Breathing induced by abdominal muscle stimulation in individuals without spontaneous ventilation.

The purpose of the study was to determine if functional electrical stimulation of abdominal muscles (FESAM) could maintain pulmonary ventilation at acceptable levels in individuals with spinal cord injury (SCI) who are unable to breathe spontaneously. This is the first published investigation of this technique in this subject population. This case series study included three individuals with SCI; two were on mechanical ventilation (MV), and one used mechanical ventilation and also had an implanted phrenic nerve stimulator (PNS). Using surface electrodes, stimulation was applied to the rectus abdominis and lateral group of abdominal muscles. Repetitive trains of pulses produced a breathing frequency of 20 breaths/min. The longest periods of breathing using only FESAM-supported ventilation for the three subjects were 30, 40, and 210 s, respectively. Airflow at the mouth and volumes were measured with a pneumotachograph and/or optoelectronic plethysmography. Oxygenation was monitored with a pulse oximeter. The tidal volumes generated exclusively by FESAM were sufficient to maintain adequate oxygenation during the periods of stimulation. When oxygenation measured with pulse oximetry dropped to 92% saturation, FESAM was discontinued, and MV or PNS was resumed. This is the first report of achieving successful ventilation in individuals with SCI who have zero tidal volume using FESAM. These preliminary results indicate the clinical potential of FESAM as an additional tool in the armamentarium of supported ventilation.

The oxygen uptake threshold during incremental exercise test.

The linear relationship between oxygen consumption (Vo2) and exercise intensity is a well established phenomenon observed during incremental exercise. Recently, a non-linear increase in Vo2 has been reported by Zoladz et al., who used a relatively complicated method to describe the phenomenon. In this study, we tried to ascertain whether the same phenomenon, which we named the oxygen uptake threshold (OUT), could be described by a simple method, using the two best fitting lines adopted for the less and more steep parts of the Vo2 increase. Our hypothesis was that the non-linear Vo2 increase was the result of a continuous Vo2 increase (oxygen drift) occurring during the more intense steps only. Therefore, we analysed the Vo2 time course during each step. Six cyclists performed an incremental exercise test on a cyclo - ergometer. The lactate threshold (LT) was calculated by using the intersection point of the two best fitting lines in the diagram of log LA (lactate concentration) dependence on log P (Power). The time course of Vo2 during each step was analysed by an exponential rise to the maximum model. The results showed that OUT could be determined in five of the six subjects, whereas LT could be determined in all six subjects. The power output determined by OUT (168 ± 13 W) was similar to that determined by LT (180 ± 25 W). The Vo2 time course during each step showed steady values during low intensity exercise. At intensities above LT and OUT, however, Vo2 increased continuously, showing oxygen drift. It may be concluded that OUT is a realistic phenomenon, which is based on oxygen drift.

Changes in blood pH, lactate concentration and pulmonary ventilation during incremental testing protocol on cycle ergometer.

We investigated mutual changes in the blood lactate concentration ([LA]), blood pH and pulmonary ventilation (VE) to obtain insight into the regulation of pH at different levels of the exercise intensity. For this purpose the ratio VE/[LA] (l/min/mmol/l) was determined at each particular pH corresponding to exercise intensity in seven healthy subjects on the cycle ergometer during incremental exercise test. Changes in VE/[LA] ratio were found to exhibit three phases. In the first phase, the ratio increased without significant changes in [LA] and pH until it reached certain individual peak value. In the second phase, VE/[LA] decreased because increases in [LA] were considerably bigger than those of VE. Decreases in blood pH followed those of VE/[LA], nevertheless differences existed among subjects depending on how successful individual subjects regulated their blood pH. In the third phase with the VE/[LA] values stabilized between 15 and 22 and pH values between 7.32 and 7.26, whereas differences between subjects became negligible. Similar trends to VE/[LA] were observed in case of the Onset of Blood Lactate Accumulation (OBLA) throughout the test at pH values below 7.32, as was manifested by the correlation coefficient. We conclude that blood pH regulation due to respiratory compensation of the lactate acidosis is more successful in subjects with better endurance (higher OBLA), but only when [LA] is slightly increased or at slight acidosis.