[1996][Open Forum Abstract]CARDIORESPIRATORY EFFECTS OF HIGH CPAP IN NORMAL VOLUNTEERS

Introduction and Background: Because of the low ambient pressure at altitudes greater than 40,000 feet life support of fighter pilots who experience cockpit depressurization at these altitudes requires both 100% inspired O_{2} and the application of high levels of CPAP. Physiological studies of pilot life support provide the opportunity to examine the cardiopulmonary effects of extremely high levels of CPAP. Previous studies have demonstrated that high CPAP is associated with involuntary hyperventilation and hypocapnia to a degree which would impair cerebral O_{2} delivery. The present study was performed in order to examine the cardiopulmonary effects of breathing supplemental CO_{2} during administration of CPAP of 30 mmHg (40.8 cmH_{2}O).

Methods: After Institutional Review Board approval and informed consent 10 healthy volunteers (M=7, F=3; mean age=27.6 years, range=19-35) were instrumented with EKG and radial artery catheters. Arterial blood samples were obtained at baseline and after 10 minutes of exposure to CPAP, at which time minute ventilation (V_{E}), heart rate (HR) and mean arterial pressure (MAP) were recorded. During CPAP the subjects breathed air with or without 4.4% added CO_{2}.

Results: Results are shown in the table below:

CPAP Insp CO_{2} V_{E} PaCO_{2} PaO_{2} HR MAP

(mmHg) (%) (L.min^{-1}) (mmHg) (mmHg) min^{-1} (mmHg)

0 0 9.4±3.3 37±4 100±9 6±7 84±3

30 0 33.9±13.3* 25±7* 120±13* 86±13* 98±8*

30 4.4 34.0±12.0* 35±6 129±10* 82±14* 92±13*

*P < .05 compared to 0 CPAP.

CPAP 30mm Hg caused a significant increase in blood pressure, heart rate, minute ventilation and PaO_{2}, and a decrease in PaCO_{2}.

Conclusions: The addition of 4.4% CO_{2} to the inspired mix prevented the hypocapnia associated with a CPAP of 30mmHg, without any adverse effect on minute ventilation, heart rate or blood pressure.

Reference: OF-96-112