts pressure on it by extending his trunk. The pressure switch then activates a videocassette recorder or can be adapted to activate a television or radio. Five children with spastic cerebral palsy participated in this evaluation of the biofeedback seat insert. The results of this evaluation show that the children used the biofeedback seat insert effectively to actively improve their sitting posture by voluntarily extending their trunk against the pressure switch. The biofeedback seat insert offers physical therapists a valuable therapeutic training tool to encourage carry-over of improved sitting posture away from the clinical setting for children with cerebral palsy.

Biofeedback, Psychology↗
PubMed2001

The use of remifentanil to facilitate the insertion of the laryngeal mask airway.

UNLABELLED: Propofol is often used as an IV induction drug for anesthesia and the insertion of a laryngeal mask airway (LMA). As a sole anesthetic, it may be associated with undesirable airway responses such as coughing and gagging. We conducted a randomized, double-blinded study to compare the conditions during insertion of the LMA in 120 patients who received normal saline (Group P), remifentanil 0.25 microg/kg (Group R1), or remifentanil 0.5 microg/kg (Group R2) before the induction of anesthesia with IV propofol. The addition of remifentanil significantly improved the conditions of insertion; in Group R1, 82.5% (33 of 40 patients), and in Group R2, 85.0% (34 of 40 patients) had excellent insertion conditions as compared with the Control group P, 32.5% (13 of 40 patients). Patients in Group P were apneic for a mean (SD) time of 85 (38) s, 186 (75) s in group R1, and 284 (130) s in group R2. There was a lesser decrease in mean arterial blood pressure in group R1. We conclude that remifentanil 0.25 microg/kg, when administered after IV propofol 2.5 mg/kg, provides excellent conditions for insertion of the LMA with minimal hemodynamic disturbances. IMPLICATIONS: Small-dose remifentanil can provide excellent conditions for laryngeal mask airway insertion with minimal hemodynamic disturbances.

Adult↗
PubMed2003

A needle-free jet-injection system with lidocaine for peripheral intravenous cannula insertion: a randomized controlled trial with cost-effectiveness analysis.

UNLABELLED: Insertion of a peripheral IV cannula is a common, although painful, procedure. We tested the analgesic efficacy, adverse effects, and cost-effectiveness of a needle-free intradermal drug delivery system (Jet) with lidocaine for the insertion of an IV cannula (18-gauge; dorsum of hand). Four-hundred patients were randomly allocated to one of four groups: (a) no treatment, (b) Jet (J-Tip), National Medical Products Inc, CA; $3.0 per device) with 0.5 mL of saline, (3) Jet with 0.5 mL of lidocaine 1%, and (4) Jet with 0.5 mL of lidocaine 2%. Pain was evaluated using a numerical verbal scale (NVS 0-10). A NVS < or =3 was considered as acceptable in this context. Incremental cost-effectiveness ratios were calculated. Without treatment, 42.4% of patients had a NVS < or = 3, 39.3% with saline, 60.7% with 1% lidocaine (relative risk [RR] compared with no treatment, 0.70; 95% confidence interval [CI], 0.53-0.93), and 86.7% with 2% lidocaine (RR, 0.49; 95% CI, 0.38-0.62). Nineteen and one-half percent of patients had a NVS >3 because of Jet treatment, 13.5% had local hyperemia, and 16.9% had minor local bleeding. Of all Jet treatments, 10.5% were technical failures, and there were 17.6% cannula insertion failures (10.1% without treatment [RR, 1.74; 95% CI, 0.92-3.32]). Compared with no treatment, costs to generate one additional patient with a NVS < or =3 were $23 with lidocaine 1% and $10 with lidocaine 2%. On insertion of an IV cannula on the back of the hand, 58% of patients report at least moderate pain. Lidocaine-Jet is analgesic; there is dose-responsiveness. However, Jet treatment is not painless, and costs incurred to achieve one success compared with doing nothing are not negligible. IMPLICATIONS: Insertion of an IV cannula is painful. Four-hundred patients were randomly allocated to test the analgesic efficacy, adverse effects, and cost-effectiveness of the needle-free intradermal drug delivery system (J-Tip); Jet). Jet with lidocaine is effective, but its application is not painless. Costs to achieve one patient with no more than moderate pain (numerical verbal scale < or =3 of 10) on insertion of an IV cannula are $10.

