1. Six normal subjects cycled to endurance or for 60 min at four work rates (WR 1-4): mean of 34 % working capacity (93 watts for 60 min); 43 % (120 watts for 56 min); 63 % (177 watts for 37 min); and 84 % (233 watts for 12 min), to determine how breathing pattern and dyspnoea change during prolonged activity. Four to six minutes were allowed to establish steady state and subsequent changes were considered to be endurance related.2. Dyspnoea (Borg scale, 0-10) increased with the duration of activity at all work rates.3. Ventilation (V(E)) did not change at WR1; increased from 44 to 47 l min-1 at WR2; from 60 to 88 l min-1 at WR3; and from 111 to 132 l min-1 at WR4. Dyspnoea was significantly and independently related to ventilation and duration of activity: dyspnoea = 0.004 V(E)1.36 time0.25 (r = 0.81; partial F 202 and 26 respectively).4. Inspiratory resistance did not increase at any work rate. Dynamic elastance remained constant during WR1, WR2 and WR3 but increased from 7.4 to 9.1 cmH2O l-1 during WR4.5. Peak inspiratory pressure did not increase, and the increase in V(E) was accomplished by an increased breathing frequency without change in duty cycle.6. Duration of activity is an important contributor to dyspnoea independent of changes in respiratory muscle contractile activity.

This study quantified the separate contributions of the intensity of exercise and its duration to muscular effort and dyspnoea during cycle ergometry. Six normal subjects estimated the perceived intensity (Borg scale 0-10) of peripheral muscular effort and dyspnoea during incremental exercise to their maximum work capacity (Wcap). On separate days, the same subjects exercised to endurance or 60 min at work rates rated for leg effort on the initial incremental test as: 2 ("slight", 33.1 +/- 1.45% Wcap) (mean +/- SE); 3 ("moderate", omission 83.6 +/- 3.87% Wcap). Perceived leg effort increased by a factor of 4.4 (2(2.13)) with a doubling of work rate and by 1.3 (2(0.39)) with a doubling of duration, as expressed by: Leg effort = k x %Wcap2.13 x Time0.39 (r2 = 0.87) Perceived dysponea increased 5.3-fold with a doubling of work rate and by 1.4-fold with a doubling of duration: Dysponea = k x %Wcap2.41 x Time0.47 (r2 = 0.75) Changes in work intensity, rather than duration, dominated symptom magnitudes such that in the performance of a given task, halving the intensity and doubling the duration of activity reduces the maximal intensity of muscular effort and dyspnoea to less than a third.

Pleural aspergillosis is rare, usually occurring in seriously ill adults against a background of tuberculosis and chronic bronchopleural fistulas.'We present a case occurring in a child that differs in many respects from previously reported cases. Case reportA 14 year old boy complained of malaise, anorexia, a dry cough, and right sided chest discomfort of three weeks' duration.He was referred for a chest radiograph, which showed a large right sided hydropneumothorax with cav- itation at the apex of the right lung.The chest radiograph taken after insertion of a chest drain is shown in figure 1.He had been in good health until aged 11 years, when two weeks after BCG vaccination he was admitted to hospital with a severe right sided pneumonia with associated cavitation, ab- scess formation, and a small pleural effusion.At that time routine cultures, Ziehl-Neelsen stains, and culture for Mycobacterium tuberculosis were negative.A presumptive diagnosis of staphylococcal pneumonia was made and he responded to ampicillin and cloxacillin; pleural intubation was not performed.His sweat sodium concentration was normal.He was well during the next 18 months, serial radiographs showing residual pneumatocoeles in the right upper lobe and apical segment of the right lower lobe.During the next two years, after discharge from regular attendance at the paediatric clinic, he had remained reasonably well.On examination he was thin and pale, but afebrile and in no acute distress.His trachea was deviated to the left and there was stony dullness on percussion over the right mid and lower chest zones.General examination revealed no other abnormality.The haemoglobin concentration was 13 g/dl and the white cell count 7-4 x 109/l with a normal differential count.A Mantoux test gave a strongly positive reaction at 1 TU strength.Fluid removed by pleural aspiration was cloudy, cytological examination showing 85% polymorphonuclear leucocytes and no malignant cells.The protein concentration was 36 g/l.Gram stains, Ziehl-Neelsen stains, and cultures for pyogenic organisms and for M tuberculosis from various sites were repeatedly negative.Closed pleural biopsy showed histiocytes but no granu- lomas, fungi, or acid fast bacilli.No fungal elements were