65) THE FOLLOWING ARE TRUE

[Editor]

a) pulmonary artery pressure is one third of mean aortic pressure
b) pulmonary vascular resistance is lower than systemic vascular resistance
c) pulmonary arterial occlusion pressure gives the left atrial pressure
d) hypoxia cause pulmonary artery dilation
e) nitric oxide is involved in the hypoxic pulmonary vasoconstriction mechanism

[Editor]

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Typically pulmonary artery pressure is 1/5 systemic circulatory pressure. Normal ranges are 15-30mmHg systolic, 0-8mmHg diastolic and 10-15mmHg mean. Normal values for systemic vascular resistance ranges from 900-1400 dynes.s/cm5. Normal values for pulmonary vascular resistance ranges from 20-120 dyne.s/cm5. Pulmonary arterial occlusion pressure is measured within the pulmonary arterial system during pulmonary artery catheterisation, with the catheter’s tip wedged in a tapering branch of one of the pulm arteries. In most patients, represents LA filling pressure, and thus LVEDP. It is an indirect indicator of LVEDV and myocardial fibre length. Hypoxia causes reflex vasoconstriction of the pulmonary arterioles in response to low PO2 (< 11-13 KPa; 80-100 mmHg). This is designed to improve the match between perfusion and ventilation by diverting blood from poorly ventilated areas to better ventilated ones.
Nitric Oxide is responsible for vascular relaxation. It is synthesised in endothelial cells during the oxidation of L-arginine to L-citrulline, the reaction being catalysed by NOS. In pulmonary hypertension inhaled NO has been used to produce selective pulmonary vasodilatation without systemic effects.