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The rate at which alveolar PCO2 (PA, CO2) rises during expiration has been measured in seven healthy medical students. PA, CO2 rate of rise [delta PA, CO2/delta t] was measured by a method utilizing constant expiratory flow rates in individual breaths in two subjects, and was calculated from airway PCO2 and expiratory tidal volume in the remaining five subjects. Steady‐state runs were recorded at two or more metabolic rates with the subject making no special effort to control mean lung volume. This was done to establish the relationship between delta PA, CO2/delta t and the rate of CO2 production (VCO2) at normal lung volume in individual subjects. Steady‐state runs were also recorded at high lung volume. In each subject delta PA, CO2/delta t was less than would have been obtained at normal lung volume. Inversion of a hypothetical relation between delta PA, CO2/delta t, VCO2 and average lung volume (VLa; DuBois, Britt & Fenn, 1952) yielded calculated values of VLa for both the normal and the high lung volume states. Lung gas volume was measured in a whole body plethysmograph, ('box volume') both for the normal and high lung volume states, in each subject. Mean VLa and ‘box volume’ estimates showed only moderately good agreement, whereas the estimated differences between normal and high lung volume obtained by the two methods were virtually identical. These experiments suggest that the expiratory PA, CO2 rate of rise is determined, in the steady state, partly by the rate of CO2 production (a directly proportional relationship) and partly by the mean lung volume (an inversely proportional relationship).

Functional intramuscular electrical stimulation of the gluteus maximus and gluteus medius on the stance side whilst walking is reported. The subject was an adult, male, post-traumatic complete paraplegic with lesion level at T7. He had been using surface stimulation to aid his walking with the adult ParaWalker Orthosis but suffered unpleasant anterior abdominal wall muscle contractions with high amplitude stimulation. The experimental use of percutaneous intramuscular Platinum/Iridium wire electrodes demonstrated that more forceful contractions of the buttock muscles could be achieved without any effect on abdominal wall musculature. This prompted the use of a permanent, implanted system. The system is inductively coupled to an external control device and is working satisfactorily 7 months after implantation.

1. Ten normal, non-asthmatic subjects performed an 18 min graduated exercise test on a static exercise bicycle on 3 separate days. They received either no medication, or propranolol 80 mg orally 2 h before, or ipratropium bromide 0.216 mg by inhalation 30 min before, the start of exercise. 2. With no medication, transpulmonary index (TPI), a measure of airway resistance, fell linearly during exercise from a resting value of 0.269 ± 0.024 to 0.170 ± 0.014 kPa·1−1·s by the end of exercise. This returned to baseline between 2 and 4 min after stopping exercise. 3. Propranolol elevated baseline TPI slightly from 0.270 ± 0.024 to 0.294 ± 0.024 before exercise and during exercise this fell linearly to 0.185 ± 0.016 kPa·1−1·s. The fall in TPI during exercise after propranolol was not significantly different from the fall seen with no medication. Six minutes after exercise stopped TPI rose to 0.336 ± 0.035 kPa·1−1·s after propranolol. All values for TPI from 4 min to 16 min after exercise were significantly higher after propranolol than the corresponding values found after no medication (P<0.05). 4. Ipratropium bromide decreased baseline TPI from 0.264 ± 0.024 to 0.163 ± 0.013 kPa·1−1·s (P<0.001) and this did not change significantly further either during or after exercise. 5. Normal subjects show considerable airway dilatation during exercise and this appears to result from inhibition of resting vagal tone. The sympathetic system does not appear to mediate the airway dilatation during exercise, but it may be important in protecting against post-exercise bronchoconstriction.

Energy expenditure is an important parameter in the assessment of gait and orthotic treatment of locomotor disabilities. Up until now oxygen uptake measurement has been the most common method used to assess this. In able bodied subjects heart rate monitoring is also increasingly used. In high thoracic level lesion paraplegics monitoring heart rate was considered to be unreliable because of suspicion of injury to the sympathetic contribution to the cardiacplexus. Bar-On & Nene1found that in paraplegics below the lesion level T3 heart rate still shows linear relation to oxygen uptake. MacGregor2,3combined the heart rate and speed of locomotion to produce a single index called physiological cost index. This study consists of monitoring heart rate and speed of 16 adult thoracic level paraplegics walking with the ORLAU ParaWalker, calculation of their physiological cost index, and establishing a range of physiological cost index of paraplegic locomotion using the ORLAU Para-Walker.

The quantitative assessment of the imaging performance of nuclear magnetic resonance (NMR) scanning equipment requires the use of test objects (Orr et al, 1983; Lerski et al, 1984). These are commonly constructed from perspex and are filled with aqueous solutions of paramagnetic salts (e.g. CuSO4or MnCl2) to provide the NMR signal with a relaxation behaviour (T1in particular) similar to tissue. The presence of the human body during the NMR imaging procedure has the effect of loading the receiver coil. This is due to energy dissipation by currents induced in the conducting tissue. The solutions of paramagnetic salts do not provide conducting pathways and subsequently have very little loading effect. The signal-to-noise ratio is degraded by coil loading and falsely high values will be obtained if measurements are made without matching this effect when using test objects. Saline-filled containers can be used to load receiver coils, but these may be difficult to construct and may interfere with the positioning of the test objects. The use of an inductive damping loop has been proposed as an alternative method of matching coil loading (Edelstein et al, 1984). This consists of an inductive loop together with a tuning capacitor and a resistance, all in series (Fig. 1).The investigation reported here considers the use of such loops with head coils, the appropriate values of inductance and the values of resistance required.