6. Digital Reconstructions of Sauropod Dinosaurs and Implications for Feeding

The study of modularity can provide a foundation for integrating development into studies of phenotypic evolution. The dentition is an ideal phenotype for this as it is developmentally relatively simple, adaptively highly significant, and evolutionarily tractable through the fossil record. Here, we use phenotypic variation in the dentition to test a hypothesis about genetic modularity. Quantitative genetic analysis of size variation in the baboon dentition indicates a genetic modular framework corresponding to tooth type categories. We analyzed covariation within the dentitions of six species of Old World monkeys (OWMs) to assess the macroevolutionary extent of this framework: first by estimating variance-covariance matrices of linear tooth size, and second by performing a geometric morphometric (GM) analysis of tooth row shape. For both size and shape, we observe across OWMs a framework of anterior and postcanine modules, as well as submodularity between the molars and premolars. Our results of modularity by tooth type suggest that adult variation in the OWM dentition is influenced by early developmental processes such as odontogenesis and jaw patterning. This study presents a comparison of genotypic modules to phenotypic modules, which can be used to better understand their action across evolutionary time scales.

To explore the effects of head and neck posture training on the electrical activity of the temporalis and masseter muscles in patients with myogenic temporomandibular disorder(TMD) under different head and neck postures. Fourteen patients with TMD who attended Hainan West Central Hospital from July 2022 to February 2023 with presence of head forward posture were selected for the study. All patients received head and neck posture training for 4 weeks, 2-3 times per week for 30 min each time. Changes in the electrical activity of bilateral temporalis and masseter muscles were compared between pre- and post-intervention patients in the natural relaxed position, the teeth lightly touching position, and the neutral head and neck position. Mandibular function, pain intensity, and maximal pain-free mouth opening were assessed for pre- and post-comparisons. In TMD patients, the electromyographic amplitude of the anterior fasciculus of the left temporalis muscle and the right masseter muscle was higher in the natural relaxed position than in the neutral head and neck position (3.4±1.4 vs. 2.5±1.0, 2.4±1.6 vs. 1.8±1.1, P＜0.05). After head and neck posture training, the patients had lower basal EMG amplitudes of bilateral temporalis and left masseter muscles in the natural relaxed position and the neutral head and neck position compared with the pre-treatment position, and the mandibular function scores and pain were significantly improved(P＜0.05). Different head and neck postures can affect the basal electromyographic amplitude of the masticatory muscles in patients with myogenic TMD, and postural training can effectively relax the temporalis and masseter muscles in patients with TMD, resulting in pain reduction and promoting functional recovery.

Ring gantry radiotherapy devices are often limited to deliver beams in the axial plane, severely limiting beam entrance angles and rendering noncoplanar beam delivery impossible. However, a ring gantry geometry greatly simplifies delivery machines and increases the efficiency of treatment with the potential to decrease the overall costs of radiotherapy. This study explores the use of lateral head flexion in order to increase beam entrance angles and extend the available solid angle space for a ring gantry stereotactic radiosurgery (SRS) application. A 1.5T magnetic resonance imaging scanner was used to scan seven healthy volunteers at three different head positions: a neutral position, a left lateral flexion position and a right lateral flexion position. The lateral flexion scans were co-registered to the neutral head position scan using rigid registration and extracting the rotational transformation. The head pitch, roll, and yaw were computed for each registration to evaluate the natural range of motion for all volunteers. A ring gantry plan geometry was used to generate two sets of single fraction SRS plans (21Gy): one coplanar set for head neutral scans, and a three-arc plan set using the head neutral and lateral head flexion scans. The conformity index (CI), intermediate dose fall-off (R50), low dose spillage (R10), and gradient measure (GM) were used to evaluate both sets of plans. The treatment plans were generated for a ring-gantry linear accelerator (linac) (Varian Halcyon 2.0) as well as radiosurgery linac (Varian Edge) for comparison. The average pitch, yaw, and roll for the lateral head flexion scans were 4.1°±4.7°, 16.9°±3.7°, and 2.5°±4.9° for the right flexion and 4.9°±4.3°, 14.0°±3.7° and 2.8°±5.4° for left flexion. When comparing the head flexion technique with a fully coplanar geometry, the ring gantry plans showed an average improvement in CI of 7.3% (1.46±0.25 vs 1.36±0.28), a decrease of 13% in R50 (5.46±1.14 vs 4.78±1.12), a decrease of 32% in R10 (85.7±20.3 vs 58.2±15.1), and a decrease of 7.8% in GM (0.53±0.05 vs 0.49±0.04). The Edge plans showed an average improvement in CI of 3.0% (1.49±0.26 vs 1.45±0.25), a decrease of 6.8% in R50 (5.19±1.03 vs 4.82±0.83), a decrease of 29% in R10 (84.1±16.3 vs 59.9±12.5), and a decrease of 5.0% in GM (0.50±0.04 vs 0.47±0.03). Lateral head flexion was shown to increase beam entrance angles considerably improving plan conformity and normal tissue sparing in this pilot study of seven sets of plans. Rigid registrations demonstrated each lateral flexion to be analogous to a 15° couch kick. The head flexion technique outlined here was shown to be a feasible solution for SRS treatments being delivered on ring gantry devices.

