A mountaineer ascends to an altitude of $3500 \text{ m}$. At sea level his arterial $\text{PO}_2$ is $95 \text{ mmHg}$, haemoglobin concentration $13 \text{ g·dL}^{-1}$ and arterial oxygen saturation $S_{a}\text{O}_2 = 0.97$. At altitude his arterial $\text{PO}_2$ falls to $55 \text{ mmHg}$ and $S_{a}\text{O}_2$ drops to $0.85$, but his haemoglobin concentration rises to $15 \text{ g·dL}^{-1}$.

Using the equation $C_{a}\text{O}_2 = (1.34 \times \text{Hb} \times S_{a}\text{O}_2) + (0.0031 \times \text{PO}_2)$, calculate
(i) the arterial oxygen content at sea level and at altitude (in $\text{mL·dL}^{-1}$), and
(ii) the percentage change in $C_{a}\text{O}_2$ from sea level to altitude.

Question

A mountaineer ascends to an altitude of $3500 \text{ m}$. At sea level his arterial $\text{PO}_2$ is $95 \text{ mmHg}$, haemoglobin concentration $13 \text{ g·dL}^{-1}$ and arterial oxygen saturation $S_{a}\text{O}_2 = 0.97$. At altitude his arterial $\text{PO}_2$ falls to $55 \text{ mmHg}$ and $S_{a}\text{O}_2$ drops to $0.85$, but his haemoglobin concentration rises to $15 \text{ g·dL}^{-1}$.

Using the equation $C_{a}\text{O}_2 = (1.34 \times \text{Hb} \times S_{a}\text{O}_2) + (0.0031 \times \text{PO}_2)$, calculate
(i) the arterial oxygen content at sea level and at altitude (in $\text{mL·dL}^{-1}$), and
(ii) the percentage change in $C_{a}\text{O}_2$ from sea level to altitude.

Accepted Answer

(i) Sea level ≈ 17.2 mL·dL⁻¹; altitude ≈ 17.3 mL·dL⁻¹. (ii) ≈ 0.3 % increase

Gce Model Questions Vol1 2021 Biology Question 4

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