Abstract
We have developed a new method to model the configuration
of the oxyhemoglobin dissociation curve at the cerebral
capillary level, which may be used to calculate the capillary,
PcapO2, and mitochondrial, PmitO2, oxygen tension in humans.
In the present study, we sought to examine whether the
estimated mean capillary P50 and mean Hill slope differ from
measured arterial values during normo- and hyperventilation
in healthy volunteers, and whether the use of the respective
values results in physiologically relevant differences in PcapO2
and PmitO2.
We obtained paired arterial-jugular venous blood samples
during resting breathing and following 15 minutes of voluntary
hyperventilation in 8 healthy volunteers. A Hill plot
was used to estimate the mean capillary P50 and Hill slope.
Global cerebral blood flow and the cerebral metabolic rate of
oxygen, J
O2, were measured by the Kety-Schmidt-technique
using 133Xe as the tracer. PmitO2 was found using a standard
value for the cerebral oxygen diffusion capacity, LO2, of 33.0
μmol/100g/min/kPa: J
O2 = LO2 (PcapO2 - PmitO2 ).
During normoventilation, neither P50 (arterial: 3.7 (0.3) kPa;
capillary: 3.7 (0.1) kPa; arterial vs. capillary: p = 0.14) nor the
Hill slope (arterial: 2.5 (0.1); capillary: 2.4 (0.1); arterial vs.
capillary: p = 0.14) changed significantly from artery to capillary.
In contrast, both P50 (arterial: 2.9 (0.1) kPa; capillary: 3.4
(0.2) kPa; arterial vs. capillary: p < 0.001) and the Hill slope
(arterial: 2.0 (0.1); capillary: 2.2 (0.1); arterial vs. capillary:
p < 0.001) increased significantly from artery to capillary
during hyperventilation. Neither PcapO2 nor PmitO2 differed
when the measured arterial rather than capillary P50 and Hill
slope were used during resting breathing (bias of -0.17 kPa
and limits of agreement of -0.71 kPa to 0.37 kPa) (Figure 1).
By contrast, the use of the capillary P50 and Hill slope resulted
in systematically higher PcapO2 and PmitO2 than when using the
measured arterial values, with a bias of 0.45 kPa and limits of
agreement of 0.35 kPa to 0.54 kPa (Figure 1).
In conclusion, measured arterial P50 and Hill slope values may
be used to provide reasonable estimates of PcapO2 and PmitO2
during resting breathing, but are probably not reliable for
this purpose when the configuration of the arterial oxyhemoglobin
curve is physiologically modulated, as exemplified by
voluntary hyperventilation.
Original language | English |
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Publication status | Published - 15 Sept 2018 |
Event | Europhysiology 2018 - QEII Centre, London, United Kingdom Duration: 14 Sept 2018 → 16 Sept 2018 |
Conference
Conference | Europhysiology 2018 |
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Country/Territory | United Kingdom |
City | London |
Period | 14/09/18 → 16/09/18 |