Conjunctival swelling is a common finding in patients positioned prone. The purpose of this study was to evaluate the effect of head position on postoperative chemosis after prone spinal surgery. On the basis of the head position, 108 patients scheduled for prone lumbar surgery were randomly allocated to 1 of 2 groups: head neutral group (n=54) versus head down (HD) group (n=54). Head position was defined as neutral when the imaginary line from the occipital protuberance to the top of C7 spine process is parallel to the operating table. HD position was maintained by adjusting the height of the prone headrest 5 cm lower than neutral position. Chemosis was evaluated after surgery. The severity of chemosis, which was graded as none, mild, moderate, and severe, showed statistically significant difference between the head neutral group [24 (44%), 25 (46%), 3 (6%), 2 (4%), respectively] and HD group [10 (19%), 23 (43%), 17 (31%), 4 (7%), respectively, P<0.01]. Positive fluid balance and duration of surgery were risk factors for the development of postoperative chemosis. This result suggested that neutral head position, smaller fluid administration, and shorter duration of surgery were useful in decreasing the development of postoperative chemosis after prone spinal surgery.

Purpose: Effective face mask ventilation is a life-saving skill. Loss of muscle tone under general anesthesia may lead to tongue fall and pharyngeal collapse and reduce the efficiency of face mask ventilation. It has been suggested that lateral head rotation may improve the efficiency of face mask ventilation. The aim of this study was to compare face mask ventilation in neutral and head-rotated positions in adult patients under general anesthesia. Methods: This randomized crossover study was conducted on 42 patients of both genders, aged 18–60 years, who were randomly assigned to group NRN (face mask ventilation performed in neutral–rotated–neutral head positions for one minute each) and group RNR (face mask ventilation performed in rotated–neutral–rotated head positions for one minute each). The primary outcome was the expired tidal volume (VTE) measured in both head positions during pressure control mode of ventilation with a peak inspiratory pressure of 15 cmH2O. Secondary outcomes included the number of patients with airway obstruction or low VTE during mask ventilation and the effects of age, height, Mallampati class, and airway obstruction or low VTE on VTE in the head-rotated position. Results: The mean VTE was significantly higher in the neutral position (637.93 ± 186.62 ml) compared to the head-rotated position (625.30 ± 183.52 ml) (p = 0.036). The VTE was comparable in group NRN and group RNR in neutral (p = 0.455) and head-rotated positions (p = 0.464). The incidence of airway obstruction was similar in both positions and no patient had low VTE during mask ventilation. Age, height, Mallampati class, and airway obstruction or low VTE in neutral position had no effect on VTE in the head-rotated position. Conclusion: There was a significant decrease in the VTE in the rotated head position compared to the neutral head position during mask ventilation in patients under general anesthesia.

