How do the intercept and the gain of the dyspnea-heart rate relationship respond to exercise in cardiac patients?

ABSTRACT

To study the dyspnea-heart rate relationship in patients with a positive exercise tolerance testing [ETT] and to compare it with normal healthy controls who had a negative ETT. This was a matched case-control study, in which all patients and their controls underwent an ETT [Bruce protocol] at the Cardiopulmonary Diagnostics Laboratory of a tertiary health care facility. Twenty two male patients, who tested positive on an ETT, were taken as cases and their dyspnea profile was measured during the ETT using the Borg scale. Age, sex and body mass index matched healthy subjects who tested negative on the ETT were recruited as controls and underwent similar dyspnea assessment. Regression analysis of the dyspnea/heart rate relationship was performed to calculate the slope and intercept for every patient and these were compared with the values of the respective controls. The dyspnea/heart rate relationship in patients was found to be linear. The mean intercept [ +/- SEM] was significantly lower in patients when compared with controls; 100.68 +/- 5.25 beats min-1 in patients compared with 113.14 +/- 3.51 beats min-1 in controls [p=0.005]. However, the slope did not show any significant difference between patients and controls. Changes in dyspnea, in this group of patients, is translated via modulation of the intercept [threshold] of the dyspnea/heart rate relationship