Position and shape of the diaphragm: implications for atelectasis formation.

To evaluate diaphragm movement, 18 consecutive patients undergoing surgery under general anaesthesia were allocated to Group 1 (n = 9: no neuromuscular paralysis) or Group 2 (n = 9: neuromuscular paralysis achieved with pancuronium). Spiral computerised tomography was performed awake and during anaesthesia at end-expiratory level and, additionally, in four patients (Group 2) at end-inspiration for subsequent analysis. There was a significant cephalad displacement of the most cephalad point of the diaphragm dome at functional residual capacity, particularly in its dependent portion, in the pancuronium group. During anaesthesia with no persisting muscle paralysis, there was only a minor and insignificant cephalad shift of the diaphragm dome. However, regional analysis showed that the most dorsal part of the diaphragm was significantly displaced cephalad. Compared with conscious, spontaneous breathing, mechanical ventilation decreased the inspiratory displacement of the dependent part of the muscle. This minor movement of the diaphragm may play an additional role in atelectasis formation.

Volumetric analysis of aeration in the lungs during general anaesthesia.

Spiral computed tomography (CT) allows volumetric analysis of formation of atelectasis and aeration of the lungs during anaesthesia. We studied 26 premedicated patients undergoing elective surgery allocated to group 1 (conscious, spontaneous breathing, investigating inspiration and expiration), group 2 (general anaesthesia with mechanical ventilation, investigating inspiration and expiration) or group 3 (general anaesthesia with mechanical ventilation, investigating changes over time). Using spiral CT, the lungs were studied either before or during general anaesthesia. CT scans were grouped into the following areas: overaeration, normal aeration, reduced aeration, poor aeration and atelectasis. The mechanism of atelectasis appeared to be both gravitational forces and a diaphragm-related force that acts regionally in caudal lung regions. Mean atelectasis formation and poorly aerated regions comprised approximately 4% of the total lung volume between the diaphragm and carina, giving a mean value of 16-20% of the normal aerated lung tissue being either collapsed or poorly aerated. The vertical ventilation distribution was more even during anaesthesia than in the awake state.

Experimental dynamic cardiomyoplasty in sheep.

To evaluate electrically stimulated muscle grafts for augmenting ventricular function in cardiac insufficiency, dynamic cardiomyoplasty was performed in nine sheep, using latissimus dorsi (LD) muscle wrapped as a pedicle around the left ventricle. Beginning 2 weeks postoperatively, LD was stimulated synchronously with the heart. After 6 and 12 weeks of stimulation, hemodynamic evaluation was done and biopsies were taken for histochemical and biochemical analysis. With intact heart function, stimulation of the muscle was not hemodynamically beneficial. During induced heart failure, cardiomyoplasty increased cardiac output by 25% in two sheep. Eight LD muscles contracted vigorously in synchrony with the heart, one was fibrosed and all were fixed to the thoracotomy incision by scar tissue. ATPase stain showed gradual transformation of muscle fibers into fatigue-resistant Type I. At 12 weeks only Type I were seen. Quantitative enzymatic analyses revealed increase in oxidative and decrease in glycolytic enzymes. Chronic electrical stimulation is concluded to change the muscle characteristics towards those of mainly oxidative and fatigue-resistant muscle, thereby improving opportunities for assisting the depressed heart. Dynamic cardiomyoplasty involves risks of adhesions to adjacent tissues and muscle trauma from chronic stimulation.

The concordance of respiratory fluctuations in oesophageal and central venous pressures.

Respiratory fluctuations in oesophageal and central venous pressures were recorded in 13 healthy subjects and compared with respect to phase and amplitude concordance. An average divergence in phase of nearly 180 degrees was obtained, with large inter-individual variations. Disregarding phase the amplitude of the respiratory central venous pressure was found to be, on the average, a good 1/4 of that of the oesophageal pressure in the supine posture, and a good 2/3 while the subjects were sitting. These figures also varied considerably. It is suggested that the findings might be referred to competition between a central venous pressure raising effect of inspiration enhanced venous return, and a central venous pressure depressing effect of the inspiratory fall in intrathoracic pressure. The partitioning of costal and abdomino-diaphragmatic breathing is considered of great significance to the outcome of this competition. It is concluded that the oesophageal balloon catheter technique for estimation of transpulmonary pressure cannot simply be replaced by the central venous catheter technique in healthy subjects. Its application in patients with certain pulmonary disorders, however, might be more successful.