Identifying borderline hypertensives: comparative value of various blood pressure measurements.

Ambulant male military aircrew patients (n = 299) were divided into two groups based on historic evidence of normotension (N) or of untreated borderline essential hypertension (BH). All patients had their blood pressure (BP) measured under various conditions and body positions. Results were analyzed to assess the capability of each BP measurement condition to assign patients correctly to their appropriate group. Clinical BP (physician-recorded with patient seated) and orthostatic stand BP (technician-recorded) showed best sensitivity and acceptable specificity. By incorporating the results of both these measurement conditions, a predictor approximating 90% for most BH and N patients was obtained. Use of these two measurements should enable recognition of most BH patients at a single evaluation.

Physical standards for high-performance fighter aircraft pilots.

The new generation of high-performance aircraft has clearly emphasized man's physiological limitations to withstand sustained high G loading. The selection and retention standards required to function in this environment have not been completely defined. The authors will offer a format of standards and screening tests, placing special emphasis on the detection of subclinical disease, particularly coronary artery disease. Cases which illustrate the spectrum of asymptomatic coronary disease will be presented. Other entities discussed will include conduction defects, mild valvular lesions, arrhythmias, and degenerative joint disease of the spine. An overall approach based on age, screening milestones, and specialized tests will be presented. Finally, a data repository on all pilots with chronic high G exposure will be discussed.

Relaxed +GZ tolerance in healthy men: effect of age.

Fifty-three healthy US Air Force aircrewmen, 26-55 yr old, volunteered for a centrifuge study designed to determine the effect of age on relaxed +GZ tolerance. Each was subjected to G forces of gradual and rapid onset, with G tolerance determined by standardized contraction of peripheral visual fields. Of the subject characteristics studied, only age was positively correlated with rapid-onset G tolerance; both age and weight were positively correlated with gradual-onset G tolerance. A combination of age and weight gave a stronger positive correlation with G tolerance (rapid- and gradual-onset) than did either characteristic alone. No significant negative correlations were observed. We conclude that aging may offer some protection from G stress; there is no evidence that aging leads to a decrement in G tolerance.

Treatment of hypertension in aviators: a clinical trial with Aldactazide.

Thirty-two USAF aircrewmen with mild or moderate, uncomplicated essential hypertension were treated with Aldactazide (spironolactone and hydrochlorothiazide). The study was designed to determine the efficacy and safety of this drug combination in aircrew subject to the stress of flying high-performance aircraft. All patients were investigated in detail before, and again 6 weeks after, beginning Aldactazide treatment. Adequate blood pressure control was achieved in 94% of patients; 84% were able to return to flying duties. Treatment was associated with a moderate loss of weight and plasma volume, and a slight reduction in renal function. Tolerance to multiple stress tests was unimpaired after treatment. Symptoms attributable to treatment were minimal. We conclude that in the dose used, four tablets or less daily, Aldactazide is a safe and fairly effective secondline treatment for hypertensive aircrewmen.

The electrocardiographic response to maximal treadmill exercise of asymptomatic men with left bundle branch block.

This study presents the results of maximal treadmill testing and coronary angiography in 31 asymptomatic USAF aircrewmen with acquired left bundle branch block. There were two subgroups: 26 men with normal coronary angiography and five men with significant angiographic coronary angiography and five men with significant angiographic coronary artery disease. The mean amount of maximal ST-segment depression induced by treadmill exercise was --0.5 mv. for both groups and the range in the normal subgroup was --0.3 to --1.0 mv. No significant differences were found between the groups. We concluded that apparently healthy, asymptomatic men with acquired left bundle branch block can have considerable ST-segment depression in response to maximal treadmill testing and that their ST-segment response cannot be used to make diagnostic decisions about them.

New practical treadmill protocol for clinical use.

