Basic science CTVS - Physiology

  1. Explain how Frank Sterlings law works to increase cardiac output during muscular exercise. [TU 2061,66/6]
    • The Frank–Starling law of the heart states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end diastolic volume) when all other factors remain constant.
    • In other words, as a larger volume of blood flows into the ventricle, the blood will stretch the walls of the heart, causing a greater expansion during diastole, which in turn increases the force of the contraction and thus the quantity of blood that is pumped into the aorta during systole.

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  2. Define arterial blood pressure. Describe in short the nervous regulation of arterial blood pressure.  [TU 2060/12]

    Describe the nervous regulation of arterial blood pressure. [TU 2073]
  3. Short note on Cardiac output. [TU 2064/5]
    Determinants of cardia output. [TU 2070/5]
    Define cardiac output. State factors that regulate cardiac output. [TU 2063/2]
    • • Cardiac output is the volume of blood pumped by heart each minute.
    • • It is product of heart rate and stroke volume and averages about 5.25L/min.

    Cardiac output = heart rate x stroke volume

    • Determinants of stroke volume - 
    • - Preload - tension on ventricular muscle before contraction determined by left ventricular end diastolic volume
    • - Afterload - pressure against which ventricles pump blood determined by total peripheral resistance

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  4. Regulation of heart rate?
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  5. What is Stroke Volume?
    • • The amount of blood that leaves the heart with each beat or ventricular contraction.
    • – Not all blood ejected
    • – Normal Adult 70 ml / beat
    • Stroke volume = end-diastolic volume – end-systolic volume
  6. Define cardiac cycle. Illustrate different events- electrical and mechanical in a cardiac cycle. [TU 2056]
    The cardiac cycle refers to the sequence of mechanical and electrical events that repeats with every heartbeat.[1] It includes the phase of relaxation diastole and the phase of contraction systole. Because the human heart is a four chambered organ, there are atrial systole, atrial diastole, ventricular systole and ventricular diastole.

    • The following is a summary of the cardiac cycle:
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  7. Explain hemodynamic changes during mid pregnancy. [TU 2056]
  8. Mention the pathophysiology of valvular heart disease. [TU 2073]
    • Pathophysiology of Aortic Stenosis
    •  A pressure gradient develops between the left ventricle and the aorta. (increased afterload)
    •  LV function initially maintained by compensatory pressure hypertrophy
    •  When compensatory mechanisms exhausted, LV function declines.

    • Pathophysiology of Mitral stenosis -
    •  Progressive Dyspnea (70%): LA dilation - pulmonary congestion (reduced emptying) - worse with exercise, fever, tachycardia, and pregnancy
    •  Increased Transmitral Pressures: Leads to left atrial enlargement and atrial fibrillation.
    •  Right heart failure symptoms: due to Pulmonary venous HTN
    •  Hemoptysis: due to rupture of bronchial vessels due to elevated pulmonary pressure

    • Pathophysiology of AR
    •  Combined pressure AND volume overload
    •  Compensatory Mechanisms: LV dilation, LVH. Progressive dilation leads to heart failure

    • Pathophysiology of MR
    •  Pure Volume Overload
    •  Compensatory Mechanisms: Left atrial enlargement, LVH and increased contractility
    •  Progressive left atrial dilation and right ventricular dysfunction due to pulmonary hypertension.
    •  Progressive left ventricular volume overload leads to dilation and progressive heart failure.
  9. Explain different types of hypoxia with examples. [TU 2067/2]
    There are four types of hypoxia:

    • (1) the hypoxemic type, in which the oxygen pressure in the blood going to the tissues is too low to saturate the hemoglobin;
    • (2) the anemic type, in which the amount of functional hemoglobin is too small, and hence the capacity of the blood to carry oxygen is too low;
    • (3) the stagnant type, in which the blood is or may be normal but the flow of blood to the tissues is reduced or unevenly distributed; and
    • (4) the histotoxic type, in which the tissue cells are poisoned and are therefore unable to make proper use of oxygen.

    In the case of anemic hypoxia, either the total amount of hemoglobin is too small to supply the body’s oxygen needs, as in anemia or after severe bleeding, or hemoglobin that is present is rendered nonfunctional. Examples of the latter case are carbon monoxide poisoning and metho-globinuria, in both of which the hemoglobin is so altered by toxic agents that it becomes unavailable for oxygen transport, and thus of no respiratory value.

