EFFECT OF RAISED POTASSIUM ON VENTILATION IN EUOXIA, HYPOXIA AND HYPEROXIA AT REST AND DURING LIGHT EXERCISE IN MAN

1. The purpose of this study was to determine whether changes in arter ial plasma potassium concentration [K+](a) affect expired ventilation (($) over circle V-E) in euoxia, hypoxia and hyperoxia during rest and light exercise in humans. 2. Three periods of ventilatory measurement s were undertaken in eight healthy subjects at rest and in seven other subjects during cycle ergometry (70 W). The first period of measureme nt was before the ingestion of 64 mmol of potassium chloride (KCl), th e second 20 min after ingestion of KCl when [K+](a) levels were elevat ed, and the third 3 h after the ingestion of KCl when [K+](a) had retu rned substantially to normal. During each period, end-tidal P-O2 was c ycled between euoxia, hypoxia and hyperoxia, whilst the end-tidal tain ed constant. The acute ventilatory response to hypoxia (AHVR) was P-CO 2, was mam calculated as the difference in ($) over circle V-E, during hypoxia and hyperoxia within each period of measurement. 3. Oral KCl produced a 1.3 +/- 0.2 mM (mean +/- 2 S.E.M.) increase in [K+](a) at r est and a 0.8 +/- 0.2 mM increase during exercise. There was no signif icant difference in ventilation during euoxia between the three period s of measurement at rest or during exercise. There was a significant i ncrease in AHVR with the rise in [K+](a) of 21 min(-1) mM(-1) at rest (arterial P-O2 during hypoxia ca 57 Torr) and 10 l min(-1) mM(-1) duri ng exercise (arterial P-O2 during hypoxia ca 52 Torr). There was a sig nificant difference in the absolute increase in AHVR with [K+](a) betw een rest and exercise, but this difference was not significant if the increase in AHVR with [K+](a) was expressed as a percentage of the ini tial AKVR. 4. We conclude that changes in [K+](a) of the order of 1 mM have little effect on euoxic ventilation at rest or during light exer cise in humans. We also conclude that [K+](a) changes of this order in crease AHVR at rest and during light exercise and that increases in [K +](a) contribute to the increase in AHVR with exercise in humans.