SUMMARY1. Transcranial magnetic stimulation was performed using a figure-of-eightshaped coil over the right motor cortex with the aim of identifying those areas involved with activation of the diaphragm.2. The response of the right and left hemi-diaphragms was recorded using surface electrodes in either the 7th or 8th intercostal spaces 3 cm lateral to the anterior costal margin on either side.3. The compound muscle action potentials recorded over the left diaphragm in response to transcranial magnetic stimulation were maximal when the centre of the figure-of-eight coil was placed approximately 3 cm to the right of the mid-line and 2-3 cm anterior to the auricular plane.4. The amplitude of the response recorded from the diaphragm depended upon the angulation of the figure-of-eight coil and hence the direction of the stimulating current.5. The response of the inspiratory muscles to magnetic stimulation of one side of the brain was predominately contralateral but a small response was seen on the ipsilateral side. Ultrasonic techniques confirmed that the diaphragm was responding contralaterally and not ipsilaterally.

Background -It is known that automatic breathing is controlled by centres in the lower brain stem, whereas volitional breathing is controlled by the cerebral cortical centres. In hemiplegia, lesions above the brain stem result in paralysis of limb muscles. This study was performed to determine whether the diaphragm might also be affected in patients with hemiplegia. Methods -Studies were performed in six normal control subjects and in eight patients with complete hemiplegia caused by a lesion above the brain stem, all with no known chest disease. Full lung function tests were performed. Diaphragmatic excursion and inspired volume (VT) were measured simultaneously by M mode ultrasonography and respiratory airflow measurements. Recordings of diaphragmatic excursion were performed on each side separately during volitional and automatic breathing at a similar range of VT. Results -Lung function tests lay within the normal range in all the control subjects. In the hemiplegic patients mean (SD) vital capacity was 79 (18)% and residual volume was 123(30)% of predicted. Total lung capacity and functional residual capacity were in the normal range. In the control subjects no significant difference in diaphragmatic excursion was found between volitional and automatic breathing for the same range of inspired volume. By contrast, there was a significant decrease in diaphragmatic excursion during volitional breathing compared with automatic breathing on the affected side in four of the eight hemiplegic patients. Conclusions -In four of eight hemiplegic patients reduced diaphragmatic movement was present on the paralysed side during volitional inspiration when compared with automatic inspiration. The hemidiaphragm may be involved on the affected side in patients with hemiplegia.

Esophageal pressure generated during a maximal sniff (sniff Pes) was compared with mouth pressure generated during a maximal inspiration against a closed airway (Pimax) as a measure of global inspiratory muscle strength in 61 patients referred for investigation of respiratory muscle function. Transdiaphragmatic pressure (Pdi) was also measured during both maneuvers to compare maximal diaphragmatic strength. Sniff Pes (males, 68 +/- 27 cm H2O; normal greater than 53; females, 66 +/- 21; normal greater than 48) was greater than Pimax (males, 45 +/- 24 cm H2O; normal greater than 42; females, 42 +/- 24; normal greater than 17) in 55 of the 61 patients, both in absolute values and as a percentage of normal. In 36 patients Pimax and sniff Pes were both normal (mean +/- 2 SD), whereas in 13 patients they were both low. In 11 patients, Pimax was low, but sniff Pes was normal. One patient had a reduced sniff Pes but a Pimax at the lower limit of normal. In the 36 patients in whom both Pimax and sniff Pes were normal, Pdi was also normal or only moderately reduced, and in the 13 patients in whom both Pimax and sniff Pes were reduced, Pdi was very low. However, in the group of 11 patients with a low Pimax but a normal sniff Pes, Pdi was normal or only moderately reduced, suggesting that Pimax was falsely low, perhaps because of difficulties with the technique. Conversely, in the single patient with a low sniff Pes but a Pimax just within the normal range, Pdi was very low. We conclude that measurement of esophageal pressure during a maximal sniff is a useful test of inspiratory muscle strength and overcomes the difficulty some patients have in carrying out the Pimax maneuver.

Background -Although real time ultrasonography has been used in the last decade to record diaphragmatic motion, the relation between diaphragmatic excursion and different inspired volumes (VT) has not been assessed by ultrasound. Methods -Ten normal subjects were studied in the supine posture. Diaphragmatic excursion and VT were assessed simultaneously by M mode ultrasonography and respiratory airflow measurements at different inspired volumes. Ultrasound recordings of the movement of the right hemidiaphragm were carried out in the longitudinal plane subcostally. The transducer was held in a fixed position by a frame, built especially to eliminate any artefactual movement caused by outward motion of the anterior abdominal wall on inspiration.Results -Mean (SD) maximal diaphragmatic excursion recorded was 6X0 (0.7) cm. Inspired volumes ranged from 15(5)% to 87(10)% of the subjects' inspiratory capacity. A linear relation between diaphragmatic excursion and VT was found in all subjects (r = 0.976-0.995).The regression line had a slope of (0.24) cm/l. This slope had no correlation with either the height (r = 0.007) or weight (r=0.143) of the subjects. In five subjects in whom diaphragmatic excursion could be recorded at volumes near total lung capacity, the relation between diaphragmatic excursion and VT became alinear at very high lung volumes. Conclusions -The relation between diaphragmatic excursion and VT was linear between 15(5)% and 87(10)% ofinspiratory capacity. Ultrasonography of the diaphragm is a simple technique that could be applied in the clinical investigation of patients with suspected abnormalities of diaphragmatic movement. (Thorax 1994;49:885-889) Until the last decade assessment of diaphragmatic movement relied traditionally on fluoroscopic measurements. The exposure to irradiation limits the duration of such studies.In addition, fixed reference points are difficult to establish because many structures within the field of view move with inspiration. Ultrasonography is a safe and accurate method which is currently used in cardiology with great reliability and reproducibility. This method has recently been used to assess normal movement of the diaphragm in subjects with no respiratory disease'2 and abnormal movement in patients with diaphragmatic pathology.3 The present study assesses the relation between diaphragmatic excursion and different inspired volumes with simultaneous ultrasonography and respiratory airflow measurements. Since inevitable movement of the transducer occurs as a result of abdominal movement during breathing if the probe is held by hand, it was necessary to build a special device to hold the transducer in a fixed position. Methods SUBJECTSStudies were performed on 10 healthy subjects (five men) with no history of respiratory disease. Their age was 31 (6) years, height 170 (9) cm, and weight 67 (11) kg. Nine of the subjects were either physiologists or technicians from the department of respiratory medicine and one was a naive subject. All gave their verbal informe...

SUMMARY1. The response of the diaphragm to both transcranial magnetic stimulation and electrical phrenic nerve stimulation was studied in thirteen normal subjects under conditions of either a 'reflex' drive to ventilation with inhaled CO2 or during volitional ventilation of similar magnitude.2. The induced compound action potential in the diaphragm was recorded using an oesophageal electrode, and in some cases transdiaphragmatic pressure was recorded using oesophageal and gastric balloon catheters.3. The response of the diaphragm to transcranial magnetic stimulation was invariably facilitated with volitional inspiration; there was either minimal or no response at functional residual capacity.4. Facilitation w-ith inspiration was also seen during a 'reflex' drive to ventila-t-on with inhaled CO2 in the presumed absence of any volitional contribution to ventilation. A similar degree of facilitation was seen with voluntary ventilation of similar magnitude and pattern.5. If the facilitation is predominantly a cortical phenomenon, then these results imply that there is a behavioural component in the previously supposed purely 'reflex' drive to ventilation with inhaled CO2. We also discuss the interpretation of these results if some of the facilitation occurs at the phrenic motoneurone.