Prof. Herbert conducts clinical research into the effectiveness of physiotherapy interventions. A focus of this research is study of the effectiveness of stretch-based interventions for prevention and treatment of contracture. His clinical research is backed by a program of laboratory research investigating the mechanical properties of human muscles.
Human Muscle Stretch Reflexes: The Effects Of Stimulus Properties, Muscle State And Subject Intention
Funder
National Health and Medical Research Council
Funding Amount
$170,604.00
Summary
The best known muscle reflex is the tendon jerk, which is usually evoked by tapping the muscle tendon with a small hammer. This tap imposes a very rapid stretch on the muscle, which produces a stretch reflex. Different stretch responses, however, can be observed to slow or fast stretches, or to vibration of muscle. Normally, when the muscles of a relaxed person are stretched, no active response is observed. However, when the person is engaged in a task and contracting their muscles, then stretch ....The best known muscle reflex is the tendon jerk, which is usually evoked by tapping the muscle tendon with a small hammer. This tap imposes a very rapid stretch on the muscle, which produces a stretch reflex. Different stretch responses, however, can be observed to slow or fast stretches, or to vibration of muscle. Normally, when the muscles of a relaxed person are stretched, no active response is observed. However, when the person is engaged in a task and contracting their muscles, then stretch modulates the muscle activity such that an increase in contraction of the muscle opposes the stretch and defends the position of the joint against the external disturbance. This is the everyday situation in which stretch reflexes operate. Despite extensive investigation for over a hundred years, there is still no consensus among researchers about the behaviour of stretch reflexes nor about their role in the control of movement. Even the demarcation of reflex from voluntary muscle activity is not always certain. One of the outstanding features of stretch reflexes is the variability of their behaviour, which depends on the particular muscle involved, its level of contraction, the type of stretch and the task in which the person is engaged. This variability has made it difficult for researchers to determine the role of reflexes in the control of movement. In order to study stretch reflex behaviour in human subjects, we will measure the electrical activity of elbow muscles, the elbow position and the force generated at the joint under a variety of conditions. A series of five experiments will investigate specific unresolved issues such as the effect of subject intention on the modulation of muscle activity and how altered modulation of muscle activity may change the stiffness of our limbs. The objective of the experimental series is to fill in important gaps in the picture of the behaviour of the stretch reflex.Read moreRead less
The Role Of Mechanoelectric Feedback In Cardiac Arrhythmogenesis
Funder
National Health and Medical Research Council
Funding Amount
$307,550.00
Summary
Arrhythmias are disruptions of the normal electrical rhythm of the heart, and can vary from asymptomatic to fatal. It used to be thought that the electrical and mechanical functions of the heart muscle were essentially separate: the electrical activity triggered contraction something like pulling the trigger of a gun- once events were in motion, the electrical events played no further role. However, in recent years it has become apparent that this is an over-simplification of the real situation. ....Arrhythmias are disruptions of the normal electrical rhythm of the heart, and can vary from asymptomatic to fatal. It used to be thought that the electrical and mechanical functions of the heart muscle were essentially separate: the electrical activity triggered contraction something like pulling the trigger of a gun- once events were in motion, the electrical events played no further role. However, in recent years it has become apparent that this is an over-simplification of the real situation. In fact, the electrical activity of the heart is influenced strongly by the degree and timing of stretch to which the heart muscle is subjected, a process called Mechano-electric feedback. Since it can be demonstrated in isolated tissues, mechano-electric feedback must be an intrinsic property of the heart muscle. It has been shown in isolated heart preparations that passive stretch produces electrical disturbances in the normal action potential shape and propagation and that these electrical disturbances can be powerful enough to generate severe arrhythmias. There are paralells in human diseases. For example, atrial arrhythmias are common in older people, and it seems that these may be due to chronic stretch of the atria, as a consequence of high blood pressure. In addition, in those patients recovering from a heart attack, it seems likely that the damaged part of the heart muscle subjects the surrounding tissue to unusual mechanical stresses, and may trigger arrhythmias. This project aims to investigate the mechanisms underlying this mechano-electric feedback, in an attempt to understand some types of arrhythmias. Using molecular biology techniques, we will look at the gene expression of a novel type of stretch-activated potassium channel in both healthy and diseased animal hearts, with the aim of seeing if changes in the level of expression of these channels is correlated with changes in the response of the heart to stretch.Read moreRead less
Cell Stretch As A Physicochemical Secondary Stimulus In Initiating Lipopolysaccharide (LPS)-Mediated Acute Lung Injury
Funder
National Health and Medical Research Council
Funding Amount
$368,750.00
Summary
Acute lung injury (ALI) is an often fatal condition caused by direct or indirect injuries. When the injury occurs directly, eg pneumonia, lung cells release mediators that attract blood cells involved in defending the body. Once in the lungs, these cells are activated and engulf or release reactive molecules that destroy the invading organism a process known as inflammation. When the injury occurs indirectly, eg sepsis, ALI can arise from the spill-over of mediators created elsewhere in the body ....Acute lung injury (ALI) is an often fatal condition caused by direct or indirect injuries. When the injury occurs directly, eg pneumonia, lung cells release mediators that attract blood cells involved in defending the body. Once in the lungs, these cells are activated and engulf or release reactive molecules that destroy the invading organism a process known as inflammation. When the injury occurs indirectly, eg sepsis, ALI can arise from the spill-over of mediators created elsewhere in the body. Reactive molecules produced can damage the lung barrier separating the blood from the air. Consequently, fluid leaks into the airspaces making breathing difficult and hindering gas exchange. Gram (-) bacteria are the major cause of sepsis, pneumonia, and ALI. The inflammation is initiated by lipopolysaccharide (LPS), the major component of the bacterial cell wall. We have shown that LPS also changes breathing and the distribution of air and blood flow in lungs. This creates localised changes in cell stretch and the amounts of carbon dioxide (CO2) in the airspaces. Previously we showed that cell stretch releases surfactant , a substance that makes breathing easier. We now hypothesise that cell stretch is an important secondary stimulus in initiating ALI. We will use: 1. isolated lung cells to determine which cell types release mediators in response to LPS, and whether: * stretch stimulates their release * release is coordinated between the cell types * release is affected by the amount of CO2 2. isolated lungs to determine whether the pattern of ventilation, blood flow, and amounts of CO2 alter the release of the mediators, and whether these changes affect surfactant secretion and the ability to inflate the lungs. 3. animal models to also determine whether the pattern of respiration changes the course of the respiratory failure. Understanding the mechanisms that cause the disease will lead to better treatments.Read moreRead less