TY - JOUR T1 - Curable hypoxia in an octogenarian with an undiagnosed inherited condition: a case commentary JF - Breathe JO - Breathe SP - 153 LP - 156 DO - 10.1183/20734735.102114 VL - 10 IS - 2 AU - Claire L. Shovlin Y1 - 2014/06/01 UR - http://breathe.ersjournals.com/content/10/2/153.abstract N2 - The accompanying case is an excellent illustration of why pulmonary arteriovenous malformations (PAVMs) have been considered very rare. Patients with PAVMs are generally asymptomatic and may be highly athletic, even in the presence of profound hypoxaemia due to right-to-left shunting through PAVMs. Data in papers published this year help explain why patients are so rarely symptomatic [1–3]; why some become symptomatic [1, 2]; and why, irrespective of respiratory symptoms, all PAVMs should be considered for treatment [4, 5]. PAVM development is usually complete by the end of puberty, and the octogenarian in this case would have spent decades undiagnosed with “silent” PAVMs and hypoxaemia. To understand how this could be the case, it is important to realise that, although this patient had low blood oxygen levels, his tissues were not more “hypoxic” than normal. Instead, as recently emphasised [1–3], PAVM patients use multiple mechanisms to maintain oxygen delivery. First, the relevant term for oxygen transport is not the arterial oxygen tension (PaO2) or arterial oxygen saturation (SaO2), but the arterial oxygen content (CaO2) which also depends upon the concentration of haemoglobin [6]. Hypoxaemic PAVM patients generally utilise polycythaemic responses so that, irrespective of the SaO2, CaO2 on standing is preserved at just under 18 mL·dL−1 [1]. Secondly, the overall transport of oxygen to the tissues also depends on the volume of blood reaching the tissues in any given period (cardiac output) [6]. Cardiac output is the product of the heart rate and stroke volume, and both are increased in PAVM patients to compensate for hypoxaemia [2, 3]. For example, in the 165 PAVM patients reported … ER -