Head and Neck Ultrasound Utilization Rates: 2012 to 2019.

Objective: We measured utilization of clinician-performed head and neck ultrasound among otolaryngologists, endocrinologists, and general surgeons, using Medicare Provider Utilization and Payment Data. Study Design: Retrospective analysis of Medicare billing database. Setting: University. Methods: For each year, the files were filtered to include 4 provider types: Diagnostic Radiology (DR), Endocrinology (ENDO), General Surgery (GS), and Otolaryngology (OTO). Billable procedures are listed by Healthcare Common Procedure Coding System code and a filter was applied to include 76536 Ultrasound, soft tissues of the head and neck. Results: In 2019, OTOs submitted charges for 2.1% of all head and neck diagnostic ultrasounds (76536) performed on Medicare beneficiaries. For each year 2012 to 2019, DRs submitted the most charges, followed by ENDOs, and then OTO and GS. Charges for all groups increased in a proportional manner across the 8-year period. 14.5% of OTOs submitted more than 100 charges apiece during 2019, that is, "super users." The percentage of super users within each specialty increased from 2012 to 2019. Overall, the data support an ever-increasing use of head and neck ultrasound (HNUS) among all provider types. Conclusion: Even with increased use among OTOs, this specialty only accounted for a small percentage of head & neck diagnostic ultrasounds performed on Medicare beneficiaries in 2019. Changes in volume of nonradiology point-of-care HNUS was not associated with changes in DR volume. A greater proportion of OTOs than DRs are "super users" among the ultrasound users within their specialty, performing more than 100 exams/year. Level of Evidence: V.

Oropharyngeal Squamous Cell Carcinoma Outcomes by p16INK4a Antigen Status in a Veteran Population.

Background: The correlation between head and neck squamous cell carcinoma (SCC) and human papillomavirus (HPV) has been of great interest. We aimed to study immunoexpression of the p16INK4a (p16) antigen, a surrogate marker for high-risk HPV infection, in oropharyngeal SCC among veterans to estimate HPV-related cancer and survival. Secondary aims included stratification of race and ethnicity, degree of tobacco and alcohol use, tumor location, stage, and age at diagnosis. Methods: A retrospective electronic health record review was performed between January 1, 2000, and December 31, 2008, at a tertiary-level US Department of Veterans Affairs (VA) medical center for veterans who were treated for oropharyngeal SCC, had follow-up for a minimum of 2 years, and for whom paraffin-embedded tissue was available. Paraffin-embedded tissue was analyzed for p16 expression. Results: We identified 66 veterans who met the inclusion criteria. p16 expression was observed in 29% of the patients. All patients were male with no difference in age at diagnosis between the groups. Among patients with p16-negative status, 60% were African American, whereas among patients with p16-postive status, 32% were African American (P = .04). Among patients with p16-postive status, 22% were tobacco-naïve, and 18% were alcohol-naïve vs 0% and 4%, respectively, of patients with p16-negative status (P = .005 and P = .12, respectively). Two-year survival was the same for both groups (P = .52). Conclusions: We observed p16 expression in 29% of VA patients with oropharnygeal SCC, which was less than observed in non-VA populations. At presentation, both groups demonstrated a predilection for tonsil location and late stage without significant difference in age or disease-specific survival. Disparities in racial distribution and tobacco use between patients with and without p16-positive status appear like that reported in non-VA populations; however, the frequently reported younger age at presentation, lower stage, and improved prognosis were not observed.

Survival and functional outcomes after total glossectomy with total laryngectomy: Case series from a high-volume tertiary institution.

OBJECTIVES: Total glossectomy with total laryngectomy (TGTL) is indicated for some cases of advanced oral squamous cell carcinoma. However, this procedure is rarely performed, as quality of life outcomes are often considered poor. Consequently, few studies to date have reported survival and functional outcomes in patients undergoing TGTL. Here, we present the largest cases series to date of TGTL patients and provide relevant data on survival and functional outcomes. METHODS: Patients met inclusion criteria if they underwent TGTL (concurrent or staged) indicated for head and neck squamous cell carcinoma. Patient demographics and disease characteristics, survival outcomes, functional oral intake scores, time to oral intake, gastrostomy tube dependence, and communication methods post-surgery were retrospectively extracted from the electronic medical record. RESULTS: Survival in patients undergoing TGTL was poor. Most patients in this study were eventually approved for some oral intake of restricted consistencies but remained gastrostomy tube dependent for most of their nutritional needs. Baseline oral intake was suboptimal in most patients but often re-achieved approximately 12 months following surgery. Communication methods following surgery included writing, text-to-speech, and augmentative and alternative communication devices. CONCLUSION: Our data provide new insights comparing survival and functional outcomes of patients undergoing TGTL. Additional investigation particularly on patient-perceived quality of life following TGTL is needed to better understand the risks and benefits for patients who are candidates for TGTL.

