The patient exhibited no respiratory distress. However, while watching television, he seemed to “forget to breathe.” Pulmonary function testing performed through the tracheostomy showed a vital capacity of 1.75 L (50 percent of predicted), forced expiratory volume in one second of 1.1 L (45 percent), and a total lung capacity determined by helium dilution of 5.12 L (92 pecent). Arterial blood gas values during wakefulness showed a pH of 7.34, P02 of 72, and PCO2 of 62 on 30 percent FIo2. His chest roentgenogram showed an elevated right hemidiaphragm. Vital capacity in the supine posture was 1.65 L, unchanged from values in the upright posture (1.70 L). Percutaneous stimulation of the phrenic nerve produced a latency of 9.2 ms on the right and 11.0 ms on the left (normal: 9 to 10 ms.) Maximal inspiratory pressures at functional residual capacity were 85 cmH20 (82 percent), expiratory pressures at total lung capacity were 90 cmHsO (48 percent). Tests of hypercapnic responsiveness with rebreathing and hypoxic responsiveness by withdrawal from administration of 100 percent 02 were abnormally low or absent. Heart rate was unchanged during testing for ventilatory responsiveness. Breathholding time was greater than 60 seconds, and the test was halted when the oxygen saturation fell below 75 percent.

Three eight-hour studies of the pattern of breathing were performed during wakefulness and sleep, four to six weeks before death. Airflow and tidal volume were measured at the open tracheostomy while the piatient breathed room air; continuous measurements of oxygen saturation were made by ear oximetry and heart rate determined by a modified C2 lead. In a fourth study (six hour night), the amount and distribution of sleep stages were also monitored. Average minute volume of ventilation was similar during wakefulness and sleep; however, periodic swings in ventilation were noted primarily during sleep. Nonobstructive apneas (18.6±SD 9 s) occurred at a rate of 10 to 15 per hour of sleep (Fig 1). Hypopneas, a fall in oxygen saturation of greater than 4 percent, occurred 20 to 25 times each hour (Fig 2). The mean duration of the hypopneas was 52± SD 28 seconds. Oxygen saturation was 92 ± SD 2 percent during wakefulness, with sleep 89 ± SD 2 percent, and with apneas and hypopneas the average nadir of oxygen saturation was 83±SD 3 percent. Heart rate during wakefulness was 103 ± SD 3 and with sleep 100 ± SD 3 (p<0.05). in detail

Figure 1. Oscillographic tracings of flow measured from a pneumotachograph placed on the tracheostomy during wakefulness and sleep. During wakefulness, respirations were more regular than during sleep. During sleep, apneas greater than ten seconds were present

 

Figure 1. Oscillographic tracings of flow measured from a pneumotachograph placed on the tracheostomy during wakefulness and sleep. During wakefulness, respirations were more regular than during sleep. During sleep, apneas greater than ten seconds were present

Figure 2. Respiratory variations of flow rate and respiratory frequency without apnea were noted during sleep. Shown are continuous tracings of oxygen saturation and airflow A-D over a three-minute period during NREM sleep. In particular, note periods of time when flow diminished and respiratory frequency increased (large triangles). The fall in oxygen saturation (small triangles) occurred with these respiratory dysrhythmias. The arrow indicates direction of flow in units in an inspiratory direction.

Figure 2. Respiratory variations of flow rate and respiratory frequency without apnea were noted during sleep. Shown are continuous tracings of oxygen saturation and airflow A-D over a three-minute period during NREM sleep. In particular, note periods of time when flow diminished and respiratory frequency increased (large triangles). The fall in oxygen saturation (small triangles) occurred with these respiratory dysrhythmias. The arrow indicates direction of flow in units in an inspiratory direction.