Effect of hypoxia on muscle oxygenation and metabolism during arm exercise in humans.

The influence of hypoxaemia on anaerobic energy production during arm exercise (AE) has been investigated. Six men were studied during maximal AE and during 10 min of sitting submaximal AE under both normoxic (AEN) and hypoxic (AEH, respiratory hypoxia, 12% O2) conditions. Peak pulmonary oxygen uptake (VO2) during maximal AE in normoxia and hypoxia was 2.25 +/- 0.15 and 2.18 +/- 0.14 l min-1, respectively (P < 0.05). The absolute workload was the same during submaximal AEN and AEH and corresponded to 54% of peak VO2 during normoxic maximal AE. To eliminate the potential influence of differences in catecholamine levels on the metabolic response, the submaximal experiments were performed during beta-adrenoceptor blockade. Oxygen deficit was 1.45 +/- 0.26 and 1.67 +/- 0.191 during AEN and AEH, respectively (n.s.). Oxygen extraction at steady state was lower during AEH than during AEN, and assuming a similar O2 demand this corresponds to a 14% higher muscle blood flow during AEH. At the onset of both AEN and AEH, O2 extraction (a-v O2) across the arm increased transiently above that at steady state, the increase being more pronounced during AEN than during AEH (P < 0.05). Muscle oxygenation, measured by near-infrared spectroscopy, demonstrated an initial decrease which was partially reversed as exercise proceeded. The reversal of muscle O2 desaturation was slower in all subjects during AEH (t1/2 = 2.4 +/- 0.2 min) than during AEN (t1/2 = 1.2 +/- 0.2 min; P < 0.01). After 10 min of exercise, arterial blood lactate was higher (P < 0.05) during AEH (5.5 +/- 0.2 mmol l-1) than during AEN (4.9 +/- 0.6 mmol l-1), whereas arterial plasma ammonia (NH3) was similar. The arteriovenous difference for both lactate and ammonia was similar during AEN and AEH. It is concluded that the high anaerobic energy production at the onset of AE is associated with a transient increase in O2 extraction and a transient decrease in muscle oxygenation. The effects of hypoxaemia on peak VO2, oxygen deficit and blood metabolites are less pronounced than previously described during submaximal leg exercise (LE).

High anaerobic energy release during submaximal arm exercise.

The anaerobic energy release during submaximal arm (AE) and leg exercise (LE) has been estimated from O2 deficit measured at the onset of exercise. Eight male subjects were studied during 8-10 min of arm or leg cycling at the same relative workload (53% of the peak exercise-induced increase in pulmonary oxygen uptake, VO2). The workloads were 78 +/- 4 W during AE and 173 +/- 11 W during LE and VO2 was 1.51 +/- 0.06 1 min-1 for AE and 2.33 +/- 0.15 1 min-1 for LE. The half-time of the VO2 on-response was considerably longer (P < 0.01) during AE (62 +/- 9 s) than during LE (33 +/- 4 s) and the peak blood lactate concentration was higher (P < 0.05) during AE (4.8 +/- 0.5 mmol.l-1) than during LE (3.5 +/- 0.4 mmol.l-1). Oxygen deficit was 1.64 +/- 0.16 and 1.78 +/- 0.16 1 for AE and LE respectively. Oxygen deficit was higher during AE than during LE when related to absolute workload (P < 0.01), or to VO2 at steady state (P < 0.001) or to limb volume (P < 0.001). The proportion of the total energy demand covered by anaerobic energy release at the onset of exercise (0-8 min) was about 54% higher (P < 0.01) during AE than during LE. It is concluded that the energy release to a greater extend is covered by anaerobic processes during AE than during LE.

Asthma from childhood to adulthood--a follow-up study of 20 subjects with special reference to work capacity and pulmonary gas exchange.

Twenty men with a mean age of 24.9 years, who had moderate to severe asthma during childhood, underwent a follow-up examination of their physical fitness, working capacity, maximal oxygen uptake, and pulmonary function during and after physical work. Comparison was made with similar data obtained at the age of 10.9 years. The young men had a normal physical working capacity with a normal oxygen uptake of 3.65 +/- 0.56 L/min. The respiratory parameters and the arterial blood gases during work demonstrated values as in healthy individuals, and no differences between groups with mild and severe asthma during childhood were observed. The alveolar-arterial oxygen difference was normalized, compared to that at 10.9 years. Only a few subjects still had exercise-induced asthma with a postexercise fall of greater than 20% in FEV1 compared to childhood. The mean FEV1 values for the whole group after exercise were lowered and had not returned to the baseline level even after 20 minutes. Oxygen pressure (tension), arterial, measured during 20 minutes after work, demonstrated continuously decreasing values. This might reflect a persisting disturbance in the pulmonary ventilation perfusion relationship caused by the underlying asthma disease.

Cardiac output measured by acetylene rebreathing technique at rest and during exercise. Comparison of results obtained by various calculation procedures.

Cardiac output (Qc) was measured by a rebreathing technique, using acetylene and a mass-spectrometer for analyzing. In addition the rate of pulmonary uptake of O2 (VO2) during the rebreathing period and during a preceding steady-state period were determined. Measurements were made on 8 adult humans at rest and at different levels of exercise up to maximum at two occasions. The ratio (VO2 during steady-state/VO2 during rebreathing) was found to be significantly below 1 when the steady-state VO2 was below about 21 . min-1 and to be about 0.55 for subjects at rest. This indicates that VO2, and hence Qc, is increased by the rebreathing procedure when this involves deeper and more frequent respirations than those of the preceding period. Accordingly, when VO2 was below about 21 . min-1, the Qc value, calculated exclusively from acetylene concentrations recorded during rebreathing, was multiplied by the above-mentioned VO2-ratio. It is shown that this correcting procedure gives more reasonable values than those obtained by acetylene data alone. It is pointed out in what respects this correcting procedure of calculation deviates from that originally used by Grollman, and it is shown that there are only moderate differences between the results obtained by the two procedures.

Comparisoin between mass spectrometry and Haldane technique in analysing O2 and CO2 concentrations in air gas mixtures.

We have evaluated a mass spectrometer for use as a gas analyser in air gas mixtures. Simultaneous determinations of O2 and CO2 concentrations with both the mass spectrometer and the Haldane technique were done in ninety-nine different samples of expired air from ordinary laboratory experiments. The mean differences (+/- SD) between the two techniques for O2 and CO2 concentrations were 0.003% (+/- 0.049%), and 0.001% (+/- 0.045%) absolute values, respectively, (P greater than 0.05 for both), r values being 0.996 for O2 and 0.994 for CO2. There was a drift in the apparatus, which decreased with operating time. Proper calibration is necessary for accurate readings. A cost-benefit balance is made.