Roger A. Wolthuis

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.

Development of medical pressure and temperature sensors employing optical spectrum modulation

Fiber optic Fabry-Perot sensors have been developed whose optical reflectance varies with optical cavity depth (pressure) or with change in a materials refractive index (temperature). These sensors employ a unique combination of features: they are interrogated by an LED; they are designed to operate within a single reflectance cycle; and their returned light is analyzed by a dichroic ratio technique. The sensors use a step index glass fiber and are relatively insensitive to absolute light levels and fiber bending. They have an expanded linear operating range and can be built for low cost disposable applications. Sensor performance meets or exceeds established medical requirements.<<ETX>>

The response of healthy men to treadmill exercise.

SUMMARYHeart 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.

Normal electrocardiographic waveform characteristics during treadmill exercise testing.

Forty asymptomatic male patients at low risk for cardiovascular disease completed maximal treadmill testing. Electrocardiograms from leads CC5, CM5, V5, Yh and Z were recorded across multiple pretest, exercise and recovery conditions. ECG waveforms were subsequently digitized, averaged and processed to provide Q-, R-, S- and T-wave amplitudes, ST-segment means and slopes, and QS- and RTinterval durations. Average R-wave amplitude increased during early exercise and then dramatically decreased to maximum effort. Average S-wave amplitude became greater as exercise progressed. Average J junction was slightly positive before exercise, became negative during exercise (except lead Z) and returned to zero after exercise. The ST-segment slope increased dramatically with progressive exercise. The response of T-wave amplitude, RT and QS intervals are also described. Separately, 22 asymptomatic male subjects each completed two maximal treadmill tests 2 weeks apart. ECG data acquisition and processing were similar to those noted above. Pooled, within-subject estimates of variability were computed for the ECG leads, ECG measurements and protocol conditions. These variability estimates are useful for interpreting ECG responses to exercise testing.

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.

Development of a medical fiber-optic pH sensor based on optical absorption

A new fiber-optic pH sensor system has been developed. The sensor uses an absorptive indicator compound with a long wavelength absorption peak near 625 nm; change in absorption over the pH range 6.8 to 7.8 is reasonably linear. The sensor is interrogated by a pulsed, red LED. The return light signal is split into short- and long-wavelength components with a dichroic mirror; the respective signals are detected by photodiodes, and their photocurrents are used to form a radiometric output signal. In laboratory tests, the sensor system provided resolution of 0.01 pH, accuracy of +or-0.01 pH, and response time of 30-40 s. Following gamma sterilization, laboratory sensor testing with heparinized human blood yielded excellent agreement with a clinical blood gas analyzer. Excellent sensor performance and low cost, solid-state instrumentation are hallmarks of this sensor-system design.<<ETX>>

Borderline hypertension versus normotension: differential response to orthostatic stress.

Summary The effects of 70-degree weight-bearing tilt and of static standing were studied in aircrewmen who were assigned to two groups, depending on whether they were normotensive or had a history of borderline essential hypertension. Noninvasive methods were used to collect cardiovascular data. During supine rest there was extensive overlap between members of both groups with respect to all measurements. Specifically, all members of the normotensive group and over 80 per cent of the members of the hypertensive group had normal BPs. During orthostasis, either 70-degree weight-bearing tilt or static standing, patients in the hypertensive group showed a significantly greater rise in DBP than did the normotensive group patients; this resulted in diastolic hypertension in most patients in the hypertensive group, while all patients in the normotensive group remained normotensive. The difference in magnitude of the rise in individual mean DBPs effectively distinguished the members of the two groups. The effects of static standing on all measurements were compared with those of 70-degree weight-bearing tilt and were found to be very similar. The practical significance of these findings is discussed.

Development of a dual function sensor system for measuring pressure and temperature at the tip of a single optical fiber

A dual function sensor system has been developed for measuring pressure and temperature at the tip of a single optical fiber. The sensor contains three parts: a filter band-edge shift temperature sensor, a short-wavelength-reflecting dichroic filter, and a diaphragm-based spectral modulation pressure sensor. The sensor system uses a separate and distinct light-emitting diode (LED) for interrogating each sensor, three 100/140 mm step-index fused couplers for managing light, and separate paired photodiode assemblies for analyzing the return light signal from each sensor. In bench tests, each sensor performed to specification and there was no crosstalk between sensors. This sensor design has potential catheter applications where catheter size must be kept to an absolute minimum.<<ETX>>

T-Waves in the Exercise ECG: Their Location and Occurrence

The automated location of T-wave fiducial points in single lead exercise ECGs is facilitated by using R-Tmax and R-Tend intervals predicted from heart rate. Predictive equations for these intervals were developed; algorithms were subsequently designed and tested on 8380 averaged ECG beats from 146 patients. Of 6775 ECG beats with monophasic T-waves, 98 percent of Tmax and 96 percent of Tend fiducial points were correctly identified by these algorithms. The predictive equations and associated algorithms are discussed.

Variations in normal electrocardiographic response to treadmill testing

Forty healthy young men at low risk for coronary artery disease underwent progressive maximal treadmill testing. Four bipolar electrocardiographic leads including CM5, CC5, inferior-superior Y, anterior-posterior Z, and a standard V5 were recorded and later computer-processed. Measurements included amplitudes of the Q, R, S, J junction and T wave, R-T and Q-S intervals and S-T segment slope. These variables are presented as the 10th, 50th (median) and 90th percentiles throughout the testing procedure to define reference values for the electrocardiographic response to maximal treadmill testing. The medians are presented graphically so that the exercise-induced changes can be visualized. In addition, the percent change of R wave amplitude in V5 compared with the supine pretest value is displayed for each subject during and after testing.