Jaw-Opening Force as a Useful Index for Dysphagia: A Cross-Sectional and Multi-Institutional Study.

INTRODUCTION: Jaw-opening force (JOF) can be a potential screening tool for dysphagia. However, confounding variables such as comorbidities or physical and oral functions that are associated with the physiology of swallowing have not previously been examined. Adjusting for these variables could reveal the relationship between JOF and dysphagia and indicate whether JOF is an independent factor associated with dysphagia. We therefore aimed to assess the efficacy of using JOF for dysphagia screening in this multi-institutional study. METHODS: Community-dwelling older adults over the age of 65 years (N = 403) who visited the university dental hospitals and participated in health surveys (mean age ± standard deviation, 77.1 ± 7.0 years; range, 65-96 years) between November 2018 and January 2020 were included in this study. The JOFs of all participants were measured. The measured JOF was compared with the presence of dysphagia, which was defined using the Functional Oral Intake Scale and the Eating Assessment Tool-10. RESULTS: Multiple logistic regression analysis revealed that the presence of dysphagia was independently associated with JOF, calf circumference, and dependence after adjusting for age and sex. DISCUSSION/CONCLUSION: Decreased JOF can be a risk factor for dysphagia in older adults.

Effects of Tablet Size and Head Posture on Drug Swallowing: A Preliminary Examination Using Endoscopy in Healthy Subjects.

Tablet size and head posture have been reported to affect swallowing of medications, but no previous studies have evaluated their effects in detail. Our aim was to investigate for the first time the effect of tablet size and head posture on drug swallowing by endoscopic evaluation in healthy subjects. Round tablets (7 , 10 , 12, and 14 mm in diameter) were swallowed by 15 healthy adults with an endoscope inserted in the neutral, head flex-ion, and head extension positions. Evaluation of swallowing difficulty using a numeric rating scale (NRS), presence or absence of pharyngeal residue and its location, and tablet oral transit time (TOTT) were recorded. In the neutral position, the NRS score was higher with the 14 mm tablets than with the 7 mm tablets. The TOTT with the 7 mm tablets was significantly shorter in the head extension than in the neutral position. Swallowing difficulty increased when the tablet diameter was more than 7 mm. Residues were found in the epi-glottis, pyriform sinus, and tongue base. These findings suggest that head extension shortens the TOTT and assists oral-pharyngeal transport.

Nutritional intervention after an early assessment by a flexible endoscopic evaluation of swallowing is associated with a shorter hospital stay for patients with acute cerebral infarction: A retrospective study.

BACKGROUND AND OBJECTIVES: It is important to evaluate the swallowing function of patients with acute cerebral infarction. The effects of nutritional intervention after an early assessment by a flexible endoscopic evaluation of swallowing (FEES) were evaluated. METHODS AND STUDY DESIGN: This retrospective study included 274 patients who were hospitalized for acute cerebral infarction and underwent a FEES between 2016 and 2018. The effects of early nutritional intervention after an assessment by a FEES within 48 h from admission were evaluated. The patients were divided into a shorter hospital stay group (<30 days) and a longer group (≥30 days). A multivariate analysis was performed to identify the predictive factors for a shorter hospital stay. RESULTS: The overall patient characteristics were as follows: 166 men; median age, 81 years old; and median body mass index (BMI), 21.1 kg/m2. No significant differences in the age, sex, or BMI were found between the shorter and longer hospital stay groups. A FEES within 48 h of admission (odds ratio [OR], 2.040; 95% confidence interval [CI], 1.120-3.700; p=0.019), FILS level ≥6 at admission (OR, 2.300; 95% CI, 1.190-4.440; p=0.013), and an administered energy dose of ≥18.5 kcal/kg on hospital day 3 (OR, 2.360; 95% CI, 1.180-4.690; p=0.015) were independently associated with a hospital stay <30 days. CONCLUSIONS: Patients with acute cerebral infarction are more likely to have a shorter hospital stay (<30 days) if they undergo a FEES early after admission and receive optimal nutritional intervention.

Risk of Delayed Healing of Tooth Extraction Wounds and Osteonecrosis of the Jaw among Patients Treated with Potential Immunosuppressive Drugs: A Retrospective Cohort Study.

