EFFECTS OF BODY TEMPERATURE ON VENTILATION, BLOOD GASES AND ACID-BASE BALANCE IN EXERCISING FOWL

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Abstract
To determine the influence of hyperthermia on respiratory, blood gas and acid-base changes in exercising birds, domestic fowl were exercised on a treadmill at ambient temperatures of 5, 20, 30 and 35.degree. C for 10 min at graded running speeds up to 4.3 km .cntdot. h-1. Ventilation and gas exchange were measured continuously and arterial blood gases, pH and the concentration of lactic acid in arterial blood were measured in samples taken during the last minute of each run. During exercise at 5.degree. C rectal temperature did not change significantly from rest (isothermic condition) and there was no sign of thermal influence on respiratory pattern, such as was observed at higher ambient temperatures. At any given running speed, increased ambient temperature caused increased ventilation by an increase in respiratory frequency (f) together with a decrease in tidal volume (VT). Under isothermic conditions, at low running speeds, birds maintained an isocapnic hyperpnea: arterial PCO2, PO2 [partial pressure of CO2 and O2, respectively] and pH and O2 extraction were unchanged. However, at higher speeds (circa > 2.5 km .cntdot. h-1) some hyperventilation occurred with subsequent falls in arterial PCO2 and O2 extraction. Arterial pH also fell significantly (P < 0.01). During hyperthermic exercise, O2 extraction, arterial PCO2 and bicarbonate concentration all fell significantly (P < 0.01) and progressively with increasing work load, and birds hyperventilated at all running speeds. This produced a significant arterial hypocapnia and alkalosis at the lower speeds (P < 0.05) but this was replaced by a hypocapnic metabolic acidosis at the higher running speeds. Blood lactate concentration rose steeply at speeds above circa 2.5 km .cntdot. h-1 but arterial pH fell by only 0.1 U or less partly as a result of buffering by blood bicarbonate. Both hyperthermia and lactacidosis are causes of hyperventilation and arterial hypocapnia during heavy running exercise in birds. Ventilatory adjustments similar to those observed in resting hyperthermic birds, viz. increased f and reduced VT prevent severe arterial hypocapnia from occurring in hyperthermic exercising birds.

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