![]() ![]() ![]() As alveolar oedema increases, diffusion of oxygen into the pulmonary capillaries is impaired, which manifests as dyspnoea venous return to the already congested heart and lungs increases when the patient lies flat, which manifests as orthopnoea and paroxysmal nocturnal dyspnoea (PND).The renin-angiotensin-aldosterone system (RAAS) increases salt and fluid retention, which initially increases preload, end diastolic volume (EDV), SV and therefore CO via the Frank-Starling mechanism, but over time leads to cardiac dilatation and a reduction in contractility and CO, together with congestion of the pulmonary and systemic veins with associated tissue oedema.Increased sympathetic tone increases SVR and stimulates renin secretion.As the heart begins to fail, compensatory mechanisms maintain CO & BP.SV depends on preload, myocardial contractility and afterload.CO = heart rate (HR) x stroke volume (SV).Blood pressure (BP) = cardiac output (CO) x systemic vascular resistance (SVR).Pathophysiology of acute pulmonary oedema ![]() Acute respiratory distress syndrome (ARDS).Non-cardiogenic: caused by injury to the lung parenchyma or vasculature.Cardiogenic pulmonary oedema: caused by elevated pulmonary capillary pressure due to decompensated LVF.Acute pulmonary oedema: rapid accumulation of fluid in the alveoli and parenchyma of the lung.High output cardiac failure: cardiac failure secondary to excessive demand.Low output cardiac failure: cardiac failure secondary to inadequate pumping and supply.Cor pulmonale: RVF secondary to chronic lung pathology eg chronic obstructive pulmonary disease (COPD).Congestive cardiac failure (CCF): LVF and RVF co-exist, the latter usually secondary to the former.Right ventricular failure (RVF): failure of the RV causing congestion of the systemic veins.Left ventricular failure (LVF): failure of the LV causing congestion of the pulmonary veins.Objective evidence of a structural or functional abnormality including cardiomegaly, third heart sound, abnormality on echocardiogram (echo).Typical signs, including bibasal crepitations, raised jugular venous pressure (JVP).Typical symptoms, including dyspnoea, orthopnoea, ankle swelling.Cardiac failure: clinical syndrome where the heart is unable to function adequately as a pump to meet the demands of the body characterised by:.Acute pulmonary oedema: Accumulation of fluid in the lung parenchyma leading to impaired gas exchange between the air in the alveoli and pulmonary capillaries. ![]()
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