Comparison of Cardiac Pacing Modes in Patients With Chronic Obstructive Pulmonary Disease – Methods
Spirometry was used to evaluate baseline lung function for each patient. This was performed prior to exercise, with the patient standing. Patients were required to perform three reproducible forced expiratory and inspiratory maneuvers. All patients were then evaluated with paired exercise testing using the Chronotropic Assessment Exercise Protocol Pulmonary gas exchange, exercise duration, heart rate, and rhythm were measured during exercise.
Although there may be some variability in exercise results with serial testing when several exercise tests are done on the same day or on different days, attempts were made to minimize any inadvertent bias by random selection of the pacing modes and strict adherence to the study protocol. A minimum of 2 h was allowed between each exercise study. Cardiac output was obtained at rest and immediately after maximum exercise using echo-Doppler techniques. Stroke volume was determined from the flow velocity integral recorded with the Doppler sample volume positioned in the left ventricular outflow tract. Cardiac output determination by echo-Doppler technique has been shown to be reliable in measuring qualitative changes. buy claritin online
However, its usefulness following maximum exercise is somewhat limited due to problems in obtaining measurements immediately after exercise at exactly the same time in serial studies. The postexercise cardiac output determinations were adjusted to equivalent maximum heart rates to partially correct for variation in precise timing. Pulmonary gas exchange was collected on a breath-bv-breath basis; 30-s averaging was used for data analysis. Maximum values were defined as the maximum value achieved during exercise. Ventilatory equivalents at 50 percent and 75 percent were defined as the ventilatory equivalents at 50 percent and 75 percent of exercise duration. Anaerobic threshold (AT) was defined using a comparison of three techniques: the change in ventilatory equivalent for oxygen (Ve/Vo2) relative to ventilatory equivalent for CO, (Ve/Vco,), the change in RER (Vco,/Vo2), and the V slope as defined by Wasserman et al. Although it is recognized that pulmonary gas exchange may be influenced by multiple factors, these effects could be minimized as each patient acted as his own control with the same variables present for each test.
Prior to entry into the study, the rate-modulated parameters of the pacemaker were programmed to achieve a clinically determined optimal set of parameters for each individual patient. These parameters were not changed for the duration of the study. In the dual chamber mode, the pacemaker AV delay was programmed to what had been previously determined to be an optimum setting for each patient; this too was not changed during the study. For those patients with certain pacemakers (Pacesetter Synchrony), the rate-responsive AV’ delay function was enabled to provide a progressive decrease in AV delay during exercise. The use of rate-responsive AV delay with exercise has been shown to be an important factor in increasing cardiac output with exercise by mimicking the progressive shortening of the PR interval during exercise with increasing heart rates as found in normal subjects.” n The results were analyzed utilizing the Student’s t test. A p value of < 0.05 was accepted as being statistically significant.