Risk factors for neonatal brachial plexus palsy attributed to anatomy, physiology, and evolution.

The inherent variable anatomy of the neonate and the uniquely-shaped maternal birth canal that is associated with the evolution of human bipedalism constitute risk factors for neonatal brachial plexus palsy (NBPP). For example, those neonates with a prefixed brachial plexus (BP) are at greater risk of trauma due to lateral neck traction during delivery than those with a normal or postfixed BP. Compared to adults, neonates also have extremely large and heavy heads (high head: body ratio) set upon necks with muscles and ligaments that are weak and poorly developed. Accordingly, insufficient cranial stability can place large torques on the cervical spinal nerves. In addition, the pelvic changes necessary for habitual bipedal posture resulted in a uniquely-shaped, obstruction-filled, sinusoidal birth canal, requiring the human fetus to complete a complicated series of rotations to successfully traverse it. Furthermore, although there are many risk factors that are known to contribute to NBPP, the specific anatomy and physiology of the neonate, except for macrosomia, is not considered to be one of them. In fact, currently, the amount of lateral traction applied to the neck during delivery is the overwhelming legal factor that is used to evaluate whether a birth attendant is liable in cases of permanent NBPP. Here, we suggest that the specific anatomy and physiology of the neonate and mother, which are clearly not within the control of the birth attendant, should also be considered when assessing liability in cases of NBPP.

Stabilization and mobility of the head, neck and trunk in horses during overground locomotion: comparisons with humans and other primates.

Segmental kinematics were investigated in horses during overground locomotion and compared with published reports on humans and other primates to determine the impact of a large neck on rotational mobility (> 20 deg.) and stability (< or = 20 deg.) of the head and trunk. Three adult horses (Equus caballus) performing walks, trots and canters were videotaped in lateral view. Data analysis included locomotor velocity, segmental positions, pitch and linear displacements and velocities, and head displacement frequencies. Equine, human and monkey skulls and cervical spines were measured to estimate eye and vestibular arc length during head pitch displacements. Horses stabilized all three segments in all planes during all three gaits, unlike monkeys and humans who make large head pitch and yaw rotations during walks, and monkeys that make large trunk pitch rotations during gallops. Equine head angular displacements and velocities, with some exceptions during walks, were smaller than in humans and other primates. Nevertheless, owing to greater off-axis distances, orbital and vestibular arc lengths remained larger in horses, with the exception of head-neck axial pitch during trots, in which equine arc lengths were smaller than in running humans. Unlike monkeys and humans, equine head peak-frequency ranges fell within the estimated range in which inertia has a compensatory stabilizing effect. This inertial effect was typically over-ridden, however, by muscular or ligamentous intervention. Thus, equine head pitch was not consistently compensatory, as reported in humans. The equine neck isolated the head from the trunk enabling both segments to provide a spatial reference frame.

Cardiac oxidative stress is elevated at the onset of dilated cardiomyopathy in streptozotocin-diabetic rats.

The association between nitric oxide synthase (eNOS and iNOS) status, oxidative stress, and cardiac function was evaluated in streptozotocin (STZ)-diabetic rats to understand the etiology of diabetic cardiomyopathy. Cardiac function was determined by echocardiography. eNOS and iNOS status and superoxide production were assessed by immunohistochemistry and chemiluminescence, respectively. In STZ-diabetic rats, stroke volume, cardiac output, and left ventricular ejection fraction were significantly lower than in controls (CT, P < .05), whereas left ventricular end-systolic volume was higher. Cardiac NOS activity increased from 161 +/- 18 cpm/mg tissue in CT rats to 286 +/- 20 cpm/mg tissue (P < .001) in STZ-diabetic rats. Furthermore, superoxide production and cardiac eNOS and iNOS levels were higher in STZ-diabetic rats than in CT rats (P < .05). An increased activation of cardiac eNOS and iNOS is observed concomitantly with decreased cardiac function. Thus, increased oxidative stress in the heart may be implicated in the development of dilated cardiomyopathy in STZ-diabetic rats.

