Alveolar deadspace and intrapulmonary shunt in healthy individuals and in individuals who have recovered from COVID‐19 infection

Following acute COVID-19 infection, unvaccinated patients have been reported to exhibit elevated alveolar deadspace (̇V_D,alv/̇V_T) and intrapulmonary shunt (̇Q_s/̇Q_T) fractions. However, as there is uncertainty surrounding the upper limits of normal for ̇V_D,alv/̇V_T and ̇Q_s/̇Q_T, we sought to replicate the findings from a separate, previously reported cohort of COVID-19 patients that also included a healthy control group never infected with COVID-19. Data from 81 participants, classified into four different groups based on the severity of prior COVID-19 infection, were used. All participants had arterial blood-gas samples drawn while highly precise measurements of their respiratory gas exchange were made. The gas exchange data were used to estimate alveolar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>P</mml:mi> <mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> <mml:annotation>${P_{{\mathrm{C}}{{\mathrm{O}}_2}}}$</mml:annotation></mml:semantics> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>P</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${P_{{{\mathrm{O}}_2}}}$</mml:annotation></mml:semantics> </mml:math> , and the differences between these values and the corresponding arterial blood-gas values provided the alveolar-arterial gradients from which ̇V_D,alv/̇V_T and ̇Q_s/̇Q_T were calculated. Mean ̇V_D,alv/̇V_T was 0.115 ± 0.062 and mean ̇Q_s/̇Q_T was 0.014 ± 0.011. No significant differences between the groups, including the uninfected control group, were detected for either ̇V_D,alv/̇V_T or ̇Q_s/̇Q_T, although if severity was instead treated as an interval measure, then a small increase in ̇Q_s/̇Q_T with severity (P = 0.00934) could be detected. Many participants, including controls, exceeded the originally proposed upper limit of normal for ̇V_D,alv/̇V_T, whereas no participant exceeded the originally proposed upper limit for ̇Q_s/̇Q_T. We conclude that prior infection with COVID-19 had no effect on ̇V_D,alv/̇V_T and little effect on ̇Q_s/̇Q_T, and that the supposedly high values of ̇V_D,alv/̇V_T are within the normal range.