Transvenous versus perinervous stimulation of the phrenic nerve to assess the diaphragmatic strength in rabbits

Diaphragmatic strength can be measured by transdiaphragmatic pressure during phrenic nerve stimulation. In order to avoid phrenic nerve dissection, a transjugular approach of the phrenic nerve can be performed. The objective of this study was to verify the identity of perinervous and transvenous techniques of phrenic nerve stimulation to assess diaphragmatic force. In intact (n = 9) or right phrenicotomized (n = 12) rabbits, we compared esophageal pressure (Peso) induced by supramaximal perinervous stimulation of the phrenic nerve with that obtained by transvenous stimulation of the phrenic nerve. Electromyography (EMG) of the thoracic muscles was studied in four animals. We found no difference between Peso induced by perinervous (PNS) and transvenous (TVS) unilateral or bilateral phrenic nerve stimulation. During unilateral stimulation, no EMG activity was recorded in the non stimulated diaphragm, or in the middle part of the esophagus, or in ipsi- and contralateral accessory inspiratory muscles. We conclude that in rabbits, unilateral or bilateral TVS of the phrenic nerve is functionally equivalent to PNS, whatever the side of stimulation; Peso is not altered by esophageal contraction in TVS. Transvenous stimulation can replace perinervous stimulation in experimental studies, when cervical access is difficult.

Selective resection of the phrenic nerve roots in rabbits. Part II: Respiratory effects

This study evaluates the delayed respiratory consequences of selective resection of one or several roots of the right phrenic nerve in rabbits. A total of 50 animals were operated on according to five modalities of root resection. A total of 11 animals served as control. The breathing pattern was analysed 8 weeks after surgery. Transdiaphragmatic pressure was measured during transjugular supramaximal stimulation of the phrenic nerve, unilaterally or bilaterally and during prolonged tracheal occlusion (PImax). No difference was observed between the esophageal pressure observed during bilateral phrenic nerve stimulation (BilPeso) in control animals when compared to animals with resection of the highest root of the right phrenic nerve (16.2 +/- 1.0 versus 14.5 +/- 1.0 cmH2O (mean +/- SE). Resection of the two highest or of the two lowest roots of the right phrenic nerve resulted in a similar BilPeso (11.3 +/- 0.8 versus 11.1 +/- 1.2 cmH2O). Preservation of only the accessory phrenic nerve (PN) resulted in a low value of BilPeso (9.8 +/- 1.0 cmH2O) similar to that obtained with complete denervation of the right hemidiaphragm. Ventilation and PImax were not different between the denervated or intact rabbits during quiet breathing. We conclude that in rabbits: (1) Diaphragmatic function is preserved after resection of the highest root of the phrenic nerve. (2) Diaphragmatic function is altered if only the APN is preserved.

Respiratory response to CO2 in patients with chronic obstructive pulmonary disease in acute respiratory failure

The aim of our study was to determine the importance of chemoreceptor stimulation by carbon dioxide in setting the level of ventilation in patients with chronic obstructive pulmonary disease (COPD) in acute respiratory failure. We studied the ventilatory and mouth occlusion pressure (P0.1) responses to CO2 in 25 COPD patients under treatment for episodes of acute respiratory failure, and in 24 normal subjects. Carbon dioxide rebreathing tests were performed in the spontaneously breathing, intubated patients, after arterial blood gases had been quasi-normalized by mechanical ventilation, which allowed us to compare both groups at similar resting arterial carbon dioxide tension (PaCO2) and acid-base status. The slopes of the ventilatory responses were markedly lower in the patients (mean +/- SEM, 1.28 +/- 0.23 versus 12.53 +/- 1.13 l.min-1.kPa-1). The slopes of the P0.1 responses were lower in the patients (0.27 +/- 0.05 versus 0.45 +/- 0.05 kPa.kPa-1), but the absolute P0.1 values were not significantly different from the normals. Increasing PaCO2 from 5.3 to 8 kPa (40 to 60 mmHg) resulted in a mean increase of 34% in ventilation. These results show that CO2 drive is a major determinant of respiratory stimulation in many COPD patients with acute respiratory failure.

Respiratory response to CO2 in patients with chronic obstructive pulmonary disease in acute respiratory failure

The aim of our study was to determine the importance of chemoreceptor stimulation by carbon dioxide in setting the level of ventilation in patients with chronic obstructive pulmonary disease (COPD) in acute respiratory failure. We studied the ventilatory and mouth occlusion pressure (P0.1) responses to CO2 in 25 COPD patients under treatment for episodes of acute respiratory failure, and in 24 normal subjects. Carbon dioxide rebreathing tests were performed in the spontaneously breathing, intubated patients, after arterial blood gases had been quasi-normalized by mechanical ventilation, which allowed us to compare both groups at similar resting arterial carbon dioxide tension (PaCO2) and acid-base status. The slopes of the ventilatory responses were markedly lower in the patients (mean +/- SEM, 1.28 +/- 0.23 versus 12.53 +/- 1.13 l.min-1.kPa-1). The slopes of the P0.1 responses were lower in the patients (0.27 +/- 0.05 versus 0.45 +/- 0.05 kPa.kPa-1), but the absolute P0.1 values were not significantly different from the normals. Increasing PaCO2 from 5.3 to 8 kPa (40 to 60 mmHg) resulted in a mean increase of 34% in ventilation. These results show that CO2 drive is a major determinant of respiratory stimulation in many COPD patients with acute respiratory failure.