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.

Protection of airline flight attendants from hypoxia following rapid decompression.

To determine the maximum time for working flight attendants to effectively initiate airline passenger mask donning after onset of a rapid, severe decompression, we exposed 10 subjects in two series of tests to a decompression from 6,500 to 34,000 ft (2,000 to 10,400 m) in 26 s, followed by descent at 5,000 ft/min (1,500 m/min) while subjects performed a light-to-moderate workload. Supplemental oxygen was provided in one series from a compressed oxygen system, and in the other series from a chemical oxygen generator system. With delays to mask doning of 10 and 15 s, no hypoxic effects occurred. With delays of 20 and 25 s, increasing hypoxic effects, similar in frequency for the two systems, occurred. Some technical problems in mask donning contributed to losses of consciousness with the latter two delays.

Effect of physical activity of airline flight attendants on their time of useful consciousness in a rapid decompression.

To determine the effect of physical activity on the "time of useful consciousness" (TUC) of airline flight attendants in a rapid, severe decompression, 10 male and 10 female subjects were exposed to a decompression profile while at rest and performing light-to-moderate work. Decompression from 6,500 to 34,000 ft (2,000 to 10,400 m) was followed by descent at 5,000 ft/min (1,500 m/min). The average TUC for the males decreased from 54 s (omega 7.1) at rest to 34 s (omega 4.4) while performing work. The average TUC for the females decreased from 54 s (omega 8.1) at rest to 32 s (omega 4.0) while performing work. Supplemental oxygen had a marked paradoxical effect when the subjects were performing work.

Paroxysmal and chronic atrial fibrillation in airman certification.

Of the 757,693 airmen with valid FAA medical certificates on Oct. 31, 1974, 125 (all males but one) had a history of paroxysmal atrial fibrillation. Episodes of paroxysmal atrial fibrillation occurred once in 91, twice in 14, and more than twice in 20 airmen, and were attributed to one or more of 23 factors in 72 of the medical records studied. Associated symptoms reported in 27 records were considered serious enough to produce pilot incapacitation. Chronic atrial fibrillation was idiopathic in all but one airman, who developed this arrhythmia following atrial septal defect repair. Medical records report no associated symptoms, and heart rates, resting and in response to exercise, were reported as within normal limits.

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.