Three-dimensional changes in the upper airway during neuromuscular stimulation of laryngeal muscles.

During swallowing, airway protection depends upon adequate glottal closure and laryngeal elevation to prevent the entry of substances into the airway. Three-dimensional changes in the upper airway during laryngeal muscle stimulation in a canine model were quantified in animals implanted with Peterson type stimulating electrodes in the inferior and superior portions of the thyroarytenoid muscle, together with a reference electrode. Computer tomography scanning was performed on an IMATRON scanner with a 3 mm slice thickness advanced at overlapping 1 mm increments. Stimulation of the thyroarytenoid muscle produced adductions of the vocal fold towards the midline and changes in the supraglottic region as well as the glottis; the glottic wall was compressed medially above and below the glottis. These results suggest that chronic neuromuscular stimulation can effect glottic protection by reducing the glottal opening and may be beneficial for patients with central control disorders affecting airway protection during swallowing.

Polypoid lesions of airways: early experience with computer-assisted detection by using virtual bronchoscopy and surface curvature.

PURPOSE: To test the application of a technique developed by the authors for the computer-assisted diagnosis of polypoid airway lesions from surface rendered virtual bronchoscopic reconstructions. MATERIALS AND METHODS: A computer algorithm was developed to detect polypoid airway lesions by means of segmentation of the bronchial surface with curvature classification. This method was tested with a bronchial phantom, five cadaveric lung specimens, and virtual bronchoscopic studies in 16 patients. RESULTS: For the patient studies, the sensitivity and specificity of the method were 47%-88% and 58%-89%, respectively, depending on the value of an adjustable parameter (the mean curvature threshold). The sensitivity increased (by 20% to 34%) when only lesions larger than 5 mm in diameter were considered. CONCLUSION: With this method, polypoid airway lesions can be detected automatically, although false-positive diagnoses present an important limitation.

Using joint geometry to determine the motion of the cricoarytenoid joint.

Facet surfaces of the cricoarytenoid joints from two cadaver larynges were digitized. The data were used to compute the optimal axis of rotation for each of the joints in the sense that the computed axis minimized the variance of the joint gap over the full range of joint motion. The optimal axis corresponded to a rocking motion of the arytenoid on the corresponding cricoid. This motion was consistent with experimental data from digitized recordings of vocal fold movement. Using the rigid laryngoscopic view, a similarity in vocal process movement, over the range in motion, between the rocking axis and the vertical axis described in the literature was found, resolving the controversy between two conflicting views of motion of the vocal processes.

Characteristics of vocal fold adduction related to voice onset.

This study examined whether vocal fold kinematics prior to phonation differed between hard (glottal), normal, or breathy onsets in men and women. Glottal landmarks were identified and digitized from videotape recorded with a rigid laryngoscope during different voice onset types. Significant linear relationships (p < or = 0.0055) were found among onset types on measures of (a) gesture duration when moving from 80% to 20% of maximum distance during adduction, (b) maximum velocity, (c) duration between the completion of adduction and phonation onset, and (d) ratios of maximum velocity to maximum distance between the vocal processes, an estimate of stiffness. The gesture duration was greatest for breathy onsets and least for hard onsets, while the maximum velocity, latency between adduction and phonation onset, and estimated stiffness were greatest for hard onsets and least for breathy onsets. The results suggest that one trajectory seems to be used with increases in gesture duration being accompanied by decreases in articulator stiffness when moving from hard to normal to breathy voice onset types.

A simulation study of vertical jumping from different starting postures.

This paper addresses the question of whether maximal vertical jump height depends on initial jumping posture. A direct dynamics computer simulation approach was used to avoid subject preference and practice effects. The human body was modeled as four rigid segments connected by ideal hinge joints, with movement constrained to the sagittal plane and driven by three single-joint torque actuators. Maximal height jumps were found for each of 125 different initial postures. For each initial posture, the optimal pattern of joint torque actuator onset times was found using a multidimensional simplex algorithm searching for maximal jump height. The model results revealed that maximal jump height is relatively insensitive to initial posture, but that the pattern of joint torque onset times necessary to effect these optimal heights varies considerably. Model kinematics indicate that the variability in onset times is necessary to allow the body to re-orient itself in different ways during the downward countermovement phase. This variable re-orientation strategy is followed by a more stereotyped upward thrust phase that is similar despite the differences in starting postures. Model center of mass, joint and segmental kinematics show many features found in experimental studies of jumping, despite the exclusive use of single torque actuators. However, a proximal-to-distal sequence of joint coordination was not found, possibly because of the omission of antagonist and bi-articular muscles. The results suggest that similar vertical jump heights should be obtained using a wide range of initial starting positions.

