Complex sentence: The weaker suction makes them more suitable for smaller sized veins, because the standardised suction of the tubes may cause the veins of elderly people or those with delicate veins, to collapse.
Split into simpler sentences: The weaker suction makes them more suitable for smaller sized veins. Because of the standardised suction of the tubes, they may cause the veins of elderly people, or those with delicate veins, to collapse.