Adolescent↗
PubMed1998

Chest tube insertion: a prospective evaluation of pain management.

OBJECTIVE: To evaluate pain associated with chest tube insertion in a group of patients with malignant pleural effusions. DESIGN: Prospective case series. SETTING: Acute care cancer center in an academic institution. PATIENTS: Fifty-two patients with symptomatic malignant pleural effusions. Twenty-six evaluated by conventional approach to chest tube insertion (group 1), 26 evaluated after institution of a new chest tube protocol (group 2). INTERVENTIONS: A new protocol was designed to improve pain control during chest tube insertion. The protocol included improved housestaff and nursing education, premedication, proper insertion techniques, and more liberal and precise delivery of local anesthetic. OUTCOME MEASURES: Both groups were evaluated by a verbal self-report scale (1-10) to assess pain and anxiety. RESULTS: The mean pain rating in group 1 was 6.2 (+/-0.76) compared with 3.7 (+/-5.6) in group 2 (p < 0.01). In group 1, pain or anxiety was 9 or 10 in 12 of 26 on a scale of 1 to 10, compared with 2 of 26 in group 2 (p < 0.001). Anxiety rating was 4.5 (+/-0.72) in group 1 compared with 1.5 (+/-0.54) in group 2 (p < 0.01). CONCLUSIONS: Chest tube insertion was associated with an unacceptably high level of pain and anxiety in our hospital. A new protocol, including housestaff education and changes in nursing policies, technical aspects, local anesthetic dose and delivery, and pre-medication, allowed us to approach the goal of a painless chest tube insertion.

Anxiety↗
PubMed2001

Femoral stem insertion generates high bone cement pressurization.

Adequate bone cement pressurization is critical in obtaining optimal femoral cement mantles during total hip arthroplasty. Pressurization can be generated during insertion of the femoral stem into the cement-filled canal. This may be clinically useful in augmenting conventional cement gun pressurization. Two factors, which were expected to influence the amount of insertion-induced pressurization, are the cement's cure state (viscosity) at the time of insertion and the femoral stem profile. This study evaluated the effect of these factors on cement pressurization during stem insertion. Femoral stems were inserted at a controlled rate into a reusable, simulated femoral canal. Intramedullary pressures were monitored at four locations along the canal's medial midline. The intrusion factor quantity, which accounts for pressure magnitude, duration of pressurization, and cement viscosity, was developed to quantify pressurization. Stem insertion into late cure stage (high viscosity) cement resulted in significantly higher intramedullary pressures (as much as 187% higher) and intrusion factors (as much as 43% higher) as compared with early stage (low viscosity) cement. The highest pressures and intrusion factors were found in the distal canal. A tapered stem profile resulted in significantly higher pressures (as much as 65%) and higher intrusion factors (as much as 63%) than a straight stem.

Arthroplasty, Replacement, Hip↗
PubMed2003

Gluteus medius tendon injury during reaming for gamma nail insertion.

The use of intramedullary hip screws such as the Gamma nail has become a popular option for treatment of proximal femur fractures. The manufacturer recommends that the Gamma nail be inserted at the junction of the anterior (1/3) and posterior (2/3) of the tip of the greater trochanter and on the tip in the same region that the gluteus medius inserts. The purpose of the current cadaveric study was to quantify the damage to the gluteus medius tendon secondary to reaming of the greater trochanter necessary for safe Gamma nail insertion. The gluteus medius was identified and its tendinous insertion was measured. A Kirschner wire was placed in the recommended entry point using the assistance of C-arm fluoroscopy and a 17-mm reamer was advanced over the wire. The tendon then was inspected to evaluate the amount of intrasubstance damage. In 27 of 34 specimens, the portal was contained completely within the tendinous insertion of the gluteus medius. The percentage of the tendon insertion disrupted by the reamer ranged from 14.8% to 52.5% with an average of 27%. During appropriate placement of the Gamma nail, damage to the gluteus medius tendon is unavoidable and should be recognized as a potential cause of postoperative morbidity.

