A shaft for a balloon dilation catheter comprises a proximal portion wherein a guidewire tubular member is disposed coaxially within an outer tubular member, a shaft transitional portion, wherein the guidewire member is disposed within the outer member, with at least one distal tubular member not present in the proximal portion, a shaft distal portion, wherein the guidewire member and the distal members are disposed side-by-side and encased within a distal body, and fluid-tight barrier within a proximal lumen blocking the flow of fluid in the proximal lumen, but allowing the proximal lumen to remain in fluid communication with a distal lumens.