Apparatus, computer system and computer program for determining intrathoracic blood volume and other cardio-vascular parameters
Apparatus, computer system, computer program and storage medium for determining intrathoracic blood volume (ITBV) and other cardio-vascular parameters of a patient by thermodilution measurements. The apparatus includes: temperature influencing means for introducing a traveling temperature deviation to a patient's blood stream, a temperature sensor device for measuring the local temperature of the patient's blood downstream of the temperature influencing means, a computer system adapted to: record local blood temperature measured as a function of time to determine a thermodilution curve, determine global enddiastolic blood volume (GEDV) and intrathoracic thermovolume (ITTV) from the thermodilution curve, determine intrathoracic blood volume (ITBV) as a function of GEDV, ITTV and the airway pressure inside the patient's lungs (P). By determining ITBV not only from GEDV but also a function of ITTV and P enhanced accuracy can be obtained, especially if the patient suffers from pulmonary edema and/or is mechanically ventilated.
1. An apparatus for determining intrathoracic blood volume (ITBV) and other cardio-vascular parameters of a patient by thermodilution measurements comprising:
a) temperature influencing means for provoking an initial local temperature change in the proximity of a first place of a patient's vascular system, thus introducing a traveling temperature deviation to patient's blood stream,
b) a temperature sensor device for measuring the local temperature of patient's blood at a second place of patient's vascular system downstream of said first place,
c) means for determining a pressure at least approximately representing an airway pressure of said patient,
d) a computer system coupled to said temperature sensor device and said means for determining said pressure and adapted to record said patient's local blood temperature measured at said second place as a function of time to determine a thermodilution curve,
e) said computer system being further adapted to determine patient's global enddiastolic blood volume (GEDV) and patient's intrathoracic thermovolume (ITTV) from said thermodilution curve,
f) said computer system being further adapted to determine patient's intrathoracic blood volume (ITBV) according to the following formula:
ITBV=f ( GEDV,ITTV,P ),
ITBV being the intrathoracic blood volume, GEDV being the global enddiastolic blood volume, ITTV being the intrathoracic thermovolume, P being said airway pressure inside patient's lungs.
2. The apparatus according to claim 1 , wherein said function f(GEDV, ITTV, P) is selected to be
f ( GEDV,ITTV,P )= a·GEDV+b+c·ITTV+d·P
a being a species dependent parameter, with 1<a<2
b being a species dependent parameter, including zero
c being a species dependent parameter, with c≦0
d being a species dependent parameter, including zero,
with the restriction that c and d may not be zero simultaneously.
3. The apparatus according to claim 1 , wherein said function f(GEDV, ITTV, P) is selected to be
f
(
GEDV
,
ITTV
,
P
)
=
a
c
(
ITTV
-
GEDV
)
(
ITTV
norm
-
GEDV
norm
)
+
d
P
P
norm
GEDV
+
b
a, b, c, and d being species dependent parameters, with 1<a/(c+d)<2, wherein ITTVnorm, GEDVnorm and Pnorm are empirical normal values of ITTV, GEDV and P, respectively.
4. The apparatus according to claim 1 , wherein said function f(GEDV, ITTV, P) is selected to be
ITBV
=
a
·
GEDV
[
c2
·
(
ITTV
-
GEDV
)
(
ITTVnorm
-
GEDVnorm
)
+
1
]
·
[
d2
·
P
Pnorm
+
1
]
+
b
+
c1
·
(
ITTV
-
GEDV
)
(
ITTVnorm
-
GEDVnorm
)
+
d1
·
P
Pnorm
a, b, c1, c2, d1, d2 being species dependent parameters, with 0.5≦a/(c2+1)(d2+1)≦10, wherein ITTVnorm, GEDVnorm and Pnorm are empirical normal values of ITTV, GEDV and P, respectively.
5. The apparatus according to claim 1 wherein P is set equal to a transmural lung pressure Ptm, being defined as
Ptm=ITP−Pmv,
ITP being a intrathoracic pressure and Pmv being a microvascular pressure.
