The phrase "deep vein" refers to blood vessels that are located deeper in our body, typically beneath the muscles. These veins carry the blood back to the heart for oxygenation and nutrient replenishment. Full definition
When he wrote it, my brother had gone through the wars, so to speak, spiritual and emotional, and it has a wry, nightmarish intensity to it, run through by deep veins of both withering cynicism and luminous faith, that I found fascinating and rather disturbing. (firstthings.com)
We can assume that The Shack has struck some sort of deep vein in our theological consciousness, and that dismissing it as kitsch will do nobody a pinch of good. (firstthings.com)
For flights longer than seven hours the risk of suffering from deep vein thrombosis goes up significantly. (compressioncarl.com)