Effect of aging on estimates of hypercapnic ventilatory response during sleep

By recording only inspired PCO2 (PICO2) in a hood and transcutaneous PCO2 (PsCO2) the Hazinski method was used to estimate nonintrusively the slope (Sr) per Torr PsCO2 of the fractional ventilatory response to approximately 18 and 30 Torr PICO2 in 17 healthy elderly subjects (10 women) and 17 younger controls (9 women) during wakefulness, slow-wave sleep (SWS), and rapid-eye-movement (REM) sleep. Eight of the older subjects had sleep disturbance indexes (RDI) greater than 5. Sr fell with SWS from 0.90 +/- 0.34 to 0.60 +/- 0.29 (P less than 0.006) in the younger group (n = 16) but in the older subjects was 0.60 +/- 0.27 awake and 0.58 +/- 0.34 (NS) asleep (n = 15). The changes from awake to REM in subsets of 9 younger and 10 older subjects who successfully completed REM tests were from 0.95 +/- 0.32 to 0.70 +/- 0.38 (P less than 0.03) and 0.53 +/- 0.31 to 0.57 +/- 0.25 (NS), respectively. We conclude that the increased incidence of respiratory disturbance during sleep in these older subjects cannot be attributed to greater sleep-induced reduction of CO2 sensitivity.