GB1500627A - Apparatus for use in determining respiratory path resistance - Google Patents

Abstract

1500627 Measuring respiratory path resistance SIEMENS AG 19 March 1975 [22 March 1974] 11528/75 Heading G1N(E) In an apparatus for determining the respiratory path resistance of a patient, the patient breathes into a mouthpiece 2 of a breathing tube 1 containing a laminae flow resistance 5 and a piston pump (providing sinusoidal pressure variations). Instead of the pump a source of pressure pulses Fig. 3 (not shown) is used to superimpose the alternating pressure variations on the respiratory flow. The result is monitored by a pressure sensitive transducer (e.g. a pressure sensitive transistor, or a Piezo microphone). The respiratory path resistance Raw can then be calculated by the computational circuit shown in Fig. 2, and according to the formula shown there. A converter 11 provides an electrical output signal proportional to the alternating component PM of the flow, which signal is fed to a multiplication device 14. There it is multiplied by a value representative of the basic resistance R o and the signal is fed to a subtraction circuit 13. The circuit 13 subtracts the signal from a further signal derived from a multiplication device 12 which forms the product between the known sinusoidal amplitude V of the alternating flow pulsations and the basic resistance value R 0 . The outputs of devices 13 and 14 are fed to a dividing device 15 whose output (proportional to the respiratary path resistance) is fed to an indicating or register device 16. A modification utilizing a bi-stable circuit responsive to the "zero point" in the alternating pressure component and to a fixed point later on in the cycle, is described for calculating the phase shift between the flow pulsations V and the received pressure P M . A formula is disclosed for calculating the respiratory path resistance from the phase shift. A further embodiment, Figs.3 and 4 (not shown), is described utilizing the pressure pulses by means of sample and hold circuits. It is suggested that if a sinusoidal filter (at the base pulsation frequency) is used, the respirator path resistance can be determined in a manner similar to Fig.2.