Effects of hyperbaric oxygen on the rat neurogenic pulmonary edema.

Neurogenic pulmonary edema was induced in rats by bilateral cervical vagotomy. One hour after surgery, 25 animals were placed in an experimental hyperbaric chamber and allowed to breathe oxygen at 1.8 absolute atmospheres for 325 min. Vagotomized controls (N = 25) breathed atmospheric air. Twenty-four h after vagotomy, arterial blood samples were obtained and the lungs removed. Lungs were weighed wet and dry and lung indexes were calculated for each animal by dividing lung wet weight and dry weight by total body weight. There was no statistical difference in total lung weight or total water among groups. However, the dry lung index was about 20% lower in oxygen-treated animals than in controls. There was no difference between hyperbaric oxygen-treated animals and non-vagotomized normal animals, but vagotomized air-breathing controls differed significantly from non-vagotomized animals (P less than 0.05). These results strongly suggest a slower formation of pulmonary edema in the hyperbaric oxygen-treated group.

The absence of the descending limb of the Frank-Starling curve of the depressed guinea pig whole ventricle.

To determine whether the descending limb of the Frank-Starling curve can be detected in the whole ventricle when contractile state is impaired, volume-active pressure relationships were investigated in deteriorated preparations of isolated guinea pig hearts. The pressure developed by the isovolumic left ventricle as well as the first derivative of the pressure were determined during progressive dilation of the left ventricle up to a resting pressure of 60 mmHg. Coronary flow was provided by a constant perfusion pressure of 75 mmHg. The descending limb of the Frank-Starling curve was not detected: when expressed as a function of resting pressure the coronary flow attained maximal values at a calculated resting pressure of 14.0 mmHg and decreased at larger ventricular volumes. These results support the view that there is no descending limb of the Frank-Starling curve when the whole ventricle is distended, even when the intrinsic contractile properties are impaired, and coronary flow is reduced by compression due to ventricular distension.

[Right ventricle--pulmonary artery diastolic blood flow (author's transl)]. / Fluxo diastólico ventrículo direito--artéria pulmonar

The authors show the possibility of the establishment of blood flow from the right ventricle to the pulmonary artery during the period of ventricular diastole, through experimental models mimetizing hemodynamic patterns described in the literature for certain cardiopathies. These models consisted of experimental hypodiastoly, associated or not with right ventricle hyposystoly. The detection of the existence or not of blood flow in the several phases of the cardiac cycle, was made recording the variations of the electrical impedance of the blood.

[Pre-systolic deflexion in pressure recordings of the right ventricle and pulmonary artery (author's transl)]. / Deflexão pré-sistólica nos registros pressóricos do ventrículo direito e da artéria pulmonar

The authors demonstrated experimentally that the origin of the pre-systolic deflexion, previously observed by many investigators in pressure recordings of the right ventricle and the pulmonary artery, is due to the effective atrial contraction, which, besides the pressure change, produces a blood flow from the ventricle towards the artery. This flow must possibly exert an important role in the maintenance of the cardiac output when a failure of the right ventricle is established.

[An impedance measuring technique for blood flow qualitative recording]. / Técnica impedanciométrica de detecção de fluxo sanguíneo.

An impedance measuring technique was developed for blood flow qualitative recordings in laboratory animals. Basically, it consists in the administration of an indicator solution (0,1 ml, NaCl 20%) which, mixing with the blood, provokes a decrease in its electrical resistance, in such way that the passage of this mixture (concentrated saline/blood) through a bipolar receptor electrode, resistively balanced by the electrical impedance of blood alone, will be detected as a sudden resistance fall. The results so far show that it is an adequate technique for blood flow qualitative studies, since, despite its simplicity, provides consistent and unequivocal recordings which, performed simultaneously with those of other circulatory events, may become a helpful tool for their understanding.