lab 15 cardiopulmonary integration Flashcards
what is the effect of gravity on the standing human?
gravity can cause a tenth of the blood volume to pool in the abdomen and lower limbs, reducing venous return and ventricular filling; this can reduce cardiac output by 40%
what happens when humans stand up?
blood pressure temporarily drops due to reduced cardiac output when posture is suddenly changed from recumbent to standing, but most often returns to normal range in less than one minute
why does a passive tilt experienced exaggerate blood pressure compared to standing up on own?
when a person stands up, contractions of leg and abdominal muscles increases peripheral vascular resistance and promotes venous pumping by the contracting muscle; this better preserves venous return
what happens (sensing, pathways, response) when a person stands up?
there is a drop in blood pressure; the drop in pressure is sensed by the decreased stretch in the baroreceptor, causing vagal withdrawal and sympathetic stimulation. this causes increased sympathetic tone which results in increased norepinephrine and epinephrine
what effects do standing up have on ventilation perfusion?
standing up tends to change ventilation-perfusion due to the pooling of blood in the lower parts of the lungs
will a change in vagal tone when standing cause effects in other organs? why?
yes, if vagal activity is withdrawn to compensate for a postural change to standing, then all organs innervated by vagus receive decreased parasympathetic tone
what changes in end tidal CO2 and O2 are associated with the transition from a supine to an upright position
an increase in ventilation and a decrease in end tidal CO2 is normally associatd with transition from a supine to upright position. this is associated with an increase in tidal volume and an increase in functional residual capacity and change in distribution of cardiac output in lung as well as reduced venous return
what is PEEP
it is positive end expiratory pressure
what are the two types of PEEP?
one that is applied by a mechanical ventilator (applied PEEP 5-10cm H2O) and one that is due to incomplete expiration
how is PEEP useful in clinical situations?
it can be used to prevent or help re-open collapsed alveoli (this can be useful to maintain functional residual capacity of lung and improves gas exchange)
what are the negative consequences that PEEP can have?
it can increase intrathoracic pressure and thus compromise venous return and cardiac output. it can also increase pulmonary artery pressure and cause lung injury
what is a pulmonary embolism
it is a mass that has become lodged in the lung and can be a detached thrombus, fat, air, tumour cells or fragmented worms
what is the effect of pulmonary embolism on the pulmonary vascular resistance?
it increases it and thus increases the demands on the right heart while decreasing venous return
what is the effect of pulmonary embolism on the pulmonary ventilation perfusion ratio?
it increases the ratio (symptoms of dyspnea, coughing, chest pain)
what is the formula for calculating venous return?
venous return=mean arterial pressure-central venous pressure/total peripheral resistance
