The effects of acute severe arterial hypoxemia on the electrocardiogram during exercise

The electrocardiogram at rest and exercise during a simulated ascent of Mt. Everest (Operation Everest II)

To evaluate the effect of extreme altitude on cardiac function in normal young men, electrocardiograms were recorded at rest and during maximal exercise at several simulated altitudes up to the equivalent of the summit of Mt. Everest (240 torr or 8,848 m). The subjects spent 40 days in a hypobaric chamber as the pressure was gradually reduced to simulate an ascent. Changes in the resting electrocardiogram were evident at 483 torr (3,660 m) and were more marked at 282 torr (7,620 m) and 240 torr (8,848 m). They consisted of an increase in resting heart rate from 63 +/- 5 to a maximum of 89 +/- 8 beats/min; increase in P-wave amplitude in inferior leads; right-axis shift in the frontal plane; increased S/R ratio in the left precordial leads; and increased T negativity in V1 and V2. No significant arrhythmias or conduction defects were observed. Most changes reverted to normal within 12 hours of return to sea level, with the exception of the frontal-plane axis and T-wave alterations. Maximal cycle ergometer exercise at 282 torr (7,620 m) and 240 torr (8,848 m) resulted in a heart rate of 138 +/- 7 and 119 +/- 6 beats/min at the 2 altitudes, respectively. No ST depression or T-wave changes suggestive of ischemia occurred despite a mean arterial oxygen saturation of 49% and a mean pH of 8 during peak exercise. Occasional ventricular premature beats were observed during exercise in 2 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Intemittent obstruction of the upper airway during sleep causing profound hypoxaemia. A neglected mechanism exacerbating chronic respiratory failure

An obese patient with a ten year history of respiratory failure presented with insomnia and marked daytime somnolence. Respriatory failure had been attributed to obesity, respiratory centre insensitivity to carbon dioxide, and to diffuse airways obstruction. To investigate the possible role of episodic apnoea with frequent nocturnal arousals, continous recordings were obtained during sleep of arterial oxygen saturation, oesophageal pressure and the motions of the rib-cage and abdomen/diaphragm. Repeated episodes of hypoventilation and profound hypoxaemia were found which were due to intermittent obstruction of the upper airway rather than to cessation of breathing efforts. During the episodes of hypoxaemia, values of arterial O2 tension fell to as low as 24 mmHg. Episodic hypoxaemia was relieved but not abolished, by the use of a collar, designed to hold the mandible forward. Previous reports indicated that recognition of intermittent obstruction of the upper airway during sleep and treatment by a permanent tracheostomy, resulted in a significant long-term imporvement of pulmonary and cardiac function and relief of insomnia and day-time somnolence. When tracheostomy is inadvisable, as in the present patient, it is hoped that similar long-term benefits will result from a supportive collar.