Hypoxic pulmonary vasoconstriction due to -
Ans. is 'b' i.e., Reversible pulmonary vasoconstriction due to hypoxiaPulmonary hypoxic vasoconstrictiono Hypoxic pulmonary vasoconstriction (HPV) is an adaptive vasomotor response to alveolar hypoxia which redistributes blood to optimally ventilated lung segments by an active process of vasoconstriction, particularly involving the small muscular resistance pulmonary arteries (PA).o HPV is intrinsic to the lung and the mechanism involves redox based O2 sensor.o Alveolar hypoxia triggers the pulmonary vessels to constrict.# Alveolar hypoxia triggers the pulmonary vessels to constrict, directing blood away from poorly/nonventilated areas to better ventilated segments thereby improving ventilation/perfusion matching.o Clinically HPV is proportional to the degree of local hypoxia and is triggered primarily in response to an alveolar oxygen partial pressure (PAO2 less than 100 mmHg.o HPV onsets within seconds of moderate hypoxia and reverses quickly on restoration of normoxic ventilation.o HPV shunts bloodfrom poorly oxygenated areas to better ventilated lung segments, thereby optimizing ventilation perfusion matching, reducing shunt fraction and optimizing O2 delivery in conditions such as atelactasis and pneumonia.The onset of HPV occurs in two phase:-# Initial rapid onset phase (minutes)# Delayed phase (hours)
Irreversible pulmonary vasocontriction hypoxia
Reversible pulmonary vasoconstriction due to hypoxia
Direct blood to poorly ventilated areas
Occurs hours after pulmonary vasoconstriction
Blood