BJA/RCoA PhD Studentship
Can the depressive effect of anaesthetics on hypoxic ventilatory responses be explained by action on background potassium channels in the carotid body?
Prof Jaideep Pandit
Background: Patients undergoing anaesthesia are at risk of 'hypoxia' (a fall in oxygen levels in the body) for several reasons (eg, partial collapse of parts of the lungs, blood flow derangements, drug effects, etc). Since oxygen is necessary for life, this is a potentially dangerous situation. In the awake state, this hypoxia triggers a reflex (called 'chemoreflex') in which the breathing is increased and the extent to which oxygen levels fall in the body are reduced or even prevented. However, anaesthetic drugs impair this reflex and so reduce the patient's ability to elicit a strong breathing response to a fall in oxygen levels. This effect lasts well into the recovery period because low doses of anaesthetic are present in the body for several hours after surgery and even these low doses severely blunt the breathing response. Anaesthesia is generally safe but hypoxia is the commonest cause of anaesthetic-related death, so the problem of how to maintain the breathing response is an important one.
Aims of the project: To develop techniques and drugs without the side-effect of impairing the chemoreflex requires us to understand how anaesthetic drugs work in the cells of the carotid body (the key organ involved in sensing oxygen). Through our own work we previously discovered that some anaesthetics preserve the breathing response better than others, and this gives us a clue. Especially interesting is the finding that some agents (one example is nitrous oxide - laughing gas) can even slightly enhance the breathing response. It is possible that agents like laughing gas which preserve the breathing response may counteract the adverse respiratory effects of another anaesthetic, if the two are used in combination.
Methods: We propose to test this idea by observing the fundamental responses of the cells and molecular channels of the carotid body, to learn more about the processes involved. This involves removing the carotid bodies from rats and mice, and then measuring their responses to lack of oxygen (the calcium levels inside the cells rises with hypoxia and we can measure this rise). We will also use very small, very fine glass electrodes to measure the electrical currents in the membrane of the cells. These currents tell us which metallic ions are moving through specific channels in the membrane during the cell's response to hypoxia, and which are inhibited in their movement by anaesthetic. This in turn helps us to learn specifically how anaesthetics are impairing the cell's response.
Conclusions: The knowledge we gain by this project will lead to better understanding of fundamental processes, leading to better methods of prevention and management of hypoxia. For example, identifying a specific metallic ion channel will help develop drugs that do not act on this channel and so do not have the side-effect of reducing the breathing response. Or, finding that a combination of two anaesthetics better preserves the chemoreflex than one anaesthetic alone might lead to clinical techniques of anaesthetic use that are safer.
Neutrophil Dysfunction in Sepsis and its Modification by Statin Therapy
Prof Fang Gao Smith
Objective: Infections (sepsis) is one of the most common reasons for admission to hospitals and deaths from infections have not changed despite many attempts to change the way in which patients with infection are treated. White cells (neutrophils) are the first line of defence against bugs (bacteria) that enter the body to cause infections. White cells travel to sites of infection by responding to signals produced by the body and by the bacteria. Once there they kill the bacteria by eating them up and by using special products that they release. A new method of killing bacteria has been found where white cells release their genetic material in strands which allows further bacterial killing to occur. These are known as neutrophil extracellular traps (NETS). As infections get more serious white cells are unable to travel to sites of infections and this leads to people becoming sicker and dying as the bacteria cannot be killed. This study aims to look at the white cells in patients with infection and try and understand why they cannot travel to where the bacteria are. In addition we aim to use statins, which are drugs used to lower cholesterol, to see if treatment with statins may make these white cells work better.
Methods: We aim to look at the white blood cell function of patients with infections. Patients who give their permission will have blood samples taken on the first day they agree to take part, the fourth day and once they are better. In addition to collecting the blood of patients we will also collect basic details about the patients, (e.g.: age, sex and reasons for admission), their observations for the period of their hospital stay (e.g. heart rate and blood pressure), and what happens to them during their time in hospital (e.g: when did they go home, did they require admission to Intensive Care or did they die). By doing this we will be able to look at any changes in white blood cell function and how these changes affect patients. We hope that 60 patients with infection will agree to take part in this research. We will use the blood samples to look at the white cells and perform tests on them using experiments which have been previously tested, to measure their ability to travel to sources of infection, their ability to eat and kill bacteria and their ability to form the "NETS." We will repeat these experiments after treating the white cells with statins to see if any improvement is seen.
Data Analysis: The help of Dr Peter Nightingale, a qualified statistician will be sought for data analysis. A well recognised statistical program (SPSS for windows) will be used to identify any differences that we observe to see whether they reach a significant level (p=0.05). This number is considered by the scientific community to represent a level which the results obtained did not occur by chance.
Mechanisms of alveolar macrophage activation during ventilator-induced lung injury
Dr Michael Wilson
Background: Acute lung injury (ALI) is a major reason people require intensive care treatment. It is a frequently fatal condition that develops as a result of some 'insult' to the lung, including influenza/pneumonia and a host of others. Studies suggest it may be linked to more deaths in the UK than breast cancer or HIV, and if a patient develops severe ALI they have only about a 50% chance of survival. A major factor determining survival is how the patient's immune system reacts to the insult. Currently no drug therapies exist for ALI, and treatment consists of supporting the patient in intensive care until they either die or recover. Unfortunately, the very treatment that a patient receives can make the lung injury worse. Specifically the mechanical ventilation that keeps patients alive can itself produce a particular type of ALI, called ventilator induced lung injury (VILI). This additional injury caused by VILI has been shown to be responsible for at least 20-25% of deaths among ARDS patients, and could be more. However, exactly how VILI begins within the lungs remains largely unknown.
Hypothesis to be tested: We hypothesise that early activation of a particular cell type within the lung, alveolar macrophages, is a crucial event during the initiation of VILI. Specifically, we propose that this initial activation relies on physical contact between macrophages and structural cells of the lung (epithelial cells).
Methods: To investigate this, we will carry out experiments in anaesthetised, ventilated mice. We will use antibodies, drugs and genetically modified animals to investigate the involvement of physical contact or soluble factors in
macrophage activation. A technique known as flow cytometry will be used to identify specific cell types within the lung and determine whether they have been activated or not. The impact of any treatments on lung injury will be evaluated using well-established physiological techniques.
Significance: It has been widely suggested that interfering with the immune system could be a useful technique to reduce VILI. However, this may be a very dangerous approach as the patient could be left at risk of developing life-threatening infections if the immune system is compromised. The current study is designed to investigate the very initial processes that start VILI. If our hypothesis is correct that physical contact between epithelial cells and macrophages is responsible for macrophage activation during VILI, we may be able to specifically target this without impairing the patients' response to infection. We believe this novel approach could potentially have significant implications for the design of future therapies for VILI, and thus mortality of patients.