Bone-modifying or antiresorptive agents that target osteoclasts, such as bisphosphonates, are known to cause delayed wound healing and osteonecrosis of the jaw (ONJ) following tooth extraction. However, there are no data on whether such adverse events are also caused by drugs that may suppress the immune system, including corticosteroids, immunosuppressants, biological agents, and disease-modifying anti-rheumatic drugs (DMARDs). The aim of this retrospective study was to examine the incidence of delayed post-extraction wound healing and identify risk factors among patients treated with potential immunosuppressive drugs undergoing tooth extraction. We performed a retrospective cohort study involving 101 patients by reviewing their medical records. The underlying diseases of the enrolled patients included dilated cardiomyopathy, hematological malignancy, sarcoidosis, rheumatoid arthritis, and systemic lupus erythematosus. The sample comprised 131 cases of tooth extraction among the 101 patients; delayed post-extraction wound healing occurred in 10 patients (12 cases, 9.2%), including ONJ in three patients (3 cases, 2.3%). The surgical tooth extraction performed for impacted teeth or a residual root (P = 0.009), the number of surgical tooth extraction (P = 0.012), decreased lymphocyte counts (P = 0.008), and decreased eosinophil counts (P = 0.009) were significantly related to delayed wound healing. Thus, among patients taking corticosteroids, immunosuppressants, biological agents, and/or DMARDs, there is a risk of delayed wound healing and ONJ. Moreover, the significant risk factors are low lymphocyte counts, low eosinophil counts, and surgical extraction. It is of particular importance to prevent surgical site infection, when the high-risk patients undergo tooth extraction.

Measurement of Pharyngo-laryngeal Volume During Swallowing Using 320-Row Area Detector Computed Tomography.

This study aimed to (1) evaluate changes in bolus and air volumes in the pharyngo-laryngeal cavity during swallowing and (2) determine how differences in these volumes during swallowing are influenced by bolus amount using 320-row area detector computed tomography (320-ADCT). Three-, 10-, and 20-ml honey-thick liquids (5% w/v) were presented to ten healthy subjects placed in a 45° reclining position. 3D images were created in 29 phases at an interval of 0.1 s for 3.15 s. Changes in bolus and air volumes in the pharyngo-laryngeal cavity were calculated. The two one-sided tests were used to determine equivalency of the pharyngo-laryngeal volume of each event (i.e., onset of hyoid elevation, soft palate closure, true vocal cord closure, closure of laryngeal vestibule, epiglottis inversion, pharyngo-esophageal sphincter opening) for each bolus volume. The pharyngo-laryngeal volume during swallowing was about 20 ml before swallowing. The volume temporarily increased with tongue loading, but decreased to about 0 ml with pharyngeal contraction. Subsequently, the volume returned to the original volume after airway opening. Most of the air was released from the pharyngo-laryngeal space before the bolus flowed into the esophagus during swallowing. As the bolus volume to be swallowed increased, the maximal pharyngo-laryngeal volume increased, but changes in air volume remained constant. 320-ADCT allowed for analysis of dynamic volume changes in the pharyngo-laryngeal cavity, which will increase our knowledge of kinematic and volumetric mechanisms during swallowing.

Jaw-opening force test to screen for Dysphagia: preliminary results.

OBJECTIVE: To assess the jaw-opening force test (JOFT) for dysphagia screening. DESIGN: Criterion standard. SETTING: University dental hospital. PARTICIPANTS: Patients complaining of dysphagia (N=95) and with symptoms of dysphagia with chronic underlying causes (mean age ± SD, 79.3±9.61y; range, 50-94y; men: n=49; mean age ± SD, 77.03±9.81y; range, 50-94y; women: n=46; mean age ± SD, 75.42±9.73y; range, 51-93y) admitted for treatment between May 2011 and December 2012 were included. INTERVENTIONS: None. MAIN OUTCOME MEASURES: All patients were administered the JOFT and underwent fiberoptic endoscopic evaluation of swallowing (FEES). The mean jaw-opening strength was compared with aspiration (ASP) and pharyngeal residue observations of the FEES, which was used as the criterion standard. RESULTS: A receiver operating characteristic (ROC) curve analysis was performed. Forces of ≤3.2kg for men and ≤4kg for women were appropriate cutoff values for predicting ASP with a sensitivity and specificity of .57 and .79 for men and .93 and .52 for women, respectively. Based on the ROC analyses for predicting pharyngeal residue, forces of ≤5.3kg in men and ≤3.9kg in women were appropriate cutoff values, with a sensitivity and specificity of .80 and .88 for men and .83 and .81 for women, respectively. CONCLUSIONS: The JOFT could be a useful screening tool for predicting pharyngeal residue and could provide useful information to aid in the referral of patients for further diagnostic imaging testing. However, given its low sensitivity to ASP the JOFT should be paired with other screening tests that predict ASP.