6. The apparatus according to claim 1 , wherein P is a pressure measured in the airway of a mechanical respirator.
7. The apparatus according to claim 6 , wherein P is a positive end expiratory pressure (PEEP).
8. The apparatus according to claim 1 , wherein P is a mean airway pressure.
9. The apparatus according to claim 1 which is adapted to determine at least one of said cardio-vascular parameters by transpulmonary thermodilution.
10. The apparatus according to claim 1 which is adapted to determine an estimate of extravascular lung water (EVLW) as
EVLW=ITTV−ITBV,
EVLW being the extravascular lung water.
11. The apparatus according to claim 1 which is adapted to determine ITTV as
ITTV=CO·MTT,
CO being the cardiac output and MTT being the mean transit time, indicating the time required by said temperature deviation to travel from said first place to said second place.
12. The apparatus according to claim 1 which is adapted to determine GEDV as
GEDV=CO ·( MTT−DST ),
CO being the cardiac output and MTT being the mean transit time, indicating the time required by said temperature deviation to travel from said first place to said second place and DST being a down slope time of said thermodilution curve.
13. The apparatus according to claim 1 further comprising a pressure sensing device coupled to said computer system.
14. A computer system comprising first coupling means to couple said computer system to temperature influencing means, second coupling means to couple said computer system to a temperature sensor device, third coupling means for coupling said computer system to means for determining a pressure at least approximately representing an airway pressure of said patient, and accessing means to access executable instructions to cause said computer system
a) to control temperature influencing means for provoking an initial local temperature change in the proximity of a first place of a patient's vascular system, thus introducing a traveling temperature deviation to patient's blood stream,
b) to record said patient's local blood temperature measured by a temperature sensor device for measuring the local temperature of patient's blood at a second place of patient's vascular system downstream of said first place as a function of time to determine a thermodilution curve,
c) to determine patient's global enddiastolic blood volume (GEDV) and patient's intrathoracic thermovolume (ITTV) from said thermodilution curve,
d) to determine patient's intrathoracic blood volume (ITBV) according to the following formula:
ITBV=f ( GEDV,ITTV,P ),
ITBV being the intrathoracic blood volume, GEDV being the global enddiastolic blood volume, ITTV being the intrathoracic thermovolume, P being said airway pressure inside patient's lungs.
15. The computer system according to claim 14 , wherein said function f(GEDV, ITTV, P) is selected to be
f ( GEDV,ITTV,P )= a·GEDV+b+c·ITTV+d·P
a being a species dependent parameter, with 1<a<2
b being a species dependent parameter, including zero
c being a species dependent parameter, with c≦0
d being a species dependent parameter, including zero,
with the restriction that c and d may not be zero simultaneously.
16. The computer system according to claim 14 , said function f(GEDV, ITTV, P) is selected to be
f
(
GEDV
,
ITTV
,
P
)
=
a
c
(
ITTV
-
GEDV
)
(
ITTV
norm
-
GEDV
norm
)
+
d
P
P
norm
GEDV
+
b
a, b, c, and d being species dependent parameters, with 1<a/(c+d)<2, wherein ITTVnorm, GEDVnorm and Pnorm are empirical normal values of ITTV, GEDV and P, respectively.
17. The computer system according to claim 14 , wherein said function f(GEDV, ITTV, P) is selected to be
ITBV
=
a
·
GEDV
[
c2
·
(
ITTV
-
GEDV
)
(
ITTVnorm
-
GEDVnorm
)
+
1
]
·
[
d2
·
P
Pnorm
+
1
]
+
b
+
c1
·
(
ITTV
-
GEDV
)
(
ITTVnorm
-
GEDVnorm
)
+
d1
·
P
Pnorm
a, b, c1, c2, d1, d2 being species dependent parameters, with 0.5≦a/(c2+1)(d2+1)≦10, wherein ITTVnorm, GEDVnorm and Pnorm are empirical normal values of ITTV, GEDV and P, respectively.
18. The computer system according to claim 14 , comprising a port coupled to a pressure sensor arranged in the airway of a mechanical respirator.
19. The computer system according to claim 14 being caused to determine an estimate of extravascular lung water (EVLW) as
EVLW=ITTV−ITBV,
EVLW being the extravascular lung water.
