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.

Pulmonary and symptom threshold effects of ozone in airline passenger and cockpit crew surrogates.

Previous studies showed that the ozone concentration for pulmonary and symptom threshold effects in flight attendant surrogates lies between 0.20 and 0.30 ppmv for a 3-h exposure with intermittent treadmill exercise at 1829 m (MSL) stimulated cabin altitude. In the present study of sedentary occupants of the in-flight airline cabin, the same protocol was used except for omitting all treadmill exercise. Symptoms were assessed with a standardized questionnaire. Pulmonary function was assessed using standardized quantitative spirometry. Male smoker and nonsmoker airline passanger and cockpit crew surrogates 40-59 years of age were used. Small but statistically significant displacements occurred in symptoms and in some spirometry parameters. In general, the younger subjects appeared more sensitive to ozone than the older subjects. No significant differences appeared between smokers' and nonsmokers' responses to ozone exposure. It is concluded that the ozone threshold of these sedentary surrogates under these experimental conditions is right at 0.30 ppmv.

Effects of ozone on symptoms and cardiopulmonary function in a flight attendant surrogate population.

Two studies were conducted to ascertain the lowest ozone concentration threshold for statistically significant adverse effects on cardiopulmonary function and symptoms in male and female surrogates of the flight attendant population. Both studies simulated in-flight environmental conditions at 1,829 m mean sea level (MSL) chamber altitude. The ozone exposures were 0.2 parts per million by volume (ppmv) for 4 h in the first study and 0.3 ppmv for 3 h in the second study. Each subject was similarly exposed to air only (no ozone) on another occasion. Treadmill exercise, equivalent to workloads of on-duty flight attendants, was performed at altitude. Cardiorespiratory measurements were made during ozone exposure, whereas spirometry and symptom assessments were made immediately before and after exposure. The ozone threshold for reversible adverse effects on symptoms and spirometry function was reached by a 3-h exposure to 0.3 ppmv. The data suggest a greater symptomatic sensitivity to ozone in females.

Lower body negative pressure box for +Gz simulation in the upright seated position.

The cost of purchasing and operating a human centrifuge is substantial. Lower body negative pressure (LBNP) is considered an acceptable experimental substitute for the +Gz stress of the centrifuge. Since civil aviation pilots are usually subjected to +Gz stress in an upright seated position, an upright seated version of the supine LBNP box was developed. In this version, a negative pressure of -40 torr is considered the equivalent of a 2 +Gz stress. This box has successfully withstood a test pressure of -120 torr. Pedal ergometry within the box is easily accomplished. The box was anthropometrically engineered to accommodate a human height range of 160-195 cm. Locating the box within an altitude chamber allows the application of LBNP at any level of chamber altitude. The total cost of fabrication is approximately $500.

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.

Differences between seated and recumbent resting measurements of auscultative blood pressure.

Clinical blood pressure measurements conventionally have been taken while subjects are seated and at rest. FFA aviation medical examiners are required to measure blood pressure while the airman is in a recumbent position. Concern for possible positional differences in blood pressure values generated this study. Calibrated apparatus and objective methodology were used to record and measure blood pressure. Subjects consisted of 100 males between 20 and 60 years of age. Three blood pressure measurements were obtained for each body position. Measurement accuracy was to 2 mm Hg. Body-position order of measurement was randomized. Age and body-position order of measurement had no significant effect on body-position differences in systolic and diastolic pressure. For the total group, the average systolic and diastolic pressure were 6.6 and 0.8 mm Hg higher, repectively, in the recumbent position than in the sitting position. Although the former value was statistically significant, its practical application is obviated by the usual error of clinical measurement.

Amplitude/frequency differences in single-lead ECG of normal versus coronary heart diseased males.

A resting "normal" ECG can coexist with known coronary heart disease (CHD). Combined sensitivity and specificity errors of at least 10% in exercise ECGs are not unusual. Improved screening for CHD was attempted using amplitude/frequency analysis of ECG recordings. Thirty normal males and 30 with documented CHD were selected. The ECGs were recorded on electromagnetic tape during supine rest. Analysis provided digital conversion, selection of four ECG segments, time-normalization and amplitude/frequency analysis. Analyses provided one digital, plot per each segment and one per each 30-subject average. The results from one ECG lead are presented. Significant differences (p less than or equal to 0.05) appeared in the comparisons between the normal and CHD groups. Retrospectively, amplitude criteria individually screened normal from CHD males to an improved degree compared with exercise ECGs.