Factors predictive of an academic otolaryngologist's scholarly impact.

OBJECTIVES: Describe the h index as a bibliometric that can be utilized to objectively evaluate scholarly impact. Identify which otolaryngology subspecialties are the most scholarly. Describe if NIH funding to one's choice of medical school, residency, or fellowship has any impact on one's scholarly output. Determine other factors predictive of an academic otolaryngologist's productivity. STUDY DESIGN: Analysis of bibliometric data of academic otolaryngologists. METHODS: Active grants from the National Institutes of Health (NIH) to otolaryngology departments were ascertained via the NIH Research Portfolio Online Reporting Tools Expenditures and Reports database. Faculty listings from these departments were gleaned from departmental websites. H index was calculated using the Scopus database. RESULTS: Forty-seven otolaryngology programs were actively receiving NIH funding. There were 838 faculty members from those departments who had a mean h index of 9.61. Otology (h index 12.50) and head and neck (h index 11.96) were significantly (P < 0.0001) more scholarly than the rest of subspecialists. H index was significantly correlative (P < 0.0001) with degree of NIH funding at a given institution. H index was not significantly higher for those that attended medical school (P < 0.18), residency (P < 0.16), and fellowship (P < 0.16) at institutions with NIH funding to otolaryngology departments. CONCLUSIONS: H index is a bibliometric that can be used to assess scholarly impact. Otology and head and neck are the most scholarly subspecialists within otolaryngology. NIH funding to an individual's medical school, residency, or fellowship of origin is not correlative with one's scholarly impact, but current institutional affiliation and choice of subspecialty are.

Validation of ultrasound as a diagnostic tool to assess vocal cord motion in an animal feasibility study.

BACKGROUND: Post-thyroidectomy dysphonia can result from recurrent laryngeal nerve (RLN) injury. Confirmation of postoperative recurrent nerve function has prompted many surgeons to advocate laryngoscopic examination. Indirect and flexible laryngoscopy permit visualization of vocal cord motion, but not all thyroid surgeons are skilled in these techniques. Indirect laryngoscopy has a significant failure rate due to gag reflexes or anatomical obstruction. Flexible fiberoptic laryngoscopy, the current gold standard, allows reliable visualization of the cords, but perioperative examination is not always feasible for lack of equipment or training. Recent studies suggest vocal fold ultrasound as an alternative to flexible laryngoscopy. It offers the advantages of being non-invasive and painless without radiation exposure or sedation. Whereas ultrasound has been compared to laryngoscopy in the clinical setting, there remains a need for correlation of laryngeal ultrasound results with known neurophysiology in the normal and injured state. An animal model was proposed that reproduces neck surgery-associated recurrent nerve injury. The model allowed simultaneous recording of laryngeal endoscopy and transcutaneous high-resolution ultrasound during stimulation of intact and injured RLNs. METHODS: One RLN was injured in each of 4 rats. Rats were kept anesthetized during the fiberoptic examination and laryngeal ultrasound procedures. Following surgery and subsequent imaging the rats were given a lethal anesthetic dose. Results of both imaging modalities were compared to the presence or absence of neuromuscular action potential following stimulation of the recurrent nerve. RESULTS: The investigators observed a 100% correlation between endoscopic and ultrasonographic assessments. CONCLUSIONS: This study validated the clinical use of diagnostic ultrasound in vocal cord dysfunction in a rodent model.

What's in the Box? The Effectiveness of a Low-Volume Massive Transfusion Protocol.

