Pulmonary function testing in spinal cord injury: effects of abdominal muscle stimulation.

The purpose of this study was to assess the effects of applying transcutaneous electrical stimulation to paralyzed abdominal muscles during pulmonary function testing (PFT) of individuals with spinal cord injury (SCI). Ten male subjects with anatomical level of SCI between C5-T7 were studied. Subjects performed PFTs with and without electrical stimulation delivered to the abdominal muscles. Subjects with the lowest percentage of predicted expiratory volumes and flows demonstrated the greatest improvement when electrical stimulation was delivered during forced expiration. The overall increases seen in percent of predicted for the study sample were 23 percent for forced vital capacity (FVC), 16 percent for forced expiratory flow in 1 s (FEV1), and 22 percent for peak expiratory flow rate (PEF). Contractions of paralyzed expiratory muscles in response to electrical stimulation during the performance of PFT maneuvers can significantly improve FVC, FEV1, and PEF in some individuals with SCI.

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.

Functional electrical stimulation of abdominal muscles to augment tidal volume in spinal cord injury.

Functional electrical stimulation (FES) of abdominal muscles as a method of enhancing ventilation was explored in six neurologically intact subjects and five subjects with spinal cord injury (SCI) who had levels of injury between C4 and C7. Pulmonary ventilation was augmented in both groups predominantly due to an increase in tidal volume. The average increase in tidal volume during FES for the neurologically intact group was 350 ml, while in the SCI group it was 220 ml. The FES caused active volume decreases in both the lower thorax and upper abdomen, which together appear to be the mechanism behind the increases seen in tidal volume. Therefore, the proposed method might be useful in future clinical practice. The results indicate that FES of abdominal muscles should be more thoroughly explored as a potential technique of ventilatory support in SCI. The results also point to the necessity for further studies of maintaining the condition of the chest wall in the pulmonary rehabilitation of individuals with tetraplegia.

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] (1/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.

Construction of anthropometric measuring chair (AMC) for lung function prediction.

An anthropometric measuring chair (AMC) was constructed in order to predict lung function parameters (vital capacity--FVC and forced expiratory flow in the first second-FEV1) in normal Caucasian subjects. Design of a chair was aimed toward the fast and reliable recording of body dimensions, particularly of the human thorax. Static and dynamic measurements of thorax dimensions, arm span and sitting height were used to predict FVC and FEV1 with an accuracy better than standard prediction equations based only on body height and age. Computer program for automatic calculation of FVC and FEV1 according to prediction equations was constructed in VisualBasic 4.0 software. The prediction values for FVC and FEV1 based on anthropometric variables could be used in paraplegic, disproportional and handicapped individuals, where standard body height is unobtainable.

Ventilatory assistance using electrical stimulation of abdominal muscles.

Nine neurologically intact subjects were studied to demonstrate the feasibility of stimulating the muscles of expiration during, and in synchrony with, naturally occurring breathing. A breath-by-breath analysis showed that both tidal volume and the frequency of respiration could be increased during periods of electrical stimulation. A single subject with complete spinal cord injury was studied to eliminate the possibility that the results from the normal subjects could be attributed entirely to either subconscious or conscious volitional response to the stimulation. The results provide a basis for future studies with patients in borderline ventilatory failure.

Double-blind placebo controlled clinical trial of almitrine bismesylate in patients with chronic respiratory insufficiency.

The efficacy and safety of almitrine bismesylate, a new respiratory stimulant, in patients with the hypoxaemic form of chronic respiratory insufficiency caused by chronic bronchitis and emphysema has been assessed. The multicentre trial of 12 weeks duration was double-blind and placebo controlled, with individual and group comparisons. Twenty three patients received almitrine 50 mg b.d. p.o. and 17 took placebo. In the almitrine group a significant increase in PaO2 was achieved (control value 54.4 mm Hg, rising to 59.1 mm Hg after 6 weeks, and to 59.4 mm Hg after 12 weeks). There was also a significant decrease in PaCO2 in the almitrine group after 12 weeks. No correlation was found between the plasma almitrine concentration, PaO2 and PaCO2. Lung function (FVC, FEV1, FEV1/FVC, Raw, TLC, RV, FRC) did not change in either group, but the degree of dyspnoea and performance in the 6 min walking test were significantly improved in the almitrine group. Adverse reactions appeared in 6 out of 23 patients on almitrine bismesylate (headache, urticaria, breathlessness, diarrhoea, chest pain, nausea and vomiting), causing drop out of 4 patients. Thus, almitrine bismesylate can be considered useful in the treatment of patients with chronic respiratory insufficiency.