Methods and apparatus for passive, proportional, valveless gas sampling and delivery

A method of delivering a medicine to a person with a flow tube (300) defining a lumen (312) having an inlet (308/PB) and an outlet (302), the lumen defining a vena contracta (310) between the inlet and the outlet, a first port (PC) between the inlet and the vena contracta, and a second port (PA) between the vena contracta and the outlet, the method comprising:

• receiving an inhalation of the person via the lumen, the vena contracta causing a fraction of the inhalation to pass through the second port to a chamber holding the medicine;
• mixing the fraction of the inhalation with at least a portion of the medicine in the chamber to form a dose of the medicine;
• conveying the dose of the medicine from the chamber to the first port of the flow tube;
• and
• delivering the dose of the medicine from the inlet to the person via the lumen.

A medicine delivery system comprising:

• a flow tube (300) having:
• a distal end (302);
• a proximal end (308/PB);
• an inner lumen (312) extending from the distal end to the proximal end to convey inhaled breaths of a person from the distal end to the proximal end, the inner lumen defining a vena contracta (310) between the distal end and the proximal end, wherein a first distance between the vena contracta and the proximal end is greater than a second distance between the vena contracta and the distal end;
• a first port (PC) between the proximal end and the vena contracta;
• and
• a second port (PA) between the vena contracta and the distal end;
• a chamber (390) to hold medicine (392), the chamber in fluid communication with the first port and the second port, to mix the inhaled breaths with the medicine to form a mixture of inhaled breaths and at least a portion of the medicine;
• a first conduit, connecting the first port to the chamber to convey the inhaled breaths from the flow tube to the chamber;
• a second conduit connecting the chamber to the second port to convey the mixture from the chamber to the flow tube;
• and
• a meter (394), disposed in the second conduit, to control a flow rate of the mixture through the second conduit.