Differential regulation of the left and right coronary arteries of swine.

Coronary artery disease is one of the leading causes of myocardial infarction. Despite the predominant role of the coronary arteries in the induction of myocardial infarction, the precise contribution of each artery to this process is not well established. The present work evaluates the histological characteristics and functional properties of the left (LCA) and right (RCA) coronary arteries in swine in order to establish if the arteries are differentially regulated. To investigate this possibility, concentration-response curves for serotonin (5-HT, from 0.1 nmol/l to 100 micromol/l) and KCl (from 5 to 40 mmol/l) were performed on both arteries to determine the receptor-dependent and independent responses, respectively. The specific subtype of the 5-HT receptor involved in the contraction of both arteries was evaluated using DL-propranolol hydrochloride (5-HT1 and nonselective beta-adrenergic receptor antagonist) and ketanserine (5-HT2 antagonist) and immunohistochemical assays. The Emax from the 5-HT concentration-response curves was 24% higher in the LCA than in the RCA (n = 59, p < 0.05). EC50 values from both curves were also significantly different (LCA 0.150 +/- 0.005 micromol/l and RCA 0.171 +/- 0.010 micromol/l, n = 59, p < 0.05). Similarly, the Emax for KCl was 36% higher in the LCA than in the RCA (n = 9, p < 0.05), and the EC50 values also differed (LCA 15.30 +/- 0.06 mmol/l and RCA: 14.30 +/- 0.11 mol/l, n = 9, p < 0.05). Ketanserine reduced the Emax by 63% in the LCA and by 67% in the RCA. DL-propranolol hydrochloride decreased Emax by 24% in the LCA and by 26% in the RCA. The dry weight and media area were larger in the LCA than in the RCA (17%, n = 40, p < 0.05, and 3%, n = 40, p < 0.05, respectively). Immunohistochemical assay results reveal that the average density of 5-HT2A receptor subtype was also higher in the LCA (41.24 +/- 1.35) than in the RCA (18.49 +/- 1.14; n = 20, p < 0.05). Together, the findings of this study suggest that a differential physiological regulation exists between the LCA and RCA in swine. This differential regulation may have arisen as a mechanism for maintaining an adequate perfusion pressure in the wall of the left ventricle, favoring a greater oxygen delivery to match the increased oxygen demand of the left ventricle.

Stabilization and mobility of the head and trunk in vervet monkeys (Cercopithecus aethiops) during treadmill walks and gallops.

The brain requires internal or external reference frames to determine body orientation in space. These frames may change, however, to meet changing conditions. During quadrupedal overground locomotion by monkeys, the head rotates on a stabilized trunk during walking, but the trunk rotates on a stabilized head during galloping. Do the same movement patterns occur during in-place locomotion? Head and trunk pitch rotations were measured, and yaw and roll rotations estimated from cine films of three adult vervet monkeys (Cercopithecus aethiops L. 1758) walking and galloping quadrupedally on a treadmill. Head and trunk rotational patterns during treadmill walks were comparable to the patterns found during overground walks. The rotational velocities of these segments during both treadmill walks and gallops were also comparable to the velocities found during natural locomotion. By contrast, whereas head and trunk rotational patterns during treadmill gallops did occur that were comparable to the patterns practiced during overground gallops, a significantly different pattern involving large and simultaneous head and trunk rotations was more commonly observed. Simultaneous head and trunk rotations may be possible during treadmill gallops because the fixed visual surround is providing an adequate spatial reference frame. Alternatively, or in addition to this visual information, a re-weighting in other sensory modalities may be occurring. Specifically, the vestibular inputs used during overground locomotion to reference gravity or a gravity-derived vector may become less important than proprioceptive inputs that are using the treadmill belt surface as a reference. Regardless, the spatial reference frame being used, blinks that occur at specific times during the largest head yaw rotations may be necessary to avoid the initiation of unwanted and potentially destabilizing lateral sway brought on by sudden increases in optic flow velocity.