Bone Nails↗
PubMed1991

Hearing aid coupler output level variability and coupler correction levels for insert earphones.

HA coupler type SPLs were independently determined by two experimenters for five repeated measurements with and without replacement of two ER-3A and two EARTONE 3A insert earphones. Measurements were made using a B&K DB-0138 coupler configured as an HA-1, HA-2 earphone coupler and HA-2 earphone coupler with entrance through a rigid tube referred to as the DB-0138 coupler. The HA-1, HA-2, and DB-0138 SPLs were found to be very stable (+/- 0.2 dB) for all intra- and interexperimenter measurements for each insert earphone and coupler type from 125 to 8000 Hz. Averaged across both experimenters and all repeated measurements, the mean HA-1 and HA-2 coupler SPLs were similar for each insert earphone from 125 to 8000 Hz. The mean HA-1, HA-2, and DB-0138 coupler SPLs were similar for each insert earphone from 125 to 2000 Hz; however, from 3000 to 8000 Hz the DB-0138 coupler SPLs were higher than the HA-1 and HA-2 coupler SPLs for each insert earphone. This occurred because of the geometrical differences between the insert earphone to coupler connections and coupler types. The HA-1 minus DB-0138 and HA-2 minus DB-0138 coupler SPL differences, or coupler correction levels, could be explained by quarter-wave resonances and stepped-diameter tubing systems creating acoustic horn effects.

Auditory Threshold↗
PubMedDate not supplied

Cortex distraction forces caused by the insertion of external fixator pins.

OBJECTIVE: Insertion of a bicortical threaded external fixator pin can cause bone damage. An unexpected crack can propagate along the bone when the pin touches the far cortex. The objective of this study was to investigate whether drilling and inserting bicortical pins into the shafts of long bones can cause large distraction forces to be generated between the cortices. DESIGN: Two flat samples of bone or bone substitute (Tufnol) were mounted parallel at each end of a specially designed force measurement column. Three common pin designs were inserted into the samples: tapered, self-threading and self-drilling, and self-threading pins. The axial thrust and the cortex distraction force between the two samples were measured as the pins were inserted. RESULTS: High distraction forces were measured between the cortices for all pin designs, typically 700 to 1,000 Newtons. CONCLUSIONS: The clinical significance of these findings is that the insertion of bicortical pins of the designs tested may generate a large distraction force between the cortices. This may drive a fracture apart or propagate an undisplaced fracture. Therefore, care must be taken to ensure that bicortical pins are inserted in locations free of local defects.

Bone Nails↗
PubMed1999

Use of endoscopic trocar-cannula for chest drain insertion in trauma patients and others.

BACKGROUND: The insertion of a chest drain into the pleural space is a common procedure used for treatment in various intrathoracic abnormalities. Recently, a new technique for chest-tube insertion for pleural cavity drainage, using the disposable endoscopic trocar-cannula, was described for the treatment of some pathologic conditions. METHODS: In a prospective study, we used this technique in the treatment of patients with chest trauma, spontaneous and iatrogenic pneumothorax, and various kinds of pleural effusion. RESULTS: One hundred twelve patients were treated by using the endoscopic trocar-cannula for tube insertion into the pleural cavity. Among them, 39 patients were treated after blunt and penetrating chest trauma. Most cannulae were of 10 to 11 mm in diameter, which enabled the insertion of large-bore drain tubes. In five trauma patients, chest-tube insertion was done successfully without antecedent chest x-ray films. The complication rate was 0.89% for intrapulmonary positioning of a chest tube in a patient who had previous ipsilateral thoracic surgery. CONCLUSION: The use of endoscopic trocar-cannulae for chest-tube insertion is a safe, simple, and effective technique for management of trauma and other diverse intrathoracic abnormalities. Its use outside the hospital should be further studied.

Adolescent↗
PubMed2003

Acute complications associated with greenfield filter insertion in high-risk trauma patients.

