Vibration-induced postural reactions: a scoping review on parameters and populations studied

Objective

Mechanical vibration is an effective way for externally activating Ia primary endings of the muscle spindles and skin mechanoreceptors. Despite its popularity in proprioception and postural control studies, there is still no review covering the wide variety of vibration parameters or locations used in studies. The main purpose of this scoping review was thus to give an overview of general vibration parameters and to identify, if available, the rationale for justifying methodological choices concerning vibration parameters.

Methods

Three databases (Pubmed, CINHAL, and SPORTDiscus) were searched from inception to July 2022. Included articles were to focus on the study of muscle spindles and skin mechanoreceptors vibration in humans and assess postural control. Following inclusion, data regarding demographic information, populations, vibration parameters and rationale were extracted and summarized.

Results

One hundred forty-seven articles were included, mostly targeting lower extremities (n = 137) and adults (n = 126). The parameters used varied widely but were most often around 80 Hz, at an amplitude of 1 mm for 10-20 s. Regarding rationales, nearly 50% of the studies did not include any, whereas those including one mainly cited the same two studies, without elaborating specifically on the parameter's choice.

Conclusion

This scoping review provided a comprehensive description of the population recruited and parameters used for vibration protocols in current studies with humans. Despite many studies, there remain important gaps of knowledge that needs to be filled, especially for vibration amplitude and duration parameters in various populations.

Changes in the pulmonary circulation due to gravitational loads in high altitude conditions

BACKGROUND

The impact of gravity on the existence of all living things has long been of interest to scientists. The force of the Earth's gravity combined with hypoxia significantly affects blood circulation and blood accumulation in various parts of the human and animal body. To date, the relationship between body position and blood circulation in pulmonary circulation under hypobaric hypoxia has not been sufficiently studied.

OBJECTIVES

Therefore, the research aims to determine the possibility of changing the body position in space on the reactions in the pulmonary circulation in the plains and highlands.

METHODS

For this purpose, research was conducted on male Wistar rats, 44 of whom spent 150 days at an altitude of 3200 m above sea level, and 25 representatives of the control group - at an altitude of 164 m.

RESULTS

The study revealed that gravitational redistribution of blood in mountainous conditions is less pronounced compared to the control group. This is explained by the remodeling of the vascular wall and an increase in its stiffness. It was found that a change in pulmonary artery pressure at the time of a change in body position was recorded both on the plains and in the highlands. On the plains, when the body position of rats was changed to passive orthostatic, a decrease in systolic and diastolic pulmonary artery pressure was noted, and when the body position was changed to passive anti-orthostatic, an increase in pulmonary artery pressure was observed. The increase in pulmonary artery pressure was a compensatory mechanism due to the increased stiffness of the pulmonary vasculature.

CONCLUSIONS

The practical significance of this research is to expand the understanding of the pathogenesis of pulmonary hypertension in high-altitude hypoxia.

Does preappointment gabapentin affect neurological examination findings? A prospective, randomized and blinded study in healthy cats

OBJECTIVES

The aim of this study was to evaluate the influence of a preappointment oral dose of gabapentin on the neurological examination of cats.

METHODS

A prospective, randomized and blinded clinical trial was conducted in 35 client-owned healthy cats. Cats were scheduled for two appointments and randomly assigned to receive either a placebo or a 100 mg gabapentin capsule prior to the second veterinary visit. A neurological examination was performed during each visit, and the results were compared between groups. Normal/abnormal response rates for each test were based on the number of cats that allowed the test to be performed.

