Factors affecting umbilical venous perfusion during experimental cord knotting.

The aim was to determine experimentally the factors that increase the risk of venous occlusion by applying a standardised tightening force to isolated perfused umbilical cords tied in a true knot in vitro. Umbilical cords were collected from patients undergoing Caesarean section. Cords were clamped, isolated and studied within 15 min. The umbilical vein was cannulated, the cord tied in a true knot and traction was applied using standard weights. The umbilical vein was perfused with modified Krebs solution at a constant pressure of 40 mmHg and the attached weight increased until perfusion ceased. The cord mass index (weight/length), hydration index/100-[(dry weight/wet weight)x100], and coiling index (coils/length) were determined. Cord morphometric analysis was performed on 193 cords. Intra uterine growth restriction was associated with decreased cord mass index (p=0.002) and increased coiling index (p=0.002). Venous perfusion experiments were performed on 75 cords. Using multivariate regression analysis, cord morphometric factors that increased the risk of cord occlusion were decreased cord mass index (p=0.008), decreased cord hydration index (p=0.004), and low venous flow capacity (p=0.001). During experimental cord knotting with applied traction, the susceptibility to venous occlusion was increased with low cord mass index, low cord hydration index and low venous flow capacity. These cord characteristics were associated with low fetal body weight and intrauterine growth restriction. An increased susceptibility to cord occlusion may contribute to the higher perinatal morbidity and mortality in growth restricted pregnancies.

A histological and radiological investigation of the nasal bone in fetuses with Down syndrome.

OBJECTIVES: Previous studies of nasal bone development in Down syndrome have used radiographs or ultrasound for the detection of nasal bone length or nasal bone absence. The aim of this study was to investigate the presence and size of the nasal bones in postmortem Down syndrome fetuses by means of radiographs and histological examination. METHODS: Thirty-three aborted human fetuses (gestational age 14-25 weeks) with Down syndrome were included. A mid-sagittal tissue block was excised from the skull base to the foramen magnum and along the lateral aspect of the spine. Radiographs of the tissue block were taken in lateral, frontal and axial projections. The length of the nasal bone was measured. The tissue blocks were cut in serial sections and stained. The crown-rump length (CRL), foot length (FL) and number of ossified bones in the hand and foot (CNO) were recorded. RESULTS: A total of 8/33 fetuses had bilateral nasal bone absence and two had unilateral absence. In fetuses with radiographically diagnosed nasal bone absence, no nasal bone could be found histologically. The majority of the Down syndrome fetuses had CRL, FL and CNO values within the range of those for normal age-matched fetuses. Nasal bone length was normal or reduced. CONCLUSIONS: Absence of the nasal bone was registered by postmortem examination in one-third of fetuses with Down syndrome. In some fetuses this could be a result of delayed maturation associated with Down syndrome. The phenotypic differences in nasal bone appearance may reflect genotypic differences in the Down syndrome group.

Comparative data from young men and women on masseter muscle fibres, function and facial morphology.

The primary aim was to relate information about masseter muscle fibres and function to aspects of facial morphology in a group of healthy young men. The secondary aim was to investigate possible sex differences using data previously obtained from a comparable group of age-matched, healthy women. Dental status and facial morphology were recorded in 13 male students aged 20-26 years. Functional examinations included bite-force measurements and electromyographic recordings of masseter activity. A biopsy was removed from the masseter of each participant during surgical extraction of a wisdom tooth, and the tissue examined for myosin ATPase activity. Further, the cross-sectional areas of the different fibre types were measured. In spite of using age-matched healthy men and women with a full complement of teeth, statistically significant sex differences were found among measures related to muscle function and some measures of facial morphology. Thus data from men and women should not be pooled uncritically. The greater bite force in men than women corresponded with the greater diameter and cross-sectional area of type II fibres. Further, the males had more anteriorly inclined mandibles and shorter anterior facial height, suggesting a relation between the greater muscle force and the shape of the face. However, linear regression analysis failed to demonstrate any significant association between bite force and facial morphology among men and women. Thus, craniofacial morphology could be a result of far more contributing factors than previously believed.

Variables related to masseter muscle function: a maximum R2 improvement analysis.

A multiple linear regression analysis, with stepwise maximum R2 improvement technique by forward selection and pair switching, was used to select the occlusal, morphologic, and histologic variables which explained most of the variation in bite force and electric masseter muscle activity. The variables comprised tooth contact and facial morphology together with thickness and fiber characteristics of the masseter muscle. The study included 13 healthy women, 21-28 yr of age, with a minimum of 24 teeth and no serious malocclusion. Significant exploratory models (R2: 0.55-0.85) were shown concerning bite force, and electromyographic amplitude during resting posture, maximal voluntary contraction (ICP), and unilateral chewing, as well as contraction time (chewing side). Muscle thickness and molar contact had a significant, positive effect on the level of forceful muscle contraction. The explorative model both demonstrated explicable relations, and offered better insight into interrelations than did univariate analysis.

Histochemical characterization of pig masseter muscle: an animal model.

