A pressure guidewire comprising: a shaft tube assembly comprising: a proximal section (124, 610, 710) comprising a first tubular body comprising a proximal end, a distal end, a proximal outside surface and a proximal inside surface, the proximal inside surface enclosing a proximal portion of a central lumen, the proximal outside surface comprising an outer surface of the pressure guidewire; a middle section (148, 713) comprising a proximal end, a middle section outside surface, a middle section inside surface, the middle section inside surface disposed about a space within the pressure guidewire, the proximal end of the middle section being separate from and coupled to the distal end of the proximal section; a sensor housing section extending distally relative to the middle section; a hypotube comprising a proximal end portion and a distal end portion, the hypotube extending through the space about which the middle section inside surface is disposed, the proximal end portion of the hypotube coupled with the distal end of the proximal section and the distal end portion of the hypotube being coupled to the sensor housing; a tip pressure sensor positioned in the sensor housing section; and characterized in: an optical fiber centered within the pressure guidewire in the proximal section and centered within the hypotube in the middle section, and in that the proximal inside surface comprises a first diameter and the middle section inside surface comprises a second diameter, the first diameter being less than the second diameter. a shaft tube assembly comprising: a proximal section (124, 610, 710) comprising a first tubular body comprising a proximal end, a distal end, a proximal outside surface and a proximal inside surface, the proximal inside surface enclosing a proximal portion of a central lumen, the proximal outside surface comprising an outer surface of the pressure guidewire; a middle section (148, 713) comprising a proximal end, a middle section outside surface, a middle section inside surface, the middle section inside surface disposed about a space within the pressure guidewire, the proximal end of the middle section being separate from and coupled to the distal end of the proximal section; a sensor housing section extending distally relative to the middle section; a proximal section (124, 610, 710) comprising a first tubular body comprising a proximal end, a distal end, a proximal outside surface and a proximal inside surface, the proximal inside surface enclosing a proximal portion of a central lumen, the proximal outside surface comprising an outer surface of the pressure guidewire; a middle section (148, 713) comprising a proximal end, a middle section outside surface, a middle section inside surface, the middle section inside surface disposed about a space within the pressure guidewire, the proximal end of the middle section being separate from and coupled to the distal end of the proximal section; a sensor housing section extending distally relative to the middle section; a hypotube comprising a proximal end portion and a distal end portion, the hypotube extending through the space about which the middle section inside surface is disposed, the proximal end portion of the hypotube coupled with the distal end of the proximal section and the distal end portion of the hypotube being coupled to the sensor housing; a tip pressure sensor positioned in the sensor housing section; and characterized in: an optical fiber centered within the pressure guidewire in the proximal section and centered within the hypotube in the middle section, and in that the proximal inside surface comprises a first diameter and the middle section inside surface comprises a second diameter, the first diameter being less than the second diameter. an optical fiber centered within the pressure guidewire in the proximal section and centered within the hypotube in the middle section, and in that the proximal inside surface comprises a first diameter and the middle section inside surface comprises a second diameter, the first diameter being less than the second diameter.