PATIENT MOVEMENT MONITORING APPARATUS

• US 3,875,929 A
• Filed: 07/23/1973
• Issued: 04/08/1975
• Est. Priority Date: 07/25/1972
• Status: Expired due to Term

• Current Assignee: John Thomas Grant
• Original Assignee: John Thomas Grant
• Inventors: Grant, John Thomas
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/381,982
• Time in Patent Office: 624 Days
• Field of Search: 128/2R,2S,2A,2N,2.08,DIG.29 340/279,258A
• US Class Current: 600/429
• CPC Class Codes: A61B 5/0507 using microwaves or terahertz waves
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: G01S 13/02 Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
• CPC Class Codes: Y10S 5/94 with alarm means

Abstract

A system for monitoring cyclic movements, such as respiration of a patient, and indicating when such movement ceases comprises a scanner arranged in use to provide a movement-sensitive field. For patient monitoring this field envelopes at least part of the patient. Circuitry for monitoring variations in the field controls indicator circuitry which provides the indication that movement has ceased. The indicator circuitry provides a signal for each successive group of a predetermined number of movement cycles and responds to the absence of such a signal in a predetermined interval from the preceding signal to provide the indication that movement has ceased. In the case of monitoring respiration, an alarm is given after a predetermined delay from cessation of breathing unless the patient'"'"''"'"'s movements provide signals in the scanner output corresponding to a predetermined number of breathing cycles. Extraneous movements near the patients are unlikely to cause this to happen, so that the system is virtually certain to provide an alarm as soon as possible after cessation of breathing without being inhibited by extraneous movements.

Claims

1. Movement monitoring apparatus comprising:

a. microwave radar means providing a limited movement-sensitive field of microwave radiation;

b. monitor circuit means monitoring disturbances of said field and providing at its output a pulsed signal indicative of the degree of field disturbance;

c. resettable aggregating circuit means coupled to the output of said monitor circuit means to aggregate said pulsed signal to provide at its output a signal voltage the level of which is indicative of said degree of field disturbance;

d. threshold circuit means defining a predetermined threshold voltage and coupled to the output of said aggregating circuit means to receive said signal voltage;

e. trigger circuit means to said threshold circuit means to be activated thereby when said signal voltage reaches said predetermined threshold voltage;

f. resetting circuit means coupled to the output of said trigger circuit means and to said aggregating circuit means to re-set said aggregating circuit means when said trigger circuit means is activated;

g. resettable delay circuit means coupled to the output of said trigger circuit means and providing a predetermined delay between the appearance at its input of an input signal caused by activation of said trigger circuit means and the appearance at its output of a pre-determined output signal level, activation of said trigger circuit means re-setting said delay circuit means to re-start said pre-determined delay; and

h. alarm circuit means connected to the output of said delay circuit means and activated by said pre-determined output signal level thereof, said predetermined threshold voltage and said predetermined output signal level of said delay circuit means being so selected in relation to the frequency of said pulsed output signal of said monitor circuit means that said delay circuit means is repeatedly re-set by the output of said trigger circuit means so long as there is a predetermined degree of movement in the movement-sensitive field and is not re-set after the degree of movement falls below said predetermined degree until there is generated a sufficient number of cycles of said pulsed output signal of said monitor circuit means to provide at the output of said aggregating circuit means a signal voltage sufficient to cause activation of said trigger circuit means.

2. A system as set forth in claim 1, in which said aggregating circuit means includes a reservoir capacitance charged via a transistor.

3. A system as set forth in claim 1, in which said trigger circuit means is a Schmidt trigger.

4. A system as set forth in claim 1, in which said re-setting circuit means includes an inverter.

5. A system as set forth in claim 1, in which said alarm circuit means is connected to the output of said delay circuit means through an inverter which inhibits operation of said alarm circuit means while the output signal level of said delay circuit means exceeds said predetermined value.

6. A system as set forth in claim 1, in which said radar means provides at its output Doppler frequencys signal indicative of movements in the movement-sensitive field and in which said monitor circuit means includes a frequency-selective amplifier for said Doppler frequency signals, having a narrow pass-band centered on a frequency corresponding to a particular class of movement to be monitored, and further trigger circuit means connected to the output of said amplifier and providing at its output said pulsed output signal of said monitor circuit means.

7. A system as set forth in claim 6, in which said further trigger circuit means is a Schmidt trigger.