Low leisure-based sitting time and being physically active were associated with reduced odds of death and diabetes in people with chronic obstructive pulmonary disease: a cohort study

Questions In people with chronic obstructive pulmonary disease (COPD), are activity phenotypes (based on physical activity and recreational screen time) associated with mortality and cardiometabolic risk factors? Design Cohort study. Participants People with COPD aged ≥ 40 years and who were current or ex-smokers were identified from the 2003 Scottish Health Survey. Outcome measures Data were collected regarding demographics, anthropometric measurements, medical history, physical activity, sedentary behaviour, health outcomes, and mortality. Analysis Participants were categorised into one of the following activity phenotypes: ‘couch potatoes’ were those who were insufficiently active with high leisure-based sitting time and/or no domestic physical activity; ‘light movers’ were insufficiently active with some domestic physical activity; ‘sedentary exercisers’ were sufficiently active with high leisure-based sitting time; and ‘busy bees’ were sufficiently active with low leisure-based sitting time. ‘Sufficiently active’ was defined as adhering to physical activity (PA) recommendations of ≥ 7.5 metabolic equivalent (MET) hours/week. ‘Low leisure-based sitting time’ was defined as ≤ 200 minutes of recreational screen time/day. Results The 584 participants had a mean age of 64 years (SD 12) and 52% were male. Over 5.5 years (SD 1.3) of follow-up, there were 81 all-cause deaths from 433 COPD participants with available data. Compared to the ‘couch potatoes’, there was a reduced risk of all-cause mortality in the ‘busy bees’ (Hazard Ratio 0.26, 95% CI 0.11 to 0.65) with a trend towards a reduction in mortality risk in the other phenotypes. The odds of diabetes were lower in the ‘busy bees’ compared to the ‘couch potatoes’ (OR 0.14, 95% CI 0.03 to 0.67). Conclusions Adhering to physical activity guidelines and keeping leisure-based sitting time low had a mortality benefit and lowered the odds of diabetes in people with COPD

The importance of haemoglobin to physical function

Haemoglobin (Hb) within erythrocytes establishes a fundamental link between oxygen (O2) in ambient air and aerobic metabolism by transporting O2 in the blood from lung to tissue. Historically, blood O2 carriage has been quantified using the concentration of Hb in whole blood ([Hb]). Anaemia, defined as a fall in [Hb] below 130 g.l-1 in males and 120 g.l-1 in females may cause fatigue and impaired fitness. [Hb] is dependent on both plasma volume (PV) and total haemoglobin mass (tHb-mass). Thus, anaemia may result when tHb-mass falls but also when PV is expanded. Therefore, reliance on [Hb] may be misleading. tHb-mass may represent a better guide to O2 carrying capacity and of aerobic fitness than [Hb]. The relationship between tHb-mass and [Hb] has, however, been studied little across disease states, nor has the relationship between tHb-mass and preoperative cardiopulmonary exercise testing (CPET) variables. I used the optimised carbon monoxide rebreathing (oCOR) method to determine tHb-mass, first seeking its test-retest reliability in healthy volunteers (HV). Typical error of repeat tHb-mass measurements was low in my hands, in keeping with other studies. Subsequently, the relationship between tHb-mass and [Hb] in HV and in different diseases was studied; inflammatory bowel disease (IBD), chronic liver disease (CLD), heart failure (HF) and those awaiting surgery. I found the relationship between tHb-mass and [Hb] varied considerably across disease states, with PV a key confounding variable affecting both [Hb] and the diagnosis of anaemia. Subsequently, in a separate cohort of surgical patients I determined the relationship between tHb-mass, [Hb] and physical fitness quantified by CPET. Unlike [Hb], I found tHb-mass to be an important variable associated with preoperative fitness. The oCOR method is feasible and well tolerated by patients and provides a more comprehensive assessment of haematological and volume status compared to relying on [Hb] and its future use is advocated