A new continuous treadmill protocol (USAFSAM) has been designed using a constant treadmill speed (3.3 miles/hour) and regular equal increments in treadmill grade (5%/3min). The constant treadmill speed requires only initial adaptation in patient stride, reduces technician adjustments and produces less electrocardiographic motion artifact than do protocols using multiple or higher treadmill speeds, or both. The regular equal increments in treadmill grade are easy to implement and provide a larger number of work loads than do protocols that are discontinuous or require larger changes in work load. The USAFSAM protocol was compared with the older Balke-Ware protocol in 26 healthy men (aged 30 to 59 years). Each fasting subject completed two maximal treadmill tests from each protocol. Measurements included minute heart rate from the electrocardiogram, auscultatory blood pressures and oxygen consumption obtained with standard techniques. Similarities in between-protocol measurements for submaximal and maximal treadmill efforts were impressive; differences were small and unimportant. Further, both protocols showed equal reproducibility for the measurements noted. Importantly, time to maximal effort was reduced by 24% with the USAFSAM protocol. The USAFSAM treadmill protocol has since been used in more than 500 clinical and screening examinations, thus confirming its advantages and practicality for routine clinical stress testing. Normal reference values previously established for the Balke-Ware protocol are shown to apply to the new USAFSAM protocol as well.

Noninvasive determination of cardiac output by a modified acetylene rebreathing procedure utilizing mass spectrometer measurements.

A modified acetylene rebreathing technique for measuring cardiac output has been developed utilizing a mass spectrometer for measuring gas concentrations. Helium serves as an indicator of mixing and system volume. The disappearance rate of acetylene is proportional to pulmonary capillary blood flow, which is taken as an index of cardiac output. The method also provides an estimate of pulmonary tissue volume. The technique was assessed by comparing 22 simultaneous acetylene and dye-dilution cardiac outputs measured at rest and during exercise in six healthy subjects. There was no significant difference between the mean acetylene and dye-dilution cardiac output values (11.5 l/min vs. 11.24 l/min, respectively). The correlation coefficient was 0.94 and the S.E.M. difference was 0.53 l. The effect of the procedure on cardiac output was evaluated in a separate study of six subjects. There was a significant positive correlation between respiratory rate and cardiac output; but the magnitude of this effect was small, indicating that accurate measurements may be made at spontaneous respiratory rates.

The electrocardiographic response to maximal treadmill exercise of asymptomatic men with right bundle branch block.

This study presents the results of maximal treadmill testing and cardiac catheterization in 40 asymptomatic and apparently healthy men with acquired right bundle-branch block. Eight of the men had significant angiographic coronary artery disease, and six of the eight only had single-vessel disease. The 40 men had normal maximal oxygen consumptions, normal maximal heart rates, and normal maximal blood pressure responses; none of the men had abnormal ST-segment changes in response to maximal treadmill testing. Thus, the sensitivity of exercise testing for coronary artery disease in men with right bundle branch block is uncertain. However, the apparently high specificity of exercise testing demonstrated by this study necessitates further evaluation for coronary artery disease in men with right bundle branch block who develop abnormal ST-segment depression in response to exercise testing.

The response of healthy men to treadmill exercise.

Heart rates, blood pressures, and functional responses to submaximal, maximal and postexertional treadmill testing are presented for a group of 704 healthy, asymptomatic aircrewmen referred to the USAF School of Aerospace Medicine. The indicated measurements are individually described by the use of percentiles. These data provide the practicing clinician with an accurate and complete description of the response of healthy men to treadmill exercise.

Angiographic findings in asymptomatic aircrewmen with electrocardiographic abnormalities.

Cardiac catheterization was used to evaluate 298 asymptomatic, apparently healthy aircrewmen with electrocardiographic abnormalities. These men were identified from annual electrocardiograms and exercise tests used to screen for latent heart disease. Data from 27 additional symptomatic aircrewmen who underwent cardiac catheterization because of mild probable angina pectoris are also included. The men were grouped according to major reason for cardiac catheterization. The order of groups by increasing prevalence of coronary artery disease was as follows: abnormal treadmill test (labile lead only), supraventricular tachycardia, right bundle branch block, left bundle branch block, abnormal treadmill test, ventricular irritability, probable infarct and angina. Approximately 60 percent of the men were completely free of angiographic coronary artery disease. Risk factors and other possible causes for the electrocardiographic abnormalities are discussed. The electrocardiographic abnormalities studied have a poorer predictive value for coronary artery disease in asymptomatic apparently healthy men than in a hospital or clinic population.