BACKGROUND: Use of Greenfield filters (GFs) to prevent fatal pulmonary embolism (PE) in trauma patients is generally well accepted. Nonetheless, a surprisingly small number of trauma surgeons insert filters in their patients. Among the reasons cited is fear of complications. METHODS: We observed three femoral arteriovenous fistulae (AVF) in trauma patients who had inferior vena caval placement of filters for PE prophylaxis in one 12-month period (academic year 1999). In an effort to document the magnitude of this problem, we evaluated trauma patients who had a GF inserted in academic year 2000. RESULTS: During that year, 133 consecutive patients (8.6% of trauma admissions) received 133 GFs through a percutaneous approach. The most common isolated indications for GF insertion included closed head injuries (n = 28), multiple long bone fractures (n = 27), pelvic and acetabular fractures (n = 6), spinal cord injuries (n = 16), and vertebral fractures (n = 3). Five patients had documented deep venous thrombosis (DVT) diagnosed by duplex ultrasonography before GF placement, and 11 patients had other indications requiring a filter. There were 37 patients with more than one indication requiring filter placement. Most patients (57%) underwent preinsertion duplex scanning of their lower extremity veins; 77% of patients underwent postinsertion scanning. Filters were inserted an average of 6.8 +/- 0.6 (SE) days after trauma. No AVF were suspected clinically or detected ultrasonographically. No operative or postoperative complications occurred. DVT was observed in 30% of patients despite 92% prophylaxis; there was a 26% incidence of de novo thrombi detected. None of the patients evidenced DVT clinically. CONCLUSION: Our data indicate that complications of GF insertion for prophylaxis against PE from DVT complicating trauma patients continue to be negligible. In addition, the incidence of insertion-site thrombosis may be lower than expected. Moreover, femoral AVF is a rare complication of this procedure.

Adolescent↗
PubMed1996

Postoperative function after implant insertion in vascularized bone grafts in maxilla and mandible.

Between 1988 and 1992, 80 Brånemark-type implants were inserted in 18 patients during reconstruction of the mandible or maxilla with vascularized iliac crest or scapula grafts with or without additional soft tissue pedicles. In these procedures, nine vascularized bone grafts were combined with a primary insertion of 32 implants and a secondary insertion of 48 implants. Twelve patients are currently wearing the implant-borne dentures. From 32 implants inserted primarily, eight could not be used for prosthodontic rehabilitation because three were lost with a graft, three were left as sleepers, and two demonstrated a lack of osseointegration. None of the implants inserted secondarily in grafts were lost. Primary implant insertion should be performed only in close cooperation with the prosthodontist and in selected cases, for example, in free-end reconstruction of the mandible with a straight graft and where a limited number of implants is needed. Although restoration of masticatory function in patients with head and neck cancer can be achieved, compared with a healthy control group, functional impairments remain. Patients subjectively favor the nonreconstructed side of the mandible or maxilla for chewing. These findings can be correlated with a postoperative follow-up investigation using a miniature force transducer and the T-scan system.

Denture, Partial↗
PubMed2000

Uses and complications of central venous catheters inserted in a pediatric emergency department.

OBJECTIVE: To describe the incidence, indications, insertion sites, duration, and complications of central venous catheter (CVC) insertion in patients in a pediatric emergency department (ED). METHODS DESIGN: Retrospective chart review. SETTING: ED of an urban pediatric teaching hospital. SUBJECTS: Patients who had a CVC inserted in the ED from January 1992 to July 1997. RESULTS: During the 5.5-year study period, 121 patients were identified. Indications for insertion were cardiac/respiratory arrest in 20 patients (17%), lack of peripheral vascular access in 78 (64%), and inadequate peripheral vascular access in 23 (19%). Presenting diagnoses included cardiac/respiratory arrest (20), dehydration (19), lower respiratory tract disease (15), seizure (15), sepsis (13), trauma (10), and other (29). Prior to the CVC insertion, 80 (66%) patients had no venous access, 28 (23%) had a peripheral intravenous catheter, and 13 (11%) had an intraosseous needle. One hundred one (83%) CVCs were inserted into the femoral vein, 12 (10%) into the subclavian, 7 (6%) into the internal jugular, and 1 (1%) into an axillary vein. There were four reported complications requiring the CVC to be removed, and all occurred with femoral line placement. There were no long-term sequelae or life-threatening or limb-threatening complications (95% CI = 0-2.5%). CONCLUSIONS: Central venous catheterization, particularly using the femoral approach, appears to a safe method of obtaining central venous access in the critically ill infant, child, or young adult.

