Rahn and Otis (1) have described the normal changes in the alveolar gases during work and demonstrated the quantitative relationships between alveolar oxygen, carbon dioxide, respiratory quotient and ventilation by means of continuous recording of gas analyses. They were able to delineate the pathways of change which are controlled by the excretion of carbon dioxide, and observe the effects of hyperpnea, hypoxia, hypoventilation and CO2 breathing as well. Pelnar (2), at first independently and later in conjunction with Rahn, observed the changes in expired air composition in normal subjects as well as in patients with cardiorespiratory impairment in relation to work. By means of a simple diagram relating the changes in 02 and CO2 content of expired air with the respiratory quotient during the stress of exercise, he felt that he could delineate respiratory function better than by any other means in a manner that paralleled the intensity of dyspnea in patients. Between the extremes of a) normal performance with a large circular curve and b) the abnormal performance with no change in these values during exercise, Pelnar found a series of results which were characteristic of the varied stages of dyspnea. view that the level of ventilation is controlled in large measure by the CO2 when breathing normal ambient air in which the strong stimulus of hypoxia is lacking. The hypoxic stimulus of breathing 15%o oxygen in normals or hypoxemia from pulmonary disease in patients clearly induces greater ventilation levels, however.With these considerations in mind we have attempted to repeat these studies in both normal subjects and patients with disease to ascertain not only the normal respiratory pathways, but also the circulatory pathways during exercise and recovery. Thus the inter-relationships between the two can be considered in a way to demonstrate how the adaptations of each complement and spare the other. The techniques employed consist essentially of controlled work-loads by means of walking on a motor-driven treadmill and continuous gas analyses of expired air as well as determinations of electrocardiographic changes in rate and pattern, blood pressure and arterial oxygen saturation (oximeter) (Figure 1). Observations have not been limited to the basal state in order to obtain an appraisal of performance to a standardized stress of exercise in relation to ordinary circumstances in regard to diet, clothing and activity. In a separate report the statistical analyses of varial)ility of normal performances under these conditions is presented (4). For the purpose of defining the normal pathways in this report, only the mean values of all pertinent observations obtained at minute intervals before, during, and after exercise are graphically considered in relation to each other. METHODS

In the preceding report (1) the complementary adaptations of respiration and circulation to the stress of exercise in normal subjects were described. Various isolated measurements, obtained by a method of continuous observation, were found to be in accord with those reported by earlier investigators employing the established TissotHaldane techniques of respiratory gas analysis. Because of the continuity of observation, various rates of change in adapting from a state of rest to a standardized stress of exercise (treadmill walking) as well as rates of recovery could be observed in relation to each other as loops of cardio-respiratory responses. These respiratory and circulatory pathways portray the representative responses in normal subjects, but a survey of the range of variability in normals and patients is needed before these pathways can be utilized properly for the study of impaired functions in patients with cardiorespiratory diseases. Pelnar (2) has critically reviewed the existing methods of functional appraisal of the causes of dyspnea in patients and expressed the opinion that his new method based upon the continuous study of the R.Q. curve during rest, exercise and recovery provides a more satisfactory appraisal of function in relation to dyspnea than any other method previously avail- 1431

In a previous communication (1) we have briefly described the electrocardiographic changes of the QT interval during exercise in normal subjects. On the average the corrected QT interval or K was 7% greater than that observed during rest, and with the onset of recovery it diminished by 9%o within the first two minutes and gradually returned to the original value at rest. There was no significant alteration of QRS complex, ST segment or T wave associated with the change of QT interval.The significance of QT interval in various conditions has been recently studied. In normal persons it varies with age, sex and heart rate (2, 3). Shortening of QT interval occurs in conditions where the blood calcium is high (i.e., hyperparathyroidism [4,5]) and after digitalis administration (6, 7). It is prolonged in many conditions including dilatation and hypertrophy of the heart (8), cardiac failure (9), myocardial ischemia and infarction (2, 3), various types of myocarditis (notably rheumatic [2, 10] and diphtheritic [2] ), disturbance of electrolytes (hypopotassemia [11], and hypocalcemia [ 12,13]), and quinidine poisoning (13).The effect of exercise on the electrocardiogram in the diagnosis of coronary insufficiency by the application of Master's two-step test has been extensively studied and is well known (14-17). The essential abnormal changes include an ST depression of more than 0.5 mm. and a reversal of T waves. But no emphasis was made on the change of QT interval. Hartwell and his associates (18) have likewise studied the effect of exercise on normal human electrocardiograms. The tracings were taken before, during, and after exercise with the 'Aided by grants from the Hochstetter and Lovejoy Funds.2 Bertha Hochstetter Buswell Research Fellow in Medicine. subject sitting on the orthopedic exerciser. They observed that the T wave was usually lowered during exercise and returned to its former height after exercise. Meier (19) during World War II examined the electrocardiographic changes before and after exercise in 45 subjects wearing gas masks. No significant changes were observed which could be ascribed either to accumulation of CO2 or to relative anoxemia. Auricular premature beats were observed in some normal subjects after severe exercise of short duration and not under conditions of moderate exercise for a longer time. In both reports the authors, too, did not mention any change of QT interval.In reviewing the literature from 1920 to 1948 only a few scattered reports on the electrocardiographic change of QT interval in relation to exercise were found. In 1920 Bazett (20) studied the QT changes after exercise in three subjects. Although he claimed that the QT interval was prolonged after exercise, it is interesting to note that in all the three subjects there was a shortening of corrected QT interval in the first one or two minutes after exercise in comparison with the late recovery.In 1929 White and Mudd (5) observed the changes of QT interval in 10 normal subjects before and after exercise (running up and down fou...

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The characteristic intracardiac pressure patterns of four patients with constrictive pericarditis are described. The significance of a high ratio between right ventricular end-diastolic and systolic pressure is demonstrated. Postoperative changes are described in one patient and the mechanism of the production of the pressure patterns is discussed.