Body fat: its relationship to coronary heart disease, blood pressure, lipids and other risk factors measured in a large male population.

Obesity is variably considered to be a major contributor to hypertension and hyperlipidemia, and its treatment is recommended in the management of coronary heart disease. Total body fat was measured by tritium dilution in a large male population and its relationship to age, blood pressure, serum lipids, uric acid and the diagnoses of coronary heart disease, hypertension and glucose intolerance was examined. In addition, three commonly used weight: height indices of obesity were correlated with each of these parameters. The correlation of body fat with blood pressure, serum cholesterol and triglycerides, although statistically significant, was of only small magnitude. Mean levels of body fat were not significantly different between patients with coronary disease and control subjects, whereas serum cholesterol and, to a lesser extent, systolic blood pressure were potent risk factors for the disease. It is concluded that obesity is only a minor determinant of blood pressure and lipid level, and that its contribution to coronary heart disease is small or nonexistent.

A comparison of two bipolar exercise electrocardiographic leads to lead V5.

ST-segment depression and slope were compared in three lead systems (V5, CC5, and CM5) and in two groups of patients using both visual analysis of electrocardiographic paper and computerized techniques. Bipolar lead CC5 was found to be comparable to lead V5 when visual analysis of electrocardiographic recordings was utilized. Bipolar lead CM5 was found not to be comparable to lead V5 and to be less sensitive if classic criteria for slope were used. The technique of computerized analysis mad measurements of slope and amplitude to a reproducible level not possible with the standard technique. Statistically significant differences were found between the exercise electrocardiographic leads utilizing computerized electrocardiographic analysis . We conclude that computerized techniques of electrocardiographic analysis require new criteria for defining an abnormal repolarization response. The criteria must be specific for different electrocardiographic leads if the repolarization changes in these leads are to have comparable diagnostic significance.

Value of exercise testing for screening asymptomatic men for latent coronary artery disease.

Treadmill exercise testing identifies a group of men at high risk for coronary atherosclerotic heart disease. However, the predictive value and sensitivity limitations are obvious. An abnormal electrocardiographic response does not absolutely predict the presence of coronary atherosclerotic heart disease, and a normal response does not rule out this possibility. Thus in appropriate instances when the minimal risk of coronary angiography is justified this procedure can be used to determine the anatomic correlation of exercise-induced functional ST-segment changes.

Prediction of maximal oxygen consumption. Comparison of the Bruce and Balke treadmill protocols.

This study investigated the hypothesis that an individual's maximal oxygen consumption can be realistically predicted by the maximal time achieved in the Balke or Bruce treadmill protocols. The range of maximal oxygen consumption that can be expected for healthy individuals of any given age and activity was also evaluated. The maximal oxygen consumptions achieved by 79 men exercised using the Balke protocol and 77 men using the Bruce protocol were linearly regressed by a least-squares fit technique on maximal treadmill time and on age with activity status classified. Statistical analysis demonstrated an inadequate relationship for predicting maximal oxygen consumption from maximal treadmill time using either protocol. Also, maximal oxygen consumption correlated poorly with age even though activity status was considered. These findings make the nomogram for predicting an individual's functional aerobic impairment a clinical technique of questionable value. Since maximal oxygen consumption can only be grossly estimated from the maximal time performed in the Bruce or Balke protocols, there is no necessity to use them in preference to other clinically acceptable protocols.

Normal values and commonly used echocardiographic formulae for adults.

Echocardiography is a valuable and widespread clinical and research tool. The normal parameters and formulae for adults are widely dispersed throughout the medical literature. The purpose of this paper is to present, in a single source, the already acquired normal values and formulae used in the field.