Transfusion ratios approaching 1:1:1 of packed red blood cells (PRBCs) to fresh frozen plasma (FFP) to platelet have been shown to improve outcomes in trauma. There is little data available to describe in what quantity that ratio should be delivered. We hypothesized that lowering the total volume of products delivered in each protocol round would not adversely affect outcomes in the bleeding trauma patient. A retrospective review of 9732 trauma patients admitted to a rural Level I trauma center over a 3-year period was performed. Patients who received a massive transfusion (greater than 10 units of blood product transfused in the first 24 hours), between January 2012 and April 2015 were identified as the study cohort. In May of 2014, our institution switched from a massive transfusion protocol (MTP) that included 6 PRBCs:6 FFP:1 platelet to a lower volume massive transfusion protocol (LVMTP) that included 4 PRBC:4 FFP:1 platelet. Data collected included patient demographics, vital signs, and outcomes. A total of 131 patients met study criteria. MTP was activated on 65 per cent of patients (57/88), receiving a massive transfusion during the 28 months before implementation of the new protocol. In contrast, LVMTP was activated in 100 per cent of patients (43/43) receiving a massive transfusion in the 12 months after implementation of the new protocol. There was no significant difference in age (36.6 vs 37.2, P = 0.87), injury severity score (29.8 vs 32.3, P = 0.45), or per cent penetrating mechanism (43.9 vs 37.2%, P = 0.503) when comparing MTP to LVMTP. In addition, there was no significant difference in mortality (47.4 vs 41.9%, P = 0.584), lengths of stay (13.5 vs 17.1, P = 0.258), or vent days (6.4 vs 8.2, P = 0.236) when comparing MTP to LVMTP. A LVMTP is safe and effective for the resuscitation of the trauma patient.

Periplasmic flagellar export apparatus protein, FliH, is involved in post-transcriptional regulation of FlaB, motility and virulence of the relapsing fever spirochete Borrelia hermsii.

Spirochetes are bacteria characterized in part by rotating periplasmic flagella that impart their helical or flat-wave morphology and motility. While most other bacteria rely on a transcriptional cascade to regulate the expression of motility genes, spirochetes employ post-transcriptional mechanism(s) that are only partially known. In the present study, we characterize a spontaneous non-motile mutant of the relapsing fever spirochete Borrelia hermsii that was straight, non-motile and deficient in periplasmic flagella. We used next generation DNA sequencing of the mutant's genome, which when compared to the wild-type genome identified a 142 bp deletion in the chromosomal gene encoding the flagellar export apparatus protein FliH. Immunoblot and transcription analyses showed that the mutant phenotype was linked to the posttranscriptional deficiency in the synthesis of the major periplasmic flagellar filament core protein FlaB. Despite the lack of FlaB, the amount of FlaA produced by the fliH mutant was similar to the wild-type level. The turnover of the residual pool of FlaB produced by the fliH mutant was comparable to the wild-type spirochete. The non-motile mutant was not infectious in mice and its inoculation did not induce an antibody response. Trans-complementation of the mutant with an intact fliH gene restored the synthesis of FlaB, a normal morphology, motility and infectivity in mice. Therefore, we propose that the flagellar export apparatus protein regulates motility of B. hermsii at the post-transcriptional level by influencing the synthesis of FlaB.

In vivo ultrasonic detection of polyurea crosslinked silica aerogel implants.

BACKGROUND: Polyurea crosslinked silica aerogels are highly porous, lightweight, and mechanically strong materials with great potential for in vivo applications. Recent in vivo and in vitro studies have demonstrated the biocompatibility of this type of aerogel. The highly porous nature of aerogels allows for exceptional thermal, electric, and acoustic insulating capabilities that can be taken advantage of for non-invasive external imaging techniques. Sound-based detection of implants is a low cost, non-invasive, portable, and rapid technique that is routinely used and readily available in major clinics and hospitals. METHODOLOGY: In this study the first in vivo ultrasound response of polyurea crosslinked silica aerogel implants was investigated by means of a GE Medical Systems LogiQe diagnostic ultrasound machine with a linear array probe. Aerogel samples were inserted subcutaneously and sub-muscularly in a) fresh animal model and b) cadaveric human model for analysis. For comparison, samples of polydimethylsiloxane (PDMS) were also imaged under similar conditions as the aerogel samples. CONCLUSION/SIGNIFICANCE: Polyurea crosslinked silica aerogel (X-Si aerogel) implants were easily identified when inserted in either of the regions in both fresh animal model and cadaveric model. The implant dimensions inferred from the images matched the actual size of the implants and no apparent damage was sustained by the X-Si aerogel implants as a result of the ultrasonic imaging process. The aerogel implants demonstrated hyperechoic behavior and significant posterior shadowing. Results obtained were compared with images acquired from the PDMS implants inserted at the same location.