Effect of Different Head Positions in Lateral Decubitus Posture on Intraocular Pressure in Treated Patients With Open-Angle Glaucoma.

Head-position angles in children for opening the upper airway

The influence of different head and neck positions on ventilation with the Ambu® AuraGain™ remains unevaluated in children. This study assessed the influence of different head and neck positions on ventilation with the AuraGain™ in paediatric patients. In this prospective, randomised crossover study, children ≤7years of age who were scheduled for elective surgery under general anaesthesia were enrolled. An AuraGain™ was placed in all patients; mechanical ventilation was performed using a volume-controlled mode with a tidal volume of 10mL/kg. Respiratory rate was adjusted to maintain a ETCO2 of 35-40mmHg. The oropharyngeal leak pressure, expiratory tidal volume, peak inspiratory pressure, ventilation score and fibreoptic bronchoscopic view score were assessed for the neutral head and neck position, and then for the flexed, extended and rotated head and neck positions in a random order. Compared with the neutral position, the oropharyngeal leak pressure increased in the flexed position (P<.001), and decreased in the extended (P=.014) and rotated position (P=.002). The expiratory tidal volume and ventilation score were significantly reduced during flexion (all P<.005), and were comparable among the neutral, extended and rotated positions. The fibreoptic score improved in the extended and rotated position (all P<.001). Only the flexion ventilation score was lower compared with the neutral position (P=.014). Clinically, the flexed head and neck positions negatively affected ventilation due to obstruction of the airway. Ventilation with AuraGain™ can be effectively performed with the head and neck in the neutral, extended and rotated position in paediatric patients.

Introduction: Respiratory function is crucial in the practice of anaesthesia. An in depth understanding of respiratory physiology is a must because it aids in the proper execution of daily general anaesthesia practice. Head and body postures have long been known to affect the patency of the upper airway. Head extension and a lateral recumbent position help to clear the upper airway. Head rotation is known to expand the upper airway’s cross-sectional area. Aim: To determine the effect of head rotation on efficiency of face mask ventilation among apnoeic patients, by measuring expiratory tidal volume. Materials and Methods: This cross-sectional study was conducted in the Department of Anaesthesiology at Jawaharlal Nehru Medical College, Acharya Vinoba Bhave Rural Hospital, Sawangi, Wardha, Maharashtra, India, from May 2021 to November 2021. Total 40 patients belonging to the age group of 20 to 40 years, American Society of Anaesthesiologists’ (ASA) class I and II, undergoing surgeries requiring general anaesthesia with endotracheal intubation, were selected as study subjects. They were administered inj. fentanyl at a dose of 1 to 2 μg/kg, inj.propofol at a dose of 1 to 2 mg/kg, and inj.vecuronium bromide (0.08 to 0.1 mg/kg). Patients were mask ventilated with pressurecontrolled ventilation, for a total of 3 minutes, during which they were ventilated in a neutral head position for 90 seconds and then rotated for another 90 seconds. Following induction, the expiratory tidal volume was measured every 30 seconds in both postures Software used was Statistical Package for Social Sciences for windows (SPSS Inc., Chicago, IL, USA), version 17.0. A p-value &lt;0.05 was considered statistically significant. Results: The mean age of patients was 48±8.3 years. The 45° head rotation was beneficial to all patients, the mean expiratory tidal volume was 423±62.5 mL in the rotated head position compared to 397±52.5 mL in the neutral head position (p-value=0.045). It was also observed that some individuals profited more than others. Patients with airway obstruction, for example, had a greater VTE at 45° head rotation than in a neutral head position. Conclusion: The most notable conclusion is that in apnoeic adult patients, a 45° head rotation showed a significant enhancement in VTE when compared to a neutral position ofthe head.

