Cardiorespiratory assessment of 24-hour crash-diet effects on altitude, +Gz, and fatigue tolerances.

Eleven male surrogates of general aviation pilots, 21-35 years old, were tested for altitude, +Gz, and fatigue tolerances with and without previous fasting for 24 h. Testing included 2 min of lower body negative pressure (LBNP) at --40 torr (equivalent to +2Gz) after 118 mn at 3,810 m chamber altitude and, after returning to ground level pressure, ergometry of 50 watts (W) for 6 min. The fast had no statistically significant effect on altitude and fatigue tolerances. One subject, who tolerated 2 min of LBNP in the nonfasting condition, lost useful consciousness during this test in the fasting condition. Although the remaining 10 subjects tolerated 2 min of LBNP in both fasting and nonfasting conditions without statistically significant differences in quantitated parameters, two of them during fasting manifested symptoms usually associated with impending syncope. Pilots should be informed that a 24-h fast may reduce the margin for safe tolerance of greater than or equal to +Gz flight maneuvers.

Cardiorespiratory assessment of decongestant-antihistamine effects on altitude, +Gz, and fatigue tolerances.

Decongestants and antihistamines are known to produce effects capable of adversely modifying physiological function and psychomotor task performance. Because of relevance to safe pilot performance, the effects of single doses of two decongestant-antihistamine preparations (Compound A and Compound B), or a placebo on cardiorespiratory responses to two equally spaced +2 Gz tests during separate 2-h exposures at 388 m (1,274 ft MSL) ground level (GL) and 3,810 m (12,500 ft) chamber altitude were assessed. Post-altitude fatigue was assessed by cardiorespiratory responses to submaximal bicycle ergometry. Compound A and Compound B appeared to exert no significant detrimental effects on short-duration post-altitude ergometric fatigue-ability. With two exceptions, all combinations of medication, altitude, and +Gz were well tolerated. Two subjects were clearly incapacitated during the first +2 Gz test under Compound A at 3,810 m (12,500 ft) altitude. It is felt that the +Gz-intolerance resulted mainly from an adverse interactive effect of Compound A and altitude on vasomotor and/or chronotropic mechanisms.

Altitude tolerance of general aviation pilots with normal or partially impaired spirometric function.

The altitude tolerance of 10 spirometrically impaired (SI) general aviation pilots with an average forced midexpiratory flow (FEF25--75%) value of 65.1% was compared to that of 10 spirometrically normal (SN) pilots. Cardiorespiratory parameters assessed at ground level (GL) and at 8,000- and 12,500-ft altitudes were blood pressure, pulmonary ventilation, oxyhemoglobin saturation, temporal artery flow velocity, heart rate, and single-lead electrocardiogram. Although altitude exposure quantitatively displaced the SI group more than the SN group, the differences were not statistically significant at the probability level of 0.05. Unifocal premature ventricular contractions were present at GL in three of the pilots and showed no further changes at altitude. Therefore, the mean FEF25--75%, values of 65% of predicted normal for the SI group becomes a reasonable option as an objective screening norm for acceptable tolerance to general aviation altitudes in the ambient-air-breathing range.

Spirometric assessment of potential respiratory impairment in general aviation airmen.

Chronic obstructive pulmonary disease continues to manifest an increasing prevalence in male Americans. A recent study of commercial airline pilots revealed a 12% prevalence of more-than-minor spirometric impairment. Because commensurate data were not available for general aviation pilots, in whom such impairment could also compromise flight safety, a parallel study was made. The BMRC and smoking questionnaires, chest expansion, and spirometric measurements of FEV1, FVC, FEV1%, MVV, and FFF 25-75% were assessed in 181 male general aviation pilots. All showed a general relationship to increasing age and smoking amount. Based on FEV1% and FEF 25-75% combined, minor or more-than-minor degrees of spirometric impairment were manifested by 25.4% of the pilots and moderate degrees by 12.7%. Very little impairment was reflected in the remaining spirometric parameters. Subsequent testing of such spirometrically impaired pilots for altitude, fatigue, and orthostatic tolerances related to general aviation flight safety is planned.

ST segment distortions by high-side frequency filtration in direct-writing ECG recorders.

ST segment depression in 12-lead resting and single-lead or multi-lead exercise ECGs is a useful screening criterion for detection of coronary heart disease (CHD). The recommended minimum frequency specification for direct-writing ECG recorders is 0.05-100 Hz (-3 dB). ST segment distortion by unintention low- and high-side frequency filtration could possibly weaken this screening capability. Consequently, one low- and two high-side potential filtration causes of such distortions were investigated in resting and exercise recordings of normal and both J-junction and ST-depressed ECGs. Of 4,914 filtered ST segments, 365 ST category changes were observed. Of these changes, approximately 15% was produced by filtration of the 0.05-0.1 Hz (amplifier function) and 45-100 Hz (60-Hz "noise" filtering) frequency bands. The remaining 85% was attributable to filtration of the 23-45 Hz (stylus overpressure) band. An optional remedy is discussed.