Aging decreases the strength of suprahyoid muscles involved in swallowing movements.

Swallowing disorders are common in the elderly, and aging is a factor that affects swallowing function. The elevation of the hyoid bone is important for swallowing and is controlled by the suprahyoid muscles. The hyoid and laryngeal elevation allows the bolus to enter the esophagus. The suprahyoid muscles, therefore, play an important role in swallowing. The effects of aging on suprahyoid muscle strength are unclear. In this study, we analyzed the effects of aging on suprahyoid muscle strength by comparing the jaw opening functions of healthy adults and elderly adults. The subjects were 150 healthy volunteers consisting of 76 adults aged < 70 years (38 men and 38 women; mean age, 48.8 ± 13.8 years; range, 23-69) and 74 elderly adults aged > 70 years (37 men and 37 women; mean age, 78.1 ± 4.8 years; range, 70-92). The jaw opening force (JOF) was measured with a jaw opening sthenometer and compared between the healthy adult and elderly groups. The mean JOF of healthy adults was about 10 kg in men and about 6 kg in women, which was significantly greater than the mean JOF of the healthy elderly subjects (about 7 kg in men and about 4 kg in women). The JOF of the men was significantly greater than that of the women in the healthy adult and elderly groups. We thus propose that aging decreases the strength of suprahyoid muscles in healthy adults. The swallowing function may decrease even in healthy adults, aged over 70 years.

Kinematics of lateral tongue-pushing movement in coordination with masticatory jaw movement: An anteroposterior projection videofluorographic study.

OBJECTIVE: During the mastication of solid food, the tongue pushes the bolus laterally to place it onto occlusal surfaces as the jaw is opened. This movement is referred to as tongue-pushing (TP). TP has an important role in efficient chewing, but its kinematic mechanisms remain unclear. The present study quantified the kinematics of TP and its coordination with masticatory jaw movements. METHODS: Videofluorography (VFG) in anteroposterior projection was recorded while 14 healthy young adults ate 6 g each of cookies and meat. Small lead markers were glued to the tongue surface (left, right, and anterior) and buccal tooth surfaces (upper molars and lower canines). The position of the tongue and lower canine markers relative to the upper occlusal plane was quantified with Cartesian coordinates, using the right upper molar as the origin. Jaw motion during chewing was divided into TP and Non-TP cycles, based on the lateral movement of the food and tongue markers. The side of the jaw that compressed food particles was defined as the working side, while the other side was termed the balancing side. Horizontal and vertical displacements of tongue and jaw markers were compared between TP and Non-TP cycles, as well as between food types. RESULTS: The mediolateral displacement of all tongue markers was significantly larger in TP than in Non-TP cycles. Vertical displacement was also significantly greater in TP than in Non-TP cycles for the anterior and working side tongue markers. TP cycles occurred more frequently with meat-chewing than with cookie-chewing. CONCLUSION: TP is accomplished by rotation and lateral movements of the tongue surface on the working side and the anterior tongue blade, along with medial movement on the balancing side. These movements produce lateral shift and rotation of the tongue surface toward the working side in concert with jaw opening. Designing exercises to improve the strength of the lateral motion and rotation of the tongue body may be useful for individuals with impaired tongue function for eating and swallowing.

Simplified cough test for screening silent aspiration.

