Patients presenting with chronic obstructive airways disease and hypoxic cor pulmonale were assessed during a period of clinical stability. Seventy two patients (53 male) with a mean age of 60 years were selected for long term oxygen therapy. Mean FEV1 was 0-78 1 and forced vital capacity 1 9 1. The mean arterial oxygen tension (Pao2) was 6-1 kPa (46mm Hg) and the mean arterial carbon dioxide tension (PCo2) 6-9 kPa (52mmHg). All patients had a Pao2 of less than 8-0kPa (60mmHg) and 57 patients had a PCO2 of more than 6-0kPa (45mmHg). Pulmonary haemodynamics were measured in 45 patients yielding the following mean values: pulmonary artery pressure 28 3 mm Hg; cardiac output 5 9 1 min 1; total pulmonary vascular resistance 59 2 kPa 1-1 s. Oxygen delivery systems, including 23 oxygen concentrators, were installed in the patients' homes. Flow rates were adjusted to raise Pao2 to more than 8-0 kPa (60 mm Hg) for at least 15 hours each day and close supervision was maintained. Overall five year survival was 62%, which is better than previously reported for this type of patient; but the 10 year survival was only 26% owing to an observed acceleration in death rate at about this time. Progressive disturbances of the pulmonary circulation were arrested. Mortality was associated with the severity of airflow obstruction, reflecting a continuing pathological process affecting the airways.Survival is poor in patients with cor pulmonale complicating chronic obstructive airways disease.-The benefits of long term oxygen therapy in these patients were examined in the nocturnal oxygen therapy (NOT) trial6 and the report of the Medical Research Council Working Party (MRC).s In the MRC study survival in women appeared to be better than in men, although the female group was small and hence few deaths occurred during the period of follow up. In men the benefit of long term oxygen therapy on survival was not apparent until about 500 days, a delay that has never been adequately explained. The five year survival in men was 42%. The mean duration of follow up in the NOT trial was 19 months. The projected three year survival in the group having continuous oxygen therapy was 63%. Timms etal7 have recently reviewed the data from the NOT trial and report that survival up to eight years is related to the fall in mean pulmonary artery pressure during the first six months of long term oxygen therapy. Survival in
Background: tV O 2 at the onset of constant work rate (CWR) exercise is a variable of aerobic fitness that shortens with physical training and lengthens with cardiopulmonary disease. Determination of tV O 2 with sufficiently high confidence has typically required multiple exercise transitions limiting its clinical application. Objectives: To design a protocol to determine tV O 2 reliably but simply. Methods: On each of three days, five healthy men performed two CWR tests on a cycle ergometer below the metabolic threshold (V O 2 h) for blood lactate accumulation as determined by gas exchange measurements followed by an incremental work rate (IWR) test. tV O 2 was determined (a) from the ontransit (on-tV O 2 ) and off-transit (off-tV O 2 ) of six CWR tests both individually and superimposed, using non-linear regression with a monoexponential model, and (b) by geometric analysis of the IWR tests (ramp-tV O 2 ).
SUMMARYThe V VO (alveolar CO2 output-alveolar 02 uptake) relationship ( V-slope) during increasing work rate (r-amp) cycle ergometer exercise has two approximately linear components: a lower component slope (S,) with a value of about 0-95 and a steeper, upper component (S2). We examined the effect of muscle glycogen depletion (protocol 1) and the rate of increase in work rate (ramp rate) without muscle glycogen depletion (protocol 2) on S1 and S2. In protocol 1, ten healthy men with a mean age of 31 4 years (S.D. 6-2) were studied on each of 3 days (days I and 3 were control days). They performed a ramp exercise test to maximum tolerance and steady-state tests at rest, during unloaded pedalling and at two constant work rates below their anaerobic threshold (AT). To deplete muscle glycogen before the test on day 2, the subjects performed 2 h of very heavy cycle exercise on the preceding day and fasted overnight. Si was reduced on day 2 (0 79 compared with 0 95, P < 0 001), as was the VC0 -VO slope derived from steady-state measurements (0 81 compared with 0 99, P < 0 001), but AT and the slope difference (S2 -S5) were unchanged. In protocol 2, seven healthy men with a mean age of 20 6 years (S.D. 2-4) performed ramp tests at three different rates of increasing work rate (1 5, 30 and 60 W min'), each ramp rate being performed twice in random sequence. The ramp rate did not affect Si but S2 was steeper with the faster rates of work rate increase (127, 143 and 163, respectively, P < 0 01). Our findings support the concept that the lower component of the Vslope plot (below AT) represents muscle substrate respiratory quotient (RQ) while the difference between Si and S2 reflects 'excess CO2' derived from bicarbonate buffering of lactic acid.
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