An equine cadaver study investigating the relationship between cervical flexion, nuchal ligament elongation and pressure at the first and second cervical vertebra

Ventilation quality and fiber optic glottic view of AuraGain laryngeal mask in neutral, moderate, and extreme lateral head and neck positions in anesthetized spontaneously breathing children

IntroductionICU's are usually faceing increase in obese patients with deranged physiology and complex condition, with airway difficulty putting challenge to airway safety in intensive care unit. Assessment of extension capacity for occipito-atlanto-axial complex is very important component in pre-intubation test for predicting Difficult visualization of larynx in ICU.ObjectivesTo evaluate Difficult visualization of the larynx in apparently normal patients, by examining the following airway predictors Modified Mallampati test, Thyromental distance (TMD). Hyomental distance in the neutral position, Hyomental distance at the extreme of head extension, and Hyomental distance ratio.Materials and methodsPre-intubation, we assessed the five airway predictors (Modified Mallampati test, Thyromental distance, Hyomental distance in the neutral position, Hyomental distance at the extreme of head extension, and Hyomental distance ratio) in adult patients undergoing tracheal intubation. All those patients belonging to either sex between the ages of 20-60 years were included in this study. A single experienced intensivist, blinded to the results of the airway evaluation, performed all of the direct laryngoscopies and graded the views using the modified Cormack and Lehane scale. DVL was defined as a Grade 3 or 4 view.ResultsThe study done on 301 patients included 152 male (50.50%) and 149 female (49.50%) patients. The highest sensitivity 26.30% observed in predicting DVL was with HMDR (26.30%), followed by HMD at extreme head extension (14.29%), HMD at the neutral head position 10%, lowest was with TMD (9.68%). Where as the specificity in this study was relatively high. The highest specificity of was 98.48% observed in predicting DVL with HMDR, followed by HMD at the neutral position 97.15%, TMD 96.30%. and HMD at the extreme of head extension at 94.14%.DiscussionsAlthough DVL is major determinant for difficult Intubation, it is not synonymous with difficult intubation. In this study we demonstrated that HMDR is very reliable predictor of DVL to a great extent because of higher specificity and sensitivity.

Influence of head and neck position on ventilation using the air-Q® SP airway in anaesthetized paralysed patients: a prospective randomized crossover study

Can a plantar pressure–based tongue-placed electrotactile biofeedback improve postural control under altered vestibular and neck proprioceptive conditions?

BackgroundSeveral potential causes can impair balance in older people. The neck torsion maneuver may be useful in demonstrating impaired balance caused by the stimulation of cervical proprioceptive input. Whereas evidence suggests impaired standing balance in older people with chronic neck pain, balance impairment during the neck torsion position and its relationship with clinical characteristics have not yet been investigated in this population. The aims of this study were to investigate whether the neck torsion position could significantly influence balance responses in older people with chronic non-specific neck pain and to determine the relationships between the balance responses and characteristics of neck pain.MethodsSixty-eight older people (34 with chronic non-specific neck pain and 34 controls) participated in the study. Balance was tested using a force plate during comfortable stance with eyes open under four conditions: neutral head on a firm surface, neutral head on a soft surface, neck torsion to left and right on a firm surface and neck torsion to left and right on a soft surface. Balance outcomes were anterior-posterior (AP) and medial-lateral (ML) displacements, sway area and velocity. Characteristics of neck pain were intensity, duration and disability.ResultsOverall, the neck pain group exhibited greater AP and ML displacements, sway area and velocity in the neck torsion position on firm and soft surfaces compared to controls (partial eta squared (η²p) = 0.06–0.15, p < 0.05). The neck pain group also had greater AP displacement, sway area and velocity in the neutral position on a soft surface compared to controls (η²p = 0.09–0.16, p < 0.05). For both groups, the neck torsion position displayed overall greater postural sway compared to the neutral position (η²p = 0.16–0.69, p < 0.05). There were no relationships between the postural sway outcomes and characteristics of neck pain (p > 0.05).ConclusionThe neck torsion maneuver, stimulating the receptors resulted in increased postural sway in older people, with a more pronounced effect in those with neck pain. The study provides evidence supporting the use of neck torsion for assessing impaired balance related to abnormal cervical input in older people with chronic non-specific neck pain.