Adolescent↗
PubMed1989

The effect of angled insertion on halo pin fixation.

This study evaluated the effect of angled insertion of halo pins on the biomechanical characteristics of the halo pin-calvarium complex. Halo pins were inserted into isolated calvarium sections at 90 degrees, 75 degrees, and 60 degrees to the surface of the bone at an insertional torque of 0.68 N-m (6 inch-pounds). Initial rigidity, load at failure, and deformation at failure of the pin-bone complex were assessed during transverse shear loading. The structural properties of the pin-bone complex were maximized at loads approaching failure when pins were inserted perpendicular (90 degrees) to the bony surface and significantly decreased at more acute angles of insertion. Perpendicular insertion of halo pins maximizes the structural properties of the complex formed by the halo pin and the calvarium. This improved structural behavior may minimize the incidence of pin loosening clinically, and may reduce the frequency of other complications currently associated with the use of the halo orthosis.

Biomechanical Phenomena↗
PubMed2004

Does cooling Sengstaken-Blakemore tubes aid insertion? An evidence based approach.

OBJECTIVE: To survey current clinical practice concerning the use of Sengstaken-Blakemore (SB) tubes and to determine whether cooling the tubes alters their stiffness. METHODS: A telephone questionnaire was conducted of gastroenterology registrars and ITU departments in the North Thames region. The current clinical practice for insertion of SB tubes and the basis for this practice were determined in each case. The stiffness of the tubes was measured at -10 degrees C and 20 degrees C by measuring the extension (in mm) resulting from an applied load (in newtons). The time for tube warming from -30 degrees C when in stationary air and when in contact with skin was also recorded. RESULTS: Fifty registrars were contacted and 20 ITU departments were surveyed. All ITU departments involved the gastroenterologists in the management of acute variceal bleeds. Eight registrars had never placed an SB tube. The majority of the remainder (95%) used a cooled SB tube. All of the registrars based this practice upon their clinical teaching, and 75% of these registrars thought cooling aided the insertion of the tube. There was no significant difference in the stiffness of the tubes at -10 degrees C and 20 degrees C. Upon warming, an SB tube took 30 s to rise from 0 degrees C to room temperature (20 degrees C) when in skin contact and 120 s when placed in stationary air. CONCLUSION: The current clinical practice of trainees for the insertion of SB tubes is to cool the tubes in the belief that this 'standard' practice aids tube insertion. We found no significant change in SB tube stiffness even after cooling to temperatures that would not be achieved during routine insertion. Furthermore, the rapid rise in tube temperature means that tubes approach room temperature by the time they reach the bedside. In the present era of evidence based medicine the current dogma that SB tubes should be cooled prior to insertion must be discarded.

Catheterization↗
PubMed2003

Readability of ocular medication inserts.

OBJECTIVE: To determine the readability of ocular medication inserts and whether they are an appropriate source of medication information for patients. MATERIALS AND METHODS: The Flesch-Kincaid and SMOG readability formulas were used to calculate the readability of 10 common glaucoma medication inserts (Alphagan, Azopt, Betoptic, Betimolol, Cosopt, Optipranolol, Rescula, Trusopt, Timoptic, and Xalatan) and 6 widely used nonglaucoma medication inserts (Alrex, Lotemax, Ocuflox, Patanol, Pred Forte, and Zaditor). RESULTS: The 10 glaucoma medication inserts surveyed required an average overall grade level of 12.9 +/- 0.6 by the Flesch-Kincaid Index and of 13.5 +/- 0.6 by the SMOG formula. The 6 nonglaucoma medication inserts had an overall grade level of 11.1 +/- 0.6 by the Flesch-Kincaid Index and of 11.7 +/- 0.9 by the SMOG formula. All medications reviewed were above the eighth-grade level recommended by the Flesch-Kincaid Index for public materials. CONCLUSIONS: Ocular medication inserts are too complex to be an adequate source of medication information for the average American adult. This study highlights the need for improving communication and education regarding patients' medications.

