A pseudo‐rebreathing technique for assessing the ventilatory response to carbon dioxide in cats.

Abstract

SUMMARY1. The ventilatory sensitivity to CO2 obtained from a non-steady-state step-ramp CO2 challenge (analogous to the Read rebreathing method) was compared with the one of the steady-state method.2. Experiments were performed during normoxia on twenty cats anaesthetized with chloralose-urethane. In eight of these cats additional measurements were carried out during metabolic acidosis and alkalosis.3. The slope of the non-steady-state ventilatory response curve to CO2 was not significantly different from the steady-state one only if the ratio of the step-wise increase in end-tidal PCO2 (PET,Co2) (A) above its resting value and the subsequent rate ofrise of the PET, C02 (R) was equal to the time constant ofthe central chemoreflex pathway (,r). This also held true during metabolic acidosis and alkalosis.4. It is predicted that in human beings during hyperoxia the ventilatory response line obtained with Read's rebreathing method is to a fair approximation shifted to the right by a value of A with respect to the steady-state response line, provided A/R = rC 5. We argue that Read's prescription that a PETC02 equilibrium should be established between mixed venous blood, arterial blood and end-tidal gas has to be regarded as an experimental condition leading to stable experiments rather than dictated by physiological mechanisms.

The steady‐state and rebreathing methods compared during morphine administration in humans.

“…This was the situation in our study. In fact, using the formula derived from the Berkenbosch et al (1986) model, we were able to account for about 80 % of the differences between SS and RB slopes that occurred in our study.…”

“…Recently, however, Berkenbosch et al (1986) examined the differences in the SS and RB technique using cats during normal STEADY-STATE AND REBREA THIVG METHODS conditions as well as during metabolic acidosis and alkalosis. In a second study they compared the two techniques in humans under normal conditions only (Berkenbosch et al 1989).…”

“…Although there has been some controversy over the comparability of the two techniques (Linton et al 1973;Irsigler, Stafford & Severinghaus, 1984;Berkenbosch, DeGoede, Olievier & Schuitmaker, 1986;Berkenbosch, Bovill, Dahan, DeGoede & Olievier, 1989) (Read & Leigh, 1967; Dempsey, 1976;Jordan, 1982). Further, it has been assumed that changes in VE, Co2s caused by various treatments (drugs, exercise, etc.)…”

On a pseudo‐rebreathing technique to assess the ventilatory sensitivity to carbon dioxide in man.

“…In our opinion the dynamic end-tidal forcing (DEF) technique (Swanson & Bellville, 1975) In a previous study in anaesthetized cats (Berkenbosch et al 1986) we showed that the ventilatory response obtained by applying a step-ramp PETCO2 input could be satisfactorily described using the empirical two-compartment model introduced by Bellville, Whipp, Kaufman, Swanson, Aqleh & Wilberg (1979 (Teppema, Vis, Evers & Folgering, 1982;Eldridge, Kiley & Paydarfar, 1987) overwhelming the effect of changes in cerebral blood flow on the central time constant. Moreover, the anaesthetics used are expected to depress the responsiveness of cerebral vessels to hypercapnia (Levasseur & Kontos, 1989).…”

“…To get some insight into the effect of changes in A and R on the non-steady-state CO2 sensitivity we performed experiments using a pseudo-rebreathing technique (Berkenbosch, DeGoede, Olievier & Schuitmaker, 1986). In a first approach we restricted ourselves to changing the step A, keeping R close to the values used by Read (1967).…”