In vivo and in vitro CO2 titration curves in the rabbit: adaptation to hypercapnic conditions

Point-of-care blood gas and electrolyte analysis in rabbits

This article outlines a practical approach for the use of blood-gas analysis in pet rabbits using the I-STAT analyzer. Sampling techniques and a theoretic approach to diagnosis are described. The following 95% RI were obtained from venous samples of 45 healthy rabbits: pH (7.245-7.533), PCO(2) (28.9-52.9 mm Hg), HCO(3) (17.0-32.5 mmol/L), total CO(2) (18-34 mmol/L), BE(ecf) (-10-8 mmol/L), AnGap (11-26 mmol/L), Na (136-147 mmol/L), K (3.4-5.7 mmol/L), Cl (93-113 mmol/L), Glu (93-245 mg/dL), BUN (9-33 mg/dL). Results from 20 arterial samples were pH (7.358-7.502), PCO(2) (29.1-36.8 mm Hg), HCO(3) (17.5-27.6 mmol/L), BE(ecf) (-7-5 mmol/L), PO(2) (75-101 mm Hg), iCa (1.67-1.85). The article also includes some conclusions obtained comparing results from healthy and ill rabbits over an 18-month period.

Ontogenetic modification of the hypercapnic ventilatory response in the zebra finch

We investigated the effect of exposure to CO2 during development on the adult ventilatory response to CO2 of zebra finches. Developing zebra finches were exposed to chronic hypercapnic respiratory environments as embryos, as nestlings or during both developmental periods. Their responsiveness to CO2 was then measured following a 125-135 day post-fledging deacclimation period. At a FICO2 of 0.06, mean ventilation of adult finches in the three groups was 74.8, 61.3 and 65.8%, respectively, of that of finches reared under normocapnic conditions. These data indicate that adult acute ventilatory responsiveness to CO2 in birds may be in part determined by CO2 exposure during early development and may help explain the observation that fossorial and semifossorial species of birds and mammals, that naturally encounter high CO2 conditions in their burrows, have a blunted hypercapnic ventilatory response.

The effect of heat exposure on blood chemistry of the hyperthermic rabbit

1. Two hours of exposure to heat stress, resulted in hyperthermia in rabbits (Oryctolagus cuniculus). 2. This was accompanied by a severe hypocapnia, partly compensated for by a significant decrease in bicarbonate (HCO3-) concentration. 3. The severest hyperthermia (Tb = 43.5 degrees) was followed by a sharp decreased in both PaCO2 (to 20.2 torr) and HCO3- (to 9.2 mM/l), resulting in extreme metabolic acidosis (pH = 7.290). 4. The significant increase in serum osmolality (27%) is interpreted by the cumulative effect of increased electrolyte and metabolite concentrations. 5. The elevation in blood BUN, creatinine, globulin and GOT levels point to a possible damage to muscle cells by hypothermia. 6. The stable cholesterol and alkaline phosphatase levels, suggest that liver tissue was not damaged. 7. The dramatic increase in glucose from 103.8 to 348.8 mg%, and the significant increase (from 22.0 to 39.9 mg%) in BUN, suggest a possible disability of the cells to metabolize carbohydrates, accompanied by a progressive proteolysis as an alternative process for energy production. 8. The data suggest that the emergence of muscle cell damage, severe hyperglycemia and acidosis under heat stress, precedes and amplifies the deteriorating effects of high Tb in heat stressed rabbits, which often lead to mortality.

Effects of CO2 inhalation on acid-base balance and thermal recovery following cold water dives by the muskrat (Ondatra zibethicus)

Thermoregulatory, cardiac, and blood gas responses of muskrats to CO2 inhalation were examined during recovery from controlled dives in 3 degrees C water. It was shown that CO2 levels previously recorded in the winter lodges of this species are sufficient to reduce postdive oxygen consumption and rate of rewarming in unrestrained animals. Postdive exposure to 5-10% CO2 reduced recovery of abdominal and subcutaneous temperature (Tb) in the middorsal lumbar region, but did not affect interscapular warming overlying brown adipose tissue. Depressed recovery of deep Tb was matched by a prolonged acidosis in restrained muskrats breathing 5-10% CO2 following 90-s submergence in 3 degrees C water. This occurred despite a comparatively high whole body buffer value (delta H+/delta PaCO2) of 0.53 nM X l-1 X mmHg-1. Protracted recovery of arterial pH did not appear to involve retention of CO2 accumulated during diving, since in all trials, PaCO2 returned to the predive baseline within 5 min of surfacing. Perturbations in PaO2, like PaCO2, were restored within 5 min of surfacing, irrespective of inspired gas mixture. Predive exposure to 5-10% CO2 had no discernible effect on establishment of bradycardia in diving muskrats. Compared to predive values, postimmersion heart rate was significantly reduced in 5-10% CO2, but not in control runs.