[Experimental studies on cardiopulmonary relation under hypoxia, hypercapnia and airway obstruction in dog (author's transl)].

On 18 dogs the effects of hypoxia (12, 10, 7.5% O2) and hypoxia and hypercapnia (10% O2 + 5, 7.5, 11% CO2) on breathing, pulmonary vascular resistance, cardiac output and on the arterial and venous oxygen pressure were investigated. The relationship between arterial oxygen pressure to Pap as to vascular resistance is not in the mean linear. There are good, bad and nearly nonresponders in respect to the vascular resistance on the dogs. Therefore, calculation and evaluation of mean values are less helpful. A similar variation on men could help to understand also better the large scatter which is always shown on correlations between PO2a : Pap or PO2a : vascular resistance. Also the different pattern of the V/Q relationship may be influenced by the amount of the vascular response to local alveolar hypoxia. An increase of PCO/a potentiates the local vasoconstrictor effect of hypoxia. Mainly this was seen in the range between hypocapnia and moderate rates of hypercapnia. Hypoxia shows an increase of breathing frequency, hypercapnia shows and increase in tidal volume. Also under hypercapnia there are nonresponders and better responders in response to the vascular resistance in the lung circulation. Mechanical airway obstruction is followed by an increase of tidal volume; obstruction caused by acetylcholine is followed by a decrease of tidal volume and an increase of breathing frequency. Changes in the arterial blood gases are caused by changes in the ventilation perfusion relationship only under acetylcholine obstruction. Influences on the lung circulation by the airway obstruction under these experimental conditions as direct effects are small or not existent.