Mechanical load on the ventilatory muscles during an incremental cycle ergometer test.

An incremental cycle ergometer test performed with a total of 40 healthy subjects (25 male, 15 female) was used to study the mechanical load on the ventilatory muscles. The parameters for the mechanical load on the ventilatory muscles are the time integral of the oesophageal pressure and the mean oesophageal pressure change per time unit (dPoe/dTI) of each breathing manoeuvre. The pressure-time integral is the area delimited by the oesophageal pressure trace and the inspiratory time axis. It is expressed as a fraction of the product of the subject's maximum oesophageal pressure (Poe(max)) and total breath cycle duration (TTOT). This parameter is called oesophageal tension time index (TTIoe). The relationship between minute ventilation and these two parameters during ergometer test showed gender-specific variations because of the differences between men and women as to anthropometric data, lung function parameters and maximum ventilatory muscle strength. Moreover, the dPoe/dTI values significantly depend on the breathing frequency. The present study has provided evidence that, in general, the TTIoe and dPoe/dTI values in terms of a specific minute ventilation (VE) are higher in women than in men. Parameters for the mechanical load on the ventilatory muscles regarding the level of pressure to be generated as well as the duration and velocity of muscle contraction should therefore also allow for the gender of the patients.

Dependence of maximal sniff generated mouth and transdiaphragmatic pressures on lung volume.

The maximal sniff generated mouth and transdiaphragmatic pressures of six healthy volunteers (three women and three men) were measured at various lung volumes between residual volume and 95% of total lung capacity. At residual volume the mean (SD) maximum transdiaphragmatic pressure was 163 (18) cm H2O (1 cm H2O = 0.0981 kPa). With increasing lung volume the maximum pressures generated declined, so that at 95% of total lung capacity the mean pressure was 68 (15) cm H2O. Mouth pressures showed a similar relation to lung volume. At residual volume the mean maximum mouth pressure was 74 (8) cm H2O, compared with 38 (6) cm H2O at 95% of total lung capacity. The relation between pressure and lung volume was linear for measurements at lung volume levels between residual volume and 85% of total lung capacity; values at 95% of total lung capacity, however, were lower than predicted from the linear regression of the other points. The use of a second order polynomial regression showed a higher coefficient of determination in all cases (0.72 and 0.69 for transdiaphragmatic and mouth pressures on the basis of all pressure values for all subjects). Sniff generated mouth and transdiaphragmatic pressures show a predictable dependence on lung volume, supporting their use as measures of global inspiratory muscle power and diaphragm strength respectively.

A method for the elimination of artefacts in electric field plethysmography of the lung.

The reliability of electric plethysmography for respiration monitoring is reduced by artefacts caused by the cardiac activity, by motions, electromagnetic cross-talk and others. For artefact suppression, a constant-current field-plethysmography technique is discussed which uses the voltage of an auxiliary electrode in addition to the conventional four-electrode arrangement. By means of a differential amplifier, a respiration signal is produced which is almost entirely free from heart artefacts, while the intensity of additional artefacts is suppressed. In principle, the technique can also be used for the separate determination of the ventilation intensity of the two lungs.