Method and apparatus for determining respiratory system resistance during assisted ventilation
First Claim
1. A method of determining respiratory system resistance (R) in a patient receiving gas from a ventilatory assist device (ventilator), comprising:
- estimating the flow rate ({dot over (V)}) and volume (V) of gas received by the patient from the ventilator;
estimating pressure near the airway of the patient (Paw);
generating a signal that results in a step decrease (negative pulse) in the pressure and/or flow output of the ventilator during selected inflation cycles;
measuring Paw, {dot over (V)} and V at a point (TO) near the beginning of the pulse (PawO, {dot over (V)}, VO), at a point (TI) near the trough of the negative pulse (Paw1, {dot over (V)}1, V1), and at a point (T−
1) preceding TO but after the onset of inspiratory effort (Paw−
1, {dot over (V)}−
1, V−
1); and
calculating the value of resistance (R) from the differences between Paw, {dot over (V)} and V at TO and at TI and where the change in patient generated pressure (Pmus) in the interval TO→
TI (Δ
Pmus(TO→
TI)) is estimated, by extrapolation, from the differences between Paw, {dot over (V)} and V at TO and at T−
1, in accordance with equation (8), as follows;
R=[(PawO−
Paw1+(Δ
t/Δ
t−
I)(PawO−
Paw−
1))−
E(VO−
V1+(Δ
t/Δ
t−
I)(VO−
V−
1))]/(VO−
V1+(Δ
t/Δ
t−
I)({dot over (V)}O−
{dot over (V)}−
1))
(8).
1 Assignment
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Accused Products
Abstract
Method and apparatus are described for determining respiratory system resistance (R) in a patient receiving gas from a ventilator. A negative pulse in the pressure and/or flow output of the ventilator during selected inflation cycles is generated and Paw, {dot over (V)} and V are measured at a point (To) near the beginning of the pulse, at a point (T1) near the trough of the negative pulse and at a point (T−1) preceding To. The value of R is calculated from the difference between Paw, {dot over (V)} and V at To and at T1 and where the change in patient generated pressure (Pmus) in the interval To−T1 is estimated by extrapolation from the different between Paw, {dot over (V)} and V and To and at T−1, in accordance with Equation 8.
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Citations
47 Claims
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1. A method of determining respiratory system resistance (R) in a patient receiving gas from a ventilatory assist device (ventilator), comprising:
-
estimating the flow rate ({dot over (V)}) and volume (V) of gas received by the patient from the ventilator;
estimating pressure near the airway of the patient (Paw);
generating a signal that results in a step decrease (negative pulse) in the pressure and/or flow output of the ventilator during selected inflation cycles;
measuring Paw, {dot over (V)} and V at a point (TO) near the beginning of the pulse (PawO, {dot over (V)}, VO), at a point (TI) near the trough of the negative pulse (Paw1, {dot over (V)}1, V1), and at a point (T−
1) preceding TO but after the onset of inspiratory effort (Paw−
1, {dot over (V)}−
1, V−
1); and
calculating the value of resistance (R) from the differences between Paw, {dot over (V)} and V at TO and at TI and where the change in patient generated pressure (Pmus) in the interval TO→
TI (Δ
Pmus(TO→
TI)) is estimated, by extrapolation, from the differences between Paw, {dot over (V)} and V at TO and at T−
1, in accordance with equation (8), as follows;
R=[(PawO−
Paw1+(Δ
t/Δ
t−
I)(PawO−
Paw−
1))−
E(VO−
V1+(Δ
t/Δ
t−
I)(VO−
V−
1))]/(VO−
V1+(Δ
t/Δ
t−
I)({dot over (V)}O−
{dot over (V)}−
1))
(8). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. An apparatus which interfaces with ventilatory assist devices (ventilators) and which determines respiratory system resistance (R), comprising:
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a flowmeter, with associated electronic circuitry, that estimates the flow rate ({dot over (V)}) and volume (V) of gas received by a patient;
a pressure sensor that estimates pressure near the airway of the patient (Paw); and
electronic circuitry which receives the Paw, {dot over (V)} and V signals from above mentioned circuitry and which is also connected to a control system of the ventilator, comprising;
circuitry that generates an output that results in a step decrease (negative pulse) in the pressure and/or flow output of the ventilator during selected inflation cycles;
circuitry that measures Paw, {dot over (V)} and V at a point (TO) near the beginning of the pulse (PawO, {dot over (V)}O, VO), at a point (TI) near the trough of the negative pulse (Paw1, {dot over (V)}I, V1), and at a point (T−
1) preceding TO but after the onset of inspiratory effort (Paw−
1, {dot over (V)}−
I, V−
1);
circuitry to calculate the value of resistance (R) from the differences between Paw, {dot over (V)} and V at TO and at TI and where the change in patient generated pressure (Pmus) in the interval TO→
TI(Δ
Pmus(TO→
TI)) is estimated, by extrapolation, from the differences between Paw, {dot over (V)} and V at TO and at T−
1, in accordance with equation (8), as follows;
R=[(PawO−
Paw1+(Δ
t/Δ
t−
1)(PawO−
Paw−
1))−
E(VO−
V1+(Δ
t/Δ
t−
1)(VO−
V−
1))]/({dot over (V)}O−
{dot over (V)}1+(Δ
t/Δ
t−
1)({dot over (V)}O−
{dot over (V)}−
1))
(8). - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47)
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Specification