Antihypertensive Agents↗
PubMed2002

A novel minimally invasive technique for insertion of peritoneal dialysis catheter.

The placement of a continuous ambulatory peritoneal dialysis (CAPD) catheter by conventional open surgical or trocar technique may cause a number of complications such as infection, hemorrhage, leakage, incisional hernia, and visceral organ perforation. Most complications are related to open surgery or insertion of the catheter with the guidewire without direct visualization. Insertion of the catheter laparoscopically under direct visualization has been previously described. The authors who described this technique used two or three ports for the camera and instruments. In this study we describe a laparoscopic technique for insertion of the peritoneal dialysis catheter under direct visualization with use of one-camera port and an accessory 2-mm umbilical incision. This prospective study was performed with the approval of the ethics committee of the Gazi University Hospital, in Ankara, Turkey. There were a total of eight patients: five males and three females, with an average age of 34.3 years (range, 11-54), who underwent laparoscopic CAPD insertion between 1997 and 2000. The catheter was inserted into the abdominal cavity 2 cm below the umbilicus. The subcutaneous tunnel was made with the assistance of a specially designed L-shaped trocar. All patients did well after the operation and had excellent cosmetic results. There was one leak in the early postoperative period, which was treated conservatively. The average operating time was 34.7 minutes (range, 25-45 minutes). The laparoscopic approach for peritoneal dialysis catheter insertion, for management of transmigrated CAPD catheters, and to resolve omental occlusions should be considered as an alternative to open surgery, especially for patients who have peritoneal adhesions secondary to a history of abdominal surgeries or recurrent peritonitis.

Adolescent↗
PubMed2005

How does the sound pressure generated by circumaural, supra-aural, and insert earphones differ for adult and infant ears?

OBJECTIVE: To determine how the ear canal sound pressure levels generated by circumaural, supra-aural, and insert earphones differ when coupled to the normal adult and infant ear. DESIGN: The ratio between the sound pressure generated in an adult ear and an infant ear was calculated for three types of earphones: a circumaural earphone (Natus Medical, ALGO with Flexicoupler), a supra-aural earphone (Telephonics, TDH-49 with MXAR cushion), and an insert earphone placed in the ear canal (Etymoup and down arrow tic Research, ER-3A). The calculations are based on (1) previously published measurements of ear canal impedances in adult and infant (ages 1, 3, 6, 12, and 24 months) ears (Keefe et al., 1993, Acoustic Society of America, 94:2617-2638), (2) measurements of the Thévenin equivalent for each earphone configuration, and (3) acoustic models of the ear canal and external ear. RESULTS: Sound-pressure levels depend on the ear canal location at which they are measured. For pressures at the earphone: (1) Circumaural and supra-aural earphones produce changes between infant and adult ears that are less than 3 dB at all frequencies, and (2) insert earphones produce infant pressures that are up to 15 dB greater than adult pressures. For pressures at the tympanic membrane: (1) Circumaural and supra-aural earphones produce infant pressures that are within 2 dB of adult ears at frequencies below 2000 Hz and that are 5 to 7 dB smaller in infant ears than adult ears above 2000 Hz, and (2) insert earphones produce pressures that are 5 to 8 dB larger in infant ears than adult ears across all audiometric frequencies. CONCLUSIONS: Sound pressures generated by all earphone types (circumaural, supra-aural, and insert) depend on the dimensions of the ear canal and on the impedance of the ear at the tympanic membrane (e.g., infant versus adult). Specific conclusions depend on the location along the ear canal at which the changes between adult and infant ears are referenced (i.e., the earphone output location or the tympanic membrane). With circumaural and supra-aural earphones, the relatively large volume of air within the cuff of the earphone dominates the acoustic load that these earphones must drive, and differences in sound pressure generated in infant and adult ears are generally smaller than those with the insert earphone in which the changes in ear canal dimensions and impedance at the tympanic membrane have a bigger effect on the load the earphone must drive.

Acoustic Impedance Tests↗