Premium
Interaction of hypoxia and hypercapnia on ventilation, tidal volume and respiratory frequency in the anaesthetized rat
Author(s) -
Cragg Patricia A.,
Drysdale D. B.
Publication year - 1983
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1983.sp014818
Subject(s) - normocapnia , hypercapnia , tidal volume , asphyxia , anesthesia , hypoxia (environmental) , respiratory system , ventilation (architecture) , respiratory minute volume , respiration , chemistry , medicine , oxygen , acidosis , anatomy , physics , organic chemistry , thermodynamics
1. Ventilation ( V̇ 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. O 2 consumption (1.2 ml (s.t.p.d.) min −1 100 g −1 ), CO 2 production (1.0 ml (s.t.p.d.) min −1 100 g −1 ), heart rate (357 min −1 ), V̇ 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% O 2 with 2‐10% CO 2 , 15, 10 or 7.5% O 2 with either no or sufficient CO 2 to maintain normocapnia and 15 or 10% O 2 with 4, 6 or 8% CO 2 were tested. Steady‐state responses were measured after 2 min of exposure. 4. Hypoxic—hypercapnic interaction on V̇ 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), V̇ 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), V̇ 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 V̇ 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 V̇ E during asphyxia and a virtually constant f during asphyxia. 8. V̇ E responses and sensitivities to hypoxia and hypercapnia, the shape of V̇ 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.