RESULTS

Gabapentin was administered to 17 cats. Gait and postural reactions were significantly affected in the gabapentin group. Comparing the gabapentin with the placebo groups, proprioceptive ataxia was identified in 4/17 (23.5%) vs 0/18 cats (P = 0.0288); paw placement deficits were seen in 10/11 (90.9%) vs 1/4 (25%) cats; table tactile placement deficits were identified in 13/17 (76.5%) vs 0/18 cats (P <0.0001); hopping deficits were seen in 5/17 (29.4%) vs 0/16 cats (P = 0.0185); and abnormalities on wheelbarrowing and extensor postural thrust were reported in 5/17 (29.4%) vs 0/18 cats (P = 0.0129). These results had no correlation with age or dose/kg received. No significant difference was noted in the assessment of level and content of consciousness, posture, cranial nerves and spinal nerves. No significant differences were noted in test compliance or examination duration.

CONCLUSIONS AND RELEVANCE

Gabapentin significantly altered gait analyses and postural reactions in this group of healthy cats. The administration of gabapentin could lead to false-positive results and, possibly, an incorrect identification of neurological lesions. In contrast, gabapentin did not impair the assessment of cranial nerves and spinal reflexes, which can be assessed in patients receiving the drug.

Limb and trunk mechanisms for balance control during locomotion in quadrupeds

In quadrupeds, the most critical aspect of postural control during locomotion is lateral stability. However, neural mechanisms underlying lateral stability are poorly understood. Here, we studied lateral stability in decerebrate cats walking on a treadmill with their hindlimbs. Two destabilizing factors were used: a brief lateral push of the cat and a sustained lateral tilt of the treadmill. It was found that the push caused considerable trunk bending and twisting, as well as changes in the stepping pattern, but did not lead to falling. Due to postural reactions, locomotion with normal body configuration was restored in a few steps. It was also found that the decerebrate cat could keep balance during locomotion on the laterally tilted treadmill. This postural adaptation was based on the transformation of the symmetrical locomotor pattern into an asymmetrical one, with different functional lengths of the right and left limbs. Then, we analyzed limb and trunk neural mechanisms contributing to postural control during locomotion. It was found that one of the limb mechanisms operates in the transfer phase and secures a standard (relative to the trunk) position for limb landing. Two other limb mechanisms operate in the stance phase; they counteract distortions of the locomotor pattern by regulating the limb stiffness. The trunk configuration mechanism controls the body shape on the basis of sensory information coming from trunk afferents. We suggest that postural reactions generated by these four mechanisms are integrated, thus forming a response of the whole system to perturbation of balance during locomotion.

Are crossed actions of reticulospinal and vestibulospinal neurons on feline motoneurons mediated by the same or separate commissural neurons?

Both reticulo- and vestibulospinal neurons coordinate the activity of ipsilateral and contralateral limb muscles. The aim of this study was to investigate whether their actions on contralateral motoneurons are mediated via common interneurons. Two series of experiments were made on deeply anesthetized cats. First, the effects of stimuli applied within the lateral vestibular nucleus and to reticulospinal tract fibers within or close to the medial longitudinal fascicle in the medulla were tested on midlumbar commissural interneurons that projected to contralateral motor nuclei. EPSPs of vestibular origin were found in 16 of 20 (80%) of the interneurons, all of which were excited monosynaptically by reticulospinal fibers. These EPSPs were evoked either monosynaptically or disynaptically. Second, the effects of stimuli applied at the same two locations were tested on contralateral motoneurons, selecting motoneurons in which large disynaptic EPSPs or IPSPs were evoked by reticulospinal fibers. When stimuli that were too weak to evoke any PSPs by themselves were applied together, similar EPSPs or IPSPs were evoked in all 26 motoneurons that were tested, indicating that spatial facilitation occurred premotoneuronally. Facilitation was strongest at those intervals optimal for summation of monosynaptic and/or disynaptic EPSPs evoked in commissural neurons by the earliest reticulospinal and vestibulospinal volleys. The same interneurons thus may be used by reticulospinal and vestibulospinal neurons to influence the activity of contralateral hindlimb muscles. Separate modulation of commands from these two descending neuronal systems may occur at the level of the interneurons that mediate disynaptic excitation of commissural neurons by reticulospinal and vestibulospinal neurons, thereby increasing their flexibility.