20. The computer system according to claim 14 being caused to determine said ITTV as
ITTV=CO·MTT,
CO being the cardiac output and MTT being the mean transit time, indicating the time required by said temperature deviation to travel from said first place to said second place.
21. The computer system according to claim 14 being caused to determine said GEDV as
GEDV=CO ·( MTT−DST ),
CO being the cardiac output and MTT being the mean transit time, indicating the time required by said temperature deviation to travel from said first place to said second place and DST being a down slope time of said thermodilution curve.
22. A computer program for determining intrathoracic blood volume (ITBV) and other cardio-vascular parameters of a patient by thermodilution measurements comprising instructions executable by a computer system to cause said computer system
a) to control temperature influencing means for provoking an initial local temperature change in the proximity of a first place of a patient's vascular system, thus introducing a travelling temperature deviation to patient's blood stream,
b) to record said patient's local blood temperature measured by a temperature sensor device for measuring the local temperature of patient's blood at a second place of patient's vascular system downstream of said first place ( 101 ) as a function of time to determine a thermodilution curve,
c) to read in a pressure at least approximately representing an airway pressure of said patient,
d) to determine patient's global enddiastolic blood volume (GEDV) and patient's intrathoracic thermovolume (ITTV) from said thermodilution curve,
e) to determine patient's intrathoracic blood volume (ITBV) according to the following formula:
ITBV=f ( GEDV,ITTV,P ),
ITBV being the intrathoracic blood volume, GEDV being the global enddiastolic blood volume, ITTV being the intrathoracic thermovolume, P being an airway pressure inside patient's lungs.
23. The computer program according to claim 22 , wherein said function f(GEDV, ITTV, P) is selected to be
f ( GEDV,ITTV,P )= a·GEDV+b+c·ITTV+d·P
a being a species dependent parameter, with 1<a<2
b being a species dependent parameter, including zero
c being a species dependent parameter, with c≦0
d being a species dependent parameter, including zero,
with the restriction that c and d may not be zero simultaneously.
24. The computer program according to claim 22 , said function f(GEDV, ITTV, P) is selected to be
f
(
GEDV
,
ITTV
,
P
)
=
a
c
(
ITTV
-
GEDV
)
(
ITTV
norm
-
GEDV
norm
)
+
d
P
P
norm
GEDV
+
b
a, b, c, and d being species dependent parameters, with 1<a/(c+d)<2, wherein ITTVnorm, GEDVnorm and Pnorm are empirical normal values of ITTV, GEDV and P, respectively.
25. The computer program according to claim 22 , wherein said function f(GEDV, ITTV, P) is selected to be
ITBV
=
a
·
GEDV
[
c2
·
(
ITTV
-
GEDV
)
(
ITTVnorm
-
GEDVnorm
)
+
1
]
·
[
d2
·
P
Pnorm
+
1
]
+
b
+
c1
·
(
ITTV
-
GEDV
)
(
ITTVnorm
-
GEDVnorm
)
+
d1
·
P
Pnorm
a, b, c1, c2, d1, d2 being species dependent parameters, with 0.5≦a/(c2+1)(d2+1)≦10, wherein ITTVnorm, GEDVnorm and Pnorm are empirical normal values of ITTV, GEDV and P, respectively.
26. The computer program according to claim 22 causing said computer system to determine an estimate of extravascular lung water (EVLW) as
EVLW=ITTV−ITBV,
EVLW being the extravascular lung water.
27. The computer program according to claim 22 causing said computer system to determine ITTV as
ITTV=CO·MTT,
CO being the cardiac output and MTT being the mean transit time, indicating the time required by said temperature deviation to travel from said first place to said second place.
28. The computer program according to claim 22 causing said computer system to determine GEDV as
GEDV=CO ·( MTT−DST ),
CO being the cardiac output and MTT being the mean transit time, indicating the time required by said temperature deviation to travel from said first place to said second place and DST being a down slope time of said thermodilution curve.
29. A storage medium having physically stored thereon a computer program as claimed in claim 22 .