Ultrasound-guided fine-needle aspiration of the tongue base: a cadaver feasibility study.

OBJECTIVE: The authors hypothesize that floor-of-mouth and tongue base anatomy can be visualized with ultrasound and that ultrasound can be used to accurately guide needle placement and dye injection into the tongue base, serving as a surrogate for fine-needle aspiration. STUDY DESIGN: Observation of experimental intervention. SETTING: Medical school cadaver anatomy laboratory. SUBJECTS AND METHODS: Ultrasound imaging was performed on human cadaveric specimens to visualize the anatomy of the floor of mouth and base of tongue in a midline transcervical approach. Methylene blue dye was injected under ultrasound guidance into the base of tongue. Specimens were dissected, and results were counted and analyzed. RESULTS: Twenty-five of 32 (78%) cadaver specimens were found to have correct placement of dye within the posterior genioglossus and intrinsic tongue musculature. Seven cadavers did not have correct placement of dye. Of these, 3 had dye staining the walls of the oropharynx and epiglottis. Two specimens had dye injected erroneously into the geniohyoid muscles. One patient was found to have had a partial glossectomy. Difference in neck circumference was not significant between those with correct (mean, 37.9 cm) and incorrect (mean, 37.4 cm) dye placement (P = .75). CONCLUSION: Anatomy of the floor of mouth and tongue base can be readily depicted with ultrasonography. After reasonable success of injecting dye into cadaver tongue bases, the authors conclude that there appears to be a future clinical role for ultrasound-guided fine-needle aspiration of the tongue base for tongue base lesions.

Histopathological and postoperative behavioral comparison of rodent oral tongue resection: fiber-enabled CO2 laser versus electrocautery.

OBJECTIVE: To compare operative time and hemostasis of fiber-enabled CO(2) laser (FECL) energy to that of the electrocautery (EC) technique for oral tongue resection, to compare return to oral intake and preoperative weight after FECL and EC resection, and to compare histologic changes in adjacent tissue after FECL and EC resection. STUDY DESIGN: Prospective animal study. SETTING: Research laboratory. SUBJECTS AND METHODS: The CO(2) laser fiber and the Bovie cautery were each used to resect the anterior tongue in 15 adult rats. Fixative perfusion and killing were performed on postoperative day 0 (n = 10), 3 (n = 10), or 7 (n = 10). Body weight, food intake, and water intake were recorded daily for 3- and 7-day survival rats. After preparation for histologic analysis, the tongue tissue was graded with a mucosal wound-healing scale (MWHS). RESULTS: A higher incidence of intraoperative bleeding and shorter operative times were noted in the EC group. No statistically significant difference in postoperative food or water intake between the EC and FECL groups was noted. The FECL group returned to baseline weight by postoperative day 6. MWHS scores were lower in the EC group by postoperative day 3 and lower in the FECL group by postoperative day 7. CONCLUSIONS: Both EC and FECL are effective for resection of the tongue in rats. EC has the advantage of shorter operative time and lower MWHS scores by postoperative day 3; FECL has the advantages of less intraoperative bleeding, faster return to baseline body weight, and lower MWHS score by postoperative day 7.

Sphenopalatine artery ligation: a cadaver anatomic study.

OBJECTIVE: To clarify endoscopic anatomy of the sphenopalatine artery (SPA) in relation to intranasal endoscopic landmarks using a human cadaver model and to simplify the surgical approach to SPA ligation. STUDY DESIGN: Prospective anatomic study from November to December 2009. SETTING: University of Tennessee Health Science Center Gross Anatomy Lab. SUBJECTS: Fifty human cadaveric sagittally sectioned heads. METHODS: The cadaveric nasal cavities were examined using a 0° endoscope, and the SPA and foramen were identified. The number of nasal cavities in which a transnasal approach successfully revealed the SPA foramen was compared with those that required maxillary antrostomy. The distance from the posterior edge of the maxillary natural ostium to the anterior edge of the SPA foramen was measured. RESULTS: Successful ligation of the SPA via a lateral nasal wall incision was achieved in 45 of 50 specimens (90%). The mean distance from the posterior edge of the maxillary natural ostium to the anterior edge of the SPA foramen was 23.79 mm (95% confidence interval, 22.03-25.55). CONCLUSION: The method of performing SPA ligation via lateral nasal wall incision alone was successful in 90% of human cadaveric heads. Maxillary antrostomy revealed the SPA in the remainder. No specimen required uncinectomy. The mean distance from the maxillary natural ostium to SPA foramen was more than 2 cm. The routine use of maxillary antrostomy and uncinectomy is not needed to locate the SPA in most nasal cavities and moreover produces unnecessary mucosal trauma in the often medically fragile or coagulopathic patient.

