Mild platelet-based bleeding disorders are among the most complex bleeding disorders to understand, due to the absence of a ‘gold standard’ test for diagnosis and the significant overlap with the bleeding phenotype observed in healthy individuals. The work in this thesis is focussed on patients with a clinically diagnosed mild platelet disorder for which no acquired cause was identified by the referring expert clinician. ADP and thromboxane A2 (TxA2) are key secondary mediators of platelet aggregation and function in synergy to facilitate robust platelet activation in the event of vascular damage. Less than ten function-disrupting inherited gene defects in the ADP P2Y12 receptor and only one in the platelet TxA2 receptor have been reported, with none in the UK. Over a period of nearly 4 years, patients with a diagnosis of platelet dysfunction made at UK Comprehensive Haemophilia Care Centres were investigated using platelet aggregation and secretion assays alongside controls and reference curves to nine platelet agonists to exhibit an abnormal bleeding phenotype in response to different platelet agonists, focusing in searching on P2Y12 receptor defects. In addition, the P2Y12 ADP receptor from 140 subjects diagnosed with mild type 1 von Willebrand Disease (VWD) from the EU MCMDM-1VWD study was sequenced in view of the similarity in bleeding phenotype of patients with type 1 VWD and mild platelet disorders and the fact that both conditions show incomplete penetrance consistent with a multifactorial basis for each disorder. The sequencing was performed by Dr Martina Daly in Sheffield. The work in this thesis has led to the identification / characterisation of a patient who is homozygous for an early missense mutation in the P2Y12 ADP receptor and two patients with heterozygous point mutations in the P2Y12 ADP receptor (who also has type 1VWD) and in the TxA2 receptor. In addition, I studied platelet aggregation and secretion, along with a number of more specialised assays, in nearly 80 other patients during the course of the thesis and have subdivided these on the basis of the observed defect. Interestingly, in nearly one third of the patients, a platelet defect was not found.

The relationship between antiretroviral treatment of HIV infection, body fat distribution, insulin resistance (HOMA), adipocytokine and apolipoprotein-B (apoB) kinetics was investigated in 12 HIV negative controls and 55 HIV-infected patients including antiretroviral treatment-naïve patients (n=15) and patients taking two nucleoside analogues plus either a protease inhibitor (PI, n=15) or non-nucleoside reverse transcriptase inhibitor (NNRTI, n = 25). The HIV positive treatment groups had mild dyslipidaemia. The apo-B fractional clearance rate (FCR) was reduced in the HIV positive groups. Peripheral fat was lower in treated patients and correlated with duration of therapy. There was a positive correlation between peripheral fat and apo-B clearance rate and a negative correlation with apo-B pool size. Adiponectin was reduced in all HIV positive groups and correlated positively with HDL-cholesterol, apo-B FCR and limb fat and correlated negatively with plasma triglycerides and HOMA. In a linear regression model which included HOMA, adiponectin level but not HOMA was predictive of apo-B FCR and HDL cholesterol. These results suggest that mild dyslipidaemia resulting from antiretroviral therapy is due to a decrease in apo-B FCR which is strongly related to loss of peripheral fat. Adiponectin may have a direct effect on lipoprotein metabolism which may be independent of insulin.

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This thesis reports a clinical study designed to assess myocardial, renal and lung outcomes following cardiac surgery. In a single centre, prospective randomized, placebo intervention-controlled trial the effects of intermittent upper limb ischaemia (remote ischaemic preconditioning (RIPC)) were compared in non-diabetic adult patients undergoing on-pump multi-vessel coronary artery surgery. Patients, investigators, anaesthetists, surgeons and critical care teams were all blind to group allocation. Subjects were randomized(1:1) to RIPC(or placebo) stimuli (3x upper limb (or dummy arm) 5 minute cycles of 200mmHg cuff inflation/deflation) during sternotomy and conduit procurement. Anaesthesia, perfusion, cardioplegia and surgical techniques were standardized. Groups were well matched on demographic and operative variables. In contrast to prior smaller studies, RIPC did not reduce troponin T (48 hour area under the curve (AUC); 6hour and peak) release, improve post-operative haemodynamics (cardiac indices; low cardiac output episodes incidence; IABP usage; inotrope and vasoconstrictor use; M mode, 2D contrastenhanced echocardiography and tissue Doppler imaging) or offer antiarrhythmic benefit (de novo left bundle branch block or Q waves; ventricular tachyarrhythmia incidence). RIPC did not afford renal (peak creatinine, AUC urinary albumin-creatinine ratios, dialysis requirement) or lung protection (intubation times, 6hour and 12 hour pO2/FiO2 ratios). Case urgency did not influence RIPC effect.