Studies on the Regulation of Respiration in Heavy Work

Abstract

Summary. The regulation of the respiration has been studied in different kinds of muscular exercise, in which the muscles are working under partly anaerobic conditions, viz.: heavy work with the legs, work with the arms and work in light CO‐poisoning. It is shown that a close relationship between the degree of anaerobiosis – as indicated by the concentration of the blood lactates – and a relatively high lung ventilation exists. It is further shown that when the muscles are working under partly anaerobic conditions (increased blood lactate concentration) oxygen breathing lowers the concentration of the blood lactates, and the ventilation, and that the lowering is proportional to the percentage of the oxygen in the inspired air. In rest and during light work (no increased blood lactate concentration) the breathing of oxygen on the other hand tends to produce a slight increase in ventilation and a decrease in alveolar pCO2. The effect of oxygen breathing on the ventilation during partly anaerobic work is not due to a decrease in acidity (see page 180) of the arterial blood or to the elimination of a previously existing arterial unsaturation. It is made probable, that the different effect of oxygen breathing in light and heavy work is due to the circumstance that oxygen breathing acts on the respiration in two different ways, viz. activating on the respiratory centre itself, and depressing on the activity of the chemoreceptors. It is assumed that in rest and during light work in which the activity of the chemoreceptors is only slight the activating effect on the respiratory centre over balances the depressing effect on the chemoreceptors, whereas in heavy work because of an increased chemoreceptor activity the depressing effect of high oxygen tension is able to overbalance considerably the effect on the respiratory centre. The results from the present experiments are best explained by the assumption that in heavy work or other kinds of work in which the muscles are working under partly anaerobic conditions a substance is produced which increases the ventilation reflexly through the chemoreceptors. The effect of oxygen breathing in heavy work then is 1. to decrease the production of this substance and 2. to depress the effect of this substance on the chemoreceptors. An identification of the active substance has not been attempted in this paper, but it is shown that it is not the lactic acid and that it has properties allowing it to appear in and disappear from the blood stream much more rapidly than does lactic acid. On the basis of these and earlier investigations the control of respiration during muscular work can be explained in the following way (see page 185–186): In light work the increase in ventilation is brought about mainly by reflexes from the working limbs. In heavy work (here defined as work in which the blood lactate concentration is increased – in this subject corresponding to oxygen uptakes above 1–1.5 1/min.) the further increase in ventilation is due mainly to an increasing production of the above me...

Respiratory Regulation During Exercise in Unconditioned Subjects 1

“…The per cent oxygen saturation gradually declined dur- ing the exercise period, falling by an average of 2.2%. A similar fall has been reported by Asmussen and Nielsen (20). The arterial oxygen tension has been found to fall during exercise (15).…”

“…The effect was greater the more severe the exercise, and for a given exercise rate the effect varied inversely with physical fitness. The finding has been confirmed abundantly (20,22,27,32,33). Conversely, it is known that ventilation for a given work rate is greater at high altitudes (13,34,35) or while breathing low-oxygen mixtures (15,27,36,37) than it is at normal oxygen tensions.…”

“…The ventilation response is very rapid, and its magnitude is many times greater than at rest. This effect appears in exercise which is severe for the subject, and the effect becomes more pronounced as the severity increases (20,24). The response is too immediate to make it likely to result from changes in blood concentration of some substance produced by anaerobically working muscles.…”

“…pH change has not been considered of first-line importance by most observers (8,22,41), but its possible importance has recently been asserted (31). Arterial oxygen tension has been dismissed as a regulatory factor because changes in arterial oxygen during exercise are slight, and change in arterial oxygen tension over a considerable range yields little respiratory response at rest (20). A rise in body temperature during exercise may stim-ulate respiration, but this is slow to develop and probably would not be very effective in less than 10 minutes (51).…”

“…From the rate of total blood CO2 loss, it is apparent that lactic acid was being formed rapidly. The rate of production of lactic acid during work can be markedly slowed by high oxygen mixtures or accelerated by low oxygen (20,36,38,39).…”