Bronchodilator response in pulmonary disease at two different states of respiratory mechanics.

It would be convenient to be able to measure airway responsiveness to bronchodilator drugs with a sequential use of oscilloresistometry and spirometry, which may allow the comparison of the response to bronchodilator at two different states of respiratory mechanics i.e., resting tidal breathing at functional residual capacity (FRC) versus forced expiratory manoeuvre from total lung capacity to residual volume. The evaluation of airway resistance and forced expiratory volume at 1 s (FEV1) may thus assist in the interpretation of bronchial responsiveness tests (BRT) to pick up responders among non-responders to administered bronchodilator. Such a concept was verified in 54 patients with respiratory disease before and 10 min after inhalation of 200 micrograms of salbutamol. Within 10 min following salbutamol challenge the increase for forced vital capacity (FVC), FEV1 and peak expiratory flow rate (PEFR) was 23, 27 and 39% in 27 asthmatic patients of group A (p < 0.005). On the other hand, 27 patients with chronic obstructive pulmonary disease in group B did not show any significant change in FEV1 and PEFR (p > 0.05). However, they showed a decrease in airway resistance of 30% (p < 0.005) during normal tidal breathing at FRC. Twenty-two normal controls in group C showed values of airway resistance and expiratory flow rates to be within the normal range and the response to administered salbutamol inhalation was not significant (p > 0.05). It may be concluded that the airway responsiveness to bronchodilators using only FEV1 as an index of BRT should be interpreted with caution in non-responders because they may not be able to tolerate the mechanical challenge in the form of an FCV manoeuvre but show a significant decrease in airway resistance during resting tidal breathing at FRC.

Factors associated with elevated serum cholesterol levels in well-to-do Pakistani schoolchildren.

Cholesterol (CH) and triglyceride (TG) levels were determined in blood drawn after an overnight fast from 388 school children aged 5-19 years from private schools in Karachi. The mean CH levels ranged from 4.4 to 4.6 mmol l-1 (170.1 to 177.9 mg dl-1) for boys and 4.4 to 4.8 mmol l-1 (170.1 to 185.6 mg dl-1) for girls. The range of TG levels was 1.0 to 1.2 mmol l-1 (88.6 to 106.3 mg dl-1) and 0.9 to 1.1 mmol l-1 (79.7 to 97.4 mg dl-1) for boys and girls respectively. Sixty-two per cent of the girls and 54% of the boys had cholesterol values greater than or equal to 4.4 mmol l-1 (170 mg dl-1), a level at which dietary intervention is recommended for children. Thirty-two per cent of all the children had triglyceride levels above the 90th percentile of the levels for similar age groups in North America. The mean cholesterol intake was 469 mg/day for girls and 518 mg/day for boys. Overweight and inactivity were associated with raised serum cholesterol levels. Forty per cent of the girls and 25% of the boys reported a strong family history of hypercholesterolaemia and/or heart disease. The results show that the prevalence of hypercholesterolaemia is high in well-to-do Pakistani school children and factors which can be modified to lower serum cholesterol levels are identified.

Mechanisms of fixed coupled ventricular ectopic complexes.

Mechanisms of fixed coupled ventricular ectopic complexes (VECs) were studied in the monitoring ECGs of 7 patients with the aid of a special purpose computer. Over 80% of the 4500 fixed coupled VECs studied had coupling intervals restricted to a range of 120 ms. The actual coupling interval varied between subjects. No special part of diastole exhibited the property of fixation. In five patients there was evidence of parasystole despite the fixed coupling. In two of these the ectopic period was clearly different from the sinus period. In the other three a difference was evident between inter-ectopic and sinus intervals, but the ectopic period could not be determined due to absence of short inter-ectopic intervals. Absence of some intervals was due to exit block or consistent coincidence of ectopic stimuli with ventricular refractoriness. In all five patients the inter-ectopic intervals showed progressive adjustment so as to become equal to a multiple of the sinus period. The coupling interval, which indicated the preferred phase relationship of the two rhythms, was altered by small changes in the sinus period. These adjustments were greater manifestations of the synchronising effects, already described, of sinus rhythm on a ventricular parasystolic rhythm. By contrast the VECs of two other patients exhibited very different characteristics. In one, the VECs restricted to 40 ms after the T wave in early diastole were probably due to ventricular re-excitation. In the other, runs of idioventricular rhythm and VECs in late diastole were due to an escape pacemaker rhythm.

Coupling interval, exit block, and periodicity of ventricular parasystolic rhythm.

The electrocardiograms in this study of parasystolic rhythm were tape recorded and then analysed with a special purpose hybrid computer. The rate of appearance of specific inter-ectopic intervals was shown to change significantly with small changes in either the sinus or parasystolic pacemaker period. Natural changes in the period of the ectopic pacemakers were observed over several hours. Changes amounting to 14% within 10 min and 18% overall were observed in one patient, and a gradual lengthening of 10% over 3 h in another. A previously undescribed form of exit block has been discovered in one patient where the block remained active for a given time only after propagation from the parasystolic focus. Different interectopic intervals were shown to contribute to specific and restricted coupling interval locations in diastole. Hence this form of exit block, by preventing some inter-ectopic intervals from propagating, limited the locations in diastole in which parasystolic ectopic complexes could appear. In this case later diastolic complexes were inhibited and hence fusion complexes were completely absent. Parasystolic rhythm, with and without the exit block described, was simulated successfully by a digital computer. The simulations aided our understanding of the clinical data.