Masseter muscle autopsies were obtained from six different areas of six pigs. The autopsies were stained for the demonstration of myosin ATPase activity by means of a conventional histochemical technique. As compared with human masseter, the pig masseter muscle contained more type II fibers. But, like the human masseter, the pig muscle had a varying distribution of fiber types in the different autopsy areas, a distribution which might be the result of an adaptation to carry out special functions such as chewing, swallowing, and jaw posture. The fiber type distribution in the pig masseter also varied among individuals, probably reflecting various levels of utilization of the muscles besides different genetic influences. Moreover, pig masseter contained fibers of intermediate staining intensity (IM fibers), a fiber type rarely seen except in human masticatory muscles. In conclusion, we consider the pig masseter to be a useful animal model to study muscular adaptations to altered function in the orofacial region.

Histochemical characterization of masseter muscle fibres in a biopsy study of normal young women.

Muscle fibres from biopsies of the anterior part of the masseter muscle (pars superficialis) were histochemically characterized in 13 healthy female students. They were 21-28 yr old with a full complement of teeth, and normal facial and occlusal relations. Before surgery, normal masseter muscle function was demonstrated by bite-force measurements and recordings of electromyographic activity. After staining for myosin ATPase activity, the relative mean areas of muscle fibres were: type I 82.9%, type IM 9.5% and type II 8.3%. The intraindividual (18-155% of mean) and interindividual (0-216% of mean) variation of the fibre size was large. The type I fibres had the largest diameter (10-80 microns, mean: 39 microns), the type II fibres (6-47 microns, mean: 21 microns) and the IM fibres (8-54 microns, mean: 28 microns) the smallest. The biopsy technique and the histochemical characterization will be suitable for reference in women with functional changes or diseases of the masseter muscle.

Ultrasound image of human masseter muscle related to bite force, electromyography, facial morphology, and occlusal factors.

The thickness of the human masseter muscle, corresponding approximately to a cross-section at the most bulky part of the superficial portion, was measured by ultrasound scanning at three sites 1 cm apart. The study included 13 women, 21-28 yr of age, with a minimum of 24 teeth and without craniomandibular disorders. Ultrasonography produced a well-defined depiction of the muscle with distinct tendinous structures. The average thickness at the measuring sites varied from 8.83 to 11.08 mm with the muscle relaxed, and increased significantly during contraction to average values between 9.84 and 12.57 mm. The study showed a connection between measures of masseter thickness and function of the muscle, as well as parameters generally associated with masseter muscle function. Muscle thickness at the voluminous anterior part of the superficial portion was systematically and significantly correlated to bite force, occlusal tooth contact and cephalometric data (anterior face height, vertical jaw relation and mandibular inclination). In conclusion, ultrasound scanning gave an uncomplicated and a reproducible access to parameters of jaw muscle function and its interaction with the craniomandibular system.

An animal model for human masseter muscle: histochemical characterization of mouse, rat, rabbit, cat, dog, pig, and cow masseter muscle.

The masseter muscle of several animal species was investigated by use of a histochemical method for the demonstration of acid-stable and alkali-stable myosin adenosine triphosphatase (ATPase). The following subdivisions of fiber types were used: Type I fibers show weak ATPase activity at pH 9.4, type IM fibers react moderately, and type II fibers react strongly. Rat and mouse masseter muscles contained type II fibers only, as did some rabbit masseter muscles, whereas other rabbit masseter muscles possessed equal amounts of type I and II fibers. Cat and dog masseter muscles possessed both type II and I fibers, with type II predominating. Cow masseter muscle consisted mainly of type I fibers, although some cow masseter muscles contained a very small number of type II fibers. Pig masseter muscle had both type I, II, and IM fibers. One of the characteristics of human masseter muscle is type IM fibers, which are rarely seen in muscles other than the masticatory muscles. Therefore, pig masseter muscle might be a suitable animal model for experimental studies, such as an investigation of the distribution and diameter of fiber types in the masticatory muscles before and after orthognathic surgery.

Effect of varying the preincubation and incubation temperature on the reaction pattern for myosin ATPase in rat skeletal muscle.

The temperature of the preincubation and incubation medium influences the staining pattern and intensity of the reverse myofibrillar ATPase in rat skeletal muscle. The activity in some fibers was raised and in others depressed by varying the temperature of the preincubation and incubation medium between 4 and 37 degrees C. This indicates the presence of reverse ATPase isoenzymes with different temperature sensitivities.

The influence of temperature on the distribution and intensity of the reaction product in rat muscle fibers obtained with the histochemical method for myosin ATPase.

The influence of temperature in the incubation medium on the localization and intensity of myosin ATPase was investigated in striated muscles from the rat using a conventional histochemical technique. It was found that the enzyme reaction was temperature-dependent since the activity in some fibers was raised and in others was depressed by alteration of the incubation temperature. There was no obvious correlation between the temperature sensitivity of ATPase in the muscle fibers and their activity for succinic dehydrogenase. It is proposed that the histochemical method for myosin ATPase can be used for demonstration of isoenzymes in striated muscle fibers.