Adequate cardiac output is necessary in order to supply oxygen and other nutrients to all body tissues. Cardiac output is influenced by stroke volume and heart rate. Factors affecting the stroke volume includes PRELOAD, CONTRACTILITY and AFTERLOAD.
In the following conditions, indicate what factor/s influence the cardiac output: PRELOAD, CONTRACTILITY, AFTERLOAD, HEART RATE. Explain the why the factor/s affects cardiac output in 1 to 2 sentences.
High blood pressure
Hypertension increases the afterload since the diastolic blood pressure increases which in turn decreases the stroke volume.
Massive bleeding
Massive bleeding decreases the venous return which causes reduced preload due to less ventricular filling.
the drug dopamine
The drug dopamine raises blood pressure. As the rate increases, α1 and β1‐ β2‐adrenergic effects are seen which generates enhanced contractility
Running a sprint
During exercise, skeletal muscle contractions compress venous vessels which force blood and increase venous return which in turn increases the preload. Exercise also increases afterload and contractility due to the higher blood pressure and higher strain on the heart.
Hyperthyroidism with increased secretion of thyroid hormones
The reduction in systemic vascular resistance results in decreased renal perfusion pressure and activation of the renin-angiotensin-aldosterone system (RAAS) which increases sodium reabsorption and blood volume, this leads to increased preload, and decreased afterload.
Massive myocardial infarction (cardiac tissue death)
During a myocardial infarction, contractility is impaired due to external pressure on the heart which also raises afterload.
Hypothermia
Cardiac output drops during hypothermia due to a drop in arterial blood pressure
Emotional distress
Stress makes the body release a rush of hormones like adrenaline and cortisol, elevating blood pressure and increasing cardiac output