Respiratory frequency response to progressive isocapnic hypoxia.

Abstract

SUMMARY1. Ventilatory, tidal volume and frequency responses to progressive isocapnic hypoxia have been measured in twenty-nine healthy subjects by a rebreathing technique.2. A strong correlation was found between ventilatory response to hypoxia (.jI/ASao.) and frequency response to hypoxia (Af/.Sao2) (r = 082, P < 0-001). There was a lesser correlation between AQ'/LSao2and tidal volume response (LXVT//ASaO2) (r = 050, P < 0-01). These findings suggest that the wide range of ventilatory response to hypoxia among subjects is mainly determined by differences in frequency response and contrast with previous findings in studies of the response to progressive hypercapnia. 3. The breathing pattern during progressive hypoxia and hypercapnia was compared in ten subjects. Ventilation/tidal volume plots were constructed and patterns of response were further analysed in terms of inspiratory duration (TI), expiratory duration (TF) and mean inspiratory flow rate (VI).4. Increments in ventilation during hypoxia were achieved with a greater respiratory frequency and a smaller tidal volume than during hypercapnia in eight of the ten subjects studied. In two subjects no difference in breathing pattern during hypoxia and hypercapnia was observed.5. Changes in respiratory frequency during progressive hypoxia were achieved in all subjects by a progressive shortening of T1 and TE. By contrast, T1 remained constant during hypercapnia until VT had increased to 3-5 times the eupnoeic value; during hypercapnia the increase in frequency was achieved mainly by a progressive shortening of TE.

The relation between tidal volume and inspiratory and expiratory times during steady‐state carbon dioxide inhalation in man

“…Most workers measure VT as the volume variable, but presumably the pulmonary stretch receptors report a quantity related to lung volume. The importance of the distinction has been shown recently (Garrard & Lane, 1975), and the discrepancy between the hypoxic-hyperoxic comparison in the present paper and those of others may be due to a difference of behaviour of end-expiratory lung volume VL,E, with differing techniques (Kellogg & Mines, 1975;Garfinkel & Fitzgerald, 1975;Saunders, Betts & Rebuck, 1975 Garrard & Lane (1975) suggest that the changes reported by Rebuck et al (1976) should be thought of in terms of the vagal volume-time component as much as the drive 607 component (see the two terms in eqn. (7) of Cunningham & Gardner, 1977), but it is changes in the latter that have been implied in the writings of most observers of hypoxic tachypnoea.…”

“…Haldane, Meakins & Priestley, 1919;Rebuck, Rigg & Saunders, 1976). At least two sources of difference appear to be involved.…”

The effect of inspiratory muscle fatigue on breathing pattern and ventilatory response to CO2.

“…Since VI was elevated following removal of the resistive load, they obtained their control measurements duringCO2 rebreathing in order to ensure a comparable VI in the two instances. Such a comparison may not be valid since a number of investigators (Haldane, Meakins & Priestley, 1919;Gautier, 1969;Rebuck, Rigg & Saunders, 1976) have shown that the breathing pattern under non-steady-state conditions differs substantially depending on the stimulus employed to augment ventilation. These differences are particularly pronounced for the first few minutes following a sudden change in stimulus intensity (Gardner, Cunningham & Peterson, 1979), which is inevitable after the removal of a resistive load.…”

An assessment of overall open-loop "gain" of CO2-ventilation feedback control system in hypoxia.

“…troversy. REBUCK et al (1976) stated that increments in VE during progressive hypoxia were achieved with a greater respiratory rate and a smaller VT than during progressive hypercapnia. On the other hand, in both hypoxia (COTTON and GRUNSTEIN, 1980) and hypercapnia (ROSENSTEIN et al, 1974), augmented VT was observed to be the main factor in increasing VE.…”