Sagittal-plane mobility of the cat cervical spine.

The present study was conducted to evaluate the nature of sagittal-plane motion across cervical vertebral joints and to identify the centers of rotation for each joint in anaesthetized cats X-rayed in a range of head-neck postures. Relative positions of adjacent pairs of vertebrae were assessed by constructing transparent templates for each vertebra that could be overlaid onto different X-rays, and then by digitizing the locations of three markers attached at a distance from each template. The finite centers of rotation for each joint were estimated using a rigid-body method. The errors associated with the estimates were quantified further by using a method in which the positions of digitized markers were fitted to concentric circles using a least-squares approach. The center of rotation between the skull and C1 was located at the cranial articular facets between the two bones. The center of rotation between C1 and C2 was situated near the tip of the odontoid process close to the site of attachment of the transverse ligaments. Centers of rotation for the other cervical vertebral joints were located in the region of the intervertebral disc. A similar range of values was obtained for centers of rotation when extended or flexed postures were used for the calculations, suggesting that the centers of rotation may not move markedly throughout a range of sagittal-plane rotations of approximately 90 degrees at the skull-C1 joint and about 15-30 degrees at the other cervical joints. These results showed that all cervical joints rotated during sagittal-plane motion. A minimal representation of the musculoskeletal mechanics of the feline neck probably requires multiple segments, each corresponding to a single vertebral bone.

Suboccipital muscles in the cat neck: morphometry and histochemistry of the rectus capitis muscle complex.

The morphometry, histochemistry, and biomechanical relationships of rectus capitis muscles were examined in adult cats. This family of muscles contained six members on the dorsal, ventral, and lateral aspects of the upper cervical vertebral column. Three dorsal muscles (rectus capitis posterior major, medius, and minor) formed a layered complex spanning from C1 and C2 to the skull. Rectus capitis posterior major was composed predominantly of fast fibers, but the other two deeper muscles contained progressively higher proportions of slow fibers. One ventral muscle, rectus capitis anterior major, was architecturally complex. It originated from several cervical vertebrae and appeared to be divided into two different heads. In contrast, rectus capitis anterior minor and rectus capitis lateralis were short, parallel-fibered muscles spanning between the skull and C1. The ventral muscles all had nonuniform distributions of muscle-fiber types in which fast fibers predominated. Dorsal and ventral muscle groupings usually had cross-sectional areas of 0.5 cm2 or more, reflecting a potential capacity to generate maximal tetanic force in excess of 9 N. Biomechanical analyses suggested that one muscle, rectus capitis lateralis, had its largest moment in lateral flexion, whereas the other muscles had large, posturally dependent moment arms appropriate for actions in flexion-extension. The observation that most rectus muscles have relatively large cross-sectional areas and high fast-fiber proportions suggests that the muscles may have important phasic as well as postural roles during head movement.

Mechanical output following muscle stretch in forearm supination against inertial loads.

Muscle stretch enhances force produced in both single fibers and voluntarily activated human muscle. This study determined how initial conditions of muscle stretch (and associated eccentric work), muscle length, and load inertia contributed to human concentric muscular output during maximal voluntary forearm supination. Outputs of angular velocity and concentric work over specific displacements and times of motion were calculated. Multiple regression analysis was performed using these outputs and initial conditions as dependent and independent variables, respectively. Initial conditions were shown to be significant and systematic determinants of muscle output in concentric contraction. Evidence of a temporary shift in the force-velocity curve was found and discussed regarding its beneficial contribution to load movement. Greater benefit was considered to be due to the fact that muscle stretch allows time for achievement of maximal muscular recruitment prior to concentric contraction. This produces large forces at the onset of the concentric phase, in comparison with contractions starting from rest. These findings were discussed with regard to both single- and multi-segment movement patterns.