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Not 100% sure on this one, but here’s how I approached it: histamine causes arterial dilation (decreased arteriolar resistance), but all of that blood has to go somewhere since you now have more blood flowing through the arteries and that somewhere is the capillaries (increased capillary hydrostatic pressure). Histamine causes increased permeability of the post-capillary venules (one of Dr. Sattar’s favorite facts) so you’d have increased capillary filtration rate.
1) higher than normal CO b/c blood is shunted from aorta to pulmonary arteries. This blood is added to the volume that was pumped into the pulmonary arteries by the RV. Now when the oxygenated blood returns to the LA & LV, the O2 content would be greater d/t higher blood volume. Also for that same reason more blood is returning to the LV (d/t LV volume plus fraction of RV volume). This increased the CO.
Right--> Left shunts have late cyanosis b/c the RV is pushing against the excess pressure generated by the LV. This leads to Eisenmenger Syndrome as RV enlarges and pushes against the pressure from the LV in the PDA. Thus shifting Left to right to right to Left and thus the late cyanosis
The anatomy is aorta-pulmonary artery-pulmonary veins-left atrium-left ventricle
Notice that the blood did not come across the right heart at all and because of the LEFT TO RIGHT shunt of the PDA, we add more volume to the LEFT side. Hence the increased left ventricular output
Tiotropium would cause constipation bc it’s an anticholinergic. Don’t have any insight into why dextromethorphan is the right answer though, other than process of elimination and diphenhydramine wouldn’t treat his symptoms.
I thought it was dextromethorphan because it would bind NMDA receptors and have weaker opioid effect = less constipation? Idk though :/
I agree. I mainly went by way of elimination but even DXM made me think of opiod-induced constipation. Though, all the other answer choices had obvious anticholinergic effects. At least, that was my reasoning for picking dxm.