Effects of sensory or motor nerve deafferentation on oromotor function in mice.

OBJECTIVE: To investigate the effect of sensory or motor nerve damage to the tongue using a mouse model. STUDY DESIGN: Animal study. SETTING: Research laboratory. SUBJECTS AND METHODS: Adult male and female mice from inbred strains B6 (n = 19) and D2 (n = 25). Following lick training, bilateral lingual-chorda tympani nerve cuts (LX) (n = 6 B6, n = 7 D2), unilateral hypoglossal nerve cuts (HX) (n = 7 B6, n = 9 D2), or sham surgery (n = 6 B6, n = 9 D2) was performed. Mice were lick tested postsurgically with both water and sucrose (4 days total). Following testing, post mortem dissections and microscopic analysis of tongue papillae were performed. RESULTS: In both strains, HX and LX mice demonstrated a significant reduction in volume per lick (VPL) in the surgical groups relative to shams. Neither motor nor sensory nerve transection affected local lick rate. In most LX mice in both strains, taste papillae were reduced compared with HX or sham mice. CONCLUSION: Mice of either strain with either a sensory or a motor nerve injury have a significant loss of VPL during ingestion of either a neutral (water) or preferred (sucrose) stimulus. This reduction in VPL reflects a deficit in licking. Lick rate was not affected by deafferentation. A reduction in fungiform papillae following LX but not HX mice was noted.

A novel surface antigen of relapsing fever spirochetes can discriminate between relapsing fever and Lyme borreliosis.

In a previous immunoproteome analysis of Borrelia hermsii, candidate antigens that bound IgM antibodies from mice and patients infected with relapsing fever spirochetes were identified. One candidate that was identified is a hypothetical protein with a molecular mass of 57 kDa that we have designated Borrelia immunogenic protein A (BipA). This protein was further investigated as a potential diagnostic antigen for B. hermsii given that it is absent from the Borrelia burgdorferi genome. The bipA locus was amplified and sequenced from 39 isolates of B. hermsii that had been acquired from western North America. bipA was also expressed as a recombinant fusion protein. Serum samples from mice and patients infected with B. hermsii or B. burgdorferi were used to confirm the immunogenicity of the recombinant protein in patients infected with relapsing fever spirochetes. Lastly, in silico and experimental analysis indicated that BipA is a surface-exposed lipoprotein in B. hermsii. These findings enhance the capabilities of diagnosing infection with relapsing fever spirochetes.

Effects of adeno-tonsillectomy on polysomnography patterns in Down syndrome children with obstructive sleep apnea: a comparative study with children without Down syndrome.

OBJECTIVE: To determine if adeno-tonsillectomy (T&A) in children with Down syndrome (DS) improves breathing, measured by apnea hypopnea index (AHI), rapid eye movement AHI (REM-AHI) and the lowest oxygen desaturation (SaO2), and sleep disruption, measured by arousal index (ArI) and time spent in stages 1-4 and rapid eye movement (REM) sleep and compare these results with a group of non-DS children with obstructive sleep apnea (OSA). STUDY DESIGN: Retrospective chart review at pediatric sleep center. PATIENTS: Eleven DS and nine non-DS children underwent pre- and post-T&A polysomnography between 1997 and 2005. OUTCOME MEASURES: Pre- and post-T&A polysomnography parameters were compared using paired t-test and independent samples test. RESULTS: Mean age in DS group was 101 months and non-DS group was 80 months (64% males in DS and 88% in non-DS group). The average BMI was 29.8 and 27.6 for DS and non-DS group. The total AHI showed significant improvement after T&A but this was not as marked as the non-DS group. REM-AHI and lowest SaO2 did not show significant change in the DS children. The non-DS group showed significant improvement in all respiratory parameters. Both groups showed mild improvement in sleep parameters. With the modest overall improvement, 27% of the DS children required no further treatment. However, 73% required CPAP, BiPAP or oxygen for persistent OSA. CONCLUSION: This study supports the fact that T&A in DS children improves some parameters of OSA, however not as markedly as in non-DS children.

