Loss of CO from the intravascular bed and its impact on the optimised CO-rebreathing method

Abstract

Total haemoglobin mass can be easily measured by applying the optimised CO-rebreathing method (oCOR-method). Prerequisite for its accurate determination is a homogenous CO distribution in the blood and the exact knowledge of the CO volume circulating in the vascular space. The aim of the study was to evaluate the mixing time of CO in the blood after inhaling a CO-bolus and to quantify the CO volume leaving the vascular bed due to diffusion to myoglobin and due to exhalation during processing the oCOR-method. The oCOR-method was also compared to a former commonly used CO-rebreathing procedure. In ten subjects, the time course of carboxy-haemoglobin (HbCO) formation was analysed simultaneously in capillary and venous blood for a period of 15 min after inhaling a CO bolus. The volume of CO diffusing from haemoglobin to myoglobin was calculated via the decrease of HbCO. As part of this decrease is due to CO exhalation, this volume was quantified by collecting the exhaled air in a Douglas bag system. Equal HbCO values in capillary and venous blood were reached at min 6 indicating complete mixing of CO. The loss of CO out of the vascular bed due to exhalation and due to diffusion to myoglobin was 0.32 +/- 0.12% min(-1) (0.25 +/- 0.09 ml min(-1)) and 0.32 +/- 0.18% min(-1) (0.24 +/- 0.13 ml min(-1)) of the administered CO volume, respectively. The loss of CO due to exhalation and diffusion to myoglobin is of minor impact. It should, however, be considered by using correction factors to obtain high accuracy when determining total haemoglobin mass.

Stability of hemoglobin mass over 100 days in active men

“…where K ϭ (ambient barometric pressure mmHg ϫ 273 o K)/(760 mmHg ϫ ambient temperature o K); MCO is CO volume administered into the system minus CO volume not bound to hemoglobin (calculated as the sum of CO volume remaining in the spirometer and the lung, as well as CO volume exhaled during the 7 min between disconnecting the subject from the spirometer and the final blood sample), which was then multiplied by 0.99 to correct for 1% loss of the CO dose to myoglobin (2,16); ⌬%HbCO is the difference between %HbCO at baseline and %HbCO in the blood samples 9 min after CO administration; and 1.39 is Hüfner's value for the CO binding capacity of hemoglobin (1.39 ml/g) (8). The 9-min concentration was calculated as the mean of the 8-and 10-min blood samples.…”

Ventilatory Chemosensitivity, Cerebral and Muscle Oxygenation, and Total Hemoglobin Mass Before and After a 72-Day Mt. Everest Expedition

“…During a visit to the laboratory either a day before or after the exercise-hypoxia test, total hemoglobin mass was assessed using CO rebreathing (COR) as described in detail by Schmidt and Prommer (2005) and modified by Prommer and Schmidt (2007). In brief, after 15-min resting in a sitting position, the subjects were connected to a specially designed closed spirometric system allowing a CO-bolus application, followed by 2 min rebreathing of approximately 3 L amount of oxygen.…”

“…The software program SpiCO corrects for the loss of CO from hemoglobin to myoglobin according to the findings of Schmidt and Prommer (2005) and by Prommer and Schmidt (2007) by 0.3% of administered CO per minute. The calculation of EV = (644 x Hct (%) x [Hb] -1 (g/L)) x tHb-mass (mmol) is based on the equations 1-3 presented by Burge and Skinner (1995).…”

“…Daily, the OSM3 was calibrated to standard and the quality of measurement was checked by means of three different quality control solutions. tHb-mass, erythrocyte volume, plasma volume and blood volume were calculated by the SpiCO Software 1.0 (Blood tec, Bayreuth, Germany), which was developed and patented by the founders Schmidt and Prommer (2005), and Prommer and Schmidt (2007). The tHb-mass was calculated based on the formula: tHb mass (g) = K x MCO x 100 x ((D%HbCO x 1.39)…”

The carbon monoxide re-breathing method can underestimate Hbmass due to incomplete blood mixing

“…If erythrocytes remain pooled in lower extremities during a CO re-breathing procedure they cannot be tagged with CO which may lead to an underestimation of Hb mass . Complete blood mixing has previously been suggested to occur within 6 to 10 min based on similar %HbCO values in blood samples obtained from the radial artery, earlobe capillaries and an antecubital vein (Garvican et al 2010;Prommer and Schmidt 2007). These studies however all failed to include blood sampling from large pooling veins of the lower body where turnover is known to be much slower.…”