    Stagnant hypoxia, in which blood flow through the capillaries is insufficient to supply the tissues, may be general or local. If general, it may result from heart disease that impairs the circulation, impairment of veinous return of blood, or trauma that induces shock. Local stagnant hypoxia may be due to any condition that reduces or prevents the circulation of the blood in any area of the body. Examples include Raynaud’s disease and Buerger’s disease, which restrict circulation in the extremities; the application of a tourniquet to control bleeding; ergot poisoning; exposure to cold; and overwhelming systemic infection with shock.
  10. Name the conditions where hyperbaric O2 therapy is useful. [TU 2067/2]
    • The following indications are approved uses of hyperbaric oxygen therapy -
    • Air or gas embolism
    • Carbon monoxide poisoning
    • Carbon monoxide poisoning complicated by cyanide poisoning
    • Central retinal artery occlusion
    • Clostridal myositis and myonecrosis (gas gangrene)
    • Crush injury, compartment syndrome, and other acute traumatic ischemias
    • Decompression sickness
    • Enhancement of healing in selected problem wounds
    • Diabetically derived illness, such as short-term relief of diabetic foot, diabetic retinopathy, diabetic nephropathy;
    • Exceptional blood loss (anemia)
    • Necrotizing soft tissue infections (necrotizing fasciitis)
  11. Explain the mechanism by which oxygen is transported in blood. [TU/6]
  12. Explain ABO blood groups and Rh antigen. What is Landsteiner law. [TU 2063/12]
  13. Mention hazards of mismatched blod transfusion. [TU 2063/12]
    • - Dose, age of product, and immunomodulation
    • Transfusion-associated circulatory overload. (TACO) - acute respiratory distress, tachycardia, relative hypertension, raised central venous pressure, natriuretic pulmonary oedema, and positive fluid balance.
    • - Transfusion-related acute lung injury - a new acute lung injury characterized by non-cardiogenic pulmonary oedema occurring within 6 h of transfusion.
    • - Haemolytic transfusion reactions and alloimmunization
    • - Non-haemolytic febrile transfusion reactions
    • - Allergic transfusion reactions
    • - Transfusion-associated dyspnoea (TAD) is characterized by respiratory distress within 24 h of transfusion which does not meet the criteria of an allergic reaction, TRALI, or TACO.
    • - Post-transfusion purpura
    • - Transfusion-associated graft vs host disease (TA-GVHD)
    • - Transfusion-related iron overload (haemosiderosis)
    • - Transfusion transmitted infection - bacterial contamination, viral contamination
    • - Complication of massive transfusion - Hypothermia, coagulopathy, acid base distrubance, electrolyte abnormalities
  14. What is massive transfusion?
    Massive transfusion is defined as the transfusion of 10 units of blood or the complete replacement of the circulating blood volume within 24 h.
  15. How do you differentiate the upper motor neuron lesion from LMN lesion. [TU 2060/4]
  16. Vasovagal syncope. [TU 2068/2]
    A vasovagal syncope, vasovagal episode or vasovagal response also called a neurocardiogenic syncope is a malaise mediated by the vagus nerve. Vasovagal syncope is the most common type of fainting.

    Signs and symptoms - Episodes of vasovagal syncope are typically recurrent and usually occur when the predisposed person is exposed to a specific trigger. Prior to losing consciousness, the individual frequently experiences early signs or symptoms such as lightheadedness, nausea, the feeling of being extremely hot or cold (accompanied by sweating), ringing in the ears (tinnitus), an uncomfortable feeling in the heart, fuzzy thoughts, confusion, a slight inability to speak or form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, black cloud-like spots in vision, and a feeling of nervousness can occur as well.

    Common triggers for vasovagal episodes include:

    • Prolonged standing or upright sitting
    • After or during urination (micturition syncope)
    • Straining, such as to have a bowel movement or during vomiting
    • Standing up very quickly (orthostatic hypotension)
    • During or post-biopsy procedures
    • Stress directly related to trauma
    • Stress

    Pathophysiology - Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. The nucleus tractus solitarii of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of parasympathetic nervous system (vagal) tone and withdrawal of sympathetic nervous system tone.

    Treatment for vasovagal syncope focuses on avoidance of triggers, restoring blood flow to the brain during an impending episode, and measures that interrupt or prevent the pathophysiologic mechanism
  17. What is the normal coronary blood flow at rest? List the factors influencing the coronary blood flow.
    • The left coronary artery supplies the anterior and left lateral portions of the left ventricle.
    • The right coronary artery supplies most of the right ventricle and the posterior side of the left ventricle. This is true in majority of people.

    Normal Coronary Blood Flow - Resting coronary blood flow is roughly 225 ml/min which results in 4- 5% of the total cardiac output. The coronary circulation is in place as only 1/10 mm of the endocardial heart layer is supplied by blood from the chambers. The rest of the heart needs its own nutrition therefore, coronary circulation is important for this function. Due to the fact that the blood is supplied directly from the aorta, the blood is highly oxygenated.

    • Control of coronary flow
    • 1. Oxygen - Coronary blood flow is regulated almost in exact proportion of oxygen demand for the cardiac muscle. If the heart needs more oxygen, then coronary blood flow must be increased. If there is a decrease in oxygen supply to the heart it is speculated that the heart causes vasodilator substances from the muscle cells to be released so the arterioles dilate.
    • 2, Nervous control - Sympathetic activation increases the coronary flow, parasympathetic decreases the coronary flow.
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Basic science CTVS - Physiology