Stabilization and mobility of the head and trunk in wild monkeys during terrestrial and flat-surface walks and gallops.

This study investigated the patterns of rotational mobility (> or =20 degrees ) and stability (< or =20 degrees ) of the head and trunk in wild Indian monkeys during natural locomotion on the ground and on the flat-topped surfaces of walls. Adult hanuman langurs (Semnopithecus entellus) and bonnet macaques (Macaca radiata) of either gender were cine filmed in lateral view. Whole-body horizontal linear displacement, head and trunk pitch displacement relative to space (earth horizontal), and vertical head displacement were measured from the cine films. Head-to-trunk pitch angle was calculated from the head-to-space and trunk-to-space measurements. Locomotor velocities, cycle durations, angular segmental velocities, mean segmental positions and mean peak frequencies of vertical and angular head displacements were then calculated from the displacement data. Yaw rotations were observed qualitatively. During quadrupedal walks by both species, the head was free to rotate in the pitch and yaw planes on a stabilized trunk. By contrast, during quadrupedal gallops by both species, the trunk pitched on a stabilized head. During both gaits in both species, head and trunk pitch rotations were symmetrical about comparable mean positions in both gaits, with mean head position aligning the horizontal semicircular canals near earth horizontal. Head pitch direction countered head vertical displacement direction to varying degrees during walks and only intermittently during gallops, providing evidence that correctional head pitch rotations are not essential for gaze stabilization. Head-to-space pitch velocities were below 350 deg. s(-1), the threshold above which, at least among humans, the vestibulo-ocular reflex (VOR) becomes saturated. Mean peak frequencies of vertical translations and pitch rotations of the head ranged from 1 Hz to 2 Hz, a lower frequency range than that in which inertia is predicted to be the major stabilizer of the head in these species. Some variables, which were common to both walks and gallops in both species, are likely to reflect constraints in sensorimotor control. Other variables, which differed between the two gaits in both species, are likely to reflect kinematic differences, whereas variables that differed between the two species are attributed primarily to morphological and behavioural differences. It is concluded that either the head or the trunk can provide the nervous system with a reference frame for spatial orientation and that the segment providing that reference can change, depending upon the kinematic characteristics of the chosen gait.

Aerial maneuvers of leaping lemurs: The physics of whole-body rotations while airborne.

Several prosimian species begin a leap from a vertical support with their back toward the landing target. To reorient themselves from this dorsally facing, head-first lift-off to a ventrally facing, feet-first landing, the animals combine an initial twist with a partial backward somersault. Cinefilms of a captive colony of ringtailed lemurs (Lemur catta) revealed that during leaps from vertical poles to horizontal supports, the backward somersaulting rotations were often initiated while the animals were airborne. How could these prosimians initiate rotations in the absence of externally applied forces without violating angular momentum conservation? The problem was approached through vector analysis to demonstrate angular momentum (H) changes about the three principal (symmetrical) axes of rotation for a series of critical body positions that were extracted from the filmed sequences. One L. catta specimen was segmented to provide the dimensions and weights necessary for modeling the various body positions. These data were also used to calculate moments of inertia about the three principal axes in order to predict if rotations about these axes were stable or metastable. Lemurs, like any projectile, must conserve the total angular momentum (HT ) established at lift-off. HT , however, is a vector quantity that is the resultant of component vectors about the three principal axes. Thus, H about the individual axes may change as long as HT remains constant. Strategically timed tail movements tilted the body, thereby changing the H value about the head-to-toe (twisting) axis. To conserve HT , also aligned along the twisting axis, angular momentum transferred to the somersaulting axis. Owing to the direction of tail-throw, the initiated rotations were partial backward somersaults that brought the hindlimbs forward for landing. This strategy for initiating specific rotations parallels that practiced by human springboard divers.