HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cragg, P. A. Articles by Drysdale, D. B. Search for Related Content PubMed PubMed Citation Articles by Cragg, P. A. Articles by Drysdale, D. B.

Department of Physiology, University of Otago Medical School, P.O. Box 913, Dunedin, New Zealand

1. Ventilation (_E), tidal volume (V_T), respiratory frequency (f) and arterial and end-tidal gas tensions were measured in seventy-one tracheostomized New Zealand white rats ( 405 g) anaesthetized with an initial dose of pentobarbitone followed by repeated small doses to ensure that a weak limb-withdrawal reflex remained.

2. O₂ consumption (1.2 ml (s.t.p.d.) min^-1 100 g^-1), CO₂ production (1.0 ml (s.t.p.d.) min^-1 100 g^-1), heart rate (357 min^-1), _E (43 ml min^-1 100 g^-1), P_a,CO2 (34 mmHg) and P_a,O2 (84 mmHg) in the control periods did not change significantly during the course of the experiment.

3. Inspirates of 21% O₂ with 2-10% CO₂, 15, 10 or 7.5% O₂ with either no or sufficient CO₂ to maintain normocapnia and 15 or 10% O₂ with 4, 6 or 8% CO₂ were tested. Steady-state responses were measured after 2 min of exposure.

4. Hypoxic—hypercapnic interaction on _E, V_T and f determined by a three-inspirate test ((i) hypoxia alone, (ii) hypercapnia and (iii) these hypoxic and hypercapnic levels combined) yielded various conclusions depending on the level of asphyxia examined. Essentially, the milder the asphyxia the more the interaction appeared additive or even multiplicative and the stronger the asphyxia the more the interaction appeared occlusive. However, this test is unsuitable for accurately showing interactions because the P_a,O2 achieved in asphyxia was higher than in hypoxia and the asphyxial P_a,CO2 was lower than in hypercapnia.

5. For isoxic conditions (P_a,O2 = 97, 77 and 51 mmHg), _E and V_T were related linearly to P_a,CO2 whilst f was related hyperbolically with convexity upwards (P_a,O2 97 mmHg) or downwards (P_a,O2 77 and 51 mmHg).

6. For isocapnic conditions (P_a,CO2 = 33, 40 and 48 mmHg), _E and V_T were inversely related to P_a,O2 with a hyperbolic curve (convexity downwards) whilst f was inversely and linearly related (P_a,CO2 33 mmHg) or constant (P_a,CO2 40 and 48 mmHg).

7. Multivariate analyses showed that the hypoxic—hypercapnic interaction was additive for V_T but occlusive for _E and f and the occlusion was more severe in the latter. This was illustrated graphically for the variable plotted against P_a,CO2 or P_a,O2 as parallel shifts in regression lines for V_T, flatter regression lines for _E during asphyxia and a virtually constant f during asphyxia.

8. _E responses and sensitivities to hypoxia and hypercapnia, the shape of _E, V_T and f regression lines against P_a,O2 and P_a,CO2 and the type of hypoxic—hypercapnic interaction on each variable in the rat were compared with other species.

9. Possible causes of the occlusive hypoxic—hypercapnic interaction in the rat were considered.

This article has been cited by other articles:

				D. C. Poole, W. L. Sexton, B. J. Behnke, C. S. Ferguson, K. S. Hageman, and T. I. Musch Respiratory muscle blood flows during physiological and chemical hyperpnea in the rat J Appl Physiol, January 1, 2000; 88(1): 186 - 194. [Abstract] [Full Text] [PDF]

				M. Bonora and M. Vizek Lung mechanics and end-expiratory lung volume during hypoxia in rats J Appl Physiol, July 1, 1999; 87(1): 15 - 21. [Abstract] [Full Text] [PDF]

				A. G. Boden, M. C. Harris, and M. J. Parkes Apneic threshold for CO2 in the anesthetized rat: fundamental properties under steady-state conditions J Appl Physiol, September 1, 1998; 85(3): 898 - 907. [Abstract] [Full Text] [PDF]