OBJECTIVE: To simplify the cough test to screen silent aspiration without sacrificing accuracy. DESIGN: Criterion standard. SETTING: University dental hospital. PARTICIPANTS: Consecutive patients (N=141; 92 men, 49 women; mean age 71±14y, range 23-94y) who had complained of some dysphagic symptoms between June 2008 and February 2010. INTERVENTIONS: All patients were administrated a simplified cough test and underwent the fiberoptic endoscopic evaluation of swallowing. Citric acid inhalation was terminated when the first cough occurred, and the time between the start of inhalation and the first cough was measured. MAIN OUTCOME MEASURES: The time when the first cough was observed by the simplified cough test was compared with the results of the fiberoptic endoscopic evaluation of swallowing, which was used as a criterion standard. RESULTS: Receiver operating characteristic curve analysis was performed for 53 patients evaluated as having aspiration by fiberoptic endoscopic evaluation of swallowing. We found that 30 seconds or less was an appropriate cutoff value for detecting patients without silent aspiration, where the sensitivity was .92 and the specificity was .94. From the receiver operating characteristic curve analyses for all patients, 60 seconds or less was determined to be an appropriate cutoff, and the sensitivity and specificity were .81 and .65, respectively. CONCLUSION: The simplified cough test is a useful screening tool for silent aspiration in patients with aspiration.

Jaw-opening exercise for insufficient opening of upper esophageal sphincter.

OBJECTIVE: To investigate the effects of the jaw-opening exercise on decreased upper esophageal sphincter (UES) opening while swallowing. DESIGN: Intervention study: before-after trial with 4-week follow-up evaluation. SETTING: A university school of dentistry dental hospital. PARTICIPANTS: Patients with dysphagia (N=8; 7 men, 1 woman; average age ± SD, 70.5±11.3y; age range, 54-86y). INTERVENTIONS: All patients performed a jaw-opening exercise to strengthen the suprahyoid muscles. The exercise involved opening the jaw to its maximum and maintaining this position for 10 seconds. Each exercise set consisted of 5 repetitions, and 2 sets were carried out daily for 4 weeks. The effectiveness of the exercise was evaluated by a videofluorographic swallowing study (VFSS). MAIN OUTCOME MEASURES: Hyoid elevation, UES opening, pharynx passage time, and pharyngeal residue after swallowing at preexercise and postexercise were compared by VFSS. RESULTS: Compared with before starting the exercise, significant improvements were observed in the extent of upward movement of the hyoid bone (P<.05), the amount of UES opening (P<.05), and the time for pharynx passage (P<.05) 4 weeks after initiating the exercise. Pharyngeal residue decreased in some subjects, and no increases were noted in any subjects. CONCLUSIONS: The jaw-opening exercise is an effective treatment for dysphagia caused by dysfunction of hyoid elevation and UES opening.

Effect of masticatory training using confectioneries on oral function in elderly patients - A randomized controlled trial.

Background/purpose: The number of patients with oral hypofunction is increasing with the aging of the population, and such hypofunction increases their risk for dysphagia and malnutrition. The purpose of this study was to measure the hardness of commercially available confectioneries, select a confectionery with a hardness suitable for masticatory training for elderly patients, and evaluate the effects of 1-week masticatory training on oral function (occlusal force, masticatory ability, and tongue pressure). Materials and methods: The average hardness values of 25 confectioneries were determined. Among them, one of the softest confectioneries that the patients felt as "chewable but difficult to chew" was selected as the training confectionery for each patient. The patients in the training group continued training, which involved eating of approximately 5 g of one selected confectionery daily for 7 days. The patients in the control group did not undergo any training. Oral function (occlusal force, masticatory ability, and tongue pressure) on the first day and after 7 days was evaluated and compared between the groups. Results: The occlusal force of the patients in the training group increased significantly. However, their masticatory ability and tongue pressure did not change significantly. Conclusion: Patients aged 65 years and older underwent masticatory training, which involved eating of a confectionery with its hardness adjusted individually for a week. A significant increase in the occlusal force was observed, suggesting that masticatory training using confectioneries with a hardness suitable for each patient is effective.

Analysis of intravenous sedation for dental treatment in elderly patients with severe dementia-a retrospective cohort study of a Japanese population.