Tick-borne relapsing fever and Borrelia hermsii, Los Angeles County, California, USA.

The primary cause of tick-borne relapsing fever in western North America is Borrelia hermsii, a rodent-associated spirochete transmitted by the fast-feeding soft tick Ornithodoros hermsi. We describe a patient who had an illness consistent with relapsing fever after exposure in the mountains near Los Angeles, California, USA. The patient's convalescent-phase serum was seropositive for B. hermsii but negative for several other vector-borne bacterial pathogens. Investigations at the exposure site showed the presence of O. hermsi ticks infected with B. hermsii and the presence of rodents that were seropositive for the spirochete. We determined that this tick-borne disease is endemic to the San Gabriel Mountains near the greater Los Angeles metropolitan area.

Identification of conserved antigens for early serodiagnosis of relapsing fever Borrelia.

Borrelia hermsii is a blood-borne pathogen transmitted by the argasid tick Ornithodoros hermsi. Since spirochaete clearance in mice is associated with an IgM-mediated response, an immunoproteomic analysis was used to identify proteins reactive with IgM. We report that IgM from both mice and human patients infected with B. hermsii not only reacted with the previously identified variable membrane proteins but also identified candidate antigens including heat-shock proteins, an adhesin protein, ABC transporter proteins, flagellar proteins, housekeeping proteins, an immune evasion protein, and proteins with unknown function. Furthermore, IgM reactivity to recombinant glycerophosphodiester phosphodiesterase was detected during early spirochaete infection and prior to a detectable IgG response. Lastly, a conserved hypothetical protein was produced in Escherichia coli and tested with immune serum against B. hermsii and Borrelia recurrentis. These results identify a much larger set of immunoreactive proteins, and could help in the early serodiagnosis of this tick-borne infection.

Characterization of a novel relapsing fever spirochete in the midgut, coxal fluid, and salivary glands of the bat tick Carios kelleyi.

Bat ticks, Carios kelleyi, from Iowa were examined for the presence of relapsing fever group borreliae. A novel spirochete was characterized by DNA sequence analysis of polymerase chain reaction amplicons for the 16S rRNA, flaB, and glpQ genes in either triturated tick pools or single ticks. All loci and the concatenated DNA sequence of 3,289 bases identified the Carios bacterium as a relapsing fever spirochete most closely related to, but distinct from, Borrelia turicatae. Spirochetes reactive with a Borrelia-specific monoclonal antibody were observed microscopically in the coxal fluid and salivary glands from one tick. These data confirm the presence of a novel species of relapsing fever spirochete in bat ticks and the potential for new enzootic foci for endemic relapsing fever that warrants further investigation. The name Borrelia johnsonii is proposed for this novel spirochete in honor of Dr. Russell C. Johnson.

Outer surface protein A protects Lyme disease spirochetes from acquired host immunity in the tick vector.

The Lyme disease spirochete Borrelia burgdorferi alters the expression of outer surface protein (osp) genes as the bacterium cycles between ticks and mammals. OspA is produced as borreliae enter the tick vector and remains a major surface antigen during midgut colonization. To elucidate the role of OspA in the vector, we created an insertional deletion of ospA in strain B31-A3. The ospA mutant infects mice when it is injected intradermally and is acquired by larval ticks fed on these mice, where it persists through the molt to the nymph stage. Bacterial survival rates in artificially infected tick larvae fed on naïve mice were compared with those in the vector fed on immune mice. The ospA mutant proliferates in larvae if it is exposed to blood from naïve mice, but it declines in density after larval feeding if the blood is from immune mice. When uninfected larvae are fed on B-cell-deficient mice infected with the ospA mutant, larvae show borrelial densities and persistence that are significantly greater than those fed on infected, immunocompetent mice. We conclude that OspA serves a critical antibody-shielding role during vector blood meal uptake from immune hosts and is not required for persistence in the tick vector.