Introduction and objectives It is recognised that age-associated changes in the chest wall and lung parenchyma lead to decreased efficiency of ventilation and gas exchange, resulting in reduced arterial partial pressure of oxygen (PaO₂) and haemoglobin saturation (SaO₂). The total oxygen content of arterial blood (CaO₂) depends upon SaO₂, as well as haemoglobin concentration. Our goal was to examine serial changes in arterial oxygen content with age in a cohort with hypoxaemia due to pulmonary arteriovenous malformations (PAVMs).

Methods Retrospective longitudinal follow-up data was collected for 100 consecutive PAVM patients presenting to a tertiary care institutional clinic between 1984 and 2001, and reviewed until 2015. Subjects provided up to 30 (median 9) separate annual datasets. SaO₂ was measured by pulse oximetry in the supine and erect postures, and the mean SaO₂ was calculated after 7, 8, 9 and 10 min standing. Haematological and biochemical blood indices evaluated haemoglobin, haematinics, and iron indices. CaO₂ in mls of oxygen per dL (ml/dL) of blood was calculated using the equation: [SaO₂ (%) x haemoglobin (g/dL) X 1.34]/100. Data were analysed using STATA IC v13.1.

Results Age and PAVM-treatment associated changes in SaO₂ were mostly accompanied by opposing changes in haemoglobin levels that maintained the CaO₂. Two major patterns were observed. The first was the expected increase in haemoglobin with lower SaO₂, due to secondary erthyrocytosis and polycythaemia. The second, less well recognised, was an increase in SaO₂ when haemoglobin fell, most commonly when subjects developed iron deficiency and anaemia. Nevertheless, excluding participants with iron deficiency, CaO₂ decreased with age (Figure 1, r² = -0.0654; p < 0.001, Figure 1).

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Abstract S52 Figure 1

 

Conclusions The body maintains arterial oxygen content within a normal range using well-known erythropoeitic mechanisms in response to hypoxaemia. Despite this feedback mechanism, in patients with pulmonary arteriovenous malformations, overall arterial oxygen content still decreases with age.