BACKGROUND/PURPOSE: Patients with severe dementia require intravenous sedation during dental treatment. However, few reports have compared the outcomes of intravenous sedation management among sedatives. Intravenous sedation in the elderly with severe dementia undergoing dental treatment was evaluated retrospectively. MATERIALS AND METHODS: Patients' characteristics and type of dementia were obtained from medical records. Midazolam (MID), dexmedetomidine (DEX), and propofol (PRO) were administered as sedatives. The systolic blood pressure (SBP), heart rate (HR), SpO2, bispectral index (BIS) values and complications were evaluated. RESULTS: Nineteen patients with severe dementia who underwent 62 instances of sedation were included. There was no difference in patient background between sedatives. The sedation time and permission time to return home were significantly longer in DEX than in MID or PRO group. Half the usual dose in MID and lower limits of the routine dose was effective in DEX and PRO. HR was significantly lower in DEX group. There were 3 cases with airway obstruction requiring nasopharyngeal airway and 4 cases of apnea when MID was administered. Two cases of Cheyne-Stokes-like respiration when MID or DEX was administered. SpO2 <94% was found in 22 cases (35%) irrespective of the sedative. A patient with dementia with Lewy bodies had experienced hallucinations during the recovery period after sedation when MID or DEX was administered. The BIS value of ≤80 was noted during complications. CONCLUSION: Intravenous sedation for dental treatment in the elderly with severe dementia, needs a dose titration. All sedatives had respiratory-related complications which mandate close monitoring.

Comparison of intravenous sedation using midazolam during dental treatment in elderly patients with/without dementia: a prospective, controlled clinical trial.

The effects of intravenous sedation with midazolam on the cerebral function of elderly patients with severe dementia are unclear. This study aimed to evaluate its effects on parameters such as brainwaves and cerebral blood flow (CBF) and compare them between elderly individuals with dementia and without cognitive impairment. Ten patients with severe dementia and 10 without cognitive impairment were registered. The bispectral index (BIS) and normalized tissue hemoglobin index (nTHI), which reflects CBF using near-infrared spectroscopy, were measured. Midazolam was administered until a Modified Observer's Assessment of Alertness/Sedation score of 2 was reached. The chi-squared, Mann-Whitney U, Wilcoxon signed-rank, and Friedman tests and multiple regression analysis were used for comparisons. Whereas a similar decline in BIS values was observed in both groups after midazolam administration (P < 0.018), there was a significant decrease by 9% in the nTHI of the dementia-positive group (P < 0.013). However, there was no significant difference in the nTHI between the dementia-positive and dementia-negative group according to the multiple regression analysis (P = 0.058). In the dementia-negative group, none of the measured values differed from the baseline values. In the dementia-positive group, sedation with midazolam resulted in a 9% decrease in the CBF.

Changes in localized arrangement into the hypoglossal nucleus after the neurectomy of unilateral hypoglossal nerve (medial branch) in cats.

We studied changes in orofacial behavior and the arrangement of bilateral hypoglossal nuclei after the neurectomy of the medial branch of the unilateral hypoglossal nerve in cats. After recovery from surgery in a head holder, the animals were acclimated to take and chew fish paste (1.8 g) from a spoon and lick milk from a wetted paintbrush. Next we performed a neurectomy in the unilateral hypoglossal nerve after training. We firstly recorded behavior during the taking of fish paste and licking of milk, and then performed a neurectomy in the unilateral hypoglossal nerve. After nerve cutting, the cats' tongue deviated toward the cut side when they licked food, and bilateral activities of EMGs in the genioglossus muscles became stable in about 1 month. After that, we injected two kinds of fluorescent dye (10% Evans blue, EB, and 3% Fast blue, FB) into the bilateral genioglossus muscles using syringes (0.15 ml in each), respectively. Although each injection of FB and EB into the bilateral genioglossus muscles in normal cats revealed cells positively stained with each dye in the hypoglossal nuclei of each injection site, in cats 1 month after nerve cutting, fluorescent dye was only observed in positive cells in the hypoglossal nucleus of the intact side and the dye injected into the neurectomy side showed a mixture into positive cells of the intact side. The findings suggest that muscles in the neurectomy side may be compensated by regeneration of the peripheral nerves on the intact side.

[Dysphagia rehabilitation in visiting home care].

Dysphagia can cause aspiration pneumonia. The condition of dysphagia is difficult to evaluate from outside. Therefore, a careful examination is necessary to grasp the state of swallowing of a patient accurately. However, it has been a difficult situation for a patient who cannot come to hospital for some reason to be examined by video fluoroscopy or video endoscopy. In recent years, a usefulness of video endoscopy in visiting home examination for dysphagia has been reported several times. And this video endoscopy examination is a valuable tool to detect a discrepancy between swallowing function and nutritional intake of the patient. Cooperative rehabilitation with such a careful examination is an important issue to be successful in dysphagia rehabilitation.

