Carbon Monoxide

Coburn-Forster-Kane Equation:

The Coburn-Forster-Kane equation is the most sophisticated approach to modeling carbon monoxide uptake by humans and animal available. Disadvantages of its use are the large number of variables that it contains and the fact that value of many of the variables must in turn be obtained from other equations.

{ A [HbCO]t - (BVCO + PICO) } / { A [HbCO]0 - (BVCO + PICO) } = e-tAVbB }

Terms of Equation:

A = Pc,O2 / M [HbO2]

[HbCO]t, see below

B = 1 / DLCO + PL / VA

VCO, see below

PICO, see below

[HbCO]0, see below

e, see below

t, see below

Vb, see below

Where:

Pc,O2 is the average partial pressure of O2 in lung capillaries (mm Hg); at sea level PIO2 (159) - 49 = 110

........... PIO2 = 148.304 - 0.0208 . PICO

M is the ratio of the affinity of blood for CO to that for O2, approximately 218

[HbO2] is ml of O2 per ml blood, or = 0.22 - [HbCO]t

[HbCO]t is ml of CO per ml blood at time t, or = [COHb%]t . 0.0022 {term to be solved for}

DLCO is diffusivity of the lung for CO (ml/min./mm Hg), or = 35VO2 . e0.33

........... VO2 = RMV / 22.274 - 0.0309

........... RMV is respiratory minute volume (L/min.)

PL is barometric pressure minus the vapor pressure of water (ie. 49) at body temp. (mm Hg)

VCO is rate of endogenous CO production (ml/min.); approximately 0.007 ml/min.

PICO is partial pressure of CO in inhaled air (mm Hg)

VA is alveolar ventilation rate (ml/min), or = 0.933 VE - 132 f

........... VE is ventilation volume (ml/min.)

........... f is ventilation frequency

[HbCO]0 is ml of CO/ml blood at the beginning of the exposure (approximately 0.8% COHb, or 0.0176 ml CO/ml blood for a non-smoker)

e is base of natural logarithms (2.7182)

t is exposure duration (min.)

Vb is blood volume (ml); assume 74 ml/kg body weight

...... Last changed 02/12/00

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