Patent Application
20080076962
One embodiment of the invention will be described below with reference to the FIGURE.
The incubator 11 has therein a filter 19 for filtering air 18 taken from the outside and a flow regulating valve 22 for regulating flow rate of oxygen 21 supplied from a known oxygen supply source (not shown). The air 18 and the oxygen 21 pass through the filter 19 and the flow regulating valve 22 respectively and are then mixed with each other, and the gaseous mixture is sent into the accommodation space 12 by a blower 23. Therefore, by controlling the flow regulating valve 22, the oxygen concentration of the gaseous mixture sent into the accommodation space 12, that is, the fraction of inspired oxygen (FiO2) is controlled. Although not shown, the gaseous mixture sent into the accommodation space 12 circulates in the accommodation space 12 and is mixed with fresh air 18 taken from the outside and fresh oxygen 21, and the resultant gaseous mixture is sent again into the accommodation space 12 by the blower 23.
In such an incubator 11, the pulse oximeter 14 measures percutaneous arterial oxygen saturation (SpO2(t)) 24 of the accommodated newborn 13 and supplies the measured value to the control unit 15, at predetermined discrete sampling times “t” (for example, every 10 seconds). To the control unit 15, percutaneous arterial oxygen saturation (Set.SpO2) 25 as a set value, that is, as a desired value predetermined for the accommodated newborn 13 is also supplied in advance by operation of a control board (not shown) of the incubator 11. The control unit 15 obtains fraction of inspired oxygen (Set.FiO2(t)) 26 as a set value, that is, as a desired value in the accommodation space 12 at the sampling times “t” by the following equation (1) and supplies it to the control unit 17.
Set.FiO2(t)=α(SpO2(t)−Set.SpO2)+(β/N)ΣSet.FiO2(t−n) (1)
Each of α and β in the first and second terms in the right side of the equation (1) is a predetermined constant coefficient. N in the second term in the right side of the equation (1) denotes a value obtained by dividing an integration period by the sampling interval. For example, when the integration period is 20 minutes (=1200 seconds) and the sampling interval is 10 seconds as described above, N=120. Further, Σ in the second term in the right side of the equation (1) obtains the sum of n=1 to N. To avoid the risk of hypoxia even when Set.FiO2(t)<21, Set.FiO2(t)=21 which is equal to the oxygen concentration of atmosphere is set as the lower limit of oxygen concentration in the accommodation space 12. As oxygen concentration enabling stable supply in an actual incubator even when Set.FiO2(t)>65, the upper limit of the oxygen concentration in the accommodation space 12 is set as Set.FiO2(t)=65. Further, in the period of t−n<0, Set.FiO2(t−n)=Set.FiO2(0) is satisfied.
The first term in the right side of the equation (1) is a proportional control term obtained by multiplying the difference between the percutaneous arterial oxygen saturation (SpO2(t)) 24 as the actual measured value of the accommodated newborn 13 and the percutaneous arterial oxygen saturation (Set.SpO2) 25 as a predetermined set value, that is, as a desired value by the coefficient α. If the difference is positive, the control unit 15 operates to decrease the fraction of inspired oxygen (Set.FiO2(t)) 26 as a set value, that is, as a desired value in the accommodation space 12. If the difference is negative, the control unit 15 operates to increase the fraction of inspired oxygen (Set.FiO2(t)) 26 as a set value, that is, as a desired value in the accommodation space 12.
In accordance with the difference, the control unit 15 operates so as to change the fraction of inspired oxygen (Set.FiO2(t)) 26 as a set value, that is, as a desired value in the accommodation space 12. Specifically, when the percutaneous arterial oxygen saturation (SpO2(t)) 24 as the actual measured value of the accommodated newborn 13 is largely deviated from the percutaneous arterial oxygen saturation (Set.SpO2) 25 as a predetermined set value, that is, as a desired value, the fraction of inspired oxygen (Set.FiO2(t)) 26 as a set value, that is, as a desired value in the accommodation space 12 is largely changed. When the percutaneous arterial oxygen saturation (SpO2(t)) 24 as the actual measured value of the accommodated newborn 13 is close to the percutaneous arterial oxygen saturation (Set.SpO2) 25 as a predetermined set value, that is, as a desired value, the fraction of inspired oxygen (Set.FiO2(t)) 26 as a set value, that is, as a desired value in the accommodation space 12 is changed only a little.
The second term in the right side of the equation (1) is an integral control term obtained by multiplying an average value ((1/N)ΣSet.FiO2(t−n)) of the fraction of inspired oxygen (Set.FiO2(t−n)) as a set value, that is, as a desired value obtained in the integral period, that is, at the N sampling times in the past by the coefficient β. Therefore, when the fraction of inspired oxygen (Set.FiO2(t−n)) as a set value, that is, as a desired value in the past continues to be high, the second term is also high. When the set value in the past continues to be low, the second term is also low.
If the percutaneous arterial oxygen saturation (SpO2(t)) 24 as the actual measured value of the accommodated newborn 13 is equal to the percutaneous arterial oxygen saturation (Set.SpO2) 25 as a predetermined set value, that is, as a desired value, the first term in the right side of the equation (1) becomes zero. Consequently, the second term in which the average value of N times in the past is multiplied by the coefficient β becomes the fraction of inspired oxygen (Set.FiO2(t)) 26 as the set vale, that is, as the desired value in the accommodation space 12.
On the other hand, the fraction of inspired oxygen measuring device 16 in the incubator 11 measures fraction of inspired oxygen (FiO2) 27 in the accommodation space 12 and supplies the measured value to the control unit 17. The control unit 17 controls the flow regulating valve 22 by supplying a valve regulation amount 28 of the flow regulating valve 22 to the flow regulating valve 22 so that the fraction of inspired oxygen (FiO2) 27 as a measured value supplied from the fraction of inspired oxygen measuring device 16 becomes equal to the fraction of inspired oxygen (Set.FiO2(t)) 26 as the set value, that is, as the desired value supplied from the control unit 15.
Therefore, the control unit 15 obtains the fraction of inspired oxygen (Set.FiO2(t)) 26 as the set value, that is, as the desired value in the accommodation space 12 by using the percutaneous arterial oxygen saturation (SpO2(t)) 24 as the actual measured value of the accommodated newborn 13 and the percutaneous arterial oxygen saturation (Set.SpO2) 25 as the predetermined set value, that is, as the desired value. The control unit 17 controls the flow regulating valve 22 so that the fraction of inspired oxygen (FiO2) 27 as an actual measured value in the accommodation space 12 becomes equal to the fraction of inspired oxygen (Set.FiO2(t)) 26 as the set value, that is, as the desired value. The percutaneous arterial oxygen saturation (SpO2(t)) 24 of the accommodated newborn 13 accommodated in the accommodation space 12 in the incubator 11 becomes rapidly close to the percutaneous arterial oxygen saturation (Set.SpO2) 25 as the predetermined set value, that is, as the desired value, and this state is stably maintained.
Although the above values are used as the sampling interval and the integral period for measuring the percutaneous arterial oxygen saturation (SpO2(t)) 24 by the control unit 15 in the above embodiment, the invention is not limited to the values but may use other values.
The present invention can be utilized for manufacture or the like of an oxygen concentration control apparatus for an incubator and an incubator using the same. While measuring oxygen in arterial blood of a newborn accommodated in an incubator, the apparatus obtains oxygen fraction of inspired gas supplied to the accommodated newborn, which is used for setting the measured value to a predetermined set value, that is, a desired value.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-255636 | Sep 2006 | JP | national |
