Abstrad. Perceived exertion waa measured using a linear grading scale, in three healthy males performing paired patterns of continuous and intermittent exercise with the same average power output. Intermittent exercise with work periods of 10 sec. alternating with recovery periods of loadless pedalling for 30 sec. was associated with lower perceived exertion grndes than when work periods were 30 or 120 sec. Perceived exertion, oxygen intake, ventilation, heart rate, and blood lactate concentration were all significantly higher for intermittent exercise than for continuous exercise vrith the same avenge power output. The relationships between perceived exertion and the physiologicnl variables was the same for the two fonns of exercise despite widely different mechanical stresse-9 on the legs. Mechanical facton were therefore thought to make a relatively unimportant contribution to perceived exertion over the range of exercise intensities studied.-The high degree of correlation between perceived exertion and the measured physiological variables suggests a wider use of exertion grading in field studies.

BJURSTEDT, H., C. M. HESSER, G. LILJESTRAND and G. MATELL. Effects of posture on alveolar-arterial CO, and 0, differences and on alveolar dead space in man. Acta physiol. scand. 1962. 54. 65-82. -The increase in ventilation and lowering of the end-tidal Pco, after changing from the supine to the standing position were observed to be associated with a significant rise in the arterial to end-tidal CO, tension difference (average + 2.1 mm Hg) in addition to an increased effective alveolar to arterial 0, tension difference (+ 4.8 mm Hg). All dead spaces increased, the alveolar dead space (= the physiological minus the anatomical dead space) on an average by 28 ml. Assuming an unchanged distribution of ventilation this can be expressed as corresponding to 6 per cent of the alveoli being unperfused. A lowering of the alveolar Pco2 during standing is thus in part due to an increased arterial to end-tidal GO, tension difference. The end result is also influenced by a certain metabolic acidosis (average decrease in BHCO,B, 7 0.6 mM/l), in addition to peripheral retention of CO,. The Eff. VA/VE ratio decreased in all subjects, indicating a decline in the respiratory gas exchange efficiency by an average of 6 per cent. The changes observed may be explained as a consequence of the influence of gravityon the blood flow and its distribution not only in the systemic but also in the pulmonary circulation. Already in 1914 LILJESTRAND a n d WOLLIN showed that the alveolar CO, tension in m a n is lower during motionless standing than in the supine position. These authors had also confirmed a n d extended the old observation that assuming the up-right position calls forth a n increase in the pulmonary ventilation (cf. LILJESTRAND and WOLLIN 1913). Both the lowered alveolar 5-623015. Acta physiol. scand. Vol. 54. 65 66 H. BJURSTEDT ET A L .C:O, tension and the increase in pulmonary ventilation have been confirmed in numerous investigations (d. The mechanisms underlying the fall in the alveolar (20, and the increase in pulmonary ventilation after changing from the supine to the standing position are not fully understood. T h e former effect cannot be explained xilelj-b y an increased blowing off of CO, b y the hyperventilation, since the amount of C 0 2 eliminated during several minutes of motionless standing does not exceed the 0, uptake, as demonstrated b y HITCHCOCK and FER-GUSON as well as by RAHS and AXENT. These authors referred the lowered alveolar Pc:p2 during standing to impaired CO, elimination from the lungs, caused by the decrease in cardiac output with a concomitant CO, retention in the tissues and in venous blood, especially in the lo\ver portion of the body.By using special tecliniqucs for the continuous and simultaneous recording of blood gas changes 011 the centrifuge, rather drastic changes in the pulmonary circulation and gas exchange have been observed, both in the dog ;BARK, BJVRSTEDT and COLERIDGE 1959) and in man (BARR 1961 a). I n the espcriments to be reported beloiv, using similar techniques on the tilt-tabl...

Pulmonary ventilation (V) and the interrelationships of airflow, transpulmonary pressure, and lung volume during inspiration and expiration were studied in eight healthy subjects who performed maximal exercise (MEx; 140% VO2 max), 15-s maximal voluntary ventilation (MVV), and forced inspiratory and expiratory vital capacity (FVC) maneuvers at 1, 3, and 6 ATA. Maximal exercise ventilation and MVV amounted to 149 +/- 7 (mean +/- SE) and 193 +/- 9 l . min-1, respectively, at 1 ATA and were both reduced by approximately 37% at 3 ATA and by 50% at 6 ATA. Expiratory peak flows during MEx and MVV were equal to the maximal flows obtained during FVC at comparable lung volumes, whereas inspiratory peak flows during MEx were 20% less than the FVC flows. Despite a sixfold increase in gas density, the rate of mechanical work of breathing decreased when the pressure was raised to 6 ATA, during MEx from 8 +/- 1 to 6 +/- 1 W, and during MVV from 28 +/- 5 to 18 +/- 3 W. With increasing gas density there was a shift of lung volumes in the inspiratory direction with consequent reductions of inspiratory-to-expiratory flow ratios. We conclude that depletion of energy stores in the inspiratory muscles contributed to limiting V during MEx at raised air pressure.

The interrelationships of ventilation (V), tidal volume (VT), inspiratory (T1), expiratory (TE) and total breath (Ttot) durations, mean inspiratory (VT/TI) and expiratory (VT/TE) flows, and lung volumes were studied in normal subjects at rest and during exercise on a cycle ergometer. The ergometric load was increased by 10 W every minute, from zero W to 200 W. The TI/Ttot ratio increased with V in the range 15 to 60 1 X min-1, indicating that with increasing V the rate of increase of VT/TI decreased whereas that of VT/TE increased. Possible mechanisms responsible for the difference in behaviour of VT/TI and VT/TE are discussed. The VT-TI and VT-TE relationships both displayed three ranges with breakpoints at tidal volumes of about 1.4 and 2.4 1. The relations of TI and TE to end-inspiratory volume were approximately linear over the entire VT range studied, whereas the relations of TI and TE to end-expiratory volume showed three ranges with different characteristics. We conclude that the termination of inspiration during cycle exercise is dependent on volume-related afferent feedback from the lungs and/or chest walls, not only in the high but also in the low volume range.