Comparison of chemoreflex gains obtained with two different methods in cats

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.

Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Berkenbosch¹,

DeGoede²,

Olievier³

et al. 1986

“…To obtain optimal time delays a 'grid search' was applied and all combinations of TJ and Tp wNith increments of I s and with T -> Tp were tried until a minimum in the residual sum of squares was found. The minimal time delays were somewhat arbitrarily chosen to be I s and rp was constrained to be at least 0 3 s (DeGoede et al 1985). For the analysis of the response of the carotid body-denervated cats Sp and Tp were set to zero, since no fast component was present.…”

Section: Measurementsmentioning

confidence: 99%

The effect of low‐dose acetazolamide on the ventilatory CO2 response curve in the anaesthetized cat.

Wagenaar

Teppema

Berkenbosch

et al. 1996

1. The effect of 4 mg kg-' acetazolamide (i.v.) on the slope (S) and intercept on the Pa,co2 axis (B) of the ventilatory CO2 response curve of anaesthetized cats with intact or denervated carotid bodies was studied using the technique of dynamic end-tidal forcing.2. This dose did not induce an arterial-to-end-tidal PCO2 (P(a-ET),co2) gradient, indicating that erythrocytic carbonic anhydrase was not completely inhibited. Within the first 2 h after administration, this small dose caused only a slight decrease in mean standard bicarbonate of 1P8 and 1P7 mmol F' in intact (n = 7) and denervated animals (n = 7), respectively. Doses of acetazolamide larger than 4 mg kg-1 (up to 32 mg kg-1) caused a significant increase in the P(a-ET),CO2 gradient. from 4'0 + 05 to 3'0 + 0-6 kPa, respectively, not significantly different from the changes encountered in the denervated animals. 5. It is argued that the effect of acetazolamide on the CO2 sensitivity of the peripheral chemoreflex loop in intact cats may be caused by a direct effect on the carotid bodies. Both in intact and in denervated animals the effects of the drug on S, and B may not be due to a direct action on the central nervous system, but rather to an effect on cerebral vessels resulting in an altered relationship between brain blood flow and brain tissue PCo2

“…Eight cats were anaesthetized with chloralose-urethane and breathed spontaneously via a tracheal cannula. To determine ventilatory sensitivity to CO2 we used the Dynamic Endtidal Forcing technique enabling us to separate the gains of the peripheral (Sp) and central (Sc) chemoreflex loops (DeGoede et al 1985).…”

mentioning

confidence: 99%

Respiration & Exercise

1994

Skeletal muscle (SM) abnormalities, which may play a role in dyspnoea and fatigue in cardiomyopathic heart failure, could be involved in causing similar symptoms in mitral stenosis. We studied the effects of percutaneous balloon mitral valvuloplasty (BMV) on SM structure and function in eight patients; before BMV as baseline, 2 weeks after BMV for effects of improved haemodynamics and 4 months after BMV for effects of resumption of normal physical activity. Patients underwent (i) exercise (25 W/ 3 min stages) to exhaustion to determine Vos,max, (ii) CT scan for right quadriceps cross-sectional area, (iii) isokinetic testing of peak quadriceps torque (60 deg s-') and fatigue (% force decrease after min of repetitive contraction/ relaxation cycles at 180 deg s') and (iv) quadriceps biopsy for histological (fibre type) and citrate synthase analysis. BMV caused an increase in mitral valve area (0i86 + 0 07 to 182 + 013 cm2 (mean +S.E.M.), P< 0-01), which remained elevated at 4 months (1P76 + 0413 cm2, P < 0-01), and an increase in cardiac output (3-8 + 0418 to 4-6 + 04191 mint, P< 0 05).