Effects of preoperative oral carbohydrate intake on catabolism, nutrition and adipocytokines during minor surgery: A randomized, prospective, controlled clinical phase II trial.

BACKGROUND: We investigated the effects of preoperative oral carbohydrate loading on intraoperative catabolism, nutritional parameters, and adipocytokine levels during anesthesia. METHODS: Study participants were randomized to two groups who were allowed to consume either no more than 250 mL of 18% oral carbohydrate solution (Arginaid Water: AW group) or no more than 500 mL of plain water (PW group) within the 2 hours before surgery, with no intraoperative glucose administration. Percentage changes from preoperative values of resting metabolic rate (RMR) and total body water (TBW), determined by bioelectrical impedance analysis (BIA), were compared. Blood levels of serum ketone bodies, free fatty acids (FFAs), insulin, 3-methyl histidine, blood glucose, retinol binding protein, adiponectin, and leptin were measured. BIA measurement and blood sampling were performed on entry to the operating room (M1) and 2 hours after the induction of anesthesia (M2). Chi squared test, Mann-Whitney U test, and Wilcoxon's test were used for comparisons of parameters. P values less than 0.05 constituted a significant difference. RESULTS: Seventeen patients per group (34 patients total) were enrolled. RMR and TBW values did not differ between M1 and M2 measurements. Participants in the AW group had lower blood ketone body and FFA levels and higher insulin levels at M1. However, their ketone body and FFA levels rose and insulin levels fell after 2 hours, although ketone body and FFA levels in the AW group were still lower than those in the PW group. Although retinol binding protein, adiponectin, and leptin levels were not different in terms of preoperative oral carbohydrate loading, the levels of these substances in both groups were lower after 2 hours compared with levels on operating room entry. CONCLUSIONS: Preoperative oral carbohydrate loading without intraoperative glucose administration appears to suppress catabolism for 2 hours after the start of surgery.

Evaluation of Pharyngoesophageal Segment Using 320-Row Area Detector Computed Tomography.

OBJECTIVES:: The aim of this study was to determine the shape and area of the pharyngoesophageal segment (PES) during swallowing using 320-row area detector computed tomography, which can acquire a volume data set covering a 16-cm area in a single rotation. METHODS:: Twenty healthy subjects were scanned during swallowing 3, 10, and 20 mL of honey-thick barium (5% w/v). PES was identified using cross-sectional images of 0.5-mm slice thickness, and the area in each section was measured. RESULTS:: The PES opening area and the anteroposterior and lateral diameters of the PES were volume dependent. However, there was no statistical difference in anteroposterior and lateral diameters between 3- and 10-mL bolus swallowing. CONCLUSIONS:: Three hundred twenty-row area detector computed tomography provided new information about PES. This technique will facilitate further understanding of the mechanisms of PES opening and swallowing physiology.

Endotoxic properties of lipid A from Comamonas testosteroni.

The lipid A from Comamonas testosteroni has been isolated and its complete chemical structure determined [Iida, T., Haishima, Y., Tanaka, A., Nishijima, K., Saito, S. & Tanamoto, K. (1996). Eur J Biochem 237, 468-475]. In this work, the relationship between its chemical structure and biological activity was studied. The lipid A was highly homogeneous chemically and was characterized by the relatively short chain length (C(10)) of the 3-hydroxy fatty acid components directly bound to the glucosamine disaccharide backbone by either amide or ester linkages. The lipid A exhibited endotoxic activity in all of the assay systems tested (mitogenicity in mouse spleen cells; induction of tumour necrosis factor alpha release from both mouse peritoneal macrophages and mouse macrophage-like cell line J774-1, as well as from the human monocytic cell line THP-1; induction of nitric oxide release from J774-1 cells; Limulus gelation activity and lethal toxicity in galactosamine-sensitized mice) to the same extent as did 'Salmonella minnesota' lipid A or Escherichia coli LPS used as controls. The strong endotoxic activity of the C. testosteroni lipid A indicates that the composition of 3-hydroxydecanoic acid is not responsible for the low endotoxicity of the lipid A observed in members of the genus Rhodopseudomonas, as has previously been suggested. Furthermore, both the lack of a second acylation of the 3-hydroxy fatty acid attached at the 3' position, and the substitution of the hydroxyl group of the 3-hydroxy fatty acid attached at position 2, do not affect the manifestation of endotoxic activity or species specificity.